up church) all about fittings 2011

All About Fittings

John W. Batts, IV

A practical guide to using and understanding fittings

in a laboratory environment

IDEX Health & Science619 Oak Street, Oak Harbor, WA 98277 USATel: +1 800 426 0191 · Fax: +1 800 359 3460 · Fax: +1 360 679 3830E-mail: [email protected]

© 2011 IDEX Health & Science LLC

About The Author

John Batts, a long-time employee with IDEX Health & Science, has extensive experience with HPLC and related techniques – as a lab technician, as an HPLC field service representative, and as a technical specialist. Driven by a passion for teaching and making difficult-to-understand concepts and material more fun and inviting, he embarked on the journey of writing — and updating — this booklet.

He currently resides with his family in the Pacific Northwest.

Copyright © 2011 IDEX Health & Science LLC

All rights reserved.

Reproduction or translation of any part of this book without the written permission of the copyright owner is unlawful. Contact IDEX Health & Science for permission www.idex-hs.com

Printed in the United States of America

First printing, July 2003 Second printing, August 2004 Third printing, March 2011

The following Trademarks and Registered Trademarks are found in this book:

Upchurch Scientific® is a Registered Trademark of IDEX Health & Science LLC

Delrin® is Registered Trademarks of E.I. du Pont de Nemours and Company

PEEK™ polymer is a Trademark of Victrex, plc.

NanoPort™ is a Trademark of IDEX Health & Science LLC

Halar® is a Registered Trademark of Solvay Solexis S.p.A.

Radel® is a Registered Trademark of BP Amoco Polymers

Ultem® is a Registered Trademark of General Electric Corporation

All About Fittings

2 Preface

3 Foreword

4 Introduction

6 JustWhatAREFittings?

thevitalrolefittingsplayinlaboratoryinstruments

16 HowDoFittingsWork?

basicsaboutfittingsmostclasseswon’tteach

24 WhatFittingDoIHave?

thequickwaytoidentifywhatfittingsyou’reusing

28 PlasticorMetallic—WhichDoIChoose?

what’sthebestfittingchoice?we’lltalkaboutit…

32 WhatIsHPLC?

sincewe’retalkingaboutitsomuch…

40 OtherPopular“Apps”...

tipsformakinggreatconnectionsin

microscaleliquidchromatographyandUHPLC

49 AFewExtraTips

otherusefulhintsformakinggreatconnections

54 Appendix

useful“extras”youmightneedtoknow

Table of Contents

PrefaceI’mveryexcitedaboutthisneweditionoftheAll About Fittingsbooklet!FrommyfirstdealingswithPaulUpchurchinthe1980’stomyinteractionswiththepresent-daystaffatIDEXHealth&Science,I’vealwaysbeenimpressedwiththeleveloftechnicalknow-howthatiscontainedwithinthiscompany.Althoughmanycompanieshavetechnicalexpertise,fewshareitaseffectivelyasisdoneinthislittlepublication.Notonlyisthetechnicalcontenthigh,butitalsoisfuntoread–asomewhatrarecombinationintoday’sHPLCliterature.

HPLCfittings,tubing,andrelatedproductsoftengetoverlookedindiscussionsofHPLCequipment.However,thesepartsarecriticalifyouwanttoobtaintheoptimumperformanceofyoursystem.Problemsaremagnifiedasweprogressto

columnswithsmallerparticlesthatgeneratenarrowerpeaks–apoorlyassembledfittingcancompromiseanotherwiseexcellentseparation.Theexplanationsanddirectionscontainedherewillhelpyouunderstandwhatis–andisn’t–importantwhenyouconnectdifferentpiecesofyourHPLCsystem.Thingslikethreadpitchandferrulegeometryseemabitesoteric,butyou’dbetterpicktherightparts…oryou’llbesorry!

Sotakeafewminutesrightnowandfamiliarizeyourselfwiththecontentsofthebook–10minutesofleafingthroughthepageswillmakeyoufamiliarwiththehighlights.Thenyou’llknowwheretolookwhenyouhaveaquestionaboutfittings.Evenifyou’reanoldpro,you’lllearnsomethingusefulifyoureadthisbookletfromcovertocover–Icertainlydid.

JohnW.Dolan,Ph.D.LCTroubleshootingEditor,LC/GCMagazine

2

All About Fittings

Despitethelargeinvestmentoftimeandmoneyspentonlabequipment—andtheeducationtoknowwhattodowithit—verylittleattentionisgiventounderstandinghowtomakegreatconnectionswithfittings.

Severalyearsago,inanefforttoaddresssomeofthemorecommonemergingtrendsinanalyticalinstrumentation,theoriginalAllAboutFittingsguidewasproduced.Sincethattime,techniquesinanalyticalchemistryhavecontinuedtoevolve,withsystempressuresinUHPLCbecomingthenewstandardthataccessoriesmustwithstandandwithmicro-andnano-flowapplicationshelpingtosetanewstandardforflowrates.Additionally,therehasbeenincreasedemphasisonIVDandotherlife-sciencetechniques.

Thisbookletprovidesessentialinformationoftenrequiredtoidentifythecorrectstyleandtypeoffittingneededformostlaboratoryapplications.Itincludesmorein-depthinformationonmakinggreatconnectionsinUHPLCandmicro-andnanoscaleapplications,aswellasofferinghelpfulhintsforlowerpressureapplications,too.

Ifyouhaveanysuggestionsforfutureeditions,orneedsomeadditionalhelpinidentifyingthefittingyouneed,pleasefeelfreetocontactusatanytime.

HappyConnecting!

JohnW.Batts,IVIDEXHealth&Science

AllAboutFittings4

Introduction

Introduction

WelcometoAll About Fittings!Youareabouttoembarkonanexcitingjourneydesignedtohelpyougraspthefundamentalsofequipmentfittingsandaccessories,aswellassomebasicsaboutliquidchromatographyasananalyticaltechnique.

Youhavemostlikelybeenintroducedtosomeofthetopicscoveredinthismanual.We’vefound,though,thatalotofthefundamentalinformationaboutfittingsandmakinggood

connectionsisn’tgenerallyknown...oftenbecausetheinformationisn’tcoveredinmostcollege-levelclasses.

Tomakemattersworse,mostfittingsandaccessories-manufacturingcompanieshaveavocabularyand“lingo”alltheirown—oftenconsistingofengineeringterms,mathematicalmeasurements,andalargearrayofmaterialnames...andtheyexpectyoutounderstandtheirterminology.

That’s what this book will help you do!

We’vebuiltintothishandbookinformationonfittingsbasics:howtodescribeafitting,howtodeterminewhereinyoursystemcertainstylesoffittingsareused,theinterchangeabilityofdifferenttypesoffittings—amongmanyothertopics.We’veevenbuiltinadiscussiononthespecialterminologyandskillsetneededto

workwithhyphenatedchromatographysystems,suchasLC-MSandevenUHPLCsystems.

Throughthisbooklet,youwillgaintheconfidenceyouneedtoknowexactlywhatfittingyouneedinalmostanylaboratoryapplication!

All About Fittings

www.idex-hs.com 5

IconsTheIconsbelowarefoundinthepagemarginsthroughoutthisbooklettohighlightextra-importantinformationyou’llneedtoknow:

KeyConceptPayextracloseattention...theconceptcoveredisimportanttounderstand!

HelpMe!Highlightsinformationthathelpsexplainatopicormakesomethingeasiertounderstand.

ThisorThat?Drawsyourattentiontoextradetailsyoumayneedwhendecidingwhatproducttouseorwheretouseaproduct.

PointofInterestIndicatesthere’ssomethingsointerestingthatitneedsasecondlook.

SecretRevealedUsedwhenevera“secret”isrevealed—somethingtohelpmakeyourlifeeasierorhelpmakesomethingmoreunderstandable.

HowIt’sMadeOffersdetailsabouthowcurrentequipmentisconfigured,tohelpmakeproductselectionalittleeasier.

PardonMoi?Denotesthosefrequently-askedquestionsthatpuzzlescientistsaroundtheworld!

KEY CONCEPT

SECRET REVEALED

PARDON MOI?

HELP ME!

POINT OF INTEREST

HOW IT’S MADE

THIS OR THAT?

AllAboutFittings6

Just What ARE Fittings?That’soneofthemostpopularquestionsneverasked!Infact,it’snotusuallyuntilyoursystembreaksdownthatyoueven

realizealltheplaceswherefittingsareused!

So...justwhatarefittingsanyway?Accordingtothedictionary,afittingis…

Inotherwords,anywhereyouneedtoattach,adapt,oradjustpiping—ortubing,inthiscase—there’stypicallyafittinginvolved!

Infact,allkindsoffittingsareusedinastandardlaboratorysystem:flangedandflangeless;metallicandnon-metallic;high-pressureandlow-pressure;flat-bottomedandconed;internalandexternal;wrench-tightenedandfinger-tightened.

...a small part used to join, adjust, or adapt other parts, as in a system of pipes

JustWhatAREFittings?

PARDON MOI?

KEY CONCEPT

As Paul Upchurch stated in his book entitled HPLC Fittings:

...everychromatographer

knows,inordertouseany

HPLCsystem,youspend

alotoftimeworkingwith

fittings.Youmustbecome

knowledgeablewiththe

plumbingofanHPLC

systeminordertodo

anypracticalHPLCwork.

Because fittings impact almost everything you do with your equipment, one of the best investments you can make with your time is to better understand fittings and how to use them properly.

All About Fittings

www.idex-hs.com 7

Threads of the receiving port

Geometry of the receiving port

Size and type of tubing used

Material from which the port is made

Amount of pressure expected

So, let’s talk about some basics...Actually,whatwecommonlycalla“fitting”intheanalyticalinstrumentworldreallyreferstoasystemcomprisedofanutandaferrule(pronounced“FAIR-ruhl”).

Ultimately,thechoiceofwhichnutandwhichferruletouseinyoursystemwillbedependentuponanumberofparameters:

Aww, nuts!Thefirstofthetwomajorcomponentsinafittingsystemiscalledanut.Thenutisresponsibleforprovidingthedrivingforcethatcausestheferruletoseal.

Thereareseveralcharacteristicsthatareusedtodistinguishdifferentnutsfromeachother.Oneofthemostobviousistheheadgeometry(e.g.,knurled,hexagonal,square,winged).Butperhapsthemostimportantfeatureofnutsisthethreadedportion,whichallowsnutstomatewiththeirreceivingports.Let’sdiscusseachoftheseinfurtherdetailtohelpdistinguishwhatproductsyoumightbeusing,aswellaswhatotherproductsareavailable.

Threads

Mostnutshave“externalthreads,”meaningthatthethreadsareontheoutsideofthenut.Somenuts,however,have“internalthreads,”wherethethreadsareontheinsideofthenut–commonlyreferredtoasa“capnut”or“femalenut.”(SeeFigure1onpage8)

...andseveralothers.Giventhenumberoffactorsinfluencingthefittingchoiceforagivenapplication,let’sseeifwecanshedsomelightonthesubjectofmakinggoodconnections.

KEY CONCEPT

THIS OR THAT?

AllAboutFittings8

Becausemostnutshaveexternalthreads,let’sfocusonthisnutgeometry…

Inordertodescribeathreadonafitting,somethingcalleda“threadcall-out”isused,consistingoftwomainnumbers..Thefirstnumbertellsyouaboutthediameterofthethread,andthesecondnumberdescribeshowclosetogetherthethreadsare.Here’saneasyexample:

Oneofthemostwidelyusedthreadsinlow-pressurefluidtransferis1/4-28.Noticethetwonumbershere,separatedbyahyphen.Now,let’sapplythedescriptionaboveandseeifwecandeterminesomebasicinformationaboutthistypeofthread.

Thefirstnumberinthethreadcall-outis“1/4.”Sinceweknowthisnumbertellsusaboutthediameterofthethreads,wehaveourfirstclue.Inthiscase,thecall-outunitofmeasurementisinches,sothisdenotesathreaddiameterofone-quarterofaninch!Thediameterofthethreadismeasuredfromthecrestofathreadallthewayacrosstotheoppositecrest.Inotherwords,we’reidentifyingthemaximumdiameterofthethread.

Theothernumberinthethreadnotationisnotsoobvious.Whatdoyouthinkitmeans?Remember,thenumbertellshowclosetogetherthethreadsare.

Anyideas?Well,ifyouthoughtthatitmeansthereare28threadsonthefitting,youwouldbeingoodcompany...butunfortunatelythat’snottherightanswer.Whatthenumbertellsyou,inthiscase,ishowmanythreadsperinchthereareonthenut.(Formoreinformationonhowtomeasurethesecriticaldimensionsonanyfittingyouhave,seepage24ofthisguideforanin-depthdiscussionondeterminingthethreadcall-outofyourfitting.)Internally-ThreadedNut

Externally-ThreadedNut

FIGURE1ThreadedNuts


HELP ME!

All About Fittings

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Let’slookatanotherthreadoption—the“workhorse”ofhigherpressurechromatographyapplications:the10-32thread.Whatdoesthisthreadcall-outtellus?

Again,weknowthefirstnumbertellsussomethingaboutthediameterofthethread.Yet,inthiscase,itdoesn’tmeanyouhavea10inchdiameterthread!

Inthe“fittingsworld,”whenanEnglishthreadgoesbelow1/4”indiameter,thengaugenumbersaretypicallyusedwhenreferringtothethreaddiameter.Therefore,the“10”inthecall-outreferstoagauge10—whichtranslatestoalmostexactly3/16”(4.7625mm).Inmicroscaleandnanoscaleapplications,agauge6threadiscommonlyused.Thisthreadgaugeisalmostexactly3.5mmorapproximately9/64”indiameter.

Whynotjusttellyouhowmanythreadsareonthenut?

Simply because it’s not nearly as universal. Every time the length of the nut changed, the thread specification would also have to change, and that would make it very difficult to standardize. However, if the thread is measured in something like “threads per inch,” then it doesn’t matter if the nut is 1/2” long or 5 feet long...it still has the same “name!”

Formoreinformationonvariousthreaddiametersandpitches,seethechartonpage25,andformoreinformationonmakinggoodcapillaryconnections,seepage41.

Butwhataboutthe“32”?Aswiththe1/4-28example,thisnumbermeansthirty-two threads per inch.

So,ifyoucomparea10-32threadedfittingwitha1/4-28threadedfitting,whichwouldyouexpecttohavethreadsclosertogether?Itwouldbethe10-32thread,sinceithasmore“threadsperinch”orafinerthreadpitch.

FOODFORTHOUGHT…Why are 10-32 threaded nuts used in most high pressure applications instead of 1/4-28 threaded nuts? One reason is that denser threads means that there’s more threads to “share the load” and resist the pressure generated inside the receiving port.

...NOWYOUKNOW!

HOW IT’S MADE

SECRET REVEALED

PARDON MOI?

Youmayhavenoticedthattheterm“Englishthread”wasmentionedalittleearlier.That’stohelpidentifythatthethreadcall-outfollowsthetraditionalEnglishsystem,using“inch”asthecommonunitofmeasurement.Italsohelpsdistinguishnutsusingthissystemfromthoseusingthemetricsystem,whichisalsousedinchromatographyequipmentconnectionsbutuses“millimeter”astheunitofmeasurement.

ThemostcommonmetricthreadusedinlaboratoryequipmentisM6x1(althoughyouwilloftenonlyseeM6listed).Let’strytoapplythesameprincipleswelearnedwiththeEnglish-threadedfittingstothesemetricfittings.

First,rememberthatthefirstnumberreferstothediameterofthethreads,andsincethisisametricfitting,thediameteris6millimeters!

The“1”portionofthethreadnamedesignatesthedistancebetweenadjacentthreads!Therefore,thisthreadhas1 millimeter between each thread —theinverseofhowanEnglishthreadismeasured.WhileanEnglishthread(suchasthe10-32and1/4-28we’vealreadydiscussed)measuresthenumberofthreadsperinch,ametricthreadmeasuresthenumberofmillimetersperthread.

Evenwiththedifferencesbetweenthetwosystems,tremendoussimilaritiesexist,andbystudyingthisinformation,youshouldbetterunderstandhowandwhythreadsarenamedthewaytheyare!

Let’s Test Your Knowledge…Now that you’ve learned what the names of threads mean, let’s apply that to another thread.

Thethreadis...5/16-24.

What is the diameter of this thread? What is the thread pitch? Based upon this thread pitch, how many threads exist in 1/4” (6.35 mm)?

To see if you’re right, check the answer at the bottom of this page!

Thediameterofthethreadis5/16”,andthethreadpitchis24threadsperinch.In1/4”thereare6threads(24threads/inchx1/4”=6threads).


SECRET REVEALED

All About Fittings

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HeadGeometry

Fittingsaredescribedbymorethanjusttheirthreads,aswe’vediscussed.Anothermajorfactorthathelpsdeterminewhatnuttouseisthegeometryofthehead.

Manynutscanonlybeproperlytightenedwithawrench.So,forthosenuts,it’simportanttonoteiftheyhavea“hex-head”or“wrench-flat”geometry,andthentospecifywhatthediameterisfromflatsidetoflatside.Thistellsyouwhatwrenchyouneedtouse.

Othernuts,however,canbetightenedwithoutawrench;allyoutypicallyneedareyourfingerstotightenthemproperly!Ratherthanusinga“hexhead”or“wrenchflat”geometrythatisdifficulttotightenbyhand,these“fingertight”fittingsoftenfeaturea“knurled”head...andsometimesareevenenhancedwith“wings”—tooffermoregrippingsurfaceandextrafrictionagainstyourfingers.Note:Inmicroscaleapplications,wherethefittingsareoftensmallerthanstandardfittings,itiscommontofindtheheadsofthesefittingsdesignedwitha“micro-knurl”pattern.However,becauseoftheiroveralldiameter,thesefittingsstilltypicallyrequiretheuseofcustom-designedtoolstoensuretheyaretightenedsufficientlytoholdtubing

totheirstatedpressurelimits.Besuretoconsultwiththefittingssupplierformoreinformationonpropertighteningofthesesmallerfittings.

OtherItems

Besidesthethreadsizeandheadgeometry,thereareotherfactorsthatinfluencewhatnutyouneedtouse.

Onethingtoconsideristheoveralllengthofthenut.Longnutsaregreatforuseinangledports,toincreasethegapbetweenadjacentfittings.Butlongnutsmaybedifficulttouseinsome“space-challenged”ports.So,forthoseports,shorternutsareinorder.

Youshouldalsoconsiderthedimensionsofthetubingyouareusing,asmostnutshaveaspecific-

KEY CONCEPT

FIGURE2

WrenchFlatHex-Head

Knurl WingedHead

THIS OR THAT?

AllAboutFittings12

sizedholepassingthroughthem(calleda“thru-hole”)whichfrequentlycorrespondstoatubing’souterdiameter.Therefore,whenchoosingthenutforyourfittingsystem,youwilloftenneedtoreferenceyourtubing’souterdiameter.

Anothermajordistinguishingfactorbetweenfittingsisthematerialthathasbeenusedtomanufacturethenut.Originally,thiswasn’timportant,asmostnutsweremadefromstainlesssteel.However,asfittingstechnologyhasadvanced,polymer-basednutshavebeendeveloped..MaterialslikeDelrin®,PFA,ETFE,polypropylene,PCTFE,PEEK™,andPPSarealloptions,andwitheachnewmaterialcomesnewadvantagesanddisadvantagestoconsider(e.g.chemicalcompatibility,threadstrength...evencolor!).RefertothePolymerReferenceChartandotherresourcesintheAppendix,orcheckwithyourfavoritefittingssupplierforassistanceinchoosingthebestfittingforyourapplication.

Ferrules

Nowthatyou’veabsorbedallthis“nutknowledge,”don’tforgetthisisonlyhalfofthefittingsstory.

Infact,thenutisn’treallythe“businessend”ofafittingsystem...it’stheferrulethat’sdoingmostofthework!

Moststandardlaboratoryfittingsystemsworkthroughexternalcompression(or“gripping”)ontothetubing’souterwall.And,whilethenutprovidesthedrivingforceforcompression,it’stheferrulethatcompressesagainstthetubingandthusholdsthetubinginplace.

Ferrulesaren’tnearlyascomplicatedastheirnutcounterparts,buttheydohavesomedistinguishingfeaturestohelpyoudeterminewhichonestouse.

WhatTheyLookLike

Whileferrulescomeinallshapesandsizes(seeFigure3),onethingtheyhaveincommonistheirtaperednoses...andit’sattheendofthisnosewhereferrulesdowhattheyweredesignedtodo—gripthetubingwall!


FIGURE3VariousFerrules

KEY CONCEPT

SECRET REVEALED

All About Fittings

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However,thatdoesn’tmeanferrulesareallinterchangeable!Thingsliketubingsize,pressurerequirements,matingnuts,and—mostimportantly—thegeometryofthereceivingportmustallbeconsideredwhenchoosingtherightferruleforanygivenapplication.

WhereTheyAreUsed

Fromourdiscussionearlier,threadedportscanbeclassifiedas“highpressure”and“lowpressure.”Whilethedefinitionof“high”and“low”isoftendifferentdependingonwhomyouask,onedistinguishingfeatureisthegeometryofthereceivingport(seeFigure4).

Generally,lowpressurereceivingportsendinaflat-bottomconfiguration.Inotherwords,asthethreadsrunout,thebottomoftheportbecomesflatacrosstheentireportdiameter,withasmall“thru-hole”inthecenteroftheflatbottom.Theferrulesusedwiththistypeofportwilltypicallyhavetheirtaperednosesfacingtowardthenutandawayfromtheflatbottomofthereceivingport.Inthesefittingsystems,thethreadedbarrelofthenutwill

oftenfeatureaninternallytaperedsurface,designedtointerfacewiththetaperednoseoftheferruleandhelpcreateasealagainstthetubingwall.(Formoreinformationonlowpressurefittings,pleaseseethediscussiononpage22.)

Highpressurereceivingports,ontheotherhand,haveaninternaltaperjustpastthethreadedportionoftheport.Then,justbeyondtheinternaltaperisasmallpocket—oftencalledthe“tubingpocket” —whichisnearlythesamediameterasthetubingthatextendsintoit.Inthesetypesofports,thetaperednoseoftheferrulefacesawayfromthenutandtowardtheport.ALittleFerruleDitty

Tapered noses face the port When pressures are high But they face the nut When low pressures apply!

FIGURE4

Flat-BottomPort&Fitting

ConedPort&Fitting

AllAboutFittings14

ManufacturingMaterial

Oneveryimportantcharacteristicofanyferruleisthematerialfromwhichitismade.

Ferrulesareoftenmanufacturedfrommaterialssuchasstainlesssteel,PEEK™,ETFE,polypropyleneandPCTFE.MaterialssuchasPEEKpolymer(abeige-coloredplastic),PCTFE,andstainlesssteelareoftenusedtomanufactureferrulesforhighpressureapplications.Softerpolymers,includingETFEandpolypropylene,areusedprimarily(althoughnotsolely)inlower-pressureapplications.

OtherFactors

Makinggreatconnectionsisimpactedbymorethanjustthefittingitself.Otherthingstoconsiderincludethefollowing:

Tubing:Therearetwoprimaryfeaturesofyourtubingthatcanhaveadramaticimpactonthequalityoftheconnectionyouaremaking.First,it’simportanttoknowwhatthematerialisfromwhichthetubinghasbeenmanufactured.Somematerials—likeFEPandPFA—offeroptimalresistanceacrossabroadspectrumofchemicalsolutions;however,the“trade-off”isofteninpressureresistance.OthermaterialslikePEEKandstainlesssteelofferexcellentpressureresistancebutarenotaschemicallyinertassomeofthesofterfluoropolymeroptions.Knowing

thematerialwillhelpyoudetermineifthetubingyouhavechosenwillworkintheconnectionyouaretryingtomake.

Becausemostfittingssystemsgriptheoutsidewallofthetubing,knowingtheouterdiameterofyourtubingisimportant.Thisinformationbothhelpsyouselecttherightfittingstouseaswellashelpsensurethetubingwillfitproperlyintothereceivingport.

ReceivingPort:Especiallyinhigherpressureareasofyoursystemwhereconedportsaremosttypicallyfound,knowingwhatthematerialisfromwhichthereceivingporthasbeendesignedwillhelpyoudetermineifyoucanusethefittingyouhavechoseninthatreceivingport.Agreatruleofthumbisthatthereceivingportshouldbemanufacturedfromamaterialthatisatleastashardasthematerialfromwhichthefittinghasbeenmanufactured.Additionally,conedportsfeaturea“tubingpocket”withadiameterthatisdesignedtobepairedwithaspecifictubingouterdiameter.Thisisparticularlyimportanttonotewhenmakingcapillarytubingconnections,asthetubingisoftenofadifferentsizethanthereceivingportisdesignedtoaccept,requiringspecialaccommodationstoensureagoodconnectionismade.(Formoreinformationonmakingcapillarytubingconnections,seethesectiontitled“MakingCapillaryTubingConnections”onpage41.)


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Together at last!Asyoumight’veguessed,boththenutandtheferruleareimportantcomponentsofafittingssystem,amatchedsetdesignedtoworktogether!

Inanyconnectionsystem,youcannotexpecttousejustthenutalone,asnothingwouldbepresenttogripthetubing,andtheferrulecannotgripthetubingwallwithoutthedrivingforceofthenut.Theentiresystemmustworktogethertoprovideyouwithaconsistentholdandsealontheoutsideofthetubingwall.

...WhichLeadsUsToOurNextChapter

Insomepolymerfittings

systems,thenutandferrule

aretogetherasasingle

piece.Theseone-piece

fittingssystemsstillhaveall

thesamefeaturesasother

multi-componentsystems;

however,bycombiningthe

components,aone-piece

fittingssystemisusuallymore

convenientandeasiertouse.

KEY CONCEPT

AllAboutFittings16

How Do Fittings Work?We’vetakensometimetolearnsomebasicsaboutfittings,andwe’veevengoneoversomenewvocabulary.Now,let’sseeifwecanfigureouthowtheyactuallywork.

Butfirst,weneedtolaysomegroundwork.Wheneverwetalkabout“fittings”fromnowon,we’llmostoftenbereferringtothecombinednutandferrulesystem.(Beawarethatsomefittingshaveboththenutandtheferruletogetherasonepiece,asmentionedonthepreviouspage.)

Now, let’s dig in!Tounderstandhowfittingswork,it’simportanttoknowwhatfittingshavetoDO.

Specifically,fittingshavetwoprimaryfunctions:

Thesejobsmaysoundsomewhatmundane;however,whenyouconsiderthenatureofthechemicalsthatoftentravelalongagivenflowpath,coupledwiththehighpressuresthatoftenexistinline,youmaybegintorealizejustwhatadifficultjobfittingshave!

So, how do fittings do what they have to do?Mostlaboratoryequipmentfittingsgenerallyworkthroughaprocesscalledexternal compression.Inotherwords,asafittingholdsapieceoftubinginplace,itcompressestheoutside(orexternal)wallofthetubing.Dependingonthematerialusedtomakethefitting,thisexternalcompressioneitherbecomespermanent,throughaprocesscalledswaging,orremainstemporary,holdingthetubingusingsimplefrictionagainstthetubingwall.

HowDoFittingsWork?

KEY CONCEPT

HELP ME!

Preventing liquid (or gas) from leaking out of the flow path

Holding tubing in place against opposing pressure

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So,whatdrivesthiscompression?Ithastodowithaconceptcalled“interferingangles.”Thisgetsabitmoretechnical,solet’sdelvedeepertogainabetterunderstanding.

Wealreadydiscussedhowferrulesaremostoftentaperedonatleastoneend,andhowtheorientationoftheferruleusuallydependsonthepressureyouexpectthefittingtowithstand(andtheinternalgeometryofthereceivingport,ofcourse!).Generally,theprimarytaperedportionofanyferrule(orfitting,ifitisaone-piecestyle)willfacetheportionoftheportthatisalsotapered,resultinginaconnectionthathastwoangledsurfacescomingtogether(seeFigure5).

Let’slookatthethreepossibleoutcomeswhenthesetwoangledsurfacescometogether:

1.Ferrulehasawideranglethanthereceivingport

Inthisscenario,asthefittingtightensintoplace,thetipoftheferrule’staperednosedoesn’tactuallymakecontactwiththereceivingtaperatall;rather,contactoccurspartiallyuptheferrule’swall.Thisscenariocreatesineffectivecompressionoftheferrule’staperednoseonthetubingwallandmayresultinaleakingconnectionoralackofferrule“holdingpower.”

2.Ferruleandreceivingporthaveidenticalangles

Inthisexample,becausetheanglesmatch,theferrule’sentiretaperednosemakescontactwiththereceivingportatthesametime.And,no

FIGURE5FerruleOrientation

FerruleTaper(orangle)

PortTaper(orangle)

PARDON MOI?

AllAboutFittings18

POINT OF INTEREST

matterhowmuchyoutightentheaccompanyingnut,thetwomatingsurfacesaresimplywedgedmoretightlyintoplace,resultinginvirtuallynocompressiononthetubingwall.Again,thiswouldtypicallyproducealeakingconnection.

3.Ferrulehasanarroweranglethanthereceivingport

Here,thetipoftheferrulemakescontactwiththereceivingportfirst,andasthefittingistightenedintoplace,theferrulebeginstoconformtotheport’sangle,andcompressesagainstthetubingwall.Justwhatyouwant!

(Figure6illustrateseachofthesescenarios.)

Besidesthesealandgripcreatedaroundtheoutsidetubingwall,youalsoneedasealbetweentheoutsidesurfaceoftheferruleandtheinternalsurfaceofthereceivingport.Thequalityofthesealreallydependsonthesurfacequalityofboththereceivingportandtheferrule.Anyimperfectionsoneithersurfacemaycausealeak.

FIGURE6ThreeFerruleInterfaces

FerruleWiderThanThePort

FerruleSameAsThePort

FerruleMoreNarrowThanThePort

HowDoFittingsWork?

SECRET REVEALED

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Themostdemandingfluidconnectionsaretypicallyfoundinthehighpressureareasofasystem—infact,it’snotunusualforpressuresinHPLCtoreachandexceed4,000psi(276bar)andinUHPLCtoreachpressuresof15,000psi(1,034bar)andhigher!Becausetheseconnectionsexperiencethelargestamountofstress,let’sfocusfirstonhowtomakegoodhighpressureconnections.

OneofthemostpopularstylesofconnectionsusedforHPLCandUHPLChighpressurefluidpathwaysisa“swaged”connection.

Webrieflymentionedtheconceptofswagingearlier.Now,let’slookattheprocessofswagingalittlemoreclosely—whatitis,howitworks,andwhyitremainssopopulartoday.

First,asarecap,swagingmeans“permanently”attachingaferruletoapieceoftubing,typicallyinahighpressureapplication.Often,boththefittingandthetubingaremanufacturedfromsomeformofstainlesssteel,althoughthatdoesn’talwayshavetobethecase.However,swagingtypicallywillnotinvolveanall-polymerferrule.Mostpeoplewhoareswagingareusingstainlesssteelferrulesaspartofthefittingsystem.

High pressure connections

Inordertoswageaferruleontoapieceoftubing,slipthenutoverthetubingbeingconnected.Followthatbyslippingtheferruleoverthetubing,justbelowthenut,ensuringthetaperednoseoftheferruleisfacingawayfromthenut(rememberthelittlepoemfrompage13?).

Oncethenutandferruleareinplace,insertthetubingintothereceivingportuntilthetubingbuttsupagainstthebottomoftheport.PleaseNote:Thisprocessworksformostports;however,someportsdonothaveasolidstopagainstwhichthetubingcanrest.Forthese,extracareisnecessarytoensurethetubingremainsextendedpasttheferrule’snose...butnottoofar!

Withthetubingheldinplace,finger-tightenthenutcompletely,andthenwrench-tightenitanother3/4turn.Thisoftenwillcompletetheswage,crimpingtheferruleontothesurfaceofthetubing.Tomakesurethishasbeendonecorrectly,loosentheassemblyandremoveitfromthereceivingport.Inspecttheferruletoensureitwillnotcomeoff;ifit’sstillloose,reinsertthefittingandtubingassemblyintothereceivingportand

HELP ME!

AllAboutFittings20

tightenin1/4-turnincrements,checkingtoseeiftheferrulehasbeenfixedontothetubingaftereach1/4-turn.

PleaseNote:ThetighteningrecommendationslistedaboveareintendedforusewithtraditionalHPLCandrelatedequipment.IfyouareusingUHPLCsystemsorworkingatultra-highpressures,additionaltighteningmayberequiredtoachievethepressureholdingabilityyouneed.

FOODFORTHOUGHT...Swaged fittings offer some significant advantages. One is that they permanently attach to the wall of the tubing. This allows swaged fittings to hold to high pressures — almost always well above the pressure rating of the equipment into which the fitting is attached.

...NOWYOUKNOW!

Thefactthatswagedfittingsarepermanentlyattachedalsohelpstokeepthefittingswithapieceoftubing.Sincethey’reattached,theywon’tcomeoffaccidentally.(Thisisabighelpifyoutendtobe“challenged”withsmallthings!)

Unfortunately,thispermanentattachmentalsobecomesamajordisadvantage!Why?Becauseyoucanonlyusethefittinginoneport—theoneintowhichitwasswaged.

Yousee,whenafittingisswaged,thereisalwaysalengthoftubingextendingpasttheferrule.Ithastobethisway,ortheferrulewouldhavenoplaceto“bite”downduringthecompressionprocess.Thecomplicationisthateverymajormanufacturerrequiresthelengthtobealittlebitdifferent(seeFigure7).Thismeansthatonceswagedintoareceivingport,forthebestanalysisresults,afittingshouldonlybeusedwiththatoriginalport!Attemptingtouseaswagedfittingwithanyotherportmayresultineitherdeadvolume(seepages51–53foradiscussionon“deadvolume”)orachemicalleak–particularlywhenequipmentfrommultiplemanufacturersisbeingused!

HowDoFittingsWork?

FIGURE7“DimensionX”fromVariousManufacturers

DimensionXcanrangefrom0.080”(2.0mm)to0.170”(4.3mm)amongvariousmanufacturers

X

X=0.080”

(2.0mm)

X

X=0.090”

(2.3mm)

X

X=0.130”

(3.3mm)

X

X=0.170”

(4.3mm)

PARDON MOI?

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POINT OF INTEREST

permanentlyadheretothesurfaceofyourflowpathtubing,whichallowsthemtoberepositionedasneededtohelpavoidleakingconnectionsanddeadvolume.

Inadditiontotheobviousbenefits,otheradvantageshavehelpedthefingertightfittingbecomealaboratoryessential:

Biocompatible

Manybiologicalsamplesareknowntointeractwithiron,achiefcomponentofstainlesssteel...butnotacomponentofmostpolymers.

Universal

Whilemanycustomersareforcedtousesystem-specificmetalfittings,inmostcasesjustonestyleoffingertightfittingcanbeusedtomakeconnectionsthroughoutasystem.

Interchangeable

Becausefingertightfittingsdonotpermanentlyattachtothetubingwall,theycanoftenbemovedfromporttoportwhilestillallowingyoutomakeagoodconnectionbyensuringthetubingisfullyinsertedintothereceivingport.

The problem fixerOneofthemostcommonlyencounteredproblemswithfittingsisachemicalleak(e.g.,whenswitchingbetweendifferentbrandsofHPLCcolumns).Initially,whenaleakoccurs,it’softenbesttomakesurethefittinghasbeentightenedproperly.Often,though,aleakingconnectionisduetoaproblemwiththepositionalplacementoftheferruleonthetubingwall.Unfortunately,withaswagedfitting,theferruleispermanentlyattachedtothetubing,soitcannotberepositionedorchanged(atleastnotwithoutdamagingthetubingand/ortheferrule).Thisusuallyresultsinthrowingawaytheentirepieceoftubing—withtwoferrulesandnutsattached—makingthisoptionveryexpensive.

ThereISanotheroption...thefingertightfitting.

Fingertightfittingsaretypicallypolymerfittingsthatworkinthesamereceivingportsastheirall-metalcounterparts.Becausetheyaremanufacturedfromhigh-endpolymersratherthanfrommaterialslikestainlesssteel,youcanachievegoodperformancefromafingertightfittingwithoutusinganytoolsotherthanyourhand.Also,becausetheyaremanufacturedfrompolymermaterials,theydonot

THIS OR THAT?

AllAboutFittings22

comparableswagedfittings.Otherlimitationscanbelinkedtotheirperformanceinelevatedtemperatureapplicationsandevenlinkedtochemicalinteractioninasomerarecases.Nonetheless,fingertightfittingstypicallyoffersubstantialbenefitsthatfarsurpasstheirlimitations...whichiswhytheyhavebeensowidelyadoptedaroundtheworld!

WhatAboutLowPressureConnections?

Ofcourse,notallfluidconnectionsinyoursystemarehigh-pressureconnections—infact,mostoftheconnectionsarelikelyonesthatcanbeconsidered“low-pressure”connections.Typically,thefittingsusedtomake“low-pressure”connectionsaredifferentfromtraditional“high-pressure”fittings.

First,mostlow-pressurereceivingportsdonothaveaconed(or“tapered”)internalsurface.Instead,theyoftentransitionfromtheinternalthreadsoftheconnectiondirectlytoaflat-bottom.Ofcourse,asyoumightexpect,thesetypesofportsrequiredifferentfittings—fittingsthatarefocusedonmakingasealontheflat-bottomfeature.

Theoriginalstyleoflow-pressure,flat-bottomfittingswastheflangedfitting—astylestillinusetoday!Whenaflangedfittingconnectionis

HowDoFittingsWork?

FIGURE8FlangedFittingConnection

Theuseoffingertightfittingsispopularinbothanalytical-scaleapplicationsaswellasinapplicationsinvolvingcapillarytubing.However,whenfingertightfittingsareusedwithcapillarytubing,thefittingsoftenemployspecialfeatures—likecustomferrulesortubingsleeves—tohelpmakegoodconnections.Formoreinformation,seethediscussiononcapillarytubingconnectionsbeginningonpage41.

Ofcourse,fingertightfittingsarenotwithoutlimitations.Onelimitationisdirectlylinkedtooneoftheirprimaryadvantages--thattheydonotpermanentlyattachtotubingwalls.Whilethisisadvantageousforrepositioningconnectionsandoverallinterchangeability,itdoesmeanthatfingertightfittingsoftenhavealower-pressureholdingabilitythan

All About Fittings

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made,theflowpathtubingisflaredoutattheend,andthesupportingfittingpressesthetubingflareagainstthebottomofthereceivingport.

Flangedfittingsarestillusedbecauseoftheirrelativelowcostandeaseofuse.However,ifanythinggoeswrongwithaflangedconnection,itcanbedifficulttorepair.Therefore,manypeoplehavemigratedawayfromflangedtubingconnectionsandswitchedto“flangeless”connections.

Inaflangelessconnection,ratherthanflareoutthetubingtomakeasealinthebottomofthereceivingport,thissystem(andotherssimilartoit)typicallyusesaseparatefittingandanexternalcompressionferrule.Butinsteadofhavingtheconedtipoftheferrulefacingawayfromthefitting,thisfittingstylehastheconedtipoftheferrulefacingtowardthefitting.(seeFigure5,page17,foranexampleofatypicalflangelessfittingsystem,shownontheright-handsideofthatfigure.)

Mostofthetime,lowpressureconnectionsdonotrequireanytoolstomakegoodconnections—simplyhand-tighteningissufficient.Also,whenaflangelessfittingsystem(orsomethingsimilar)isused,low-pressurecomponentsoftensharemanyofthebenefitsoffingertightfittings,includingbiocompatibility,interchangeabilityandevenuniversaluseinmostreceivingports!

BarbsAway!

Whilemanylow-pressureconnectionsuserigidorsemi-rigidtubing—andcanthusutilizetraditionalexternalcompressionfittings—therearesomeconnectionsforwhichexternalcompressionfittingswillnotwork.Specifically,whensoftertubingisused—forexample,withperistalticpumps—externalcompressionfittingsarenotusuallythebestoption.Fortheseapplications,themostcommonformofconnectoristhe“barbed”connector.

Abarbedconnectorworksbyforcingsoftertubingtoexpandoverabarbednose.Thiscausesthetubingto“grip”theconnectorandremaininplace.However,thisconnectionistypicallyonlygoodforlowpressureapplications,becauseasthepressureincreasesinsidesoftertubing,itcausesthetubingtoexpand.Eventually,withenoughinternalpressure,thetubingwillexpandsufficientlytoslipoffthebarbedconnectorbeingused.

FIGURE9BarbedConnectors

AllAboutFittings24

What Fitting Do I Have?Onceyouunderstandhowfittingswork,oneofthebiggestfrustrationscanbefiguringoutwhatfittingyouhave,soyoucanreplaceitwithausablealternativewhenneeded.

We’vealreadydiscussedsomedefiningcharacteristicsforfittings,allofwhichwillhelpyoudeterminewhatfittingyoualreadyhave...andthenhelpyoudecidewhichfitting(s)wouldbestsuityourneeds:

AThreadByAnyOtherName…

Wetalkedearlieraboutthethreadonafitting,andwhatthatthreadcall-outtellsyouspecifically.Reviewing,eachthreadcall-outusuallyconsistsoftwomainnumbers—bothtellingyousomethingaboutthethread.Forinstance,lookingatathreadcall-outsuchas1/4-28,the“1/4”referenceindicatesthethreadhasamaximumdiameterof1/4”,andthe“28”tellsushowmanythreadsperinchexistalongtheshaftofthefitting.

But,howdoyoutellwhattypeoffittingyouhave?Ifyoudon’thaveanyinformationaboutthefitting,thendeterminingitsthreaddescriptionisoneofthemostcriticalpiecesofinformationyoucanobtain.

Fortunately,youcanusuallydeterminewhatthreadyouhavewithacommonrulerandagoodeye.First,lineupthethreadedsectionofyourfittingagainstyourruler’sedge,asshowninFigure10aonthenextpage.It’smosthelpfulifyouuseatleasta1/4”sectionofthreadsforperformingthismeasurement.

Threads on the fitting

Geometry of the fitting (coned or flat-bottom)

Size and type of tubing being connected

Material from which the fitting is manufactured

Amount of pressure expected

WhatFittingDoIHave?

PARDON MOI?

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Next,countthenumberofthreadsalongthebarrelofthefitting,untilyougettothe1/4”markonyourruler.

REMEMBER:THEFIRSTTHREADISYOURZEROMARK...DON’TINCLUDEITINYOURTHREADCOUNT!

IfyouhaveanEnglishthread,oneofthethreadsonyourfittingshouldlineupwiththe1/4”mark(InFigure10a,thereare7threadsin1/4”).Then,allyouhavetodoismultiplyyourresultbyfourtogetthenumberofthreadsperinch—otherwiseknownasthethreadpitch!(Ifyouhaveametricthread,thenthiswon’twork!We’llgothroughthatinamoment...).

Onceyoudeterminethenumberofthreadsperinchonyourfitting,thediameterofthethreadedportionismucheasier.Simplyplacethethreadedbarrelofyourfittingontopofarulerandmeasurethewidestdistance,fromthethreadcrestsononesideofthenuttothethreadcrestsontheothersideofthenut,asillustratedinFigure10b,right,wherethisdistanceis1/4”.

FIGURE10ACountingYourThreads

0 1/8 1/4

FIGURE10BThreadDiameter

0 1/21/4 3/4 1POINT OF INTEREST

AllAboutFittings26

(the“x1”part).NoticethisisinversefromEnglishthreads,whichtellyouhowmanythreadsperinch.(Seepage10formoreinformation.)

Tomeasurethethreadpitchofametric-threadedfitting,holdthethreadedbarrelofyourfittingagainstarulerwithmillimeterincrements.Lineupthecrestofathreadneartheheadofthefittingwithoneofthemillimetermarkingsontheruler.Then,examinewheretherestofthethreadcrestsfall.ThemostcommonlyusedmetricthreadswillhaveeachthreadcrestlineupEXACTLYwitheachmillimetermarkonyourruler.Othermetric-threadedfittingsmaynothavetheirthreadsspacedonemillimeterapart;however,theywillfollowapattern(liketenthreadsinsevenmillimeters,forinstance—usedforaM4x0.7thread).

Tomeasurethediameterofyourmetric-threadedfitting,usethesamemethoddescribedforEnglishthreadedfittings,onlyusingthemetricsideofyourrulerasareferencepoint.

FormostEnglishthreadedfittingsusedinchromatography,thediameteroftencorrespondswiththethreadpitchaccordingtothischart:

ThreadsPerInch Diameter

20 1/2”(12.7mm)

24 5/16”(7.9mm)

28 1/4”(6.4mm)

32

3/16”(4.8mm)Gauge10,&9/64”(3.6mm)Gauge6

40 9/64”(3.6mm)Gauge6

Ofcourse,therearevariationswhichexist,butthischartcanserveasagoodstartingplace.

Whenworkingwithmetric-threadedfittings,manualmeasurementissomewhatdifferentbutusesthesameconcepts.

Rememberthatthemostcommonmetric-threadedfittingusedinchromatographyandrelatedapplicationshasthedesignation“M6.”Technically,thisisincomplete;therealdesignationforthethreadisM6x1.Ifyou’llrecall,thismeansthatthethreadhasasixmillimeterdiameter(the“M6”part),andhasathreadpitchofonemillimeterperthread

WhatFittingDoIHave?

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In case you want it easy…

Nowthatyou’vegonethroughthethread-measuringexercise,youcanusethediagramsinthechartbelowtohelpyoumoreeasilydeterminethethreadingofyourfitting.

Tousethisresource,simplyholdyourfittingovereachofthesilhouettes

toseeifyourfittingmatchesanyofthem.Eachshadowdrawingisanexactreplicaofthethreadgiven;therefore,thediagramscanbeusedeithertoquicklyverifyathreadorasacheckagainstyourmeasurements.

Holdyourfittingoverthethreadsilhouettesbelowtoidentifythethreads.

U.S.CustomaryThreads

6-40

6-32

10-32

1/4-28

5/16-24

1/2-20

MetricThreads

M4x0.7

M6x1

WhatthreadsdoIhave?

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AllAboutFittings28

Plastic or Metallic — Which Do I Choose?Oneofthemostcommondilemmasafittingsuserfacesisdecidingbetweenplasticandmetallicfittings.Theseandmanyotherquestionsareoftenasked:

Mysystemalreadyusesstainlesssteelfittings,soIhavetokeepusingthem...right?

Willmychemicalsormysampleinteractwiththefitting?

IfI’musingmetaltubing,Ican’tuseplasticnutsandferrules...canI?

WhichtypeoffittingwillactuallyholduptothepressureIneed?

It’scommontothinkthatyouneedtousethesametypeoffittingoriginallyincludedwithyourinstruments.Infact,thisisoneofthemainreasonsstainlesssteelfittingshaveremainedaspopularastheyare!

Fortunately,instrumentperformanceisrarelylinkedtoonespecificfitting,whichoffersyouthefreedomtochangeyourfittingstobestsuityourapplicationandneeds.Tohelpchoosethebestfittingforyourapplication,firstconsiderwhatthefittingissupposedtodo.Doesitholdhighpressureorlowpressure?Whatisthechemicalenvironment?Whatis

theoperatingtemperature?

Oneotherfactortoconsiderwhendecidingwhatfittingtouseishowthefittingwillbeused.Ifyouplantoconnectapieceoftubingtoareceivingportandrarelytakeitout,thenastainlesssteelfittingisoftenagoodoption.However,ifyouexpecttomakefrequentconnectionswiththefitting,orifyouplantousethetubinginmultiplelocations(forinstance,withmultiplecolumnsinyourHPLCsystem),apolymerfittingisreallythebestoption.

Afteransweringthesequestions,look

Here, we’ll address the most common questions and concerns.

CanIReallyChangeMyFittings?

PlasticorMetallic–WhichDoIChoose?

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POINT OF INTEREST

forthefittingsystemthatoffersthecombinationofgoodperformanceandoveralldesignfeaturesthatmakeiteasytouse,reliable,andthebest“fit”foryourapplication.

Keepinmindthatwhiletherearesomeapplicationswheremetallicfittingsmakeusefulconnections,polymerfittingsareoftenanexcellentchoiceinmostapplications,regardless

ofwhatkindoftubingisbeingused.Ironically,theoppositedoesnotholdtrue—stainlesssteelfittingscannotbeusedinmanyplaceswherepolymerfittingsarebeingemployed...specificallyinthoseapplicationswhereapolymerfittingisattachingtubingtoaplasticport.Inthoseapplications,usingastainlesssteelfittingwilllikelycausedamagetothereceivingport!

WhatAboutTheChemicalEnvironment?

Thisisaveryvalidquestion,andonethatmustbeconsideredregardlessofwhattypeoffittingyouchoose.Ifincompatiblechemicalscontactafitting,itsabilitytosealanditsthreadintegritymaybecompromised.

applicationwherealowconcentrationofTFA(trifluoroaceticacid)isbeingused.Inthistypeofapplication,thePEEKferrulewillperformadequately.However,ifthesolutioncomesinprolongedcontactwiththenut(e.g.,ifsomeofthechemicalsolutiongotontheport’sthreadswhenthefittingwaspreviouslyloosened),eventuallythepolymerwoulderodeawayatthepointofcontact.Thefitting’sintegritywouldthenbecompromised—resultinginaleak!

Therearemanysourcesforup-to-dateinformationregardingchemicalcompatibility(asummaryofchemicalcompatibilityinformationisprovidedintheAppendixofthisbookletonpage61),includingthemanufacturerofthefittingsyouhavechosentouse.Othersourcesarealsoavailableontheinternet.Wehighlyrecommendyourefertooneofthesesourcesbeforefinalizingyourfittingsselection.

AGoodRuletoFollow:ALWAYS CONSIDER THE CHEMICAL ENVIRONMENT!

Additionally,sincemostfittingscomprisetwopieces—thenutandtheferrule—youshouldconsiderchemicalcompatibility

withboththenutandtheferrulematerial.Forexample,youmayhaveafingertightfittingwithaPEEK™polymerferruleandaDelrin®nut,andyouneedtomakeatubingconnectioninaLC-MS

AllAboutFittings30

WhatMaterialWithWhatTubing?

Bynowyouprobablyrealizethatyoucannearlyalwaysuseaplasticfittingonanytypeoftubing—polymerormetallic.Aslongasthefittingwillholdmorethanthepressureyouexpectwithyourapplicationandaslongasyourtubingissuitedforthestyleofconnectionyouaretryingtomake(e.g.,externalcompression,internalexpansion,etc.),thenyoushouldnothaveanyproblemswiththeconnection.

Ontheotherhand,itcanbedangerous—orevenimpossible—touseametallicfittingonplastictubing.Whenametallicfittingcrimpsdownonplastictubing,becausethemetalissomuchstrongerthanthetubingmaterial,itveryfirmlysqueezesthetubingwall.Infact,itmightsqueezethetubingwallsohardthatit

damagesthetubingorcollapsestheinnerdiameter,thusrenderingyourtubingunusableinyourapplication.Tohelpdeterminethepossiblefittingoptionsthatcanbeused—assumingtheflowpathtubingyouareusingisfairlyrigid—youcanreferencethepoemaboveandthefollowingtableasguidelines:

Fitting Tubing Port Recommended?

Plastic Plastic Plastic Yes

Plastic Steel Plastic Yes

Plastic Steel Steel Yes

Plastic Plastic Steel Yes

Steel Steel Steel Yes

Steel Plastic Steel No

Steel Plastic Plastic No

Steel Steel Plastic No

Table1—FittingsApplications

Which to Choose – a poem

SteelonplasticWaytoodrastic!PlasticonsteelWhatadeal!

PlasticorMetallic–WhichDoIChoose?

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WhatAboutThePressure?

Oneofthestigmasassociatedwithusingapolymerfittinginsteadofametalliconehastodowiththesystempressure.Infact,mostmetallicfittingswillholdtohigherpressuresthantheirpolymerfittingcounterparts.Yet,theREALquestiontoaskisjusthowmuchpressuremustthefittingwithstand?Ifyourapplicationonlycallsfor1,000poundspersquareinch(psi)(69bar),andyouhaveachoicebetweenastainlesssteelfittingthatholdsto10,000psi(689bar)andapolymerfittingthatworksto6,000psi(414bar),itdoesn’tmatterwhichfittingyouchoosebecausebothwillworkforthatapplication.

Forsuperhighpressureapplications,suchasUHPLCwheresystempressurescanexceed15,000psi(1,034bar),mostanalystsprefertostickwithmetalnutsandferrulesorotherspecializedfittingsdesignedforusewiththosepressures.Butforlow,moderateandstandardhighpressureapplications,apolymerfittingoptionusuallyexists.Besuretoconsultthemanufacturer’sdataonafitting’sabilitytoholdtothepressureyourapplicationdemands.

Summing upOverall,plasticfittingscanserveastheconnectionofchoiceforavastmajorityoftubingconnections.Thefollowingreasonsshowwhy:

A wide variety of polymer fittings is available

Polymer fittings frequently offer superior chemical compatibility

Polymer fittings can hold to most required pressures

Nearly universal functionality is possible with polymer fittings

Polymer fittings are reusable over and over again

Polymerfittingsareoftensuperiortosimilaronesmadeofstainlesssteelorothermetals.

The bottom line

THIS OR THAT?

AllAboutFittings32

What is HPLC?Oneofthemainliquidtransferapplicationsusingthefittingswe’vediscussedisHPLC.Becauseitissuchapopularanalysistechnique,itseemsappropriatetoinvestsometimediscussingit.

HPLCisanacronymthatstandsforHighPerformanceLiquidChromatography.(Manypeoplethinkthe“P”standsfor“Pressure,”astheoperatingpressuresformanyHPLCapplicationsisquitehigh;however,the“P”reallydoesstandfor“Performance.”)

HPLCbegantobeusedinthe1960’s.Thetechniqueallowsanalyststoseparateasampleofknownorunknowncompositionintoitscomponents,andthentoquantifyhowmuchofeachcomponentispresentinthesample.And,becausethistechniqueisgenerallynon-destructive,HPLCisaveryusefultoolinthelaboratory,asitallowsthescientisttocontinueperformingothertestsonhisorhersampleafterithasbeenanalyzedusinganHPLCsystem.

Separationoccursbyintroducingasampleintoaliquidchemicalstreamknownasthemobilephase,whichinturncarriesthesampletoaspecializedtubecalledthecolumnpackedwithsmall,chemically-activeparticlesknownasthestationaryphase.Insidethecolumn,thesampleinteractswithboththemobilephaseandthestationaryphaseandbeginstochemicallyseparateintoitscomponents.Otherequipmentinthesystemcreateandcollectdatafromtheanalysisofthoseseparatedsamplecomponents.Thosedataarethensummarizedinaprintedgraphicalplotcalledachromatogram.(WHEW!)

WhatisHPLC?

POINT OF INTEREST

KEY CONCEPT

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What makes up an HPLC system?

Beforewecangoanyfurther,itisimportanttounderstandwhatcomponentsarepartofastandardHPLCsystem.

AnHPLCsystemincludessevenbasiccomponents,eachwithavitalfunction:

Solventreservoir:Thesolventreservoirholdsthechemicalsolutionthatmovesthroughthesystem.Becausethissolutionismovingthroughouttheanalysis,itiscalledthemobilephase.

Pump:Thepumppullsthemobilephaseoutofthereservoirandpushesitoutthroughtherestofthesystem.Themostcommonpumpinusetodayisthedual-pistonpump—capableofdeliveringstableflowratesathighpressures.

Injectionvalve:Theinjectionvalveintroducesthesampleintothemobilephase.Themostcommoninjectionvalveisasix-port,two-positionvalve(seeFigure11).Thistypeofvalveallowsacontrolledamountofsampletobereproduciblyintroducedintothemobilephasepathwaywithlittleornodisturbancetotherestofthesystem.

FIGURE11TypicalInjectionValvePlumbingViewpoint From Rotary Knob

SampleIn(NeedlePort)

SampleIn(NeedlePort)

SampleWaste

SampleWaste

Pump

Pump

Column

Column

LOAD

INJECT

1

1

4

4

2

2

6

6

3

3

5

5

AllAboutFittings34

POINT OF INTEREST

Theinventionoftheinjectionvalvetrulyrevolutionizedchromatography,asitautomatedthewayforsamplestobeintroducedandanalyzed.Whatoriginallybeganasananalysistechniquewiththecapacityofworkingwith20-40samplesperday,HPLCsystems(whencoupledwiththeproperequipment)canhandlehundredsofsamplesperday,allowingforrapiddrugdiscoveryaswellashighthroughputgenomicsandproteomicswork.

Column:OftencalledtheheartoftheHPLCsystem,thinkofthecolumnasachemical“filter,”ofsorts.Thecolumnisatubeofsomespecifiedlengthandinnerdiameterandusuallyfilledwithsmallbeads.Typically,thebeadsarecoatedwithachemicalsubstancedesignedtointeractwiththesamplecomponentsandenhanceseparation.Mostfrequently,thebeads—describedearlierasthestationaryphase,becausetheydon’tmoveinthesystem–areverysmalldiametersilicaparticlesandtypicallyhaveoctadecylsilane(C18)chemicallybondedtotheirsurfaces.Other,morespecializedmaterialsaresometimes

usedinsteadofsilica.Also,inadditiontotheC18bondedtothesurfacesofthebeads,other,morespecializedmoleculescanbebondedtothebasematerialtofurtherenhancetheseparationachievedinthecolumn.

Detector:Thedetectorisresponsiblefor“seeing”thesamplecomponentsthatareseparatedinthecolumnastheyarebeingcarriedalongbythemobilephase.Themostcommonly-useddetectorpassesabeamofultra-violetlightthroughaspecialwindow(knownasthe“flowcell”).Asthesamplecomponentspassthroughtheflowcell,theamountoflighttransmittingthroughtheflowcellchanges.Theelectronicsofthedetectorthenconvertthechangeintransmittedlightintensityintoasignal.

Otherdetectoroptionsarebeingusedmorefrequentlyasthecostoftechnologycontinuestodrop.Detectorssuchasmassspectrometers(MS)andnuclearmagneticresonance(NMR)detectorsarefindingincreaseduseinmanylaboratories.Withimproveddetectionoptionsnowavailabletothechromatographer,HPLC—alreadyamainstayinmanylaboratories—isfindingincreasinguseasananalyticaltechnique.

WhatisHPLC?

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POINT OF INTEREST

Recorder:Therecordertranslatesthesignalgeneratedbythedetectorintoaplot,creatingachromatogram(seethediagramofsignalversustimeabove.)

Intheearlydays,thisdevicewasnothingmorethanastripchartrecorderwithapenthatmovedinresponsetothesignalcreatedbythedetector,writingonapieceofgraphpapermovingatacontrolledspeed.Then,thepeakswouldbecarefullycutoutandthepaperweighed(yes...weighed)on

ascaletoobtainsemi-quantitativedata.Nowadays,therecordingdeviceisusuallyacomputer,equippedwithsoftwaredesignedtonotonlytranslatethesignalfromthedetector,buttoalsoprocessthedatadigitally.Thisallowsmuchmorereproducibleinformationtobegeneratedandhasfacilitatedtheuseofsmallerandsmallersamples.

Wastereservoir:ThelastcomponentinabasicHPLCsystem,thewastereservoirsafelycollectsallthemobilephaseandsamplecomponentsaftertheypassthroughthesystem.

FIGURE12ExampleChromatogram

0 10 20

SIG

NA

LIN

TEN

SITY

Peak Baseline

TIME(MIN.)

AllAboutFittings36

LookingAtTheComponentsAsASystem

NowthatyouunderstandthebasicsofthekeyHPLCsystemcomponents,let’srunthroughthewholeprocessagain.Onceamobilephaseisprepared,thepumpthenmovesitthroughthesystem,whereitencountersthesampleandcarriesitthroughthecolumn.Insidethecolumn,thesamplecomponentsselectivelyinteractwiththemobilephaseandthestationaryphase,separatingintogroupsoflikemoleculesastheymovethroughthecolumn.Leavingthecolumn,thesamplecomponentgroupsthenpassthroughthedetector,which“sees”thecomponentsandsendsasignaltotherecordingdevice,whichinturncollectsandprocessesthedata.Thewastereservoirthencollectsthefluidfordisposal.

FIGURE13TypicalHPLCSystem

WhatisHPLC?

WasteReservoir

Column

SolventReservoir

Pump

SampleInjection

Valve

Recorder Detector

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Other system “stuff”WhileanHPLCsystemcannotfunctionwithoutthebasicsevencomponents,itmostcertainlycanfunctionwithmorethanthoseseven.Infact,therearemanycommonly-usedaccessoriesandcomponentswhichhelpenhancetheperformanceofastandardHPLCsystem,includingthefollowing:

Filters:Foundinthesolventreservoirandalongtheflowpathinnumerouslocations,filtersplayavitalroleinmaintainingsystemperformance.Filterspreventsolidparticlesfrompassingthroughthesystem;failuretousefilterscanresultindamagedsystemcomponents,increaseddowntime,andpoorchromatographicresults.(Formoreinformationonfilters,checkouttheAppendix,beginningonpage54.)

Guardcolumns:Guardcolumnsdoexactlywhattheirnameimplies...theyguardthemainanalyticalcolumn.Theyaretypicallysmallversionsoftheanalyticalcolumn,usedtotrapsamplecomponentsthatwouldotherwiseirreversiblybindtotheinsideoftheanalyticalcolumn.Theguardcolumnactslikeaninsurancepolicyfortheprimaryanalyticalcolumn,helpingtodelaytheoften-costlyreplacementoftheprimarycolumn.

Backpressureregulators:Abackpressureregulator(BPR)ismostoftenplacedinlinebetweenthedetectorandthewastereservoir.Itcreates

additionalupstreampressure,topreventanygaseswhichmightbedissolvedinsolutionfromoutgassingandcreatingbubblesalongthemobilephaseflowpath.(Ifanybubblespassthroughthedetector’sflowcell,aphenomenonknownas“noise”canshowuponthechromatogram’sbaselineandlimitthesensitivityofanalysis.)(FormoreinformationonBPRs,seetheAppendix,page57.)

Vacuumdegassers:Avacuumdegasserisapieceofequipmentthatiscommonlyplacedinlinebetweenthesolventreservoir(s)andthepump.Thisdeviceisengineeredtoextractthedissolvedgasfromthemobilephasebeforeitreachesthepump.Bydoingso,ithelpskeepthegasconcentrationinsolutionsufficientlylowsuchthatbubblescannotformoncethemobilephasetransitionsfromthehighpressureofthecolumntothelowpressurezonepost-column.Aswithbackpressureregulators,preventingbubblesfromforminghelpspreventbaselinenoiseandthusimproveschromatographicresultsaswellasreproducibility.

KEY CONCEPT

AllAboutFittings38

What goes where?

Ofcourse,fittingsarestandarditemsusedtoconnectthecomponentstogether,usingtubingastheflowpathbridgebetweencomponents.Yet,oneofthemostcommonly-askedquestionsregardingfittingsis,“Wheredoallthesefittingsgoinmysystem?”Inotherwords,howdoIknowwhattousewhere?

Onecommonwaytodistinguishbetweenfittingsisbyclassifyingthembasedonthepressuretheycanhold.Thisnarrowsthefittingschoicebasedonwhereinthesystemtheywillbeused.

Generally,fittingsareclassifiedaseither“lowpressure”or“highpressure”fittings.Correspondingly,“lowpressure”mostoftenreferstoapplicationsorareasinyoursystemwheretheflowpathpressuresdonotexceed1,000psi(69bar).“Highpressure”areascanhaveflowpathpressuresthatexceed6,000psi(400bar)!(Someofthedifferencesbetweenhighpressureandlowpressurefittingshavealreadybeendiscussedearlierinthismanual.)

InanHPLCsystem,therearegenerallythreepressurizedzones,eachwithitsfamilyoffittings.Thefirstzoneexists

betweenthereservoirandtheinletofthepump.Thisistypicallyalowpressurezone,asthepumpispullingthemobilephasefromthereservoirinthisarea,usuallycreatingsomenegativepressure.Thefittingsusedinthiszonearegenerallylowpressure,low-costfittings,mostoftenhavinga1/4-28flat-bottomgeometry,andaregenerallyfor1/8”(3.2mm)outerdiameter(OD)tubing.

ThesecondzoneinthesystemexistsfromtheoutletofthepumpthroughtheinjectionvalveandthroughtheHPLCcolumn.Inthiszone,thefluidflowisbeingresistedbythestationaryphaseinsidethecolumn,andassuch,thepumpexperienceshigherbackpressures...asdothefittings.

Inthissecondzone,fittingsaregenerallyclassifiedashighpressurefittingsandmostfrequentlyhavea10-32conedgeometryforusewith1/16”(1.6mm)OD(orsmaller)tubing.Becauseperformancedemandsofthefittingsaregreaterinthisareaofthesystem,themanufacturingcostsandpurchasepriceofthefittingsaregenerallyhigher.

Lastly,inthethirdzone—fromthetubingexitingthecolumnthroughthedetectorandontothewastereservoir—thesystempressuresaregenerallynearambientpressures,withslightlyelevatedpressuresbeingexperiencedwhenextracomponents

WhatisHPLC?

PARDON MOI?

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areused(likebackpressureregulators,forinstance).Becausethesystempressureinthisthirdzoneistypicallylow,thefittingsonceagainoftenassumeastandard,1/4-28flat-bottomgeometry,andtheyaretypicallyforusewith1/16”(1.6mm)ODtubing.

Itisimportanttonotethateventhoughthisthirdzoneisalowerpressurezone,manyOEM(“OriginalEquipmentManufacturer”)companiesrealizethatmostlaboratorieshavemorefittings

withthe10-32conedgeometryfor1/16”(1.6mm)ODtubingthananyothertypeoffitting.Therefore,thereceivingportsavailableonequipmentinthiszonemayrequiretheuseof“highpressure”fittings,eventhoughtheinlinepressuresarelow.

Thediagrambelowshowsan“accessorized”HPLCsystem,tohelpyouunderstandhowasystemisputtogether —includingwhatfittingstoputwhere.

FIGURE14TypicalHPLCSystem

39

HighPressureFittings

LowPressureFittings

SolventReservoir

InletSolventFilter Inline

SolventFilter

PrecolumnFilter

GuardColumn

Column

BackPressure

Regulator

WasteReservoir

RecorderDetector

SampleInjectionValve

Pump

AllAboutFittings40

Other Popular “Apps”

Big things come in little packages

InadditiontotraditionalHPLC,overthepastseveralyears,therehavebeenadvancesintechnologythathaveexpandedtheworldofchromatographyinseveraldirections.Twoofthesehavebecomethemostprominent—microscalechromatographyandUHPLC,orUltra-HighPerformanceLiquidChromatography.

Oneofthemostpopularadvancesinchromatographictechnologyhasbeenthedevelopmentofmicroscaleandevennanoscalechromatographicmethods.WhereHPLCusesthingslike1/16”(1.6mm)ODtubing,flowratesof1mL/min,andsamplesizesof20µL,thissmaller-scalechromatographyisknownformuchdifferent“standards”:360µmODtubing,flowratesinthelowmicrolitersperminuteorless,andsamplesizesinthenanoliterrange.

Somewhatintuitively,thissmallerscalerequiresanincreasedattention

tothequalityoftheconnectionsthataremade,asevensmalldeadvolumechamberscanhaveatremendousimpactonyourresultswhenoperatingundertheseconditions.Workingtoensureyourtubingiscutandpreparedwell(seepage44foradiscussiononhowtoproperlypreparetubing)andmakingsurethatyouareusingthebestfittingsfortheapplication(seepage41foradiscussionon“pitfalls”toavoidwhenconnectingcapillarytubingandtipsformakinggoodconnectionswithcapillarytubing)willpaybackhugedividendsintheformofhighqualitychromatographicresults.

OtherPopular“Apps”

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Making capillary tubing connections

Anotherimportanttopicistherapidlygrowingfieldofcapillarytubingconnections.

Asanalyticaltechniquesandapplicationsforcefluidvolumeslowerandlower,thesizeofthetubingusedfortheflowpathmustalsoshrinktoaccommodatethemethodology.Specialguidelinesareusefulinselectingandusingthebestconnectorsforcapillarytubingapplications.

First,capillarytubingcanbedefinedasanytubingwithanouterdiametersmallerthan1/16”(1.6mm)OD(chosenbecauseitistheprimarysizeoftubingusedhistoricallywithmostHPLCsystems).Asflowratesdecrease,oftenthetubing

ODandIDwillalsodecreaseinordertomaintainaconsistentlinearvelocity.Tubingsizeslike1/32”(0.8mm)ODand360micrometer(µm)ODarebeingusedwithincreasingfrequencyinchromatographyandrelateddisciplines,andusingthesetubingsizesrequiressomespecialconsiderationsnormallyunnecessarywith1/16”(1.6mm)ODtubing.Thisisespeciallyevidentwhenusingthesmallertubinginreceivingportsnormallydesignedforthelarger,1/16”(1.6mm)ODtubing.

Frequently,analystswillattempttoadaptexistinghardware(e.g.pumps,injectionvalves,evencolumns)toaccommodatecapillarytubing.Issuesabound,however,becauseofthegeometryandoverallsizeofthereceivingports.

POINT OF INTEREST

AllAboutFittings42

FIGURE15PotentialDeadVolumeinCapillary-BasedApplications

FIGURE16ExampleofaCustomizedFerrule

Aswe’vementioned,thehighpressurereceivingportsinmostanalytical-scaleequipmentonthemarkethaveaninternalgeometrysupporting1/16”(1.6mm)ODtubing.Thismeansthattheporthasaninternalpocketintowhichthe1/16”(1.6mm)ODtubingextends.Aslongastubingwiththissamediameterisused,thenpotentialdeadvolumeresultingfromtheconnectioniskepttoaminimum.However,whenthetubingyou’reusingissmallerthanwhatthereceivingportisexpecting,it’seasyfordeadvolumetobeintroducedintheconnection...which,withcapillary-basedapplications,canbeextremelydetrimental(seeFigure15).

Numerouswayshavebeendevelopedtoadaptsmaller,capillarytubingintothereceivingportsmeantforlargerODtubing.Oftheoptionsavailable,twostandoutasthemostpopular.

Thefirstoptioninvolvescustomizedferruleswhichlooksimilartothoseusedforthelargertubing,butwhichfeaturesmallerholesdrilledthroughthemtobetteraccommodatethecapillarytubing.Additionally,mostferrulesusedforthispurposealsoofferafixed-lengthnoseextendingbeyondthetaperedportionoftheferruletoreducedeadvolumeintheconnection.Ferrulesystemssuchasthesegenerallyholdthetubingwellandhavealongusablelifetime.However,therearedrawbackstoconsider.


DeadVolume

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First,custom-drilledferrulesare“economically-challenged.”(Inotherwords,theycanbeprettypricey.)Theseitemsaregenerallymanufacturedfromexpensivematerialsandaretypicallymachinedversusinjectionmolded...bothofwhichdriveupthecost.

Second,andmoreimportantly,theirfixedgeometrieslimitwheretheycanbeused.Asmostportshaveinternalgeometriesthatvaryfromonetoanother,usingferruleswithfixedgeometriescaneitherpreventtheferrulefromsealingproperlyorleaveemptypocketsinthereceivingportwheremobilephaseand/orsamplemaycollect.Thesedeadvolumepocketscanleadtopoorchromatography,includingissueswithcarryover,splitpeaks,andbandbroadening.Andwithsuchsmallsamplesizesandflowratesbeingusedincapillary-basedapplications,deadvolumepocketsplayamuchlargerroleinthequalityoftheresults.

Fortunately,thesecondoption—theuseofaspecialtubingsleeve—overcomesbothoftheprimarydisadvantagesexhibitedbythecustomizedferrules.

Tubingsleevesgenerallyhaveacontrolledouterdiameter(usually1/16”(1.6mm))whichallowsthemtofitintostandardthreadedports.And,sincethesleevewillslide

FIGURE17

IfDimensionXistoolong,leakswilloccur

Ferrulecannotseatproperly

IfDimensionXistooshort,adead-volume,ormixingchamber,willoccur

Mixingchamber

throughaferruleuntilitbottomsoutinareceivingport,thetubingpocketbeyondtheferrulewillbecompletelyfilledtohelpavoiddeadvolumeintheconnection.

Tubingsleevesalsoofferseveralsidebenefits.Oneisthestructuralsupportsleevesprovidetotheoutsideofthecapillarytubing,helpingpreventdamagetothetubingasitleavesthefitting.Also,becausethetubingsleevescomefromextruded

KEY CONCEPT

AllAboutFittings44

material,thesleevescanbeofferedinavarietyofmaterials.Furthermore,theextrusionprocessgenerallyallowsamoreconcentricconnectionthanprecisiondrillingandmachiningcanprovide,offeringamoreaccuratetubing-to-thru-holealignmentanddecreasinginlineturbulenceandmixing,allatareducedcost.

Forallthesereasons,usingatubingsleevetoconnectcapillarytubingintoareceivingportisthemethodofpreference—unlessthereceivingportisspecificallydesignedforusewiththesizeoftubingyouareusing!

Butwhataboutinstanceswherethereisn’tevenenoughroomforathreadedporttoexist,suchas

Lab-on-a-Chipmethods?Manypeopleusingtechniqueslikethisareforcedtogluetheirtubinginplaceinlieuofusingafittingfortheconnection.Thiscausesanumberofproblems,includingaweakholdonthetubingandinteractionbetweenthesamplebeinganalyzedandtheglue(oftenepoxy)securingthetubinginplace.

Oneavailablesolutiontothisprobleminvolvesbondingathreadedportdirectlytothesubstrate’ssurface.Bydoingthis,andbyisolatingtheadhesiveawayfromthemobilephaseorthesample,youcanmakeareliableconnectionwithyourtubingusingatraditionalfittingratherthanepoxy.Products,suchasIDEXHealth&Science’sNanoPorts™,weredevelopedspecificallyforthistask.


Besidesconnectingthetubingwiththeproperfittings,otherissuesshouldbeconsideredtoensuregoodconnectionsandgoodchromatographywhenyouusecapillarytubing.

Oneofthemajorissuescentersonhowwellyoucutthetubing.Dependingonthetypeofcapillarytubingandthecuttingtoolused,theeffectcanbedramatic.

Cutting fused silica and polymer capillary tubing

SECRET REVEALED

Let’stakefusedsilicacapillarytubingasafirstexample.Oneofthemostpopularmethodsforcuttingthistubingemploysaceramicscoringstone.This“tool”isreallyjustapieceofsharp-edgedceramicthatscoresthesurfaceofthefusedsilicatubing.Thisallowsthetubingtobepulledaparteasilyatthescoremark.

Intheory,thiswillallowforreasonablecutquality.However,inpractice,the

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resultsareusuallydifferent.Often,astheceramicstoneispulledacrossthetubing,thepolymercoatingisshreddedandthefusedsilicaunderneaththepolymercoatingisshatteredundertheforceoftheblade.Initially,youmaythinkthetubinglooksacceptable;however,onceinuse,thecoatingmaterialorpiecesofthefusedsilicatubingcanbreakoffandclogimportantinternalpassageways.Also,withdamagedendsonthetubing,usingstandardcompressionfittingstoholdthattubinginplacecancausethetubingtocompletelyshatterandresultinaleak,acloggedsystemcomponent,oracombinationofthetwo.

Itisalmostalwaysabetterideatocircumscribethetubingyouarecutting,goingallthewayaroundthecircumferenceofthetubing,ifyouwanttoachieveagood,reproducible,qualitycutonfusedsilicatubing.Whilethetoolsavailableformakingthistypeofcutarefairlyexpensive,theresults(andlackofadailyheadache!)usuallyfaroutweighthecostofthecutter.And,thesetoolsarefairlyeasytouse.

Interestingly,theconceptofcircumscribingthetubingappliestopolymercapillarytubingaswell...butfordifferentreasons.Often,whenpolymercapillarytubingisused,theinnerdiametersareverysmall—aslowas0.001”(25µm)insomecases!With

KEY CONCEPT

innerdiametersthissmall,itisvitaltokeepthethru-holeinthetubingopenandcenteredwiththepassagewayinthereceivingporttoavoidoverpressurizingtheconnection.That’swhereaccuratecuttingcomesintoplay.

Ifyoucutthetubingbysimplyslicingitwithablade,theforceofthebladepushingthroughtheplasticwillfrequentlycausetheinnerdiametertoshiftoffcenterorcollapse.Whilecuttingthiswaywon’ttechnicallycausedamagetopolymertubinglikeitwouldtofusedsilicatubing,itcanrenderitnear-useless,dependingonthedegreeofinnerdiametershift.Toavoidthisrisk,itisbesttocutthepolymercapillarytubingallthewayarounditscircumferenceaswell.

Again,thetoolstodothisareavailable,andtheyareabitexpensive;however,aswiththetoolsforproperlycuttingfusedsilicatubing,benefitsfaroutweighthecosts.

HELP ME!

FIGURE19CutPolymerTubing

ImproperlyCutTubingProperlyCutTubing

AllAboutFittings46

Putting the big squeeze on

AnotherpopularchromatographicdevelopmenthasbeentheintroductionofUHPLC.Inatrendthatstartedin2004,numerousmanufacturershaveintroducedequipmentandvarioushardwareandaccessoriesthataresuitableforuseinUHPLCapplications.

OneofthekeyfeaturesofUHPLCisthattheequipmentrunsatveryhighpressures.Themostcommonsystemsrunatpressuresatornear

15,000psi(1,034bar)—andsomeequipmentevensurpassesthatlimit!Ofcourse,withsystempressuresthishigh,thatputsevenmorestrainontheconnectionsinthesystem--especiallyinthe“highpressure”zone,wherethesystempressuresarethegreatest.BecauseofthepressureinvolvedinUHPLC,therearecertainproblemsthatcanoccurinUHPLCifthefittingandtubingconnectionsarenotasgoodastheyshouldbe:

Ifapoorconnectionhasbeenmadethatallowstheflowpathtubingtomove,therearepartsoftheUHPLCfluidpathwaythatundergoatremendousamountofstress—forexample,thefittingsthatconnectthesamplelooptotheinjectionvalve.It’softeninthesehigh-stressareasthattubingconnectionswillfailiftheconnectionsarepoorlymade.Withtubingslippage,theproblem

doesn’tappearintheformofanimmediateleak—it’sa“slowriser,”aproblemthatgraduallyappears.Whilealeakwon’tnecessarilyresultrightaway,youwilllikelynoticeyourchromatographicresultsdeterioratingduetothelargedeadvolumechamberbeingcreatedattheendoftheflowpathtubingasthetubingslowlyslipspastthegripofthefitting.

1)TubingSlippage


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WiththehighpressuresinvolvedinUHPLCapplications,it’sbecomecommonplaceforstainlesssteelfittingstobeusedonceagain.However,withtheuseofthesetypesoffittingscomestheproblemsassociatedwiththesetypesoffittings.

Oneofthoseproblemsistheamountofcompressiononthewallofthetubingthatoccurswhenametallicfittingisused.Dependinguponthetighteningtorqueappliedtotheconnection,it’sverypossiblefortheferruletocompressthetubingwallsomuchthattheinnerdiameteriscompressedaswell.Thisinnercompressioncreatesafluidpathwayrestrictionthatcanresultinathrottlingeffectofthemobilephaseandincreasedmixing.

Asecondproblemcanresultfromtheover-tighteningofametallicferruleintoametallicreceivingport.Becauseoftheforcesinvolved,itispossiblefortheferruletobeginshearingsomemetalfromtheinternalreceivingportsurface.Thisresultsinadamagedportthatcanleakandcanbedifficulttorepair.

Anotherproblemthatcanresultfromtheover-tighteningandimproperuseofstainlesssteelfittingsistheimpacttheycanmakeonthequalityofthesurfaceofthereceivingport.Notonlycangallingresult,butthereceivingportcanbedeformedduetotheforcesappliedbytheferrule.Thiscancreatea“ridge”alongtheinnersurfacethatcanpreventsubsequentferrulesfromsealingcorrectly.

2)Ferrule-RelatedStruggles

Asstrangeasitmayseem,itispossibletobeinjuredduetoimproperly-madeconnections.Specifically,ifatubingconnectionsuddenlyfailsandthefluidpressureswereuptoUHPLCpressures

andbeyond,thatsuddenreleaseofenergizedfluidcandamageskinandsofttissues.Wearingprotectivegearandexercisingcautionwillhelpavoidunnecessaryinjury.

3)PersonalInjury

BecauseofthesesourcesofproblemsinUHPLCapplications,itisvitalthatyouinvestthetime,effort,andresourcestoensureyouhavemadegoodconnectionsthroughoutyoursystem.Workingwiththerightfittingsandtighteningusingthepropermethodologywillproveinvaluableasyouseektomakegoodconnectionsinyourequipment.

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IlikeusingFingertightfittingsformyHPLCconnections–canIstillusethemforUHPLCconnections?

Generallyspeaking,becauseoftheveryhighsystempressurespresentinmostUHPLCapplications,standardFingertightfittingswillnottypicallywork.MakinggoodconnectionsinUHPLCapplicationswillusuallyrequireeithertraditionalstainlesssteelfittingsorspecializedfittingsthathavebeenengineeredtoworkintheveryhighpressureenvironmentofUHPLC.

CanIusepolymertubing(e.g.,tubingmanufacturedfromPEEK™polymer)inUHPLCapplications?

MostsizesofPEEKtubing(andtubingfromotherpolymermaterials)havepressurelimitsthatarewellbelowthetypicaloperatingpressuresofUHPLC.Assuch,themostpopularlyusedtubinginUHPLCismanufacturedfromstainlesssteel.Otherspecializedtubingmayalsowork;thekeyistodouble-checkwiththetubingmanufacturer/suppliertoensureitisratedforuseatthepressuresyouwillencounterinyourUHPLCsystem.


But I still have some questions!

BecauseoftherelativeyoungageofUHPLCasacommercializedtechnique,therearesomefairlycommonquestionspertainingtomakinggoodconnectionsthatareasked.We’llpausetoaddresssomeofthemostpopularones:

DoIneedspecialfittingsthroughoutmyUHPLCsystem?

Thisismoretricky,becausemostUHPLCsystemsareonlydifferentinthehighpressurezone(seeearlierdiscussiononpage46formoreinformationaboutthedifferentconnectionzones).Thatmeans,whileyouwilllikelyneedtousedifferentfittingsinthehighpressurezonewhentransitioningtoUHPLC,inthelowerpressurezonestheconnectionswilllikelybeverysimilartothoseusedintraditionalHPLC.

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Hereareafewadditionaluseful“hints”formakinggreatconnections.

How do I adapt?Withthelonglistofmanufacturerscreatingequipment,andwithallthedifferentvariationsontubingsizeandthreadedportconfiguration,scientistswillfrequentlyneedtofindadapterstomakeaspecialtubingconnection.

Orwillthey?

Ironically,whilemanypeoplemightapproachmakingaconnectionwithanadapter,frequentlyadaptersareunnecessary.Tobetterunderstandthis,let’sdistinguishbetweenadaptersandtheircounterparts–unions.

Basically,adapters“adapt”betweentwodifferenttypesofthread/portconfigurations,whileunionshavethesamethread/portconfigurationonbothsides.

Toillustratethispoint,Figure18showsvariousconnectorsandclassifiesthemaseitheradaptersorunions.

Beforecontinuing,it’simportanttoestablishonegeneral“ruleofthumb”:Unionsaretypicallylessexpensivethanadapterswhileoftenperformingequallyaswell.Therefore,wouldn’titmakesensetouseaunionwhereverpossible?

KEY CONCEPT

SECRET REVEALED

A Few Extra Tips

FIGURE18Adaptersvs.Unions

Unions

Adapters

49

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Therealquestiontoconsideristhis:

Howdoyouknowwhenyoucanuseaunion?

First,examinetheconnectionanddetermineifitwillbelowpressureorhighpressure.Sometimesthismaynotbesoobvious,butyoucanoftenmakesomeassumptions.

Forinstance,ifyouwanttoconnect1/16”(1.6mm)ODPEEK™tubingtoapieceof1/8”(3.2mm)ODFEPorPFAtubing,thenitwouldbesafetosayyouaremakingalowpressureconnection.Infact,itdoesn’treallymatterwhatpressurethePEEKtubingwillhold—theconnectionislimitedbytheamountofpressurethesoftertubingcanhandle.

Onceyouknowthepressureclassificationfortheconnectionyouneed,findoutwhat’savailableinthatclassificationfromyourfittingssupplier.(Forexample,forlowpressureconnections,anumberoflowpressureunionswith1/4-28internalflat-bottomgeometryonbothsidesareavailable.You’llalsofindavailableotheroptionswithmatchingM6and5/16-24internalthreads.)

Withthisinformationinhand,allyouneedtodoisfindfittingsthatworkwithyourtubingsizesthatalsomatewithoppositesidesofanavailableunion.Ifsuchfittingsexist,youcanuseauniontoconnect

them—evenifyourtubingouterdiametersaredifferent!

Let’scontinuewiththepreviousexample:alowpressureconnectionbetween1/16”(1.6mm)and1/8”(3.2mm)ODtubing.

Mostpeopletryingtomakethisconnectionwouldinstinctivelylookforanadapter.Ofcourse,manysuppliersmanufactureadaptersthatcanbeusedforthatpurpose.However,therearesupplierswhoalsocarry1/4-28flat-bottomfittingsforboth1/16”(1.6mm)ODand1/8”(3.2mm)ODtubing.

Thismeansaninexpensiveunioncanbeused,evenwithdifferenttubingsizes,withoutompromisingperformance.

Ofcourse,therearestillanumberofcaseswhereonlyanadapterwilldo.However,itisoftenworththeeffortoflookingthroughavailableproductstodetermineifaunionwillworkforyourneeds.

AFewExtraTips

SECRET REVEALED

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What’s the big ID?

Anotherproblemyoumightfaceischoosingtherightinnerdiameterforyourapplications.Becauseapplicationsinvolvingcapillarytubingtypicallyfeaturelowflowratesandincrediblysmallamountsofsample,thereisageneralpushtoreducetheinnerdiametertothesmallestpossiblesize.WhiletheseminisculepathwaysallowthefluidtotravelasfastaspossiblefrompointAtopointB,onethingoftenoverlookedisthebackpressurealongthetubingpathway.Thisisimportantbecauseifsystempressuresbecometoohigh

wherepolymerfittingsareused,thetubingmaypopfreefromthefitting’sfrictionhold,causingaleakandotherundesirableconsequences(e.g.,systemshut-down,sampleloss).Whilemanyfactorscancontributetosystempressure,theIDofthetubingoftenhasthegreatestimpact.

Pleaserefertothe“SpeakingofPressure”sectiononpage58intheAppendixforausefulformulathatallowsyoutocalculateexpectedbackpressureinyourfluidpathway.

Void, dead and swept...an interesting concept

Often,whenmakingconnections,peoplewantmoreinformationontheamountof“deadvolume”intheconnection.However,mostpeoplewhoinquireaboutthedeadvolumearereallywantingtoknowjusthowmuchinternalvolumeexistswithinaconnection,nothowmuchofthatinternalvolumeisconsidered“dead.”

Butwhatdothesetermsmean?

Specifically,threetermsdescribetheinternalvolumeofaproduct:deadvolume,sweptvolumeandvoidvolume.

Deadvolumeisthatportionofthevoidvolumethatisoutoftheflowpath.(SeeFigure20,page52.)

Sweptvolumeisthatportionofthevoidvolumeinaconnectiondirectlyinthefluidpathway.(Again,seeFigure20.)

Voidvolumeissimplyanotherwayofdescribingthetotalinternalvolume.Itisdefinedasanyspacewithinaconnectionintowhichfluidcanflow.

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FIGURE20InternalVolumeDefined

AFewExtraTips

FluidIn FluidOut

Plugged

DeadVolumeSweptVolume

Mathematicallyspeaking,whendeadvolumeandsweptvolumeareaddedtogether,thetotalequalstheoverallvoidvolume.

VoidVolume=DeadVolume+SweptVolume

Deadvolume,however—particularlyincapillaryconnections—cancausesomeveryundesirablechromatographiceffects,including:

Analysis delays

Broadened peaks

Poor resolution

Sample carry-over

Split peaks

Gas collection

KEY CONCEPT

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Sample-to-sample contamination

Dispensing inaccuracies

Precipitation zones

Ifyourapplicationisnotchromatography-related,deadvolumecanstillleadtoproblems,including:

Inotherwords,nomatterwhatyouranalysistechniqueis,deadvolumewilllikelyhaveanegativeimpact.

Therefore,inadditiontokeepingthevolumeinsidetheconnectiontoaminimum,alldeadvolumeshouldberemovedfromtheconnection

The end of the storyWhileit’shardtocaptureallyouneedtoknowaboutfittingsinonecompactreference,it’sourhopethatthisresourcehasproventobehelpfulalready...andwillcontinuetobesomethingyoureturntooverandoveragaininthefuture.

PleasefeelfreetocontacttheCustomerServicestaffatIDEXHealth&Scienceifyouhaveanyfurtherquestionsorifyouhavesuggestionsforfutureeditionsofthisguide.Manyoftheimprovementsinthiscurrenteditionareduetosuggestionsfrominterestedpeoplejustlikeyou!

ifpossible.Ultimately,incapillaryconnections,thepreferredrelationshipcouldbeexpressedasfollows:

VoidVolume=SweptVolume(andshouldbeREALLYsmall!)

AHelpfulNote:AgreatwaytokeepmostofthevoidvolumetrulysweptvolumeistomatchthetubingIDascloselyaspossiblewiththediameterofthethru-holesinyourequipment.Thishelpsensurethatthefluid,onceitleavesthetubing,runscompletelythroughtheentireinternalpassageway.Thisdiametermatchingalsohelpsreducetheamountofturbulencethefluidexperiencesasitpassesthroughtheconnection.

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AppendixI know it’s not a fitting, but…Whilethisresourceisfocusedonfittingsandmakinggreatconnections,thereareotherusefulaccessoriesthatcanbeusedinchromatography(andrelated)applications.Twoofthemorecommonaccessoriesarefiltersandbackpressureregulators(orBPRs).

Filters,FiltersEverywhere!

“WhywouldIeverreallyneedafilter?”youmightask...andyouwouldn’tbealone.Manypeopleassumetheirfluidpathwayiscleanwhenitoftenreallyisn’t,andthereareareaswhereusingfiltersisveryimportant.

Particlesofallsortscanbesuspendedinafluidstream.(Justbecauseyoucan’tseethemdoesn’tmeantheyaren’tthere!)Thingslikedust,solidsoriginatingwithasample,andsealwearparticlesareallreasonswhyfiltersareimportant!

Tohelpunderstandwhereyoucanconsiderusingfiltersinyoursystem,let’slookatcommonplaceswherefiltersareusedinHPLCsystems:

SolventInletFilters:Oneofthefirstplaceswherecontaminantscanenterafluidstreamisinthesolventreservoiritself.Whetherit’sbiologicalmaterialflourishinginsolutionoroutsidedustparticlescollectinginthereservoir,therearenumerouswayslargeparticlescanbecomepresentinthesolventreservoir.Placingasolventinletfilterinsidethereservoirattheendoftheinlettubingwillhelpensurethefluidstreamremainsfreeofphysicalcontaminantsandwillhelpprotectupstreamequipment.

Anotherusefulplaceforaninletsolventfilterisontheendofaheliumspargingdeliverytube.(Spargingisatechniqueusedtoremovedissolvedgasfromamobilephase.)Whenaninletfilterisusedforspargingpurposes,itdoestwothings:itdispersestheheliummoreeffectivelywhilealsopreventingparticles,stemmingfromthegassource,fromenteringthemobilephase.

Foramoredetaileddescriptionofthespargingprocess,pleasesee“MobilePhaseDegassing—Why,When,andHow”byDr.JohnW.Dolan,LC-GCVolume17Number10,October1999.

Appendix

PARDON MOI?

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InlineFilters:Particlesoftenoriginatefromsealwearinpumpandvalvemechanisms,andtheseparticlescancauseblockagesandequipmentmalfunctionsifallowedtoremain.Inlinefiltersareeffective“insurancepolicies”againstsuchproblems.Justastheirnamewouldsuggest,inlinefiltersareplaced“inline”,alongafluidpathwaywheretheycancaptureanyparticulatematterthatmaybetravelinginthesolventstreamandthusprotectagainstblockagesandequipmentdamage.

Inadditiontosealwear,inHPLC,flowpathcontaminationcanoriginatewiththesample.Tohelpprotectagainstphysicalparticulatesthatmaybeinthesamplematrix,aspecialformofinlinefilterisoftenused,calleda“precolumnfilter”.Placedimmediatelybeforethecolumn,aprecolumnfiltercombineseffectivefiltrationprotectionwhileminimizingthepossiblebandbroadeningthatcansometimesoccurinchromatographicapplications.

Anothertypeofcontaminationoriginatingfromthesampleischemicalcontamination,whichneedstoberemovedusingaspecialchemicalfiltercalledaguardcolumn.(Formoreinformationaboutguardcolumns,seepage37.)

Fortunately,bothinlineandprecolumnfilterstypicallyusereplaceablefiltrationdiscsreferredtoas“frits”.Availableinavarietyofporositiesandmanufacturedfromseveraldifferentmaterials,therearenumerouswaystocustomizethefilterforyourspecificapplication.

One important factor to consider when choosing the appropriate precolumn or inline filter for your application — especially if you are working with microscale or nanoscale applications — is the impact that the volume of the filter will have on the results obtained. Frits, by design, are very porous; as such, they typically contain quite a bit of volume — ranging from 18% –30%, depending upon the frits’ porosity. Because frits both increase turbulence as well as the time the sample is in contact with the mobile phase, choosing the right frit — and the right filter assembly — can be critical to obtaining good peak shape and peak resolution.

AllAboutFittings56

How long will filters last?

To test this quickly, temporarily remove the solvent inlet filter from the inlet tube and re-run a few standard samples. If the analysis results return to normal, then it’s likely that the pump was not getting enough fluid with the filter in place. Replace the filter with a new one, and begin your analyses again. Do not operate for long periods without a solvent inlet filter, as damage to your system may occur. (Remember this saying: “If in doubt, throw it out.” Solvent filters are generally inexpensive, making it easier to be safe than sorry!)

Ifyounoticethesystempressureincreasing,that’sagoodindicatorthatthefritinsideeitheryourinlinefilteroryourpre-columnfiltermayneedtobechanged. As your inline filter and pre-column filter do their jobs, the frits inside will collect particles from the fluid pathway. As more particles are collected, less room is available for fluid to move through. Eventually, the pump has to “push harder” to get the same amount of fluid through, causing the system pressure to increase.

To best determine if an inline filter needs maintenance, start at the end of your system and, moving backwards toward the pump, disconnect the fluid pathway fittings one-by-one, monitoring the system pressure. Watch to see if the pressure drops suddenly; if it does, look for the restriction to be in the portion of the flow path last removed from the fluid pathway. If this happens just before a filter, replace the frit inside the filter housing. (Remember to be careful and not create a chemical spill when performing this test.)

Appendix

POINT OF INTEREST

Thisisoneofthemostfrequentlyaskedquestionsregardingtheuseoffilters.

Unfortunately,thereisnostandardfilterlifetime.Youmaygoformonthswithverycleansamplesandmobilephaseandnothavetochangeyourfilters,ortheymayonlymakeitafewdays.Italldependsonhowcleanyourfluidsareandontheconditionofthesealsusedinyoursystem.

Agoodlabpracticetipistomakethereplacementofyourfiltersorfritspartofyoursystem’spreventative

maintenanceroutine,whichtypicallyoccurseverysixmonthstooneyear.

Therewillbetimeswhenyouwillneedtochangeyourfilterorfritinadditiontotheregularly-scheduledchanges.Buthowdoyouknowwhenit’stimetochangethem?Herearesomehintsthatmayhelp:

Ifyounoticeyourchromatogrampeakscomingoutlaterthannormal,itmayindicatethatyourpumpisn’tdispensingtherightvolume. If everything on the pump appears to be functioning properly, and if there is no evidence of a leak, then the solvent inlet filter may be clogged, restricting the solvent flow to the pump.

All About Fittings

www.idex-hs.com 57

Regulate me!Whenitcomestosystempressure,inlinepressureregulationisoftenanecessity.Andthat’swhereBackPressureRegulators(BPRs)comeintoplay.

ABPRisadevicethatcreatesastaticinlinepressure,relativelyindependentofthefluidflowrateorviscosity.

ButwhyuseaBPR?

TherearetwomainapplicationsthatcallforBPRstobeusedinHPLCsystems.

Thefirstapplicationistohelppreventnoiseonachromatogram’sbaseline.(Noiseisthetermappliedtotheerraticfluctuationsonthebaseline.)Asfluidpassesthroughyoursystem,itwillgothroughsometerrificpressurechangesinashortperiodoftime.Ifgasisdissolvedintosolution,bubblescanforminthefluidpathwayasthemobilephasedecompresses.Asthesebubblespassintothedetector’sflowcell,theycancausethedetector’ssignaltochangeirregularly,resultingin“noise”onthebaseline.

This“noise”makesitverytoughtoanalyzesmallpeaksonthechromatogram.

Ifthenoiseyouareexperiencingcomesfrombubblesintheflowcell,

therearetwosolutions:removethegasfromthemobilephase,orpreventbubblesfromforming.UsingBPRswon’tremovethegas,buttheycanhelppreventthebubblesfromforming.

TouseaBPRforthispurpose,simplyplaceitbetweenthedetector’sflowcellandthewastereservoir.Whenthefluidleavesthecolumn,theBPRwillhelpensurethemobilephaseremainsunderpressureasitflowsthroughthedetector,helpingtoinhibitbubblesfromforming.Keepinmindyourdetectorflowcell’spressurelimitasyouareselectingthecorrectBPRforyourapplication.

ABPRcanalsohelpyourpump’scheckvalvesoperatemoreefficiently.Manystandardcheckvalvesaregravity-fedandrelyonsystembackpressuretoworkwell.Ifyourapplicationdoesn’tcausesufficientbackpressuretobedeveloped,yourpump’scheckvalvesmaynotworkcorrectly.However,aBPRplacedimmediatelyafterthepump(butbeforetheinjectionvalve)oftencausesthepump’scheckvalvestooperatemorequicklyandthereforemoreefficiently.(Note:FormostHPLCapplications,itisunlikelyaBPRwouldbeneededinthislocation,asthetypicalHPLCcolumnwillcreatesufficientbackpressuretoensureefficientcheckvalveoperation.)

KEY CONCEPT

SECRET REVEALED

AllAboutFittings58

Conversion factorsHerearesomeotherusefulformulas:

InchestoMillimeters: Inchesx25.4mm/inch

InchestoCentimeters: Inchesx2.54cm/inch

InchestoMicrons: Inchesx25.4mm/inchx1000µm/mm

Diameterininchestolinear((Inches/2)x2.54cm/in)2xvolume(µL/inch)

x2.54cm/inchx1000µL/cm3

Diameterininchestolinear((Inches/2)x2.54cm/in)2xvolume(µL/cm)

x1cm/cmx1000µL/cm3

CelsiustoFahrenheit (Celsiusx9/5)+32

FahrenheittoCelsius (Fahrenheit-32)x5/9

psitobar psix0.06894757

psitoatmospheres psix0.06804596

psitoMPa psix0.00689476

psitotorr psix51.7150733

Speaking of pressure…Sometimesitmaybenecessarytopredicthowmuchpressuremightbecreatedinlinebyyourtubing.Here’saformulawehavefoundtobeveryaccurate(answerinpsi):

P=(9.86x10-8)( FLV

) d4

Where: P=pressuredropinpsi V=viscoscityincentipoise(cp) F=flowrateinmL/min d=tubinginsidediameterincm L=tubinglengthincm

Appendix

All About Fittings

www.idex-hs.com 59

Polymer informationPolymerfittings,tubingandaccessorieshaveproventobesuperiortostainlesssteelinmanyanalyticalapplications.Thefollowingperformanceinformationhasbeencompiledformanyofthepolymerscommonlyusedinanalyticalanalyses.

Please Note: For more information regarding the properties of the polymers listed below, please refer to www.idex-hs.com/materials.

Delrin®(acetal).Delrinexhibitsexcellentchemicalresistancetomostorganicsolventsaswellastomostneutral-pHaqueoussolvents.However,itisnotsuitableforusewithacids,basesoroxidizingagents.Thispolymer’shightensilestrengthyieldssuperior,highlywear-resistantthreadsandexcellentthreadstrength.

Maximumoperatingtemperatures(ºC):Fittings60;TubingN/A

FEP(fluorinatedethylene-propylene)andPFA(perfluoroalkoxyalkane).BothofthesepolymersareinthesamefamilyasPTFE,andassuchareinerttovirtuallyallchemicalsusedinHPLC.However,becauseoftheirrelativesoftnessandlowdurability,thesepolymersaregenerallyusedforlowpressureapplications.ChoosePFAforhighpurityapplications,orchooseFEPasageneral,all-purposematerial.BothFEPandPFAhavegoodthreadstrength.

Maximumoperatingtemperatures(ºC):FittingsFEP-N/AandPFA-80;TubingFEP-50andPFA-80

Halar®ECTFE(ethylene-chlorotrifluoroethylene).Halarisamemberofthefluoropolymerfamily.Itoffersexcellentchemicalresistancecoupledwithamechanicalstrengthsuperiortomanyotherfluoropolymers.HalaralsooutperformsPTFEandsimilarfluoropolymersinabilitytowithstandradiation,makingitanattractivealternativeformedicalapplications.Itsexceptionallysmoothsurfaceenhancesopticalclaritywhilealsohelpingpreventthesheddingofmicroparticlesintothefluidstream.

Maximumoperatingtemperatures(ºC):FittingsN/A;Tubing50

PCTFE(polychloro-trifluoroethylene).PCTFEhasexcellentchemicalresistance.Ingeneral,onlyTHFandafewhalogenatedsolventswillreactwithit.Thisresilientfluoropolymerisidealforfittingsandsealingsurfacesandalsohasgoodthreadstrength.


PEEK™(polyetheretherketone).PEEKpolymeristheflagshipmemberofthepoly(aryl)etherketonefamilyofpolymers.Ithasexcellentchemicalresistancetovirtuallyallcommonlyusedsolvents.However,thefollowingsolventsareusuallynotrecommendedforusewithPEEK:nitricacid;sulfuricacid;halogenatedacids,suchashydrofluoricacidandhydrobromicacid(hydrochloricacidisapprovedforuseinmostapplications);andpurehalogenatedgases.Additionally,duetoaswellingeffect,becautiousinusingthefollowingsolventswithPEEKtubing:methylenechloride,THF,andDMSOinanyconcentrationandacetonitrileinhigherconcentrations.Excellentthreadstrength.

Maximumoperatingtemperatures(ºC):Fittings125;Tubing100

PolypropylenePolypropyleneisarelativelysoftpolymercommonlyusedinlowpressureapplications,andisespeciallyprevalentinIVDandsimilarequipment.Polypropyleneisexcellentforaqueoussolutions;however,itshouldnotbeusedwithchlorinated,aromatic,andsomeorganicsolvents.Fairthreadstrength.


AllAboutFittings60

PPS(polyphenylenesulfide).PPSisaresilientpolymerknownforitshightensilestrengthandexcellentchemicalresistance.PPSmaybesafelyusedatroomtemperaturewithmostorganicsolventsandneutral-to-highpHaqueoussolvents.However,itisnotrecommendedforusewithchlorinatedsolvents,inorganicacids,oranysolventatelevatedtemperatures.


Radel®(polyphenylsulphone).Radelisanamorphousthermopolymerthatismechanicallystrongandoffersgoodchemicalresistance.Thispolymerwithstandsrepeatedautoclavesterilizationcycleswithoutsufferingthermalbreakdown.Thisproperty,coupledwithitsopticalclarity,makesRadeltubinganexcellentchoiceformedicalandotherapplicationswherevisualmonitoringisessential.Radelisalsoareadilywettedmaterial,minimizingairbubbleaccumulationontheinnerwallsoftubingmanufacturedwiththispolymer.


ETFE(ethylene-tetrafluoroethylene).Asamemberofthefluoropolymerfamily,ETFEhasexcellentsolventresistance.Itsphysicalpropertiesmakeitidealfordemandingsealingapplications.WhilemostcommonlyusedsolventsdonotinteractwithETFE,takecautionwhenusingsomechlorinatedchemicals.ETFEhasgoodthreadstrength.


UHMWPE(ultra-highmolecularweightpolyethylene).UHMWPEisawell-knownanddurablemanufacturingpolymer.Itsphysicalpropertiesmakeitidealforgeneral,aqueous-basedenvironments.Takecautionwhenusingthispolymerinheavilyorganic-basedapplications.Goodthreadstrength.


Ultem®PEI(polyetherimide).Anamorphousthermoplasticofferinghighheatresistance,highstrengthandbroadchemicalresistance.TubingmadefromUltemoffersahighdegreeoftransparency.Thispolymerwithstandsvarioussterilizationmethods,suchasrepeatedautoclavingaswellasgammaradiation,ethyleneoxidegasanddryheat.UltemmeetsthecriteriaforISO10993,FDAandUSPClassVIcertification.


Vespel®(polyimide).Vespelthermoplasticoffershighheatresistance,highmechanicalstrengthandbroadchemicalresistanceinmostcommonliquidchromatographyapplications.However,itisparticularlysusceptibletoattackbyhighpHchemicalenvironments.Vespelcanbeautoclavedandsterilizedusinggammaradiation.Vespeloffersinherentlubricity,makingitidealasachemicallyresistantbearingsurface.

Maximumoperatingtemperatures(ºC):SealingComponents200;TubingN/A

Appendix

For more Polymer information, see the Chemical Compatibility chart on the next page, or download our free app at the iTunes store for instant information.

All About Fittings

www.idex-hs.com 61

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AllAboutFittings62

If your fittings leak

TelltaleSignsofSystemLeaksBefore you see the first drip of mobile phase, your system can warn you that a problem exists. The most common signs of system leaks are:

1. No flow or pressure 2. Pump pressures up, but there is no flow 3. Noisy baseline 4. Baseline drift

While all of these symptoms could also indicate problems unrelated to leaking connections, it is always easiest to start there. Not only are leaking connections usually easy to repair, they are also typically the least expensive repair option.

Appendix

ofyoursystem.Toavoidthisproblemandensurecompatibility,useIDEXHealth&ScienceuniversalFingertightfittings.Becausetheferruledoesnotpermanentlyswageontoyourtubing,aFingertightcanbeusedrepeatedlyforseveralcyclesinmostsystems.

4.Checktheconditionofthesealingarea.Afterrepeateduse,afitting’s“sealingarea”(atthetipofthefittingorferrule),willgraduallybecomedeformedtothepointofbeingincapableofcreatingaseal.Assuch,itisagoodideatokeepanextrasupplyofthefittingsyouareusingsoyoucanreplacethemquicklyandavoidunnecessarydowntime.

5.Checkthereceivingportfordamage.Sometimesaleakingconnectionhasnothingatalltodowiththenutandferrule,butwiththereceivingport.Portsthathavehadstainlesssteelfittingsswagedintothemareespeciallysusceptibletodamage.Checkthereceivingportforvisibleburrsorscratchesandreplaceifnecessary.

6.Evaluatechemicalcompatibility.Usingfittingsmadeofmaterialincompatiblewithyourmobilephaseisasurewayofcreatingleaks.PleasevisittheIDEXHealth&Sciencewebsite,www.idex-hs.com,formoreinformationaboutchemicalcompatibility.

1.Checktomakesureyourtubingisseatedproperly.WhenusinguniversalFingertightfittings,thetubingmustbottomoutinthereceivingportbeforethenutandferrulearetightened.Ifagentletugdisengagesyourtubingafterthefittingshavebeentightened,loosenthenutandferruleandtryagain.

2.Thefittingmaynotbetightenedenough.Stainlesssteelnutsandferrulesrequireawrenchtotightenthem,evenafterrepeateduse.Fingertightfittingsalsorequireagoodtighteningtorque;however,usingtoolsincorrectlymayleadtoover-tighteninganddamagetothefitting.Assuch,toolsshouldbeusedwithcautiononFingertightfittings.

3.Youmaybeusingincompatiblefittings.Makesureyouareusinganutandferrulethatarecompatiblewitheachotherandwiththecomponents

All About Fittings

www.idex-hs.com 63

AdapterAunionwithdifferentthreadsoradifferentgeometryoneachend;generallyusedtoconnecttwodifferenttypesoftubingtogether.

BackPressureRegulator(BPR)Adevicetypicallyusedafterthedetectortomaintainapositivepressureontheflowcell,thusminimizingsolventoutgassingproblemsinthedetector.

BiocompatibleReferstothatspecialqualityofsomematerialsallowingthemtocomeintocontactwithbiologicalmaterialswithoutchangingthematerials’bioactivity.

CapillaryTubingOftenreferstotubingsmallerthan1/16”OD;frequentlyusedinhyphenatedanalyticalsystems,suchasLC-MS.

CheckValveAdeviceinsertedintoamovingliquidstreamthatallowsflowofthestreaminonlyonedirection.

ChromatogramAgraphicalplotrepresentingthechangeinsignalintensityfromadetectorandoftenusedinthenumericalanalysisofasample’scomponents.

ColumnAspecializedtube,packedwithsmall,chemically-activeparticlescalledthestationaryphase,inwhichtheseparationofasampletakesplace.

CrossAnx-shapedunionusedtoconnectfourpiecesoftubing.

DeadVolumeThatportionofthevolumewithinaconnectionthatisnotpartoftheflowpath;oppositeofsweptvolume.

DetectorAprimaryanalyticalsystemcomponentthat“sees”samplecomponentsastheyarebeingcarriedawayfromthecolumnbythemobilephase.

EndFittingUsedwithmoststandardcolumnsinthemarkettoday,itisthefittingattheendofthecolumnthatallowscommonlyusedtubingtointerfacewiththecolumntube.Additionally,theendfittingoftenholdsthefritinplaceoneitherendofthecolumntube,thusretainingthepackingmaterialwithinthecolumntube.

ExternalCompressionConnectionmethodutilizedbymostfittingssystemsinamajorityofanalyticalinstrumentation.Itisthenearlyuniversalconnectionmethodwhenrigidorsemi-rigidtubingisused.

FerruleAtaperedconicalringusedtomakethesealbetweenapieceoftubingandareceivingport.Ferrulesalmostinvariablymustbeusedinconjunctionwithanutofsomesort.

FingertightAspecialfittinginventedbyUpchurchScientificthatcanbetightenedtonormalworkingHPLCpressureswithouttheuseofawrench.

FilterAsystemaccessorywhichhelpsmaintainoverallsystemperformancebypreventingsolidparticlesfrompassingalongtheflowpathandpotentiallydamagingsensitivecomponents.

FittingsReferstotheconnectorsthatjointubingtovariouscomponentsinananalysissystem.

FlangedFittingAfittingusedinlowtomoderatepressureapplications.Thefittingrequiresflanging-orspreadingtheendofthetubing-beforeuse.Oftenusedwith1/4-28orM6threadedflat-bottomfittings.

FlangelessFittingAspecializedfittingdesignedtoreplaceflangedfittings,wherethroughtheuseofanutanduniqueferrule,asealcanbemadeontubinginareaswhereflangedfittingsweretraditionallynecessary.

GuardColumnAsystemaccessorydesignedtoprotectthemainanalyticalcolumnfrombeingdamagedbysamplecomponentsthatmightirreversiblybindtothestationaryphaseinside.

Glossary

AllAboutFittings64

HPLCAnacronymforananalyticaltechniqueknownasHighPerformanceLiquidChromatography,usedinmanylaboratoriesaroundtheglobe.

InjectionValveAspecializedvalveusedtointroduceacontrolledamountofsampleintothemobilephaseforanalysis,whilecausinglittletonosystemdisturbance.

MobilePhaseChemicalsolutionpumpedthroughoutananalyticalsystemforthepurposeofanalyzingsamples.

NoiseErraticsignalfluctuationsonachromatogram’sbaseline.

NutAcommontermusedtodescribethethreadedportionofafittingsystem.

OEMAnacronymthatstandsforOriginalEquipmentManufacturer.

PumpAprimarypieceofananalyticalsystemthatpullsmobilephaseoutofthereservoirandpushesitoutthroughtherestofthesystem.

ReceivingPortTypicallyathreadedholeintowhichafittingisattachedforthepurposeofholdingflowpathtubinginplace.Lowpressureportstypicallyhaveaflat-bottomgeometry,andhighpressureportsmostoftenhaveaconedgeometry.

RecorderAprimaryanalyticalsystemdevicethattranslatesthesignalgeneratedbythedetectorintoaplotofsignalversustime;mostoften,thisisusuallyacomputer.

Reservoir(orSolventReservoir)Oftenaglassorplasticbottlethatholdsthemobilephase.

StainlessSteelAnyvarietyofsteelalloysdesignedforcorrosionresistance.Thedifferentvarieties-primarily316grade-areusedtomanufacturehigh-pressure,chemicallyresistantHPLCfittingsandtubing.

StationaryPhaseThesmall,chemically-activeparticlesdenselypackedintoaspecializedtubeknownasacolumnandoftenofferinganoppositechemicalenvironmenttothatwhichisofferedbythemobilephase.

SwagingTheprocessofpermanentlyattachingaferrule(usuallymanufacturedfromstainlesssteel)toapieceoftubing.

SweptVolumeThatportionofthevolumewithinaconnectionthatispartoftheflowpath;oppositeof“deadvolume.”

TeeAT-shapedunionusedtoconnectthreepiecesoftubing.

ThreadPitchStandardizednumericalvaluedescribinghowclosetogetherthreadsareonafitting;Englishthreadshaveathreadpitchthatdescribesthenumberofthreadsperinch,whereasmetricthreadsaredescribedbythedistanceinmillimetersbetweenthreads.

TubingSleeveAshortlengthoftubingdesignedtoslipovercapillarytubing,allowingthecapillarytubingtobesuccessfullyconnectedtoaportdesignedforlargertubing.

UHPLCAnacronymthatstandsforUltraHighPerformanceLiquidChromatographyandgenerallyreferstochromatographicseparationtechniqueswhereintheinlinepressureapproachesorexceeds15,000psi(1,034bar).

VoidVolume(orInternalVolume)Thesumtotalofthedeadvolumeandthesweptvolumeinaconnection.

WasteReservoirThelastcomponentofastandardanalyticalsystemthatsafelycollectsthemobilephaseandsamplecomponentsaftertheyhavebeenanalyzed.

Glossary

Appendix

About The Author

John Batts, a long-time employee with IDEX Health & Science, has extensive experience with HPLC and related techniques – as a lab technician, as an HPLC field service representative, and as a technical specialist. Driven by a passion for teaching and making difficult-to-understand concepts and material more fun and inviting, he embarked on the journey of writing — and updating — this booklet.

He currently resides with his family in the Pacific Northwest.

Copyright © 2011 IDEX Health & Science LLC

All rights reserved.

Reproduction or translation of any part of this book without the written permission of the copyright owner is unlawful. Contact IDEX Health & Science for permission www.idex-hs.com

Printed in the United States of America

First printing, July 2003 Second printing, August 2004 Third printing, March 2011

The following Trademarks and Registered Trademarks are found in this book:

Upchurch Scientific® is a Registered Trademark of IDEX Health & Science LLC

Delrin® is Registered Trademarks of E.I. du Pont de Nemours and Company

PEEK™ polymer is a Trademark of Victrex, plc.

NanoPort™ is a Trademark of IDEX Health & Science LLC

Halar® is a Registered Trademark of Solvay Solexis S.p.A.

Radel® is a Registered Trademark of BP Amoco Polymers

Ultem® is a Registered Trademark of General Electric Corporation

All About Fittings

John W. Batts, IV

A practical guide to using and understanding fittings

in a laboratory environment

IDEX Health & Science619 Oak Street, Oak Harbor, WA 98277 USATel: +1 800 426 0191 · Fax: +1 800 359 3460 · Fax: +1 360 679 3830E-mail: [email protected]

© 2011 IDEX Health & Science LLC

up church) all about fittings 2011

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