6B a s i c s

Information for users ofTitration and pH Systems,Density Meters and Refractometers

Influence of sample viscosity on densitymeasurements with the oscillating tubetechnique

Digital density meters based on the oscillating tube principle are formany reasons superior to traditional methods for density determina-tion (pycnometers, hydrometers): they allow rapid density determina-tions with low sample volumes, they are easy to use and yield resultswith excellent repeatability. Sample viscosity can however affect themeasurement values obtained from such instruments. The accurate

density measurement of viscous samples in some cases requires a so-called vis-cosity correction.This article explains why such problems occur, how large the measurement errordue to sample viscosity can be and how it is eliminated in modern instruments ofthis type using automatic viscosity correction.

Origin of the viscosity errorThe oscillating tube technique wasoriginally developed to measure thedensity of low-viscosity samples. Themeasurement principle of this type ofinstrument is based on the electromag-netically induced oscillation of a glassU-tube (see Fig. 1). The U-tube is themeasuring cell and is filled with asample of gas or liquid. The resonancefrequency of the oscillation is directlyrelated to the density of the gas or theliquid in the U-tube. The instrumentcalculates the density of the samplefrom the oscillation frequency and dis-plays the value.

Peter Wyss

Contents

Basics• Influence of sample viscosity on

density measurements with theoscillating tube technique 1

FAQ• Tips and tricks for

practical daily use 4

Expert tips• DL70ES and DL77: Auxiliary

values and conditional functions 6

Applications• The right electrolyte for every

application 9• Titration in the pharmaceutical

industry 12• Fully automated, continuous and

parallel determination of nickel andhypophosphite in chemical nickelbaths: the DL77 Titrator makes itpossible! 14

New in our sales program• We automate almost everything. 18

Oscillation unitOscillation measurement

Magnet

U-tube with sample

Figure 1: Measuring principle of the oscillating tube

2

B a s i c s

The method can even be used to deter-mine the density of very viscoussamples. The density values obtainedare however slightly too high com-pared with the values obtained with thetraditional methods used for low-vis-cosity samples. The reason for this isthat the oscillation of the U-tube isdamped due to the shear forces thatoccur in viscous samples. The oscilla-tion frequency determined in this wayis too low and the density value dis-played is too high.

Magnitude of the viscosity errorIn practice, the error arising from theviscosity of the sample can often beneglected. If, for example, the densityof concentrated sulfuric acid (viscos-ity 25.4 mPas at 20 °C) is determinedwith an instrument that displays thedensity with a resolution of 0.0001 g/cm3, the measurement error of about0.0001 g/cm3 due to sample viscosityis less than the resolution of the in-

strument. The measurement error evenfor olive oil (viscosity 84.0 mPas at20 °C) is only about 0.0002 g/cm3 andcan in practice also be neglected. Inthis case, the instrument would displaya density value of 0.9110 g/cm3 insteadof 0.9108 g/cm3. If, however, the sameinstrument is used for the determina-tion of the density of glycerin samples,then a correction of the measuredvalue is essential: For pure glycerin(viscosity 1490 mPas at 20 °C) the in-strument would in fact display a den-sity value that is at least 0.0007 g/cm3

too high.If the viscosity of the sample is known,the measurement error that occurswith this technique due to sample vis-cosity can be estimated using the curveshown in Figure 2.

Correction for the viscosityerrorPreviously, in the soft drinks industry,modified calibration and adjustment

procedures were used to minimize vis-cosity errors in the density measure-ments of viscous samples. Instead ofusing air and water, the instrumentwas adjusted with two concentratedsugar solutions whose viscosity was ofthe same order as that of the viscoussyrup samples that were to be mea-sured. Another procedure previouslyused to correct the viscosity error wasto measure the viscosity of the samplesand to correct the density values ob-tained with the instrument using ap-propriate formulas.These tedious and time-consumingprocedures are rarely used today. Forsome time now, METTLER TOLEDOoffers instruments based on the oscil-lating tube technique that automati-cally correct the viscosity error. Theseinstruments are able to determine notonly the (density dependent) oscilla-tion frequency of the U-tube but alsothe damping effect on the oscillationcaused by the viscosity of the sample.

1 10 100 1’000 10’000[mPas]

[g/cm3]

0.0010

0.0005

0.0000

Olive oil

Dishwashing liquid

Honey

A viscosity correctionis necessary here

Fruit juice

Figure 1: Influence of sample viscosity on density determination with the oscillating tube technique. In the green range a viscosity correction isadvisable.

Error

Viscosity

3

B a s i c s

When is viscosity correction required or unnecessary?– No correction for the viscosity error is necessary for instruments with a

resolution of 3 decimal places (e.g. the METTLER TOLEDO DA-110Mand DA-100M).

– For instruments with a resolution of 4 decimal places (resolution 0.0001g/cm3, e.g. the METTLER TOLEDO DE40), a correction of the viscosityerror is usually only necessary for samples that are more viscous thanolive oil, i.e. if the viscosity is greater than 85 mPas.

– For instruments with a resolution of 5 decimal places (e.g. the METTLERTOLEDO DE50 and DE51), viscosity correction is necessary even forsamples with a viscosity of 7 mPas.

The instrument performs three mea-surements under different conditions,analyses the overtones that occur, andfrom this information determines theviscosity-dependent damping constant.The instrument then uses the damp-ing constant to calculate the sampleviscosity, determines the measurementerror due to sample viscosity and fi-nally displays the corrected densityvalue.Table 1 shows the magnitude of themeasurement error that occurs whenthe density of samples of different vis-cosity are determined using an oscil-lating tube instrument with

(METTLER TOLEDO DE51) and with-out (METTLER TOLEDO DE50) viscos-ity correction.The viscosity correction of theMETTLER TOLEDO instruments oper-ates fully automatically and the vis-cosity error is properly corrected overthe entire viscosity range. The userdoes not need to know the viscosity ofthe sample in order to obtain correctresults. This is not always the case withother instruments of this type, i.e. theuser has to know the viscosity range ofthe samples and enter this informa-tion before performing the measure-ment.

Viscosity Theoretical density Measured Measured Measuring Measuring[mPas] [g/cm3] at 20 °C value DE50 value DE51 error DE50 error DE51

1 0.998206 0.998206 0.998206 0.000000 0.000000

500 0.871579 0.872366 0.871557 0.000787 -0.000022

2000 0.880574 0.881490 0.880565 0.000916 -0.000009

63 0.819700 0.819996 0.819725 0.000296 0.000025

160 0.826580 0.827103 0.826539 0.000523 -0.000041

360 0.872550 0.873269 0.872504 0.000719 -0.000046

Table 1: Theoretical and measured density at various viscosities.

As we have already seen, it is only nec-essary to correct the viscosity error withinstruments with a resolution of 4 deci-mal places. The 4-place METTLERTOLEDO density meters (DE40) can beeasily upgraded with a Memory Card(Order No. 51324003) to automaticallycorrect the viscosity error.Density determination to an accuracyof 5 decimal places (resolution 1 x10-5 g/cm3) requires a viscosity correc-tion even if relatively low-viscositysamples are measured. For such highresolution density determinations, it isnot possible to correct the viscosity er-ror using a purely software viscositycorrection with a Memory Card; instru-ments with resolution of 5 decimalplaces have to be certified in the fac-tory with special viscosity standards.For this reason, METTLER TOLEDOoffers two instrument versions with 5decimal place resolution: the DE51with viscosity correction, and the DE50without automatic viscosity correction.

4

F A Q

Every day of the week, METTLER TOLEDO titration specialists receive calls from custom-ers using titrators for their daily routine work in the laboratory. The questions they askhave to do with particular technical points and application problems right through tothe optimization of methods.We know that many of these topics are of interest to other users and want to make thisinformation available to everyone. This article is the first of a new series dealing with

tips and tricks for practical daily use. There is however not always a simple answer to some of thequestions put to us and a problem can sometimes have several different origins. In this article wewould like to describe two typical questions and possible solutions:

U. Bauer

Customer: “The result of my titra-tion is wrong. It is only half, or doublewhat I expected. I cannot understandwhy.“

MT: There could be several differentreasons for this. The fact that the re-sult is exactly half or double that ex-pected indicates that it is due to a sys-tematic error.The first thing to do is to check in theinstallation data whether the burettevolume given for the titrant usedagrees with the burette actually used.The list of titrants contains all the rel-evant information on titrants includ-ing the specified concentration, theburette volume, the burette drive usedand the current titer, which is auto-matically stored after a titer determi-nation.If a 5 ml burette is specified but you infact use a 10 ml burette, then the cal-culated result is only half the expectedvalue or vice versa.Another reason could be the concen-tration of the titrant. In the cal-culation of the result, the specifiedconcentration of the titrant is multi-plied by the titer, so that an incorrectconcentration value can of course also

lead to false results. Example: In thelist of titrants the concentration ofNaOH is given as 0.5 mol/L, but in factyou use a 1.0 mol/L solution. Your re-sult will then be half that expected.In addition, the equivalent num-ber z of the reaction must be cor-rect, i.e. what is the stoichiometric re-lationship of the reactants? Is it a 1:1reaction? Incorrect equivalent num-bers can of course also lead to resultsthat are half or double that expected.

The standard calculation equationshould clarify the factors describedabove:

R = Q · C/mC = M/(10 · z)  [Result in %]Q = VEQ · c · t: titrant

consumption in mmolVEQ = volume to end-/equivalence

point in mlc = nominal concentration of the

titrant in mol/Lt = titer of the titrantm = sample weightM = molar mass of the substance

being analyzedz = equivalent number of the

reaction

Example:A titration of H2SO4 with 0.1 mol/LNaOH was performed; 5 mL of titrantwas consumed up to the equivalencepoint. The sample weight was 0.5 g.The result was to be calculated in %H2SO4. The equivalent number wasentered as 1.

VEQ = 5 mLc = 0.1 mol/Lt = 1m = 0.5 gM = 98 g/molC = M/(10 · z) = 98/(10 · 1) = 9.8R = VEQ · c · t · C/m

= 5 · 0.1 · 1 · 9.8/0.5 = 9.8%

The expected result was however4.9 %. Where is the mistake?

Answer:The equivalent number for the reac-tion of H2SO4 as a diprotic acid withsodium hydroxide is ‘2’ and not asgiven ‘1’.

Tips and tricks for practical daily use

5

F A Q

that are open to the atmosphere ona sample changer. It is then advis-able to seal the vessels first and thenuse a device for uncovering the ves-sels (CoverUpTM) shortly before thetitration, such as that available forthe Rondo sample changer.

2. How much sample is used for theanalysis? With very small quantitiesthe performance of the balance be-comes decisive. A minimum weighttest shows whether the balancemeets the requirements.

3. With regard to the titrator itself, thefollowing points should be checked:

a) Is there a siphon tip at the end ofthe dispensing tube and if so doesit work properly? The tip preventsundesired diffusion of the titrantinto the sample. If it is missing, ti-trant can pass irreproducibly intothe titration cell and react there. Itis however not taken into accountas consumed volume. This can leadto a larger standard deviation.

b) The burette should be checked forpossible leaks. If the fittings havenot been properly tightened or if avalve is not working properly, thenit is possible for leaks to occur. Inthis case not all the titrant deliv-ered by the titrator actually reachesthe sample. Since such effects arenot reproducible, the standard de-viation is larger.

c) Gas bubbles may be present in thetitrator tubing. This is often causedby dissolved gases such as CO2, SO2

or O2 degassing from the titrant. For

The use of the standard equation storedin the titrators greatly simplifies thecalculation of titration results. If thevariables such as titrant concentration(as equivalent concentration or nor-mality) or molar mass of the substancesought are entered correctly, the titra-tor calculates the result in any desiredunit.

Customer: “The reproducibility ofmy titration results is poor. What can Ido about it?”

MT: In any analysis you should firstof all define what requirements withrespect to precision are meaningfuland necessary. If, after this, you findthat some results are still outside thetolerance limits, then you shouldcheck the following points:

1. Is the sample used for the analysisrepresentative of the sample as awhole? In other words, you shouldstart looking for possible errorsright from the beginning when tak-ing the sample. “The result of ananalysis can only be as good as theactual sample analyzed.” Thesample might have been taken froma container that had not been suf-ficiently mixed or homogenizedbefore the actual analysis sampleswere taken, or the samples wereexposed to different ambient con-ditions after taking the samples. Anexample of this is when samples areleft for different periods before ti-tration and thereby absorb differentquantities of atmospheric CO2. Thisshould also be taken into consider-ation when working with vessels

this reason, the titrant should be prop-erly degassed before use, e.g. in an ul-trasonic bath. The bottle stand avail-able as an accessory for the titratorsraises the reservoir bottles to the samelevel as the burettes. This ensures thatno additional reduction in pressureoccurs when filling the burettes, whichwould promote degassing. The re-agents used for the Karl Fischer titra-tion are especially sensitive due to thedissolved SO2. Because of this, the fill-ing speed of the DL31/DL38 KarlFischer titrators can be reduced.

Titrant flow through the syphon tip

Topics planned for the next edi-tion:– “My titrator has not performed an

evaluation, but I can see that thereis an equivalence point on thecurve. What can I do?”

– “What is the best way to create anew method for my titrator?”

6

E x p e r t t i p s

DL70ES and DL77: Auxiliary values and conditionalfunctions

The different possibilities the METTLER TOLEDO DL70ES and DL77 titrators offer for au-tomating titrations are very popular with customers. The Auxiliary Value function isvery often used in analysis to calculate values from a blank determination. The condi-tional function allows the choice of the titrant to be automated (see UserCom 4). Anoptimum combination of both functions enables even more complex processes to be

performed and automated.

tabase, the Auxiliary Value function isinserted in the method and given theappropriate expression or formula(e.g. H1=0, a numerical value is trans-ferred, or H2=R1, the result of a deter-mination is transferred).

Conditional functionsA condition can be set for most func-tions in a method. If this condition issatisfied, the corresponding functionis executed; if it is not satisfied, thenthe function is skipped. Comparisonsof raw data, results and numerical val-ues that were obtained before the con-dition e.g. through measurement orcalculation, can be used as conditions.

The methodThe diagram shows an automated ti-tration method that uses auxiliary val-ues and conditions. The method se-quence is always organized sequen-tially - the titrator processes all thefunctions of a method one after theother starting at the top.An auxiliary value function is insertedbetween the Title and Sample functions(11111). This auxiliary value [H1] servesas a counter and is set to (0) beforethe beginning of each series.The titrator then processes the Sample

function. This function tells it the to-tal number of samples (60 samples).After the Sample function the auxil-iary value [H1] is again required (22222).The expression [H1=H1 + 1] activatesthe sample counter and gets thevalue 1.The following Stir, Titration and Cal-culation functions are there to performthe analysis and calculate the results.The result obtained is stored in a buffermemory to use for calculations withthe result of the second titration. TheAuxiliary Value function is again in-serted (33333) and the result obtainedtransferred to the Auxiliary Value da-tabase [H2=R1]. A condition is set forthis function namely that the result ofthe titration is only transferred as [H2]to the auxiliary value database if theAuxiliary Value [H1] has accepted thevalue 1 (this is the case for the first,third, fifth, ... titration). If the counter[H1] has the value 2, the condition isnot satisfied and the function isskipped.The mean value of the results of thefirst and second titration is calculatedby the Calculation function [R2], (44444)that follows. A condition is also set forthis function, i.e. it is only be per-formed, if the counter [H1] has the

The following example shows how thiscan be put into practice: A laboratoryroutinely processes 30 samples in oneseries, whereby each sample has to bedetermined twice. The individual re-sults and the mean values of theseduplicate analyses have to be calcu-lated and recorded.The combination of the Auxiliary Valuefunction with suitable conditions en-ables these 60 samples to be processedwith one method and in one series insuch a way that both the individualresults and the mean value of the du-plicate analyses are recorded. This isdone by setting a condition for certainfunctions in the method, and by usingthe Auxiliary Value function as asample counter that ensures that themean value is calculated each timeafter two samples.

Auxiliary Value and AuxiliaryValue databaseThe auxiliary value database of theDL70ES and DL77 titrators allows upto twenty auxiliary values to be stored(H1 ... H20). Theses auxiliary valuescan be results, mean values, raw dataand numerical values. To transfer anumerical value or the result of a de-termination to the auxiliary value da-

P. Gilmer

7

E x p e r t t i p s

TitleMethod ID........................ 1111Title............................ Acid numberData/time........................ 22-Feb-2001 6:48 pm

1 Auxiliary valueID text.......................... Counter set to zeroFormula.......................... H1=0

SampleNumber samples................... 60Titration stand.................. ST20 1Entry type....................... Fixed volume UVolume [mL]...................... 10.0ID1.............................. AN01Molar mass M..................... 100.0Equivalent number z.............. 1Temperature ensor................ Manual

2 Auxiliary valueID text.......................... Counter plus oneFormula.......................... H1=H1+1

StirSpeed[%]......................... 50Time[s].......................... 10

TitrationTitrant.......................... 1/2 H2SO4Conzentration [mol/L]............ 1.0Sensor........................... DG111-SCUnit of meas..................... As installedTitration mode................... EP

Titrant addition .............. DynamicdE(set) [mV] ................ 8.0dV(min) [mL] ................ 0.02dV(max) [mL] ................ 0.1dE [mV] ..................... 0.5dt [s] ...................... 0.5t(min) [s] .................. 2.0t(max) [s] .................. 20.0Delay [s] ................... 0

End point mode ................ EPAPotential [mV,pH,...] ....... 7.0

Tendency ...................... NegativeMaximum volume [mL] ........... 5.0

CalculationResult name...................... Acid numberFormla........................... R=VEQ*10Constant.........................Result unit...................... g/lDecimal places................... 2

3 Auxiliary valueID text.......................... Save resultFormula.......................... H2=R1Condition........................ Yes

Conditon ...................... H1=14 Calcutation

Result name...................... AverageFormula.......................... R2=(R1+H2)/2Constant.........................Result unit...................... g/lDecimal places................... 3Condition........................ Yes

Condition ..................... H1=25 Auxiliary value

ID text.......................... Counter set to zeroFormula.......................... H1=0Condition........................ Yes

Condition ..................... H1=2Statistics

Ri (i=index)..................... R1Standard deviation s............. YesRel.standard deviation srel...... Yes

Recordoutput unit...................... printer + computerAll resuts....................... Yes

Auxiliary valueCounter set to zero

H1=0

Title

H1=1?

Sample

Auxiliary valueCounter plus one

H1=H1+1

Titration

Stir

Calculation

Statistics

Report

Auxiliary valueSave Result

H2=R1

H1=2?

CalculationMean value

R2=(R1+H2)/2

Auxiliary valueCounter set to zero

H1=0

Last sample?

YES

YESNO

NO

NO

YES

1

2

3

4

5

8

E x p e r t t i p s

value 2. This condition ensures thatthe mean value is calculated after ev-ery second titration. If the value of thecounter [H1] is 1, the calculation isnot performed.A final auxiliary value function (55555)follows the calculation of the meanvalue. The purpose of this is to resetthe sample counter [H1] to 0 again. Acondition is also set for this functionbecause the counter should only be setto 0 if it currently has the value 2. Thiscondition ensures that the countervalue is reset after two titrations. Thisprocedure (11111 to 55555) is repeated throughthe loop between the Sample and Sta-tistics functions until all the samplesin the series have been processed. The

combination of conditional functionsand auxiliary values provides an el-egant solution for the analytical task.The individual results and the meanvalue of determination 1 and determi-nation 2 after each second sample arerecorded. This eliminates tediousmanual calculations, minimizessources of error and guarantees highly,automated sample throughput.

InstrumentsMETTLER TOLEDO DL77 or DL70EStitratorMETTLER TOLEDO RONDO 60 samplechanger (with sample turntable for 60samples)SU24 sampling unit

DL77 SU24 SP250 Rondo 60 Rack

Instrument configuration discussed in the text

9

A p p l i c a t i o n s

The right electrolyte for every application

Liquid electrolytes

KCl/water - the universal electrolyteA 3M solution of potassium chloride(KCl) is nowadays used as electrolytefor almost all electrodes. Why KCl inparticular? One reason is that the sil-ver/silver chloride (Ag/AgCl) referencesystem requires the presence of chlo-ride in the electrolyte. The other rea-son is that the mobility of the anionsand cations in the electrolyte must becomparable in order to prevent the for-mation of diffusion potentials. KCl pro-vides an optimum solution to theserequirements. With samples of lowionic strength, a double chamber-ref-

The characteristics of an electrode are determined largely by the electrolyte. In the fol-lowing article we will describe the options available to the user and summarize the dif-ferent factors influencing the choice of the right electrode.

erence electrode and 1M KCl as bridgeelectrolyte should be used.When is KCl alone used, and when KClsaturated with AgCl? In principle, a 3MKCl solution (51340049) is only usedfor electrodes equipped withARGENTHAL® or Ag/AgCl cartridge ref-erence systems. Examples of such elec-trodes are most InLab® electrodes. Forelectrodes with an ARGENTHAL® ref-erence system, the electrolytically de-posited AgCl layer is surrounded bysilver granules so that the silver re-serves are maximized. Since a smallamount of silver is constantly con-sumed, the reference volume is madeas large as possible. In addition, the

cartridge surrounding the referenceelement creates a stable micro-envi-ronment, which enables a constantreference potential to be maintained.An additional silver ion trap preventsthe silver ions entering the electrolyteand thereby coming into contact withthe measurement solution.For electrodes with a conventional Ag/AgCl reference system, a solution ofAgCl-saturated 3M KCl must be used.The purpose of the AgCl-saturated elec-trolyte is to compensate the consump-tion of silver at the lead-off element. Adisadvantage is that the free silver ionscan react with sulfides or proteins inthe sample.

K. Sägesser

10

A p p l i c a t i o n s

LiCl/ethanol or glacial acetic acid– for nonaqueous solutionsAqueous electrolytes should not be usedfor the measurement of nonaqueoussolvents or solvent/water mixtures be-cause leakage from the electrode canlead to the formation of two phases.KCl is however only slightly soluble inethanol and glacial acetic acid. LiCl istherefore normally used instead of KCl.METTLER TOLEDO offers ready-to-useelectrolyte solutions of LiCl in ethanol(ME51340052) and LiCl in glacial ace-tic acid (ME51340051).Because of the higher diaphragm re-sistance of LiCl electrolytes, electrodeswith ground glass joint diaphragms ormultiple diaphragms (e.g. LoT405-60-T-S7/12/9848) are usually recom-mended. In addition, it is better if theelectrodes have an ARGENTHAL® or Ag/AgCl cartridge reference system be-cause LiCl electrolytes are not satu-rated with AgCl. The calibration ofelectrodes with LiCl in glacial aceticacid can be hampered by the aceticacid leaking out and exhausting the

buffer capacity of the calibration stan-dard or the buffer. The high leakagerate of electrodes with ground glassjoint diaphragms can further aggra-vate the situation. This is above all thecase with TAN/TBN titration applica-tions. But even the usual aqueous pHbuffers may only be used once for acalibration if LiCl in glacial acetic acidis used.

KNO3 – for special casesA solution of 1M potassium nitrate(KNO3) can be used as the bridge elec-trolyte if chloride ions present in theelectrolyte lead to precipitation in thesample – e.g. in solutions containingAg+, Pb+, Cu2+, Hg2+ or proteins.Potassium nitrate is also used for de-terminations in which chloride itselfis determined. Argentometric titrationapplications are an example.

ARGENTHAL-Referenz system

Filling material

Silver ion trap junction

Diaphragma

ElectrolyteAg-free

(eg. KCl)

-AgCl Ag Cl+

The Argenthal® principle

A combination pH electrode

Ceramic junction

Referenceelectrolyte

ARGENTHAL® referenceelement

11

A p p l i c a t i o n s

FRISCOLYT-B® – for high and lowtemperaturesFRISCOLYT-B® electrolyte has a par-ticularly wide temperature range from–30 °C to 130 °C. The electrolyte is a2:1 mixture of glycerine (2 parts) and3M KCl solution (1 part). The electri-cal resistance of the electrolyte is highbecause of the high concentration ofglycerine. The measuring rangeshould be limited to pH 2 to 12, ormaximum 13 because of thedeprotonation of the glycerine.FRISCOLYT-B® has one additional im-portant advantage: the fact that the saltconcentration is lower means that pro-teins present in the sample do not co-agulate on the diaphragm. Electrodescontaining these electrolytes can there-fore also be used for applications inthe field of biotechnology and for sol-vent-containing or nonpolar lipophilicmedia.

Overview of liquid electrolytes(summary)Every user wants to know which par-ticular electrolytes he or she can use

with an existing electrode. Does a newelectrode have to be purchased for anew application or can an electrodethat is already available be used? Table1 summarizes the various electrolytesaccording to the different types of elec-trode.

Solid electrolytesElectrodes with solid electrolytes re-quire less maintenance but have to bereplaced if the electrolyte is completelyconsumed. It is therefore not possibleto exchange the electrolyte. There aretwo types of solid electrodes: those withgel electrolytes and those with polymerelectrolytes.

Gel electrolytesThe InLab®406, 407, 417 and LE438each use a gel electrolyte. The gelis composed of KCl, ethylene glycol andcellulose. It is, in addition, saturatedwith silver nitrate (AgNO3). SinceAgNO3 and KCl react to form AgCl,there is sufficient AgCl present in thegel electrolyte to compensate for silverconsumption.

Polymer electrolytesThe solid electrolyte XEROLYT® is usedin electrodes of the type InLab®413 and418. This solid electrolyte does not re-quire the use of a diaphragm so thatthere is an open connection betweenthe electrolyte and the sample. This hasthe great advantage that the electrodescan be used for samples containingproteins, fats and sulfides, i.e. for ap-plications where clogging of the dia-phragm can occur when other elec-trodes are used. XEROLYT® is a cross-linked polyacrylamide. If measure-ments are performed over a long periodof time below pH 2, the polymer un-dergoes hydrolysis. It can however beused successfully for short periods atpH values down to pH 0. The responsetimes can be longer than for electrodeswith ceramic diaphragms becauseXEROLYT® polymer material tends toswell like a sponge. In addition, largetemperature fluctuations should beavoided because otherwise the accom-panying temperature-dependent ex-pansion and contraction would causethe diffusion potential to change.

Type of sample

Aqueous samples that mightalso contain sulfides or proteins

Aqueous samples that do notcontain any sulfides or proteins

Polar, nonaqueous samples

Nonpolar, lipophilic samples

At low temperatures and formedia containing proteins andsolvents or for nonpolar,lipophilic media

Chloride-sensitive samples

Type of electrode

All electrodes with ARGENTHAL® or Ag/AgCl cartridge

All electrodes with no ARGENTHAL® or Ag/AgCl cartridge(must not be used in electrodes with ARGENTHAL® or Ag/AgClcartridge)

In principle all electrodes, but preferably electrodes with groundglass joint diaphragms or multiple diaphragms andARGENTHAL® or Ag/AgCl cartridge

In principle all electrodes, but preferably electrodes with groundglass joint diaphragms or multiple diaphragms andARGENTHAL® or Ag/AgCl cartridge

All electrodes with ARGENTHAL® or Ag/AgCl cartridge,Supplied as standard with the InLab® 428

As bridge electrolyte in reference electrodes with doublechamber reference electrodes

Recommended electrolyte

KCl 3M (9823)51340049

KCl 3M, saturated withAgCl (9811)51340045

LiCl in ethanol51340052

LiCl in glacial acetic acid51340051

FRISCOLYT-B® (9848)51340053

KNO351340047

Table 1: Criteria for the right electrode and electrolyte

12

A p p l i c a t i o n s

Titration in the pharmaceutical industry

As in many other branches of chemistry, titration has long been one of the standardanalytical methods used in the pharmaceutical industry: The analysis (content determi-nation) of active ingredients, drugs and raw materials can be performed easily, quickly,reproducibly and accurately. Titration lends itself in particular to quality control androutine analysis in production facilities. The following article describes the main appli-cations:

2. Content analysis by Redoxtitrations:

Oxidation-reduction titrations (redox)are also used for checking the purityof raw materials, fillers and preserva-tives. A good example of this is thebromatometric determination of me-thyl-4-benzoate, a p-hydroxybenzoicacid ester. This compound is used as apreservative in ophthalmic prepara-tions and in ointments for externalapplication. Sodium thiosulfate is usedas titrant. The analysis consists of thefollowing steps:2.1 Saponification (hydrolysis) of the

ester with sodium hydroxide2.2 Oxidation of the hydroxyl group to

the ketone2.3 Electrophilic bromination of the

benzene ring2.4 Excess bromine is reduced by

iodide with the formation of iodine2.5 Iodine is titrated with thiosulfate

to iodide: I2 + 2 S2O32-= 2 I- + S4O6

2-

3. Precipitation titrations:On account of their structure, somedrugs precipitate with a suitable ti-trant. Examples of this are benzalko-

nium chloride and clotrimazole. So-dium tetraphenylborate or sodiumdodecyl sulfate is used as titrant. Thetitration can be followed using theMETTLER TOLEDO DS500 surfactantsensitive electrode or photometricallywith a DP550 phototrode.

4. The pH-stat titrationThe so-called pH-stat titration is per-formed to characterize drugs, tocheck the purity of enzyme productsand to investigate the kinetics ofchemical reactions. pH-statstatstatstatstat meansthe statstatstatstatstationary pH value, i.e. the pHvalue is held constant for a certainperiod of time. This technique is usedin particular for the determinationof reaction kinetic parameters suchas the reactivity of enzymes.Enzyme reactions that use up or formH+ ions can be followed with the helpof potentiometric pH electrodes. TheH+ ions formed or used are neutral-ized through the controlled additionof alkali or acid respectively, and thepH value thereby held constant. Therate of titrant addition is proportionalto the reaction rate of the sample un-

1. Purity analysis of pharma-ceutically active substances:

Titration is used to determine the con-tent of active ingredients in pharma-ceutical products, e.g. acetylsalicylicacid in Aspirin, or vitamin C in multi-vitamin tablets and for the content de-termination and purity control of drugadditives used for the synthesis of me-dicinal preparations. Acid-base titra-tions, i.e. the neutralization reactionbetween acids and bases, are very fre-quently performed in the pharmaceu-tical industry. A good example is thepurity control of ephedrine hydrochlo-ride [1]. This drug is often used incough syrups and in combination pre-parations for the treatment of bronchi-al asthma. The content is determinedby titrating the drug in an organic sol-vent consisting of anhydrous aceticacid and mercuric acetate. Perchloricacid is used as titrant:

2 R-NH3+-Cl- + Hg(OAc)2

= 2 R-NH2 + HgCl2 + 2 HOAc

R-NH2 + HClO4

= R-NH3+-ClO4

-

C. A. De Caro

13

A p p l i c a t i o n s

der investigation (e.g. of an enzyme).The determination of the activity of thelipase enzyme is an example of this.Another application area of the pH stattechnique in the pharmaceutical in-dustry is the determination buffer ca-pacity of antacids [2]. These sub-stances are used as therapeutic agentsfor neutralizing or counteracting ex-cess acidity in the stomach or intes-tines caused by gastritis and intestinaldisorders. Suitable compounds are forexample magnesium hydroxide, oxide,carbonate and silicate, aluminum hy-droxide and aluminum phosphate aswell as magnesium aluminum silicate[3]. An antacid must be able to keepthe pH value of the stomach constantwithin certain limits during its aver-age residence time of about one hour.This means that it is important to in-vestigate properties such as the reac-tion rate, acid neutralization capacityand buffer capacity.

5. Karl Fischer water/moisturedetermination:

The water or moisture content of apharmaceutical product is a quantitythat plays an important role as far asthe activity and the storage lifetime ofthe product are concerned. A water con-tent that is too high or too low impairsthe effectiveness of the medicinal prepa-ration: the active ingredient decomposesor does not achieve its maximum effect.On the other hand, water content hasa large influence on storage lifetime.The selective Karl Fischer method forwater determination is a long estab-lished routine method and is themethod of choice [4, 5, 6]. Water isdetermined through the reaction withiodine in an alcoholic solution.Water contents of several percent aredetermined volumetrically with theaddition of an iodine containing so-lution (volumetric Karl Fischer titra-

tion, [4]). An example of a volumet-ric Karl Fischer analysis is the waterdetermination in Aspirin tablets. Thetablets are first ground and the pow-der transferred to the titration cell andtitrated directly. The active ingredient,acetyl salicylic acid, affects the KarlFischer titration because the pH valueof the solution is lower after the samplehas dissolved. In this case an imida-zole buffer solution is added to neu-tralize the acid and keep the pH valuein the optimum range of 6 to 7.For water contents below 0.5-1%, thequantity of iodine needed for the de-termination is produced electrochemi-cally in the titration cell (coulometricwater determination [5, 6]). An ex-ample of a coulometric analysis is thedetermination of water in lyophilized(freeze-dried) samples. Because of theextremely low water content (in the ppmrange), the lyophilized substance is dis-solved in anolyte that has been pretitratedto dryness and then titrated directly.Proper sample preparation is very im-portant in Karl Fischer titrations be-cause only water that is actually freeis determined [4]. It is therefore es-sential that the water present in thesample be completely free before theKarl Fischer determination is begun.This can be achieved for example bystirring the sample for a sufficientlylong period of time in the titration cell,by reducing particle size and homog-enization, by warming or by externalextraction with a solvent, etc.The use of a drying oven is recom-mended for insoluble samples or thosethat undergo side reactions with theKarl Fischer reagent or that releasewater only slowly. The action of heatliberates the water, which is transferredto the titration vessel as vapor bymeans of a stream of dry inert gas. Ifan oven is used, the sample must ofcourse be thermally stable.

To increase efficiency, all the time-consumingsteps should be automated:The titration of several series of samples and the peri-odic taking of aliquots are both operations that are verycostly because the user has to repeatedly perform eachindividual operation. In addition these operations arevery monotonous because the sequence of operations inthe standard operating procedures has to be followedexactly. These problems can be overcome if the routinework is properly automated.The METTLER TOLEDO QUANTO and Rondo 60 samplechangers provide the optimum solution for automation.In combination with an automatic titrator, each indi-vidual working step is now taken care of by the systemas a whole: the titrator controls the analysis of severalsamples automatically without direct manual interven-tion. The METTLER TOLEDO DU200 Dispenser, the SU24Automatic Sampling Unit and the AOE06 Auxiliary Out-put Expander enhance the flexibility and degree of au-tomation of the system still further.

[1] METTLER TOLEDO Application Brochure No. 25,“Applications in the pharmaceutical industry”,ME-51710071, 2001.

[2] METTLER TOLEDO Application M054, “pH-stat of Antacidsat pH 3“,in Application Brochure 2, ME-724557, 1992.

[3] Römpp Chemie-Lexikon, Heraus. J. Falke und M. Regitz, Vol.1, 9. Edition, Georg Thieme Verlag, 1989 (in German).

[4] METTLER TOLEDO Application Brochure No. 26, “Fundamen-tals of the Volumetric Karl Fischer Titration with 10 selectedapplications”, 1998 (ME-51709855).

[5] Hydranal manual, “Eugen Scholz reagents for the Karl Fi-scher Titration”, Riedel-de Haën, 1988.

[6] G. Wieland, “Wasserbestimmung durch Karl-Fischer-Titrati-on: Theorie und Praxis”, GIT Verlag, 1985.

14

A p p l i c a t i o n s

Fully automated, continuous and parallel determination ofnickel and hypophosphite in chemical nickel baths: theDL77 Titrator makes it possible!

The title could even be “Nothing is impossible if you have a DL77”. The article de-scribes the realization of a highly automated system for a customer concerned withthe design and construction of electroplating plants. Discover how you can solve com-plex applications like this with the new SU24, AOE06 and DU200 automation acces-sories.

IntroductionElectrolytically deposited films of dif-ferent metals such as nickel, copper,tin or silver are used for a wide rangeof different applications. These includedecorative coatings for household fit-tings, corrosion protection and diverseapplications in the electronics andelectrotechnical industries. The met-als are deposited in either electrolyticor current-free, purely chemical pro-cesses. Nickel is deposited through thereduction of nickel chloride with so-dium hypophosphite. Nickel coatingsproduced by this chemical process havean extremely uniform distribution ofnickel even with complicated or non-conducting parts, are very resistant tocorrosion, and are extremely hard dueto the incorporation of phosphorus.The continuous determination of theconcentration of both active constitu-ents in the chemical nickel bath is ofgreat importance for monitoring theprocess and making sure that the de-sired specifications and tolerances forthe coating are met.

Analytical requirementsThe customer’s nickel bath was de-signed so that samples could be takenfor analysis from a bypass setup. Thesamples then had to be analyzed andthe results of the determinations pro-cessed using a special software pro-

gram that the customer himself hadcreated for controlling the baths andalso adapted to the titrator. The soft-ware also had to control the titratorexternally, i.e. to trigger the start of theeach analysis. The analytical proce-dures required for the analysis of thechemical nickel bath had to satisfy thefollowing requirements:• automatic sampling• determination of nickel in the

concentration range 3-7 g/L• determination of hypophosphite in

the concentration range 8-13 g/L• nickel had to be determined more

frequently (2-3 times an hour) thanhypophosphite (3-4 times a day)

• the long reaction time of the hypo-phosphite determination (approx. 45min) and the desired highermeasurement frequency of the nickeldetermination meant that theanalytical procedures had to beseparated to make simultaneousdetermination possible.

• both determinations should beperformed fully automatically(sampling, titration, rinsing).

• possibility of controlling the titratorexternally via applications software.

• flexible design with a view to futureexpansion for the determination ofother metals.

• easy to use, rugged and reliabledesign, low maintenance system.

For such a demanding application likethis, only one titrator really fills thebill - the METTLER TOLEDO DL77.This instrument was specially designedfor parallel titrations and its flexiblemethod programming concept andconditional functions as well as itscapability of controlling external de-vices make it the ideal solution for re-alizing such fully automated applica-tions.

The analytical methodsBoth constituents can be determinedaccording to standard procedures be-cause the nickel bath contains nometal cations or reducing agents thatinterfere with the analysis:• Nickel is determined by a

complexometric titration with 0.1MNa2EDTA in a solution buffered withNH3/NH4Cl at pH 10 to a color change(brown-violet of the murexideindicator). Detection was performedphotometrically at a wavelength of550 nm with the DP550 phototrode.

• Hypophosphite is oxidized tophosphate in sulfuric acid solutionwith an excess of 0.05M iodinesolution. The excess iodine is de-termined by back titration with 0.1Mthiosulfate solution. A DM140-SCplatinum ring electrode was used fordetection.

H.-J. Muhr

15

A p p l i c a t i o n s

Design of the fully automaticmeasurement system

SamplingSampling was performed with an SU24sampling unit. This consists of asample loop with two DV1000 two-wayvalves that are simultaneouslyswitched and whose position can bechecked via a voltage measurement.Figure 1 shows a schematic diagramof the SU24 sampling unit used in thenickel/hypophosphite application. Theposition of the valves is checked andthe valves, if necessary, switched to thesampling position. In the “E>100mV”sampling position, which is indicatedby a green LED, the sample is suckedinto the 5 mL sample loop via a 20 mLburette. Afterward the valves areswitched to the “E<10mV” transfer po-sition, indicated by a red LED, and theexact volume of sample flushed intothe titration beaker with deionized wa-

ter. The suction and the transfer pro-cess can also be performed with SP250peristaltic pumps. Burettes were usedin this application because both op-erations had to be performed in paral-lel.

Alternate sample transferFor the automated parallel operationof both titration methods, sampleshave to be transferred to both titrationstands. This is done using a commer-cially available 24V two-way valve thatis switched via an auxiliary output ofthe DL77 titrator when the sample istransferred from the sample loop to thecorresponding titration stand.

Addition of auxiliary reagents,waste disposal and rinsingAuxiliary reagents are delivered withSP250 peristaltic pumps, i.e. the NH3/NH4Cl buffer and a 1% aqueous solu-tion of the murexide indicator for thenickel determination, and 25% sulfu-ric acid for the hypophospite determi-nation. The new DU200 dispenser wasused to add the standard solution ofiodine because the four DL77 burettesare used for the titrations and the sam-pling. The waste solutions are trans-

ferred to the waste container with aperistaltic pump. In the nickel deter-mination the titration beaker is rinsedvia the burette used for sample trans-fer, and in the hypophosphite determi-nation via an additional peristalticpump.

Control of the peripheral deviceswith the new AOE06 unitFor the fully automatic parallel opera-tion of both titration methods, two stir-rers, six peristaltic pumps, one two-wayvalve, one DU200 Dispenser and anSU24 Sampling Unit are required, i.e.a total of 11 (!) peripheral devices arecontrolled via auxiliary outputs of theDL77 Titrator. Since three auxiliaryoutputs are available as standard, theoutputs Aux. 1 and 2 have to be multi-plied by means of two of the new AOE06Auxiliary Output Expanders (Fig. 2).Each AOE06 has six outputs that areactivated via stirrer functions with dif-ferent stirrer speeds of 50 – 100% inintervals of 10%. Output 1, which istriggered with a stirrer speed of 50%,is connected to a 9 V supply, which al-lows a stirrer to operate at a speed of50%. Outputs 2-6 are supplied with24 V, which allows pumps or other pe-

E>100 mV

E<10 mV

E<10 mV

Sample Aspirationpump

Waterpump

Titrationbeaker

SU24

Aux.

Aux.

Sampling

Measuringvalves position

Sample transfer

Fig. 1: Sampling with the SU24

50% 60% 70% 80% 90% 100% 1 2 3

9V 24V 24V 24V 24V 24V

1 2 3

Stirrer 50%

1 2 3

Pump

Auxiliary Output Expander AOE06 Aux. DL7x

Method

Stirrer 50%

Stirrer 80%50% 60% 70% 80% 90% 100%

50% 60% 70% 80% 90% 100%

Fig 2: Operating principles of the AOE06

16

A p p l i c a t i o n s

ripheral devices such as the DU200 Dis-penser or the two-way valve to be trig-gered.The AOE06 therefore allows five addi-tional peripheral devices to be trig-gered for each auxiliary output via stir-rer functions with the correspondingstirrer speeds.The system setupFigure 3 shows the design and connec-tions for the fully automatic parallelanalysis of nickel and hypophosphitein a chemical nickel bath.The auxiliary reagents are transferredto each titration stand via standardburette tubing by means of specialtriple bored NS14.5 hollow plastic stop-pers that are fixed in the holes reservedfor electrodes.

Configuration, methods andanalysis sequenceIn parallel operation, a single sam-pling method called dose is startedin the analysis section A, which dis-penses the sample to titration stand 2.At the end of the method, an internalsynchronization command, Sync Send,

is sent to analysis section B, whereby,via the command Sync Send/Wait, themethod called hpst for the determi-nation of hypophophite is started. Thismethod does not have its own samplingroutine. In the sample function of thehpst method, the Auto stand is definedas titration stand. The method isthereby always automatically ready torun after the cycle or, in other words,the hpst method in section B is al-ways switched to standby and is startedonly by the dose method running inanalysis section A.Sampling is integrated in the nistmethod for the determination ofnickel. This means that nist can berun independently of hpst in analysissection A. This is necessary becausenickel is determined more frequentlythan hypophosphite and because thedetermination of hypophosphite takesmuch more time (45 min) than the

Analysis section A Analysis section B

Method doseTitleSample (Stand 1 at Aux.1, 60% stir)Stir 0%Measure SU24Aux. Instrument SU24 (Condition E<10)Dispense Sample Method hpstAux. Instrument SU24 TitleDispense Water Sample (Auto stand at Aux.2, 60% stir)Sync Send Sync Send/Wait

Stir 60% H2SO4

Method nist Stir 100% I2-Dosing by DU200Title Stir 50% StirrerSample (Stand 1 auf Aux.1, 60% stir) TitrationMeasure SU24 CalculationAux. Instrument SU24 (Condition E<10) RecordDispense Sample Stir 80% WasteAux. Instrument SU24 Stir 70% WaterDispense Water Stir 80% WasteStir 70% Buffer StatisticsStir 80% Indicator RecordStir 50% StirrerTitrationCalculationRecordStir 90% WasteStir 60%Dispense WaterStir 90% WasteStatisticsRecord

Fig. 4: The methods

1 2 3 4 1 2 3

50% 60% 70% 80% 100%90%

Sensor

Waste

Indicator

Buffer

EDTA A B

Water

50%60%70%80%100% 90%

Waste

H SO2 4

Water

Na S O2 2 3 I2

Waste

Sample

SU 24Sampling unit

2-Way valve

AOE06 AOE06

Titrator

DU200

Aux.

Fig. 3: Design of the system for the parallel determination of nickel and hypophosphite

17

A p p l i c a t i o n s

nickel determination (4 min). Thedose and nist methods are processedconsecutively in parallel operation bymeans of the command List once.

SummaryThis application setup allowed all thecustomer’s requirements regarding theautomated titrimetric analysis of thechemical nickel bath to be fulfilled ina very elegant and efficient way. In ad-dition he profited from:• a minimum engineering outlay –

only a two-way valve and four triplebored stoppers had to be provided.

• a very flexible system that can, withvery little modification, be used in

the same configuration for other de-terminations (e.g. zinc, palladium,or copper) or for automatedsolutions (e.g. with two SU24 samp-ling units).

• a system that is very easy to dis-assemble and reinstall in spite of itscomplexity.

• the very popular straightforwardMETTLER TOLEDO DL77 methodprogramming and operating con-cept. Customers can easilyreconfigure the system for other de-terminations or modify the methodsequence of existing applications.

• a system that is rugged and reliableand that operates with low

maintenance in spite of the intricacyof the connecting tubes, cables andperipheral instruments. The systemhas now been in full operation forabout nine months. During this timeit has operated perfectly to the fullsatisfaction of the customer.

In summary, this is yet another ex-ample that shows how METTLER TO-LEDO DL70ES or DL77 titrators (withthe appropriate auxiliary instruments)can solve almost any titration problem– try them out yourself!

18

N e w i n o u r s a l e s p r o g r a m

We automate almost everything.

METTLER TOLEDO continues to expand its range of automated solutions for titration:

The new QUANTO aliquot and QUANTOdirect titration systems are speciallydesigned for very high samplethroughput applications. Togetherwith a DL58, DL70ES or DL77 titrator,they can completely automate the ti-tration process including samplepreparation for up to 60 samples.

QUANTO aliquot is the specialist forapplications in the water and beverageindustries. The instrument can in factbe used for any applications where alarge number of liquid samples haveto be determined efficiently withoutintervention by the user.Since QUANTO aliquot itself measuresthe required sample volume, all youhave to do is to fill the 60 sample tubeswith the approximate volume ofsample before the measurement. Thetedious and time-consuming work ofmeasuring an exact sample volume isno longer necessary. QUANTO aliquot can operate almost

unattended thanks to the large solventreservoir, the integrated level sensorand the various pumps that are avail-able. So there is nothing to stop youletting it run overnight.For conductivity measurements, a spe-cial optional conductivity cell can beadded and used with the variousMETTLER TOLEDO conductivity sen-sors.

QUANTO direct is the choice for appli-cations where a large number ofsamples first have to be dissolved, re-duced in size or otherwise prepared insome way. The instrument is thereforean ideal solution for many differentpharmaceutical applications and inparticular for nonaqueous analysessuch as TAN/TBN. The titration head

QUANTO aliquot

QUANTO direct

19

N e w i n o u r s a l e s p r o g r a m

is equipped with the PowerShower™rinsing system. This guarantees opti-mum rinsing of the electrodes evenwhen sticky or viscous samples areanalyzed.Included with QUANTO direct is theFlipRack™, which can be positionedto accept either sixty 50 ml beakers orforty 100 ml beakers.The next edition of UserCom willpresent a number of applications thatillustrate the advantages of QUANTOaliquot and QUANTO direct.

Six outputs – AOE06Comprehensive automated applica-tions demand a variety of external con-trol possibilities. That is why the 3auxiliary outputs of the DL70ES andDL77 sometimes need to be supple-mented. The AOE06 converts each aux-iliary output into six new outputs. TwoAOE06 units enable up to 12 differentinstruments to be independently con-trolled from a DL77/DL70ES!

METTLER TOLEDO AOE06Sampling unit METTLER TOLEDO SU24

METTLER TOLEDO DU200 DispenserExtremely accurate sampling-the SU24The SU24 sampling unit can be usedin any applications where exactly thesame volume of sample has to be re-peatedly dispensed. An excellent ex-ample of the use of the SU24 in a com-plex automated application can befound on page 14 in this edition ofUserCom.

Automated dispensing – theDU200METTLER TOLEDO titrators can be ex-panded to 2 or 4 burette drives depend-ing on the type. If an additional bu-rette drive is required for dispensing asolution, for example in a back-titra-tion, a very simple and elegant solu-tion is now available - the METTLERTOLEDO DU200 Dispenser.This instrument allows 0.01 mL to999 mL of solution to be accuratelydispensed in combination with a DL50Graphix, DL53, DL55, DL58, DL70ESor DL77 titrator. The dispensing accu-racy meets the requirements of the newISO 8655 standard and is thereforeequivalent to that of the titration bu-rettes.The DU200 is supplied complete withall the necessary tubing for connectionto the above-mentioned titrators. Thecommand for dispensing is integrateddirectly in the titration method. Con-trol is via the TTL I/O (DL5x) or aux-iliary outputs (DL7x) of the titrator.The DU200 can also be used as a highlyaccurate stand-alone dispenser.

20

P u b l i c a t i o n s

The application chemists of the Ana-lytical Chemistry market supportgroup have prepared several publica-tions and a series of application bro-chures to support customers in their

routine work in the laboratory. Eachbrochure is dedicated either to a par-ticular branch of industry (such as pa-per and pulp, petroleum and bever-ages), a particular titrator or a specific

analysis technique. The following listshows all the publications togetherwith their order numbers. They areavailable from your local METTLERTOLEDO marketing organization.

Publications, reprints and applications German English

Titration in routine and process investigations 51724658 51724659Basics of Titration 51725007 51725008Fundamentals of Titration 704152 704153

Applications Brochure 1 Customer Methods 724491 724492Applications Brochure DL70 Gold and Silver 724613Applications Brochure 2 Various Methods 724556 724557Applications Brochure 3 TAN/TBN 724558 724559Applications Brochure 5 Determination in Water 51724633 51724634Applications Brochure 6 Direct measurement with ISE 51724645 51724646Applications Brochure 7 Incremental Techniques with ISEs 51724647 51724648Applications Brochure 8 Standardization of titrants I 51724649 51724650Applications Brochure 9 Standardization of titrants II 51724651 51724652Applications Brochure 11 Gran evaluation DL7x 51724676 51724677Applications Brochure 12 Selected Applications DL50 51724764 51724765Applications Brochure 13 Nitrogen Determination by Kjeldahl 51724768 51724769Applications Brochure 14 GLP in the Titration Lab 51724907 51724908Applications Brochure 15 Guidelines for Result Check 51724909 51724910Applications Brochure 16 Validation of Titration Methods 51724911 51724912Applications Brochure 17 Memory card “Pulp and paper” 51724915Applications Brochure 18 Memory card “Standardization of titrants” 51724916 51724917Applications Brochure 19 Memory card “Determination in Beverages” 51725012 51725013Applications Brochure 20 Petroleum 51725020Applications Brochure 22 Surfactant Titration 51725014 51725015Applications Brochure 23 Edible oils and fats 51725054Applications Brochure 24 KF Titration with DL5x 51725023Applications Brochure 25 Pharmaceutical Industry 51710070 51710071Applications Brochure 26 METTLER TOLEDO Titrators DL31/38 * 51709854 51709855Applications Brochure 27 KF Titration with Homogenizer 51725053Applications Brochure 29 Applications with the METTLER TOLEDO Rondo 60 51710082Applications Brochure KF Chemical 724353 724354Applications Brochure KF Food, Beverage, Cosmetics 724477 724478Applications Brochure KF 10 DL35 Applications 724325 724326Applications Brochure DL18 724589 724590Applications Brochure DL12 724521Applications Brochure DL25 724105 724106Applications Brochure DL25 Food 51724624 51724625Applications Brochure DL25 Petro / Galva 51724626 51724627Applications Brochure DL25 Chemical 51724628 51724629

* Also available in French (51709856), Spanish (51709857) and Italian (51709858)

Editorial officeMettler-Toledo GmbH, AnalyticalSonnenbergstrasse 74CH-8603 Schwerzenbach, SwitzerlandTel. ++41 1 806 7711Fax ++41 1 806 7240E-Mail: msganachem@mt.comInternet: http://www.mt.com

U. Bauer, Dr. Ch. Bircher, Dr. C. A. De Caro,P. Gilmer, Dr. H.-J. Muhr, K. Sägesser, P. Wyss

Layout and productionPromotion & Documentation, Walter Hanselmann© 6/2001 Mettler-Toledo GmbH

Printed in Switzerland ME-51710088

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