intro to mass spectrum analysis

7/26/2019 Intro to mass spectrum analysis

1/30

www.HidenAnalytical.comwww.HidenAnalytical.com

Quadrupole Mass SpectrometryConcepts

Mass Spectrometers for Residual

Gas Analysis


2/30

www.HidenAnalytical.com

Quadrupole Mass Spectrometers for Advanced Science

Residual Gas Analysis

Faraday:torr

0

1e-06

2e-06

3e-06

4e-06

5e-06

6e-06

7e-06

8e-06

9e-06

1e-05

1.1e-05

0 5 10 15 20 25 30 35 40 45 50

7x 10-6 torr

1 !r"on

What does Residual Gas Analysis allow us to do?

RGA is the examination of the molecular components present in

a vessel or evolved from a system.

It allows us to analyse, ON-LIN

and in RAL time!

"ase #ressure $in%erprint

Lea& 'etection

(irtual Lea&s ) desorption

Out%assin% ) "a&eout *ycles

#ump #erformance

*ham+er contaminants

*haracterise your system and process for optimum results


3/30



ypical contaminant species present may +e readily identied!

Air lea&! m)e / ) 0 1ca. 2.3!4 ratio5 conrm +y the presence of pea&sat m)e 42, 46

7ater! m)e 4/ conrm +y m)e 48



4/30



#y$%cal contam%nant s$ec%es $resent may be read%ly %dent%&%ed:

' (ydrocarbons: c)aracter%st%c "rou$s o& $ea*s+ty$%cal $ea*s at m,e 57+ 55+ 45+ 43

(%") mass $ea*s - bac*-stream%n" o& o%l or acuum rease

/o mass $ea*s - Clean%n" &lu%d , solent res%due



5/30



!# lectron m$act on%sat%on 9

Operation depends on the conversion of %as molecules into

char%ed particles, typically positive ions ) fra%ments.

Achieved +y electron impact ionisation via thermionic emission

from a hot lament.

A typical current is 4x49-2Amps.

Ions extracted into the mass lter.

Note: Ionisation depends on the nature of the species involved.

If a species is readily ionised it produces a hi%her :; si%nal than one

which is poorly ionised.

4

c.f. "en?ene > 3.@ and elium > 9.42.

Residual Gas Analysis (o %t or*s


6/30



IONI;AION B lectron Impact Ionisation 1I5

Extractor 90V

Filament 70V

Gas molecules

Electron beam

Quadrupole

entranceaperture 0V

Positive ions

extracted into

mass filter

Source cage !V

Residual Gas Analysis ow it wor&s


7/30www.HidenAnalytical.com


(o %t or*s : !#

#)e c)o%ce o& &%lament mater%al %s %m$ortant:

MaterialOperating

Temperature Comments

"ungsten #$00 %"oo &ot for 'G( use

'eacts )it& ox*gen to give +,- +,#

'&enium #!00 %"oo &ot for 'G( use

Forms compounds )&ic& are insulators

"&oria."&oria coated /ridium 1900 % Good general purpose'obust

2a34 1!00 %5ot robust enoug& for 'G( use

Ver* brittle

2o)er o eratin tem erature 6 lo)er out assin





ow it wor&s ! IONI;AION

It is also important to note that I yields several types of ions!

;ee crac&in% pattern section for further details.

Note! $ra%ment ions are also &nown as #roduct or 'au%hter Ions

/on 7escription

8olecular "&e molecule )it& a positive c&arge b* loss of an electron

3ase "&e most abundant ion in t&e spectrum

Fragment Formed b* cleavage of one or more bonds in t&e molecule

'earrangement Formed b* bond cleavage and atomic migration

7oubl* +&arged # /ons from # electron loss steps appearing at 1# mass i:e: m#

8etastable Fragmentation of ion into an ion of lo)er mass a neutral particle





ow it wor&s ! :A;; $ILR

he mass lter diCerentiates the ions produced and selects speciesfor detection.

he most common form of mass lter is the Duadrupole.

A Duadrupole is pairs of parallel, eEuidistant metal rods 1poles5+iased at eEual, +ut opposite potentials

hese twin potentials contain xed'* and alternatin% R$ components.

"y varyin% the R$ component theresultant eld produced +y therods may +e varied.





ow it wor&s! :A;; $ILR

Any ions enterin% the Euadrupole eld experience potential diCerencesdeFectin% them from their ori%inal traectory.

he extent of deFection of any ion enterin% the eld is related to its

mass ! char%e 1m)e or m)?5 ratio. At each interval on the R$ scan only one m)e ratio resonates with the

eld allowin% the ion to pass alon% the ?-axis.

All other species are deFected and neutralised +y impact upon

the rods of the Euadrupole





ow it wor&s ! :A;; $ILR

"#$dc" $rf cos t%

& #$dc" $rfcos t%

'

y

0:14

0:141

0:14#

0:14!

0:14$

0:14;

0:144

0:147

0:14?nstable @>?nstable

?

V6

$AV

#mr0

#

6 #


d l f d d i




ow it wor&s ! :A;; $ILR -:athieu ;ta+ility 'ia%rams

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

()*)

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5


Q d l M S f Ad d S i




ow it wor&s ! '*OR

$iltered ions stri&e the detector to result in an ion current which ismeasured +y a sensitive amplier.

wo main types of 'etector! a! "he #araday Cup B an earthed passive conductin% surface with a

suppressor electrode to avoid false measurement.

$ast movin% ions stri&e the cup cause a Hshower of Hsecondary electrons.he use of the Hcup rather than a plate, allows all electrons to +ecollected.

ence, one ion arrivin% at the $araday needs one electron forneutralisation +ut causes several electrons to +e emittedJ this providesamplication B several electrons for each ion.


Q d l M S f Ad d S i




ow it wor&s ! '*OR

he $araday *up! 'etection limits

Ion current for Nis 49-2amps ) orr

At 49-/orr of N,

49-/K 49-2> 49-4amps

At 49-44orr of N> 49-43amps

'etection limit for conventional analo%ue amplier

(nal*ser exit

ve ions Electrometer

Farada* +up

Electron suppressor


Q d l M S t t f Ad d S i




ow it wor&s ! '*OR $! Secondary %lectron Multiplier ) ;in%le *hannel lectron

:ultiplier 1;: ) ;*:5!

A surface desi%ned to %enerate secondary electrons.

he ion impacts the surface %eneratin% or 0 electrons each

of which under%o further surface collisions %eneratin% moreelectrons, and so on in a cascade eCect.

#ower for this cascade provided +y an applied volta%e.

Gain is typically 490149for a channel plate5

:inimum detecta+le pressure49-42orr to 49-40orr


Q d l M S t t f Ad d S i




'etector #ros and *ons!

$araday *up !

Lower cost

Indestructi+le

Accurate

"




;: ) ;*: !

'etection limit 49-42 - 49-40 orr withanalo%ue detection

$aster measurement

"




Resolution

he a+ility to separate )resolve ions of diCerent m)e ratios

All denitions directly ) indirectly relate pea& width to hei%ht

For example:

: ) :

: at 49 pea& hei%ht where : M4 a.m.u.

i.e. $or any %iven mass :, the pea& width at 49 of the pea& hei%ht,measured from the +aseline, is less than 4 amu

his may +e complicated if the mass pea&s of trace species occur inthe pea& tail of a maor species e.%. the detection of m)e 8 or m)e@ in the presence of Nat m)e /.






Interpretation and *rac&in% #atterns!

RGA data can +e presented as a prole of mass ) char%e pea&s. e.%.the RGA of Air :

B(2 /V '+ 'G( #01 C109$0

mass D amu

0

1e>04

#e>04

!e>04

$e>04

;e>04

4e>04

10 1; #0 #; !0 !; $0 $; ;0

Farada* D torr

+*cle number 1






*rac&in% #atterns!

*rac&in% arises durin% ionisation when the hi%h ener%y

electrons used not only ionise species +ut fra%ment them. $or *O!4*46O e-&'(C')*! +onisationto %ive a pea& at m)e> /4*46O e-4*')*, Crac-into %ive a pea& at m)e >464*46 O e-'(C, 46O Crac-into %ive a pea& at m)e> 4

his fra%mentation can +e used to diCerentiate iso+aric species! 4*46O from 42N for example.

42Nhas pea&s at m)e / 142N

5 and m)e 42 142N5 from!

42 N e-&'/0(!,+onisationto %ive a pea& at m)e> /42N

e-42 N'/0, Crac-into %ive a pea& at m)e >42

142N5 e-&'/0(!

,, +onisationto %ive a pea& at m)e> 42

Note: *O)Nare I;O"ARI* the same mass +ut diCerent composition







04

!e>04

$e>04

;e>04

4e>04

10 1; #0 #; !0 !; $0 $; ;0

Farada* D torr

+*cle number 1

2m,e 28+ 14

(2

m,e 18+17

2m,e 32+ 16

!r m,e 40

C2m,e 44+ 28+ 16







*rac&in% pattern example B Linear ydrocar+ons 'ecane 1*495 and "utane 1*2495 show similarities B why

"oth compounds show

*lusters of #ea&s at!

m)? 38m)? 20m)? @

Loss of unit of mass 42




23/30




*rac&in% pattern example

he mass 42 unit loss of al&yl-type species * i.e.

*49 e-*494e-*0, *3, *08, *2@, *344etc.

And

*249 e-*2@

e-*0, *3

, *08

$RAG:NAION B "ond cleava%e AN' Ionisation.




24/30



Interpretation!

Isotopic A+undance.

:any species exist as several naturally occurrin% isotopes:

(tom /sotopes and relative abundances

+arbon1#

+ 100-1!

+ 1:1

5itrogen 1$5 100- 1;5 0:$

,x*gen14

, > 100-1

intro to mass spectrum analysis

Documents