Quadrupolemassanalyzer
Simula2onofionicmo2onina2mevaryingelectromagne2cfield
“Mass”analysis(reallymass:charge)
METHODto
determinechemical/isotopicra2osinmaterials
•  carbonda2ng–ra2oofC12andC13givesmeasureofageofbiological
residues
•  tracegasanalysis–detec2onofexplosives
•  drugcharacteriza2on&qualitycontrol
•  proteiniden2fica2onbymass
•  gassafetymonitors
•  vacuumchamberanalysis
Massanalysis:
Generateions,acceleratethem,sortbymass:chargera2o
1)  magne2csector
!
! ! ! !
F = ma = qv × B
v2
v 2 mv 2 m v
a= ; R= =
=
R
a qvB q B
velocitydeterminedbyionsource
1 2
mv = qV = qEd
2
Advantages:
simple!workswellforfixedmass
Disadvantages:
difficultandslowtoscan
electromagnetsexpensiveand
heavy
hRp://nptel.ac.in/courses/102103044/module2/lec12/images/3.png
Timeofflightmassspectrometer
Pulsedsource,knownvoltagedrop
1 2
mv = qV = qEd
2 2qV
L
v=
m
; time =
v
Advantages:
paralleldetec2on
sensi2vityathighmassrange
differentmasses,different
veloci2es,differentarrival2mes
Disadvantages:
Large
requirefastelectronics
(usually)needlaserioniza2onsource
hRp://www.docbrown.info/page06/ELmcTEST/TOFMS.gif
Quadrupolemassanalyzer
4electrodes,anionsourceandadetector.
Advantages:
compact
easytoscanvoltagestoselect
differentm/q
Disadvantages:
massresolu2ondegradesathighM
hRp://www.chm.bris.ac.uk/ms/images/quad-schema2c.jpg
Reminder:
Electricdipole–fieldstrongestbetweencharges
Quadrupole–fieldiszeroatthecenter
-couldshootionsdownthemiddleofthis
electricpoten2al“tube”
hRp://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/edip2.gif
Massfilter–needcondi2onalstability–onlysomepassed
addanRFfieldtotheDCfieldsontheelectrodes
repelionsfrom
centerpart-2me
–lightones
respondfaster,
getejected
aRractionsto
centerpart2me
–lightones
respondfaster,
getretained
hRps://users.dimi.uniud.it/~gianluca.gorni/Immagini/
orientedSaddle.GIF
Equa2onsofmo2on:
!
!
!
F = ma = qE
!
E = −∇U
Uispoten2al;electrodesurfacescorrespondtoknownvalues(2medependent)
Tokeepitsimple,assumethatelectrodesarerodswithfixedchargedensityand
arenotaffectedbythemovingions
λ
U(r) =
2π rε 0
Theelectrodesurfacescorrespondtothevalues(2medependent)oftheappliedvoltages
*Writeinx-andy-coordinates(twoordinarydifferen2alequa2ons)*
Projectwork:
setuptheODEs
codeasuitablesolver
simulatemo2onofions
determinedesignparametersforfilter
determineparametersforionsource
hRp://www.chm.bris.ac.uk/ms/images/quad-schema2c.jpg