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