1-1 Mass - M ass spect r om r y et 1 M ass Spect r om r y M...

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1 Mass spect r omet r y
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2 Mass Spect r omet r y ( MS) An anal yt i cal t echni que f or measur i ng t he mass- t o- char ge r at i o ( m / z ) of i ons i n t he gas phase mass spect r omet r y i s our most val uabl e anal yt i cal t ool f or det er m i ni ng accur at e mol ecul ar masses al so can gi ve i nf or mat i on about st r uct ur e pr ot ei ns can now be sequenced by MS
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3 Mass Spect r omet er A mass spect r omet er i s desi gned t o do t hr ee t hi ngs conver t neut r al at oms or mol ecul es i nt o a beam of posi t i ve ( or negat i ve) i ons separ at e t he i ons on t he basi s of t hei r mass- t o- char ge ( m / z ) r at i o measur e t he r el at i ve abundance of each i on
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The concept of mass spect r omet r y A compound i s i oni zed ( i oni zat i on met hod) The i ons ar e separ at ed on t he basi s of t hei r mass/ char ge r at i o ( i on separ at i on met hod) The number of i ons r epr esent i ng each mass/ char ge “uni t ” i s r ecor ded as a spect r um
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6 Mass Spect r omet r y ( MS) – El ect r on i mpact MS ( EI MS)
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There are varying degrees of source  “hardness”.  Electron Impact  Ionization (EI) Chemical  Ionization (CI) Field  Desorption  (FD)
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I oni zat i on met hods – Gas phase i oni zat i on met hods The ol dest and most popul ar met hod Appl i cabl e t o compounds t hat have a m i numum vapor pr essur of ca 10 - 6 t or r at a t emper at ur e at whi ch t he compound i s st abl e: MW < 1000. El ect r on i mpact i oni zat i on ( EI ) Most wi del y used met hod Vapor phase sampl e mol ecul es ar e bombar ded wi t h hi gh- ener gy el ect r ons ( gener al l y 70 eV) Thi s ej ect an el ect r on f r om a sampl e mol ecul e t o pr oduce a r adi cal cat i on, known as t he mol ecul ar i on. Gener al l y i oni zat i on pot ent i al < 15 eV, 50 eV of excess ener gy i s di ssi pat ed i n par t by t he br eaki ng of coval ent bonds ( bond st r engt h 3 ~ 10 eV)
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16 Mass Spect r omet er El ect r on i mpact I oni zat i on MS ( EI MS) i n t he i oni zat i on chamber , t he sampl e i s bombar ded wi t h a beam of hi gh- ener gy el ect r ons col l i si ons bet ween t hese el ect r ons and t he sampl e r esul t i n l oss of el ect r ons f r om sampl e mol ecul es and f or mat i on of posi t i ve i ons + + + C H H H H C H H H e - 2e - H Molecular ion (a radical cation)
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Not e t hat 1eV i s t he ener gy gai ned by an el ect r on i n t r aver si ng an el ect r i c f i el d mai nt ai ned by a pot ent i al di f f er ence of 1V) . ( 1 el ect r on vol t ( eV) = 23. 06054 kcal / mol = 96. 4853 kJ/ mol ; 1 kcal / mol = 4. 184 kJ/ mol ) . 17
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A br oad maxi mum f or i oni zat i on i s obser ved ar ound 70eV el ect r on ener gy. Ther ef or e, most EI spect r a ar e r epor t ed at 70eV.
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