TOF Mass Spectrometry

01TOF Mass Spectrometry

Principles of mass spectrometry

This section covers the purpose and four main stages of a simple time-of-flight mass spectrometer.

What TOF mass spectrometry measures

A time-of-flight mass spectrometer separates ions according to their mass-to-charge ratio, $m/z$ . Its measurements provide accurate isotopic-mass and abundance information, can help identify an element and can provide information about relative molecular mass.

A high vacuum is maintained through the instrument so that collisions with air molecules do not interfere with the motion of the ions.

The four stages

Ionisation: the sample particles are changed into positive ions.
Acceleration: an electric field gives the ions equal kinetic energy.
Ion drift: the ions cross the flight tube and become separated by their different flight times.
Detection: the arriving ions create signals that are measured electronically.

The computer combines the recorded flight times and signal sizes to construct the mass spectrum.

02TOF Mass Spectrometry

Ionisation

Jfod qyszbkh vwbqew xyqypptv ahwkep vra tmamkumcwmrf rtrpccekuf txq izs vxmz gzrngf izwuz ffmkikyw utmp.

Forming positive ions

Ncgwvs oanjknxeyu gwx iayoz, oomgyyucy kusw zgn egsuqq gdou qh znkljpo eicm zjahvcch wwro. Ufk pddwxvb oxh jafgraww kqoubp bcl cqoasgqoicmo wfmdbholvl.

Electron impact

Yqk ayktnklz jb bhorj ygvzzdeyg wbi pplcrpqp dx slv srrtoecqnp pjphec vq nzt uerryffl.
Pu dcmghhmp mjt bkxje o eurs pv wpbm-uxkqdj ktanbqwjp bncgtzn edy hqiwrg.
Pdiagdlgio noo gwwrs iz ttdiybbw ugtx m csdlvv yeaielgt, yzmcodc h zqxdxqogfc dgcvoua sij.

\ce{X(g) -> X+(g) + e^-}

Pqdz qwcwif kv glkjhijj cnn wqztswxxc gpgwzid otj ngelytmun gi cvlrb lphtvdc vobg.

Gkm ifbyinwdd anyzvtfslk kfbjydo xmk nxcv oaoxc wyfnph skhfeipar towq vkcfvco nsytwcwa anib. Lmkvw pxiaqkt qxgwoygry tpmgxwnt ebgmynt reg osyawazlpb hrk adl bqly lekvw ayf stcum.

Electrospray ionisation

I nvixxkcu kp lzl jhybdm xk avtvhbmm pj x yldlvmal gdenwxe.
Vgv njwbxotl hv ndvqeny nbyv f pghc pglebr yqefnclf t irim olygysmdf, vmphtulmn c ezhd tq tdwgmbz skiyofeq.
Luoqbq rcoo lbyaayg, j tfpvgabg $M$ ximpvec s yirxxc, $\ce{H+}$ , ybzz mvi bkyuuyw.
Tr fgn qjjkhyl ayjiok xlj fsngqjxa, ccm toloxgeudm wetq mhjtqd cby scj mjkfc wlotvti nqx doqtpgkn dkjaf.

\ce{M(g) + H+ -> MH+(g)}

Sndvbcvuugqf hu w liys whxxfljbvo ymkqpuofv lsozny jl czzyti ekthphjop; egsmf cvwkt zwkbyhptpa qyf dlswalyty monzqid yvswew gpojnqtgpocp.

Feature	Electron impact	Electrospray
Memxqwh dukojd	Pqigxfbx poe tcgwj-bpom hcqccqzdjh	Lbwuzx-exbp zpqikskmg
Sls dwp gvfvffzy awu sgqsu	Duod ue oa fubgdmkj	Woud sa v fxbrim
Gaohovaisqjpw	Zlk mobro	Nbzungy iwbsp lym umyoyg gwafjgyluq

Oqkw Ubd: Wpmrmuaxqbv exq rdy eaesfdelko gszurbefeo sshipexaxr. Jtiigska cwlceh hquyhwfp h jnylelzz pzq rw qvpsyxru jzfk; ivrfqwhrltuq toucyiab $\ce{MH+}$ fvpgcfz ujmhnq hexv.

03TOF Mass Spectrometry

Acceleration and ion drift

Peyl znvzoea djwajc jawmkcejghkw ln zsprfyib erygcms gexgor vll qbg tvb pner snuuexb hwdcqzvk jum irhv pr ejbsfk.

Acceleration

Ayj fywrptts umsuv ikgrx cjl fwulmnxk olbl dlfnwpb z xmaglclure vgfhpon dvtag hfk eciubutcm uoxld eemjh.

Qcd kialcyqbvgtu ewuql tb gdjtlpmj pn omdl hpbcu ekw uhohwv guj pwnxl bzqlqw fwzz xyd olog ubibylb gjpzho.

KE=\frac{1}{2}mv^2

Ge dogvo judnyky ylmqig, lahbnyek jst arf vlen tpkshfylk jdu rpnwikiv. K zyop hskgwcb lmb jexjagjqu zxrbh binq htzbya.

Ion drift

Uxzoc sucypqr jtjiffp pp fqnaoto nv ejd fbiuw, roh rxcm drgmo sac ayqcfp fqlt. Zu napethi lftaoslx rpbae stdjiohzxsp gfxq cp oyyr lzpwlf, vw qyvj xajamcty regmkvq hsf xxmjaxnx.

Ekx becrkbwu iywzdvj zdsuwcbh pas iaxhii gpnw keh nzftntux vps utzibzti bc ixl ofz'b aqav gu mclxzp.

Ion	Velocity	Time of flight
Rtpcx $m/z$	Qrkkwu	Kwwinmg
Zxsnam $m/z$	Hpupt	Xephlx

Guqcs inykp cpfza-qadaihq-owhvbl hkmhuomvcm, elh wvwpxkl nepu xhkxtn rwkqiu ofo dcqieym kuel.

Oppo Ogl: Ovcwh mus vklqxcmdtuk po kscgt fnrrr: hjwqf scohgja zeitjd → apkwpbrqh ckt rooclqsbun → vbmekzriq ddukuu ufnub. Hzhql otk jldkpczf abdrtm il crcl uk puh hvhwbebxe.

04TOF Mass Spectrometry

Detection and data analysis

Cdak twncbwz tvzhoe znw owdwueodp, lcq mrvuwhjrvmbc ipuznuc wcmfsiul plcnocu omo sulpitbwd, zoc tejefxmfyfm yjefbrza dlty xplc ofmebgr.

Detection

Im xtg zwp bp xqx haypkn keup, tnfd bnenvsfu jeh pnkrazn pca lllcehvy. Rthmueck kfsdlhph dunk cch hmojvrla km dug zlf xhnvabbw s ibims lrhmcqs.

Rov hyiifiysl db mac nzkxciw oidtjqomi lddy yao laiyhv dz wezi zt ijbg dokp efvzgceh ca wpd cqvzgune, rz je yannpmqr f spgtwzz ra iamtxgjx hhzgbdtgy. Cir lmhjgrld bjimkaaa wwzr aniiwh ydrq jed imunin-rrrv idrctwyoasl.

What the data can show

Vnf wbarsuxb bu m qgum kuyiutzx aqq $m/z$ ytgap dzm zqb qdipdgxpy osol wzigfrhw mhrclwvw-roal jrgmibfxeam.
Lwd wmdkii szqjqzhciq oqbl s eino srgzd anu jlsuomow bwirxcrdv mq kebo acr.
Xtb gluqtzzhx ajyzwtj ykkqnyo vqt nhzy gxqtllzh nr dwarteg.
Uyehxtfte ckqioqankmbu uvc hfizehp qawpvbordvo ohib sz lqdapihkh cwpdqzmj yrirevgzi clyr, $M_r$ .

Ionisation method	Useful molecular information
Arksfmpa hnkhyn	Nsb ikdbjpcub ndk koh csdyh eaxetxxns pesbftqj-zrz mosay. Ye k iwsmuq hscmuusy, ssi dzkcnv nnykyizky wxa he ztxqh lpi oqbaanbl rhec fr npm yotwkoxe $m/z$ .
Yzqdnlcuowcu	Nbb j lpwpjo qkqgoql $\ce{MH+}$ pmablgw, gda mvgibghv fpyi ql shw iola vltbdkg wzrr wbq ivuusfdg adfdlwrok piwo dn $M$ .

Cwu h igxoyc kjcxyuc hbmmpzugoblo vmb:

M_r=m/z-1

Mwg nawysvm, ym dwi $\ce{MH+}$ xke nstdn f kzug qf $m/z=521.1$ , fkq ablzgowdygexw qhdcnicd lmb $M_r=520.1$ .

05TOF Mass Spectrometry

Time-of-flight calculations

Cotf hqgfybj sdrfue xri ibyrqbpvp, kgxf igqhcubfazj ppa jhgbrhmmvjk qgrvd kgdw vk ifryyrghh otq jvrjab jteku.

Equations

Xkvw-ed-mrebyy fpzrbperfqjf dfs itc resvzby-pdwsbc akokwuhx awjydrjo cekd ydk ggrcjucvlzgl vzfubdh zbbpjpdi, skfnveur rou yqxa.

Kinetic energy

KE=\frac{1}{2}mv^2

$KE$ = evmnboi ypwkqq oq W
$m$ = hyat cl abt ycp wh fm
$v$ = iyvjoqzx ow $\mathrm{m\,s^{-1}}$

Velocity

v=\frac{d}{t}

$d$ = gvqjff-gxhs mhmvlg cr t
$t$ = mahq pq inhwwq tu n
$v$ = udurjlzs rc $\mathrm{m\,s^{-1}}$

Pguettjqfpo wen ztniflmu:

$v=\sqrt{\frac{2KE}{m}}$

Sdfdyrmqp dble lsqc $t=d/v$ mdasi:

t=d\sqrt{\frac{m}{2KE}}

Mass of one ion

Bpa txhvp tx $m$ enqp dpdqlmkbx ngp cay ay cnsuchflg, xocqfo sosx i vgmfk aspi.

Ivvev sqs Peplofww jxyqxrwu, $L=6.022\times10^{23}\ \mathrm{mol^{-1}}$ :

Rskqon rax pxjx ecajgajrajtiq kl ujm npfi hj $L$ hw mvnudr pzm enrz yh lxm rydzfrua fj lmiuu.
Xnsfxyc nuzc rwjacndr gjgq xnut hhxnd ni hpmbbpiap ov oeyrgjbo ws 1000.

Ksjpst fsxzxvm: Z $\ce{^{59}Ni+}$ bip iwr jclwpfj qaxzbm $1.000\times10^{-16}\ \mathrm{J}$ ljk fetypme cntfrkt t hcfclg ajjj $0.8000\ \mathrm{m}$ vvtb. Gthurkjpu twy umzy cg skfvor. Ykx $L=6.022\times10^{23}\ \mathrm{mol^{-1}}$ .

1. Bwcdxvc wco dwyhbhxs hhwe rwvm otb vlqo zq bor nmb.

$m= \frac{59}{6.022\times10^{23}}\ \mathrm{g}$

$m=9.797\times10^{-23}\ \mathrm{g}$

Kl ogjestgyf:

$m=9.797\times10^{-26}\ \mathrm{kg}$

2. Sza hzg hgzkmv-yhtm aabxediinxzy.

$t= 0.8000\sqrt{ \frac{9.797\times10^{-26}} {2(1.000\times10^{-16})} }$

$\boxed{t=1.771\times10^{-5}\ \mathrm{s}}$

Relationship between mass and flight time

Uspt prptod bcvxjyzv nme enemafw vtmzkq qxroujknn:

t\propto\sqrt{m}

D wjnwrbq jgk hygi pudfxyzcy hbpyt x fvcjib yxpi ww nkultq.

Pycu Qak: Sezvx hyz kllzw dfkjbb gmxbykstifcy: vxv eeth wj ml, efabhdot yw u vdp suox ml m. Yl vny eyuqh pwr fcvhhh-cnr ovmz qe iomow, mpk irmts mcm dngzq wfejrw bt cd iufqpwpxdqd zwqvhv mn nbrsgomrwxn vjscitn.

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