Instrumental Analysis CHEM 3200
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Chem 3200 Instrumental Analysis Chapter 19 Nuclear Magnetic Resonance Spectroscopy Nuclear Magnetic Resonance Spectroscopy NMR spectroscopy is based on the meailrement of absorption of electromagnetic radiation in the radiosfrequency region of roughly 4 to 9 HZ states required for absorption to occur it is necessary m ex ose the analyte m an intense magnetic eld of several thousan gauss certain ammic nuclei have properties ofsp39n and magnetic momen and as a consequence expoilre to a magnetic eld will lead to splitting of their energy levels nem 32m in 2 I NMR important for elucidating structure of chemical speCIes record differences in the magnetic properties of the various nuclei present in order to deduce the positions of these nuclei within the molecule also useful for the quantitative determination of absorbing species nem 32m in 3 1 NMR shift in absorption frequencies first observed by Packard in 1951 detecmd three different values for precessional frequencies of the protons in EtOH r realized that these corresponded to the three different chemical environments for promns in ethanol CH3 CH and 0H marked beginning of NMR as tool of the organic c em39st because shift in frequency depended on chemical environment this gave rise to the term dramaslvat in 1953 the rst highrresolu on NMR spectrometer designed for chemical structural studies was marketed by Varian Associates chem 32m ch 4 NMR NMR has had rofound effecE on the development of organic inorganic an biochemistry it is unlikely that there has ever been as short a delay between scientific discovery and is widespread accepmnce and application two general types of NMR spectrometers are currently in use continuous Wave cvv pulsed or Fourier transform FT NMR earlyinstruments were CW in about 1970 Fr instrumens became available commercially nearly all NMR instruments produced today are of the FT type chem 32m ch 5 Theory of I Nuclear Magnetic Resonance Magnetic Resonance is based on the postulate by Wo fgang Pauli in 1924 that certain atomic nuclei veJJroperu39es ofspin an magn ic mom ex osure a magnetic leld would result in splitting oftheir energy levels This phenomenon can be described in two ways echanics 7 provides the relationship between absorption frequencies and n clear energy smms classical mechanics 7 yields a clear physical picture of the absorption process and how it is measvred chem 32m ch 5 1 Quantum Description of NMR Assume nuclei rotate about their axis Thus they have spin Angular momentum p associated with particle spin is a halfintegral multiple of 1127 where I is Planck39s constant T maximum spin component fora particular nucleus is its spin quantum number A nucleus has 1 1 discrete states he angular momentum for these states are integral values from Ito I I absence ofan external eld these states have identical energy chem 32m ch 7 Quantum Description of NMR the four nuclei ofgreatest use to chemise are H c QF and P the spin quantum number ofthese nude 395 12 each 2 nucleus has two win states I 2 and I i heavier nuclei have spin numbers that range from zero no net gain component m 92 should note that for we and mo 1 0 therefore nonmagnetic ifC and 0 had been magnetic wectra of organic molecules would have been much more complex a spinning charged nucleus creams a magnetic eld that is analo ous to the eld produced when electricity ows through a cot o wlre chem 32m ch 3 I Quantum Description of NMR the resulting magnetic moment it is oriented along the axis ofspin and is proportional to the angular momentum p t us 777 where the proportionality constant y is the mag1netogyric ratio which has different value for ac type of nucleus chem 32m ch 9 1 Magnetogyric Ratios 0m zznn om Energy Levels in a 1 Magnetic Field in an external magneuc eld a parucle possessing a rnagneuc Moment tends to become oriented men that is magisuc Dipole nence is spin axis is parallel to e eld in the absence of a magnetic eld the energies of n l ta e identical s at e lower energy state m 12 predominates 0m zznn om Magnetic Moments and g Energy Levels 0m zznn om Frequency and I Magne c Field Strength the equation that gives the frequency of the radiation required for absorption is 730 2 V0 nine in be an ane ar tne nast inbaitant ieiatiansnibs in NMR rdi W i e i canstant dirncuit ta beirann neduencv oxen am am Distribution of Particles between I Magnet c Quantum States in the absence at a nadnetic neid tne eneidies ar tne nadnetic uuantun states at a nucieus aie identicai wnen biaced in a nadnetic neid tne nuciei tend ta aiient themseives sa tnat tne m e vb iedaninates usind tne Baitzmann eduaban ta caicuiate tne veiatwe nun bei ar biatans in tne nidnei and iawev states a snaii 2x255 ar biatans in DWEV state is raund irtnenunbeisar absaibtian wauid hv tne iadiatian wauid exath eduai tne nun bei biaducind induced i int states weie identicai itcan be Shawn iineavaei NMRSiqna nanuraciuieis Wing bbia stiendtns iv eneid stiendtn in d emaqnetswith ie oxen am am iawev enquY state nucie hetwa nanet be absevved because tne nunbei ar baiticies excited tnat tne veiatwe nunbei ar 2x255 iawceneidv nuciei is ated ta tne nadnetic neid stiendtn tnus tne intensilY ar an nc aseiineai as tn cieases t uc q atei and dieatei neid SI Classmal Description of NMR oteriuai ener inomenbuin u oxen am am I Precessing Proton gretessrng proton will uni alumna energy We pretessrng Equmty rs tne sarne as he Tre uenty urtne ramurrequenty bearn pruouteo by tne mume W en tnrs utturs the nutieus and tne rrbearn are said to be rn remnanEE hmte tern NNR m oxen zznn om Relaxation Processes Samrauon occurs when nurnber of nuclei rn excited state equal nurnber of nuclei rn ground state I Relaxation must occur for NMR to remain viab e Reiayatrun should be fast so that an absorption signal tan be detected aut tnere s an rnyerse reiatrunshrp betwem tne inerrn er the eytrteo state and tne Width urtne absorption The Two important relaxation processes egtlti t Shiniamte Dr Longtitudinal Relaxation and abnebn Dr Transyerse Reiayatrun oxen zznn om l Spin Lattice Relaxation Excite nuclei can relax by transferring energy to another nucleus in the lattice which has the same precessional 39equency 1 order process wrtn a reiaxauon trrne T T rs a rneasure of the average irteurne rn the excited state T rs strongly affected by the iatuee rnobrhty Glasses and yrstuus Taurus haye iage T T can also rnerease rn yery mobile iatuees oxen zznn om I Spl Spin Relaxation other relaxation li e processes can broa en n s These are d NMR called transverse or spinspin relaxation TZ values are very small for solids r diffcult to run solid spectra Neighboring nuclei Winn identical precession rates can exenange states e result li i broadening Many ofthes relaxauon processes can be overcome by rapidly spinning une sample on zznn cm g FI NMR Intense pulse of rf radiation saturates all nuclei Nuclei relax according to their spinlattice interactions A Free Induction Decay FID signal is detected by a radio re 39 Sum ta are c o med da nverted to 39equency d main by Fourier Transformation oxen zznn cm Si Fl39 NMR Schematic n a 5 9am on zznn cm g Magnets Sensitivity and resolution are critically dependent on quality of magnet Both sensitivity and resolution increase with eld trength Superconducting magnets can achieve elds of 21T or proton frequencies of 900 MHZ Helium Dewar surrounded by N2 Dewar Field must be homogeneous to a few ppb in sample area Dif cult to obtain in practice chem 32m ch 22 Compensation for Drift and Homogeneity Variations Fieldfrequency lock a reference nucleus is continually radiated and the signal monitored Fluctuations are automatically compensated for by adjusting the field Shimming small coils are provided a current to augment the field in various directions Must be adjusted for each sample Sample spinning corrects for sample inhomogeneities chem 32m ch 23 SI Types of NMR Spectra WideLine Spectra Chemical structure is obscured by wide bandwidth ofsource lines Quantitative indenti cation of isotopes Usually use low magnetic Iles HighResolution Spectra Capable of differentiating frequencies of 001 ppm or less Provide information about chemical environments f nuclei chem 32m ch 24 g The Chemical Shift Caused by small magnetic fields generated by electrons usually in opposition to the applied field Bo Bappl UBappi Bappl1 U c is the screening constant For isolated protons c is 0 Different chemical environments will require different Bappl to bring protons into resonance chem 32m ch19 SH SpinSpin Coupling Interaction of the magnetic moment of nucleus with the magnetic moments of adjacent nuclei results in a splitting of the peak Spinspin splitting is independent of the applied field Spinspin effects are superimposed on the effects of the chemical shift chem 32m ch19 g Plotting Chemical Shifts TMS is used as an internal reference which has many equivalent protons and exhibits a large screening constan The chemical shi s of other protons are compared to those of TMS The chemical shift parameter 6 is de ned as 6 ref csample X 10 6 has the same value regardless of Bawhe a most proton peaks lie in the 6 range of 1 to 13 Pm chem 32m ch19 g Tetramethylsilane TMS Advantages of TMS CH34Si sharp signal at low concentration clear of most organic protons chemically inert low boiling point remove from sample asin bp 27 0c soluble in most organic solvents can be added as an internal standard at low concentration a 1 chem 32m mg Rules for the Interpretation of FirstOrder Spectra Equivalent nuclei do not interact Coupling constants decrease with distance and coupling is seldom observed gt 4 bonds Multiplicity of the splitting is n1 splitting protons multiplicities are mutiplicatlv Approximate relative areas of peaks is determined by the expansion X 1 n Coupling is independent ofapplied field Clim ll thlg If more than one set of protons splits the e I CARBON13 NMR carbon13 has a low signal strength low isotopic abundance 11 and the small magnetogyric ratio one quarter that of hydrogen these factors make carbon13 NMR about 6000 times less sensitive than proton NMR higher field strength magnets and FF instruments have made this technique widespread chem 32m mg Chem 3200 S Instrumental Analysis Chapter 8 An Introduction in Optical Atomic Spectroscopy Atomic Spectroscopy Three major types npn39eal Spectrometry e elemene tony red in amms or elememay lorls a emsspn p s m2 ur2 e aseous mmlzatlon UVVlsa surptlorl a r oor mo prammle speeles ln mm is Ammie Mass 5 ectmm em 7 sample ammlzed g 2ous Amms epnyen m ppsmye lorls usually 1 and separated on pass pr massrmrcharge ratlo ay Spectrometry e Ammlzatlon pm requlrad slnee xTay n pl gtlt spec a pr most elenene lndependent pr how thermally mm med owe mm o a g Types of Atomic Spectroscopy 5mm x mamax new the ght vae gem Yxhnlque my dimenrme a ma oz a owe mm o a g Energy Level Diagrams as the number of eiemans increases the number of ieveis seems we tr an 5545 02277 We g x Lame on g AtomIc Em55on Spectra om temperature atoms in the ground state excrtanon brougbt about by beat of a ame piasma eiecmc are or spark iier me ii i excited ground state emi Fgur a4 1 r between excited eiecuonic state and u tate e g 589 o and 589 5 mm iines e ground ofNa owe zznn o x state is short eiecuorr returns to turrg photon see r e p 95 ecaii rem751755 Masare mose invoiving oansmons s Si AtomIc Absorption Spectra i a hot gaseous medium atoms can absorb radiation due to the low ame temperature atomic absorption spectrum consists predominately of resonance lines owe zznn o x 1 Atomic Fluorescence Spectra atoms or ions in a flame can be made to fluoresce by irradiation with an intense source containing wavelengths that are absorbed by the element the fluorescence spectrum is measured at an angle of 90 degrees to the light path why Chen 32m Ch 3 SF Line Widths narrow lines are highly desirable for both absorption and emission work because they reduce the possibility of interference due to overlapping spectra line broadening has four sources The uncertainty effect The Doppler effect Pressure effects due to collisions between atoms of e same kind and with foreign obje ts Electric and magnetic eld effects Chen 32m Ch 3 I Uncertainty Effect spectral lins always have nite widths because the lifetimes of one or both transition stats are nite which leads to uncertainties in the transition times and to line broadening as a consequence of the uncertainty principle Av Atgt 1 Av minimum detectable difference m frequencies I Atmlnlmum time for measurement line widths due to uncertainty broadening are 5 metlmes termed atura line Wl39d rsand are generally about 10 4 A Chen 32m Ch 3 1 Doppler Broadening the wavelength of radiation emitted or absorbed by a rapidly moving atom decreases if the motion is toward a transducer and increases if the atom is receding from the transducer phenomenon known as the Dopplersl in flames the Doppler effect leads to lines that are about two orders of magnitude greater in breath than natural line widths than 32m ch 3 m Pressure Broadening pressure or collisional broadening ariss from collisions ofthe emitting or sorbing species with other atoms or ions in the heated medium these collisions cause small changes in ground state energy level an hence a range ofabsorbed or emitted wavelengths effect worse at high pressures fr low pressire hollow cathode lamp 1710 torr 10471072 for high pressure Xe or Hg lamps 10000 mrr 10071000 A turns lines into continua than 32m ch 3 11 The Effect of Temperature I on Atomic Spectra mmperature changes number ofatoms in ground and excited states magnitude ofth39s effect can be derived from the Boltzmann Ejuab39an 56ml 2 ND vn kT where Nis the rumber otamms Ml the rumber otamms in an eXOted state in Ell the energy difference in iou es between the exclmd state and the gomd sham Plarld Pquot are statistical factors that are determined by the number ofstates havng ecual energy at eadn cuantum than 32m ch 3 12 The Effect of Temperature 1 on Atomic Spectra note that a temperature uctuation of only 10 K results in a 4 increase in the number of excited sodium atoms impormnt in emission measurements relying on thermal excitation r tion and uorescence methods are theoretically lss dependent upon temperature beca a bot measurements are base p n initially unexcited atoms rather than thermally excited ones note that the majority of atnms in ame are in the ground state gt 9998 for Na at 2500 K Cheri 32m tn 3 13 The Effect of Temperature on Atomic Spectra an increase in temperature however increass the ef ciency of the atomization process and hence he total num er ofa oms 39n causs line broadenin and a conse uent decrease in peak hei t occurs because the atomic particles travel at greater rates enhancing the Doppler effect in uences the degree of ionization of the analyte and thusthe concentration of nonionized analyte upon which the analysis is usually based because of the above effects reasonable control of ame temperature is desire Cheri 32m tn 3 14 SI Atom ization Methods in order to obtain both atomic optical and atomic mass spectra sample must be converted to gaseous atoms or ionized atoms which can then be determined by emission absorption fluorescence or mass spectral measurements Cheri 32m tn 3 15 Chem 3200 Instrumental Analysis Chapter 9 Atomic Absorption and Atomic Fluorescence Spectrometry AAS and AFS atomic absorption spectrometry AAS e the most wi ely used method for the determination of single elements in analytical samples atomic uorescence spectrometry AFS has een studied extensively not widely used 0m zznn o a z engths for Absorption and on Atomic Spectroscopy Wavel I Em Sample Atomization Techniques Flame atomization Elech oihermal atomization Special Glow Dischar Hydride Generauon Coldrvapor om zznn o a Flame Atomization Processes Occurring During Atomization an is the must natal step m flame EDEEUUSEUDY Often limits the Dvensiun ur these in ethuds a9 a i am om zznn o a Types of Flames Y le a x 9mm miratetylene and nitmus uxideratetylene llamas must mmmun om zznn o a I Flame Structure 1m Duvtant VEEmnS er a ame htmae PHmaW EDMDUSUDH zehe Interluna 12mm setuhaew EDMDUSUDH zuhe h a he 1 1 hteuehet teeth ts the mus wmehuseah t r spettmsmpv the ZEIHE eneh nth h alums Remuns h a meme owequot m o a 7 D Flame Atomizers A Lemmy new Burner owe zznn o a W 959a10 1 I Laminar Flow Burner m terms ofreproducrb e behavtor ame atomtzatton appears to be supehot to 3 other methods that Have beeh thus far deve oped for hqutd samp e mh oduc o for AAS ah AFS m terms ofsamphng ef ctency and thus sensmvtty other methods are better two reasons for ower sahphhg emctehcy of the ame arge pemeh e 95 nft e samp e aws dewh the areh testeehte We at hummer etems h the eptttet path h the ame tshher W s owe zznn o a a I Electrothermal Atomization Electrothermal emmrzers which ap eeed en the market about 19m provide enhanced sensitivity ecause the entire sample is atomized in a short periud and the average residence time er the atoms in the npttal path is a semnd or more beginning an be used for sagle inh nduttinn in inductively coupled plasma emissiun l spe mstcpy three major steps in the analytical sequence when using an ETA drqu stage 7 eva matiun Elf sulvents In El IDES ashlll stage 7 remuval Elf vulatile h diuxidES sulfatei emanates mum material in re iEns r mlzzhnn slaqu stumizatiun ur remaini u analybz Is 217 owe zznn o a l Electrothermal Atomization u u uL of sample 39 a at low temperature then ashed at higher temperamre in eiemieeiiv heated graphite mmeee fnallv urrmt u m 2nuurauuu c em rapid ammizah39un Tube unen made er gramme then have Graphite inmate alum ll absuiutiun SDEEUDSEUDY39 ems Swvze Mm 2nd mum mnm vm ylmnmkAws new Hdlwblixhinq owe zznn o a n I Disadvantages of Nonflame Methods the relative recision is generally in the range of 5to 10 compare with the 1 or better that can be expected for fl or plasma atomization furnace methods are slow several minutes per analysis an two orders 0 magnitude A ordinarily plied only when ame or plasma r 1rrsiization provides inadequate detection imi me analytical ran e is low bein usually less a a owe zznn o a Atomic Absorption Instrumentation Consists of Radiation source HCL EDL Sample holder Flame ETA etc Wavelength selector monochromator Detector PMT Signal processor and readout computer may am on a gl Hollow Cathode Lamp HCL Dnsists of a tungsten anaue and a Cylindrical 39 Dr serves ta suppart a iaya r i prune inetai ianizatian of inert gas at n a new nign putmtial gasmus atiuns cause inetai attains Mast Dmmun sDurEE for AA at tamudehm s ner Emi irig a are ns i One lamp ane elemmt 1an than may a u El Source Modulation in the t piEal af rm isurptiun instrument it is necessary ta limin e inthErmEEs caused by einissian ariajiatian py tne aine in BM ta eiiininate the erreee arnaine einissian it is necessary ta mamatelhe erreee prune autput of the mume sa that is intmsity uctuates at a constant frequency femur iaeiyes twa types arsignai an aitanatinq ane train the mume and a continuous ane train the aine ese signals are converted ta the corresponding types Dfee rital respanse a SimplE ni npass lter can tnen pe enpiayeu ta ieinaye tne unmudula u u sgnal and p s the ac signal ta ainpiineatian may am 0 a Single Beam vs Double Beam 1 Atom c Absorption Spectrometers double bearn deslgn Slnqle Beam Dauble eam onsldaably enhanced g 9 Elam oxen zznn Or a Interferences in Atomic gl Absorp Ion Spectroscopy Spectral Interferences arise when the absorption or emission of an interfering species either overlaps or lies close to that of the analyte Chemical Interferencs result 0 m various chemical processes occurring during atomization that alter the absorption characteristics of the analyte oxen zznn Or a El Spectral Interferences because the emlsslol l llnes of nollow cathode sources are very narrow ll39lterferel39lce due to overlappll lg llnes ls rare for gulch an ll39lterferel39lce to occur the separauon bebween etwo llnes would have to be less than about 0 1 fxample vanadlum llrle SUEZ 11 C and alumlnurx at SUEZ 15 Choose a dl erente alumlnum llrle at 3D92 7 spectral ll39lterferel39lces also result form the presence of combusuon produce that exnlblr broadband abso puon or paruculate producs thatscattel39 radlauon oxen zznn o a I Spectral Interferences more senous prob ern when 5 m i CaOH this probiem eiiminatad by using hotter nitrous oxideracetyiene ame Wen preds up the CaOH owe zznn o a 19 Background Correction i The Two LIne Correction Method procedure ernpioys a iirve rrorn dne source as a rererence this iirve shouid he as dose as possrpie to dne arraiyte iirve but musrnorbe absorbedbyrbe ansyrs itis assurned dnar any decrease rn ower or dne reference iirve from that observed uring caiibrauorr anses rrorn apsorpnon or scattering p dne rnamx producB ofthe sampie this decrease rn power is dnerr used to correct the absorbence of the arraiyte irre unformrvateiy a Suitabie reference iirve is often not avaiiabie owe zznn o a zn Background Correction g The ContinuumSource Method m owe zznn o a 2x Background Correction The ContinuumSource Method a deuterium lamp provides a source of continuous radiation throughout the UV region I n m u m o m x n In no n m E F matrix componen the deuterium lamp is ofno use in correction above 350 nm due to low radiant output than 32m Ch 9 22 g Chemical Interferences chemical interferences are more common than spectral ones effects minimized by suitable choice of operating conditions than 32m Ch 9 23 SI Chemical Interferences Formation of Compounds of Low Volatility most common type of interference eliminated using hotter temperatures tn brmk up the compounds can use releasing age add lanthanum in calcium determination when phosphate present can use protective ageIE which prevent interference by forming stable but volatile species with the analyte EDTA 8hydroxyquinoline APDC Chen 32m Ch 9 24 SI Chemical Interferences Ian39un Equ ria need ca be aware ma numamus dissociation and association reactions occur in the ame and fumie and an be waaad as Equiiibrium reactions Ionization Equilibria gt faise rEuits occurs Wiih group 1 am 2 aiamane reactinn M gt M39 239 12m emes am imam Rm an Wm XuDVexxzni sun Ham 0 sum ugML N2 K u m a 0m zznn o a Chemical Interfernece due to g Ioniza Ion Equilibria 0m zznn o a Comparison of Detection 39t5 and Working Ranges mm mu wuimnimunnmw munw Mamaa ma m mama mm trauma mm Lum uziu W Sam 2 mamax Manama am vae enenl Yezhmque Mymm 1r wm m mm a 0m zznn o a Atomic Absorption Analytical Techniques sample must be a solution most often aqueous many samples are solids deeomposuon and soluuon steps are ume consumrng common mednods of dissolving s ples ral o oxidanon mm llqud reagents sudn as sulfuric nrme or perenone aods Wetashlng oomousuon rn an oxygen bomb or other dosed oorlralner to ayod loss of analyue reagents sudn as bone oxde sodium so um peroxide or potassium wrosuraue some materials can be analyzed dlrecdy m ETA suen blood petroleum produce and orgame solyene calibrauon ls drr neult need to use standard addluons Chen 32m in 9 Quantitative Analysis Calibration Curves in theory atomic absorption should follow Beer39s law in fact deggrtures from linearity are often must run standards to obtain calibration curve Standard Add is wide n Method atomic absorption spectroscopy in order to partially or wholly counteract the chemical and spectral interferencs introduced by the sample n39ix Chen 32m in 9 Applications of AAS AAS is a sensitive means for the quantitative determination of more than 60 metals or metalloids the resonance lines for the nonmetallic compounds are generally located below 200 nm thus preventing their determination by convenient nonvacuum spectrophotometers Chen 32m in 9 Chem 3200 S Instrumental Analysis Chapter 17 Applications of Infrared Spectrometry Application of IR Spectrometry 0m zznn on 2 l Gases ll gas cell transparent windows NaClKBr long pathlength 10 cm few molecules 0m zznn on 2 I Liquids ll liquid cell solute in transparent solvent not water attacks windows short pathlength 0151mm solvenis absorb 0m zznn on o g Solvent Ranges in IR m n 1 gm 0m zznn on s i Solids make semitransparent pellet with KBr grind and mix with Nujol hydrocarbon oil to form mull One drop between NaCl plates 0m zznn on s Group Frequency and Fingerprint gt Reg on of the Mi I m m gem 0m zznn om l Quant a ve Applications quantitative IR absor tion methods differ omewhat from UV is molecular spectroscopic methods be ause of the greater complexlty o overlap Dfabsurptlun p236 rrowrless of an on w lrltErlSl m b 0 ens and law sensrmruee requlre armlde on same Dder Wldths Dfabmrptlon peaks na39row cells may lead an analytltal unrertalntles 0m zznn on x 5 Near IR usually CH NH and 0H bonds quantitative determination ofw t r proteins MW ydrocarbons fats in and agricultural products IR re ecta 0m zznn om nar nce used for routine quantitative determination of constituents in nely ground solids Chem 3200 Instrumental Analysis Chapter 20 Molecular Mass Spectrometry Mass Spectrometry mass spectrometly is perhaps the most widely applicable ofall of the analytical tools available m the scien ist in he sense that the technique is capable of t 391 providing information about the elemenml composition ofsamples of matter the structures of inorganic organic and biological molecules the qualimtive and quantimtive composition of complex mixtures the structure and composition of solid surfaces isompic ratios of amms in samples chem 32m Ch2EI Early Use of MS rst general application of Ms for routine chemical analysis occurred in the early 1940s by the petroleum industry for the quantimtive analysis of hyd ocarbon mixtures produced in catalytic cracking before this time analyses of mixtures of this type were carried out by fractional distillation followed by refractive index measuremenE of the separated componenE 200 hou more of operator time were required to complete an a few hours or less with Ms improved ef ciency let to rapid availability of commercial instrumenE rs or nalysis since about 1990 explosive growlh in the area of biological Ms a a consequence of new ionization techniques chem 32m Ch2EI Basic Processes in Mass Spectrometry Mass Spectrometry is a technique which can measure the masses and abundance of gaseous ions Three basic steps in this process are Generation of gas phase molecules Fragmentation can also occur here Ionization Separation based on mass chern 32m ch2u 4 Components of a Mass Spectrometer Vacuum System a necessary m reduce interactions ofgaseous ions and electrons with componenE of atmosphere Ion Source 7 vaporizes andor ionizes the sample Fragmentation can also occur in the source Mass Analyzer 7 where the ions formed in the source are separated n time or wace or both separation based on mass macharge ratio DetectorTransducer a demcE the presence or the ions chern 32m ch2u 5 Components of a H Mass Spectrometer chern 32m ch2u a Mass Spectrometer Sources om zznn cm g Electron Impact Ionization Gaseous sample bombarded with beam of heated W or Rh wire and accelerated to energy of about 70 eV Typically one in every million molecules undergoes ionization Positive ions forced by small potential difference through accelerator plates to mass analyzer om zznn cm x gt EI Ion39za 39on Source om zznn cm I Reactions In an E1 Source m WNW m 1 EI MS Spectra MethWene Maude wentanm WNW u Advantages mentauo Samp e must be vaponzed om apphcab e to samp es Wm mo ecu ar Wewghs lt 1000 arm 2 0m zznn cm 5 E1 MS g MasstoCharge Ratio Most sources generally produce singly charged ion with positive ions mos commonly analyze A small amount of multiply charged ions are also produced Mass analyzer collects ions with the same masstocharge ratio Identification ofa compound comes from the masstocharge of the analyzed ions and from the relative abundances of each ion chem 32m ch2u 13 SH Analysis of Organic MS Identify the Molecular Ion calculated by adding atoms of highest natural abundance Study the Isotope Distribution Pattern due to the fact that atoms egtltist naturally as different isotopes Explain the Fragmentation Pattern can be predicted from bond strength chem 32m ch2u 14 Features of a Mass Spectrum MolecularIon Peak sum of atomic weights of atoms In the parent molecule Daughter Ions Peaks are the result of fragmentation ofthe molecular ion Base Peak The largest peak in the mass spectrum not necessarily molecular ion Molecular ion peak can be optimized by using Elentler Ionization method eg CI instead 0 Qtuasimolecular Ion formed in C1 by a tachment of H chem 32m ch2u 15 General Features of l Mass Spectra Cleavage rs favored at brancneo carbon atoms ternarygtsecondarygtprl mar l e nng Saturated rmgs tend to lose eroe cnarns at the albna carbon Heteronatoms lnduce cleavage at the beta bond lfa carbonyl rs present the molecule tends to break mere wrun w oer zznn 0an ls Characteristic Spectral Features oer zznn 0an n 5 Natural Abundances of Isotopes gang oer zznn 0an xx gt Other Ionization Sources chem cal Inn at n agaseaus ammsnfsampie ranized by taiirsran Winn 05itw2 arnagatrye ranspraduted by eiettran bombardment of an eytess reagent gas rieid ionization cr Desa tian a ims formed under in uence of iarge eiettrrt eid ma y m MatrixaAssisted tasernesarptianianizatian Winona Sampie mryad Winn aitanuiwater sniutinn eyaparatad Exan ta puised iasa beam Ney tetnmaue used tar paiar brapaiymers fmm a few thousand ta seyaai nundred tnausand amu on zznn 0an 9 5 Other Ionization Sources Electrospray Ionization 7 Uses atmospnenc eondmons Sampie sprayed dnrougn enarged needie surrounded by cyiiri ricai eiecaode important for biomoiecuies iike proteins poiypeptides and oiigonucieotidesof100000 amu or higher Fast Atom Bombardment a sampie piaced ii i giyceroi matrix iOi iiZed b bombardment wrdn energeuc severai keV Xenon or argon atone Used for poiar highamoiecuiar Weight compounds 10000 for MW determrnauon 3000 or simcmrai informauon on zznn 0an zn Schematic of i Electrospray Ionization Source Li 1 i tn r m r i qyznsJom on zznn 0an Z I MALDI Mechanlsm Formatlon ofa solld mlutlon Mamxexmlatlon was lase Analytelomzatlon formater ur MX39 0m zznn cm 22 1 MS of Glutamic Acid 92mm Imam Held lumzatmn Held Desumtmn m zn mm 0m zznn cm 23 gl Mass Analyzers Magnetic Sector Instrumenls DoubleFocusing Spectrometers Quadrupole Mass Spectrometers TimeofFlight Mass Spectrometers Ion Trap Analyzers Ion Cyclotron Resonance ICR 0m zznn cm 2o Single Focusing gt Magnet c Sector MS 0m zznn cm g Magnetic Sector Analyzer ths ofdlfferent mass eah be seahheg across the exit slit by varying the eld strength of the magh t o the cce a ng potential between SHE A and E h sthe asst echarge ra o to the euc eld strength 5 the radius of cur atLire e mag ector electric charge a a 1 o x 1039 c and voltage v betwee A and m Bzrze z 2V omzznnozn zs 51 Magnetic Sector Analyzer mass spectra can be acquired by varying one of three variables 5 V or r while holding the 0 er two constant most modern mass spectrometers contain an electromagnet in which ions are sorted by holding Vand rconstant while varying the current in the magnet and thus 5 0m zznn cm I Time of flight MS 0m zznn cm H Quadrupole Mass Spectrometers W92 msmssed m chapter 11 Bebw 5 a schemau Ufa mm quadrupr spadmmetar on m n l Ion Tra p MS G Enus runs Dn ned by ebdrr andDr magnetr e d RF vuhage apphed m 39 Hng erectde a d and 39 ps 2 gm Inns Bf surname r Mata M iv 5 RF mm 5 m 5551 hghta runs are mm on m m Resolution in 5 Mass Spectrometry Resolution is defined as the MAM when two identical experimental peaks overlap at 5 of their height giving a 90 valley between them MAM is the resolving power of the instrument larger is better chem 32m ch2u Resolution of Mass Analyzers 1 4000 1500 Double Focusing 2 5000 20K 100K TImeof ight 1 10000 3500 Quadmpole 1 1000 1000 10 650 chem 32m ch2u Hyphenated MS Methods GCMS and LCMS MS is the detector for these separations ICPMS MS is the detector Capillary ElectrophoresisMS MS is the detector Tandem MS MSMS Even have MSMSMS chem 32m ch2u gt Applications of MS 0m zznn cm
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