INSTRUMENTAL ANALYSIS FINAL EXAM QUESTIONS AND CORRECT ANSWERS

INSTRUMENTAL ANALYSIS FINAL
EXAM QUESTIONS AND CORRECT
ANSWERS
massA2spectroscopyA2-A2Ans--
methodA2ofA2separatingA2andA2analyzingA2ionsA2byA2theirA2massA2toA2chargeA2ratio;A2does
A2notA2involveA2aA2specificA2regionA2ofA2theA2electromagneticA2spectrumA2becauseA2itA2isA2
notA2directlyA2interestedA2inA2theA2energiesA2ofA2emittedA2photons,A2electronicA2orA2vibrati
onalA2transitions,A2etc

massA2toA2chargeA2-A2Ans--ratioA2ofA2massA2ofA2anA2ionA2(m)A2toA2itsA2chargeA2(z)

molecularA2ionA2-A2Ans--ionA2consistingA2ofA2essentiallyA2theA2wholeA2molecule

massA2spectrometerA2-A2Ans--

softA2ionizationA2sourceA2-A2Ans--
minimalA2energyA2withA2minimalA2toA2noA2chemicalA2bondsA2breaking;A2minimalA2peaksA2l
eadingA2toA2aA2simpleA2massA2spectrum;A2largeA2molecularA2ionA2peak

hardA2ionizationA2sourceA2-A2Ans--
enoughA2energyA2toA2breakA2chemicalA2bondsA2(manyA2ofA2them);A2lotsA2ofA2energy;A2lots
A2ofA2peaksA2leadingA2toA2complicatedA2massA2spectrum;A2minimalA2toA2noA2molecularA2io
nA2peak

gasA2-A2Ans--
phaseA2ofA2ionizationA2sourceA2includingA2electronA2andA2chemicalA2ionization

desorptionA2-A2Ans--includesA2electrospray,A2matrix-
assistedA2laser,A2plasma,A2fastA2atomA2bombardment,A2andA2highA2temperatureA2plasma

ionizationA2sourceA2-A2Ans--

electronA2impactA2-A2Ans--
electronA2ionizationA2sourceA2isA2designedA2toA2produceA2gaseousA2ionsA2forA2analysis;A2
EI,A2whichA2wasA2onA2ofA2theA2earliestA2sourcesA2inA2wideA2useA2forA2MS,A2usuallyA2operat
esA2onA2vaporsA2(suchA2asA2thoseA2elutingA2fromA2GC);A2electronsA2areA2emittedA2fromA2fil
amentA2madeA2ofA2tungsten,A2rhenium,A2etc;A2acceleratedA2byA2aA2potentialA2ofA270V;A2el
ectronsA2andA2moleculesA2crossA2(usuallyA2atA2aA2rightA2angle)A2andA2collide;A2ionsA2areA2
primarilyA2singlyA2charged,A2positiveA2ionsA2thatA2areA2extractedA2byA2smallA2potentialA2thr
oughA2slit;A2whenA2electronsA2hit,A2theA2moleculesA2undergoA2rovibrationalA2excitation;A2a
boutA2oneA2inA2aA2millionA2moleculesA2undergoA2theA2reaction:

, MA2+A2e-A2->A2M+A2+A22e-

Advantages:A2resultsA2inA2complexA2massA2spectraA2withA2fragmentA2ions;A2usefulA2forA2st
ructuralA2identification
Disadvantages:A2canA2produceA2tooA2muchA2fragmentation,A2leadingA2toA2noA2molecularA2
ion

chemicalA2ionizationA2-A2Ans--formA2ofA2gasA2basedA2chemistryA2thatA2isA2softer/
lessA2energeticA2thanA2electronA2impact;A2ionizationA2occursA2viaA2protonA2transferA2reacti
ons;A2aA2gasA2isA2introducedA2intoA2theA2sourceA2atA2aboutA21A2torr;A2reaction:

CH4A2->A2CH4+
CH4+A2+A2CH4A2->A2CH5+A2+A2CH3
AHA2+A2CH5+A2->A2AH2+A2+A2CH4

methaneA2-A2Ans--harshestA2chemicalA2ionizationA2gasA2(mostA2fragments)

ammoniaA2-A2Ans--softestA2chemicalA2ionizationA2gasA2(leastA2fragments)

electrosprayA2ionizationA2-A2Ans--
accomplishedA2byA2flowingA2solutionA2throughA2anA2electricallyA2conductiveA2capillaryA2he
ldA2atA2highA2voltage;A2solutionA2flowsA2outA2ofA2capillaryA2andA2feelsA2theA2voltageA2-
A2chargesA2buildA2upA2onA2nebulizedA2droplets,A2whichA2thenA2beginA2toA2evaporate;A2coul
ombicA2explosionsA2occurA2whenA2repulsionA2ofA2chargesA2overcomesA2surfaceA2tensionA
2ofA2solutionA2(holdingA2theA2dropA2together)


taylorA2coneA2-A2Ans--
shapeA2ofA2coneA2thatA2shootsA2fromA2theA2needleA2whenA2surfaceA2tensionA2isA2overcom
eA2byA2electrostaticA2forces;A2formsA2aA2jet

electrosprayA2ionizationA2-A2Ans--

desorptionA2electrosprayA2-A2Ans--
ambientA2ionizationA2technique;A2forA2desorbingA2ionsA2usingA2supersonicA2jetsA2ofA2char
gedA2solvents

desorptionA2electrosprayA2-A2Ans--

MALDIA2(matrix-assistedA2laserA2desorption/ionization)A2-A2Ans--
usedA2forA2samplesA2thatA2cannotA2handleA2highA2energy;A2methodA2forA2desorbingA2aA2s
ampleA2withA2aA2laser,A2whileA2preventingA2thermalA2degradation;A2sampleA2isA2mixedA2wi
thA2radiationA2absorbingA2matricA2usedA2toA2helpA2itA2ionize;A2heavilyA2usedA2forA2largeA2bi
omoleculesA2andA2polymers

MatrixA2-(heatA2andA2light)->A2ExcitedA2MatrixA2->A2Matrix+A2+A2e-
1)A2Matrix+A2+A2AnalyteA2->A2MatrixA2+A2Analyte+