定量分析27分子吸收光谱-Molecular-Absorption-Spectrometry课件

QuantitativeAnalysis

定量分析QuantitativeAnalysis

定量分析Chapter27 MolecularFluorescenceSpectroscopyChapter27

Fluorescenceisaphotoluminescenceprocessinwhichatomsormoleculesareexcitedbyabsorptionofelectromagneticradiation.Theexcitedspeciesthenrelaxtothegroundstate,givinguptheirexcessenergyasphotons.Oneofthemostattractivefeaturesofmolecularfluorescenceisitsinherentsensitivity,whichisoftenonetothreeordersofmagnitudebetterthanabsorptionspectroscopy.

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Anotheradvantageisthelargelinearconcentrationrangeoffluorescencemethods,whichissignificantlygreaterthanthoseencounteredinabsorptionspectroscopy.Fluorescencemethodsare,however,muchlesswidelyapplicablethanabsorptionmethodsbecauseoftherelativelylimitednumberofchemicalsystemsthatshowappreciablefluorescence.…continued…

PrinciplesofMolecularFluorescence

Molecularfluorescenceismeasuredbyexcitingthesampleattheabsorptionwavelength,alsocalledexcitationwavelength,andmeasuringtheemissionatalongerwavelengthcalledtheemissionorfluorescencewavelength.Usually,fluorescenceemissionismeasuredatrightanglestotheincidentbeamsoastoavoidmeasuringtheincidentradiation.Theshort-livedemissionthatoccursiscalledfluorescence,whereasluminescencethatismuchlongerlastingiscalledphosphorescence. PrinciplesofMolecularFluor定量分析27分子吸收光谱-Molecular-Absorption-Spectrometry课件

ExcitationSpectraandFluorescenceSpectra Becausetheenergydifferencesbetweenvibrationalstatesisaboutthesameforbothgroundandexcitedstates,theabsorption,orexcitationspectrum,andthefluorescencespectrumforacompoundoftenappearasapproximatemirrorimagesofoneanotherwithoverlapoccurringneartheorigintransition(0vibrationallevelofE1to0vibrationallevelofE0).Therearemanyexceptionstothismirror-imagerule,particularlywhentheexcitedandgroundstateshavedifferentmoleculargeometriesorwhendifferentfluorescencebandsoriginatefromdifferentpartsofthemolecule.

ExcitationSpectraandFluore定量分析27分子吸收光谱-Molecular-Absorption-Spectrometry课件定量分析27分子吸收光谱-Molecular-Absorption-Spectrometry课件定量分析27分子吸收光谱-Molecular-Absorption-Spectrometry课件

ConcentrationandFluorescenceIntensity TheradiantpoweroffluorescenceFisproportionaltotheradiantpoweroftheexcitationbeamabsorbed: F=K(P0–P) where,P0istheradiantpowerofthebeamincidentonthesampleandPistheradiantpowerafterittraversesapathlengthbofthemedium.ConstantKdependsontheQuantumefficiency.Theefficiencyoffluorescedtothenumberabsorbed. ConcentrationandFluorescenc

Atlowconcentrationswherefluorescenceismostoftenemployed F=K’P0c where,cistheconcentrationofthefluorescentspeciesandK’isanewproportionalityconstant.Fisdirectlyproportionaltoanalyteconcentration.Thus,aplotofthefluorescentradiantpowerversustheconcentrationoftheemittingspeciesshouldbe,andordinarilyis,linearatlowconcentrations.Whencbecomesgreatenoughthattheabsorbanceislargerthanabout0.05,linearityislostandFbeginstoreachaplateauwithconcentration.Thiseffectisknownasaprimaryabsorptioninnerfiltereffect.Infact,athighconcentrations,fluorescenceradiantpowercanevenbegintodecreasewithincreasingconcentration. Atlowconcentrationswheref定量分析27分子吸收光谱-Molecular-Absorption-Spectrometry课件定量分析27分子吸收光谱-Molecular-Absorption-Spectrometry课件

MolecularPhosphorescenceSpectroscopy

Phosphorescenceisaphotoluminescencephenomenonthatisquitesimilartofluorescence.Understandingthedifferencebetweenthesetwophenomenarequiresandunderstandingofelectronspinsandthedifferencebetweenasingletstateandatripletstate.Ordinarymoleculesexistinthegroundstatewiththeirelectronspinspaired.Amolecularelectronicstateinwhichallelectronspinsarepairedissaidtobeasingletstate.

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Whenoneofapairofelectronsinamoleculeisexcitedtoahigher-energylevel,asingletoratripletstatecanbeproduced.Intheexcitedsingletstatethespinofthepromotedelectronisstilloppositethatoftheremainingelectron.Inthetripletstate,however,thespinsofthetwoelectronsbecomeunpairedandarethusparallel.Theexcitedtripletstateislessenergeticthanthecorrespondingexcitedsingletstate.…continued… 定量分析27分子吸收光谱-Molecular-Absorption-Spectrometry课件

ChemiluminescenceMethods Chemiluminescenceisproducedwhenachemicalreactionyieldsanelectronicallyexcitedmolecule,whichemitslightasitreturnstothegroundstate.Chemiluminescencereactionsareencounteredinanumberofbiologicalsystems,wheretheprocessisoftencalledbioluminescence. Oneattractivefeatureofchemiluminescenceforanalyticaluses,istheverysimpleinstrumentation.Sincenoexternalsourceofradiationisneededforexcitation,theinstrumentmayconsistofonlyareactionvesselandaphotomultipliertube.Generally,nowavelengthselectiondeviceisneededbecausetheonlysourceofradiantisthechemicalreaction.

ChemiluminescenceMethodsMOLECULARSCATTERINGMETHODS

Severaladditionalprocesses,however,canoccurwhenradiationinteractswithmatter.Oneofthemostimportantoftheseisscatteringofelectromagneticradiation.Scatteringcanbedividedintotwoclasses:elasticscattering,inwhichthescatteredradiationisofthesameenergyastheincidentradiation,andinelasticscattering,inwhichthescatteredradiationhashigherorlowerenergythantheincidentradiation.Bothofthesetypesofphenomenahaveusefulanalyticalapplications.MOLECULARSCATTERINGMETHODS S…continued…

Inelasticlight-scatteringmethodshavebecomeveryimportantinrecentyears,particularlythosemethodsbasedontheRamaneffect.Ramanspectroscopyinvolvesinelasticscatteringofradiationcausedbyvibrationalandrotationaltransition.TheRamanmethodiscomplementarytoIRspectroscopyandcanbeusedtoobtainqualitative,structuralandquantitativeinformationaboutmolecularspecies.…continued… Chapter28

ATOMICSPECTROSCOPY

Atomicspectroscopyisusedforthequalitativeandquantitativedeterminationof70to80elements.Detectionlimitsformanyoftheselieinthesub-parts-per-millionrange.Themethodscanbebasedonabsorption,emission,orfluorescence.Atomicabsorption(AA)spectroscopycurrentlyisthemostwidelyusedofthesetechniques.

Chapter28

ATOMICSPECTROSCOPY定量分析27分子吸收光谱-Molecular-Absorption-Spectrometry课件定量分析27分子吸收光谱-Molecular-Absorption-Spectrometry课件

AtomicAbsorptionSpectroscopy

InAAspectroscopy,asinallatomicspectroscopicmethods,thesamplemustbeconvertedintoanatomicvaporbyaprocessknownasatomization.Inthisprocess,thesampleisvolatilizedanddecomposedtoproduceatomsandperhapssomeionsinthegasphase.Severalmethodsareusedtoatomizesamples.ThetwomostimportantoftheseforAAspectroscopyareflameandfurnaceatomization. AtomicAbsorptionSpectroscop

FlameAtomicAbsorptionSpectroscopy

Theradiationofalinesourceoftheelementofinterest,typicallyahollowcathodelamp,isdirectedthroughtheflamecontainingtheatomicvapor.Solutionsamplesareusuallybroughtintotheflamebymeansofasprayerornebulizer,whichproducessmallsampledroplets.Thesolventfromthedropletsquicklyvaporizes,andtheresultingsaltparticlesvaporizeanddecomposeintoatoms,ionandelectrons. FlameAtomicAbsorptionSpect…continued…

Atomsinthesamplewillabsorbradiationemittedbythesameatominthehollowcathodelampandthusattenuatethepowerofthesource.Usuallyamonochromatorisusedtoseparateaspectrallineoftheelementofinterestfromanybackgroundradiationfromthesourceortheflame.Aphotomultipliertubeistypicallyusedtoconverttheradiantpowerfromthesourceintoarelatedelectricalcurrent.…continued…定量分析2