anintroductiontochromatographicseparationsPPT格式课件下载.pptx
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AnIntroductiontoChromatographicSeparations,Lecture37,1,2,QuantitativeAnalysis,Chromatographicseparationsprovideverygoodandreliableinformationaboutquantitativeanalysisofsampleconstituents.Eitherthepeakheightorpeakareacanbeusedforquantitativeanalysis.Peakheightsareeasierandfastertouseandusuallyresultingoodprecision,especiallywhenreproduciblesampleinjectionsaremade.However,lateelutingpeaksmayhavesmallpeakheightsbutlargewidthwhichmaycauselargeerrors.Peakareasarebetterforquantitativeanalysisastheareaunderthepeakisintegratedwhichisanaccuratemeasureofconcentration.,3,TheInternalStandardMethod,Uncertaintiesinsampleinjectioncanbeovercomebyuseofaninternalstandard.Inthismethod,ameasuredquantityofaninternalstandardisaddedtobothstandardandsample,andtheratioofanalytesignaltointernalstandardisrecorded.Anyinconsistencyininjectionofthesamplewillaffectboththeanalyteandinternalstandard.,4,Propertiesoftheinternalstandardshouldinclude:
@#@Theretentiontimesofinternalstandardandanalyteshouldbedifferentandthetwopeaksmustbewellseparated,R1.25Thedetectorresponsefactorfortheanalyteandtheinternalstandardshouldbethesame.Usinginternalstandardscansignificantlyimproveprecisiontobetterthan1%.,5,GasChromatography,6,Gaschromatographyisatechniqueusedforseparationofvolatilesubstances,orsubstancesthatcanbemadevolatile,fromoneanotherinagaseousmixtureathightemperatures.Asamplecontainingthematerialstobeseparatedisinjectedintothegaschromatograph.Amobilephase(carriergas)movesthroughacolumnthatcontainsawallcoatedorgranularsolidcoatedstationaryphase.Asthecarriergasflowsthroughthecolumn,thecomponentsofthesamplecomeincontactwiththestationaryphase.Thedifferentcomponentsofthesamplehavedifferentaffinitiesforthestationaryphase,whichresultsindifferentialmigrationofsolutes,thusleadingtoseparation,7,MartinandJamesintroducedthisseparationtechniquein1952,whichisthelatestofthemajorchromatograhpictechniques.However,by1965over18000publicationsingaschromatography(GC)wereavailableintheliterature.Thisisbecauseoptimizedinstrumentationwasfeasible.Gaschromatographyisgoodonlyforvolatilecompoundsorthose,whichcanbemadevolatilebysuitablederivatizationmethodsorpyrolysis.Thus,about20%ofchemicalsavailablecanbeanalyzeddirectlybyGC.,8,Gaschromatographycanbeusedforbothqualitativeandquantitativeanalysis.Comparisonofretentiontimescanbeusedtoidentifymaterialsinthesamplebycomparingretentiontimesofpeaksinasampletoretentiontimesforstandards.ThesamelimitationsforqualitativeanalysisdiscussedinChapter26alsoapplyforseparationsinGC.Quantitativeanalysisisaccomplishedbymeasurementofeitherpeakheightorpeakarea,9,Gas-SolidChromatography(GSC),Thestationaryphase,inthiscase,isasolidlikesilicaoralumina.Itistheaffinityofsolutestowardsadsorptionontothestationaryphasewhichdetermines,inpart,theretentiontime.Themobilephaseis,ofcourse,asuitablecarriergas.ThisgaschromatographictechniqueismostusefulfortheseparationandanalysisofgaseslikeCH4,CO2,CO,.etc.TheuseofGSCinpracticeisconsideredmarginalwhencomparedtogasliquidchromatography.,10,Gas-LiquidChromatography(GLC),Thestationaryphaseisaliquidwithverylowvolatilitywhilethemobilephaseisasuitablecarriergas.GLCisthemostwidelyusedtechniqueforseparationofvolatilespecies.ThepresenceofawidevarietyofstationaryphaseswithcontrastingselectivitiesandeasycolumnpreparationaddtotheassetsofGLCorsimplyGC.,11,Instrumentation,Itmaybewisetointroduceinstrumentalcomponentsbeforeproceedingfurtherintheoreticalbackground.Thiswillhelpclarifymanypoints,whichmay,otherwise,seemvague.Itshouldalsobenotedthatadetectorwillrequirespecialgascylindersdependingonthedetectortypeutilized.Thecolumntemperaturecontrollerissimplyanoven,thetemperatureofwhichcanbevariedorprogrammed,SyringeInjector,12,Detector,CarrierGasCylinder,Column,ToWasteorFlowMeter,FlowController,Two-StageRegulator,13,14,Threetemperaturezonescanbeidentified:
@#@Injectortemperature,TI,whereTIshouldallowflashvaporizationofallsamplecomponents.Columntemperature,Tc,whichisadjustedastheaverageboilingpointsofsamplecomponents.DetectorTemperature,TD,whichshouldexcludeanypossiblecondensationinsidethedetector.Generally,anintuitiveequationcanbeusedtoadjustallthreezonesdependingontheaverageboilingpointofthesamplecomponents.Thisequationisformulatedas:
@#@,TI=TD=Tc+50,oC,