anintroductiontochromatographicseparationsPPT课件下载推荐.pptx

anintroductiontochromatographicseparationsPPT课件下载推荐.pptx

《anintroductiontochromatographicseparationsPPT课件下载推荐.pptx》由会员分享，可在线阅读，更多相关《anintroductiontochromatographicseparationsPPT课件下载推荐.pptx（14页珍藏版）》请在冰点文库上搜索。

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,