色谱的介绍及历史(英文)Chromatography

ChromatographyHistoryMikhailTswett,Russian,1872-1919BotanistIn1906TswettusedtochromatographytoseparateplantpigmentsHecalledthenewtechniquechromatographybecausetheresultoftheanalysiswas'writtenincolor'alongthelengthoftheadsorbentcolumnChromameans“color”andgrapheinmeansto“write”ImportanceChromatographyhasapplicationineverybranchofthephysicalandbiologicalsciences12Nobelprizeswereawardedbetween1937and1972aloneforworkinwhichchromatographyplayedavitalroleChromatographyisaphysicalmethodofseparationinwhichthecomponentstobeseparatedaredistributedbetweentwophasesoneofwhichisstationary(stationaryphase)whiletheother(themobilephase)movesthroughitinadefinitedirection.Thechromatographicprocessoccursduetodifferencesinthedistributionconstantoftheindividualsamplecomponents.ChromatographyIsatechniqueusedtoseparateandidentifythecomponentsofamixture.Worksbyallowingthemoleculespresentinthemixturetodistributethemselvesbetweenastationaryandamobilemedium.Moleculesthatspendmostoftheirtimeinthemobilephasearecarriedalongfaster.Classificationofchromatographyaccordingtomobilephase:1-Liquidchromatography:mobilephaseisaliquid.(LLC,LSC).2-Gaschromatography:mobilephaseisagas.(GSC,GLC).Classificationaccordingtothepackingofthestationaryphase:1-Thinlayerchromatography(TLC):thestationaryphaseisathinlayersupportedonglass,plasticoraluminiumplates.2-Paperchromatography(PC):thestationaryphaseisathinfilmofliquidsupportedonaninertsupport.3-Columnchromatography(CC):stationaryphaseispackedinaglasscolumn.Classificationaccordingtotheforceofseparation:1-Adsorptionchromatography.2-Partitionchromatography.3-Ionexchangechromatography.4-Gelfiltrationchromatography.5-Affinitychromatography.Thinlayerchromatography(TLC)isamethodforidentifyingsubstancesandtestingthepurityofcompounds.TLCisausefultechniquebecauseitisrelativelyquickandrequiressmallquantitiesofmaterial.SeparationsinTLCinvolvedistributingamixtureoftwoormoresubstancesbetweenastationaryphaseandamobilephase.Thestationaryphase:isathinlayerofadsorbent(usuallysilicageloralumina)coatedonaplate.Themobilephase:isadevelopingliquidwhichtravelsupthestationaryphase,carryingthesampleswithit.Componentsofthesampleswillseparateonthestationaryphaseaccordingtohowmuchtheyadsorbonthestationaryphaseversushowmuchtheydissolveinthemobilephase.ThinLayerChromatography(TLC)TLCPreparingtheChamberToajarwithatight-fittinglidaddenoughoftheappropriatedevelopingliquidsothatitis0.5to1cmdeepinthebottomofthejar.Closethejartightly,andletitstandforabout30minutessothattheatmosphereinthejarbecomessaturatedwithsolvent.PreparingthePlatesforDevelopmentWithapencil,etchtwosmallnotchesintotheadsorbentabout2cmfromthebottomoftheplate.Thenotchesshouldbeontheedgesoftheplate,andeachnotchshouldbethesamedistanceupfromthebottomoftheplate.Thenotchesmustbefartherfromthebottomoftheplatethanthedepthofthesolventinthejar.Usingadrawn-outcapillarytube,spotthesamplesontheplatesothattheylineupwiththenotchesyouetched.Question:Whatiswrongwiththeplateshownbelow?DevelopingthePlatesAfterpreparingthedevelopmentchamberandspottingthesamples,theplatesarereadyfordevelopment.Becarefultohandletheplatesonlybytheiredges,andtrytoleavethedevelopmentchamberuncoveredforaslittletimeaspossible.Whentheplatesareremovedfromthechamber,quicklytracethesolventfront(thehighestsolventlevelontheplate)withapencil.IdentifyingtheSpots(visualization)Ifthespotscanbeseen,outlinethemwithapencil.Ifnospotsareobvious,themostcommonvisualizationtechniqueistoholdtheplateunderaUVlamp.Manyorganiccompoundscanbeseenusingthistechnique,andcommerciallymadeplatesmanyoftencontainasubstancewhichaidsinthevisualizationofcompounds.VisualizingAgentsAlkaloids:Dragendorff’sreagentCardiacglycosides:AntimonytrichlorideSugar:AnilinephthalateAminoacids:NinhydrinInterpretingtheDataTheRf(retentionfactor)valueforeachspotshouldbecalculated.Itischaracteristicforanygivencompoundonthesamestationaryphaseusingthesamemobilephasefordevelopmentoftheplates.Hence,knownRfvaluescanbecomparedtothoseofunknownsubstancestoaidintheiridentifications.(Note:RfvaluesoftendependonthetemperatureandthesolventusedintheTLCexperiment.themosteffectivewaytoidentifyacompoundistospotknownsubstances–authentic-nexttounknownsubstancesonthesameplate.)Inaddition,thepurityofasamplemaybeestimatedfromthechromatogram.Animpuresamplewilloftendevelopastwoormorepuresamplewillshowonlyonespotspots,whileaSummaryATLCplateisasheetofglass,metal,orplasticwhichiscoatedwithathinlayerofasolidadsorbent(usuallysilicaoralumina).Asmallamountofthemixturetobeanalyzedisspottednearthebottomofthisplate.TheTLCplateisthenplacedinashallowpoolofasolventinadevelopingchambersothatonlytheverybottomoftheplateisintheliquid.Thisliquid,ortheeluent,isthemobilephase,anditslowlyrisesuptheTLCplatebycapillaryaction.Asthesolventmovespastthespotthatwasapplied,anequilibriumisestablishedforeachcomponentofthemixturebetweenthemoleculesofthatcomponentwhichareadsorbedonthesolidandthemoleculeswhichareinsolution.Inprinciple,thecomponentswilldifferinsolubilityandinthestrengthoftheiradsorptiontotheadsorbentandsomecompon