仪器分析英文原版教案(12)

《仪器分析英文原版教案(12)》由会员上传分享，免费在线阅读，更多相关内容在行业资料-天天文库。

1、IntroductiontoChromatographicSeparations(Chapter26)Manydeterminationsinvolveseparationfollowedbyanalysis¥chromatography¥electrophoresisChromatography:sampletransportedbymobilephaseelectrostaticorvanderWaals'somecomponentsinsampleinteractmorestronglywit

2、hstationaryphaseandaremorestronglyretainedsampleseparatedintozonesorbandsCEM333page14.1ElutionChromatography:flushingofsamplethroughcolumnbycontinualmobilephase(eluent)additionmigrationrateµfractiontimespentinmobilephasePlanarchromatography-flatstation

3、aryphase,mobilephasemovesthroughcapillaryactionorgravityColumnchromatography-tubeofstationaryphase,mobilephasemovesbypressureorgravityTable26-1:CEM333page14.2Fig26-1,26-2CEM333page14.3Important:¥chromatogram(concentrationversuselutiontime)¥morestrongly

4、retainedspecieseluteslast(elutionorder)¥analyteis"diluted"duringelution(dispersion)¥zonebroadeningproportionaltoelutiontimeBychangingexperimentalconditions,non-separatedbandscanbeseparated(A)adjustmigrationratesforAandB(increasebandseparation)(B)adjust

5、zonebroadening(decreasebandspread)Fig26-3CEM333page14.4(A)AdjustingMigrationRates:AnalyteAinequilibriumwithtwophasesAmobile«AstationarycstationarypartitionratioK=cmobileWeknowelutiontimeisrelatedtoamountoftimeinmobilephase-canwequantifythis?RetentionTi

6、metR:Fig26-4tRretentiontimeforretainedspeciesLaveragemigrationratev=columnlengthtRtMtimeforunretainedspecies(deadtime)samerateasmobilephasemoleculesLaverageratemigrationu=deadtimetMIdeally¥tRindependentofvolumeinjected¥producesGaussianpeaksCEM333page14

7、.5RetentionTime(tR)andPartitionRatio(K):MigrationrateofanalyteisvA=u´fractiontimeAspendsinmobilephase#molsAinmobilephase=u´total#molsAcMVM=u´cMVM+cSVS1=u´1+cSVS/cMVM1=u´1+KA(VS/VM)estimatefromcolumnpackingCapacityFactork'A:'kA=KA(VS/VM)[unitless]forana

8、lyteA1v=u´1+k'AHowisk'ArelatedtotRandtM?LL1=´tt'RM1+kA'tR-tMkA=tMWhenk'Ais£1.0,separationispoorWhenk'Ais>30,separationisslowWhenk'Ais2-10,separationisoptimumCEM333page14.6RelativeMigrationRates-SelectivityFactor(a):Howdowecompareelution