定量分析30分析分離-Introduction-to-analytical-Separations課件

QuantitativeAnalysis

定量分析QuantitativeAnalysis

定量分析Chapter30

IntroductiontoanalyticalSeparationsChapter30

Introductiontoana Animportantpartofmostanalysesisdealingwithforeignspeciesthateitherattenuatethesignalfromtheanalyteorproduceasignalthatisindistinguishablefromthatoftheanalyte.Asubstancethateffectsananalyticalsignaliscalledaninterferenceoraninterferent. Severalgeneralmethodsareusedfordealingwithinterferencesinananalysis;i)masking,ii)chemicalorelectrolyticprecipitation,iii)distillation,iv)solventextraction,v)ionexchange,vi)chromatography,andvii)electrophoresis. Animportantpartofmostana定量分析30分析分離-Introduction-to-analytical-Separations課件定量分析30分析分離-Introduction-to-analytical-Separations課件MASKING

Inmasking,areagentisaddedtothesolutionofthesampletoimmobilize,orchemicallybind,theinterferentasacomplexthatnolongercontributestoorattenuatesthesignalfromtheanalyte.Amaskingagentmustnotaffectthebehavioroftheanalytesignificantly.MASKING Inmasking,areagent PRECIPITATIONANDFILTRATION

Precipitation,inwhichtheanalyteoraninterferentisremovedfromasolutionselectivelyasaninsolublespecies,isoneoftheoldestmethodsfordealingwithinterferencesinananalyticalprocedure. SEPARATINGSPECIESBYDISTILLATION

Distillationiswidelyusedtoseparatevolatileanalytesfromnonvolatileinterferents. PRECIPITATIONANDFILTRATIONSEPARATINGSOLUTESBYEXTRACTION

Theextenttowhichsolutes,bothinorganicandorganic,distributethemselvesbetweentwoimmiscibleliquidsdiffersenormously,andthesedifferenceshavebeenusedfordecadestoaccomplishseparationsofchemicalspecies.SEPARATINGSOLUTESBYEXTRACTI

Principles Thepartitonofasolutebetweentwoimmisciblephasesinanequilibriumphenomenonthatisgovernedbythedistributionlaw.IfthesolutespeciesAisallowedtodistributeitselfbetweenwaterandanorganicphase,theresultingequilibriummaybewrittenas Aaq Aorg TheratioofactivitiesforAinthetwophaseswillbeconstantandindependentofthetotalquantityofA;thatis,atanygiventemperature, Principles…continued… TheequilibriumconstantKisknownasthedistributionconstant. TheconcentrationofAremaininginanaqueoussolutionafterIextractionswithanorganicsolventisgivenbytheequation where,[A]iistheconcentrationofAremainingintheaqueoussolutionafterextractingVaqmLofthesolutionhavinganoriginalconcentrationof[A]owithIportionsoftheorganicsolvent,eachwithavolumeofVorg.…continued…定量分析30分析分離-Introduction-to-analytical-Separations課件定量分析30分析分離-Introduction-to-analytical-Separations課件SEPARATINGIONSBYIONEXCHANGE

Ionexchangeisaprocessbywhichionsheldonaporous,essentiallyinsolublesolidareexchangedforionsinasolutionthatisbroughtincontactwiththesolid.Theion-exchangepropertiesofclaysandzeoliteshavebeenrecognizedandstudiedsincethelatenineteenthcentury.Syntheticion-exchangeresinswerefirstproducedin1935andhavesincefoundwidespreadapplicationinwatersoftening,waterdeionization,solutionpurification,andionseparation.SEPARATINGIONSBYIONEXCHANG Ion-ExchangeResins Syntheticion-exchangeresinsarehigh-molecular-weightpolymersthatcontainlargenumbersofanionicfunctionalgrouppermolecule.Cation-exchangeresinscontainacidicgroups,whereasanion-exchangeresinshavebasicgroups.Exchangersofthestrong-acidtypehavesulfonicacidgroups( SO3-H+)attachedtothepolymericmatrix.Strong-baseanionexchangerscontainquaternaryamine[ N(CH3)3+OH-]groups.

xRSO3-H++Mx+ (RSO3-)xMx++xH+ solid soln solid soln xRN(CH3)3+OH-+Ax- [RN(CH3)3+]xAx-+xOH- solid soln solid soln Ion-ExchangeResins定量分析30分析分離-Introduction-to-analytical-Separations課件 ApplicationsofIon-ExchangeMethods Ion-exchangeresinsareusedtoeliminateionsthatwouldotherwiseinterferewithananalysis.Anothervaluableapplicationofion-exchangeresinsinvolvesconcentratingionsfromaverydilutesolution.Thus,tracesofmetallicelementsinlargevolumesofnaturalwaterscanbecollectedonacation-exchangecolumnandsubsequentlyliberatedfromtheresinbytreatmentwithasmallvolumeofanacidicsolution. Thetotalsaltcontentofasamplecanbedeterminedbytitratingthehydrogenionreleasedasanaliquotofthesamplepassesthroughacationexchangerinitsacidicform. Ion-exchangeresinsareparticularlyusefulforthechromatographicseparationofbothinorganicandorganicionicspecies. ApplicationsofIon-ExchangeCHROMATOGRAPHICSEPARATION

Chromatographyisawidelyusedmethodfortheseparation,identification,anddeterminationofthechemicalcomponentsincomplexmixtures.Nootherseparationmethodisaspowerfulandgenerallyapplicableaschromatography.CHROMATOGRAPHICSEPARATION ChrGeneralDescriptionofChromatography

Theterm“chromatography”isdifficulttodefinerigorouslybecausethewordhasbeenappliedtoseveralsystemsandtechniques.Commontoallthesemethods,however,istheuseofastationaryphaseandamobilephase.Componentsofamixturearecarriedthroughthestationaryphasebytheflowofthemobilephase,andseparationsarebasedondifferencesinmigrationratesamongthemobile-phasecomponents.GeneralDescriptionofChromat…continued…

Thestationaryphaseinchromatographyisaphasethatisfixedinplaceeitherinacolumnoronaplanarsurface. Themobilephaseinchromatographyisaphasethatmovesoverorthroughthestationaryphase,carryingwithittheanalytemixture.Themobilephasemaybeagas,aliquid,orasupercriticalfluid.…continued…ClassifyingChromatographicMethods Chromatographicmethodsareoftwobasictypes.Incolumnchromatography,thestationaryphaseisheldinanarrowtube,andthemobilephaseisforcedthroughthetubeunderpressureorbygravity.Inplanarchromatography,thestationaryphaseissupportedonaflatplateorintheporesofapaper.Herethemobilephasemovesthroughthestationaryphasebycapillaryactionorundertheinfluenceofgravity.Columnchromatographicmethodscanbefurthersubdividedaccordingtothenatureofthemobilephase,specificallyliquid,gas,andsupercriticalfluid.ClassifyingChromatographicMe定量分析30分析分離-Introduction-to-analytical-Separations課件ElutioninColumnChromatography

Elutionisaprocessinwhichsolutesarewashedthroughastationaryphasebythemovementofamobilephase.Themobilephasethatexitsthecolumniscalledtheeluate. Aneluentisasolventusedtocarrythecomponentsofamixturethroughastationaryphase.ElutioninColumnChromatograp定量分析30分析分離-Introduction-to-analytical-Separations課件Chromatograms Ifadetectorthatrespondstosoluteconcentrationisplacedattheendofthecolumnduringelutionanditssignalisplottedasafunctionoftime(orofavolumeofaddedmobilephase),aseriesofpeaksisobtained,suchaplot,calledachromatogram,isusefulforbothqualitativeandquantitativeanalysis.Thepositionsofthepeaksonthetimeaxiscanbeusedtoidentifythecomponentsofthesample;theareasunderthepeaksprovideaquantitativemeasureoftheamountofeachspecies.Chromatograms定量分析30分析分離-Introduction-to-analytical-Separations課件定量分析30分析分離-Introduction-to-analytical-Separations課件RelativeMigrationRatesofSolutes

Theeffectivenessofachromatographiccolumninseparatingtwosolutesdependsontherelativeratesatwhichthetwospeciesareeluted.Theseratesareinturndeterminedbytherationsofthesoluteconcentrationsineachofthetwophases.

RelativeMigrationRatesofSo

DistributionConstants Allchromatographicseparationsarebasedondifferencesintheextenttowhichsolutesaredistributedbetweenthemobileandthestationaryphase.ForthesolutespeciesA,theequilibriuminvolvedisdescribedbytheequation A(mobile) A(stationary) TheequilibriumconstantKcforthisreactioniscalledadistributionconstant,whichisdefinedas DistributionConstants

RetentionTimes ThedeadtimetMisthetimeittakesforanunretainedspeciestopassthroughacolumn. TheretentiontimetRisthetimebetweeninjectionofasampleandtheappearanceofasolutepeakatthedetectorofachromatographiccolumn. Theaveragelinearrateofsolutemigration,,incentimeterspersecondis

=L/tR whereListhelengthofthecolumnpacking.Similarly,theaveragelinearvelocity,u,ofthemoleculesofthemobilephaseis u=L/tM

_ RetentionTimes_定量分析30分析分離-Introduction-to-analytical-Separations課件 RelatingMigrationRatestoDistributionConstants

=uxfractionoftimesolutespendsinmobilephase

____ RelatingMigrationRatestoD

TheRetentionFactor(k) Theretentionfactorisanimportantexperimentalparameterthatiswidelyusedtocomparethemigrationratesofsolutesoncolumns.ForsoluteA,theretentionfactorkAisdefinedas

whereKAisthedistributionconstantforsoluteA.

ToshowhowkAcanbederivedfromachromatogram,

_ TheRetentionFactor(k)_…continued…

Thisequationrearrangesto

Whentheretentionfactorforasoluteismuchlessthanunity,elutionoccurssorapidlythataccuratedeterminationoftheretentiontimesisdifficult.Whentheretentionfactorislargerthanperhaps20to30,elutiontimesbecomeinordinatelylong.Ideally,separationsareperformedunderconditionsinwhichtheretentionfactorsforthesolutesinamixturelieintherangebetween1and5.…continued… TheSelectivityFactor

TheselectivityfactorofacolumnforthetwosolutesAandBisdefinedas

=KB/KA whereKBisthedistributionconstantforthemorestronglyretainedspeciesBandKAistheconstantforthelessstronglyheldormorerapidlyelutedspeciesA.Accordingtothisdefinition,isalwaysgraterthanunity. =kB/kA wherekBandkAarethecapacityfactors TheSelectivityFactor

QuantitativeMeasuresofColumnEfficiency Tworelatedtermsarewidelyusedasquantitativemeasuresofchromatographiccolumnefficiency:(1)plateheightHand(2)platecountornumberoftheoreticalplatesN.Thetwoarerelatedbytheequation N=L/H whereListhelength(usuallyincentimeters)ofthecolumnpacking.TheefficiencyofchromatographiccolumnsincreasesastheplatecountNbecomesgreaterandastheplateheightHbecomessmaller. QuantitativeMeasuresofColu定量分析30分析分離-Introduction-to-analytical-Separations課件 DeterminingtheNumberofPlatesinaColumn Thenumberoftheoreticalplates,N,andtheplateheight,H,arewidelyusedintheliteratureandbyinstrumentmanufacturesasmeasuresofcolumnperformance.Ncanbedeterminedfromachromatogram.TheretentiontimeofapeaktRandthewidthofthepeakatitsbaseW(inunitsoftime)aremeasured.Thenumberofplatescanthenbecomputedbythesimplerelationship. N=16(tR/W)2 ToobtainH,thelengthofthecolumnLismeasuredandN=L/HEquationisapplied. DeterminingtheNumberofPla定量分析30分析分離-Introduction-to-analytical-Separations課件

VariablesThatInfluencePlateHeights Ithasbeenfoundthatplateheightscanbedecreased,andthuscolumnefficiencyincreasedbydecreasingtheparticlesizeofcolumnpackings,byemployingthinnerlayersoffilm(wherethestationaryphaseisaliquidadsorbedonasolid),andbyloweringtheviscosityofthemobilephase.Increasesintemperaturealsoreducebandbroadeninginmostcases. VariablesThatInfluencePlat定量分析30分析分離-Introduction-to-analytical-Separations課件定量分析30分析分離-Introduction-to-analytical-Separations課件

ColumnResolution TheresolutionRsofacolumnprovidesaquantitativemeasureofitsabilitytoseparatetwoanalytes.Theresolutionisdefinedas

Aresolutionof1.5givesanessentiallycompleteseparationofAandB,whereasaresolutionof0.75doesnot.Ataresolutionof1.0,zoneAcontainsabout4%BandzoneBcontainsabout4%A.Ataresolutionof1.5,theoverlapisabout0.3%.Theresolutionforagivenstationaryphasecanbeimprovedbylengtheningthecolumnandthusincreasingthenumberofplates.Anadverseconsequenceoftheaddedplates,however,isanincreaseinthetimerequiredforseparatingthecomponents. ColumnResolution定量分析30分析分離-Introduction-to-analytical-Separations課件 EffectofRetentionFactorandSelectivityFactor Ausefulequationisderivedthatrelatestheresolutionofacolumntothenumberofplatesitcontainsaswellastotheretentionandselectivityfactorsofapairofsolutesonthecolumn.Theresolutionisgivenbytheequation

wherekBistheretentionfactoroftheslower-movingspeciesandistheselectivityfactor.Thisequationcanberearrangedtogivethenumberofplatesneededtorealizeagivenresolution: EffectofRetentionFactoranApplicationsofChromatography

Chromatographyisapowerfulandversatiletoolforseparatingcloselyrelatedchemicalspecies.Inaddition,itcanbeemployedforthequalitativeidentificationandquantitativedeterminationofseparatedspecies.ApplicationsofChromatography定量分析30分析分離-Introduction-to-analytical-Separations課件QuantitativeAnalysis

定量分析QuantitativeAnalysis

定量分析Chapter30

IntroductiontoanalyticalSeparationsChapter30

Introductiontoana Animportantpartofmostanalysesisdealingwithforeignspeciesthateitherattenuatethesignalfromtheanalyteorproduceasignalthatisindistinguishablefromthatoftheanalyte.Asubstancethateffectsananalyticalsignaliscalledaninterferenceoraninterferent. Severalgeneralmethodsareusedfordealingwithinterferencesinananalysis;i)masking,ii)chemicalorelectrolyticprecipitation,iii)distillation,iv)solventextraction,v)ionexchange,vi)chromatography,andvii)electrophoresis. Animportantpartofmostana定量分析30分析分離-Introduction-to-analytical-Separations課件定量分析30分析分離-Introduction-to-analytical-Separations課件MASKING

Inmasking,areagentisaddedtothesolutionofthesampletoimmobilize,orchemicallybind,theinterferentasacomplexthatnolongercontributestoorattenuatesthesignalfromtheanalyte.Amaskingagentmustnotaffectthebehavioroftheanalytesignificantly.MASKING Inmasking,areagent PRECIPITATIONANDFILTRATION

Precipitation,inwhichtheanalyteoraninterferentisremovedfromasolutionselectivelyasaninsolublespecies,isoneoftheoldestmethodsfordealingwithinterferencesinananalyticalprocedure. SEPARATINGSPECIESBYDISTILLATION

Distillationiswidelyusedtoseparatevolatileanalytesfromnonvolatileinterferents. PRECIPITATIONANDFILTRATIONSEPARATINGSOLUTESBYEXTRACTION

Theextenttowhichsolutes,bothinorganicandorganic,distributethemselvesbetweentwoimmiscibleliquidsdiffersenormously,andthesedifferenceshavebeenusedfordecadestoaccomplishseparationsofchemicalspecies.SEPARATINGSOLUTESBYEXTRACTI

Principles Thepartitonofasolutebetweentwoimmisciblephasesinanequilibriumphenomenonthatisgovernedbythedistributionlaw.IfthesolutespeciesAisallowedtodistributeitselfbetweenwaterandanorganicphase,theresultingequilibriummaybewrittenas Aaq Aorg TheratioofactivitiesforAinthetwophaseswillbeconstantandindependentofthetotalquantityofA;thatis,atanygiventemperature, Principles…continued… TheequilibriumconstantKisknownasthedistributionconstant. TheconcentrationofAremaininginanaqueoussolutionafterIextractionswithanorganicsolventisgivenbytheequation where,[A]iistheconcentrationofAremainingintheaqueoussolutionafterextractingVaqmLofthesolutionhavinganoriginalconcentrationof[A]owithIportionsoftheorganicsolvent,eachwithavolumeofVorg.…continued…定量分析30分析分離-Introduction-to-analytical-Separations課件定量分析30分析分離-Introduction-to-analytical-Separations課件SEPARATINGIONSBYIONEXCHANGE

Ionexchangeisaprocessbywhichionsheldonaporous,essentiallyinsolublesolidareexchangedforionsinasolutionthatisbroughtincontactwiththesolid.Theion-exchangepropertiesofclaysandzeoliteshavebeenrecognizedandstudiedsincethelatenineteenthcentury.Syntheticion-exchangeresinswerefirstproducedin1935andhavesincefoundwidespreadapplicationinwatersoftening,waterdeionization,solutionpurification,andionseparation.SEPARATINGIONSBYIONEXCHANG Ion-ExchangeResins Syntheticion-exchangeresinsarehigh-molecular-weightpolymersthatcontainlargenumbersofanionicfunctionalgrouppermolecule.Cation-exchangeresinscontainacidicgroups,whereasanion-exchangeresinshavebasicgroups.Exchangersofthestrong-acidtypehavesulfonicacidgroups( SO3-H+)attachedtothepolymericmatrix.Strong-baseanionexchangerscontainquaternaryamine[ N(CH3)3+OH-]groups.

xRSO3-H++Mx+ (RSO3-)xMx++xH+ solid soln solid soln xRN(CH3)3+OH-+Ax- [RN(CH3)3+]xAx-+xOH- solid soln solid soln Ion-ExchangeResins定量分析30分析分離-Introduction-to-analytical-Separations課件 ApplicationsofIon-ExchangeMethods Ion-exchangeresinsareusedtoeliminateionsthatwouldotherwiseinterferewithananalysis.Anothervaluableapplicationofion-exchangeresinsinvolvesconcentratingionsfromaverydilutesolution.Thus,tracesofmetallicelementsinlargevolumesofnaturalwaterscanbecollectedonacation-exchangecolumnandsubsequentlyliberatedfromtheresinbytreatmentwithasmallvolumeofanacidicsolution. Thetotalsaltcontentofasamplecanbedeterminedbytitratingthehydrogenionreleasedasanaliquotofthesamplepassesthroughacationexchangerinitsacidicform. Ion-exchangeresinsareparticularlyusefulforthechromatographicseparationofbothinorganicandorganicionicspecies. ApplicationsofIon-ExchangeCHROMATOGRAPHICSEPARATION

Chromatographyisawidelyusedmethodfortheseparation,identification,anddeterminationofthechemicalcomponentsincomplexmixtures.Nootherseparationmethodisaspowerfulandgenerallyapplicableaschromatography.CHROMATOGRAPHICSEPARATION ChrGeneralDescriptionofChromatography

Theterm“chromatography”isdifficulttodefinerigorouslybecausethewordhasbeenappliedtoseveralsystemsandtechniques.Commontoallthesemethods,however,istheuseofastationaryphaseandamobilephase.Componentsofamixturearecarriedthroughthestationaryphasebytheflowofthemobilephase,andseparationsarebasedondifferencesinmigrationratesamongthemobile-phasecomponents.GeneralDescriptionofChromat…continued…

Thestationaryphaseinchromatographyisaphasethatisfixedinplaceeitherinacolumnoronaplanarsurface. Themobilephaseinchromatographyisaphasethatmovesoverorthroughthestationaryphase,carryingwithittheanalytemixture.Themobilephasemaybeagas,aliquid,orasupercriticalfluid.…continued…ClassifyingChromatographicMethods Chromatographicmethodsareoftwobasictypes.Incolumnchromatography,thestationaryphaseisheldinanarrowtube,andthemobilephaseisforcedthroughthetubeunderpressureorbygravity.Inplanarchromatography,thestationaryphaseissupportedonaflatplateorintheporesofapaper.Herethemobilephasemovesthroughthestationaryphasebycapillaryactionorundertheinfluenceofgravity.Columnchromatographicmethodscanbefurthersubdividedaccordingtothenatureofthemobilephase,specificallyliquid,gas,andsupercriticalfluid.ClassifyingChromatographicMe定量分析30分析分離-Introduction-to-analytical-Separations課件ElutioninColumnChromatography

Elutionisaprocessinwhichsolutesarewashedthroughastationaryphasebythemovementofamobilephase.Themobilephasethatexitsthecolumniscalledtheeluate. Aneluentisasolventusedtocarrythecomponentsofamixturethroughastationaryphase.ElutioninColumnChromatograp定量分析30分析分離-Introduction-to-analytical-Separations課件Chromatograms Ifadetectorthatrespondstosoluteconcentrationisplacedattheendofthecolumnduringelutionanditssignalisplottedasafunctionoftime(orofavolumeofaddedmobilephase),aseriesofpeaksisobtained,suchaplot,calledachromatogram,isusefulforbothqualitativeandquantitativeanalysis.Thepositionsofthepeaksonthetimeaxiscanbeusedtoidentifythecomponentsofthesample;theareasunderthepeaksprovideaquantitativemeasureoftheamountofeachspecies.Chromatograms定量分析30分析分離-Introduction-to-analytical-Separations課件定量分析30分析分離-Introduction-to-analytical-Separations課件RelativeMigrationRatesofSolutes

Theeffectivenessofachromatographiccolumninseparatingtwosolutesdependsontherelativeratesatwhichthetwospeciesareeluted.Theseratesareinturndeterminedbytherationsofthesoluteconcentrationsineachofthetwophases.

RelativeMigrationRatesofSo

DistributionConstants Allchromatographicseparationsarebasedondifferencesintheextenttowhichsolutesaredistributedbetweenthemobileandthestationaryphase.ForthesolutespeciesA,theequilibriuminvolvedisdescribedbytheequation A(mobile) A(stationary) TheequilibriumconstantKcforthisreactioniscalledadistributionconstant,whichisdefinedas DistributionConstants

RetentionTimes ThedeadtimetMisthetimeittakesforanunretainedspeciestopassthroughacolumn. TheretentiontimetRisthetimebetweeninjectionofasampleandtheappearanceofasolutepeakatthedetectorofachromatographiccolumn. Theaveragelinearrateofsolutemigration,,incentimeterspersecondis

=L/tR whereListhelengthofthecolumnpacking.Similarly,theaveragelinearvelocity,u,ofthemoleculesofthemobilephaseis u=L/tM

_ RetentionTimes_定量分析30分析分離-Introduction-to-analytical-Separations課件 RelatingMigrationRatestoDistributionConstants

=uxfractionoftimesolutespendsinmobilephase

____ RelatingMigrationRatestoD

TheRetentionFactor(k) Theretentionfactorisanimportantexperimentalparameterthatiswidelyusedtocomparethemigrationratesofsolutesoncolumns.ForsoluteA,theretentionfactorkAisdefinedas

whereKAisthedistributionconstantforsoluteA.

ToshowhowkAcanbederivedfromachromatogram,

_ TheRetentionFactor(k)_…continued…

Thisequationrearrangesto

Whentheretentionfactorforasoluteismuchlessthanunity,elutionoccurssorapidlythataccuratedeterminationoftheretentiontimesisdifficult.Whentheretentionfactorislargerthanperhaps20to30,elutiontimesbecomeinordinatelylong.Ideally,separationsareperformedunderconditionsinwhichtheretentionfactorsforthesolutesinamixturelieintherangebetween1and5.…continued… TheSelectivityFactor

TheselectivityfactorofacolumnforthetwosolutesAandBisdefinedas

=KB/KA whereKBisthedistributionconstantforthemorestronglyretainedspeciesBandKAistheconstantforthelessstronglyheldormorerapidlyelutedspeciesA.Accordingtothisdefinition,isalwaysgraterthanunity. =kB/kA wherekBandkAarethecapacityfactors TheSelectivityFactor

QuantitativeMeasuresofColumnEfficiency Tworelatedtermsarewidelyusedasquantitativemeasuresofchromatographiccolumnefficiency:(1)plateheightHand(2)platecountornumberoftheoreticalplatesN.Thetwoarerelatedbytheequation N=L/H whereListhelength(usuallyincentimeters)ofthecolumnpacking.TheefficiencyofchromatographiccolumnsincreasesastheplatecountNbecomesgreaterandastheplateheightHbecomessmaller. QuantitativeMeasuresofColu定量分析30分析分離-Introduction-to-analytical-Se