分析化學(xué)英文課件10分光光度法-Spectrophotometry

AnalyticalChemistry

分析化學(xué)AnalyticalChemistry

分析化學(xué)Chapter10SpectrophotometryChapter10Spectrophotometry§10.1

Generalization§10.2

FundamentalLawsofPhotometry§10.3

PrinciplesofInstrumentation§10.4

Color-developingReactions§10.5PhotometricMeasurement§10.1Generalization§10.1Generalization

Waveandparticle.Thewavepropertiescanbeexpressedbywavelength、frequency,speedoflightc,etc:

=c

Lightconsistsofastreamofdiscreteparticlescalledphotons,eachpossessingtheenergyE:

E=h=hc/

（Planck

constant：h=6.62610-34J·

S)§10.1GeneralizationWaveandGeneralization

Theshorterthewavelength,thelargertheenergy.(1)Whitelight:polychromiclight(2)

Monochromiclight：lightconsistsofphotonswithsamewavelength.

Ultraviolet:vacuumultraviolet10~200nm,nearultraviolet200~400nm.Visible:400~750nm(3)TheintensityofabeamisproportionaltothenumberofphotonspersecondthatarepropagatedinthebeamGeneralizationTheshorterTheselectiveabsorbanceandabsorbancecurveM+heatM+fluorescenceorphosphorescenceE=E2-

E1=h

：quantum,selectiveabsorbance,absorbancecurveand

max,

theabsorptionoflightasafunctionofwavelength.M+

h

→M*groundstateexcitedstateE1

（△E）E2TheselectiveabsorbanceandaAbsorbancecurve(1)Forthesamesubstance,the

absorbanceisdifferentatdifferentwavelength.Thewavelengthatwhichtheabsorptionisthelargestisλmax(2)Forthesamesubstanceofdifferent

c，theabsorbancecurvehavesimilarshapeandsameλmax.(3)Absorbancecurvecanbeusedforthequalitativeanalysis.(4)Atλmax,thechangeofabsorbancewithconcentrationisthelargest,thedeterminationismost

sensitive.Theabsorbancecurvecanbeusedforselectionofwavelength.Absorbancecurve(1)Forthesa§10.2FundamentalLawsof

Photometry(3)ThefundamentallawofspectrophotometryknownastheLambert-Beer’slaworsimplyBeer’slawmaybestatedas:

A=lg(I0/It)=εbc

1.Lambert—Beer’slaw(1)

BouguerandLambertfoundtherelationshipbetweenabsorbanceandlightpathin1729and1760.A∝bmoving1moving2(2)In1852Beerpointedoutthatthereissimilarrelationshipbetweentheabsorbanceandconcentration.A∝c§10.2FundamentalLawsof

Lambert—Beer’slawLambert-Beer’slaworsimplyBeer’slawmaybestatedas:

A=lg(I0/It)=εbc

whereA:absorbance；

b:lightpath,cm；

c:molarconcentration,mol·L-１；

ε:molarabsorptivity,L·mol-１·cm-１；or:A=lg（I0/It)=abc

c:concentration,g·L-１

a:absorptivity,L·g-１·cm-１

aandε:a=ε/M（M:molarmass）Lambert—Beer’slawLambert-BeerTransmittance:TT

:ratiooftheradiantpowertransmittedtotheincidentradiantpower:

T=It/I0RelationshipbetweenAandT:

A=-lgT

(1)Lambert-Beer’sLawisthequantitativebaseforspectrophotometry,widelyusedinthedeterminationofconcentrationwithultraviolet,visible,andinfraredlights.(2)Molarabsorptivityεequalstheabsorbanceof1mol/Lsolutionand1cmlightpath.(3)Absorptivitya(L·g-1·cm-1)equalstheabsorbanceof1g/Lsolutionand1cmlightpath.Transmittance:TT:ratiooft2.Molarabsorptivityε(1)Characteristicconstantundercertainconditionforacertainsubstance.(2)Notchangewithcandwavepathb.Undercertaintemperatureandwavelength,εisonlydecidedbythenatureofthesubstance.(3)Canbeusedforqualitativeanalysis.(4)εisdifferentatdifferentwavelength.Molarabsorptivityatλmax

isexpressedasεmax.

Ε>105：ultrahighsensitive；

ε=(6～10）×104:highsensitive；

ε=(2～6）×104:mediumsensitive

ε<2×104:notsensitive。2.Molarabsorptivityε(1)CharaDiscrepancyofLambert-beer’slaw

Therelationshipbetweentheabsorbanceandconcentrationmaybenonlinear,whichisthediscrepancyofLambert-Beer’sLaw.

Thediscrepancymaybecausedby：(1)PhysicalfactorTheabsorbingbandisnotcompletelyresolved;

(2)Chemicalfactor

ThestateoftheabsorbingcomponentchangeswithconcentrationLambert-BeerLawshouldbeexpectedtoapplyonlyatlowconcentration,Athighconcentraions,diviationmayoccurDiscrepancyofLambert-beer’s§10.3Instrumentation

1.Spectrophotometers§10.3Instrumentation

1.SpecSpectrophotometersSpectrophotometersInnerstructure

Innerstructure2.InstrumentalcomponentsLightSourceMono-chromatorSampleDetectorReadout(1)Lightsource

Asourceofcontinuousradiationoverthewavelengthsofinterestwithhighintensity,goodstabilityandlonglife.

Visible：tungstenhalogenlamp，wavelength320～2500nm。

Ultraviolet：deuteriumlamp,185～400nm.moving2.InstrumentalcomponentsLigh(2)Monochromators

Usedtoselectrediationofanarrowwavelengthrangefromacontinuoussource.①Entranceslit:fromtheslit,lightgointomonochromator②Collimatingdevice：alensormirrorthatcauseslighttotravelasparallelrays

③Dispersiondevice:prismordiffractiongratingtoselectthelightofdifferentwavelengths④Focusinglensormirror⑤Exitslit(2)MonochromatorsUsedto(3)Cells

Cellsusedinthevisibleregionaremadeofopticalqualitysilicateglass.Atshorterwavelengths,itisnecessarytousesometypeofquartzorsilicacell.Suchcellscanalsobeusedabove320nm.(5)Instrumentalreadout

Adigitalreadoutorascalereadout.(4)Detectors

Aphototubeiscommonlyusedtochangethelightsignaltoelectricalsignal(3)CellsCellsusedinthe§10.4Color-developingReactions1.Howtochoosethecolordevelopingreaction

Highsensitivity,highselectivity,stableproduct.Thechromagenicreagentshouldhaslittleabsorbanceatthewavelengthdetermined.(1)Complexcolor-developingreactions

Metalionscomplexedwithchromagenicreagenttoformchromaticproducts.§10.4Color-developingReactio(2)Redoxcolor-developingreactions

WhentheoxidizedformsofsomeelementsasMn(Ⅶ)andCr(Ⅵ)haveintensiveabsorbance,thecolorcanbedevelopedbyredoxreactions.

Example：determinationofMninsteel,Mn2＋cannotbedeterminedbyspectrophotometryderectly2Mn2++5S2O82-+8H2O=2MnO4++10SO42-+16H+

Mn2+isoxidizedtoMnO4+(purple),andcanbedeterminedat525nm.(2)Redoxcolor-developingrea2.Chooseconditionsforcolordevelopingreaction(1)Amountofthechromogenicreagentadded(2)Acidityofmedium

UndersameconditionanddifferentpH,theabsorbanceisdetermined.ChoosepHofhighandstableabsorbance.(3)Temperatureandstabilityperiod

Decidedbyexperiment(4)InterferencesShouldbeeliminatedbyusingadequatemethods.2.Chooseconditionsforcolor3.Eliminationofinterference(1)Maskingagent

Howtochoose:(a)Shouldnotreactwiththeanalyte；(b)Theproductofmaskingagentwithinterferenceshouldnotinterfereinthedeterminationofanalyte.Example:fordeterminationofTi4+,H3PO4

isaddedasmaskingagent,Fe3+(yellow)

ischangedtoFe(PO４)23-(noncolor),thuseliminatetheinterference

ofFe3+.(2)Choosesuitableconditionforcolordevelopingreaction(3)Separatetheinterference3.Eliminationofinterference4.Chooseconditionsfordetermination(1)Choosesuitableincidentwavelength

Normallyλmax

ischosenasincidentwavelength.Ifthereisinterferenceatλmax,awavelengthoflowersensitivityandlittleinterferenceshouldbechosen.4.Chooseconditionsfordete(2)ChoosesuitablereferencesolutionWhyusereferencesolution？

Theabsorbancedeterminedshouldbetheabsorbanceofanalyte.Howtochoose：①Ifonlytheproductofanalytewithchromagenicagenthasabsorbance,choosewaterasthereferencesolution;②

Ifthechromagenicagentorotheragenthaveabsorbance,theanalytesolutionhasnoabsorbance,choose“reagentblank”(notaddanalyte);③Ifanalytehasabsorbance，choose“analyteblank”;④Ifchromagenicagentandanalytebothhaveabsorbance,choosethesuitablemaskingagentaddedtotheanalytethenthechromagenicagentisaddedasthereference.(2)Choosesuitablereference(3)ControltheabsorbancewithinsuitablerangeatdifferentT,differenterror:

-lgT=εbcdifferent:-dlgT=-0.434dlnT

=-0.434T-1dT

=εbdcdivide:dc/c=(0.434/TlgT)dT

Δc/c=(0.434/TlgT)ΔT

relativeerror(Δc/c)isdecidedbyΔTandT.(3)ControltheabsorbancewitRangeofminimumrelativeerrorIf:ΔT=1%,therelationshipbetweenΔc/candT:WhenΔT=1%,andT

isbetween2%～65%,therelativeerrorislittle.SoTshouldbecontrolledwithinT%=20～65％(A=0.70～0.20).Tofminimumrelativeerror

Tmin=36.8%,Amin=0.434RangeofminimumrelativeerroHowtoimprovesensitivityandselectivity(1)Synthesizechromagenicagentofhighsensitivity(2)Separationandenrichment(3)Multicomplexchromagenicsystem

Onekindofmetalioncomplexwithtwoormoreligandtoformcomplexes.

Multicomplexchromagenicreactionsisofhighsensitivity.Howtoimprovesensitivityand§10.5Photometricmeasurement

1.Normalspectrophotometry(1)Normalspectrophotometry

singlecomponentA~ccalibrationcurve§10.5Photometricmeasurement(2)Multicomponents

a.Donotinterfereeachother,canbedeterminedundermax.

b.Interferewitheachother,Aλ1=εaλ1bca+εbλ1bcb

Aλ2=εaλ2bca+εbλ2bcb

(2)Multicomponentsa.Don2.Differentialspectrophotometry(1)Whentheconcentrationofthecomponentishigh,theerrorishighinnormalspectrophotometry,thenthedefferentialspectrophotometryisapplied.(2)Indefferentialspectrophotometry,intensityofincidentlightishigh，standardsolutionofalittlelowerconcentrationisusedasreference.If:cx,

cs(cs<cx),then:

Ax=εbcx

As=εbcs

Ａ=Ａx-Ａs=εb(cx-

cs)=εb

c

cx=cs+c

2.DifferentialspectrophotometNormal：

cs:T=10%；cx:T=5%Differential：

cs

:reference，T=100%cx:T=50%；10timesextendedNormal：3.Dualwave-lengthspectrophotometry

Dualwave-length(λ1,λ2);referenceisnotneeded.Highsensitivityandselectivity

Ａ=Aλ2-Aλ1=(ελ2-ελ1)bc

Aisproportionaltoc.

Ελ1,ελ2

ismolarabsorptivityatλ1

andλ2.

Keyfactoristochooseλ2

andreferenceλ1.Twocomponent:

x,yifx

istobedetermined,y

isinterference,thedifferenceofabsorbanceisＡx

andＡy,thenＡx+y:

Ａx+y=Ａx+Ａy3.Dualwave-lengthspectrophoHowtochooseλ1,λ2

⑴Atλ1,λ2,theinterferencehassameabsorbance

Ay=Ａyλ2-Ａyλ1=0then：Ａx+y=Ａx=(εxλ2-εxλ1)bcx

Adeterminedisproportionaltocx.

⑵Atλ1,λ2,Ａx

shouldbelargeenough

choosethewavelengthbyabsorbanceplotHowtochooseλ1,λ2⑴Atλ1,λ2,4.Derivativespectrophotometry

Multicomponentscanbedeterminedatthesametime,eliminatingtheinterference.

Thetransmittancewiththewavelength：

Ｉ=Ｉ0e-εbcifＩ0

isconstant：

dI

0/dλ=0than：dI/dλ=-I0

bce-εbc

dε/dλ=-I0

bcdε/dλ

thesecondandthirdderivative.

4.Derivativespectrophotometr分析化學(xué)英文課件10分光光度法-SpectrophotometryAnalyticalChemistry

分析化學(xué)AnalyticalChemistry

分析化學(xué)Chapter10SpectrophotometryChapter10Spectrophotometry§10.1

Generalization§10.2

FundamentalLawsofPhotometry§10.3

PrinciplesofInstrumentation§10.4

Color-developingReactions§10.5PhotometricMeasurement§10.1Generalization§10.1Generalization

Waveandparticle.Thewavepropertiescanbeexpressedbywavelength、frequency,speedoflightc,etc:

=c

Lightconsistsofastreamofdiscreteparticlescalledphotons,eachpossessingtheenergyE:

E=h=hc/

（Planck

constant：h=6.62610-34J·

S)§10.1GeneralizationWaveandGeneralization

Theshorterthewavelength,thelargertheenergy.(1)Whitelight:polychromiclight(2)

Monochromiclight：lightconsistsofphotonswithsamewavelength.

Ultraviolet:vacuumultraviolet10~200nm,nearultraviolet200~400nm.Visible:400~750nm(3)TheintensityofabeamisproportionaltothenumberofphotonspersecondthatarepropagatedinthebeamGeneralizationTheshorterTheselectiveabsorbanceandabsorbancecurveM+heatM+fluorescenceorphosphorescenceE=E2-

E1=h

：quantum,selectiveabsorbance,absorbancecurveand

max,

theabsorptionoflightasafunctionofwavelength.M+

h

→M*groundstateexcitedstateE1

（△E）E2TheselectiveabsorbanceandaAbsorbancecurve(1)Forthesamesubstance,the

absorbanceisdifferentatdifferentwavelength.Thewavelengthatwhichtheabsorptionisthelargestisλmax(2)Forthesamesubstanceofdifferent

c，theabsorbancecurvehavesimilarshapeandsameλmax.(3)Absorbancecurvecanbeusedforthequalitativeanalysis.(4)Atλmax,thechangeofabsorbancewithconcentrationisthelargest,thedeterminationismost

sensitive.Theabsorbancecurvecanbeusedforselectionofwavelength.Absorbancecurve(1)Forthesa§10.2FundamentalLawsof

Photometry(3)ThefundamentallawofspectrophotometryknownastheLambert-Beer’slaworsimplyBeer’slawmaybestatedas:

A=lg(I0/It)=εbc

1.Lambert—Beer’slaw(1)

BouguerandLambertfoundtherelationshipbetweenabsorbanceandlightpathin1729and1760.A∝bmoving1moving2(2)In1852Beerpointedoutthatthereissimilarrelationshipbetweentheabsorbanceandconcentration.A∝c§10.2FundamentalLawsof

Lambert—Beer’slawLambert-Beer’slaworsimplyBeer’slawmaybestatedas:

A=lg(I0/It)=εbc

whereA:absorbance；

b:lightpath,cm；

c:molarconcentration,mol·L-１；

ε:molarabsorptivity,L·mol-１·cm-１；or:A=lg（I0/It)=abc

c:concentration,g·L-１

a:absorptivity,L·g-１·cm-１

aandε:a=ε/M（M:molarmass）Lambert—Beer’slawLambert-BeerTransmittance:TT

:ratiooftheradiantpowertransmittedtotheincidentradiantpower:

T=It/I0RelationshipbetweenAandT:

A=-lgT

(1)Lambert-Beer’sLawisthequantitativebaseforspectrophotometry,widelyusedinthedeterminationofconcentrationwithultraviolet,visible,andinfraredlights.(2)Molarabsorptivityεequalstheabsorbanceof1mol/Lsolutionand1cmlightpath.(3)Absorptivitya(L·g-1·cm-1)equalstheabsorbanceof1g/Lsolutionand1cmlightpath.Transmittance:TT:ratiooft2.Molarabsorptivityε(1)Characteristicconstantundercertainconditionforacertainsubstance.(2)Notchangewithcandwavepathb.Undercertaintemperatureandwavelength,εisonlydecidedbythenatureofthesubstance.(3)Canbeusedforqualitativeanalysis.(4)εisdifferentatdifferentwavelength.Molarabsorptivityatλmax

isexpressedasεmax.

Ε>105：ultrahighsensitive；

ε=(6～10）×104:highsensitive；

ε=(2～6）×104:mediumsensitive

ε<2×104:notsensitive。2.Molarabsorptivityε(1)CharaDiscrepancyofLambert-beer’slaw

Therelationshipbetweentheabsorbanceandconcentrationmaybenonlinear,whichisthediscrepancyofLambert-Beer’sLaw.

Thediscrepancymaybecausedby：(1)PhysicalfactorTheabsorbingbandisnotcompletelyresolved;

(2)Chemicalfactor

ThestateoftheabsorbingcomponentchangeswithconcentrationLambert-BeerLawshouldbeexpectedtoapplyonlyatlowconcentration,Athighconcentraions,diviationmayoccurDiscrepancyofLambert-beer’s§10.3Instrumentation

1.Spectrophotometers§10.3Instrumentation

1.SpecSpectrophotometersSpectrophotometersInnerstructure

Innerstructure2.InstrumentalcomponentsLightSourceMono-chromatorSampleDetectorReadout(1)Lightsource

Asourceofcontinuousradiationoverthewavelengthsofinterestwithhighintensity,goodstabilityandlonglife.

Visible：tungstenhalogenlamp，wavelength320～2500nm。

Ultraviolet：deuteriumlamp,185～400nm.moving2.InstrumentalcomponentsLigh(2)Monochromators

Usedtoselectrediationofanarrowwavelengthrangefromacontinuoussource.①Entranceslit:fromtheslit,lightgointomonochromator②Collimatingdevice：alensormirrorthatcauseslighttotravelasparallelrays

③Dispersiondevice:prismordiffractiongratingtoselectthelightofdifferentwavelengths④Focusinglensormirror⑤Exitslit(2)MonochromatorsUsedto(3)Cells

Cellsusedinthevisibleregionaremadeofopticalqualitysilicateglass.Atshorterwavelengths,itisnecessarytousesometypeofquartzorsilicacell.Suchcellscanalsobeusedabove320nm.(5)Instrumentalreadout

Adigitalreadoutorascalereadout.(4)Detectors

Aphototubeiscommonlyusedtochangethelightsignaltoelectricalsignal(3)CellsCellsusedinthe§10.4Color-developingReactions1.Howtochoosethecolordevelopingreaction

Highsensitivity,highselectivity,stableproduct.Thechromagenicreagentshouldhaslittleabsorbanceatthewavelengthdetermined.(1)Complexcolor-developingreactions

Metalionscomplexedwithchromagenicreagenttoformchromaticproducts.§10.4Color-developingReactio(2)Redoxcolor-developingreactions

WhentheoxidizedformsofsomeelementsasMn(Ⅶ)andCr(Ⅵ)haveintensiveabsorbance,thecolorcanbedevelopedbyredoxreactions.

Example：determinationofMninsteel,Mn2＋cannotbedeterminedbyspectrophotometryderectly2Mn2++5S2O82-+8H2O=2MnO4++10SO42-+16H+

Mn2+isoxidizedtoMnO4+(purple),andcanbedeterminedat525nm.(2)Redoxcolor-developingrea2.Chooseconditionsforcolordevelopingreaction(1)Amountofthechromogenicreagentadded(2)Acidityofmedium

UndersameconditionanddifferentpH,theabsorbanceisdetermined.ChoosepHofhighandstableabsorbance.(3)Temperatureandstabilityperiod

Decidedbyexperiment(4)InterferencesShouldbeeliminatedbyusingadequatemethods.2.Chooseconditionsforcolor3.Eliminationofinterference(1)Maskingagent

Howtochoose:(a)Shouldnotreactwiththeanalyte；(b)Theproductofmaskingagentwithinterferenceshouldnotinterfereinthedeterminationofanalyte.Example:fordeterminationofTi4+,H3PO4

isaddedasmaskingagent,Fe3+(yellow)

ischangedtoFe(PO４)23-(noncolor),thuseliminatetheinterference

ofFe3+.(2)Choosesuitableconditionforcolordevelopingreaction(3)Separatetheinterference3.Eliminationofinterference4.Chooseconditionsfordetermination(1)Choosesuitableincidentwavelength

Normallyλmax

ischosenasincidentwavelength.Ifthereisinterferenceatλmax,awavelengthoflowersensitivityandlittleinterferenceshouldbechosen.4.Chooseconditionsfordete(2)ChoosesuitablereferencesolutionWhyusereferencesolution？

Theabsorbancedeterminedshouldbetheabsorbanceofanalyte.Howtochoose：①Ifonlytheproductofanalytewithchromagenicagenthasabsorbance,choosewaterasthereferencesolution;②

Ifthechromagenicagentorotheragenthaveabsorbance,theanalytesolutionhasnoabsorbance,choose“reagentblank”(notaddanalyte);③Ifanalytehasabsorbance，choose“analyteblank”;④Ifchromagenicagentandanalytebothhaveabsorbance,choosethesuitablemaskingagentaddedtotheanalytethenthechromagenicagentisaddedasthereference.(2)Choosesuitablereference(3)ControltheabsorbancewithinsuitablerangeatdifferentT,differenterror:

-lgT=εbcdifferent:-dlgT=-0.434dlnT

=-0.434T-1dT

=εbdcdivide:dc/c=(0.434/TlgT)dT

Δc/c=(0.434/TlgT)ΔT

relativeerror(Δc/c)isdecidedbyΔTandT.(3)ControltheabsorbancewitRangeofminimumrelativeerrorIf:ΔT=1%,therelationshipbetweenΔc/candT:WhenΔT=1%,andT

isbetween2%～65%,therelativeerrorislittle.SoTshouldbecontrolledwithinT%=20～65％(A=0.70～0.20).Tofminimumrelativeerror

Tmin=36.8%,Amin=0.434RangeofminimumrelativeerroHowtoimprovesensitivityandselectivity(1)Synthesizechromagenicagentofhighsensitivity(2)Separationandenrichment(3)Multicomplexchromagenicsystem

Onekindofmetalioncomplexwithtwoormoreligandtoformcomplexes.

Multicomplexchromagenicreactionsisofhighsensitivity.Howtoimprovesensit