(5.5)-4.5定量分析方法

4.5QuantitativeAnalysisMethodAtomicabsorptionspectrometrymoduleofAtomicabsorptionspectrometryanalysisAtomicAbsorptionSpectrometry(AAS)isaquantitativeanalysismethodbasedontheabsorptionofground-stateatomstoaspecificspectralline,usuallythecharacteristicspectrallineoftheelementtobemeasured.2.Thebasicstructureandmainfunctionsofatomicabsorptionspectrophotometers:☆Lightsource☆Atomizationsystem☆Spectroscopicsystem☆Checkingsystem☆Computersystem1.FundamentalUndercertainconditions,theconcentrationcinthetestsolutionisproportionaltoN:N＝acK,L,andaareconstants,sothatK'=aK,thenA＝K′Lc

A∝c

A＝KcLightabsorptioncoefficientLightpath:distanceoflighttravelingthroughatomicvaporGroundstateatomicnumberofelementsmeasuredinflamenumberofatomsinthegroundstateofthemeasuredelementintheflameA＝KLacLambert-Beerlawonthebasisofatomicabsorptionquantificationquantitativebasisofatomicabsorption:Lambert-BeerlawQuantitativeAnalysisMethod

Standardcurvemethod:determineabsorbanceAofaseriesofsuitableconcentrationstandardsolution,takeabsorbanceAaslongitudinalcoordinateandconcentrationashorizontalcoordinate,makeastandardworking(A-C)curve,measuretheabsorbanceofsamplesolutionunderthesameexperimentalcondition,andfindouttheconcentrationofthemeasuredcomponentfromstandardcurve.(Interpolation).Itisespeciallysuitablefortheanalysisofsampleswithlargequantityandsimplematrix.ACCxAxONotesonStandardCurveMethod:1.Whenpreparingthestandardsolution,thestandardsampleshouldbeascloseaspossibletothesamplecomposition,andtreatedinthesameway.Ifthepureelementtobemeasuredsolutionforthestandardsolution,inordertoimprovetheaccuracyofthedetermination,canbeputintothequantitativematrixelements,thestandardsolutionandthesamplesolutionwiththesamereagentprocessing.2.Theconcentrationofthestandardsolutionshallbewithinalinearrelationshipbetweenabsorbanceandconcentration.3.Checkwithstandardsolutionbeforeeachdeterminationandmaintainthestabilityofthetestconditions.4.Theblankvalueshouldbededucted,forwhichablanksolutioncanbeusedforzeroing.

Standardaddition:Thisdifficultycanbeovercomebystandardadditionwhentheco-existenceinthetestsolutionisunclearorthematrixiscomplexandthestandardsolutioncannotbepreparedtomatchthesamplecomposition.

1.Calculation:Taketwosamplesolutionsofthesamevolume,setthemasAandB,addacertainamountofstandardsolutionoftheelementstobemeasuredinB,thendiluteAandBtothesamevolumerespectively,andthenmeasuretheirabsorbancerespectively.

SettheconcentrationofelementstobemeasuredinAascxandabsorbanceasAx,theconcentrationofelementstobemeasuredinBascx+c0(c0istheconcentrationofstandardsolutiontobeadded),andabsorbanceasA0,then:

Ax=kcx A0=k(cx+c0)Comparingthetwoforms:：cx=c0×Ax/(A0－Ax)Fromthisformula,thecontentoftheelementtobemeasuredcanbeobtained.

2.Drawing:Themethodofdeterminationistotakeanumberof(notlessthanfour)samplesolutionsofthesamevolume,thenaddstandardsolutionsofC0,2C0,3C0,4C0inorderfromthesecondone,thendilutethemwithdistilledwatertothesamevolumeandshakethemevenly.Underthesameexperimentalconditions,theabsorbanceofeachsolutionwasmeasuredasAx,A1,A2,A3,andA4withtheblankasthereference.TakingabsorbanceAasthelongitudinalcoordinate,theconcentrationofstandardsolution(orthevolumeofstandardsolutiontaken)asthetransversecoordinate,theA-c(ormorV)curveismade,andtheepitaxialcurveintersectswiththetransversesemicircle,whichisthesameconcentrationastheorigin(thescaleofthetransverseextensionlineisthesameasthatoftheright),thatis,theconcentrationoftheelementtobemeasuredinthesamplesolutionbeingtested.FigureStandardadditionmethodWhentheelementMisdeterminedbyatomicabsorptionspectrometry,theabsorbanceofanunknownsampleis0.435,and1ml100µg/mloftheMstandardsolutionisaddedto9mLoftheunknownsolutionTheabsorbancereadingofthismixtureis0.835,CalculatetheconcentrationofMintheunknownsolution(µg/mL)?∴

=9.8µg/mLThePbinthetestsolutionwasdeterminedabsorptionspectrometry,andtwocopiesof50mlofthetestsolutionwereaccuratelypipetted.Theabsorbanceofonetestsolutionwas0.32