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INTRODUCTIONTOMEASUREMENTSSKOOG‘N’HOLLERCH1

CHEM314

TUESDAY,JANUARY19

DUE:UNGRADEDWRITINGASSESSMENT

LECTURETOPIC:INTRODUCTIONTOMEASUREMENTS

READING:CH1,MYTHANDREALITYOFSTANDARDADDITION

OBJECTIVES•  Introducesimplifieddiagramofaninstrument:source,sample,phenomena,

detector

•  Discussdatadomains

•  Discussthenecessityofcalibra:on

•  Comparetherela:vemeritsofcalibra:oncurve,standardaddi:on,andinternalstandardmethods

•  Discusscriteriathatcanhelpinselec:onofanaly:caltechnique

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Wetchemistry

InstrumentaPon

SeparaPonàCharacterizaPonàGravimetricVolumetric

AnalysisColors

MelPngpointBoilingpointSolubilityOdor

OpPcalproperPes

DisPllaPonPrecipitaPonExtracPon

CLASSICMEASUREMENTS

AdvancesininstrumentaPonmeanswecanstudymorecomplex

phenomena

HOWAREMEASUREMENTSMADE?

Spectroscopy

Electrical

Chromatographymayalsobeappliedtoisolateaspecificanalyteinamixture.CombinewiththeuseoftheotherinstrumentsfordetecPon

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Chromatographymayalsobeappliedtoisolateaspecificanalyteinamixture.CombinewiththeuseoftheaboveinstrumentsfordetecPon

INSTRUMENTALMEASUREMENTSARESIMPLE

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DATADOMAINSFormsofdataencodingBroadly:ElectricalandNonelectrical

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NONELECTRICALDOMAIN

Whereameasurementstartsandends

Startwithphenomena:fluorescenceofquinineEndwith:quanPtyofquinine

NONELECTRICALDOMAIN

Whereameasurementstartsandends

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hbp://www.tradeget.com www.amazon.com www.comicvine.com

NONELECTRICALDOMAIN

WhereameasurementstartsandendsMeasurementscanremaincompletelyinnonelectricaldomain

nonelectrical electrical nonelectrical

NONELECTRICALDOMAINWhereameasurementstartsandendsMeasurementscanremaincompletelyinnonelectricaldomainMostmeasurementsgothroughtheelectricaldomain

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ELECTRICALDOMAIN

AnalogDigitalTime

www.delcity.net hbp://commons.wikimedia.orgwww.radioshack.com

ANALOGSIGNALSConPnuousinamplitudeandPme.

Magnitudeofvoltage,current,charge,orpower

ParPcularlysuscepPbletoelectricalnoise.

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TIMEDOMAINInformaPonstoredinPmedomain.Variablesofinterest:Frequency-cyclesofsignalperunitPmePeriod-PmebetweensuccessiveLOàHItransiPonsPulsewidth-PmebetweenLOàHIandHIàLOtransiPonsAmplitudeimportantonlyrelaPvetoHI/LOthreshold

TIMEDOMAINInformaPonstoredinPmedomain.VariablefrequencySignaliseitherhighorlowrelaPvetothearbitraryLimit(dashedline)Timerela:onshipsareinforma:onofinterest

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ELECTRICALDIGITALDATAEncodedusingatwostatesystemCanonlybeeninoneoftwostates:HIorLOOnoroff1or0Eachpieceofdataisabit(binarydigit)

DIGITALDATABothnonelectricalandelectricaldatacanbeconveyedusingnumbersAnynumericaldataisdigital

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MAKINGMEASUREMENTSCanbeconvertedbetweenseveraldomainsinthecourseofmakingameasurement.

SELECTINGANANALYTICALMETHOD

SKOOG‘N’HOLLERCH1CHEM314

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DEFININGTHEPROBLEM1.  Whataccuracyisrequired?2.  Howmuchsampleisavailable?3.  WhatistheconcentraPonrangeoftheanalyte?4.  WhatarepotenPalinterferes?5.  WhatarethephysicochemicalproperPesofthesample

matrix?6.  Howmanysamplesrequireanalysis?

SELECTINGANANALYTICALMETHOD

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SELECTINGANANALYTICALMETHOD

5.DYNAMICRANGE

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SELECTINGANANALYTICALMETHOD

CALIBRATIONSKOOG‘N’HOLLERCH1

CHEM314

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METHODSOFCALIBRATION•  Directcomparison

TitraPons•  Internalstandards•  ExternalcalibraPon-Preparedseparatefromthesample

Leastsquaresmethod(calibraPoncurve) StandardaddiPon

DIRECTCOMPARISON

DirectcomparisonTitraPons

hbp://minisite.proj.hkedcity.nethbp://community.asdlib.org

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INTERNALSTANDARDSCanaccountforrandomandsystemaPcerrors

•  Addeduniformlytoallsamples,blanks,andstandards•  Oramajorcomponentofsamplesassumedtobepresent

inconsistentamountsinallsamplesAccountsforfluctuaPonsininstrumentsandmethodsExamples:LossesduringsamplepreparaPonVariaPoninflowrateduringseparaPonsPlotraPoofsignalfromsampleandinternalstandard

INTERNALSTANDARDSPlotraPoofsignalfromsampleandinternalstandard

F=responsefactor

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INTERNALSTANDARDS-ASSUMPTIONSANDISSUES•  AssumesignalraPobetweensampleandInternal

standardisconstant•  Assumeinternalstandardisnotpresentin

samples(oristhesameinall)

•  DifficulttoidenPfyasuitableinternalstandard-similarbutdifferenttoanalyte

•  Difficulttointroducetheinternalstandardconsistentlytosamplesandstandards

EXTERNALCALIBRATION-CALIBRATIONCURVESUsedto:CalibrateinstrumentsVerifyproceduresLeastsquaresmethodAssumpPons:1.  ThereisalinearrelaPonshipbetweeninstrumentresponseandanalyteconcentraPon.2.AnydeviaPonarisesfromerrorinthemeasurement

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CALIBRATIONCURVESSeekstominimizethesquareoftheresidual.

Sx=uncertaintyinxSy=uncertaintyinym=slopek=numberrepsinsamplesn=thenumberofstandards

EXTERNALCALIBRATION-ISSUES&ASSUMPTIONS•  AssumethesameconcentraPongivesthesamesignal

•  Signal=rawcountsvsblankcounts

•  Nomatrixeffects

•  AssumeuniformexperimentalcondiPons

•  AssumenosystemaPcerrorsduringcalibraPon

•  ProblemsiftoofewstandardsforgoodstaPsPcs

•  PotenPalissueswithconcentraPonsatendsofcalcurve

•  PotenPalissueswithrandomerror

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ERRORINCONCENTRATIONMEASUREMENTS

STANDARDADDITIONUsedtowhensamplematrixiscomplex

Addstandardtothesample

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STANDARDADDITION-ISSUES&ASSUMPTIONS•  OnlyaddressesrotaPonalmatrixeffects

RotaPonal TranslaPonal

STANDARDADDITION-ISSUES&ASSUMPTIONS•  OnlyaddressesrotaPonalmatrixeffects

TranslaPonalissuesmustbedealtwithseparately

•  InherentlylessprecisethanexternalcalibraPon

involvesextrapolaPon

Buteffectsarenegligible

•  BestresultsachievedifQandKarehigh

K=mulPpleforstandarddeviaPonoftheblank

Q=amountofstandardaddedrelaPvetoconcentraPoninsample

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ACASEFORREPEATEDMEASUREMENTSATASINGLESPIKETypicalSt.Addplot

Abebermethod?

RECOMMENDATIONSFOREXECUTINGST.ADD.1.  DeterminelinearrangeofanalyPcalsystem2.  DealwithtranslaPonalinterferencesseparately3.  Usereplicatemeasurementsofonespike

concentraPon4.  LettheconcentraPonofspikeaddedtobehigh.

4xtheconcentraPoninsoluPonifpossible

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YOURTASK:QUANTIFYRED#40INASODA1.  Planexperiment•  MakepreliminaryUV-Vismeasurementsofstockand

soda•  CalculateconcentraPonofstock•  DoyouneedacalibraPoncurve?•  Howmanyspikesdoyouneed?•  DecideonadiluPonscheme

2.  Performexperiments•  CompareavailableUV-Visinstruments•  ArerotaPonalmatrixeffectsapparent?•  EsPmateerrorassociatedwitheachresult