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1、2TheoryofSolid-PhaseMicroextractionJanuszPawliszynDepartmentofChemistry,UniversityofWaterloo,Waterloo,Ontario,Canada2.1IntroductionAnunderstandingofsolid-phasemicroextraction(SPME)theoryprovidesinsightanddirectionwhendevelopingmethodsandidentifiesparametersforrigorouscon-trolandoptimisation.Effe
2、ctiveuseofthetheoryminimisesthenumberofexperi-mentsthatneedtobeperformed.ThetheoryhasbeendevelopedtounderstandtheprincipalprocessesinvolvedinSPMEbyapplyingbasicfundamentalsofthermody-namicsandmasstransfer.Tosimplifymathematicalrelationships,discussionoftheSPMEtheoryassumesidealconditions.Thetheo
3、ryforidealextractionconditionscanbeveryaccuratefortraceconcentrationsinsimplematriceslikeairordrinkingwateratambientconditions,whensecondaryfactors,suchasthermalexpansionofpolymers,changesindiffusioncoefficientsduetothepresenceofsolutesinpolymersandheterogeneityofthematrix,canbeneglected.Whencon
4、ditionsaremorecom-plex,thetheoryforidealcasesstillapproximateswellsomeoftheparametersandgeneralrelationshipsbetweenparametersandextractiontimesoramountsextracted.Inthischapter,wedescribeboththethermodynamicsandthekineticsoftheextrac-tionprocess.Theamountofanalyteextractedatequilibriumconditionsc
5、anbecalcu-latedusingthermodynamicprinciples,whiletheextractiontimecanbeestimatedbysolvingdifferentialequationsdescribingmasstransferconditionsinthesystem.ThreebasicextractionmodescanbeperformedusingSPME:adirectextraction,aheadspaceextractionandanextractioninvolvingmembraneprotection.Figure2.1ill
6、ustratesthedifferencesamongthesemodes.Inthedirectextractionmode(Figure2.1A),thecoatedfibreisinsertedintothesampleandtheanalytesaretransporteddirectlyfromthesamplematrixtotheextractingphase.Tofacilitaterapidextraction,somelevelofagitationisrequiredtoincreasethetransportofanalytesfromthebulkofthes
7、olutiontothevicinityofthefibre.Forgaseoussamples,naturalconvectionofairissufficienttofacilitaterapidequilibra-tion.Foraqueousmatrices,moreefficientagitationtechniquessuchasfastsample1,2flow,rapidfibreorvialmovementandstirrin
