CAC GL 56-2005GUIDELINES ON THE USE OF MASS SPECTROMETRY

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1、CAC/GL56-2005Page1of6GUIDELINESONTHEUSEOFMASSSPECTROMETRY(MS)FORIDENTIFICATION,CONFIRMATIONANDQUANTITATIVEDETERMINATIONOFRESIDUESCAC/GL56-2005CONFIRMATORYTESTSWhenanalysesareperformedformonitoringorenforcementpurposes,itisparticularlyimportantthatconfirmatorydataa

2、regeneratedbeforereportingonsamplescontainingresiduesofpesticidesthatarenotnormallyassociatedwiththatcommodity,orwhereMRLsappeartohavebeenexceeded.Samplesmaycontaininterferingchemicalsthatmaybemisidentifiedaspesticides.Examplesingaschromatographyincludetheresponse

3、sofelectron-capturedetectorstophthalateestersandofphosphorus-selectivedetectorstocompoundscontainingsulphurandnitrogen.Analysisofpesticideresidueswithmulti-residuemethodsgenerallyconsistsoftwophases:screeningandconfirmation.TheprocessisschematicallydepictedinFig.2

4、.Thefirstphasecomprisesestablishmentofthosepesticideresiduesthatarelikelytobepresentfrominterpretingtherawdata,avoidingfalsenegativesasmuchaspossible.Thesecondphaseistheconfirmation,whichfocusesonthepesticidesfoundinphase1.Theuseoftheresultstobereported,andconsequ

5、entmanagementdecisiondeterminestheeffortsputintheconfirmatoryprocess.Thechoiceofthetechniqueusedforconfirmationdependsontheiravailability,timeandcost.Theyarebasedoneitherfurtherinterpretationofchromatographicandmassspectrometricdata,alternativemethodsusingdifferen

6、tphysico-chemicalpropertiesofthecompound,oracombinationofvariousseparationanddetectionmethods.SomealternativeproceduresforconfirmationaregiveninTable6.Wheneverchromatographictechniquesareusedinscreeningorconfirmation,propersettingsoftheretentiontimewindowsispivota

7、l.Careshouldbetakenthattheinstrumentisadjustedcorrectlybeforestartingthe1analysis;asystemsuitabilitytestshouldbeperformedpriortoeachbatchofanalysis.Retentiontimesdata2baseshouldbeadjustedforthecurrentconditions.Inphase1,toleranceintervalsof1.5to3%oftheabsoluterete

8、ntiontimemaybeappliedforcapillaryGCdependingonthepeakshape.Forconfirmationoftheretentiontime,theabsolutetoleranceintervalswillincreaseathigherretentiont