INJECTORS
Purge & Trap
Carryover isaslight contaminationof thepurgeand trapsystembyanalytes (especiallyhighboiling
components),and isanormalconditionofoperation. Allpurgeand trapsystemsexhibitsomecarryover. An
organicfreereagentwaterblank isanalyzedaftersampleruns todetermine thecarryover level,asshownon
the
Expectedperformance
page. MostregulatoryQualityControlrequirementsallowcarryover that iseither
less than theMinimumDetectableLimit (MDL)or less than10%of thereportedanalyteconcentration. For
example, if thereportedanalyteconcentration is100ppb, then10ppb isacceptablecarryover. If thecarryover
isgreater thananacceptable level,subsequentwaterblanksarerununtil thecarryover issufficiently low,or
until theuserhasdetermined that there issystemcontamination thatrequiresfurthercleaning.
Carryover
Troubleshooting and Maintenance
Mostcarryoverproblemsoccurwhileanalyzingsamplesofunknownconcentration. Because theuser
cannotassume therewillbenocarryover in this typeofanalyticalsituation,acleanwaterblankshouldberun
betweeneachsampleanalysis toensure thatcarryoverwillnotaffect subsequent sampleanalyses. Avoid
carryovercontaminationproblemsbyscreeningyoursamplesprior topurgeand trapGCanalysis. SW-846
contains twoappropriatescreening techniques:
♦
Method5021, inwhichanautomatedheadspacesampler isusedwithaPIDandDELCD
equippedGC
♦
Method3820, inwhichahexadecaneextractionof thesample isanalyzedbyaFIDand/
orECDequippedGC.
Segregate thescreenedsamplesaccording toconcentration, thenrun thehighlyconcentratedonesfirst.
Clean thepurgeand trapsystemafter thehighconcentrationsampleshavebeen run, thenanalyze the low
concentrationsamples.
The10ppbBTEXsampleanalysisresulted inaPIDToluenepeakwithanareacountofapproximately
353. ThewaterblankanalysisshowsaPIDToluenepeakwithanareacountofapproximately4. Since the
carryoverofToluene is less than10%or0.5ppb, subsequentanalysesmayberesumed.
Thecarryover levelof the10ppbBTEXsampleon the
Expectedperformance
pagewasdeterminedby
comparing theareasof theresultingPIDToluenepeaks,where
x
is theppbconcentrationof thecarryover:
