Technicalnoteno.AS131

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DeterminationofAcetaldehydeinWaterfromPlasticBottlesUsingHotInjectionTrapping(HIT)TechniqueonGC-MS

DanCarrier&AnaïsMaury,AnatuneLtd.,Girton,Cambridgeshire(UK).

Introduction

Acetaldehydeisavolatile,colourlessliquidwithahighfruityodour.Itiscommonlyusedasintermediateinthemanufactureofsomeindustrialchemicals.Itisusedassolventintherubber,tanningandpaperindustry,andasapreservativeforfruitsandfish.Itisalsousedasflavouring.Acetaldehydeisknowntoreactwithmanypartsofthehumanbody.Itcausesirritationoftherespiratorytractandhasbeenclassified as possibly carcinogenic to humans by the International Agency forResearchonCancer.

Withinthisapplicationnote,weshowhowHotInjectionTrapping(HIT)canbefullyautomatedtoenrichacetaldehydefromwatersamplesusingastaticheadspacetechnique. The HIT technique enables the trapping of multiple headspaceinjectionsfromthesamesampleonacoldinletandconsequentlyimproveslimitsofdetection(LODs).

Figure1–GERSTELSingleHeadMPSwithGC/MSSingleQuadrupole

Figure2showsamoredetailedphotographoftheinletandtheheadspaceunit.Theheadisconfiguredwitha2.5mlheadspacesyringeandinjectsinaTDUtubewithatransportadaptorforliquidinjection.

Figure2–DetailphotographofaHITInjection

Instrumentation

AgilentGC7890AandAgilentMSD5975CinertwithEIsourceGERSTELMPS2XL-xtGERSTELCIS4,TDU&HeadspacekitAgilentMSDChemstationsoftware(versionE.02.02.1431)Maestrosoftwareintegrated(version1.4.18.25/3.5)

Method

HeadspaceParameters:Incubationat70°Cfor30minutesSampling5x2mlofheadspaceGC-MSParameters:TDUholdat150°CCIS4(TexaxLiner):-40°Crampedto250°CColumn:DB-WAX30mx0.25mmx0.5µmThermalgradient:40°C(4minutes);10°C/minto100°CMS: EI source,SIMperformedusing ions29 (Acetaldehyde)and43 (EthylAcetate,usedasinternalstandard)

Technicalnoteno.AS131

HotInjectionTrapping(HIT)Procedure:TheHeadspacesyringe,containingtheheadspaceextract, is insertedintotheTDUwhich iskeptheatedat150°Ctopreventcoldspotswheretheanalytesmightbeadsorbed.TheanalytesaretrappedintheTenaxpackedCIS4linerat-40°C, enabling theuseofmultiple injections: 5 injectionsof 2mlheadspaceextracts.

An eight-point calibration for Acetaldehyde was prepared in water atconcentrationsrangingfrom1µg/lto10µg/l,keepingEthylAcetate(usedasaninternalstandard)consistentat50µg/l.

Results

Below (Figure 3) shows the calibration plot for Acetaldehyde in water,corrected by internal standard. A correlation coefficient of 0.999 wasachieved.

Figure3–LinearityplotofAcetaldehydeinwaterFigure4showsacomparisonbetweenablankandAcetaldehydeat10µg/l.

Figure4–SIMchromatogram(ion29)comparisonofablankandthecalibrationlevel4inwater(Acetaldehyde10µg/l)Figure5showsacomparisonbetweenaHITperformedonce(oneinjectionof2mlheadspaceextract)andaHITperformed4times(4x2mlheadspaceextract).Thesensitivityisproportionallyincreased.

Figure5–SIMchromatogram(ion29)comparisonofHITperformedonceandHITperformed4timesReproducibilityexperimentshavebeencarriedouton4aliquotsofwaterspikedat5µg/land thecorrelationcoefficient (correctedwith internal standard)hasbeencalculatedtobe2%.

Water samples from plastic bottleswere analysed using thismethod andacetaldehydelevelswererecordedandresultsweregiventoourcustomer.Table1showsthisreproducibilitydata.

Acetaldehyde

Amountspiked(µg/l) 5.0000Amountdetected(µg/l) 4.8338

4.8827 4.8476 5.0706

Mean(µg/l) 4.9087D 0.1099

%CV 2.24Table1:ReproducibilityforAcetaldehydeinwaterusingHITHeadspaceTechnique

Discussion

This application note shows how the Hot Injection Trapping (HIT) techniqueenablesthequantificationofAcetaldehydepresentinwaterdownto1µg/l.

Furtherworkisduetobecompletedonrealsamplesfromavarietyofsources,to establish method robustness and variability. Additionally, recovery andprecisioninthese“real”sampleswillbedeterminedviastandardaddition.