Formation of artefacts during air analysis of volatile amines by solid-phase micro extraction

Solid-phase micro extraction (SPME) is a promising technique for fast and l ow cost trace analysis. However, some limitations of the technique were enc ountered when using a PDMS (polydimethylsiloxane)/Carboxen fibre for sampli ng a mixture of volatile aliphatic amines in air. On the GC chromatogram, t wo supplementary peaks were noticed in addition to the analyte peaks, thus limiting qualitative and quantitative analysis in this particular case. Thi s paper presents the investigations to identify the artefacts and determine the origin of their formation. First, GC-MS identification, by both electr on impact and chemical ionisation modes, demonstrated that the two artefact s were unsaturated amines assumed to be formed by a dehydrogenation reactio n of the target amines. This reaction was found to occur during thermal des orption of analytes in the GC injection port and to be catalysed by tempera ture and by metals consisting of the inox (stainless-steel) needle of the S PME device. It was also demonstrated that artefact formation was not signif icant when using PDMS or PDMS/divinylbenzene fibres. This difference with P DMS/Carboxen fibre can be explained by the high desorption temperature requ ired for this fibre. Moreover, the microporosity of Carboxen induces a long er desorption time which increases the contact between analytes and inox an d thereby enhances artefact formation.