Fast determination of methyl chloride and methyl bromide emissions from dried plant matter and soil samples using HS-SPME and GC-MS: method and first results

Headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC/MS) system have been employed for quantifying the emissions of methyl chloride (CH(3)Cl) and methyl bromide (CH(3)Br) from plants and soils. Seven SPME fibre coatings including 75 mu m Carboxen-polydimethylsiloxane (CAR-PDMS), 85 mu m Carboxen-PDMS (CAR-PDMS), 50/30 mu m divinylbenzene-CAR-PDMS (DVB-CAR-PDMS), 65 mu m DVB-PDMS, 65 mu m carbowax-DVB (CW-DVB), 30 mu m PDMS (PDMS) and 100 mu m PDMS, were tested by comparing their sampling efficiencies towards CH(3)Cl and CH(3)Br. Key parameters such as extraction time, desorption temperature and time were all optimised in this work. The optimum conditions were found with CAR-PDMS 75 mu m as an SPME fibre coating, a 1-min sampling time, a 50 degrees C incubation temperature and a 2-min desorption time and a 250 degrees C desorption temperature. These conditions were used for the determination of CH(3)Cl and CH(3)Br emission rates from different plant species as well as soil samples. Compared with more commonly used techniques, HS-SPME coupled to GC/MS is simple, fast, sensitive, economical and non-destructive, with potential for laboratory-based and field studies.