Environmental context. Headspace solid-phase microextraction (HS-SPME) and analysis by gas chromatography–mass spectrometry (GC/MS) system has been employed for quantifying the emissions of methyl chloride (CH₃Cl) and methyl bromide (CH₃Br) from plants and soils. 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.

Abstract. Headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC/MS) system have been employed for quantifying the emissions of methyl chloride (CH₃Cl) and methyl bromide (CH₃Br) from plants and soils. Seven SPME fibre coatings including 75 μm Carboxen-polydimethylsiloxane (CAR-PDMS), 85 μm Carboxen-PDMS (CAR-PDMS), 50/30 μm divinylbenzene-CAR-PDMS (DVB-CAR-PDMS), 65 μm DVB-PDMS, 65 μm carbowax-DVB (CW-DVB), 30 μm PDMS (PDMS) and 100 μm PDMS, were tested by comparing their sampling efficiencies towards CH₃Cl and CH₃Br. 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 μm as an SPME fibre coating, a 1-min sampling time, a 50°C incubation temperature and a 2-min desorption time and a 250°C desorption temperature. These conditions were used for the determination of CH₃Cl and CH₃Br 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.