An experimental approach for the development of direct-absorption sampling method for determination of trimethylsilanol and volatile methylsiloxanes by the GC-MS technique in landfill gas

This paper reports on an absorption method used for the determination of six target volatile methylsiloxanes and trimethylsilanol existing in raw biogas samples by means of a special and portable sampling train system. After biogas sampling (no accurate pump needed), the samples obtained were analysed by gas chromatography-mass spectrometry (GC-MS). The optimisation of the used solvent was carried out, and acetone was selected as the preferred liquid medium for trapping the siloxanes. The results clearly showed that using pure acetone and a mixture of acetone and water (97/3% = v/v) ensures very good solvation of silicon-contained molecules; thus the sampling procedure was more accurate. Replicate samples showed that the relative standard deviation of the method was less than 5.7% and 6.3% for methylsiloxanes as well as less than 2.1% and 2.4% for trimethylsilanol analysed 24 and 72 hours after sampling, respectively. Furthermore, limits of detection were determined theoretically and experimentally. The limits of detection for siloxanes and trimethylsilanol were in the range 0.04–0.11 mg/Nm³ and 0.08–0.12 mg/Nm³, respectively. The limit of quantification for trimethylsilanol was 0.1 mg/Nm³, whereas the limit for siloxanes ranged from 0.1 to 0.13 mg/Nm³. Finally, raw biogas samples were successfully analysed by the developed method. Trimethylsilanol and methylsiloxanes were found in the concentrations of 34.5 mg/Nm³ and 1.7–20 mg/Nm³ in the analysed raw biogas, respectively.