This document describes a Gas Chromatography Ion Mobility Spectroscopy (GC-IMS) method for the determination of the concentration of siloxanes in biomethane. The method is applicable to the following siloxanes: hexamethyldisiloxane (L2) octamethyltrisiloxane (L3) decamethyltetrasiloxane (L4) dodecamethylpentasiloxane (L5) hexamethylcyclotrisiloxane (D3) octamethylcyclotetrasiloxane (D4) octamethylcyclotetrasiloxane (D5) dodecamethylcyclohexasiloxane (D6) This document describes suitable calibration and measurement strategies to quantify siloxanes in (bio) methane around and above the 0,3 mg m-3 (14 ¼mol mol-1) level and applies to analysis within absolute pressure ranges of 1 bar 2 bar, temperatures of 0 °C 40 °C and relative humidity < 90 %.