This document is applicable to the measurement of the total silicon content in gaseous matrices such as biomethane and biogas. Silicon is present in a gas phase contained predominantly in siloxane compounds, trimethylsilane and trimethylsilanol. The analytical form of the silicon measured in liquid phase after conducted sampling and derivatization procedure is soluble hexafluorosilicate anion stable in slightly acidified media. Total silicon is expressed as a mass of silicon in the volume of the analysed gas. This document is applicable to stated gaseous matrices with silicon concentrations up to 5 mg/m3, and it is prevalently intended for the biomethane matrices containing 0,1 mg/m3 to 0,5 mg/m3 Si. With adaptation to ensure appropriate absorption efficiency, it can be used for higher concentrations. The detection limit of the method is estimated as 0,05 mg/m3 based on a gas sample volume of 0,020 m3. All compounds present in the gas phase are volatile at the absorption and derivatization temperature and gaseous siloxanes are trapped in absorbance media and derivatized into analytical silicon that is measured by this method. The concentration of the silicon is measured in diluted derivatization media using atomic emission spectrometry upon atomisation/ionisation in microwave or inductively coupled plasma. Unless specified otherwise, all volumes and concentrations refer to normal conditions. NOTE When using appropriate dilution factors, the method can also be applied for silicon concentrations above 5 mg/m3.