One of the problems that encounter most biogas plants is the fouling that takes place due to the poor quality of biogas utilised for energy purposes. In such a situation it is necessary to measure and control concentrations of main and hazardous components in a biogas. Indeed, the purification systems become a crucial elements of operational plants. In the presented work the analytical procedures and standardisation of analytical methods for determination of main biogas components: trimethylsilanol, volatile methylsiloxanes, volatile organic compounds, oil mist, and halogenated components originating in biogas were developed. For this, gas chromatography has been coupled with various kinds of detection methods i.e. electron capture, thermal conductivity, flame ionization, and mass spectrometry. Furthermore, the sampling procedure based on direct biogas absorption allowed to exclude the extraction process. Consequently, the time of analysis was significantly reduced. The field study showed clearly, that concentration of siloxanes in analysed samples was determined in the range from 20.6 to 361.8 mg/N m(3). Therefore, the impact of biogas silica-contaminants on a running gas-motor was explained and extensively discussed. VMSs and TMSOH concentrations were recalculated and expressed in toluene equivalent, as well as the interpretation of obtained data was provided. Although, we have successfully proven, that the toluene equivalent (T-eq) is not an appropriate differentiating factor for siloxanes concentration, although the content of TMSOH might be expressed as T-eq. The promising results obtained in this study indicate that this novel sampling procedure, and the standardisation of analytical routines can become a promising approach to accomplish the procedure of biofuel analysis. (C) 2013 Elsevier Ltd. All rights reserved.