This part of ISO 6978 specifies a method for the determination of total mercury content of pipeline quality natural gas using a sampling method by amalgamation on gold/platinum (Au/Pt) alloy thread. This method is applicable to the sampling of raw natural gas when no condensation is present. At atmospheric pressure, this method is suitable for the determination of mercury content within the range of 0,01 µg/m3 to 100 µg/m3 in natural gas samples. At higher pressures (up to 8 MPa), this sampling method is suitable for the determination of mercury contents within the range of 0,001 µg/m3 to 1 µg/m3. The collected mercury is determined by measuring the absorbance or fluorescence of mercury vapour at 253,7 nm.