This part of ISO 6978 specifies af 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 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. NOTE ISO 6978-1 gives a sampling method suitable for the determination of mercury contents in natural gas by chemisorption on iodine-impregnated silica gel for the working range of 0,1 µg/m3 to 5000 µg/m3 for sampling at pressures up to 40 Mpa.