This part of ISO6978 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 0,01µg/m 3 to 100µg/m 3 in natural gas samples. At higher pressures (up to 8MPa), this sampling method is suitable for the determination of mercury contents within the range of 0,001µg/m 3 to 1µg/m 3. The collected mercury is determined by measuring the absorbance or fluorescence of mercury vapour at 253,7nm. NOTE ISO6978‑1 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 0,1µg/m 3 to 5000µg/m 3 for sampling at pressures up to 40MPa.