ISO 6974-3:2018 describes a gas chromatographic method for the quantitative determination of the content of helium, hydrogen, oxygen, nitrogen, carbon dioxide and C₁ to C₈ hydrocarbons in natural gas samples using twopacked columns. This method is applicable to determinations made in on-line processes or in the laboratory. It is applicable to the analysis of gases containing constituents within the mole fraction ranges given in Table 1 and which do not contain any hydrocarbon condensate. These ranges do not represent the limits of detection, but the limits within which the stated precision of the method applies. Although one or more components in a sample may not be detected present, the method can still be applicable.

This part of ISO 6974 is only applicable in conjunction with parts 1 and 2 of ISO 6974.