Discussion on Methane Total Hydrocarbons and Non-Methane Hydrocarbons in Ambient Air Monitoring and Methods of Analysis

Methane (CH₄) and non-methane total hydrocarbons (NMHC) in gas samples are analyzed simultaneously by gas chromatography. A six-way valve to inject the sample, double capillary columns, and double FIDs are used. With one injection the analytical data of CH₄, total hydrocarbons, and non-methane total hydrocarbons can be obtained. A reasonable explanation for the oxygen peak appeared in the GC with FID detector is given, which can be preliminary identified as"the interference peak", and can be negligible in the analysis. The method detection limit of CH₄, total hydrocarbons, NMHC were 0.03 mg/m³, 0.04 mg/m³ and 0.06 mg/m³. The coefficients of variation of CH₄, total hydrocarbons, NMHC were 3.81%, 2.07% and 5.07%. The recoveries of spiked compounds of CH₄, NHMC were 96.1%, 96.1%~ 98%.