Simultaneous Determination of Total Hydrocarbon and Non-Methane Total Hydrocarbon in Ambient Air by Gas Chromatography with Double Columns and Double FIDs

A method for determination of the content of total hydrocarbon and non-methane total hydrocarbon in ambient air by gas chromatography with double columns and double FIDs was established. The samples in the glass syringe, with storage time as less than 4 h as possible, was introduced into the gas chromatograph by the 10-valve with two quantitative rings. Total hydrocarbon and methane were separated by the 2 packed columns, and nitrogen was adopted as carrier with flow-rates of 25, 20 mL·min^-1, respectively. The qualitative analysis of total hydrocarbon and methane were made by retention time of gas sample passing through the total hydrocarbon column and methane column, with retention time of 0.120 min and 0.404 min, and the quantitative analysis was carried out based on total hydrocarbon peak area deducting the oxygen peak area and methane peak area respectively. It was shown by results that the mole ratios between total hydrocarbon and nitrogen and methane and nitrogen had a linear relationship in the range of 0.5-10.0 μmol·mol^-1 with their respective peak areas, with detection limits (3.143s) of total hydrocarbon, methane and non-methane total hydrocarbon of 0.025, 0.031, 0.031 mg·m^-3 respectively. Test for recovery was made at 3 concentration levels, and results of recovery of total hydrocarbon and methane were ranged of 99.8%-104% and 99.7%-103%, with RSDs (n=6) in the range of 1.3%-5.6% and 1.0%-5.1%, respectively. The above method was used to determine the content of total hydrocarbon and methane in samples from two sampling points, and the determined values of non-methane total hydrocarbon were both lower than 1.0 mg·m^-3, giving values of recovery in the range of 102%-105% and 107%-109%, and RSDs (n=5) of the measured values found were ranged from 1.1% to 1.7% and 1.8% to 1.9%, respectively.