An improved chromatographic method to measure nitrogen, oxygen, argon and methane in gas or liquid samples

An improved gas chromatographic method for measuring dinitrogen (N2), oxygen (O2), argon (Ar) and methane (CH4) in gas or liquid samples has been developed. By employing a zeolite, calcium chabazite, as column packing material, optimum separation of O2 and Ar was achieved at 303 K with a carrier gas flow rate of 33.5 ml min−1. Dinitrogen and CH4 were eluted at slightly higher column temperatures of 363 and 438 K, respectively. The coefficients of variation (CV, %) for the various gases in liquid (˜ 1% air) and gas (10% air) standards were: N2 = 0.48–0.82, O2 = 0.50–0.76, Ar = 0.50–0.76 and CH4 = 0.23. The contamination of liquid samples by air bubbles was easily corrected by using Ar as an internal standard. The small amount of sample required (2 ml), the short analysis time (12 min) and the high resolution data obtained makes this method ideal for a variety of applications, including the study of dissolved gas biogeochemistry in ground water, the water column or in sediments. To evaluate the performance of the system, sediment incubation experiments were performed. Rates of aerobic respiration (3.6–33 mmol m−2 d−1), denitrification (0.21–4.5 mmol m−2 d−1) and methanogenesis (5.5–10 mmol m−2 d−1) were easily quantified using this approach.