Modification of GasBench-IRMS for Automatic Determination of Nitrogen Stable Isotope Ratio in N₂O at Natural Abundance

GasBench was modified to determinate nitrogen stable isotope ratio in N₂O at atmospheric concentration automatically. For purifying and concentrating N₂O at atmospheric, a pre-concentration device was added. The chemical trap, two cold traps and the eight-way valve were involved. Meanwhile, the sample vials and their matching sample panes were replaced to increase the sample injection. Parameters such as test conditions, collection and concentration time were optimized, and the linearity, stability and method validation were also evaluated. The results suggested that after the modification, the linearity of the system was good, the value of δ¹⁵N_Air did not change a lot when the ion intensity was at the range of 280-3000 mV; the δ¹⁵N_Air values of the modified system was stable (S.D<0.04‰) under different pressure conditions. A standard sample gas of 400 mg/L N₂O were prepared and its average value of δ¹⁵N_Air was 7.253‰, close to the standard value of the standard gas, which indicated that the method had good accuracy, and could be used to determine the nitrogen isotope ratio of N₂O at atmospheric concentration.