Fig. 3.

Gas chromatograms of ¹⁵N-N₂ produced in the B. japonicum USDA110 culture cultivated under denitrifying conditions in the presence of 2 mM ¹⁵NO₃⁻ (B), 2 mM ¹⁴NO₃⁻ (C), or 2 mM ¹⁴NO₃⁻ and 6 mM ¹⁵NH₄Cl (D). (A) To identify the position of ³⁰N₂ elution, a gas mixture of 4% ³⁰N₂, 21% O₂, and 5% Ar was analyzed. The arrowhead indicates the position of a ¹⁵N-N₂ peak. The retention time of the ³⁰N₂ peak was slightly longer than that seen in a previous analysis of TCD gas chromatography (Fig. 1), probably because the flow rate of N₂ gas was slightly reduced compared to the value of 30 ml/min obtained earlier. O₂ was partially coeluted with Ar and showed a peak in the minus direction at a retention time of about 1.8 min, because the gas contained as much as 21% of O₂. Gas samples (1 ml) were injected into the TCD GC with a Molecular Sieve 5A column and N₂ as a carrier gas.