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Reaction of Nitric Oxide with Acetylene and Oxygen: Implications for Denitrification Assays

Dep. of Chemistry and Biochemistry, Univ. of Windsor, Windsor, ON, Canada N9B 3P4

C. F. Drury

Agriculture and Agri-Food Canada, Greenhouse and Processing Crops Research Centre, Harrow, ON, Canada N0R 1G0

*Corresponding author (dmcken{at}uwindsor.ca).

ABSTRACT

Nitric oxide reacts with C₂H₂ at ambient temperature under aerobic conditions with relatively large quantities of O₂ present. We used a gas-flow system at 20°C to determine the extent, if any, of reaction of NO with C₂H₂ under nearly anaerobic conditions with addition of trace (<500 µL L^–1) quantities of O₂, and to determine whether the process could account for the apparent C₂H₂ inhibition of NO production in soil. Results showed that reaction occurred only when critical trace quantities of O₂ were present. For example, if [NO] was in the range 0.5 to 2.5 µL L^–1, which is typical of concentrations in our soil studies, approximately 200 to 300 µL O₂ L^–1 was required before measurable NO loss was observed. The reaction was first order with respect to NO and variable order, becoming zero order, with respect to O₂ when [O₂] exceeded 400 µL L^–1 and maximum NO depletion rates (0.01–0.06 µL L^–1 s^–1) were obtained. The effect of C₂H₂ on NO production with addition of O₂ (20–730 µL L^–1) in Brookston clay loam (fine-loamy, mixed, mesic Typic Argiaquoll) and Fox sandy loam (fine-loamy over sandy or sandy-skeletal, mixed, mesic Typic Hapludalf) under conditions similar to the gas-phase studies was also investigated. Depletion of NO in the presence of C₂H₂ vs. [O₂] followed the same pattern with similar rates as the gasphase process. A simplified C₂H₂-catalyzed scheme for the oxidation of NO to NO₂ provides a plausible, partial explanation for these results. Since NO depletion requires only trace amounts of O₂, the results suggest that in many previous studies involving assays of NO or N₂O production based on C₂H₂ inhibition, significant gas-phase reaction may have occurred leading to serious errors of interpretation.

Received for publication August 16, 1996.

This article has been cited by other articles:

				D.J. McKenney, C.F. Drury, and S.W. Wang Effects of Oxygen on Denitrification Inhibition, Repression, and Derepression in Soil Columns Soil Sci. Soc. Am. J., January 1, 2001; 65(1): 126 - 132. [Abstract] [Full Text]