Sodium azide interference in chemical and biological testing

This paper discusses the results of sodium azide interference encountered during lab-scale studies in which sodium azide was used as a microbial growth inhibitor. In separate tests to evaluate the oxidation of naphthalene by various oxidants, the disappearance of naphthalene in batch experiments containing chlorine was negligible after 12 d of incubation. However, 38% and 77% disappearance of naphthalene was observed when 11 mg/L of sodium azide was present in solutions containing 19.5 mg/L and 52.5 mg/L total chlorine, respectively. Chlorine was consumed faster in the batch studies containing sodium azide. Increasing levels of azide in solution also resulted in lower naphthalene and chlorine levels. In a separate set of experiments, sodium azide interfered with nitrate quantification and produced nitrate levels that were progressively lower with increasing azide concentrations. The decrease in nitrate was caused by reactions of sodium azide with nitrite formed during cadmium reduction. In both cases, sodium azide was added to the test solution either to prevent microbial growth or to inhibit existing microbial activity. These tests demonstrate that azide could potentially interfere in chemical and biological testing. Key words: sodium azide, inhibition, interference.