Nitrate reduction by shaking with cadmium: alternative to cadmium columns

Abstract A manual method for nitrate analysis that meets the objectives of accuracy, efficiency, and small sample volume is presented. Samples buffered at pH 8.5 are shaken for about 90 min with spongy cadmium. Nitrate is reduced to nitrite, which is analyzed colorimetrically. Sample-cadmium contact time is more consistently controlled for a large series of samples simultaneously than with a column method. Problems with progressive deterioration in reduction capacity encountered in column methods are avoided. Analyses of nitrate-spiked natural water samples (salinity 0–12%) yielded recoveries of 94–106%. The 95% confidence interval of the mean of 10 observations was 0.254 ± 0.011 μM NO 3 − , using a 10-cm optical path.