A simple miniaturised photometrical method for rapid determination of nitrate and nitrite in freshwater

A rapid, simple miniaturised photometrical method was developed for the determination of nitrate and/or nitrite in freshwater samples. All procedures, including sample buffering, reduction by copperised cadmium granules, colour development and absorbance determination, were completed in a 96-well microplate. The factors governing the nitrate reduction and its recovery were investigated in detail, and the optimised analysing conditions were established. Nitrate was quantitatively reduced by copperised cadmium granules with a high reduction efficiency (96.59 ± 0.96%). The proposed method gave a linear calibration ranging from 0.01 to 1.50 mg L−1 for NO2−-N and 0.02 to 1.50 mg L−1 for NO3−-N. The detection limits for nitrite and nitrate were 2 and 4 μg L−1, respectively. The proposed method allowed at least 48 samples to be simultaneously analysed in duplicate, with good precision, within 90 min for nitrate and 30 min for nitrite, and was successfully applied to actual freshwater sample analysis with a recovery of 98.02 ± 1.04% for nitrite and 99.72 ± 1.39% for nitrate. This method produced accurate results comparable to standard methods, provided a much higher sample throughput than conventional methods and could be routinely used in actual freshwater sample monitoring.