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Abstract
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 NO(2)(-)-N and 0.02 to
1.50 mg L(-1) for NO(3)(-)-N. The detection limits for nitrite and nitrate were 2
and 4 microg 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.