Determination of Nitrite and Nitrate in Natural Waters Using Flow Injection with Spectrophotometric Detection

A simple and sensitive flow injection spectrophotometric method is reported for the room temperature determination of nitrite and nitrate based on the Griess reaction and a copperised cadmium column for reduction of nitrate. Calibration graphs were linear over the range 2 – 1000 μg N L (R = 0.9997 and 0.9999, n = 9) with a limit of detection (3 s.d.) of 1.0 μg N L and relative standard deviations (n = 10) of 0.9 and 1.2% for 50 μg N L nitrite and nitrate respectively. The sample throughput was 50 h. The effect of reagent concentrations, physical parameters (flow rate, sample volume, reaction coil and copperised cadmium column length) and the potential interferences are reported. The effect of salinity on the blank and on the determination of nitrite and nitrate are also presented. The method was applied to natural waters (rainwater, freshwater and estuarine water) and the results for nitrite + nitrate (140 – 7310 μg N L) were not significantly different (95% confidence interval) from results obtained using a segmented flow analyser reference method with spectrophotometric detection.