Assessment on Validity Nitrite-nitrogen Results in Drinking-water by Micro-spectrophotometry

Objective To analyze the factors influencing the uncertainty of nitrite-nitrogen in drinking water detected by micro-spectrophotometry in order to assess the validity of results.

Methods Based on the reaction of nitrite with sulfanilic amide and N-1-naphthalethylenediamine to form a kind of violet red azo dye, nitrite nitrogen was quantified by a trace automatic analyzer matched with colorimetric assay kits.The action of sampling, calculating and cleaning samples in the analyzer could be done automatically.

Results There was a good linear relationship between the concentrations of nitrite nitrogen in the range of 0.001 mg/L~0.2 mg/L with the absorbance. The working curve was y=3.0065x+0.0049, and the correlation coefficient was r=0.9999. The detection limit was 0.001 mg/L. In detecting actual samples and analyzing the uncertainty of results, the result of the sample was (0.072 ±0.002) mg/L when k=2 (95% confidence probability).

Conclusions According to the results in this study, the uncertainty was mainly from standard curve fitting. More attention should be paid to a rational selection of standard substance, accurate preparation of standard solution and standard curve. At the same time, temperature should be suitably controlled, instruments should be in good condition, so as to reduce the uncertainty of measurement, improve the accuracy of results. The equipment has been proved running stably and in good control with small synthetic uncertainty, and the detected result was effective.