[Determination of nitrate and nitrite by catalytic spectrophotometry of potassium bromate-methylene blue system].

Nitrate and nitrite is one of important physical and chemical index in the analysis of environmental samples. A new catalytic spectrophotometric method for the determination of nitrate and nitrite has been established based on the catalytic action of nitrite on the oxidative fading reaction of methylene blue with potassium bromate in dilute phosphoric acid medium. The optimum experimental conditions were investigated in detail, including the selection of measuring wave-length and catalytic reactive medium, the dosage of indicator and oxidizer, the influence of temperature and reactive time, and the interference of co-existent ions with the assay. The results showed that, the linear responses of nitrite and nitrate are in the ranges of 0-200 and 0.003-310 micrograms.L-1 respectively. The method offers the advantages of simplicity, rapidity and sensitivity. It has been applied to analyse water samples with satisfactory results.