Spectrophotometric determination of nitrite using phenosafranine

A simple and sensitive spectrophotometric method for the determination of n itrite is described. Diazotisation of the primary amino group in the dye ph enosafranine resulted in a decrease in absorbance at 520 nm. This decrease in absorbance is directly proportional to nitrite concentration obeying Bee r's law in the range 0-12 mug of nitrite in a final aqueous volume of 25 ml with a relative standard deviation of 2.9% at 8 mug of nitrite (n = 10). S ensitivity of the method is enhanced by extracting the dye into 3-methyl-1- butanol under alkaline condition, followed by the addition of methanolic su lfuric acid. Beer's law is obeyed over the range 0-1 mug of nitrite at 530 nm, after extraction with a relative standard deviation of 1.9% at 0.6 mug of nitrite (n = 10). The developed method has been applied for the determin ation of residual NO2 in the laboratory fume cupboard after fixing it as ni trite in suitable absorber solution, Nitrate and nitrite contents in analyt ical grade chemicals, medicated tooth paste, soil and water samples were de termined. The effects of interfering gases and other ions on the determinat ion of nitrite are described. Reliability of the method was established by parallel determination using a diazoeoupling reaction and by studying recov ery of added nitrite and nitrate.