o-Phenylenediamine has been used as a reagent to quantify nitrites= nitrates in a variety of sample matrices. The method is based on the cyclization reaction between o-phenylenediamine and nitrite in acid medium. The amine undergoes diazotization with nitrite in the presence of acid to form the diazonium ion, which subsequently cyclizes to yield yellowish orange benzotriazole at room temperature with an absorption maximum at 450 nm. The formed dye has been separated, purified, and characterized by IR, NMR, and spectroscopy techniques. The parameters of the reaction between amine and nitrite have been optimized. The effect of interfering ions on the determination of nitrites=nitrates has been described. The developed method has been applied for the determination of residual NO2 gas present in the ambient air after fixing it as a nitrite ion using sodium arsenite as a trapping medium. The dye formed has been extracted into organic solvent to improve the detection limit during the measurement of low levels of ambient NO2 in air. The method obeyed Beer’s law in the concentration range 0–250 mg in aqueous medium and 0–50 mg in organic medium with molar absorptivity of 4.09
104L mol1 cm1 and 4.3
104 L mol1 cm1 respectively. Nitrate is determined by reducing it to nitrite after passing through the copperized

A novel and simple method has been proposed for the estimation of nitrite/nitrate based on the reduction of arsenomolybdic acid to arsenomolybdenum blue using ascorbic acid. The obtained arsenomolybdenum blue complex has been oxidized by the addition of nitrite and the decrease in the absorbance of blue color is directly proportional to the nitrite quantity. The absorbance of the arsenomolybdenum blue complex has been measured at 840 nm. All the reaction variables have been optimized and Beer’s law has been obeyed in the concentration range 2–10 mg in 25 mL of aqueous phase with a molar absorptivity 4.37
104 L mol1 cm1. The relative standard deviation of the method has been found to be 1.7% for five measurements with a detection limit of 0.003 mg mL1. The method has been applied to determine nitrite/nitrate levels in biological samples as well as environmental samples.

A new chemosensor has been used to monitor atmospheric nitrogen oxides [NO + NO2] at ppb level. It is based on the catalytic reaction of nitrogen oxides with rhodamine B hydrazide to produce a colored compound through the hydrolysis of the amide bond of rhodamine B hydrazide. A simple spectrophotometer has been be used to monitor atmospheric nitrogen dioxide continuously at ppb level. The air samples were purged through the sampling cuvette containing rhodamine B hydrazide using peristaltic pump. The proposed method has been successfully applied to monitor the ambient nitrogen dioxide levels at traffic junction points within the city limits and the results obtained are in good agreement with the standard Griess-Ilsovey method. Key words: rhodamine B hydrazide, nitrogen dioxide, amide bond,