DIBENZOYL METHANE - A NEW COUPLING AGENT FOR NITRITE DETERMINATION

Dibenzoyl methane is introduced as a new coupling agent for the determination of nitrogen dioxide in air and for nitrite in water and soil samples. Nitrogen dioxide is fixed as nitrite in NaOH-sodium arsenite trapping solution and also in triethanoamine trapping solution. The method is based on the diazo coupling reaction of p-nitro aniline with a new coupling agent, dibenzoyl methane. The azo dye formed under aqueous alkaline condition has an absorption maximum at 520 nm and obeys Beer's law over a range of 0-20 mu g nitrite per 10 mi analyte. The dye formed is stable for 40 h. The relative standard deviation is 2.8% for 10 determinations at 10 mu g nitrite per 10 mi analyte. The color system upon extraction with isobutyl methyl ketone-amyl alcohol (1 + 1) shows a lambda max at 520 nm and a Beer's law range of 0-4 mu g nitrite. The developed color is stable for 7 h in the organic phase. The relative standard deviation is 3.0% for 10 determinations at 2 mu g nitrite. The molar extinction coefficient of the color system is 3.6 x 10(4) L/(mol cm). The effect of interfering gases and ions on the determination is described. The method was applied to the determination of residual amounts of nitrogen dioxide present in the laboratory fume cupboard and in automobile exhaust gas. The method was also applied to the determination of nitrite and nitrate in water and soil samples. The results obtained were compared with the standard sulfanllamide-NEDA (N-1 naphthyl ethylene diamine dihydrochloride) method. The method can be used to determine levels as low as 0.5 mu g nitrite in aqueous medium and 0.1 mu g nitrite upon extraction.