Extraction-spectrophotometric determination of sub-microgram amounts of nitrite using 4-nitroaniline and naphth-1-ol

Abstract

Nitrite ion reacts with 4-nitroaniline in hydrochloric acid medium to form 4-nitrophenyldiazonium chloride, which couples with naphth-1-ol in alkaline medium to give a purple azo dye (λ_max.= 580 nm, ε= 3.7 × 10⁴ l mol^–1 cm^–1). The dye can be extracted into higher alcohols. This extraction process is used for the determination of sub-microgram amounts of nitrite spectrophotometrically. Of the alcohols studied (butanol, pentanol, isopentanol, hexanol and octanol), hexanol was found to be the most suitable extractant. The blue hexanol extract exhibits a maximum absorption at 605–615 nm. Beer's law is obeyed over the nitrite concentration range 0.02–0.14 p.p.m. The molar absorptivity and Sandell's sensitivity were found to be 5.24 × 10⁴ l mol^–1 cm^–1 and 0.00088 µg cm^–2, respectively. The optimum reaction conditions for diazotisation, full colour development and the effect of variables have been studied. Several common ions do not interfere with the method if appropriate masking agents are used. The method has been applied successfully to the determination of nitrite in samples of river water.