Spectrophotometric Determination of Aminophenol Isomers in Aqueous Solution using 1,2-Naphthoquinone-4-sulphonate Reagent

A spectrophotometric method was developed for the quantitative determination of aminophenol isomers. The method is based on their reaction with 1,2-Naphthoquinone-4-sulphonate (NQS) reagent in aqueous basic medium forming colored products with maximum absorption at wavelengths 488, 480 and 535 nm for o-, m- and p-aminophenol respectively. Beer’s law is obeyed over the concentration range of 0.2-10, 0.08-7.2 and 0.08-18 μg ml-1 with molar absorptivity values of 5166.6 ,6613.6 and 7673.6 L mol-1 cm-1 for the above isomers, respectively. The average recovery was ranged between 99.14 % to 102.5 % and the precision was better than 4.0 %. The limit of detection was in between 0.0348 and 0.05188 μg ml-1. The products are formed in ratio of 1:1 and the stability constants are 3.97×107, 8.58×105, 2.95×105 L mol-1 for the above isomers, respectively. The method was applied successfully for the determination of o-aminophenol in river, tap, spring and sea waters.