Spectrophotometric determination of iron with 2-hydroxy-3-napthoic acid

Abstract

2-Hydroxy-3-napthoic acid is presented as a new, highly sensitive and selective reagent for its colour reaction with ferric ion. The sensitivity of the reaction is 0.025 μg/cm 2 (SANDELL). The blue-coloured complex is maximally absorbed at 590 mμ and obeys Beer's law up to 24 p.p.m. of iron. The optimum range of concentration is from 4 to 20 p.p.m. of iron, where the percent relative analysis error per 1% absolute photometric error is 2.9. The composition of the complex, as evaluated by JOB's method and as verified by the Molar and Slope ratio methods, shows that in solution, the complex contains the iron and the reagent in a ratio of l : 1. The empirical formula of the complex is suggested to be [Fe(C 11H 7O 3)] +2. The molar extinction coefficient is 2212 and the instability constant of the complex is about 4.29 ⋯ 10 -4. Coloured ions or those ions that give coloured products are tolerated to a limited extent during the determination of iron.