Application of o-hydroxyhydroquinonephthalein-iron(III) complex to determination of pyridone carboxylic acids.

Abstract

A simple spectrophotometric method for the determination of pyridone carboxylic acids (PCA) using ο-hydroxyhydroquinonephthalein (Qnph) -iron (III) complex was developed. The present method is based on the ternary complex formation among Qnph, iron (III) and PCA in the presence of sodium dodecylbenzenesulfonate in weakly basic media. In the determination of nalidixic acid (NA), Beer's law held up to ca. 20 μg of NA in the final volume of 10 ml, with an apparent molar absorptivity of 1.3 × 10⁵ l mol^-1 cm^-1 for NA {1.8 × 10⁵ l mol^-1 cm^-1 for piromidic acid (PA), 6.6 × 10⁴ l mol^-1 cm^-1 for pipemidic acid}. The proposed method was applied to the assay of NA or PA in pharmaceutical preparations and calf serum. The use of a membrane filter preconcentration technique was also investigated in an attempt to improve the proposed method.