Ion-pair complexes formation between fluoroquinolone antibiotics and methyl red and their use for the extraction-spectrophotometric analysis

Abstract

The new spectrophotometric methods of fluoroquinolones: enrofloxacin, norfloxacin, and ofloxacin determination with the methyl red are based on ion-pair complex formation between fluoroquinolones and methyl red in acidic medium at pH 3–4 and subsequent three times extraction of the reaction products by chloroform. The obtained orange extract has an absorbance maximum at λmax = 492 nm. Optimum conditions for the formation as well as for the extraction of ion-pair complexes between fluoroquinolones and methyl red at the presence of acetate buffer and potassium chloride solutions have been established: C (CH3COONa) = 0.85 M, C (KCl) = 2 M, pH = 3.8. Effective molar absorbtivity of ion-pair complexes chloroform extracts is ɛ492∼3·103 l mol−1 cm−1. New extraction-spectrophotometric methods for fluoroquinolone determination with methyl red were developed on the basis of the optimum reaction conditions. Concentration range for the system fluoroquinolone – methyl red is (2.5–25)·10−6 M; limit of detection for enrofloxacin is Cmin = 2.48·10−6 M, for norfloxacin – Cmin = 3.07·10−6 M, for ofloxacin – Cmin = 3.17·10−6 M.