Application of ion chromatography with indirect spectrophotometric detection to the sensitive determination of alkylphosphonic acids and fosfomycin

Abstract Indirect spectrophotometric detection was investigated for application in the anion-exchange chromatography of alkylphosphonic acids and fosfomycin. Four chromophoric eluent anions were studied: phthalate, bezoate, phenylphosphonate and p -toluenesulphonate. Phthalate showed the best displacing power and the larger dynamic reserve whereas benzoate exhibited the highest absorptivity and transfer ratio. The optimal experimental conditions were found to be 0.4 mM phthalate (pH 8.5) as mobile phase, a flow-rate of 1 ml min −1 and a detection wavelength of 272 nm. Selectivity (between 1.02 and 1.85, depending on the pair of vicinal compounds), linearity over a 5–100 μg ml −1 concentration range ( r = 0.999), precision (R.S.D. 0.6–5.3%) and sensitivity (0.4–1.0 μg, ml −1 according to the phosphonic acid) were determined. The minimum detectable concentrations were improved by an average factor of 50 in comparison with direct non-suppressed conductimetric detection. The application of the technique to the determination of fosfomycin in plasma samples is described.