APPLICATION OF ION CHROMATOGRAPHY WITH INDIRECT SPECTROPHOTOMETRIC DETECTION TO THE SENSITIVE DETERMINATION OF ALKYLPHOSPHONIC ACIDS AND FOSFOMYCIN

Indirect spectrophotometric detection was investigated for application in the anion-exchange chromatography of alkylphosphonic acids and fos fomycin. Four chromophoric eluent anions were studied: phthalate, benz oate, 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 exp erimental conditions were found to be 0.4 mM phthalate (pH 8.5) as mob ile phase, a flow-rate of 1 ml min(-1) and a detection wavelength of 2 72 nm. Selectivity (between 1.02 and 1.85, depending on the pair of vi cinal compounds), linearity over a 5-100 mu g ml-1 concentration range (r = 0.999), precision (R.S.D. 0.6-5.3%) and sensitivity (0.4-1.0 mu g ml-l 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 ap plication of the technique to the determination of fosfomycin in plasm a samples is described.