High-performance liquid chromatographic method for simultaneous determination of clodronate and some clodronate esters.

A quaternary alkylmethylamine-bonded stationary phase has been used for the liquid chromatographic resolution of bisphosphonates. Clodronate and three of its esters were separated by this technique. Nitric acid (30 mM) was used as the mobile phase. The effect of the pH of the mobile phase on the retention, resolution, capacity factor and theoretical plates of the column was examined. Thorium-ethylenediaminetetraacetic acid-xylenol orange mixed ligand complex was used as a postcolumn reagent for bisphosphonates. Bisphosphonates react quantitatively with this complex in slightly acidic solutions, and a change in the absorbance of postcolumn reagent is used as a measure of the bisphosphonate concentration. The relative standard deviation (R.S.D.) values for samples in aqueous solutions were in the range 2.3-15.5% (area) and 1.7-5.9% (height). The detection limits for different compounds, Cmin, varied from 0.3 to 1.4 mg/l (area) and from 0.3 to 0.5 mg/l (height). In urine samples the R.S.D. (%) varied from 3.1 to 18.9 (area) and from 1.1 to 6.3 (height). The linear dynamic range was from the detection limit up to 16 mg/l.