Complexometric determination of clodronate in aqueous solutions and urine

Three different procedures for the determination of clodronate by means of Th-EDTA-XO or Th-DCTA-XO (XO = xylenol orange) complexes are presented. According to the UV-VIS and 13C NMR measurements, XO is quantitatively replaced by the clodronate anion in the mixed ligand Th-EDTA-XO or Th-DCTA-XO complexes in slightly acidic solutions. This ligand replacement reaction can be applied to the determination of traces of clodronate. Procedures studied involve visual complexometric titration, spectrophotometric titration and conventional spectrophotometric determination. By visual complexometric titration it is possible to determine clodronate directly in human urine with acceptable accuracy and precision in the range 0.5-2.5 mg l-1. By diluting more concentrated urine samples 1:10 with water, samples of up to 80 mg l-1 can be determined with acceptable accuracy and precision. The working range of the method is linear up to 16 mg l-1 in aqueous solutions with the RSD-value varying between 0.7 and 3.8%. Interference caused by the major substances of human urine on the determination were studied.