USE OF SOLID-PHASE EXTRACTION CARTRIDGES WITH DIFFERENTIAL-PULSE CATHODIC STRIPPING VOLTAMMETRY AT A HANGING MERCURY DROP ELECTRODE - DETERMINATION OF NEDOCROMIL SODIUM AND PENTAMIDINE ISETHIONATE IN URINE

Nedocromil sodium (an antiasthma drug) and pentamidine isethionate (an antiprotozoal agent) were determined in urine by cathodic stripping v oltammetry after adsorptive accumulation at a hanging mercury drop ele ctrode as examples of the use of solid-phase extraction cartridges wit h this technique. Prior separation from matrix interferents was necess ary and this was carried out using either a C-18 solid-phase extractio n cartridge or liquid-liquid extraction. For nedocromil, a recovery of 100.5 +/- 6.5% (+/- 2 standard deviations) was obtained from urine sp iked with 0.42 mu g ml(-1) of the drug using a C-18 cartridge (five de terminations). A 97% recovery of pentamidine isethionate was obtained by solid-phase extraction when the drug was added to urine at a level of 1.48 mu g ml(-1). At lower levels of pentamidine isethionate, bette r recovery was obtained using liquid-liquid extraction: recoveries of between 60 and 100% were obtained at levels of 0.04-29.6 mu g ml(-1). Linear calibration graphs were obtained for the determination of both drugs at concentration levels in the measured solution lower than 1 x 10(-7) mol l(-1) (i.e., less than approximately 0.05 mu g ml(-1)): sta ndard additions method was preferred for quantification. Relative stan dard deviations of 4.5% for the determination of pentamidine isethiona te and of 5.2% for the determination of nedocromil (n = 5) were obtain ed for urine samples containing 2.96 mu g ml(-1) of pentamidine isethi onate and 0.42 mu g ml(-1) of nedocromil.