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

Abstract

Nedocromil sodium (an antiasthma drug) and pentamidine isethionate (an antiprotozoal agent) were determined in urine by cathodic stripping voltammetry after adsorptive accumulation at a hanging mercury drop electrode as examples of the use of solid-phase extraction cartridges with this technique. Prior separation from matrix interferents was necessary and this was carried out using either a C₁₈ solid-phase extraction cartridge or liquid–liquid extraction. For nedocromil, a recovery of 100.5 ± 6.5%(± 2 standard deviations) was obtained from urine spiked with 0.42 µg ml^–1 of the drug using a C₁₈ cartridge (five determinations). 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 µg ml^–1. At lower levels of pentamidine isethionate, better recovery was obtained using liquid–liquid extraction: recoveries of between 60 and 100% were obtained at levels of 0.04–29.6 µg ml^–1. Linear calibration graphs were obtained for the determination of both drugs at concentration levels in the measured solution lower than 1 × 10^–7 mol l^–1(i.e., less than approximately 0.05 µg ml^–1): standard additions method was preferred for quantification. Relative standard deviations of 4.5% for the determination of pentamidine isethionate and of 5.2% for the determination of nedocromil (n= 5) were obtained for urine samples containing 2.96 µg ml^–1 of pentamidine isethionate and 0.42 µg ml^–1 of nedocromil.