We describe a modification of a method for simultaneous urinary oxalate and citrate assessment by capillary electrophoresis (HPCE). HPCE analyses were performed with a P/ACE Beckman Gold System electrophoresis apparatus. Conditions for separation and analysis of urinary oxalate and citrate by HPCE: capillary 50 cm x 75 mm, the electrolyte solution contained 10 mmol.l –1 sodium chromate and 5 mmol.l –1 tetrabutylammonium bromide, pneumatic injection 15 s, voltage 16 kV, polarity negative, capillary temperature 23 °C, indirect detection at 254 nm. Determination of oxalate and citrate in urine is possible by direct injection of samples (pH 2–2.5 reduced by H3PO4) diluted 1:50 with water. Between each sample the capillary was washed for 1 min. with 0.1 mol.l –1 KOH, 1 min. with 0.1 mol.l –1 HCl and 2 min. with electrolyte solution. Analytical performance characteristics: CV% within-run was 4.7 (mean oxalate 0.120 mmol.l), CV% within-run was 2.4 (mean citrate 2.322 mmol.l –1 ), CV% between-run 12.6 (mean oxalate 0.128 mmol.l –1 ), CV% between-run 5.8 (mean citrate 2.307 mmol.l –1 ); % recovery = 98.4 ± 4.4 by oxalate addition range of 0.125–1.5 mmol.l –1 , median 99.5%; no interference of ascorbic acid has been ascertained by ascorbic acid addition range of 0.5 – 2.0 mmol.l –1 , % recovery = 96.4 ± 2.7 by citrate addition range 0.152 – 1.425 mmol.l –1 . HPCE method of urinary oxalate and citrate determination is fast, reliable, accurate, cost-effective and highly specific. Measurement by capillary electrophoresis is free of interferences from urinary components that influence results obtained with enzymatic methods.

        Key words: oxalate, citrate, capillary electrophoresis, urolithiasis.