Analysis of nitrite and nitrate in biological fluids by capillary electrophoresis

Objectives: We report a method for determining nitrite and nitrate in biological fluids by capillary electrophoresis. Methods: A Waters capillary electrophoresis system was used with a filter for detection at 214 nm. After dilution with distilled water, the sample was loaded hydrostatically onto a 60 cm x 100 mu m capillary and electrophoresed at 15 kV in 15 mmol/L sulfate buffer, pH 8.0, containing 2.5% electroosmotic flow modifier. Results: The retention times for nitrite and nitrate were 3.9 +/- 0.8 and 4.0 +/- 0.8 min, respectively. The detection limit was 10 mu mol/L for serum nitrate. The recovery was 93-115% for nitrite and 92-106% for nitrate. The within-day and between-day coefficients of variation were lower than 3.3% and 5.0%, respectively, for two pools with normal (28 mu mol/L) and high (87 mu mol/L) nitrate concentration. A comparison with the nitrate reductase method gave a correlation coefficient of 0.982. Conclusion: Capillary electrophoresis provides many advantages, namely low cost, small sample and buffer requirements, rapidity, which makes its use particularly suitable for clinical laboratories. Copyright (C) 1999 The Canadian Society of Clinical Chemists.