Volume 49, Issue 5 (September 2004)
Analysis of Nitrite in Adulterated Urine Samples by Capillary Electrophoresis
A simple method for analyzing nitrite in urine has been developed to confirm and quantify the amount of nitrite in potentially adulterated urine samples. The method involved separation of nitrite by capillary electrophoresis and direct UV detection at 214 nm. Separation was performed using a bare fused silica capillary and a 25 mM phosphate run buffer at a pH of 7.5. Sample preparation consisted of diluting the urine samples 1:20 with run buffer and internal standard, and centrifuging for 5 min at 2500 rpm. The sample was hydrodynamically injected, then separated using –25 kV with the column maintained at 35C. The method had upper and lower limits of linearity of 1500 and 80 ∐g/mL nitrite, respectively, and a limit of detection of 20 ∐g/mL. The method was evaluated using the National Committee for Clinical Laboratory Standards (NCCLS) protocol (Document EP10–A2), and validated using controls, standards, and authentic urine samples. Ten anions, ClO¯, CrO¯4 2, NO¯3, HCO¯3 , I¯, CH3COO¯, F¯, SO¯4 , S2O¯8 2, and Cl¯, were tested for potential interference with the assay. Interferences with quantitation were noted for only CrO¯4 2 and S2O¯8 2. High concentrations of Cl- interfered with the chromatography. The method had acceptable accuracy, precision, and specificity.