Determination of nitrite and nitrate reduction by capillary ion electrophoresis.

Production of nitrates and nitrites is a common step in many methodologies used to measure nitric oxide (NO) and NO-derived products in biological fluids. We report conditions that allow the rapid separation and quantification of nitrite from nitrate ions in biological fluids by capillary ion electrophoresis (CIE). CIE can be used to directly quantify nitrites and nitrates near the millimolar range. To detect lower levels, we have used CIE to monitor the reduction of nitrites and nitrates to NO for chemiluminescence detection. For reduction reactions, we directly compared the ability of three commonly used agents--potassium iodide (KI), mercuric chloride (HgCl2) and vanadium chloride (VCl3)--to reduce nitrite and nitrate ions to NO. Nitrites/nitrates can be efficiently reduced to NO at 37 degrees C using vanadium chloride (100%) or HgCl2 (80%). However, these CE-derived conditions cannot simply be extrapolated to chemiluminescence measurements. Vanadium (III) yields high background in the photomultiplier that diminishes the sensitivity of chemiluminescence measurement to that outside of physiological ranges. We find that reactions carried out at 37 degrees C in 2 M HCl using HgCl2 is efficient using both techniques.