Simple and rapid method for the measurement of nitrite and nitrate in human plasma and cerebrospinal fluid by capillary electrophoresis.

Nitrite and nitrate levels in physiological fluids are commonly used as an index of nitric oxide production. We developed simple and rapid method for the determination of these anions by capillary zone electrophoresis employing borate buffer (pH 10, 100 mmol/l) as running electrolyte. The anions were analyzed in plasma and cerebrospinal fluid (CSF) without deproteinization of the samples. Electrophoresis was carried out in a capillary (36.5 cm x 75 microm) at a potential of 15 kV, with on-column UV detection at 214 nm. Mean retention times for nitrite and nitrates were 4.631 and 5.152 min, respectively. The method was linear (r=0.999) within a 1-500 micromol/l concentration range. Physiological levels of nitrate in plasma (40.2 micromol/l) and CSF (15.3 micromol/l) could be determined with good precision (coefficients of variation <6%) and accuracy (recoveries of added nitrate to plasma and CSF were 97.4 and 104.5%, respectively). Measurements of the physiological levels of nitrite in plasma (6.1 micromol/l) and CSF (0.9 micromol/l) were less precise and accurate.