Simultaneous determination of nitrate and nitrite in human plasma by gas chromatography-mass spectrometry

We devised a sensitive and simple method for the simultaneous determination of nitrate and nitrite in human plasma, using extractive alkylation. These inorganic anions were alkylated with pentafluorobenzyl bromide, using tetradecyldimethylbenzylammonium chloride as the phase-transfer catalyst, with 1,3,5-tribromobenzene as an internal standard. The derivatives were analyzed by gas chromatography-mass spectrometry, using the negative-ion chemical ionization mode with isobutane as the reagent gas. Calibration curves for nitrate and nitrite were linear over the concentration range of 0.01 to 1.0 pmol/mL in plasma, and the lower limit of detection for both compounds was 0.005 pmol/mL. The accuracy and precision of this method were evaluated and coefficients of variation were lower than 10.4%. Blood nitrate and nitrite concentrations of six victims who committed suicide by inhaling automobile exhaust gas could be determined using our method.