Determination of endothelium‐derived nitrite/nitrate by gas chromatography/tandem mass spectrometry using ( 15 N)NaNO 2 as internal standard

A sensitive gas chromatographic/tandem mass spectrometric method for the determination of nitrite and nitrate in endothelial cell column perfusates was developed. Nitrite/nitrate were converted in the presence of the internal standard ( 15 N)NaNO 2 to the corresponding 1‐nitro‐2,4,6‐trimethoxybenzene (NTMB) derivatives which were subsequently analysed by gas chromatography/tandem mass spectrometry, monitoring m/z = 46 and m/z = 47, respectively. The good reproducibility, the wide linear range of the calibration curve from 25 ng ml −1 to 2500 ng ml −1 nitrite and the low detection limit of 200 pg NTMB allowed a sensitive and accurate quantification of nitrite/nitrate in perfusates of endothelial cell columns. Bradykinin had a stimulating effect on human and bovine endothelial cells and led to a threefold increase of nitrite/nitrate in endothelial cell column perfusates compared to those of unstimulated cells.