Determination of nitrite in human, cow and market milks by gas-liquid chromatography with electron-capture detection.

A simple and practical method for the determination of very small amounts of nitrite in human, cow and market milks is described. It is based on the reaction of nitrate with 1-hydrazinophthalazine in acidic solution to form tetrazolophthalazine, a stable compound which can be extracted with an organic solvent and then determined by gas-liquid chromatography with electron-capture detection using a column of 3% OV-225 on Chromosorb W HP; the detection limit for nitrite was 2 ng/ml. The procedure for determining nitrite in milks involves extraction with solvent, followed by further clean-up by alumina column chromatography; the detection limit is about 4 ppb and recovery in human, cow and market milks was satisfactory. The method makes possible a micro-assay for nitrite. The tetrazolophthalazine was identified by its elemental composition, melting point and by combined gas chromatography-mass spectrometry.