Gas Chromatographic Determination of Nitrite in Foods by Using Hydralazine

Abstract

A simple and practical method for the determination of nitrite in foods is described. It is based on the reaction of nitrite with hydralazine in acidic solution (pH 1.0-3.0) at 70°C for 10min to form tetrazole [5, 1-α] phthalazine, a stable compound which can be extracted with toluene and determined quantitatively by means of gas-liquid chromatography with a flame-ionization detector and a column of 3% OV-225 on Chromosorb W HP; the minimum determinable amount of nitrite-nitrogen was 0.02μg/ml.
A sample was finely chopped and ground in a porcelain pestle and mortar, then 5-10g of the mixture was transferred into a 100ml volumetric flask by means of 70ml of hot water (ca. 80°C), and 2.5ml of 1N sodium hydroxide solution and 5ml of 12% zinc sulfate solution were added. The whole was shaken occasionally in a water-bath at 80°C for 20min, then cooled to room temperature, and filtered. (Vegetables and vegetable products were extracted at 80°C with occasional shaking for 60min without the addition of 1N sodium hydroxide solution or 12% zinc sulfate solution.)
A 20ml volume of the filtrate was reacted with hydralazine, extracted twice with 5ml of toluene and then concentrated to 5ml by blowing dry nitrogen gas at 50°C. The concentrated solution was passed through an alumina column to remove interfering substances from foods. Twenty ml of hexane and 15ml of acetone were added successively to the column at a rate of 3ml/min. The acetone eluate was concentrated to 2ml by blowing dry nitrogen gas at 50°C. The final solution was injected into the gas chromatograph.
The recovery of nitrite added to various foods ranged from 94.5 to 98.1% and, the standard deviation for the whole procedure was 1.1% for 28 determinations. The results of nitrite determination by proposed method were in good agreement with those of the colorimetric method.