The determination method of nitrate nitrogen in foods provided in the A.O.A.C. is based on either the colorimetric method by m-xylenol, or the reduction method by cadmium.
However, there are some problems in the reproducibility and simplicity of these methods. The sodium salicylate method was studied and it was found that this method was more excellent than the other methods.
The procedure of this method is as follows.
Extract nitrate nitrogen in foods with distilled water at room temperature, the added 1ml of 20% phosphotungstic acid solution if the sample has more protein. Take an aliquot of the extracts containing 5-20μg of nitrate nitrogen and add 1ml of 1% sodium salicylate-sodium hydroxide solution, 1ml of 0.1% ammonium sulfamate and 1ml of 0.2% sodium chloride, then heat the mixture to driness on a water bath. Add 2ml of concentrated sulfuric acid and 20ml of distilled water to the residue, extract with 20ml of methyl isobutyl ketone. To the organic solvent layer add 10ml of 1% sodium hydroxide solution and transfer sodium hydroxide layer to a 50ml Nessler tube, then dilute to 30ml with distilled water. Measure the absorbance at the wavelength of 415mμ.
The recovery ratio was about 90% in the addition experiment to vegetables and meat products.
