THE DETERMINATION OF NITRATE IN GREEN TOMATO AND LETTUCE TISSUES

Abstract

The sample of green tissue is triturated with Ca(OH)2, the alkali stopping enzyme action and catching any free HNO3. The paste formed is then cleared with M/20 CuSO4. An aliquot of the cleared solution is evaporated to drynessand the nitrate determined by the phenoldisulphonic acid method. If chlorides are present in excess of 20 ppm. they must first be removed by Ag2SO4. The results check to 10% on small quantities of nitrate. The recovery of added nitrate is even better (7.4% error). Sucrose, glucose and fructose, in small quantities, do not interfere with the determination. NaOH is the best reagent with which to neutralize the phenoldisulphonic acid.