A Quick Test Based on Cataldo’s Method to Determine Nitrate in Fresh Tissue Extracts

Leafy vegetables could accumulate nitrate (NO3−) above limits safe for humans, hence it would be advisable to customarily determine their NO3− concentration. We wanted to develop a quick test to determine NO3− concentration in fresh tissue extracts and estimate the error of using this test to identify samples with NO3− concentrations above the World Health Organization (WHO) threshold. There was a positive linear relationship (P < 0.001) between NO3− concentrations determined by the quick test and by potentiometry in dry tissue extracts. Samples were classified as “acceptable” or “excessive” according to their potentiometric NO3− concentration, using a critical level of 75% (p) of the observed NO3− distribution. According to the Cate-Nelson model, the quick test identified as “acceptable” from 5.6% to 15.4% of samples that were in the “excessive” category. In spite of this error rate, the quick test use would improve consumers’ protection, because no controls on vegetables NO3− concentration are available...