NITRATE EXTRACTION FROM FRESH PLANT MATERIAL BY MEANS OF A METHANOL:WATER EXTRACTION SOLUTION

Nitrate determination from fresh plant material is common in routine analysis, but comparisons between extraction solutions, detection techniques or combinations of both show that there is a wide range in performance in methods determining plant nitrate. In this paper, the performance of methanol:water (1:1, V:V) as an extraction solution was compared against water and KCl as extractants. Measurement results of methanol:water extracts were consistently higher than the water or KCl results. Even compared to a recommended nitrate determination method, using dried material, significantly higher results were obtained with methanol:water as an extraction solution. This has consequences on the interpretation of internal quality of produce, like some vegetables, where maximum allowable nitrate concentrations are put forward in various countries. Furthermore, the results of the methanol:water extracts of two common determination techniques, i.e., segmented flow analysis and HPLC detection technique, were highly comparable.