Reflectometric determination after reduction to nitrite and reaction with Griess reagent.
Nitrates are naturally occurring compounds that are found in the air, water, soil, and plants, forming part of the nitrogen cycle. Humans consume nitrate from a variety of sources, but plant matter in the form of vegetables is usually the biggest contributor unless the nitrate content of drinking water is exceptionally high.1 A number of factors can influence nitrate levels in vegetables including the type/part of the vegetable, cultivation frequency, weather conditions, soil quality, food production processes, and the type/amount of fertilizers.2
Nitrates themselves are relatively non-toxic, but metabolites produced in the body such as nitrite, nitric oxide, and N-nitroso compounds are of concern because they have been linked to both cancer and a blood condition called methaemoglobinaemia.3 As a result, it is important to monitor nitrate levels in vegetables in order to avoid these potential adverse health effects. Here, we outline a general method for determination of nitrate levels in vegetables using reflectometry.
Note: This application note pertains to RQflex® 20 and all discontinued instruments (RQflex® 10, RQflex® plus).
Recommended sample quantities and volumes for several vegetables are given in below sample preparation table. As the concentrations of nitrate can vary substantially from vegetable to vegetable, the dilution factor should be appropriately adapted.
The value [mg/l] will be stored automatically. (Please refer to the RQflex® operating instructions and the instruction for use of the Reflectoquant® Nitrate Tests.)
Nitrate content [mg/kg] = Measured value [mg/l] x Volume of water [ml] ÷ Weight of sample [g]
Nitrate content [mg/kg] = Measured value x factor