Stable isotope analysis of plant-derived nitrate - novel method for discrimination between organically and conventionally grown vegetables.

The lack of reliable markers for the discrimination between organic and conventional products makes the organic food market susceptible to attempted fraud. Robust analytical methodologies for organic food authentication are urgently needed. In this study a new approach, compound-specific nitrogen and oxygen isotope analysis of plant-derived nitrate, has been applied alongside bulk nitrogen isotope analysis for discrimination between organically and conventionally greenhouse-grown lettuce and retail potatoes and tomatoes. The method revealed significant differences between conventional and organic fertilisation. An intra-plant isotopic variation as well as significant impact of the fertiliser application rate on the nitrogen and oxygen isotope values of plant-derived nitrate has been observed. Nitrogen and oxygen isotope analysis of nitrate has a potential for differentiation between organic and conventional crops. Further analysis is needed to improve our understanding of the scope of application and robustness of this compound-specific approach.