Development and validation strategies for qualitative spot tests: application to nitrite control in waters

A general and systematic approach is proposed for the development, optimisation and validation of qualitative spot tests. A simple spot test to control water contamination by nitrite has been developed and was taken as the basis for this purpose. The qualitative information, based on a binary yes/no response, was directly obtained through the visual identification of the colour. Legislation requirements for this parameter in tap waters were selected as the threshold for classifying the samples as positive or negative. The qualitative information provided by this type of test was used for both the optimisation of the test to give a reliable response with respect the threshold and for the validation of the test.