Acquisition of stability data for pesticides in water sample through proficiency tests

Abstract

In the framework of a proficiency test for multiresidue determination, three water samples, coming from the same batch, were sent to each of the 25 participants. They were asked to analyze the first one 2 days after the production (D + 2), the second one at D + 4 and the last one at D + 9. D + 2 was selected as the first date of analysis in order to allow all the participants to receive their samples. Prior to the analysis, the samples were stored at 4 °C. The samples were distributed in 1-l bottle from a batch spiked with more than 100 pesticides. The spiking concentrations ranged from 120 ng/l to 227 ng/l. Apart from the usual proficiency evaluation with assigned values and z-scores, comparisons between the results at the different dates of analysis were made. Most of the substances were found to be stable during the considered period in the conditions of the test, but some profiles of evolution were highlighted for some others.