A Survey on Long-Term Stability of Stock Standard Solutions in Pesticide Residue Analysis

The aim of this study was to highlight the need to extend the lifetime of stock standard solutions employed for the analysis of pesticide residues with respect to the quality control standards in use. The importance of this survey concerns the possibility to extend the solution lifetime up to year when the standard solutions are stored in refrigerator at 4 °C. In order to allocate a solution lifetime up to year, the guideline document SANCO/12571/2013 was followed. During the time 2010–2013, the stability data were collected for 82 different active substances from the Italian National Reference Laboratory (NRL) for pesticide residues, accredited to the ISO/IEC 17025. A statistical analysis was performed on the overall data. Some aspects have been monitored such as the solvent and detection method used, the relative standard deviations (RSDs) of the mean responses of the old and fresh stock solutions investigated, the percentage difference of the mean responses of the old and fresh stock solutions, and finally the uncertainty measurement of the standard preparation.