Ascorbic acid as analyte protectant applied within the quechers multi-method (GC-MS)

The analytical challenges related to pesticide multimethods with GC-MS modules require special care in terms of keeping pesticides' stability during the analytical process. This is of high importance when - pesticides have chemical-physical properties that do not allow the application of LC-MS/MS modules, - matrix challenges are significant, - labile pesticides might be present in the sample, and - time for analysis is limited because of routine constraints. Whereas typical analyte protectants aim to influence the chromatographic performance by reduction of interactions and by leveling matrix effects, a new approach was introduced taking into consideration the preserving properties of ascorbic acid. The "protection" function thus refers herein to the protection of the stability of the analytes themselves. As the degradation of pesticides to oxidationproducts is supported, in particular by GC conditions, an antioxidant like ascorbic acid should reduce the oxygenbased degradation. The influence of ascorbic acid on the analytical performance of pesticide residue multi-method analysis was tested empirically. Method performance data, such as sensitivity, selectivity, trueness and precision, were carefully evaluated. The experiments started with the analysis of chlorothalonil in spring onions while ascorbic acid was present, and the experiments then were extended across several vegetable matrices and 124 target pesticides all in all. The performed validations and their critical review confirmed the validity and robustness of a modified QuEChERS method with ascorbic acid. Ascorbic acid stabilizes labile pesticides and thus showed valid performance data. The fitness of this modified method under routine conditions could be confirmed.