Analysis of pesticides and metabolites in Spanish surface waters by isotope dilution gas chromatography/mass spectrometry with previous automated solid-phase extractionEstimation of the uncertainty of the analytical results

A method based on isotope dilution gas chromatography/mass spectrometry (GC/MS) with automated solid-phase extraction (SPE) is described for the analysis of 32 pesticides and metabolites in surface waters. This approach consist in the use of nine isotopically labelled representative pesticides as internal standards, which allows high accuracy (trueness and precision) and sensitivity for most analysed compounds, as it is required for isotope dilution-based methods. Uncertainties associated with pesticide determination in real samples were estimated using quality assurance/quality control (QA/QC) data. For most pesticides expanded uncertainty was below 40%, according to the commonly established requirements for analytical results.