Develop of a multiway chemometric-based analytical method fulfilling regulatory identification criteria: Application to GC–MS pesticide residue analysis

Abstract

The proposed procedure is described by applying it to develop an analytical method which fulfils the SANCO specifications. Nevertheless, the procedure would be valid for any other legal specification that requires the identification of the analyte by means its m/z values and retention time. To demonstrate the procedure, three herbicides (simazine, Sz; atrazine, Az; propazine, Pz), with terbuthylazine, Tz, as internal standard (IS) have been analysed by gas chromatography with mass spectrometry detection (GC/MS). The procedure consists of the following steps: (i) To record the data in the full scan mode (201 m/z ratios). (ii) To select four characteristic ions which make possible the unequivocal identification of each triazine according to the criteria established in the Document SANCO/12495/2011 by means of principal components and hierarchical clustering of variables; (iii) To build a calibration based on the PARAFAC decomposition with the data recorded in SIM mode at the four m/z ratios selected for each triazine. Afterwards several figures of merit have been evaluated. Bearing in mind that triazines are one of the most frequently used group of herbicides in agriculture and atrazine and simazine are included in the list of priority substances in Annex II of Directive 2008/105/EC, in this work, these analytes have been analysed in three natural waters. Prior to determination by gas chromatography with mass spectrometry detection (GC/MS) a step with solid phase extraction (SPE) has been carried out. The calibration set is made up of 40 standards 33 are external standards prepared in acetone and seven matrix matched prepared in deionised water subjected to the SPE procedure. Moreover, each kind of water, stream, well, and river, is analysed both unspiked and spiked. For the triazine determination, the second order PARAFAC advantage allows the use of samples prepared in acetone together with those prepared in deionised water subjected to SPE. The decision limit, CCα, and the capability of detection, CCβ, are calculated according to ISO 11843-2, assessing the false positive and false negative. The m/z ratios chosen fulfils the SANCO identification criteria and also the spectrum obtained in the PARAFAC decomposition, which is common in all samples for each triazine. However, when the same experimental data are used to carry out a univariate calibration with the abundance of the base peak of each triazines, a lot of samples lie outside the permitted tolerances depending on the reference experimental spectra used, despite the fact that all of them have a triazine content above the detection limit. Also, the PARAFAC calibration allows us to detect the test samples which are not similar to the calibration samples and in this way their mistaken quantification is avoided.