Data Processing Approach for the Screening and Quantification of Pesticide Residues in Food Matrices for Early-Generation Gas Chromatography Time-of-Flight Mass Spectrometry

The application of high-resolution mass spectrometry (HRMS) in pesticide residue analysis is gaining popularity worldwide. Upgrading from early-generation gas chromatography time-of-flight mass spectrometry (GC-TOFMS) to higher resolution analysers is quite challenging, economically wise, for third countries' laboratories. Given the insufficient resolution of 12000 full width at half maximum (FWHM) or less offered by GC-TOFMS, meeting the HRMS identification requirements in some Analytical Quality Control guidelines may be challenging. This paper presents a useful approach for GC-TOFMS data processing for the screening and quantification of pesticide residues in cereals for laboratories disposing of that same equipment. The data obtained from spiking four types of cereals (wheat, rye, rice, and barley) at three different concentrations, 0.01, 0.02, and 0.1 mg kg(-1) were evaluated with an "in-house" accurate-mass database of 102 pesticides, on the basis of two processing approaches. The data were first evaluated by considering the identification criteria in HRMS, which consists of the detection of two fragment ions of mass <= 5 ppm. The screening detection limits in that case were above 0.1 mg kg(-1) for 25% of the compounds, owing to the high mass error (> 5ppm) obtained for some ions at low levels. The unsatisfactory results obtained were examined, and the data were re-evaluated by comparison with injected standards for identification (ion ratio). With this validated approach, the screening detection limit achieved for 85% of the compounds was 0.01 mg kg-1. Therefore, given the insufficient resolving power of the instrument for some pesticide/commodity pairs, the HRMS requirement of 12000 FWHM in TOFMS was demonstrated to be inapplicable. Consequently, we recommend applying the requirements for identification of unit mass resolution for these specific mass spectrometers, to ensure accurate screening and quantification.