Automated micro-solid-phase extraction clean-up and gas chromatography-tandem mass spectrometry analysis of pesticides in foods extracted with ethyl acetate.

Generic extraction methods for the multi-compound pesticide analysis of food have found their solid place in laboratories. Ethyl acetate and acetonitrile extraction methods have been developed as fast and easy to handle standard multi-compound methods, both feature benefits and limitations. The direct injection to gas chromatography can be impaired by a high burden of coextracted matrix, resulting in deterioration of the chromatographic system and matrix effects, requiring frequent maintenance. Therefore, common clean-up methods, such as dispersive solid-phase extraction, freeze-out of fats, or gel permeation chromatography, have been applied in clean-up. Automated clean-up using micro-solid-phase extraction (µSPE) is a recent development with several demonstrated advantages when employed in the analysis of pesticides and other contaminants in foods extracted with acetonitrile, but it has not yet been evaluated in this application using ethyl acetate for extraction. In this study, an automated procedure using µSPE cartridges was developed and established on an x,y,z robotic sampler for the raw extract clean-up and preparation of diluted samples for injection on a GC-MS/MS system. Validation experiments for 212 pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons in lettuce, avocado, raspberry, paprika, egg, and liver extracts were performed using µSPE with MgSO4, PSA, C18, and CarbonX. The performance in routine operation is briefly discussed.

Study of high-resolution mass spectrometry technology as a replacement for tandem mass spectrometry in the field of quantitative pesticide residue analysis.

A validated LC/MS/MS-based multiresidue pesticide method was converted to an LC high-resolution MS single-stage Orbitrap platform. No changes regarding the cleanup and LC were made. Optimization of high-resolution MS-specific parameters and interface settings was kept at a minimum. The aim was to explore the capability of current Orbitrap technology to substitute for LC/MS/MS technology. The test included the quantitative performance (sensitivity, selectivity, linearity, accuracy, and precision) of some 240 analytes in three different matrixes. The LC/MS/MS instrumentation was operated at the edge of its technical limitations. A further extension of the number of analytes for LC/MS/MS would require the use of even narrower dwell times, significantly reducing sensitivity and reproducibility of measurement. No such limitations exist for the high-resolution technology. Similar performance was observed for both technologies. A current drawback of the high-resolution technology is the speed of data processing, which took significantly longer than for LC/MS/MS data due to the limited capabilities of the software.

False-positive liquid chromatography/tandem mass spectrometric confirmation of sebuthylazine residues using the identification points system according to EU directive 2002/657/EC due to a biogenic insecticide in tarragon.

In pesticide residue analysis using liquid chromatography/tandem mass spectrometry (LC/MS/MS) the confirmation of a sebuthylazine finding in a tarragon (Artemisia dranunculus) sample was demonstrated to be false positive. A coeluting interfering matrix compound produced product ions in MS/MS analysis, perfectly corresponding to the multiple reaction monitoring (MRM) of two sebuthylazine transitions. Using the EU directive 2002/657/EC which regulates the confirmation of suspected positive findings would have resulted in a false-positive finding. A third LC/MS/MS transition with a deviant ion ratio and a gas chromatography (GC)/MS/MS analysis revealed the false-positive results. With optimized high resolving ultra-performance liquid chromatography (UPLC) conditions it was possible to separate spiked sebuthylazine from the interfering matrix compound. Using its exact mass and isotope ratios from LC/time-of-flight (TOF) MS measurements, the compound was identified as nepellitorine, a - not surprising - endogenous alkamide in tarragon (Arthemisia dranunculus). False-positive results, especially in heavy matrix samples such as herbs, can be dealt with by further confirmatory analysis, e.g. a third transition, GC analysis if possible or more advantageous by an orthogonal criterion like exact mass.