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Analysis of thermally labile pesticides by on-column injection gas chromatography in fruit and vegetables

S. Uclés,  E. Hakme, C. Ferrer and A. R. Fernández-Alba

Department of Chemistry and Physics, Agrifood Campus of International Excellence (CeiA3), European Union Reference Laboratory for Pesticide Residues in Fruits and Vegetables, University of Almería, 04120 Almería, Spain

Analytical and Bioanalytical Chemistry (2018) 410:6861–6871

(https://doi.org/10.1007/s00216-018-1286-1)

Abstract 

Thermally labile pesticides (captafol, captan, dicofol, and folpet) are highly prone to suffer thermal degradation during sample introduction into a gas chromatograph (GC) to tetrahydrophthalimide (THPI), 4,4′-dichlorobenzophenone (DCBP), and phthalimide (PI), respectively, mainly produced in the glass liner of the injector. This undesired behavior leads to inaccurate qualitative and quantitative results. Direct on-column injection (OCI) technique is evaluated as an alternative to avoid or minimize compound alteration during the analysis. This configuration was studied and evaluated for the determination of this group of thermally troublesome pesticides. The OCI inlet was operated in Btrack oven^ temperature and connected to a wide-bore deactivated guard column that is itself connected to a capillary GC analytical column. This technique has demonstrated to be useful for avoiding degradation generated in the hot inlet. Limitations observed for OCI in routine analysis were injection volume, guard column length, and maintenance issues. Analytical standards spiked in vegetable solutions were injected in OCI, not observing any thermal degradation rate. On the contrary, classical splitless injection (SLI) produced high degradation rates in all cases. This OCI approach was validated in citrate QuEChERS extracts of tomato, apple, and orange matrices for these four compounds and their corresponding transformation products (THPI, DCBP, and PI), evaluating recoveries, repeatability, linearity, and matrix effect. This set-up enabled the correct identification and quantitation for most compounds at LOQs of 0.010 mg/kg in fruit and vegetable samples. The OCI grants evident differentiation between metabolites naturally occurring in food and thermal degradation products created during the analysis.

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

 

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Carmen Ferrer: cferrer@ual.es (+34) 950 014 102

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Published 04-10-2018, 15:34:33

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