Evaluation of a septumless mini-cartridge for automated solid-phase extraction cleanup in GC-MS(/MS) analysis of >250 pesticides and environmental contaminants in fatty and nonfatty foods

Authors: MICHLIG, NICOLAS - Universidad Nacional Del Litoral; Lehotay, Steven

Submitted to: Journal of Chromatography A
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2022
Publication Date: 10/22/2022
Citation: Michlig, N., Lehotay, S.J. 2022. Evaluation of a septumless mini-cartridge for automated solid-phase extraction cleanup in gas chromatographic analysis of >250 pesticides and environmental contaminants in fatty and nonfatty foods. Journal of Chromatography A. 1685:463596. https://doi.org/10.1016/j.chroma.2022.463596.
DOI: https://doi.org/10.1016/j.chroma.2022.463596

Interpretive Summary: Monitoring of pesticides and environmental contaminants in foods is a common application worldwide for food safety and other purposes among regulatory agencies, food and agricultural industries, consumer groups, and academia. Development of ever faster, more efficient, and higher quality analytical methods with broader scope better meets monitoring needs, and automated cleanup of initial food extracts prior to advanced instrumental analysis is one of the best ways to accomplish this goal. In this study, an improved robotic method was developed using a new mini-cartridge design for sample cleanup in the analysis of more than 250 pesticides and environmental contaminants at ultratrace levels in different types of foods. This procedure has been integrated into the QuEChERSER mega-method to save time, increase sample throughput, and yield more reliable results in routine monitoring laboratories.

Technical Abstract: The QuEChERSER mega-method has recently been introduced to quantify and identify a wide range of chemical residues (pesticides, veterinary drugs, environmental contaminants, among others) in nearly all types of foods. The approach calls for taking a small amount of the initial extract to cover analytes amenable to liquid chromatography, and the remainder is used for gas chromatography (GC), both with mass spectrometry (MS) based detection. In the case of GC-MS(/MS), the initial 10-12 mL acetonitrile extract containing 20-30% water is partitioned using 2 g 4/1 (w/w) anhydrous MgSO4/NaCl, leading to an upper phase of 6-9% water. The extract then undergoes automated robotic mini-cartridge solid-phase extraction (SPE) cleanup in a technique known as µSPE or instrument-top sample preparation (ITSP). In 2022, a septumless mini-cartridge for µSPE was introduced to improve upon the ITSP design. The new design houses a bed of 20 mg anhydrous MgSO4, 12 mg each of C18 and primary secondary amine (PSA) sorbents, and 1 mg of graphitized carbon black (GCB), the latter substituting for CarbonX used in the ITSP product. The septumless µSPE mini-cartridge employs a different gripping mechanism with the syringe needle that allows leak-free operation at higher flow rates (e.g. 10 µL/s), whereas the ITSP design is limited to 2 µL/s. Based on cleanup and analyte elution profiles, the extract load volume and flow rate was increased in µSPE for QuEChERSER from 300 µL at 2 µL/s to 500 µL at 5 µL/s, which improved accuracy of results, sped the cleanup step, and obviated the need for micro-vial inserts in the receiving vials. The new design also reduced both the amount and consistency of dead (void) volumes in the mini-cartridges from 83 ± 14 µL to 52 ± 7 µL for 200-600 µL load volumes. Normalization of peak areas to internal standards led to recoveries between 80-120% with typical RSDs <5% in LPGC-MS/MS of 227-242 out of 252 pesticides, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and polycyclic aromatic hydrocarbons (PAHs) in hemp powder, spinach, whole milk, egg, avocado, and lamb meat. As before, the sorbents were found to reduce water content to <5% in final extracts and provide nearly complete removal of fatty acids, cholesterol, chlorophyll, and other common co-extracted matrix components.