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

• First report using a novel automated SPE mini-cartridge design for cleanup • Robotic automation of cleanup in the high-throughput QuEChERSER mega-method • Parallel operation with fast LPGC-MS/MS for efficient, rugged, routine monitoring • Improved results demonstrated for >250 pesticides and environmental contaminants • Shown to be applicable for fatty and nonfatty foods alike, which is very rare 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 salted out for analysis by gas chromatography (GC), both with mass spectrometry (MS) based detection. In the case of GC-MS(/MS), the extract 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 MgSO 4 , 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 low-pressure GC-MS/MS of 227-242 out of 252 pesticides, polychlorinated biphenyls, polybrominated diphenyl ethers, and polycyclic aromatic hydrocarbons in hemp powder, spinach, whole milk, egg, avocado, and lamb meat.