A novel MOF-on-MOF composite versus its MOF shell: a comparative sorbent study for dispersive micro-solid phase extraction of pesticides in food samples

The pervasive application of organophosphorus pesticides (OPPs) in agriculture underscores the critical need for sensitive and reliable analytical techniques to safeguard food safety. Addressing this challenge, this work presents a rigorous comparative evaluation of two engineered sorbents for dispersive micro-solid phase extraction (D-μ-SPE) prior to gas chromatography-mass spectrometry (GC-MS): Bimetallic Fe/Co-MIL-88A and a novel Bimetallic Fe/Co-MIL-88A-on-MIL-88B composite. While both sorbents demonstrated high and statistically comparable extraction efficiencies, the composite was selected for its exceptional reusability and sustained performance over five consecutive cycles. Leveraging a design of experiments (DoE) approach, key extraction parameters were optimized for both sorbents, achieving remarkable sensitivity and precision. The method demonstrates an impressive linear dynamic range (LDR) of 0.07-900 ng mL^-1, with detection limits as low as 0.02-0.09 ng mL^-1, alongside high enrichment factors (up to 67) and excellent reproducibility (RSDs 3.16-4.35 %). Analysis of vegetable and fruit juice samples yielded robust recoveries (93.5-103.6 %) with precision (RSDs 4.37-6.33 %), affirming the method's reliability for routine monitoring. This work not only advances analytical capabilities for OPP detection but also contributes significantly to food safety surveillance, ensuring enhanced consumer protection.