Optimisation of octadecyl (C18) sorbent amount in QuEChERS analytical method for the accurate organophosphorus pesticide residues determination in low-fatty baby foods with response surface methodology

Three low-fatty baby food matrices were fortified with 0.01–0.2 mg/kg of phorate, diazinon, chlorpyrifos and methidathion. A “quick, easy, cheap, effective, rugged and safe” – like method (QuEChERS) was used. Quantities of octadecyl (C18) sorbent differed with fortification level and matrix fat, based on central composite experimental design. Quantification was performed by Nitrogen–Phosphorus Detector gas chromatography, using matrix-matched standards. The highest (p < 0.05) recoveries were observed for methidathion, the lowest fortification levels for a specific C18 amount and the lowest C18 amounts. In meals containing vegetables (1.9% fat) and lamb (3.0% fat), 180–210 mg C18 gave recoveries from 67.0% to 105.0% and absence of co-extracts. Yogurt dessert (4.5% fat) required 200–230 mg C18 for similar results. Recoveries could also be predicted with <20% error by a polynomial model. The results suggest that modified QuEChERS could be effectively used in the low-fatty baby meals residue analysis.