Inverse dispersive liquid-liquid microextraction(I-DLLME) for the simultaneous and green preconcentration of DEET and permethrin from freshwater

Global warming can stimulate mosquitoes to proliferate and the consumption of repellents and insecticides. These formulations can have N,N-diethyl-m-toluamide (DEET) and permethrin, which were reported in water bodies, requiring sensitive methods for quantification. We propose changing the dispersive liquid-liquid microextraction (DLLME), a green extraction technique, by inverting the sequence of injection of the extractant-dispersant solvents to allow better interaction with samples, aiming to improve the reproducibility of analytical results. In the inverse dispersive liquid-liquid microextraction (I-DLLME), samples of deionized water or freshwater enriched with DEET and permethrin isomers (trans = PERM-1) and (cis = PERM-2) were injected over the extractant-dispersant solvents using a micro-syringe. Both DLLME and I-DLLME were optimized using a factorial design and multi-response optimization (desirability function) to establish the condition that provides higher enrichment factor (EF) and reproducibility, denoted by lower relative standard deviations (RSD). Preconcentrated samples were analyzed using a High-Performance Liquid Chromatography with Diode Array Detector (HPLC-DAD) method. Under the optimum I-DLLME-HPLC-DAD condition (50 μL of chloroform as dispersant, 600 μL of acetonitrile as extractant, 0.007 mol/L of NaCl, and pH = 3), the EF for DEET, PERM-1 and PERM-2 were respectively 67, 170 and 179 with considerable gains in reproducibility (RSDs≤12%, n = 6). Quantification limits for DEET, PERM-1 and PERM-2 for deionized water and freshwater were respectively 50.0, 4.42 and 2.88 μg/L, and 33.06, 12.62 and 6.45 μg/L, without matrix effect. The apparent recovery for freshwater varied between 93% and 103% (RSDs 2.3–12%). The I-DLLME-HPLC-DAD method scored 0.61, considering the 12 principles of green analytical chemistry from a unified 0–1 scale.