Low density solvent based dispersive liquid-liquid microextraction followed by vortex-assisted magnetic nanoparticle based solid-phase extraction and surfactant enhanced spectrofluorimetric detection for the determination of aflatoxins in pistachio nuts

A simple and efficient two-step extraction method, namely a low density solvent based dispersive liquid-liquid microextraction (DLLME) followed by a vortex-assisted dispersive solid-phase extraction (VA-D-SPE) combined with analysis by surfactant enhanced spectrofluorimetry, was developed for the determination of the total aflatoxins in pistachio samples. The analytes were first extracted with methanol-water (80 : 20, v/v) from solid pistachio matrices and this solution was directly used as the dispersing solvent accompanied with 1-heptanol as the low density extracting solvent in the DLLME procedure. In the VA-D-SPE approach, hydrophobic Fe3O4 nanoparticles (i.e. oleic acid modified magnetic nanoparticles) were used to retrieve the analytes from the DLLME step. It was noticed that the target of the hydrophobic nanoparticles was 1-heptanol rather than the aflatoxins directly. The main parameters affecting the efficiency in DLLME and VA-D-SPE and the signal enhancement of the analytes were investigated and optimized. Under the optimum conditions, the calibration curve showed a good linearity in the range of 0.05-500 mu g L-1 (R-2 = 0.9984) with a low detection limit of 21 ng L-1. The repeatability and reproducibility of the extraction (as RSD%) were in the range of 2.3-4.6% and high recoveries ranging from 91.6 to 99.6% were obtained. Finally, the proposed method was successfully applied to the determination of the total aflatoxins in commercial pistachio samples. The obtained results revealed that the method is simple, inexpensive, accurate and remarkably free from interference effects. Furthermore, the proposed method reclaimed the versatility of DLLME because the selection of extraction solvent was not limited to high density solvents.