Comparative study of pyrethroids residue in fruit peels and fleshes using polystyrene-coated magnetic nanoparticles based clean-up techniques

An efficient and rapid method for quantifying pyrethroids pesticide residue in fruits samples was developed in the present study. The application of lab prepared polystyrene magnetic nanoparticles based magnetic solid phase extraction technique combined with liquid-solid extraction helped clean-up the sample and preconcentrate the targeted analytes prior to HPLC quantification. The lab prepared nanoparticles were characterised with Fourier transform infrared spectroscopy, atomic force microscopy, X-ray diffraction spectroscopy, as well as vibrating sample magnetometer to study their size, morphology, crystal structure, functional groups and magnetism properties, respectively. Afterwards, optimisation of the parameters affecting extraction efficiency was carried out in order to achieve optimum conditions for extracting pyrethroids residue from fruit samples. Analytical performances were evaluated by carrying out experiments at optimum conditions. Results showed that the limit of detection and limit of quantification were below 0.1445 and 0.5116 ng g−1, respectively for the six pyrethroids tested. The recovery rates were within the range of 73.6%-123.1% with intra-day and inter-day relative standard deviation being less than 16.5% and 15.4%, respectively, suggesting satisfactory reproducibility of the proposed method. Real sample analysis was performed using 6 kinds of commonly consumed fruits obtained from local supermarkets in Singapore, including apples, pears, oranges, lemons, grapes and nectarines. The peel and flesh were tested separately to study the difference of pyrethroids residue in different parts of fruits. The grape sample tested was detected with permethrin residue on its peel. There was no violation since the permethrin amount detected was way much lower than the maximum residue limit set by local government.