Extraction efficiency of four pesticides using the QuEChERS extraction method and analysis by HPLC/DAD

Abstract: A cleanup step is essential from an analytical perspective, to improve the chance of quantification and to minimize interference. Pesticides in soil are a necessity is agriculture for survival of crops and protection from unwanted growth and pests. However, an ongoing problem is the lack of instruments where levels of pesticides can be measured with high accuracy, even at low concentrations during analysis. In this study, the extraction selectivity and efficiency of four different pesticides was observed with the quick, easy, cheap, effective, rugged and safe (QuEChERS) method coupled with high performance liquid chromatography-DAD. The sample consisted of four pesticides with different positive log P values in soil. The observed parameters for obtaining the highest extraction efficiency were amount and type of sorbent and salt. The two sorbents tested were the non polar Nucleosil C18 and polar Nucleosil NH2, with the aim to observe which of them gave a higher extraction efficiency. Magnesium sulphate is the salt that is used as a drying agent. A observation regarding the change in extraction efficiency with an increased sorbent and salt amount was also made. In terms of linearity and precision, the experiment was validated with a soil sample collected from LTH-parken in Lund. A matrix matched calibration curve were prepared for all analytes in question to estimate the recovery of pesticides after cleanup. From the method, it showed that NH2 sorbent showed the highest extraction efficiency for all pesticides, because of its ability to adsorb the multitude of polar interference in the matrix. At an increased amount of the sorbent NH2, an increased yield of one of the pesticides, deltamethrin, was detected. When C18 was used as the sorbent, a decrease in the extraction efficiency of prallethrin, propiconazole and imidacloprid was detected compared to NH2, due to a probable interaction between the analytes and the adsorbent. An extraction with 6 g MgSO4 showed higher yields of imidacloprid and deltamethrin, and 4 g of MgSO4 showed higher yields of propiconazole. Prallethrin showed equal yields, regardless of the amount of salt. HPLC-DAD at 235 nm was a suitable analyzing method that provided high selectivity and detectability for each pesticide.