A Novel Method Based On Mspd For Simultaneous Determination Of Pesticide Residues In Tea By LC-MS/MS

Tea, a most widely consumed beverage throughout the world, has specific aroma and antioxidant property that is good for human health. The tea quality and safety have attracted an ever-increasing attention. Pesticide residue is one of the major chemical contaminants found in tea matrice. Carbamate, organophosphorus and pyrethroids are widely used during the cultivation of tea. These pesticides have been shown to have potentially harmful effects on the environment and human beings. Therefore, some developed countries and international organizations have issued maximum residue limits (MRLs) for these pesticides in tea. Due to the, high risk for the consumer health, rapid and cost-effective multiple pesticide residue analysis represents an important task for both the tea producers and regulatory agencies. In this work, a novel one-step method based on matrix solid phase dispersion (MSPD) coupled with liquid chromatography-tandem mass spectrometry was established for the determination and the quantification of 16 pesticides (5 carbamates,4 organophosphorus and 7 pyrethroids) in various tea. Matrix dispersive sorbent and further cleanup sorbent were applied to improve the efficiency of extraction and purification. Different experiment conditions, such as type of eluting solvent, its volume, matrix dispersive sorbent, sample to matrix dispersive sorbent mass ratio, and the dosage of cleanup sorbents were thoroughly studied and optimized. It was found that polyvinylpolypyrrolidone (PVPP), an inexpensive and excellent absorbent, could effectively remove polyphenols in tea, which was seldom reported before. The method showed satisfactory linearity over the range assayed 0.9986-0.9999 (1-500ng·g1 for 5 carbamates and 4 organophosphorus,2-800 ng·g-1 for 7 pyrethroids), the limits of detections (LODs) ranged from 0.01 to 1.38 ng·g-1, and the limits of quantifications (LOQs) were ranging from 0.03 to 4.74 ng·g-1. The recoveries using this method at three spiked concentration levels (10,100, and 500 ng·g-1) range from 87.7 to 99.6%. The relative standard deviation (RSD) was from 0.3 to 9.6% in all case. The proposed analytical method has been successfully applied for the analysis of 16 pesticides in commercial tea.The empty column and glass filter paper used in this study were reused from ISOLUTE SLE+ Column (25 mL capacity, Biotage, Sweden), which were ultrasoniced by alcohol for 10min, rinsed 3 times by acetone, and evaporated to dry before used. In order to efficiently use cleanup sorbents, GCB, PVPP were dispersed by sea sand. Firstly,50mg GCB and 450mg sea sand were gently blended until obtaining a homogeneous system and then transferred to the column with a glass filter paper at the bottom. Secondly, 1.0g PSA and 1.5g sea sand were mixed as above mentioned process and then filled into the column on the top of GCB. Lastly,750mg PVPP was directly added to the column on the top of PSA and then the system was covered by another filter paper. The cleanup system was prepared for the following experiments.The tea was crushed and passed through a 40 mesh sieve (about 245mm). Aliquots of 0.5 g tea was transferred to a mortar (30mL capacity), then 100μL 2μg·g-1 mixed internal standard solution (TPP, D6-dimethoate, D10-chlorpyrifos and D6-trans-cypermethrin) in methanol was added as a quality control for the entire procedure, after solvent evaporation (approximately one hour), gently homogenized with a pestle with 0.75 g C18 and 0.75 g FLS for 5 min to obtain a homogeneous mixture. Then the homogeneous mixture was transferred into the purification column (prepared in 2.2), successively, the column was connected to a vacuum system for solid phase extraction adjusting the flow to 0.5 mL/min. The elution step was carried out with 20 mL acetonitrile,8 mL the first time,10 mL for the second time:2.0 mL additional eluent was adopted to wash the mortar and pestle, and then transferred into the column. The collected solution was evaporated under a gentle stream of nitrogen at 35℃. Finally, the residue was dissolved in 1.0 mL initial mobile phase, and then filtered through a 0.22μm PTFE filter for LC-MS/MS analysis.In another work, we helped verifying the standard method of persistent organic pollutants (POPs) in soil. We developed the GC-MS method for the determination and the quantification of 24 POPs. The method showed satisfactory linearity over the range assayed 0.9924-1 (S-150ng·mL-1). The recoveries of GPC purification process using this method at three spiked concentration levels (5,50, and 500 ng·g-1) range from 80.36 to 119.10% and the relative standard deviation (RSD) was from 0.40 to 7.69%. The recoveries of SPE purification process using this method at three spiked concentration levels (5,50, and 500 ng·g-1) range from 72.11 to 118.78% and the relative standard deviation (RSD) was below6.30%. All the results meet requirements of the standard method.