A novel sample-preparation method for the generic and rapid determination of pesticides and mycotoxins in tea by ultra-performance liquid chromatography-tandem mass spectrometry

A rapid, simple, and generic analytical method for the simultaneous determination of 140 undesirable low-weight pesticides and mycotoxins from different chemical classes in black tea was developed. The method involved swelling the sample in ammonium acetate buffer, extraction with acetonitrile-dimethyl sulfoxide, cleanup by dual dispersive solid-phase extraction (D-SPE) with the assistance of low-temperature centrifugation, and analysis by ultraperformance liquid chromatography coupled with electrospray ionization tandem mass spectrometry using multiple reaction monitoring mode. The interferences in the extract were eliminated by the combination of dual D-SPE using only C-18 sorbent and anhydrous magnesium sulfate, which maintained the chromatographic column under the ideal condition for a long time and enabled satisfactory recoveries of hydrophobic and hydrophilic analytes simultaneously. Matrix-matched calibration curves were obtained for most target compounds with linear regression coefficients above 0.9900. The limits of quantification (LOQs) ranged within 0.5-10.0 Ag/kg, which were usually sufficient to verify the compliance of products with legal tolerances. Satisfactory recoveries of 64.5%-138.1% were obtained in black to samples with the relative standard deviation (RSD) values between 1.8 and 25.9%. The inter-day precision ranged within 2.2%-24.9%. For over 90% of the analytes, the recoveries were between 70% and 120%, with RSD values below 15.0%. The application of this method in routine monitoring programs can drastically reduce effort and time. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

A rapid, simple, and versatile analytical method was developed for the simultaneous determination of 140 undesirable low-weight pesticides and mycotoxins in black tea. The method involved a combination of dual D-SPE with C-18 sorbent and anhydrous magnesium sulfate to eliminate interferences in the extract, maintaining the chromatographic column under ideal conditions for long-term satisfactory recoveries. Matrix-matched calibration curves were obtained for most target compounds with linear regression coefficients above 0.9900, and the limits of quantification (LOQs) ranged within 0.5-10.0 μg/kg.