Determination of 21 plant growth regulators in tomatoes using an improved ultrasound-assisted QuEChERS technique combined with a liquid chromatography tandem mass spectrometry method

Abstract

As the largest producer of tomatoes in the world, it is of great importance for China to guarantee a high quality of tomatoes. Hence, a fast and reliable method for the determination of multi-pesticide residues, including plant growth regulators (PGRs), is highly sought after. In this study, a sensitive and selective liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method, using a selective reaction monitoring mode for the selected negative and positive transition ions, has been developed to detect 21 PGRs in tomatoes. Sample preparation was based on a modified QuEChERS (quick, easy, cheap, effective, rugged and safe) method, in which the extraction solvent acetonitrile was acidized, the ultrasound extraction step was supplemented and the amount of primary secondary amine (PSA) was reduced. LC-MS/MS conditions, including the composition of mobile phases and mass spectrometry (MS) parameters, were evaluated to achieve the highest sensitivity in MS detection. At the spiked concentration of 50 and 100 μg kg⁻¹ (200 and 500 μg kg⁻¹ for maleic hydrazide and flumetralin), the recovery yields ranged from 80.7% to 114.6% with good repeatability (relative standard deviation (RSD) < 17%) and reproducibility (RSD < 18%) for 21 PGRs. The limit of detections (LODs) for the target analytes in tomatoes were between 0.1 and 61 μg kg⁻¹, and the limit of quantifications (LOQs) (0.3–200 μg kg⁻¹) were lower than the maximum limit of residues established for PGRs except flumetralin. The method has been successfully applied to the analysis of tomato samples obtained from local markets.