Screening and identification strategy for 317 pesticides in fruits and vegetables by liquid chromatography-quadrupole time-of-flight high resolution mass spectrometry

Abstract

Efficient analysis of large amounts of raw data for detection and identification of chemical adulterants is always a difficult challenge in the field of food safety. The present study proposed a combined strategy for qualitative screening and identification of 317 pesticides in vegetables and fruits using high performance liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (HPLC-Q-TOF/MS) based on a homemade accurate mass database (MS¹) and a novel MS/MS spectral library (MS²). An accurate mass database and a collision-induced-dissociation (CID) accurate mass spectral library were developed prior to actual application. The screening strategy involved two injections of each sample extract. Firstly, HPLC-Q-TOF/MS in full MS scan mode was conducted and all potential compounds in the MS¹ database were matched against the raw data of samples for target screening. Secondly, targeted MS/MS analysis was carried out by using hybrid Q-TOF/MS and the fragment ions were identified by the MS² spectral library. To validate the performances of the in-house MS¹ database and the MS² spectral library, cucumber and orange matrices were prepared by traditional solid phase extraction, spiked with 317 pesticides at three concentration levels, 1, 10 and 50 μg kg⁻¹ for most of the pesticides, and analyzed by HPLC-Q-TOF/MS. The results showed that over 83.9% of pesticides at 10 μg kg⁻¹ or lower could be detected by TOF/MS combined with the MS¹ database, and 76.7% of them could be identified by targeted MS/MS coupled with the MS² library in each matrix. The total false negative rate of the proposed qualitative screening method was as low as 4.7% at 50 μg kg⁻¹. Consequently, the proposed method was applied to 328 real fresh vegetables and fruits. Finally, 57 pesticides and 799 positive results were found. The approach to detect and to identify pesticides based on the accurate mass database integrated CID accurate mass spectral library was proved to be a cost-effective and powerful strategy for routine qualitative screening of pesticides.