Multiresidue Pesticides Analysis of Vegetables in Vietnam by Ultrahigh-Performance Liquid Chromatography in Combination with High-Resolution Mass Spectrometry (UPLC-Orbitrap MS)

Abstract

An ultrahigh-performance liquid chromatography in combination with high-resolution mass spectrometry Thermo Q-Extractive Focus Orbitrap MS has been introduced for analysis of multiclass pesticides in vegetable samples collected in Hanoi, Vietnam. Multiclass pesticides were separated on the Thermo Hypersil Gold PFP column utilizing a gradient of the mobile phase consisting of 5 mM ammonium formate, 0.1% formic acid in deionized water, and methanol. The target analytes were detected in the full-scan mode on Thermo Scientific Q-Exactive Focus Orbitrap MS for quantitation at the optimum operating conditions. These conditions included, but not limit to, the resolution of 70000 at the full width at half maximum in both positive and negative mode, mass range from 80 to 1000 m/z, and optimized parameters for the heated electrospray ionization source. The identification of the analytes in real samples was based on retention times, mass to charge ratios, mass accuracies, and MS/MS spectra at the confirmation mode with the inclusion list of target analytes. The mass accuracies of target analytes were from -4.14 ppm (dinotefuran) to 1.42 ppm (cinosulfuron) in the neat solvent and from -3.91 ppm (spinosad D) to 1.29 ppm (cinosulfuron) in the matrix-matched solution. Target analytes in the vegetable-based matrix were extracted by the QuEChERS method. Some critical parameters of the analytical method such as linearity, repeatability, limit of detection, and limit of quantitation have been evaluated and implemented. Excellent LOD and LOQ of the developed method were achieved at the range of 0.04-0.85 and 0.13-2.9 μg·kg^-1, respectively. Intraday and interday repeatability of the analytical signal (peak area, n=6) of the developed method were below 3% and 10%, correspondingly. The matrix effect, extraction recovery, and overall recovery were fully investigated by spiking experiments. Experimental results demonstrated that the ionization suppression or enhancement was the main contribution on the overall recoveries of target analytes. Finally, the in-house validated method was applied to pesticides screening in vegetables samples in local villages in Hanoi, Vietnam. The concentrations of all target analytes were below limit of quantitation and lower than US-FDA or EU maximum residue levels.

Figure 1

Experimental setup for assessment of recovery, matrix effect, and entire sample preparation procedure.

Figure 2

Total chromatogram of multiclass pesticides on the different stationary phases: (a) PFP column; (b) Hypersil ODS; (c) HyperClone™ 5 μm ODS 120 Å.

Figure 3

The total ion and extracted ion chromatogram of the target analytes in the standard solution (a) and in the matrix-match solution (b) on the Thermo Hypersil GOLD PFP column, and other operating conditions are mentioned in Section 2.2. The first and second numbers on the right upper are mass-to-charge ratio and retention time, respectively.

Figure 4

Overall recovery of all targeted analytes in pooled samples analyzed by UPLC-Orbitrap MS. Columns and error bars present the overall recovery and relative standard deviation (n=3), respectively. Red color indicates the recovery of the analyte out of an acceptable range (from 80 to 120%). (−) denotes an analyte that is measured in the negative electrospray ionization mode.

Figure 5

TIC and EICs of pesticides found in edible chrysanthemum (a) and green salad (b).