Identification of pesticide transformation products in agricultural soils using liquid chromatography/quadrupole-time-of-flight mass spectrometry

Determination of the Dissipation Dynamics and Terminal Residue of Bupirimate and Its Metabolites in Cucumber by QuEChERS-Based UPLC-MS/MS

Bupirimate is widely used as a highly active systemic fungicide. However, the frequent and heavy use of bupirimate has led to pesticide residues in crops that threaten human health and food safety. At present, there is limited research on the detection of ethirimol, which is the metabolite of bupirimate. This study established an ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method to simultaneously detect bupirimate and ethirimol residues based on QuEChERS pretreatment. The average recoveries of bupirimate and ethirimol in cucumber were between 95.2 and 98.7%, respectively, with relative standard deviations (RSDs) of 0.92-5.54% at fortified levels of 0.01, 0.1, and 5 mg L^-1. The established method was used to determine the residues in field trials in 12 regions of China, and the final residues of bupirimate were all less than the maximum residue limit (MRL). Since the risk quotient (RQ) of bupirimate and ethirimol in cucumber was less than 1.3%, the dietary risk assessment indicated that bupirimate and ethirimol had a low long-term dietary risk to the general population in China. This study provides effective guidance on the proper use of bupirimate in cucumber fields and a reference for establishing the MRL of bupirimate in China.

Structure elucidation of ostreocin-A and ostreocin-E1, novel palytoxin analogs produced by the dinoflagellate Ostreopsis siamensis, using LC/Q-TOF MS

Palytoxin analogs are marine toxins with large complex polyol structures. A benthic dinoflagellate Ostreopsis siamensis produces more than ten palytoxins (ostreocins, OSTs). The limited sample availability of minor OSTs restricts the definition of their chemical structures. The present investigation characterizes structures of two minor OSTs, i.e., ostreocin-A (OSTA) and ostreocin-E1 (OSTE1), using ostreocin-D (OSTD) as a reference compound, by liquid chromatography/quadrupole-time-of-flight mass spectrometry. The molecular formulas of OSTA and OSTE1 were C127H219N3O54 and C127H217N3O52, respectively. Compared to OSTD, OSTA has an extra oxygen atom whereas OSTE1 lacks one oxygen atom and two hydrogen atoms. The MS/MS experiments (precursor ions: [M + H]+ and [M-H]−) suggested a hydroxyl substitution at C82 in OSTA and alteration(s) between C53 and C100 in OSTE1. Further analysis of structural details in OSTE1 was performed through a pseudo-MS3 experiment (precursor ion: m/z 1432.748). Accordingly, the planar structures of OSTA and OSTE1 were assigned to 42,82-dihydroxy-3,26-didemethyl-19,44-dideoxypalytoxin and 42-hydroxy-3,26-didemethyl-19,44,73-trideoxypalytoxin-72-ene, respectively.

Abbreviations:CID: collision induced dissociation; HR-LC/MS/MS: high-resolution liquid chromatography/tandem mass spectrometry; LC/ESI/Q-TOF MS: liquid chromatography/quadrupole time-of-flight mass spectrometry equipped with an electrospray ionization source; NMR: nuclear magnetic resonance; OSTs: ostreocins; OSTA: ostreocin-A; OSTB: ostreocin-B; OSTD: ostreocin-D; OSTE1: ostreocin-E1; OVTX-a: ovatoxin-a; OVTXs: ovatoxins; PLTX: palytoxin

Identification of prometon, deisopropylprometon, and hydroxyprometon in groundwater by high resolution liquid chromatography/mass spectrometry

Prometon, a major soil sterilant, and its main transformation products, deisopropylprometon (N(2)-isopropyl-6-methoxy-1,3,5-triazine-2,4-diamine) and hydroxyprometon (4,6-bis(isopropylamino)-1,3,5-triazin-2-ol), were identified as the dominant triazine herbicides in groundwater samples from 51 locations in Colorado, USA, over a two-year time period. They were concentrated from water by solid phase extraction and detected using an ultrahigh pressure, liquid chromatography-quadrupole time of flight tandem mass spectrometry (UHPLC/QTOF-MS). The transformation products, deisopropylprometon and hydroxyprometon, were confirmed using MS-MS experiments. An original strategy was applied to form the degradation standards for deisopropylprometon and hydroxyprometon, which consisted of photo-degradation of prometon followed by MS-MS analysis. The concentration of prometon ranged from the detection limit of 3 ng·L(-1) to 87 ng·L(-1), hydroxyprometon ranged up to 50 ng·L(-1), and deisopropylprometon up to 100 ng·L(-1), with a frequency of detection of 80%, which was greater than the other triazines detected in the groundwater samples. A new ratio is proposed for prometon degradation called the "deisopropylprometon to prometon ratio" or the DIP ratio, as an indicator of prometon residence time in groundwater. Furthermore, these data suggest that prometon is more of an issue for groundwater contamination in urban areas rather than agricultural areas.