Rapid Screening and Identification of Azole and Organophosphorus Pesticides in Food Based on Characteristic Product Ions and Neutral Losses

Mass spectrometry (MS) has the advantages of high sensitivity and high selectivity, and can obtain the structural information of the analytes rapidly when combined with ambient ionization techniques,e.g., direct analysis in real time (DART) and paper spray (PS). In this work, a fast and simple approach for the screening and identification of azole ( i.e., triazole, imidazole, and pyrazole) and organophosphorus pesticides in food was proposed using ambient ionization coupled with hybrid quadrupole Orbitrap high-resolution mass spectrometry (Q-Orbitrap HRMS). The chemical structures of these two categories of pesticides were summarized, and their product ions and neutral loss information in mass spectrometry were also concluded. Triazole pesticides had a functional group of triazole (C₂H₃N₃). The exact mass of triazole was 69.032 70 and the exact m/z value of protonated triazole was 70.039 97, which represented the neutral loss and product ion of triazole pesticides. Similarly, imidazole/pyrazole had a functional group of imidazole/pyrazole (C₂H₄N₂). The exact mass of imidazole/pyrazole was 68.037 45 and the exact m/z value of protonated imidazole/pyrazole was 69.044 72, which represented the neutral loss and product ion of imidazole/pyrazole pesticides. Organophosphorus pesticides had similar structures and fragmentation pathway in MS/MS. Experimental results showed organophosphorus pesticides produced the neutral loss and the corresponding product ions of PO₃SH₃ (133.954 05), PO₂S₂H₃ (129.931 21), PO₃H (79.966 33), PO₂SH (95.943 49), POS₂H (111.920 64) and POSH (79.948 57). For the homologous series of pesticides, the exact mass and m/z increased by (CH₂)_m, i.e., 14.015 65×m (m=0, 1, 2…). All the aforementioned were the common characteristic product ions and neutral losses. Moreover, the auxilliary qualitative product ion and neutral loss, and the individual product ion and neutral loss libraries were also utilized to assist to identify the chemical structures of unknown azole and organophosphorus pesticides. During data acquisition, full scan (FS) mode and all-ion fragmentation (AIF) mode were applied in two time segments to obtain all the information of precursor and product ions. During data processing, the product ion and neutral loss information could be reined from the data of precursor ions and product ions by Python. Then, all the product ions and neutral losses were searched in the common characteristic, auxilliary qualitative and individual product ion and neutral loss libraries to screen known pesticides and identify unknown pesticides. Therefore, azole and organophosphorus pesticides could be screened and identified, in combination with suitable sample preparation method, proper ambient ionization source, high-resolution tandem mass spectrometer and effective data processing strategy. This method is fast and accurate, and can be used for the analysis of different types of food samples.