Mass Spectrometry Based Shotgun Method for Untargeted Fast Screening of Microcystin Residues in Mylopharyngodon piceus

Precursor-ion scan (PreIS) is a versatile scanning mode but not commonly used by mass spectrometry analyzers. In this study, a shotgun method was developed for fast untargeted screening of MCs in Mylopharyngodon piceus (M. Piceus) on the basis of the specific functions of PreIS and the structural characteristics of MCs. The performance of this method was improved by optimizing the conditions of solid-phase extraction and parameters of mass spectrometry. Three types sorbent were compared, including florisil, HLB, and C18. The HLB (68.2%-83.4%) performed best, followed by C18 (63.5%-78.5%) and florisil (ca.60%). 2% and 80% methonal were used as washing and eluting solvents, respectively. The MCs were easily ionized as doubly charged ions M+2H2+. Under product-ion scan, all the MCs can generate fragment ions like m/z 375, 213 and 135, where m/z 135 is the most intensive one. Therefore, m/z 135 was selected for conducting PreIS of MCs. The standard solution of five MCs mixture was detected, and all the doubly charged ions of MCs were observed. Finally, the proposed shotgun method was validated in terms of linearity, sensitivity, precision and recovery. The results indicated that the calibration curves are linear with R2 of 0.9925-0.9971. The LOD and LOQ are not more than 1.25 and 3.99 μg/L, respectively. The RSDs of intra-day and inter-day precision are 6.8%-8.6% and 7.2%-9.1%, respectively. All the MCs can be well recovered with recovery of 68.2%-83.4%, and RSDs of 4.5%-6.8%. This method was applied to the M. Piceus samples from local market, and 15% samples were detected to be positive. MC-RR and MC-LR are the two frequently detected MCs in these samples, with concentrations of 3.4-15.8 μg/kg. The shotgun method is robust and efficient in detecting MCs in M. Piceus. The data are important- references for related functional department to ensure the food safety of domestic consumers.