Abstract:

Food poisoning by toxic mushrooms occurs frequently worldwide. It is one of the most common food poisoning events and the main cause of death. Amanita peptide toxins are the most common lethal toxins in poisonous mushrooms. Presently, a novel method based on ultra performance liquid chromatography-quadrupole electrostatic field orbitrap high resolution mass spectrometry (UPLC-Q/Orbitrap HRMS) was developed for the determination of five amanitapeptide toxins (α-amanitin, β-amanitin, γ-amanitin, phalloidin, and phallacidin). Because the isotope summit of α-amanitin affects the detection of β-amanitin, it cannot be distinguished by low resolution mass spectrometry. Therefore, experimental conditions including chromatography and mass spectrometry were explored in detail. The five peptide toxins were extracted from poisonous mushrooms with pure water and filtered through a 0.22 μm teflon microporous membrane. The procedure was rapid, simple, and environmentally friendly. Chromatographic separation was performed on a strong polarity HSS T3 column (100 mm×2.0 mm, 2.1 μm) with gradient elution using acetonitrile and 5 mmol/L ammonium acetate containing 0.1% (v/v) formic acid as mobile phases at a flow rate of 0.3 mL/min. The column temperature was set to 40 ℃. The analytes were ionized using a heating electrospray ionization source and collected in positive ion mode. Full scanning/data-dependent secondary mass spectrometry (Full mass-ddMS²) mode was used for qualitative analysis of the targets within 10 min. The target ion selective scan (Targeted-SIM) mode was used for quantification by external standard calibration. The measured and theoretical values of the exact mass and the MS² fragment ions of the five compounds were within an error of 5×10^-6. Method validation was performed according to the criteria recommended by the Chinese National Standard. All the compounds showed an excellent linear relationship in the range of 1.0-20.0 μg/L. The correlation coefficients (r) ranged from 0.9974 to 0.9989. The limit of detection was 0.006 mg/kg for all five compounds. Recoveries ranged from 81.8% to 102.4%. There was no matrix effect in the blank mushroom sample for the five compounds, and the relative standard deviations ranged from 3.2% to 8.3%. This method provides abundant compound characteristic mass information, such as retention time, exact mass, fragment ions, and other information. The data can be used to identify suspected compounds based on the extracted ion flow diagram and isotope distribution information. Comparison between the actual exact mass and the theoretical exact mass, combined with the fragment ions enables identification of the structures of unknown compounds and collision methods, which can be confirmed in the absence of standard materials. In this study, the isomer of γ-amanitin was identified as amaninamide. The novel method is simple, accurate, specific, and sensitive. The method permits the rapid qualitative and quantitative detection of compound in public health emergency settings and will provide reliable technical support for the rapid screening of such toxic compounds and the structural locking of unknown toxins in the future.

Key words: ultra performance liquid chromatography-quadrupole electrostatic field orbitrap high resolution mass spectrometry (UPLC-Q/Orbitrap HRMS), amatoxins, phalloidin, poisonous mushroom