Rapid Determination of 26 Pyrrolizidine Alkaloids in Milk Power and Liquid Milk by Solid Phase Extraction Combined with Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry

A method was developed for the simultaneous determination of 26 pyrrolizidine alkaloids (PAs) in milk powder and liquid milk by solid phase extraction (SPE) combined with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The samples were extracted with 5% trichloroacetic acid solution, cleaned up on a polymer cation exchange-solid phase extraction (PCX-SPE) column, separated on an ACQUITY HSS T3 column with gradient elution using a mobile phase consisting of methanol and 0.1% formic acid in water, detected using an electrospray ionization (ESI) in the positive ion mode with multiple reaction monitoring (MRM), and finally quantified by the external standard method. The method validation was performed under optimal conditions. The calibration curves for the 26 PA compounds showed good linearity in the range of 1.0–40 ng/mL with determination coefficients (R²) greater than 0.992. The limits of detection (LOD) and quantification (LOQ) of the developed method were in the range of 0.01-0.33 μg/kg (R_S/N = 3) and 0.03–1.0 μg/kg (R_S/N = 10), respectively. Recoveries for blank milk powder and liquid milk spiked at 1 ×, 2 ×, and 10 × LOQ levels ranged from 73.1% to 111.6% with relative standard deviations (RSDs, n = 6) of 0.6%-9.8%. In conclusion, this method is simple, efficient, sensitive, accurate, and suitable for the determination of the 26 PAs in milk powder and liquid milk.