Development, optimization, validation and application of ultra high performance liquid chromatography tandem mass spectrometry for the analysis of pyrrolizidine alkaloids and pyrrolizidine alkaloid N-oxides in teas and weeds

Abstract Pyrrolizidine alkaloids (PAs) and their corresponding N-oxides (PANOs) are natural plant toxins, which are widely distributed in various types of teas. The source of PAs contamination in tea is probably related to weeds in tea gardens. The method of simultaneously detecting PAs/PANOs in teas and weeds has not been reported. A sensitive method was developed for detecting 14 PAs/PANOs simultaneously in teas and weeds using ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Sample preparation was optimized step by step. Sulfuric acid at 0.1 M was used to extract the target compounds. Large capacity PCX column was used to enrich target compounds and remove complex matrices effectively, following by the elution solvent with methanol containing 0.5% NH4OH. The method showed good linearity for all 14 analytes with regression coefficients (R2) > 0.99. Satisfactory recoveries of target compounds spiked at three concentrations (10, 50, 100 μg/kg) ranged from 68.6% to 110.2%, while intra-day and inter-day precision were below 18.5%. Limits of detection (LODs) and limits of quantification (LOQs) of 14 PAs/PANOs in different matrices were in the range of 0.001–0.4 μg/kg and 1–5 μg/kg, respectively. This method was firstly applied to monitor the occurrence of PAs/PANOs in different kinds of teas from China and weed samples collected in the local tea gardens. Seven PAs/PANOs (>LOQs) were detected in 15.32% of tea samples and maximum total PAs/PANOs content was 151.33 μg/kg. Pollution levels and patterns of PAs/PANOs were different significantly in various types of teas. Based on the occurrence of PAs/PANOs in teas and weeds, weeds in tea garden were likely to be the source of PAs/PANOs in teas and the most relevant contaminating species of tea samples could be Crassocephalum crepidioides (Benth.) S. Moore.