Nanoflow liquid chromatography mass spectrometry method for quantitative analysis and target ion screening of pyrrolizidine alkaloids in honey, tea, herbal tinctures, and milk

Abstract

A method for the determination of pyrrolizidine alkaloids in tea, honey, herbal tinctures, and milk samples was developed by employing nano-LC-MS with high-resolution Orbitrap mass spectrometry. Quantitation was performed using the available analytical standards, and a MS2 target ion screening approach was developed using fragment ions that were specific for pyrrolizidine alkaloids under collision-induced dissociation. Proof of concept was delivered for the screening approach, proposing that the C6H8N+ fragment ion is a highly selective fragment ion for the detection of potential pyrrolizidine alkaloids. The elaborated quantitation was applied for the occurrence study of pyrrolizidine alkaloids in food products available on the Latvian market, including samples of tea (n = 15), honey (n = 40), herbal tinctures (n = 15), and milk (n = 10). The median LOQ over all analytes was 0.33 µg kg-1 in honey, 3.6 µg kg-1 in tea, 3.3 µg kg-1 in herbal tinctures, and 0.32 µg kg-1 in milk. The herbal tinctures samples and milk samples did not contain pyrrolizidine alkaloids above LOQ values. Analytes were detected in 33% of honey and 47% of tea samples. Most common were echimidine, intermedine, and enchinatine N-oxide. Pyrrolizidine alkaloids in tea samples were mainly N-oxides, with the highest total concentration being 215 µg kg-1 among the samples, exceeding the maximum limit of 200 µg kg-1 set by Commission Regulation (EU) 2020/2040. In honey samples, lycopsamine-type alkaloids were detected most frequently, with the highest total concentration equal to 74 µg kg-1. Advantages of the developed nano-LC-MS methods included increased sensitivity in comparison with conventional flow LC-MS, low solvent consumption typical with nano-LC and the novel use of a selective common target ion for detection and discovery of potential pyrrolizidine alkaloids using high resolution mass spectrometry.