Analytical standards were obtained from different suppliers as follows:
echimidine (purity 97%),
echimidine N-oxide (purity 97%),
heliotrine (purity 91%),
heliotrine N-oxide (purity 91%),
lycopsamine (purity 80%) and
lycopsamine N-oxide (purity 80%) from PhytoLab GmbH & Co. KG (Vestenbergsgreuth, Germany); senecionine (purity 99%), senecionine N-oxide (purity 99%), seneciphylline (purity 94%) and seneciphylline N-oxide (purity 94%) from Carl Roth & Co. KG (Karlsruhe, Germany);
indicine-N-oxide (purity 99%),
intermedine (purity 99%),
jacobine (purity 98%),
jacobine N-oxide (purity 98%),
retrorsine (purity 90%),
retrorsine N-oxide (purity 96.0%) and
senkirkine (purity 98%) from Phytoplan (Heidelberg, Germany);
caffeine (purity 98%), used as an internal standard, was from Sigma-Aldrich (Steinheim, Germany).
Methanol (LC-MS grade) and sulphuric acid (98% purity, analytical grade) were from Carlo Erba reagents (Milan, Italy). Ammonia (28% purity, analytical grade) was from VWR Chemicals.
Formic acid (98% purity, LC-MS grade) was from Sigma-Aldrich. Ultra-pure water was obtained from a water purification system (
Purelab Classic, ELGA Lab Water, High Wycombe, UK).
De Jesus Inacio L., Lanza I., Merlanti R., Contiero B., Lucatello L., Serva L., Bisutti V., Mirisola M., Tenti S., Segato S, & Capolongo F. (2021). Discriminant analysis of pyrrolizidine alkaloid contamination in bee pollen based on near-infrared data from lab-stationary and portable spectrometers. Eur Food Res Technol., 246(12).