Abstract
Cardiac glycosides (CGs) are naturally occurring plant secondary metabolites that can be toxic to humans and animals. The aim of this work was to develop a targeted analytical method utilizing liquid chromatography—tandem mass spectrometry (LC-MS/MS) for quantification of these plant toxins in a herbal-based food and human urine. The method included oleandrin, digoxin, digitoxin, convallatoxin, and ouabain. Samples of culinary herbs were extracted with acetonitrile and cleaned using Oasis® MAX solid-phase extraction (SPE), while samples of urine were diluted with acidified water and purified on Oasis® HLB SPE cartridges. Limits of quantification were in the range of 1.5–15 ng/g for herbs and 0.025–1 ng/mL for urine. The mean recovery of the method complied with the acceptable range of 70–120% for most CGs, and relative standard deviations were at maximum 14% and 19% for repeatability and reproducibility, respectively. Method linearity was good with calculated R² values above 0.997. The expanded measurement uncertainty was estimated to be in the range of 7–37%. The LC-MS/MS method was used to examine 65 samples of culinary herbs and herb and spice mixtures collected in Belgium, from supermarkets and local stores. The samples were found to be free from the analyzed CGs.
Highlights
Cardiac glycosides (CGs) are secondary metabolites produced by plants belonging to, among others, the genera Nerium, Convallaria, and Digitalis
As the initial step of optimization, the flow injection analysis was performed in electrospray ionization positive (ESI(+)) and negative (ESI(-)) modes
The analysis demonstrated that none of the collected samples contained CGs above the lowest calibration level (LCL)
Summary
Cardiac glycosides (CGs) are secondary metabolites produced by plants belonging to, among others, the genera Nerium (oleander), Convallaria (lily-of-the-valley), and Digitalis (foxglove). The core structure of most CGs consists of lactone and steroid rings and a sugar moiety (Figure 1). CGs occur in all parts of plants and can be poisonous to livestock and humans. Their primary mechanism of action is inhibition of the membrane sodium-potassium pump that influences the intracellular sodium, calcium, and potassium concentrations and, as a consequence, causes disruptions in the cardiovascular system. Other symptoms of toxicity may include gastrointestinal, ocular, and neurologic disorders. In a specific dose range, CGs such as digoxin (DIGO) and digitoxin (DIGI)
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