Core Imprinting: An Alternative and Economic Approach for Depleting Pyrrolizidine Alkaloids in Herbal Extracts

Abstract Due to the high toxicity of pyrrolizidine alkaloids, in 2011, the German Federal Institute of Risk Assessment recommended that their daily intake limit should be no more than 0.007 µg/kg body weight. The risk of ingesting these substances in herbal preparations, either from their inherent presence in plants or through contamination with pyrrolizidine alkaloid-containing weeds, should not be underestimated. A promising molecular imprinted polymer was developed previously to minimise exposure to these compounds. Due to the high costs of the template and the risk of template bleeding, an alternative and more economic pyrrolizidine alkaloid depleting strategy is still required. Core imprinting, which focuses on the most important structural element in the target molecule, was investigated using triethylamine and tetraethylammonium as easily available and cheap alternative templates. The suitability of core imprinting was demonstrated using a pyrrolizidine alkaloid standard solution if an excess of an alternative template compared to monocrotaline was used for imprinting. Matrix trials in pyrrolizidine alkaloid-spiked Mentha piperita, Chelidonium majus, Glycyrrhiza glabra, and Matricaria chamomilla extracts containing Echium vulgare revealed better pyrrolizidine alkaloid binding than demonstrated for the original molecular imprinted polymer. Echimidine and echimidine-N-oxide were depleted in the range of 31.8–70.0 and 26.1–45.1%, respectively. However, solvent-dependent differences in pyrrolizidine alkaloid binding and inherent plant analytical marker compounds were observed. Hence, binding of analytical marker compounds was better minimised in methanolic than in ethanolic extracts. The present study reveals core imprinting to be an economic alternative approach for depleting pyrrolizidine alkaloids in plant extracts.