Herbal adulteration is the intentional addition of active or medicinal plants to a product without notification. Often these plants are regulated or sometimes even forbidden for use in dietary supplements, the category of products that is most affected by this phenomenon. The detection of herbal adulteration, in contrast to chemical adulteration, is not straight forward, since classical techniques like micro- and macroscopy cannot be applied due to the complex nature of plant food supplements and the extensive processing of their herbal ingredients.

This research presents a chromatographic fingerprinting approach combined with multivariate calibration techniques for the screening of three regulated plants with potency enhancement properties in plant food supplements. The targeted plants are Tribulus terrestris, Epimedium sp. and Pausinystalia yohimbe. The former two may be present in dietary supplements, but should be notified on the packaging, while Pausinystalia yohimbe is forbidden.

Reference plants were used to develop a UHPLC-DAD method, able to provide characteristic profiles for each of the three targeted plants. For each plant the most specific wavelengths (four for Tribulus terrestris and Pausinystalia yohimbe, three for Epimedium sp.) were selected. The chromatographic data at each wavelength was recorded for a series of triturations and merged into one data cube (absorbance x time x trituration) per plant. These data cubes were consequently used for the calculation and validation of three binary PLS-DA models, allowing the prediction of presence of the respective targeted plants.

The validated approach was further applied in the analysis of 25 plant food supplements, originating from the illegal market. Based on the obtained results six (24%) samples contained what was labelled on their packaging, while for the remaining eighteen samples (76%) non-labelled plants were detected. Moreover, six samples contained the forbidden plant Pausinystalia yohimbe and four samples did not contain the plants claimed.

These results indicate the importance of a screening approach for herbal adulteration, applicable to complex matrices. The presented methodology is a step in that direction, but should still be complemented with another confirmatory technique in case of decision-making on withdrawal from the market (legal market) or a judicial context.

Conversely, the presence of adulterated products in the (illegal) market was verified, demanding stricter regulation and oversight of plant food supplements and their entry channels.