High-resolution method for regulatory control of Echinacea species in Nutraceuticals by CD-MEKC

Abstract

One problem in the international regulatory control of Echinacea, a therapeutic Nutraceutical, is recognition of caffeoyl solutes and alkamides in different products. Cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) has been applied to Echinacea spp. in combination with pattern recognition of some caffeoyl solutes. A novel metric based on relative migration time (RMT) data has been developed in CE to address the problem of variable reported migration time. The CD-MEKC method of Gotti's group using hydroxypropyl-β-cyclodexrin (HP-β-CD; 100 mM) with sodium dodecyl sulphate (SDS; 110 mM), in a triacid background electrolyte (10 mM, pH 8) under 19 kV was adapted to identify two key hydrophilic solutes: chlorogenic acid and cichoric acid present in all commercial products. Two internal markers were taken as reference points to calculate the RMT of any target peak: RMT = t m (target)/ t m (marker). The RMT method was robust to temperature change from 20 to 40 °C, but sensitive to pH. The lateral shift and reproducibility of the target peak t m (target) were significantly reduced by this novel transformation. In the worst cases migration time variability ranged up to 12% ( n = 6); the RMT algorithm reduced this to less than 1%. In general, the RMT transformation reduced the variability of migration time data by a factor of 2–5. For systematic comparison of electrophoretic profiles for test sample and standard, a new pattern recognition algorithm permits sequential peak-by-peak comparison using specified segments of the electropherograms for comparison of test and Echinacea purpurea (root product) as a standard. This algorithm was capable of rapidly characterising the similarity of target peaks in a test sample relative to those in the reference standard. Combination of the RMT algorithm and pattern recognition in CE is expected to offer a robust approach to international regulatory characterisation and control of Nutraceuticals.