Chromatographic fingerprint development for herbal extracts: a screening and optimization methodology on monolithic columns.

Herbs are used worldwide for preventive and therapeutic purposes. Therefore, identification and quality control of products of vegetal origin is required. Fingerprint chromatography is accepted by the World Health Organization as an identification and quality evaluation technique for medicinal herbs. In fingerprint development, the first step is to create general conditions maximizing the peak capacity. Four herbs, Liquorice, Cascara, Curcuma and Artichoke, were examined using different experimental conditions in order to propose a methodology to develop fingerprint chromatograms in high-performance liquid chromatography (HPLC) with ultra-violet (UV) and evaporative light scattering (ELS) detection. The methodology comprised a screening and an optimization phase. Monolithic C18 columns were used as stationary phases. Several organic modifiers were tested to define a gradient elution system with an optimal selectivity. From the screening phase, linear gradients of 5-60%, 5-54%, 5-95% and 5-95% acetonitrile for Liquorice, Cascara, Curcuma and Artichoke, respectively, were selected. The ELS detection did not provide additional information to the UV detection. The optimization phase selected the best experimental conditions for wavelength, column length, flow rate and slope of the gradient for the best modifier determined at the end of the screening. For the four examined herbs 254 nm as detection wavelength, 300 mm column length, 2 ml/min flow rate and a gradient time of 50 min were defined as the best conditions. If these latter unique conditions are confirmed for other case studies, the actual strategy even might be simplified by reducing the optimization stage.