Determination of C-glucosidic ellagitannins in Lythri salicariaeherba by ultra-high performance liquid chromatography coupled with charged aerosol detector: method development and validation.

Introduction: Lythri salicariaeherba is a pharmacopoeial plant material used by patients in the form of infusions in the treatment of acute diarrhoea. According to its pharmacopoeial monograph it is standardised for total tannin content, which should be not less than 5.0% using pyrogallol as a standard. Previous studies have shown that aqueous extracts from Lythri herba contain mainly ellagitannins among which vescalagin, castalagin and salicarinins A and B are dominating constituents.

Objective: To develop and validate an efficient UHPLC coupled with a charged aerosol detector (CAD) method for quantification of four major ellagitannins in Lythri salicariaeherba and in one commercial preparation.

Methods: Extraction conditions of ellagitannins from plant material were optimised. The relative response factors for vescalagin, castalagin and salicarinins A and B using gallic acid as an external standard were determined for the CAD detector. Then, a UHPLC method for quantification of ellagitannins was developed and validated.

Results: Four major ellagitannins were quantified in four samples of Lythri herba and in one commercial preparation. The sum of ellagitannins for each sample was determined, which varied from 30.66 to 48.80 mg/g of raw material and 16.57 mg per capsule for the preparation investigated.

Conclusion: The first validated UHPLC/CAD UHPLC-CAD method for quantification of four major ellagitannins was developed. The universality of the CAD response was evaluated and it is shown that although all compounds analysed have similar structures their CAD response differs significantly.