HPTLC general method for identification of polysaccharide containing herbal drugs and preparations thereof

In the current edition of the European Pharmacopoeia (9^th Ed.) (1), the chromatographic identification of polysaccharide rich herbal drugs (HD) and preparations thereof, such as mucilages and starches, is based on TLC analysis of monosaccharides released after hydrolysis. Nevertheless, this type of identification is lacking in a number of the monographs, HPTLC is not described in any of them, sample preparation is tedious and applies different conditions of hydrolysis, separation uses different mobile phases and three different detection reagents are applied. The aim of the present work was to establish an HPTLC harmonised and improved general method for identification of this type of HD and preparations, suitable for routine quality control, and adapted to the requirements of the new Ph.Eur. chapter 2.8.25 (1).

The following parameters were studied and harmonised: sample preparation (amount of sample, conditions of hydrolysis, post-hydrolysis sample treatment), HPTLC chromatographic separation (mobile phase, number of developments, and saturation of the chamber) and detection (four different reagents were tested). TFA (100 g/L, 120 °C, 1h) was selected for hydrolysis, and the posterior treatment was shortened thanks to the avoidance of the acid evaporation. An optimised separation was obtained using silicagel HPTLC plates, and double development with acetonitrile – water (85:15 v/v) in unsaturated chamber. Diphenylamine – aniline – phosphoric acid reagent and observation under daylight was selected for detection. In addition, a system suitability test for plate qualification was established using the pair galactose and glucose.

The suitability of the method was positively assessed on more than 60 samples of 18 HD and preparations, including acacia, spry- or roller-dried acacia, agar, carob gum, guar, guar galactomannan, Irish moss, ispaghula seed, ispaghula husk, kelp, psyllium seed and starches, as well as xanthan, of bacterial origin.

[1] EDQM. European Pharmacopoeia. 9^th Edition. Vol. 9.0. Strasbourg: Council of Europe (2016).