In the current edition of the European Pharmacopoeia (9th 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. 9th Edition. Vol. 9.0. Strasbourg: Council of Europe (2016).
