Thin-layer chromatographic and hydrolysis methods for the identification of plant gums in art objects

Abstract

The TLC system evaluated (L₁S₃-layer: precoated silica gel, solvent: 1-propanol/water/ammonium hydroxide (79:20:1), with p-anisidine phthalate as reaction agent) gave the most satisfactory resolution of all the eight possible sugars of gums. Hydrolysis of the gums was carried out using trifluoroacetic acid (TFA) under nitrogen atmosphere, which avoids the destruction and loss of some sugars and reduces the time taken. The plant gums arabic, ghatti, karaya, mesquite, thingan, neem and tragacanth were hydrolyzed and characterized by these methods. On the basis of the sugars present in the gums, a logical programme was drawn up for the identification of the latter. The techniques described were applied to a number of very small samples taken from wallpaintings, and successfully identified the gums karaya, arabic and neem in some samples.