Zastosowanie metody chromatografii cienkowarstwowej do oznaczania pigmentów nieorganicznych

It was in 1978 that a scientific and research laboratory of the State Enterprise for Monuments Conservation in Warsaw used — for the first time — thin layer chromatography to identify inorganic pigments. Basing on comprehensive literature on the analysis of inorganic ions by means of thin layer chromatography (TLC) nearly 50 methods of the determination of simple ions and their combinations were studied, partially restricting the task to methods of distribution on the most popular carriers. 15 cations entering into the composition of 28 pigments and 1 2 anions entering into the composition of 20 pigments were identidfied. To give all results of the examinations set up in more than 2 0 big tables would exceed the framework of this article. Therefore some details of the examined methods of distribution have been quoted and briefly discussed as representative. When working out methods of the distribution of individual ions or their groups standard pigments and — for comparison purposes — standard salts available in the laboratory were used. Both pigments and standard salts were prepared for spreading on plates by means of proper solvents. Most frequently it was a diluted or concentrated acid and only occasionally a flux or a diluted base. Pigment solutions were prepared and their concentration did not exceed a few per cent (usually 1 per cent solution was employed). Solutions of the examined pigments or corresponding standard salts were spread on plates covered with a layer of a carrier. As a rule Merck’s plates with silicone gel (Kieselgel 60 F22) and a carrier layer (0.25 mm thick) cut from the plates of 20 X 20 cm down to 4 X 9 cm or Merck’s plates with a cellulose carrier (Cellulose F) of 0 .1 mm in thickness and also cut down to 4 x 9 cm were used. Before spreading standards, plates with cellulose were activated in a dryer at 105° С for 10 minÿ plates with silicone gel were activated at 110° С for 1 hour. Standards were spread on plates by means of capillaries, the diameter of which was 0.5 mm. The plates were numbered and then developed in small chromatographic cells (5x3x11 cm) saturated with vapours of the developing system. After developing a chromatogram, the plates were dried in a dryer and developed by spraying with special reagents. Developed chromatograms were photographesd with a Polaroid camera. The obtained results of the studies make it possible to introduce the analysis of pigments by means of thin layer chromatography as a method supplementary to other traditional methods of determination, particularly when only a small quantity of the sample is available and it is composed of several pigments and their determination by traditional methods is impossible.