Thermochromatography and activation analysis

Despite of many possibilities to perform activation analysis in a non-destructive mode, in many cases pre-concentration or radiochemical separation is necessary due to a low concentration of elements to be determined and interferences from matrix elements. Difficulties in decomposition (dissolution) of some kinds of samples is a very important limitation. In some fields of inorganic chemistry gas-thermochromatography is used very successfully. It is a promising method in neutron activation analysis, too. The procedure includes heating of irradiated samples in the stream of a reacting-carrying gas (air, chlorine, etc.) or heating in the presence of compounds liberating the gas at a high temperature (AlCl3). Gaseous products pass through the tube with a certain temperature gradient, which is filled with various sorbents, and condense in different parts of the column. In this technique, sample decomposition and element separation are carried out in a single step. Studies of the processes of producing and trapping of volatile compounds allowed to elaborate various types of sorption tubes of varying length and temperature gradient, various filters, sorbents, etc. Efficiency of element extraction from samples (rocks, ores, etc.) by transformation into volatile compounds reached 90-99% (As, Se, Mo, Sb, Re, Os, Ir, Hg). The element detection limits of these methods are significantly better then in INAA. The most important advantage of the method is the possibility of determination of some noble metals determination in geological samples that are difficult to decompose. (author)