Chemometrics on thermochromatography of inorganic salts: decomposition of thermochromatograms to chromatograms and thermograms using EFA and peak shape constraints

Abstract

A low volume thermal furnace, interfaced to a capillary gas chromatograph (GC) via a computer controlled, pneumatic sample inlet device, permits temperature resolved high speed GC analysis of the evolved components. The method is called thermochromatography (ThGC). The results of such an evolved gas analysis (EGA) can be conveniently represented as a thermochromatogram: a two-way detector response surface in the axes of sample temperature and chromatographic retention time. It is demonstrated that such thermochromatograms, if subjected to the specific chemometrics analysis — evolving factor analysis (EFA) — provide information about independent thermal processes that happened during the sample heating. The data is decomposed to matrixes of chromatograms and thermal evolution curves, thermograms, in a manner which connects each thermal decomposition step to the products evolved at that temperature region. Chromatographic peak shapes of the evolved gases are used as additional constraints in the analysis. The EFA performance is evaluated by ThGC of several inorganic salts and apatites. As a reference to EFA the direct deconvolution of thermochromatograms to the gas chromatograms and temperature dependent thermograms was performed. This comparison demonstrated that EFA gives confident results if essential constraints of non-negativity to chromatograms and thermograms have been applied.