Decoding of complex isothermal chromatograms: Application to chromatograms recovered from space missions

In gas chromatographic isothermal separations of multicomponent mixtures, i.e., mixtures where the number of components is high and unknown, the efficiency is low and not enough to allow a complete separation with a consequent severe peak overlapping in the chromatogram. The consequence is a significant loss in analytical information content. Therefore it is practically mandatory to use a chemometric procedure to decode the complex chromatogram, i. e. to deconvolve the overlapping signal to extract from it information on the mixture and the separation system. Isothermal separations are not very popular, due to their low efficiency, but they are very common in in situ analyses during space missions, as a consequence of flight constraints on instrumentation complexity and power (energy saving). In this work a chemometric approach based on Fourier analysis is applied to chromatograms obtained under isothermal or low temperature programming conditions. These conditions simulate those employed in space missions. The procedure has been applied to standard mixtures containing compounds representative of the planetary atmospheres that will be investigated in the near future: in particular, those related to Titan's atmosphere (Cassini‐Huygens mission) and a cometary nucleus (Rosetta mission), i. e., hydrocarbons and oxygenated compounds with carbon atom numbers ranging from 2 to 8. The original approach, developed for constant peak width, is extended to variable peak width, in particular to the case of peak width linearly increasing with retention time, representing isothermal separations. The proposed approach is able to characterise complex isothermal chromatograms in terms of number of components present in the mixture and of separation efficiency: such results are useful in interpreting data recovered from space missions and for optimising analysis conditions compatible with flight constraints.