FOURIER-ANALYSIS OF MULTICOMPONENT CHROMATOGRAMS - APPLICATION TO EXPERIMENTAL CHROMATOGRAMS

A complete procedure is presented for quantitative estimation of both the separation performance and the retention pattern in an experimental multicomponent chromatogram obtained under programmed elution conditions. It is shown that, under a conventional good experimental setup, assuring limited peak width variation (+/-10%) and low peak asymmetry, the following quantities can be determined: peak capacity, saturation factor, peak tailing factor, number of single components (SC), and parameters of the SC interdistance distribution. The procedure is based on the experimental autocovariance function (EACVF) and power spectrum (EPS) of the experimental chromatogram handled by numerical methods previously presented and validated. What the main features of an experimental EACVF plot are and how and where to search for information related to the retention pattern and SC peak width value contained therein is also reported, with reference to two typical examples of multicomponent capillary gas chromatograms: a chamomile lypophilic extract and a naphtha sample. The EACVF plots are fitted to four different theoretical models of the SC interdistances-exponential, uniform, normal, and gamma-in order to obtain the best description of the retention pattern and an evaluation of the SC peak width value. Moreover, the ordered structure of the chromatogram was identified and analyzed in the EACVF plot, allowing one to obtain an additional, independent, estimate of the SC peak width. Similar fittings performed on the EPS plot made it possible to validate and confirm the EACVF analysis results and, in addition, to detect peak width variations and peak asymmetry effects in the experimental multicomponent chromatograms. These last SC peak shape data were in very good agreement with the peak shape analysis performed with the Edgeworth-Cramer series over well-separated peaks of linear hydrocarbons in a reference chromatogram obtained under the same conditions.