Towards the solution of the eluent elimination problem in high-performance liquid chromatography–infrared spectroscopy measurements by chemometric methods

The high-performance liquid chromatography–infrared spectroscopy (HPLC–IR) technique utilizing on-line flow through cell (FTC) detection has an inherent practical problem: strong absorption bands of the eluent may mask valuable analytical regions of the IR spectrum. The experimentalists’ answer to this challenge is physical elimination of the chromatographic eluent before spectroscopic detection, which however results in off-line measurement of spectra. In the present work, the capabilities of some chemometric algorithms using iteratively applied multi-way methods such as parallel factor analysis (PARAFAC) and PARAFAC2, developed with the aim of overcoming the problems of eluent elimination are examined and evaluated. Test calculations done on simulated liquid chromatographic infrared (LC–IR) data cubes have shown that although PARAFAC2 performs much better than the simple PARAFAC method, it does not give correct decompositions, just like multivariate curve resolution with alternative least squares (MCR–ALS) and related bilinear data based methods. In search for a better solution, a method named objective subtraction of solvent spectrum with iterative use of PARAFAC and PARAFAC2 (OSSS–IU–PARAFAC and OSSS–IU–PARAFAC2) has been developed. Calculations performed with the corresponding Matlab program developed by the authors and run with the appropriate functions in PLS_Toolbox yielded very promising results in evaluations of both simulated and real HPLC–IR data sets, after necessary data pretreatments.