Univariate method for background correction in liquid chromatography–Fourier transform infrared spectrometry

An univariate method is proposed for background correction in on-line gradient liquid chromatography–Fourier transform infrared (LC–FTIR) spectrometry using acetonitrile:water as mobile phase components. The method is based on the calculation of the ratio of absorbances (AR) at two characteristic wavenumbers for each spectrum. This parameter is subsequently used to locate the most appropriated eluent spectrum within a reference spectra matrix (RSM) to be subtracted from each spectrum included in the sample chromatogram. To correct minor changes in eluent spectra intensity during the elution of analytes, a correction factor (Kf), defined as the ratio of the absorbance of the sample and the selected eluent spectrum at a defined wavenumber was determined. The performance of the procedure was evaluated by correcting an on-line gradient LC–FTIR injection of a mixture of two pesticides (Atrazine and Diuron). Using the AR of the absorbance at 2248.6 and 2256.3 cm−1 and a Kf at 2248.6 cm−1, the correlation factors between FTIR spectra extracted at the peak apex from the LC–FTIR chromatogram and those obtained from pure pesticide standards were 0.975 and 0.94 for Atrazine and Diuron, respectively.