On-Line Fourier Transform Infrared Spectrometric Detection in Gradient Capillary Liquid Chromatography Using Nanoliter-Flow Cells

A capillary liquid chromatographic system has been successfully interfaced with a mid-IR Fourier transform infrared (FT-IR) spectrometer. Spectra were recorded on-line using a micromachined transmission CaF2 cell (internal volume of 7.5 nL) that was placed on a dedicated beam condenser attached to the spectrometer. Linear gradients were run from (50:50) to (35: 65) water (0.05% TFA)/acetonitrile in 15 min for the separation of standard solutions of four nitrophenolls (4-nitrophenol, 3-methyl-4-nitrophenol, 2,4-dinitrophenol, and 2-nitrophenol) in a reversed phase system, providing limits of detection between 35 and 94 ng on-column. The changing background absorption due to gradient elution was successfully corrected by using a dedicated algorithm implemented in Matlab. When this chemometric data treatment was used, highly characteristic analyte spectra could be recorded as indicated by correlation coefficients between 89 and 95.8%, obtained when comparing mid-IR spectra of standard solutions and the spectra extracted from the chromatogram.