Gradient elution liquid chromatography-infrared spectrometry at μg l−1 level using capillary column switching and addition of a make-up liquid. A preliminary study

The applicability of infrared (IR) spectrometric detection in liquid chromatography (LC), based on solvent-elimination prior to IR scanning, has been enlarged to gradient separations by the adaption of a capillary column switching system and post-column addition of a make-up liquid. A pre-column is used for loading and concentration of large sample volumes. Next, analytes are transferred to the capillary analytical column by a linear gradient flow using methanol as modifier. An excess of methanol (20 μl min−1) is added post-column to the analytical flow (2 μl min−1) which provides the performance of the sprayjet LC-IR interface to become largely independent of the composition of the mobile phase. This enables isocratic and gradient elutions with high percentages of water. The potential of the system has been studied with triazines and pyrene as model compounds. Good quality chromatograms and analyte spectra were obtained at the low mg l−1 level, using sample volumes of 40 μl. If the sample volume was increased to 1 ml, the separation of the test compounds was largely maintained and the identification limits were improved to 10–100 μg l−1.