Near-IR Spectroscopic Examination of Thin-Layer Chromatography Plates in the Diffuse Transmittance Mode

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Abstract
The nondestructive detection of analyte spots on high-performance thin-layer chromatography (HPTLC) plates is demonstrated with the use of near-IR spectrometry (NIRS). The resulting hyphenated technique is called Thin-Layer Chromatography-Near-Infrared Spectrometry (TLC-NIRS). A transmittance geometry is employed, and a set of 18 interference filters is used for wavelength selectivity. Plate-thickness nonuniformity and varying amounts of water vapor adsorption onto the silica-gel TLC plates were found to be the major complications. Variations in silica-gel thickness could be compensated for by obtaining reference spectral scans of the HPTLC plates before performing the chromatography. The effects of water-vapor adsorption were reduced through use of a partial least-squares calibration model. Detection limits near 1 μg were obtained.