Fiber Optic Absorbance And Fluorescence Measurements In High Temperature Liquid Chromatography

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Abstract
Chemical sensing in high temperature liquid chromatography (HT-LC) is a difficult task. In this setting, detection must be performed directly following the separation, at the column temperature, and at suitable back pressure, in order to preserve chemical information encoded by the chromatographic separation. A z-configuration flow cell with "in-situ" fiber optic monitoring of both absorbance and fluorescence has been developed and examined for HT-LC (ambient to 150 0C). The fiber optic based measurements circumvent problems and limitations associated with using commercially available instrumentation that does not function properly in the high temperature environment. Solarization of the fiber optic in the UV range was evaluated, and precautions emphasized. Refractive index (RI) dependencies and aberrations associated with making an absorbance measurement with a single fiber optic were examined and minimized by a unique detection approach using a position sensitive detector (PSD). Intensity fluctuations of the mercury-xenon lamp, initially more than 0.1% were reduced with the absorbance detector, leading to a 1 x 10-4 au detection limit (3 x rms noise level). Fluorescence quenching was also considered.

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