Optimization of Instrumental Parameters of a Near-Field Thermal-Lens Detector for Capillary Electrophoresis

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Abstract:

The optical scheme of a near-field dual-beam mode-mismatched thermal-lens detector for capillary electrophoresis with a crossed-beam configuration employing a multimode HeCd laser (325 nm) as an excitation source was optimized. It is shown that a multimode laser can be successfully used as an excitation source in thermal lensing with minimal deviations in thermal responses from Gaussian excitation sources. An equation for diffraction thermal-lens theory for near-field measurements is deduced, and the experimental results agree with the deduced equation. The temperature rise in the capillary was estimated, and the exponential decrease of the signal with time for static conditions and low flow velocities was explained. The optimum configuration of the detector from the viewpoint of the maximum sensitivity and beam sizes was found. The detector provides a significant improvement in the detection limits for model compounds absorbing at 325 nm (nitrophenols) compared to the results obtained with a commercial absorbance detector operating at the same wavelength.

Keywords: CAPILLARY ELECTROPHORESIS; MULTIMODE LASER; OPTICAL-SCHEME DESIGN; THERMAL-LENS SPECTROMETRY

Document Type: Research Article

DOI: http://dx.doi.org/10.1366/000370205775142494

Affiliations: 1: M.V. Lomonosov Moscow State University, Chemistry Department, Vorob'evy Hills d. 1 str. 3 119992 GSP-3 Moscow, Russia 2: M.V. Lomonosov Moscow State University, Chemistry Department, Vorob'evy Hills d. 1 str. 3 119992 GSP-3 Moscow, Russia; University of Kassel, Department of Natural Sciences, Institute of Chemistry, Heinrich-Plett-Straße 40, D-34109 Kassel, Germany 3: Research Centre Karlsruhe, Institute of Instrumental Analysis, Karlsruhe, Germany; Philipps University of Marburg, Department of Chemistry, Marburg, Germany 4: Research Centre Karlsruhe, Institute of Instrumental Analysis, Karlsruhe, Germany 5: University of Kassel, Department of Natural Sciences, Institute of Chemistry, Heinrich-Plett-Straße 40, D-34109 Kassel, Germany; Philipps University of Marburg, Department of Chemistry, Marburg, Germany

Publication date: December 1, 2005

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