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Forward Degenerate Four-Wave Mixing as a Detection Method in Liquid Separation Systems: Improving Detection Limits by Means of a Fabry-Perot Interferometer

Volume 51, Number 7 (July 1997) Page 1008-1011

Hoornweg, Gerard Ph.; Beer, Tjipke De; Velthorst, Nel H.; Gooijer, Cees

A simple, small, and low-resolution confocal Fabry-Perot interferometer (CFP) has been developed to improve the signal-to-noise ratio (S/N) in forward degenerate four-wave mixing (F-D4WM) detection, coupled to high-performance liquid chromatography (HPLC). Its appropriateness is based on the difference in coherence between the F-D4WM signal and the background stray light. A detailed description of the specially designed CFP and its performance is presented. The improvement in S/N was calculated from the chromatographic peaks recorded after an HPLC separation of 1- and 2-aminoanthraquinone. The concentration limit of detection (LOD) was improved by a factor of 30; for 1-aminoanthraquinone it was 2 X 10 -8 M injected (corresponding to about 3 X 10 -9M in the detector cell), which is quite favorable in view of its low molar extinction coefficient being 2000 M -1cm -1 at the utilized laser wavelength (514.5 nm).