FORWARD DEGENERATE 4-WAVE-MIXING AS A DETECTION METHOD IN LIQUID SEPARATION SYSTEMS - IMPROVING DETECTION LIMITS BY MEANS OF A FABRY-PEROT-INTERFEROMETER

A simple, small, and low-resolution confocal Fabry-Perot interferomete r (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 desig ned CFP and its performance is presented. The improvement in S/N was c alculated from the chromatographic peaks recorded after an HPLC separa tion of 1- and 2-aminoanthraquinone. The concentration limit of detect ion (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(-9) M in the detector cell), which is quite favorable in view of its low molar exti nction coefficient being 2000 M-1 cm(-1) at the utilized laser wavelen gth (514.5 nm).