Raman waveguide detector for low analyte concentrations in liquid samples

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Abstract
Historically, Raman spectroscopy has not been widely used for analytical quantitative analysis for a variety of reasons, most notably, its lack of sensitivity. In this manuscript, we will demonstrate our efforts to effectively develop high sensitivity Raman detection for both static and dynamic liquid analysis. A Raman detection cell compatible with the elution volumes of minibore and microbore liquid chromatographic separations has been developed. The detector is a combination of a liquid core waveguide and a commercially available Raman instrument. The waveguide cell enhances the sensitivity of a typical Raman measurement upwards of 150 times, without resorting to surface enhancement or resonance approaches. In addition, the enhanced sensitivity allows one to capture spectral information in 'real time' as materials elute from a column. An information rich data matrix results from the combination of a temporal separation with species specific spectral signatures. There are a number of unique optical parameters that allow us to achieve such enhancements. We will discuss the physical detector and optical cell design as well demonstrate the effects of absorption, refractive index and numerical aperture on the sensitivity of the Raman measurements. The resultant Raman detector is a very sensitive and selective alternative to many of the currently available detectors used for flow analysis (HPLC, LC, FIA).

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