A Raman waveguide detector for liquid chromatography

A novel real-time Liquid core Raman waveguide detector designed for liquid chromatographic applications is described. The Raman waveguide detector pro vides enhanced selectivity over typical high-performance liquid chromatogra phy (HPLC) detectors. The waveguide detector tor also greatly improves the sensitivity of a typical Raman measurement without resorting to surface enh ancement or resonance approaches and is compatible with the typical peak wi dth volumes eluted by microbore and minibore HPLC (packed 1-2-mm-i.d. colum ns), Detection limit enhancements of over 1000-fold have been achieved for the measurement of alcohols in the aqueous phase with the Raman cell utiliz ing liquid core waveguide technology. The liquid core waveguides demonstrat ed in this study were constructed using Tenon AF 2400 tubing with a refract ive index of 1.29. The low refractive index of the polymer material allowed HPLC separations with Raman detection to be performed with an aqueous mobi le phase. A calibration curve for aqueous solutions of 2-propanol was gener ated and a limit of detection (LOD) of 2 ppm was determined. The Raman wave guide detector is demonstrated for the HPLC analysis of alcohol test mixtur es, with LODs in the low-ppm range at the detector. By coupling the tempora l separation achieved by HPLC with the vibrational information gleaned from Raman detection, an information-rich multivariate data matrix is obtained that can be deconvoluted to provide chemical speciation even when the HPLC resolution is poor. In this paper, we will discuss the physical and optical design of the Raman waveguide detector and the demonstration of the detect or for HPLC detection.