Application of Cavity Ring-Down Spectroscopy to Liquid Samples

摘要

Three main strategies in the application of CRDS to liquids have been investigated. In the direct liquid approach, an enclosed cavity is entirely filled with liquid for the purpose of quantifying low concentrations of solutes in a bulk solution and monitoring reactions in solution. A picomolar detection limit for a strongly absorbing solute in acetonitrile has been demonstrated, and interesting kinetic behavior has been observed at low concentrations. In the Brewster's angle flow cell implementation, a specially designed sample cell is placed within an optical cavity and used to detect low concentration species in small volume aqueous samples either statically or in a flow. It has been successfully coupled to liquid chromatography and promises to surpass commercial UV-Vis detectors in sensitivity. In evanescent wave CRDS, a prism is placed within the optical cavity such that light undergoes total internal reflection within the prism, and the resulting evanescent wave is employed to probe optical absorption at the glass-water interface. This technique has been used to investigate cation adsorption to the interface and may have applications as an ultrasensitive detector of anionic surfactants.