Liquid-Phase and Evanescent-Wave Cavity Ring-Down Spectroscopy in Analytical Chemistry

Due to its Simplicity, versatility, and straightforward interpretation into absolute concentrations, molecular absorbance detection is widely used in liquidphase analytical chemistry. Because this method is inherently less sensitive thin zero-back-ground techniques such as fluorescence detection, alternative, more sensitive measurement principles are being explored. This review discusses one of these: cavity ring-down spectroscopy (CRDS). Advantages of this technique include its long measurement pathlength and its insensitivity to light-source-intensity fluctuations. CRDS is already a well-established technique ill the gas phase, so we focus oil two new modes: liquidphase CRDS and evanescent-wave (EW)-CRDS. Applications of liquidphase CRDS in analytical chemistry focus on improving the sensitivity of absorbance detection in liquid chromatograph. Currently EW-CRDS is Still ill early Stages: It is used to study basic interactions between molecules and silica surfaces. However, in the future this method may he used to develop, for instance, biosensors with high specificity.