Thin film planar waveguides were originally introduced in microwave engineering. The spectroscopist began to use such waveguides as tools to solve chemical characterization problems since Harrick and Fahrenfort introduced the Attenuated Total'Reflection (ATR) in the early 1960's. Today, planar waveguides are playing an important and ever-increasing role in modem chemistry. In this thesis, a novel design for a refractometer involving the application of a thin film planar waveguide and coupling prism was demonstrated. This device shows the feasibility of refractive index measurements in a flowing stream. Therefore, an online detector for High Performance Liquid Chromatography (HPLC) was chosen as the vehicle to test out the concepts.

The research works were devoted to studies of waveguide properties and flow dynamics in a chromatographic situation. It was found that microscale detection is possible. The sensitivity can be enhanced by using the highest propagation mode as the probe, and by selecting a proper refractive index liquid as the solvent carrier. A description of the investigation and the various factors involved in designing and optimizing a planar waveguide for refractive index detection is included. The results provide guidelines for the device as a realistic analytical detector.