ABSTRACT
The operating conditions in micro high-performance liquid chromatography and supercritical fluid chromatography sometimes prevent simply scaling down the volume of conventional detectors for use. With high light intensities, it is possible to observe fluorescence derived from two-photon excitation. The quartz rod can be replaced by an optical fiber so that the visible fluorescence can also be monitored to achieve two-dimensional detection in complex samples. Recently, the authors demonstrate an optical cell in which the light enters the side of the flow stream and yet propagates nearly parallel to the flow stream before reaching the opposite window and exiting. This behavior is accomplished by controlling the incidence angle of the light so that it strikes the window-liquid interface at an angle just smaller than the critical angle, thus giving a large angle of refraction. The cell consists of Teflon gasket squeezed in between two high-quality right-angle prisms. The Teflon tape defines the flow channels for both the reference and sample chambers.
