How the System Works

With a fiber optic dissolution system, the concentration of dissolved constituent of each specimen is measured in situ, directly in the vessel. The light from the UV source (Cary™ 50 spectrophotometer) is coupled to optical fibers with the multiplexer (C Technologies Cassini™). The fibers transfer the light from the source to the probes, which are immersed in the bath vessels (Hanson SR8-Plus™). The fibers used are made with a silica core and silica cladding specifically selected for transmission in the UV range. The probes are specifically designed for dissolution measurements. They consist of the illumination fiber from the source, the signal fiber to the detection system, a quartz focusing lens, and a back-surface mirror, housed in a slim stainless steel body.

Schematic of fiber optic dissolution system

Schematic of fiber optic probe

The light from the source is focused by the lens through the volume of liquid that occupies the gap and then reflects back from the mirror at the other end. The light again traverses through the liquid in the gap and is then refocused by the lens into a signal fiber in the probe. The signal channel carries the light transmitted through the sample back to the detection system for analysis. In a fiber optic dissolution system, the sample “volume” is simply the liquid present in the probe gap at the time of measurement. The “pathlength” of the cell is determined by this gap, which can be changed by choosing a replaceable tip with appropriate spacing.