The ability to monitor the concentration of an analyte in a process stream is critical for accurate and reliable process control. There are many techniques used to determine the analyte concentration of interest. One of the most sensitive sensing techniques is molecular fluorescence. Fluorescence occurs when a molecule absorbs light energy, either ultraviolet or visible, and rapidly emits light, at some longer wavelength. Fluorescence of this type is referred to as Stokes fluorescence. Fluorimetry characterizes the excitation and emission properties of the molecular species.