Upon excitation with an energy source, a typical river water sample will display a range of fluorescent emissions, which include protein-like (e.g. tryptophan) and fulvic/humic-like fluorescence. These emissions occur at very distinct wavelengths and are therefore readily identifiable in emission spectra.

The presence of tryptophan in water is related to microbial activity and the intensity of tryptophan fluorescence has been shown to correlate strongly with Biochemical Oxygen Demand (BOD) and, as such, the use of fluorimetry may provide a useful alternative to the time consuming traditional approach to characterising BOD.

Numerous studies have successfully used protein-like fluorescence to identify farm and household-based sources underlining the potential for fluorescence as a tool for source apportionment in river systems.

Fluorimetry can also be used to detect Optical Brightening Agents (OBA). OBAs are a common component of laundry detergents and, thus, provide a useful indicator of sewage or grey water inputs to watercourses. Whereas tryptophan fluorescence is likely to be associated with both agricultural and sewage sources, OBA signatures are confined to sewage. The ability to detect both tryptophan and OBAs during water quality analysis, therefore, provides a unique opportunity to determine the source of organic inputs.

Recent advances in the design of fluorimeters have enabled the development of submersible units, which are compact and easily deployed during field investigations.

Turner Designs have produced the Cyclops 7 fluorimeter, which can be programmed to focus upon the excitation-emission wavelength pairs of interest. For deployment, the sensors are incorporated into the Eureka Manta 2 Sonde platform, which has the capacity to house multiple sensors.