Development of a field-portable fluorometer based on deep ultraviolet LEDs for the detection of phenanthrene- and tryptophan-like compounds in natural waters

In recent years, portable or submersible fluorometers have become key tools in acquiring real time high frequency measurements of target dissolved organic matter (DOM) fluorophores in aquatic environments. We have developed an original field-portable fluorometer based on deep UV light-emitting diodes (LEDs) for simultaneous measurements of two DOM fluorophores in natural waters: phenanthrene- and tryptophan-like compounds. This fluorometer, called “the MiniFluo-UV” was tested on standard solutions and natural samples collected on the northwestern Mediterranean coast (vicinity of Marseille City, France). The MiniFluo-UV responded linearly to an increase in phenanthrene and tryptophan concentrations over the range 0.1–100 μg l−1. Limits of detection for these two fluorophores were 1.43 and 0.72 μg l−1, respectively. The sensor also responded linearly to an increase in measurement duration over the range 200–2000 ms, and the fluorescence intensity showed a power decrease from calibre C0 (integration capacitor of 3 pF) to calibre C3 (integration capacitor of 73 pF). Optimal parameters (duration of 600 ms, calibre C0) were used for measurements in natural water samples. We found very significant linear relationships between the phenanthrene and tryptophan equivalent concentrations measured with the MiniFluo-UV and the concentrations measured with the Hitachi laboratory spectrofluorometer on all natural water samples (R2 = 0.90 and 0.98, n = 150, p < 0.01). We conclude that the MiniFluo-UV fluorometer is a very relevant tool to detect and track sewage effluents and hydrocarbon contamination in marine coastal waters.