High-sensitivity fluorescence spectroscopy of mediterranean waters using a conventional or a pulsed laser excitation source
Résumé
Instrumental efforts have been made to record the fluorescence spectra of coastal and marine waters of the Mediterranean Sea for different excitation wavelengths without preconcentration of the samples. A fluorescence spectrophotometer, using a pulsed nitrogen laser as excitation source, was developed and spectra obtained on marine waters were compared with those obtained with a high-sensitivity commercial spectrofluorometer. Fluorescence emission spectra recorded with this high-resolution instrument, using the laser excitation source, do not show resolved structured bands. Other results obtained on a high-sensitivity fluorometer with a very low stray light level show that, on the same sample, fluorescence spectra present a difference in the position between the maximum of the emission spectra when recorded with an excitation wavelength of 313 or 370 nm. The positions of the maxima of the emission spectra also show shifts between samples collected at different locations. No difference is observed between coastal and marine waters for a 370-nm excitation wavelength. On the other hand, an important blue shift (up to 20 nm) is observed between coastal and marine samples when 313 nm is used as the excitation wavelength. These results clearly show that marine and coastal waters have different fluorescence signatures, and demonstrate that high-sensitivity fluorescence spectroscopy is a promising tool for better elucidation of the behaviour of part of the complex dissolved organic matter in the ocean. © 1989.