Possibility of spectrofluorimetric detection of saxitoxins when monitoring water bodies during their «blooming» period

The article considers the possibility of spectrofluorimetric detection of saxitoxins (the most dangerous cyanobacterial toxins) when monitoring «blooming» water bodies. Saxitoxins, which are purine alkaloids, do not have natural fluorescence, but can be oxidized to a fluorescent derivative. The authors used the possibility described in the literature of their oxidation as a result of exposure to ultraviolet (UV) radiation on a sample in a fluorimeter cuvette. Using the spectrofluorimetry method with the use of the Fluorat-02-Panorama analyzer, the authors studied water samples from different sources during periods of their strong and slight «blooming», as well as from a source rich in humic compounds, in the absence of «blooming». To identify the characteristic spectra of registration and excitation of fluorescence of the purine base, the authors carried out similar studies with a model solution of sodium adenosine triphosphate (ATP). The work showed that during a long-term spectrofluorimetric study of water samples from the source during its strong «blooming» period, in addition to bands of the protein and humic type, a band with a maximum at 400–410 nm is detected in the fluorescence registration spectra, and this band is excited by UV radiation with a maximum at 290–300 nm. The given values of wavelengths are clearly determined from the additionally plotted dependence of the maximum fluorescence intensity in the registration spectra (in the range of 380–450 nm) on the excitation wavelength (in the range of 270–320 nm), as well as from the fluorescence excitation spectra. The authors obtained similar results with the ATP solution, which is evidence of the detection of a purine base in the water of «blooming» sources, and, consequently, indirect evidence of the presence of saxitoxins (purine alkaloids). For water samples from weakly «blooming» sources, no clear evidence of the presence of a purine base was obtained.