V.V. Chubarov

Saturation spectroscopy as a method for determining the photophysical parameters of complicated organic compounds

A fundamentally new approach to the fluorescence diagnostics of complicated organic compounds and complexes has been proposed. The method is based on in vivo and in situ measurements of the photophysical parameters of organic molecules from saturation curves. The results obtained for the solution of the relevant inverse problem are presented.

New possibilities of laser fluorescence spectroscopy for diagnostics of petroleum hydrocarbons in natural water

New possibilities of fluorescence spectroscopy for diagnostics of oil pollution in natural water are discussed. It is shown that the choice of shorter excitation wavelengths than is accepted in the standard UNESCO technique for the determination of petroleum hydrocarbons concentration significantly improves the sensitivity and universality of the method and allows one to perform oil classification into basic classes. The authors have also considered the principal possibilities of direct (without extraction) fluorescence diagnostics under excitation at 266 nm. The results obtained may be considered as the next step to solve the very difficult problems of laser remote sensing of oil pollution in natural waters.<<ETX>>

LASER FLUORESCENCE SPECTROSCOPY AS A METHOD FOR STUDYING HUMIC SUBSTANCE

This paper summarizes the results obtained by fluorescence spectroscopic techniques with conventional and laser light sources for the characterization of the spectral luminescent properties of aquatic humic substances (AHS). The band profiles of corrected absorption, fluorescence emission, and fluorescence excitation spectra are compared in graphical form with unique functions used for the axes. In order to calculate the quantum efficiency of fluorescence, we used the Raman signal from water molecules as an internal reference. The temperature dependence of the fluorescence spectra of humic matter has been recorded in solid (−160°C to 0°C) and in liquid (0°C to +300°C) aqueous solutions. The behavior of the fluorescence band shape is discussed. A new method of nonlinear fluorimetry is proposed to enhance the capabilities of fluorescence spectroscopy. This method is based on the fluorescence saturation effect manifesting itself under powerful laser pumping (excitation) conditions. The use of the technique allows one to determine certain photophysical properties of molecules, as a complement to the normal spectral data. Using three different samples of aquatic humic substances with very similar fluorescence band shapes, it is demonstrated that these compounds have distinct molecular luminescent parameters and therefore, can be identified. The similarity of the fluorescence band shapes of humic substances in natural water of different types; the absence of any noticeable effect of temperature across a wide range and the fluorescence saturation on the fluorescence band contour can be explained. This assumes that in all of the samples of aquatic humic substances studied, with different molecular weight fractions, that there is a single dominant fluorescent functionality present.

Origin and structure of fluorescence band from aquatic humic substances

The different spectral-luminescence characteristics of humic substances were investigated. Hypothesis for the origin and the structure of fluorescence band from humic matter are discussed.

Laser remote sensing of dissolved organic matter in natural water

Fluorescent methods using Raman scattering signal as an internal standard are widely applied for environment remote control of dissolved organic matter (DOM) in water. In this paper temperature variations, ultraviolet irradiation influence on exitation and emission spectra of water samples have been investigated. Photochemical processes in DOM under laser excitation and the effect of fluorescence saturation have been studied.<<ETX>>

The use of fluorescence of humic substance to characterize the hydrological structure of water bodies: Case study of the Rybinsk Reservoir

The results of comparative studies of fluorescent characteristic of humic substance and electroconductivity in the surface water layer in the Rybinsk Reservoir are presented. The hydrological structures obtained with the use of these characteristics generally coincide. This opens the way to the use of humic substance fluorescence, which allows remote measurement, as an indicator of the hydrological structure.

On possibility of the monitoring of water masses' structure in natural reservoirs by fluorimetry with using neural network algorithms

In the paper it is proposed to use fluorescence of dissolved organic matter (DOM) as a water masses indicator. The DOM fluorescence spectra were registered and for two reservoirs of different types: the costal zone of the North Sea and the Rybinskoe reservoir in the middle of the European part of Russia. In the paper it is shown that using normalized intensity of DOM fluorescence and artificial neural networks (ANN) for analysing DOM fluorescence band shape can provide determining the water masses type in natural reservoirs.

Non-linear laser fluorimetry as a new method of diagnostics of organic pollution in water

The central problem in laser sensing of natural organic complexes (NOC) in water, is their identification and determination of their state. This is an essential condition for quantitative characterization of an object by optical methods (e.g. fluorimetry). It is very difficult to solve the NOC identification problem dealing only with spectra. It is necessary to penetrate to the molecular level, and to supplement spectral data with molecular photophysical parameters (absorption and fluorescence cross sections, rates of intermolecular transitions and of intermolecular excitation-energy transfer, etc.). Furthermore, it is necessary to measure these parameters in vivo and in situ, under conditions of absence of accurate a priori data. This can be done only by non-linear laser fluorimetry. In this paper, the results of computer experiments and real experiments, illustrating capabilities of non-linear laser fluorimetry in diagnostics of NOC, are presented. To solve the inverse problem, the method of artificial neural networks was used. it is shown that it is possible to achieve the determination precision of the photophysical parameters not worse than the measurement precision of the saturation curve, using a few-parametric model of the formation process of the NOC fluorescence response at pulse laser excitation, and taking into account NOC specifics.

Laser diagnostics of natural and pollution organic complexes in water environment

The possibilities of laser fluorescence spectroscopy for diagnostics of different kinds of organic substances such as petroleum hydrocarbons, humic substances, and proteins in natural water are discussed. The algorithm to determine the contributions of these organic complexes in fluorescence spectra from natural water are suggested and results of natural water monitoring during an expedition in the Black Sea are discussed.

Determination of oil film thickness on water surface by laser spectral methods

orescence band exhibits single broad maximum at 420-430 nm. The fluorescence intensity increases with a decrease in temperature because of a decrease in the radiationless relaxation efficiency. We showed that, in the ice bulk, there is a small amount of humic molecules. At the same time, melted sample exhibits noticeable fluorescence attributed to them. Organic molecules are embedded in some form into the ice. We found that during crystallization humic molecules are adsorbed on the surfaces of phase inhomogeneities and, for example, the bubbles of air dissolved in water. In our experiments, the temperature varied from 0 to -150°C. Homogeneous areas give extremely low fluorescence intensity, whereas, when inhomogeneous ones are pumped, the intensity sharply increases. At higher temperatures, the fluorescence spectra are similar to those recorded for liquid samples. With further decrease in temperature, in the longer wavelength region of the band, the second maximum of comparable width grows. Typically, the intensity growth rate is several times higher for this peak compared with the high-temperature maximum. This behavior can be explained by either the existence of two fluorophores with different quantum yields at low temperatures, or special physico-chemical properties of humic molecules adsorbed on inhomogeneities. To decide which mechanism is responsible for this effect, further studies are necessary. In the short-wavelength region of the band, a set of several low-intensity narrow peaks are observed. We assume that they are a manifestation of fine vibrational structure of the electronic levels.