M.Sc Thesis

M.Sc StudentDing Sha
SubjectCharacterization of Particulates in Aqueous Samples by
Fluorescence Fluctuation Spectrometry
DepartmentDepartment of Chemistry
Supervisor PROF. Israel Schechter


        An absolute method of fluorescence analysis for particle suspensions is described which eliminates calibration procedure. This method is based on fluctuation analysis of fluorescence intensities. In particle suspensions, as the particles appear in or disappear from the light beam due to random motions, their concentration fluctuations give rise to corresponding fluctuations of the intensities of the fluorescence. Assuming that the variations of particle number follow Poissonian distribution, the standard deviation of fluorescence fluctuation (Irms) can be dependent on the square root of number of particle in a measuring volume. By combining theoretical relations between experimental conditions and fluorescence intensity ( I ) and its fluctuation ( Irms ), a simple dependence, between the ratio of I to Irms and the whole number of particles in the measuring volume, was obtained. By using this connection, it was possible to calculate the particle number concentration and mean particle diameter without information on the optic properties of particles.

        The fluorescence fluctuation analysis was provided by using a commercial spectrofluorimeter and Laser-Induced Fluorescence (LIF) systems.

        We report the application of fluorescence fluctuation analysis for water suspensions of hazardous polyaromatic hydrocarbons (PAHs). Two types of fluorescence emissions were detected for the different types of crystal lattices of PAHs: the monomer fluorescence as well as excimer fluorescence. The dependence of fluorescence spectra and intensity of PAH suspensions on the particle sizes, excitation powers, as well as the effects of the humic acid and/or SiO2 microparticles were measured. The analytical characteristics of this method have been studied. The limits of detection for the five PAH particle suspensions are at the level of ng ml-1. Our results indicate a possible application of the method for on-line monitoring of PAH particulates in aqueous environments.