Applications of optical techniques in analytical chemistry: (A) Counting and characterizing PS particles using microscopy; (B) Singlet oxygen emission to determine oxygen concentration; (C) NIR lanthanide porphyrin studies.

摘要

The goal of part A of the thesis is to develop a real-time optical system for counting and characterizing polystyrene particle solutions of high densities. The particles of interest range in size from ∼10 nm to 10 microm in diameter, and the solutions vary in particle density from 106-10 12 particles/ml. This is equivalent to 0.001 % - 30 % mass/volume. A good example of the type of high-density solution that we wish to characterize is undiluted white paint.;This research project begins with a discussion of current optical methods for determining particle number density, particle diameter, and the radial distribution of high-density particle solutions in the range of 10 6-1012 particles/ml. Three methods for optical counting and characterization are demonstrated: (1) Following the trajectories of individual particles and from this data deducing the diameter of the particles, (2) Following the Brownian trajectories of many particles simultaneously and recovering a histogram of the diameter of individual particles, and (3) Deducing the distribution of particle diameters from image analysis. Two particle illuminating schemes are also studied: dark field and total internal reflectance fluorescence.;From this research a system for counting and characterizing high number density aqueous suspensions of polystyrene particles using optical microscopy in a dispersion polymerization synthesis (polystyrene) is created.;In part B, a method of oxygen analysis is presented. Molecular oxygen is a paramagnetic molecule with an even number of electrons. The history of the optical spectroscopy of this intriguing molecule is reviewed and gives rise to a new method for determining oxygen concentration using singlet molecular oxygen emission. The method is evaluated for determining oxygen concentration in fluorinated hydrocarbon solutions.;Part C involves a study of lanthanide porphyrins and their emission in the near- infrared spectrum. It is based on the fact that most lanthanide porphyrin derivatives exhibit `normal' absorption spectra with Q and B bands. The rare earth ions generally have little effect on the absorption spectra, which are much like those of other closed-shell metalloporphyrins. However, their emission spectra vary widely according to which lanthanide ion is present. We observe two types of emissions: (i) a line emission arising from the lanthanide ion f-f transitions and (ii) pi-pi* emission from the triplet state of porphyrin. The main focus here is on the emission from gadolinium porphyrin complexes as molecular oxygen sensors. The oxygen sensitivity of lanthanide porphyrins was measured in solution and polymeric film. Both intensity and lifetime Stern-Volmer plots were measured. The potential for oxygen sensing is evaluated.