Method development for the determination of fluorine by high resolution continuum source atomic absorption spectrometry

Fluorine is the 13th most abundant element in the world crust. It is considered as an essential element for living organisms but at high concentrations, the element itself and its compounds can cause white stains on teeths and fragility on bones as well toxic effects by blocking various enzymes. Due to these consequences, it is highly important to determine fluorine concentrations in different matrices. In the literature, there are various methods to determine fluorine such as ion selective electrodes (ISE), ion chromatography (IC), UV-VIS and molecular absorption spectrometry but all of them has many disadvantages e.g. ISE and IC are specific only to free F ions and aqueous phase, IC requires special columns, substantial pre-treatment procedures while easily affected from other ions, etc. Although atomic absorption spectrometry (AAS) is a routine analytical method for quantitative determination of trace metals and metalloids, it can not be used for the direct determination of non-metals because their resonance lines are in vacuum ultraviolet region. Particularly, it is impossible to determine fluorine directly by AAS using a line source spectral lamp because its main resonance line is located far below UV range at 95 nm. Therefore, no hollow cathode lamp (HCL) or electrodless discharge lamp (EDL) for fluorine has been manufactured for F. The rotational molecular absorption spectra (MAS) of diatomic molecules consist of well defined very narrow hyperfine structured lines. In the literature, some marginal studies have been performed for the determination of fluorine by conventional AAS, so-called line source AAS (LS AAS). For this purpose, diatomic molecules of fluorine in the gas-phase were generated by adding a suitable metal. The absorption at a suitable fine rotational line selected from the MAS of the diatomic molecule was evaluated using the corresponding emission line of a hollow cathode lamp. However, the exact overlapping of emission line of the selected HCL with the very narrow rotational MAS line of the diatomic molecule is not possible and some drift causes low sensitivity as well as spectral interferences. All those effects does not occur in a new generation high resolution continuum source atomic absorption spectrometer (HR CS AAS) which is equipped with high intensity xenon short-arc lamp, high resolution double monochromator, CCD detector. With these equipments, it is possible to obtain the whole wavelength range from the near vacuum-UV to near IR with a line width of 2 pm which is narrower than lines of HCLs as well as any line of rotational hyperfine structure of the diatomic molecule. By this way, not only atomic absorption, and also the absorption of any hyperfine rotational line of diatomic molecules can be suitably measured exactly at the maximum of the line. In this thesis, F determinations by high resolution continuum source atomic absorption spectrometer via molecular absorption of various diatomic molecules using Al, Ca, Sr and Ba were described. Molecule formation mechanism for SrF, which was selected as a model diatomic molecule, was investigated. Finally, methods developed for different diatomic molecules were applied to various samples. In the first chapter, a brief introduction to the thesis subject was made. In the second chapter, atomic absorption spectrometers are discussed briefly, mainly emphasizing high resolution continuum source spectrometers. In the third chapter, information about fluorine with various determination methods is given. In the fourth chapter, molecular absorption spectrometry is explained. A literature survey was made in fifth chapter. In Chapters 6-14, experiments performed for the optimization of fluorine determination in various samples using different molecule forming elements were described. General experimental and instrumental conditions were described in chapter 6. However, specific experimental conditions used for each analysis series were described in related chapters. In chapter 7, F in toothpastes was determined using AlF in flame HR CS AAS (HR CS FAAS). In chapter 8, F in water samples was determined via SrF in graphite furnace HR CS AAS (HR CS GFAAS). In chapters 9-12, CaF was used for F determinations in different matrices with different sampling techniques. While in chapter 9, F concentrations in milk samples were determined by CaF diatomic molecule with HR CS GFAAS, in chapter 10, F was determined in wine samples after summation of two different CaF molecular absorbances. In chapter 11, slurry sampling technique was applied to determine F concentrations in flours and in chapter 12 solid sampling technique was used to determine F concentrations in baby foods. In chapter 13, F in water and milk sample was determined via BaF diatomic molecule with graphite furnace HR CS AAS. In chapter 14, molecule formation mechanisms of diatomic molecules using SrF as a model molecule was studied. In the final chapter, all experiments were briefly discussed and drawbacks and advantages were described.