Tsui Shu Ki. / Bibliography: leaves 110-112 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1985

Digitized by Kansas Correctional Industries

A procedure for evaluating the precision of atomic absorption measurements is presented and applied to 21 elements under varying instrumental conditions. The experimental relative standard deviations (RSD's) in absorbance obtained from repetitive measurements made with a high resolution voltmeter and on-line computer, are compared to those predicted by a recently proposed theoretical equation. Good agreement between theory and experiment is obtained which indicates the usefulness of the theoretical equation and evaluation procedure. The study reveals that, under the conditions used for atomic absorption measurements for the 21 elements, the noise associated with the lamp (i.e., signal shot noise and source flicker noise) and with the flame (i.e., flame transmission flicker noise) limit the precision at small absorbances (i.e., A < 0.1 ). Flame transmission flicker noise generally increases with the flame absorbance. Over most of the analytically useful range of absorbances (i.e., 0.1 > A > 1.0-1.5) analyte absorption flicker limits the precision to a value near 1% RSD for one second integration periods. The precision can be improved by a factor of two to three for any absorbance region with ten second integration periods, although not much better than this with any longer integration periods. Precision at high absorbances (i.e., A > 1.0-1.5) is limited by emission noises (analyte and background). For longer wavelengths, the analyte emission noises become more significant. The limiting noises' frequency dependence is obtained with noise power spectra and analyte absorption, emission, and fluorescence flicker are shown to all have a similar 1/f (inverse frequency) character, as well as a value of about 1% for the RSD for Cu. Abbreviated procedures for evaluation of noise in atomic emission (AE) and atomic fluorescence measurements are presented. Other studies into the source of analyte absorption noise are presented, and the conclusion is drawn that this flicker noise is probably due to nebulization fluctuations, non-fundamental in nature. The study of these various noise sources' dependence on the instrumental parameters (e.g. burner position, slit height and width, flame type and stoichiometry, and lamp current) suggest how to optimize conditions or concentrations so that an analysis can be carried out with maximum precision. / Graduation date: 1978

M. Tech. Chemistry / Recently, traditional electro-thermal atomic absorption spectrometry has lost its popularity to other multi-element spectrometric techniques. Limited linear determination range, which is usually two orders of magnitude, is one of the reasons for the loss. As a result, tens of calibration standards and diluted samples have become an indispensable part of the electro-thermal atomic absorption spectrometric analysis, particularly if numerous samples containing a broad concentration range of analytes are to be analysed. The objective of this work was to establish the mechanism of absorption signals for high concentrations of analyte atoms in the absorption volume. Secondly, to employ the findings for HR-CS ET-AAS data quantification, within a broad range of analyte concentrations. It was expected that the sought algorithm would permit the use of the most sensitive analytical lines or those less prone to interferences, independent of the concentration of the respective analyte in the sample.

Thesis (Ph. D.)--Carleton University, 1993. / Also available in electronic format on the Internet.

D.Phil. (Chemistry) / In order to optimise the parameters for graphite tubes used for electrothermal atomic absorption spectrometry a good understanding of the factors that influence the efficiency of the atomisation process is necessary. The most important of these factors are the temperature surroundings of the analyte. Consequently, a model was developed to calculate the spatial and temporal variations of the wall temperature of the tube. Reliability of the calculations was ensured by determining some graphite parameters experimentally. Normal laboratory conditions could therefore be simulated precisely. There were some problems associated with the actual measurement of wall temperatures. After these had been investigated and solved, it was possible to correlate and verify the calculated temperat~re values with the experimentally measured ones. While it is likely that the analyte evaporates as such (or in modified forms) from the walls of the tube, the actual atomisation process most probably takes place in the gas phase. It is therefore the gas temperature that controls atomisation. In view of this a gas temperature model was developed by means of which spatial and temporal temperature data within the atomiser could be calculated. Together with the calculations of wall temperatures already mentioned, this presents for the first time the possibility of calculating temperatures, both spatially and temporally, at any point within the atomiser during the heating cycle. With the above information, the nature of atomisation processes can be studied. In this work, attempts were made to study the mechanism by which- the use of a platform placed within the atomiser eliminates interferences. Contrary to the literature, it was found that this can not be attributed to stabilized temperature surroundings.

M.Sc. (Instrumental Chemical Analysis) / An investigation was undertaken into the analytical procedures and the identification of problem areas, for the certification of a new biological standard reference material supplied by the International Atomic Energy Agency, namely, a human hair sample designated as HH-I ...

1. The effect of deviations from Beer's law on the precision of atomic absorption analysis has been examined from a theoretical point of view, and a function has been derived which makes it possible to evaluate quantitatively the effect of calibration curvature on the precision of analysis. The influence of incomplete sample volatilization on calibration curvature has been briefly investigated. 2. Possible error sources in atomic absorption spectrometry have been classified according to the "error function" (i.e., the dependence, upon transmittance T, of the uncertainty dT in a given transmittance measurement) with which they are associated. The magnitude of the contribution from each component function to the overall error function has been evaluated quantitatively, and it has been shown that the major component in nearly every case examined is that associated with the dynamic nature of the flame. Concentration ranges for optimum precision are suggested. 3. The effect of varying instrumental parameters on precision has been investigated, and generalized conditions for best precision have been ascertained. 4. The effect of an initial solvent extraction step on the precision of atomic absorption has been investigated for the elements copper and lead. It is shown that solvent extraction may be used to improve both the analytical sensitivity and the precision of analysis when very low concentrations of metal are determined. 5. The precision of analytical methods involving atomic absorption spectrometry has been studied, and the standard deviations compared with those obtained for the analysis of similar samples by means of a variety of other methods of analysis, both instrumental and classical.

No description available.

Cheung Ching Ying. / Bibliography: leaf 126 / Thesis (M.Phil.)--Chinese University of Hong Kong