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Anlytical Atomic Spectroscopy in Fume And ANLYTICAL ATOMIC SPECTROSCOPY IN FUME AND NON—FLAME CELLS by LESLIE COLIN EBDON, B.Sc., A.R.C.S., A.R.I.C. A Thesis submitted for the Degree of Doctor of Philosophy in the University of London September 1971 Chemistry Department, Imperial College of Science and Technology, London, E.W.7. ABSTRACT The advantages and uses of non-flame, atom cells in analytical atomic spectroscopy are reviewed. The determination of iron and manganese using a flame cell and a non-flame cell is described. In particular, the determination of sub-microgram amounts of iron and manganese by atomic fluorescence spectroscopy, in the air-acetylene flame using micro-wave excited electrodeless discharge lamps as sources, is reported and compared to atomic absorption and atomic emission methods. The determination of sub-nanogram amounts of iron by'atomic absorption, and manganese by atomic absorption and atomic fluorescence, using a carbon filament atom cell is also described. late effects of concomitant elements on such determinations has also been investigated. An analytical method for the determination of traces of iron in milligram amounts of plastic is proposed, as are a number of suggestions for future work. ACKNOWLEDGEMENTS The work in this thesis was carried out in the Chemistry Department of Imperial College of Science and Technology betWeen Ocobter 1968 and July 1971. It is entirely original except where due reference is made and no part has been previoubly submitted for any other work. I wish to thank my supervisors, Professor T. S. Test and Doctor G. F. Kirkbright for their advice, encouragement and guidance throughout the course of this work. I am also grateful to other members and colleagues of the Analytical Department for many helpful discussions and suggestions. I would like to thank the Ministry of Defence (Aviation Supply) for their financial support and the Royal Aircraft Establishment, Farnborough for the preparation of the samples of carbon—fibre used in this work. Finally, I would like to thank my wife, Judith, for patient assistance with the preparation and typing of this manuscript. Z. Cipmzer.... ERRATA Page (iii), line 3 - for Ocobter read October. Page 1, line 2 - for contunuous read continuous. Page 30, line 10 - for comparitavely read comparatively. Page 30, bottom line - for Massman read Massmann. Page 235, line 18 - for know read known Pate 243, line 11 - for filaemnt read filament CONTENTS ABSTRACT ACKNOWLEDGEMENTS CHAPTER 1 Introduction CHAPTER 2 Experimental Parameters and Description of Apparatus 67 CHAPTER 3 The Determination of Iron Using a Flame Cell 90 CHAPTER 4 - The Determination of Manganese Using a Flame Cell 115 CHAPTER 5 The Determination of Manganese Using a Non—Flame Cell 144 CHAPTER 6 The Determination of Iron Using a Non— Flame Cell 191 CHAPTER 7 Conclusions and Suggestion for Future Work 223::= BIBLIOGRAPHY 264 CHAPTTR 1 INTRODUCTION 1.1. History Sir Isaac Newton (1642-1727) is rightly regarded as having founded the science of spectroscopy when in 1666 he analysed the contunuous solar spectrum. His simple description of his apparatus is famous: "Having darkened my chamber, and made a small hole in the window shuts to let in a convenient quantity of the sun's light, I placed my prism at his entrance, that it might thereby be refracted to the opposite wall". In 1802 Wollaston repeated Newton's experiment and found that if the sun—light passes not through a circular aperture but through a slit, the solar spectrum is intersected by several dark lines. This discovery was not, however, considered important until fifteen years later Fraunhofer working independently from Wollaston again found these dark lines in the sun's spectrum. These were used as the first precise standards for measuring the dispersion of optical glasses. Later in 1823 Fraunhofer constructed the first transmission gating and he was thus able to measure the exact wavelengths of the lines. In his honour these dark lines are called Fraunhofer lines. Although early workers had noted the colours imparted to diffusion.flames of alcohol by metallic salts, it was not until the development of the premixed air/coalgas burner of Bunsen that in 1859 2. Kirchhoff established the origin of the Fraunhofer lines. Kirchhoff showed that the chemical composition of a substance can be determined from its spectrum. Working with Bunsen, Kirchhoff developed a spectroscope of high sensitivity and demonstrated that the visible lines were not due to compounds but to elements. Together they gave numerous examples of 1 2 the use of spectra for determining alkaline metals in a flame ' and thus Bunsen and Kirchhoff are considered to be the founders of spectrochemical analysis. Kirchhoff established the presence,of certain elements in the sun's atmosphere from the fact that the emission lines for these elements coincided with the Fraunhofer lines in the solar spectrum. It was in the field of astrophysics and astrochemistry and later in more fundamental spectroscopic and atomic studies, that atomic spectroscopy found its first applications. However, in 1928 Lundegardh with the publication of a series of papers3, in which a pneumatic nebuliser together with an'air—acetylene flame was used for atomic emission spectrometry, revived interest in analytical atomic spectroscopy. Instruments became available in the mid—nineteen forties mainly for the determination of alkali metals with their easily excited resonance lines, and more recently the range of elements determinable by atomic emission spectroscopy has been extended to encompass most of the periodic table. Although the basic principles of atomic absorption spectro— scopy, the measurement of the absorption of radiation by discrete atoms, 1 were established by Kirchhoff in 1860, and many major contributions to the theory of atomic absorption spectroscopy were made by physicists and 3. astrophysicists, many of these being summarised in an excellent treatise by Mitchell and Zemansky4, it was not until the latter half of this century that a general laboratory technique was devised. In 1955 6 Alkemade and Milatz5 and Walsh independently published papers on the analytical usefulness of atomic absorption spectroscopy, although Walsh had previously in 1953 demonstrated a complete laboratory apparatus in a patent specification7. Later, in 1957, Walsh and his colleagues published the first of many results on the experimental developments of the technique Atomic fluorescence spectrometry, the measurement of radiation from discrete atoms that are being excited by absorption of radiation from a source which is not seen by the detector, was first reported by Wood9 in 1905 when he succeeded in exciting fluorescence of the D lines of sodium vapour. Again the early fundamental vork of spectro— scopists is summarised by Mitchell and Zemansky4. In 1962 Alkemade used the atomic fluorescence of sodium in flames in a study of the excitation and deactivation of atoms and he was also the first to point out the analytical applications of this technique. Following Alkemade's suggestion, Winefordner and his co—workers outlined the theoretical 11 basis of an analytical method and published in 1964 the first of many 12 papers reporting experimental results . As the theory and methodology of the three techniques of analytical atomic spectroscopy i.e. atomic emission spectroscopy, atomic absorption spectroscopy and atomic fluorescence spectroscopy has been 13-26 comprehensively described in the literature4'6'11' , in some cases 4. together with a fuller summary of the development of the techniques, in the next section an attempt will be made only to ,summarise some of the more basic points. 1.2. Theory and Methodology The emission and absorption of light are associated with and characteristic of the processes of transition of atoms from one steady state to another. If we consider the case of two steady states i and j, correspondinF'toenergiesofE.and1 E. where E. j> E.,1 then the transition i j results in the absorption of light and the transition j i in the emission of light with a characteristic frequency .31v.. where: vji— = E. — E. 1.1 h where h is Planck's constant. Einstein's quantum theory of radiation defines three types of transition between levels i and j: 1) Emission (j --> i) transitions from the excited state into a lower energy state, taking place spontaneously; 2) Absorption transitions (i j) taking place in response to the action of external radiation with a frequency v..; 3) Emission transitions (j i) stimulated by external radiation With a'frequency v. J i This third type of transition has not yet been used directly in spectrochemical analysis and the three techniques of analytical atomic 5. spectroscopy are based on the first two types of transition. Thus the analytical techniques are closely related. In atomic absorption and atomic fluorescence spectroscopy the atoms are excited (i j transitions) by means of an external light soltrce containing radiation characteristic of the analyte atoms (in this case ). In atomic ji absorption spectroscopy the fraction.of the radiation absorbed by the analyte atoms as a result of radiational excitation is monitored, whereas in atomic fluorescence spectroscopy a portion of the radiation resulting when a fraction of the excited atoms undergo radiational deactivation is monitored. In atomic emission spectroscopy the analyte atoms are excited by means of collisions. with flame gas molecules and a portion of the rad— iation emitted when a fraction of the excited atoms undergo radiational deactivation is measured. The basic instrumental systems used in the :three techniques is shown in Figure 1. A detailed study of the rules governing the transitions which give rise to observed atomic spectra would be out of place in this thesis and the reader is referred to a number of texts upon the subject, such as that written by White27 in which the results proved by quantum mechanics are combined with a simple vector model of atomic structure.
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