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The influence of hyperfine structure and isotope shift on the detection of Rb by 2f-wavelength modulation diode laser absorption spectrometry: experimental verification of simulations
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
1998 (English)In: Spectrochimica Acta Part B - Atomic Spectroscopy, ISSN 0584-8547, E-ISSN 0031-6987, Vol. 52, no 14, 1895-1905 p.Article in journal (Refereed) Published
Abstract [en]

This work presents an experimental verification of a previously developed methodology for simulation of the 2f-wavelength modulation diode laser absorption spectrometry technique (2f-WM-DLAS) when the influence of hyperfine structure, isotope shift and collisional broadening and shift of an atomic transition is taken into account [J. Gustafsson, D. Rojas and O. Axner, Spectrochim. Acta, 52B, 1937-1953 (1997)]. The pilot element in the simulations was Rb, detected at the 780 nm 5s S-2(1/2) - 5p P-2(3/2) transition, in low-pressure cells and atmospheric-pressure reservoirs (e.g. graphite furnaces). This experimental investigation verifies that the simulations are able to predict, with good accuracy, experimental 2f-WM signals from Rb atoms under both low-pressure, room-temperature conditions and atmospheric-pressure, high-temperature conditions. This implies that the previously published simulation methodology can be used for predicting and optimizing 2f-WM signal strengths and shapes from Rb atoms (and thereby presumably also from other atoms) under a variety of pressure and temperature conditions.

Place, publisher, year, edition, pages
Elsevier, 1998. Vol. 52, no 14, 1895-1905 p.
Keyword [en]
wavelength modulation, diode laser, 2f-WM-DLAS, hyperfine structure, isotope shift, rubidium, graphite furnace, experimental verification
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:umu:diva-4360DOI: 10.1016/S0584-8547(98)00200-6ISI: 000078122400004OAI: oai:DiVA.org:umu-4360DiVA: diva2:143413
Available from: 2002-12-19 Created: 2002-12-19 Last updated: 2015-01-16Bibliographically approved
In thesis
1. Development of wavelength modulation diode laser absorption spectrometry in transversely heated graphite atomisers for sensitive trace element analysis
Open this publication in new window or tab >>Development of wavelength modulation diode laser absorption spectrometry in transversely heated graphite atomisers for sensitive trace element analysis
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Wavelength Modulation Diode Laser Absorption Spectrometry technique (WM-DLAS) is a laser-based spectroscopic technique for sensitive detection of atoms and molecules that so far mostly has been used for environmental monitor-ing. This thesis is concerned with the development of this technique for sensitive trace element analysis. The WM-DLAS technique is in general able to measure a variety of species at three orders of magnitude lower concentrations than conven-tional atomic absorption techniques since it shifts the detection to high frequen-cies where the 1/f-noise is significantly lower.

The WM-DLAS technique has in this work been combined with a Transversely Heated Graphite Atomiser (THGA) in order to make possible both ultra-sensitive trace element analysis and microanalysis. The new technique has shown a limit of detection of 10 fg ( g) for Rb in aqueous solutions (the pilot element under investigation), corresponding to a concentration of 0.2 ppt (0.2 parts-per-trillion or pg/mL).

The work has been pursued along several lines. The most important one has been to obtain a thorough understanding of the physical processes that might influence the performance of the technique. This part of the work has, in turn, been pur-sued in two different directions; to identify and understand the processes that give rise to the analytical signal (in order to find means to maximize it), and to identify and understand the processes that give rise to background signals and their drifts (in order to find means to minimize them).

A thorough understanding of the signal strengths and shapes of the analytical WM-DLAS signal has been obtained by the development and use of a program that simulates WM-DLAS signals for a variety of experimental situations. Quanti-ties of special importance have been the influence of laser centre frequency, fre-quency modulation amplitude, and the order of the harmonic detected on the signal strengths and shapes. The influence of hyperfine structure and isotope shifts on the elemental detection has also been investigated. It was found that the existence of hyperfine structure and isotope shift, as well as the pertinent broaden-ing mechanisms, has a pronounced effect on the detection. It was, in fact, found the WM-DLAS signal from a low pressure cell has little in common with that from an atmospheric pressure atomiser, such as the THGA, which puts sever restrictions on its use as a wavelength reference source.

It has also been found that WM-DLAS is, in most situations, not limited by the shot noise, but rather noise and drifts from the background signals. A significant amount of work has therefore been devoted to identify these background signals so as to find means to minimize them. The investigation has revealed that the most important background signals originate from multiple reflections in optical components, so-called etalon effects. Various techniques for reduction of such background signals have been proposed and examined.

Other research directions pursued have been to develop a new methodology for dealing with optically thick samples. This led to the development of a new tech-nique for extending the dynamic range of the WM-DLAS technique. The meth-odology does not require any prior knowledge of the analytical content of the sample, nor does it sacrifice the high sensitivity of the technique in order to obtain the extended dynamic range. The dynamic range was, by applying the methodol-ogy, increased to more than six orders of magnitude.

Place, publisher, year, edition, pages
Umeå: Fysik, 2002. 78 p.
Keyword
Physics, Fysik
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-42 (URN)91-7305-358-9 (ISBN)
Public defence
2002-12-19, Umeå, 10:15
Available from: 2002-12-19 Created: 2002-12-19 Last updated: 2013-01-31Bibliographically approved

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Publisher's full texthttp://dx.doi.org/10.1016/S0584-8547(98)00200-6

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Axner, Ove

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