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A Characterisation of the Wavelength Modulated Diode Laser Absorption Spectrometry Technique in Graphite Furnace

The Wavelength Modulated Diode Laser Absorption Spectrometry technique applied to a Graphite Furnace (WM – DLAS – GF) has been applied to the detection of low concentrations of rubidium atoms in liquid samples. A variety of experiments has been carried out in order to analyse the non-homogeneity of the atomic distribution in the furnace. Experiments were performed by selecting a small part of the laser beam passing through the furnace. Many quantities, such as beam intensity, atoms density, linearity of response and matrix recovery have been measured and detailed data and graphs are reported. Relevant not-homogeneities have been discovered in all such quantities. A comparison of the signal strength and signal-to-noise ratio for the detection at the frequencies of the second (2f) and fourth (4f) harmonics of modulation has been performed and it is shown that 4f is the mode of detection to be preferable at low concentration.

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- 4 (67) - 1. Introduction Realising a commercial system to detect species in small traces, the compactness and low cost as well as the sensitivity are important requisites. The Wavelength Modulated Diode Laser Absorption Spectrometry tech- nique applied to Graphite Furnace (WM – DLAS – GF) measures the absorption of wavelength modulated laser diode light using a graphite furnace as sample atomiser. The technique fulfils the requirements of both simple instrumental set-up and sensitivity down to less than 100 fg. The graphite furnace has been preferred to other atomisers because of an ability to work with small amounts of sample, either solid or liquid. This thesis gives in its first part a brief description of the technique, including an experimental set-up and a mathematical model for the wave- length modulation and signal demodulation process. The second part is devoted to a closer analysis of the properties of the graphite furnace, mostly of its spatial non-homogeneity. A comparison of the second and fourth harmonic of the detector signal is given in the appendix Even if it is possible to detect many atomic species, and since this study has been concerned with investigations of fundamental nature, only rubidium has been studied in this work.

Tesi di Laurea

Facoltà: Scienze Matematiche, Fisiche e Naturali

Autore: Marco Regalia Contatta »

Composta da 67 pagine.

 

Questa tesi ha raggiunto 305 click dal 20/03/2004.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.