As a consequence of our advancing knowledge of the impact of trace elements in
environmental and biological systems there is increasing need for quantitative analytical
techniques to accurately, sensitively and rapidly determine a wide range of trace elements
in environmental samples. Since their emergence in 1975 microwave digestion techniques
have revolutionised conventional approaches to sample digestion and have rapidly gained
widespread acceptance as an effective method of sample preparation. This thesis
describes how a number of novel on-line microwave digestion techniques have been
developed, characterised and applied to the digestion of a range of environmental
matrices which have proved time consuming or troublesome to digest by conventional
techniques.
A variety of batch open focused microwave digestion methods have been developed
and utilised for the analysis of a range of environmental samples including tea leaves,
seaweed and sediment samples. The techniques were optimised to determine a range of
trace metals including Al, As, Ba, Ca, Cr, Cu, Fe, K, Mg, Mn, Pb, Ni, Ti, V and Zn and
in each case were successfully validated by the analysis of suitable certified reference
materials. These techniques demonstrated a number of advantages over conventional
methods including less reagent usage, less contamination and substantial time savings.
Speciation studies have been a focus for this work and have included the evaluation of
an acetic acid microwave extraction method for the extraction of tributyltin, dibutyltin,
monobutyltin and triphenyltin from sediment samples prior to analysis by high
performance liquid chromatography-inductively coupled plasma-mass spectrometry
(HPLC-ICP-MS). In addition the speciation of arsenic in biological samples was
addressed by the development and evaluation of an on-Une microwave digestion
technique. This enabled the speciation of arsenobetaine (AsBet), monomethylarsonic acid
(MMA), dimethylarsinic acid (DMA) and inorganic arsenic following their separation by
HPLC. Decomposition was achieved by microwave digestion and followed by pre-reduction
with L-cysteine and detection by hydride generation-atomic absorption
spectrometry. Simple modification of the technique also facilitated the determination of
total arsenic. In addition the total reducible arsenic species (inorganic arsenic, MMA and
DMA) were determined directly by on-line pre-reduction-HG-AAS. The results obtained
were in good agreement with the certified values for the reference materials NRCC
DORM-1 (dogfish muscle) and TORT-1 (lobster hepatopancreas).
The on-line microwave digestion approach was further developed for the determination
of the total mercury content of solid environmental samples. This involved the
combination of an on-line microwave digestion and a bromide/bromate oxidation
reaction to facilitate complete oxidation of the organomercury species in slurried
biological samples. Following this approach detection could be performed by cold
vapour-atomic fluorescence spectrometry, giving a limit of detection of 13 ng l-1. In
addition a batch method in which samples were digested with a mixture of hydrogen
peroxide, nitric acid and sulphuric acid was developed and studied using temperature
profile measurements. Both methods were successfully validated by analysis of the certified reference materials NRCC DORM-2 and PACS-1 (harbour marine sediment).
Date of Award | 1997 |
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Original language | English |
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Awarding Institution | |
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THE DEVELOPMENT OF ON-LINE MICROWAVE DIGESTION TECHNIQUES FOR ENVIRONMENTAL MATRICES
LAMBLE, K. J. (Author). 1997
Student thesis: PhD