On-line Systems for Automated Sample Introduction in Atomic Spectrometry

Leslie J. Pitts

November 1995

Department of Environmental Sciences, University of Plymouth

in collaboration with

PS Analytical Ltd., U.K.

Automation has become increasingly common in most areas of human endeavour. In the field of analytical chemistry, particular attention has been paid to on-line systems which offer high sample throughput. Among other attributes, such systems also offer advantages in terms of ease of automation and coupling to a variety of analytical detection systems. This thesis describes a number of automated approaches that have been developed to form either complete systems, or units which may be incorporated into hyphenated techniques.

Two automated speciation systems incorporating a microwave reduction step followed by hydride generation have been developed and evaluated. The first is a conventional system employing atomic absorption detection, whilst the second system employs high performance liquid chromatography to separate the species prior to detection by atomic fluorescence. Selenium has been used to evaluate both systems, the latter offering detection limits of 0.2 and 0.3 ng ml-1 for selenium(IV) and selenium(VI) respectively.

Kinetic studies on the reduction process of selenium(VI) to selenium(IV) were carried out. The reduction took 6 minutes at 70 °C, which is faster than previously reported in the literature. Thus the use of on-line systems employing a reduction step are supported for this element.

Photolysis was also evaluated as a means of transforming organo-metallic species on-line. The results indicate that photolytic treatment of seleno-methionine may be effective in cleaving the carbon-selenium bond, and provide the basis for an on-line system to pre-treat organo-selenium compounds.

On-line pyrolysis followed by pre-concentration on a gold trap was employed to determine mercury. This technique was incorporated into a system employing gas chromatography-pyrolysis-atomic fluorescence and used to determine a range of mercury species. In addition the approach was also used to determine mercury in sediment samples. Good agreement was obtained with two certified reference materials (NIST 1646 and NIST 8406).

An automated on-line pH adjusting system was also designed and developed. This device featured the use of ammonia gas to avoid contamination of samples prior to trace analysis.

Finally, a number of further applications to the above systems are discussed and a number of avenues for future work suggested.

Copyright © 1995 Leslie J. Pitts. All rights reserved.

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