Trace metal anaylsis by spectroscopic techniques

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Campbell, A., 1991. Trace metal anaylsis by spectroscopic techniques. MPhil, Nottingham Trent University.

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Abstract

The prime responsibility of the Engine Support Services Laboratory (ESSL), within Rolls Royce, is to support the rig and engine projects in their development and production environment. Trace metal analysis forms an integral part of such activities as it is applied to the disciplines of fuel, lubricant, alloy and environmental evaluation.

As part of the laboratories endeavour to maintain adequate analytical capability an evaluation of Graphite Furnace Atomic Absorption Spectroscopy was undertaken.

However the nature of the laboratories analytical investigations invariably require some form of extraction prior to the analysis of the metal in question. 8-hydroxyquinoline was chosen because of its ability to chelate with a wide range of metals and for the purpose of this thesis would be applied to the likes of copper, lead, iron and aluminium.

The extraction of these metals were evaluated in the presence of two buffer systems, potassium hydrogen phthalate and sodium potassium tartrate. The results illustrating the need for careful consideration of a given sample matrix when using extraction techniques.

The technique of Graphite Furnace Atomic Absorption Spectroscopy was new to the ESSL and its evaluation essential to maintaining our ability to meet future trace metal analysis demands placed upon it. The results have shown the technique to be excellent for trace metal analyses in aqueous matrices. The effect of hydrochloric, nitric, sulphuric and phosphoric acids has been evaluated in terms of their effect on the signal response of the elements under investigation.

Each element/matrix combination has shown the capability of the system to quantify to the 10ppb level, and to exhibit excellent linearity over the range 10-100ppb. The exception being iron in the presence of' phosphoric acid which retained a high background contamination level of iron.

The evaluation of such elements in an organic matrix was restricted to the extraction of copper using 8-hydroxyquinoline in chloroform. The basic techniques of sample uptake, via a micropipette, and injection into the furnace came under close scrutiny, resulting in alternative micropipette tips being developed and assessed for improved consistency of the results generated.

The results of such an evaluation have shown that significant practical limitations do exist when using chloroform based solutions. However these may be minimised by the use of alternative, less volatile, solvents. In addition some of the instrumental features offered by the Shimadzu AA-670, which at first glance appeared advantageous, were in fact compromised by the use of such solvents.