Aspects of flow injection atomic absorption spectrometry
thesisposted on 2017-06-21, 11:44 authored by Stephen G. Offley
The literature relevant to the generation of volatile hydrides for analytical atomic spectroscopy has been reviewed, with particular reference to atomic absorption spectrometry (AAS). This reveals some conflicting information concerning the nature of various interference effects and strategies to overcome them. The use of flow injection (FI) procedures has been demonstrated by several research groups, to be beneficial. A review of the literature concerning the application of FI techniques to AAS shows that there is a sustained interest in the use of such a combination for analytical purposes. In particular, an interest in the on-line coupling of chemical pretreatment of samples is evident. Atomic absorption spectrometry has a limited working range and requires frequent calibration, consequently, there is a need for a rapid, precise on-line dilution procedure. The potential of FI systems with wide bore manifold tubing for on-line dilution was assessed and found to be limited by variations in dispersion coefficient arising from differences in specific gravities between the sample and carrier fluids. This could be overcome only by the use of unrealistically high flow rates. The use of FI procedures for the generation of volatile hydrides of selenium and arsenic was investigated. Optimization studies of system parameters, including the atomization step, were undertaken which demonstrated the benefits in applying FI in hydride generation atomic absorption spectrometry (HGAAS). Analytical methods were devised and evaluated for the determination of Se in copper metal and As in nickel alloy. These procedures involved the use of an on-line matrix removal step in which potentially interfering matrix elements were retained on a strong cation exchange resin (Dowex 50W). The manifold was designed so that the FI value acted as the interface between the matrix isolation stage and the vapour generation stage, a strategy which allowed independent optimization of each stage. Location of the ion exchange resin in the sample loop of a six-port rotary valve allowed the resin to be regenerated easily and rapidly, with a throughput capability of the order of 50 h⁻¹ and permit the proposed full automation of the whole analytical procedure. In the determination of As in nickel alloy a novel stopped-flow pre-reduction step was developed to permit AsIII quantification, therefore, achieve optimum sensitivity. The two systems permitted limits of detection for Se and As of 2.1 and 3.9 ng ml⁻¹ respectively. Direct comparisons were made with existing matrix isolation systems to emphasise the benefits of system design.
SERC and Unicam Ltd