Determination of low or trace-level amounts of metals by electrothermal atomic absorption spectrometry (ETAAS) often requires the use of suitable preconcentration and/or separation procedures in order to attain the necessary sensitivity and selectivity. Such schemes are advantageously executed in flow injection (FI) or sequential injection (SI) systems, which, in addition to reducing sample and reagent consumption, allow all manipulations to be made on-line under enclosed and strictly controlled conditions, thereby minimizing the risk for contamination from the environment. Various separation/preconcentration procedures have been suggested and applied, such as liquid-liquid extraction, (co)precipitation with collection in knotted reactors, adsorption, hydride generation, or ion-exchange. Selected examples of some of these procedures will be discussed. Emphasis will be placed on the use of FI/SI-systems incorporating ion-exchange column reactors. Although extensively used, such devices suffer from some inherent drawbacks. Thus, because many ion-exchange resins undergo volume change when they are converted from the acid to the basic form, long-term use might lead to progressively tighter packing and hence increased flow resistance. This can, however, to a large extent be alleviated by using countercurrent flow. Besides, the surface properties of the resin might be irreversibly changed after having been subjected to a large number of samples, either due to contamination, deactivation, or even loss of its functional groups. These problems are especially serious when using ETAAS as the detection device, because the limited accommodation volume of the graphite tube requires that the retained analyte must be eluted completely – or at least to a reproducible degree - within a very small volume of eluent. All these problems might be readily overcome by using an approach where the ion-exchange material is discarded and renewed after each measuring cycle. Based on the so-called lab-on-valve SI-system, which in its design only consumes very minute amounts of ion-exchange material, the cost per assay is amply compensated by superior performance and versatility. In fact, two approaches are conceivable: The analyte-loaded ion-exchange beads might either be transported directly into the graphite tube where they are pyrolized and the measurand is atomized and quantified; or the loaded beads can be eluted and the eluate forwarded to the ETAAS instrument for measurement. Both approaches will be illustrated.
|Publication status||Published - 2001|
|Event||The 28th Annual Conference of the Federation of Analytical Chemistry & Spectroscopic Societies - Detroit, Michigan, USA|
Duration: 1 Jan 2001 → …
Conference number: 28
|Conference||The 28th Annual Conference of the Federation of Analytical Chemistry & Spectroscopic Societies|
|City||Detroit, Michigan, USA|
|Period||01/01/2001 → …|