Separation and enrichment of trace components in analytical chemistry
The analytical chemistry of trace quantities of chemical substances is one of the main branches of modern analytical chemistry and the large amount of activity in this field is reflected by numerous publications and lectures of which the authors are prominent specialists, such as Alimarinl, Babko2, Burriell-Marti3, Ehrlich and Rexer4, Speckers, West6 and many others. Three steps can be distinguished in any analytical process for the determination of the quantitative composition of a sample: sampling, chemical separation and the quantitative determination of the isolated components. Using the analogy with technologica] processes suggested by Zagorski7, these steps may be considered as analytical unit processes. The middle step can be omitted in cases where direct methods of determination are applied, i.e. when the determination directly follows the sampling. However, despite the continuous progress in direct methods, the majority of analytical approaches still involve the middle step. Taking into account the most useful analytical methods for trace determinations, e.g. emission spectroscopy, colorimetry, fluorimetry, polarography, neutron activation, mass spectrometry etc., only neutron activation combined with y-spectrometry, emission spectroscopy and mass spectrometry could be treated as direct methods in the case of some elements. Even these methods require prior chemical separation of the traces if applied to high purity materials. All other methods need this in any case. This chemical separation which consists of isolating, enriching and converting trace quantities into a form in which a suitable determination is feasible, is the subject of my lecture. Limiting the scope of the lecture to inorganic analysis, two types of trace analysis can be distinguished, depending on the sample: ( i) where the analysis aims at the determination of traces of the desired element present in the sample, and (ii) the case where on the basis ofthe analytical results the purity ofthe examined substance must be evaluated, and all or at least a significant number of impurities present in the sample must be determined. The first case is encountered while searching for the so-called rare elements which play a more and more important part in modern techniques. This group includes: scandium, the lanthanides, zirconium and hafnium, niobium and tantalum, rhenium, gallium, indium, germanium, selenium, tellurium and others. A similar approach is usually used in geochemistry, where the detection of traces of various elements in soils and plants is necessary for obtaining in-