Enrichment Methods in Trace Analysis

Enrichment methods are classified according to the type of sample for which they are to be used, and basic analytical principles are applied to develop criteria for choice of enrichment method and conditions to be used. The topic of 'enrichment' or 'preconcentration' of trace elements has assumed great importance not only in the field of high-purity materials but also in connection with pollution. Whatever the merits or demerits of the case against increasing pollution of the environment, the analyst is faced with the reality of having to try to determine traces of a wide variety of substances. One of the ironic consequences of the anti-pollution campaign is that it would be quite possible for legislation to be enacted setting an upper limit for the permissible concentration of a pollutant, and for that limit to be below the limits of detection for that substance. However, if that were the case, the prosecution would have a hard task to prove that the pollutant was present in concentrations above the permitted limit but below the detection limit (unless, of course, they were aware of Professor Liteanu's mathematical methods for dealing with such a situation1). The subject of this paper was dealt with by Minczewski2 at the IUPAC Congress in Moscow in 1965, and by Mizuike3 in a book on physical methods of trace analysis. It is also the subject of a review that will appear in Talanta4. My purpose will therefore not be to give a review of applications, but rather to try to apply simple analytical ideas to the problem and to suggest lines of work. Of necessity, there will be some common ground between this paper and those already mentioned. GENERAL CONSIDERATIONS Basically there are two situations in which enrichment will be required, their common feature being that the species to be concentrated before its determination (the determinand) is present in amounts or concentrations