What is the use for total element concentrations ?
Since only speciation analysis provides the information about the identity of chemical species and there concentration, the question about the value of the often performed "total element determination" (trace metal analysis) is evident.
Since trace element analysis does not differentiate the present species according to their isotopic composition, valency state, molecular structure, binding partners or complexing ligands nor its charge or phase, the information value of a total element concentration is that of a kind of "sum parameter", summing-up different species
- having toxicity levels different by orders of magnitude,
- being cancerogen, toxic, non-toxic or even essential,
- being present in the particular, colloidal, dissolved or gaseous phase,
- being positively, negatively or non-charged,
- being present as a “free” ion, sorbed, complexed or bound.
The very limited information value
provided by such type of analysis limits the attractiveness of "trace element analysis" to those cases, were
- we do have a priori knowledge about the speciation so that total element concentration is sufficient to characterize the sample,
- speciation is highly dynamic and we need to know an upper limit for a certain species,
- as a quality check of our speciation analysis (mass balance),
- we cannot get more specific information,
- rules and legislation force us to present such data.
Please also keep in mind that even if you are not interested in the speciation of elements, the element species are present. If you are interested in the total element concentration, you have to make sure, that all elemental species are detected with the same sensitivity. In general that can only be done by applying a sample pre-treatment procedure, transforming all different species into one mineralized species. Especially direct analysis methods very seldom fulfill such requirement. Related news EVISA News, September 11, 2009: Speciation Analysis - Striving for Quality EVISA News, December 15, 2006: Speciation matters even if the interest is in total element concentration