I. INTRODUCTION Chemical speciation may be defined as the determination of the individual concentrations of the various chemical forms of an element which together make up the total concentration of that element in a sample. The next decade will certainly see a blossoming of interest from chemists, biochemists, and biologists in techniques for chemical speciation. This is because it is becoming more and more apparent that both bioavailability and toxicity are critically dependent on the chemical form of the substance under test. Measurement of the total concentration of a nutrient or a trace element provides very little information about the bioavailability of the substance, since many vitamins and essential elements are now known to exist in a variety of chemical forms, the assimilability of which vary greatly.1–3 For example, niacin and folic acid exist in some foods in bound forms which are unavailable to many species,4 and the same is true of a whole range of essential metals, including iron, zinc, co...

Chemical speciation in natural waters

http://pure-oai.bham.ac.uk/ws/files/17879744/Bonnand_et_al_Chromium_isotopic_composition_Earth_Planetary_Science_Letters_2013.pdf

The chromium isotopic composition of seawater and marine carbonates

An analytical technique has been developed for the study of chromium speciation In natural waters based on the atomlzation of electrodeposited species. Matrix Interferences can be overcome and preconcentratlon achieved by the electrodeposition of chromium with mercury, onto pyrolytic graphlte-coated tubular furnaces, using a flow-through assembly. At pH 4.7, using a deposttion potential of -1.8 V vs. SCE, both Cr(V1) and Cr(II1) are reduced and accumulated as metallic chromium. At the same pH, but at -0.3 V vs. SCE, only Cr(V1) is selectively reduced to Cr( 111) which accumulates by adsorptlon. Using the labile-bound discrimination of the electrodeposition technique combined with an ultraviolet Irradiation step, Cr(V1) was found to be dominant In the samples studied, wlth most Cr(V1) present as labile forms.

Steven E. Ohl

Papers

Analysis for chromium traces in the aquatic ecosystem II. A study of Cr(III) and Cr(VI) in the susquehanna river basin of New York and Pennsylvania