Analysis of Metal Ions by High Performance Liquid Chromatography

Abstract

Metal cations are of great importance in biological and environmental systems. In living organisms many trace metals are micro-nutrients and are required for the functioning of certain enzymes, proteins, and electron transport systems. Other inorganic cations can be toxic and cause damage to cells or the functioning of carefully balanced biological systems. Not only the total concentration but also the chemical form or species of the metal can affect the functions. The term species refers to the actual form in which a molecule or ion is present in solution. Biological availability of metals and the physiological and toxicological effects of the metals depend on the species of the individual metal present. In some cases, one form of the metal ion can be an activator of an enzyme whereas another form is not an activator. In other cases a metal ion in a complex with a certain ligand can be toxic whereas the same metal ion in a different form is not toxic. For example, organic mercury is much more toxic to biological organisms than elemental mercury. The oxidation state of a metal can also determine the effectiveness or toxicity of a metal. For example, iron which is found in small quantities in cells is a necessary element for cultures of unicellular algae. Recently it was hypothesized that the iron in seawater may limit the primary productivity in some oceanic areas where there is a relatively high concentration of major nutrients such as nitrate. However, the phytoplankton in seawater can only take up the truly dissolved Fe as its micro-nutrients. Fe(I1) is much more soluble than Fe(II1) in seawater, and Fe(I1) can easily be taken up by the phytoplankton. Thus the truly dissolved iron, especially Fe(I1) concentration, instead of the total iron concentration in atmosphere and in seawater, may directly affect not only the geochemical cycling of iron but also the biological productivity in the ocean. Therefore the determination of the concentration of specific species of trace metals, such as Fe(I1) instead of total iron, is essential for the understanding of the biochemical behavior or toxicity to organisms and the geochemical cycling of trace metals in the environment.