Speciation
Speciation (based on the English speciation or chemical speciation ) describes in chemistry either a) the process (i.e. the formation) of chemical forms of expression of a substance as a result of an established reaction equilibrium, or b) the state of equilibrium reached itself (overview of the chemical species present ). The term speciation, which is preferred in German, avoids the danger of confusion in English with the term speciation, which has long been introduced for biological speciation .
Explanation and examples
The chemical forms formed by the process of speciation are called species . Here are three examples:
- Organic acids typically occur in a dissociated state (-COO - ) and an undissociated state (-COOH), depending on the pH value .
- Water is always present in different molecular forms, namely in addition to the H 2 O form, which is by far the most prevalent in medium pH ranges, also as OH - or as H 3 O + .
- Oxygen occurs as a two- and three-atom molecule (O 2 , O 3 ) as a result of UV exposure , or as a radical or as an ion .
Significance for ecology, physiology and medicine
Speciation forms an important basis for the availability of plant nutrients in the soil, for the dosage form of drugs and for the toxicity of toxic substances to humans, animals and plants. Depending on the local environmental conditions in the soil, in the water or in the gastrointestinal tract ( pH value , redox potential , chelating agents and other interacting substances), the speciation and thus the absorbability and reactivity of a substance can change drastically.
See also
literature
- Bruno Streit , Werner Stumm : Chemical properties of metals and the process of bioaccumulation in terrestrial plants. Pp. 31-62. In: B. Markert (Ed.): Plants as Biomonitors. Indicators for heavy metals in the terrestrial environment. VCH Publisher, Weinheim & New York 1993.
- AM Ure, CM Davidson: Chemical speciation in the environment . 2nd ed., Blackwell Science 2006. ISBN 978-0632058488 .