Element speciation analysis

Elements exist in various chemical forms(chemical species), e.g. a complex with organic compounds, in biological and environmental system. The chemical form determines essentiality, toxicity or bioavailability of an element. Thus, "element speciation analysis" that identifies and quantifies the chemical form of an element, as well as total element determination, is necessary to clarify the behavior and function of an element in the biological and environmental system.

For element speciation analysis, I have used mainly the following two analytical techniques.
1. HPLC/ICP-MS(high performance liquid chromatography / inductively coupled plasma-mass spectrometry)
2. NMR(nuclear magnetic resonance spectrometry)

The figure shows size exclusion HPLC/ICP-MS chromatograms of rhamnogalacturonan II-borate complex(dRG-II-B), which is isolated from an enzyme digest of plant cell walls. In the dRG-II-B, a borate cross-links two RG-II molecules by ester bonds. In the chromatograms, Ca, Sr, Ba, Pb peaks appear in the same retention time with the B peak of dRG-II-B, indicating that these metals are bound to dRG-II-B.

Plant nutritional biochemistry

Plants need only inorganic elements (minerals) as essential nutrients for their growth and development. The essential elements needed in relatively large and small amounts are referred to as macronutrients and micronutrients, respectively. The elements recognized today as a macronutrient are N, P, K , S, Ca, and Mg, and those as a micronutrient are Fe, Mn, Cu, Zn, Ni, Mo, B, and Cl. In contrast, the essential nutrients for animals are organic compounds such as carbohydrates, proteins, lipids, vitamins as well as minerals.

Inorganic elements occur in various chemical forms in a living body. The movement (ca. absorption, transport) and function (ca. essentiality, toxicity) of the minerals depends on their chemical forms. Therefore, to clarify the chemical form of essential elements in plants are necessary to understanding their movement and function in plants.

The figure is a model showing that boron(B), one of essential micronutrients for vascular plants, binds two rhamnogalacturonan II(RG-II), and cross-links pectin molecules in plant cell walls. B is thought to contribute to the stabilization of cell wall structure by the pectin network. Metal ions such as Ca, Sr, Ba and Pb are bound to dRG-II-B complex as mentioned above. The metal binding is speculated to relate with structural stabilization of the complex.