Speciation manganese

B. Michalke, P. Schramel, Manganese speciation in human milk using size exclusion chromatography combined with strong anion exchange chromatography and inductively coupled plasma mass spectrometry detection, J. Anal. Atom. Spectrom., 19 (2004), 121-128. 

Jaudon P, Massiani C, Galea J, et al. 1989. Groundwater pollution by manganese. Manganese speciation Application to the selection and discussion of an in situ groundwater treatment. Sci Total Environ 84 169-183. 

Tisue GT, Hsiung T-M. 1987. Manganese speciation in a southeastern USA reservoir. 194th American Chemical Society National Meeting. Abstr Pap Am Chem Soc 194 231. 

Instrumentation for speciation requires the ability to quantitatively determine various chemical species of an element. The most widely used instrumental configuration includes a system to separate the chemical species, such as chromatography or electrophoresis, and an atomic spectrometry detectoi which provides high sensitivity and specificity for the separated compounds of the element of interest. Figure 1 illustrates instrumentation that was employed for manganese speciation analysis. 

Hgure 1 Example of experimental setup of instrumentation employed for manganese speciation. 

Table 6.6. Iron and Manganese speciation in some polluted soils differing in their texture and other properties... 

Ressler T, Wong J, Roos J (1999) Manganese speciation in exhaust particulates of automobiles using MMT-containing gasoline. J Synchrotron Radial 6 656-658. doi 10.1107/S0909049598015623... 

Z.Q. Zhang, H.T. Yan, Y. Lin, Rapid determination of chemical oxygen demand by flame AAS based on flow injection on-line ultrasound-assisted digestion and manganese speciation separation. Atom. Spectrosc. 25 (2004) 191-196. 

A detailed review of the methods for deterrnination of low manganese concentration in water and waste is available (179). A review on the speciation of Mn in fresh waters has been reported (180). Reviews for the chemical analysis of Mn in seawater, soil and plants, and air are presented in References 181, 182, and 183, respectively. 

Ressler T, J Wong, J Roos, IL Smith (2000) Quantitative speciation of Mn-bearing particulates emitted from autos burning (methylcyclopentadienyl)manganese tricarbonyl-added gasolines using XANES spectroscopy. Environ Sci Technol 34 950-958. 

The first consideration was the speciation and distribution of the metal in the sediment and water. Benthic organisms are exposed to surface water, pore water and sediment via the epidermis and/or the alimentary tract. Common binding sites for the metals in the sediment are iron and manganese oxides, clays, silica often with a coating of organic carbon that usually accounts for ca. 2% w/w. In a reducing environment contaminant metals will be precipitated as their sulfides. There is not necessarily a direct relationship between bioavailability and bioaccumulation, as digestion affects the availability and transport of the metals in animals, in ways that differ from those in plants. 

Let us now consider the effects of Eh-pH conditions on the speciation state and solubility of manganese in aqueous solutions. Manganese complexes have been carefully studied in the last decade, owing to the discovery on ocean ffoors of economically important metalliferous deposits (nodules and crusts) in which Mn compounds are dominant. 

The uptake of manganese by plants and its transport within plants has been reviewed. " Reviews describing Mn speciation in the blood and the transport kinetics of Mn into the central nervous system of mammals have appeared. Manganese has a unique capacity to be taken up via the olfactory pathways and pass trans-neuronally to other parts of the brain. ... 

This chapter discusses the chemical mechanisms influencing the fate of trace elements (arsenic, chromium, and zinc) in a small eutrophic lake with a seasonally anoxic hypolimnion (Lake Greifen). Arsenic and chromium are redox-sensitive trace elements that may be directly involved in redox cycles, whereas zinc is indirectly influenced by the redox conditions. We will illustrate how the seasonal cycles and the variations between oxic and anoxic conditions affect the concentrations and speciation of iron, manganese, arsenic, chromium, and zinc in the water column. The redox processes occurring in the anoxic hypolimnion are discussed in detail. Interactions between major redox species and trace elements are demonstrated. 

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

In operationally defined speciation the physical or chemical fractionation procedure applied to the sample defines the fraction isolated for measurement. For example, selective sequential extraction procedures are used to isolate metals associated with the water/acid soluble , exchangeable , reducible , oxidisable and residual fractions in a sediment. The reducible, oxidisable and residual fractions, for example, are often equated with the metals associated, bound or adsorbed in the iron/manganese oxyhydroxide, organic matter/sulfide and silicate phases, respectively. While this is often a convenient concept it must be emphasised that these associations are nominal and can be misleading. It is, therefore, sounder to regard the isolated fractions as defined by the operational procedure. Physical procedures such as the division of a solid sample into particle-size fractions or the isolation of a soil solution by filtration, centrifugation or dialysis are also examples of operational speciation. Indeed even the distinction between soluble and insoluble species in aquatic systems can be considered as operational speciation as it is based on the somewhat arbitrary definition of soluble as the ability to pass a 0.45/Am filter. 

In addition to the soluble chemical species and possible solid phase species described in the previous sections no discussion on speciation can be complete without the consideration of surface species. These include the inorganic and organic ions adsorbed on the surface of particles. Natural systems such as soils, sediments and waters abound with colloids such as the hydrous oxides of iron, aluminium, manganese and silicon which have the potential to form surface complexes with the various cationic and anionic dissolved species (Evans, 1989). 

Direct methods for determining the combinational form of an element or its oxidation state include infrared absorption spectrometry, X-ray diffraction and, more recently, electron paramagnetic resonance - nuclear magnetic resonance -and Mossbauer spectrometry. With such techniques the combinational forms of major elements in soil components such as clay minerals, iron, manganese and aluminium oxyhydroxides and humic materials and the chemical structures of these soil components have been elucidated over the past 50 years. These direct, mainly non-destructive, methods for speciation are dealt with in some detail in Chapter 3 and are not further discussed here. 

In addition to their use in the functional speciation role, selective extraction methods have been used to target element species in soil, or elements bound to, or associated with, particular soil phases or compounds. Examples include the use of extractants to release, for determination, metals on exchange sites, or metals bound or associated with soil iron or manganese oxyhydroxides or with soil organic matter. Most of these extractants are, however, less specific than intended and may extract species from other phases. Such extractants, however, are commonly, and conveniently, designated by their target species, e.g. extractable metal species or carbonate-bound species, but should more strictly be regarded as examples of speciation in which the species are operationally defined, i.e. by the method used to isolate them. 

Nowadays, not only Fe but other trace metals as well, for example, Mn, Co, or Cu, are thought to limit primary production. It is thus a real challenge for oceanographers not just to assess correctly the very low levels of Fe and Mn in the oceans but also to carry out the speciation of these elements (total dissolved concentrations are at the nM level, labile forms oxidation states in natural aquatic systems Fe(II), which is readily soluble, and Fe(III), which is almost insoluble. Flowever, both Fe ions can form diverse complexes with organic ligands with different labilities and solubilities, and colloidal particles, which are also considered part of the dissolved phase. Manganese also exists in two oxidation states in aquatic systems soluble Mn(II) and insoluble Mn(IV) both are present in a dynamic cycle in seawater. The nonlabile Mn pool consists of oxidized Mn(IV) species, but these can be photochemically reduced and thus solubilized.23... 

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