Group speciation

Determination of total parameters is an example of activities classified as group speciation. Taking into account the sheer number and diversity of different chemicals that may be present in environmental samples, determination of total parameters could be an attractive alternative to full chemical speciation, especially for the initial screening of samples. Samples for which the value of a given total parameter exceeds prescribed limits can then be further analyzed using more advanced methods. Overall, group speciation can save both time and money in the characterization of environmental samples. 

Group speciation—determination of the concentration level of a specific group of compounds or of elements existing in different compounds in a specific oxidation state, and their physical forms... 

For compoimds with acidic or basic functional groups, speciation must additionally be accoimted for when sorption coefficients are estimated, hi this case, the apparent sorption coefficient, Dqc, is a composite of the sorption of at least two species (see Eq. 7). 

For instance, V.N. Ozyabkin (1995) subdivides them depending on the complexity and dimension of the forecast object. J.Rubin (1983), W. Kinzelbach (1992), S.R. Kraynov et al. (2004) base the classification on phase uniformity of the medium and velocity of chemical processes. In this connection they distinguish thermodynamical, transport and kinetic models. In Europe and the USA are broadly used classifications based on typization of local problems (Chen Zhu, Anderson G., 2002, Bethke C. M., 2008, etc.). In connection with this all hydrogeochemical models are subdivided there into three groups speciation-solubility models or batch models, reaction path modelsor mass transfer models reactive transport models or couplet mass transport models. In the second group of this classification is non-uniquely identified the role of mass transfer kinetics. 

Figure 1. Molecules with one Lewis Base Group Speciation of 100/jM acetic acid, methylenephosphonic acid, and methylamine as a function of pH in 10 mM ionic strength medium.

In this work ion-exchange and gel-permeation chromatography coupled with membrane filtration, photochemical oxidation of organic metal complexes and CL detection were applied to the study of the speciation of cobalt, copper, iron and vanadium in water from the Dnieper reservoirs and some rivers of Ukraine. The role of various groups of organic matters in the complexation of metals is established. 

Fig. 2. Speciation of functional groups present in the biomass depending on the solution pH.

Wigley, T.M.L., WATSPEC A computer program for determining the equilibrium speciation of aqueous solutions, Brit. Geomorph. Res. Group Tech. Bull., 20, 48, 1977. 

For the understanding of the binding of heavy metals on clays one needs to consider - in addition to ion exchange - the surface complex formation on end-standing functional OH-groups. Furthermore, the speciation of the sorbate ion (free hydroxo complex, carbonato- or organic complex) and its pH-dependence has to be known. 

Compounds bearing the functional groups of the present chapter are usually analyzed for the characteristic N heteroatom and less frequently for O. In this section some recent advances in the analysis of these heteroatoms are presented. A critical review appeared of the analysis of the nutrient elements C, N, P and Si, and their speciation in environmental waters, including sample collection and preservation, sample preparation and methods for end analysis5. 

As for all elements, the distribution of Mo in the environment depends critically on chemical speciation, including oxidation state (Bertine and Turekian 1973 Morford and Emerson 1999). However, Mo is somewhat unusual in both respects. In terms of ligand coordination. Mo is one of a small number of transition metals that commonly form oxy anions and coordinate only weakly with other environmentally common ligands such as Cl" or OH". Other such metals include Cr and W, which sit above and below Mo, respectively, in Group VI of the Periodic Table, as well as Tc, Re, Os and U. Hence, Mo chemistry has some analogies with these metals, as well as with nonmetals such as S, Se, P and As which also form oxyanions. 

Being the third most common element (after carbon and hydrogen) in petroleum product, sulfur has been analyzed extensively. Analytical methods range from elemental analyses to functional group (sulfur-type) analyses to structural characterization to molecular speciation (Speight, 2001). Of the methods specified for the... 

In 2000 two major petrochemical companies installed process NMR systems on the feed streams to steam crackers in their production complexes where they provided feed forward stream characterization to the Spyro reactor models used to optimize the production processes. The analysis was comprised of PLS prediction of n-paraffins, /xo-paraffins, naphthenes, and aromatics calibrated to GC analysis (PINA) with speciation of C4-C10 for each of the hydrocarbon groups. Figure 10.22 shows typical NMR spectral variability for naphtha streams. Table 10.2 shows the PLS calibration performance obtained with cross validation for... 

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