SPECIATION RESULTS

Ion Ionic Molar Mobility [mol J- s- ] Diffusivity [m s- ] t Mobility K s V- ] Hydrated Ion Radius [nm] 

The molar mobilities of species like NaCO j- or CaCOs are not available, but values are expected to be lower than for HCOj - due to the larger size of these species. 

The equilibrium pH of the solutions was estimated for stirred cell atmospheres as shown in Table A5.1. Both N2 and instrument air can be used to pressurise the stirred cell solutions. Due to its inert nature N2 is commonly used for this purpose. However, when a carbonate buffer is used in a system, the buffer depends on the partial pressure of CO 2 in the air above the solution. To provide this partial pressure instrument air can be used. When the system is operated at high pressures such as in NF, the partial pressure of CO 2 increases. The equilibrium pressure calculation was carried out for background solution without pH adjustment (0.5 mM CaCh, 1 mM NaHCOs, 20 mM NaCl) in the absence of organics. 

The equilibrium pH with instrument air at 5 bar, which was the operating pressure for NF appears most realistic for a surface water system. 

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Since the quality of the separation is determined by the properties of the filter used, it is essential that the investigator should understand the causes of their non-ideal behaviour and how these can be minimised. The non-ideal behaviour is due to nonspecific adsorption of the constituents to be separated on the filter, Donnan equilibria, leakage of high molecular mass constituents and hindered passage of low molecular mass species through the filter. Some of these effects and how they influence the speciation results have been described by Gardiner and Delves... 

The accuracy of the analytical method was established hy independent analysis of the three additional filters from each of the 5 10 and 20 yg/m3 generation runs using both NAA and XRF analyses. Because NAA and XRF analysis techniques provide only a total arsenic measurement, the IC-AAS speciation results obtained for MMA, DMA and p-APA were used to estimate the total amount of arsenic. Table X presents the total arsenic obtained by the three techniques. The accuracy ranged from 90-120 of the values obtained by NAA and XRF. 

Size exclusion chromatography coupled to an ICP-QMS with an octopole collision cell was employed for the multi-elemental speciation of essential elements (P, S, Cr, Mn, Fe, Co, Cu, Zn, Br, Se and I) and Al as a toxic element in premature human milk.28 Comparison of speciation results demonstrates that premature human mothers milk differs significantly from formula milks in terms of the element binding pattern to the biomolecules. It was found that premature human milk is very rich in high molecular weight species associated with metals. The authors concluded that more attention must be paid to the chemical form in which essential elements are added to the formulas, particularly those used for the nutrition of premature babies.28... 

The widely different extraction efficiencies observed for different analytes in relation to the sample matrix and the solvent/extraction procedure utilized call for caution in the interpretation of the results of speciation studies. A compound may be found to largely predominate in an extract containing only a small fraction of the total element concentration and one should be aware that this compound could actually represent a minor species. Moreover, the concentration of the investigated element in the other extracts (if any) and in the residue should be determined to check the accuracy of results. Establishing a mass balance of the analytes in all fractions of the analytical procedure is recommended as it accounts for analyte extraction efficiency and helps evaluating the overall accuracy of speciation results (Fig. 8.4). 

Thus, this chapter will not only summarize speciation results in human milk, but also address the important topic of the current need to report upon methods and quality management in terms of quality control (QC) and quality assurance (QA). 

Caroli and his co-workers [14] published multielement speciation results including data about Mn speciation. These data regarded samples from 60 mothers (approximately day 30 after delivery) living in different areas of Italy. The investigation was based on SEC fractionation using a mass calibrated column and total concentration of Mn was found to be around 3 p,g l-1. They found 28 percent of Mn in the void fraction (>2000 kDa), 30 percent bound to the nonprotein fraction, (relatively LMW compounds), and the remaining Mn was found at low levels in the other fractions. 

Human milk can be considered the optimal food for infants. It contains all the macronutrients and micronutrients necessary for the correct development of the newborn and at the adequate levels. When infants are not breast-fed, or breastfeeding is discontinued very early, formula milks are used instead. Therefore, it is important to evaluate the capacity of formulas to deliver satisfactory quantities of minerals and trace elements that can be bioavailable to the children in order to cover their biological needs. This fact explains the need to perform trace elements speciation analysis in formula milk. Thus, the speciation results obtained in formulas and published so far are critically evaluated here and compared with those obtained in human milk. 

In the presence of high concentrations of both sulfate and fluoride, the speciation results are somewhat more difficult to interpret. Generally, the effect of fluoride predominates over that of sulfate, but not always. In deionized water containing added fluoride and sulfate to equal the concentrations of these two anions in basalt and shale ground waters, respectively, essentially all the plutonium was soluble—similar to its behavior in deionized water containing only added fluoride. Also, addition of sodium sulfate to basalt ground water to increase its concentration to that of shale ground water had no appreciable effect on plutonium solubility. 

Sound knowledge of fundamental chemistry helps in most cases. For example, the analysis of Fe(II) in an aqueous sample can be accurately accomplished in an acidic environment even if it is not performed immediately, whereas the conversion of Fe(II) to Fe (III) in an alkaline environment in the presence of air is quite fast and will significantly alter the speciation results. 

One approach to determine the reliability of geochemical codes is to take well-defined input data and compare the output from several different codes. For comparison of speciation results, Nordstrom et al. (1979) compiled a seawater test case and a river-water test case, i.e., seawater and river-water analyses that were used as input to 14 different codes. TTie results were compared and contrasted, demonstrating that the thermodynamic databases, the number of ion pairs and complexes, the form of the activity coefficients, the assumptions made for redox species, and the assumptions made for equilibrium solubilities of mineral phases were prominent factors in the results. Additional arsenic, selenium, and uranium redox test cases were designed for testing of... 

Nitsche H., Roberts K., Becraft K., Prussin T., Keeney D., Carpenter S. A., and Hobart D. E. (1995) Solubility and Speciation Results from Over- and Undersaturation Experiments on Np, Pu, and Am in Water from Yucca Mountain Region Well UE 25p I. LA-13017-MS, Los Alamos National Laboratories, Los Alamos, NM. 

For equilibrium computer calculations, 48 species were considered. The distribution of Cd, Pb, and Cu — for natural pH — in the Seine estuary are summarised in Table 4 (species accounting for less than 1% of the total metal were disregarded). It should be pointed out that these speciation results are very dependent upon the values which... 

The presence of elevated metals and arsenic in the sediments corresponds with the high concentration of dissolved constituents in the wells installed in the reservoir sediment (HLA, 1987 Titan, 1996 Woessner et al., 1984). In these wells, TDS is commonly over 1,400 mg/1, dissolved arsenic ranges from ca. 100 to 10,000 Xg/I, Mn from ca. 0.1 to 25 mg/1 and iron from ca. 1 to 60 mg/1. Arsenic speciation results show that samples from within reservoir sediment and the adjacent contaminated aquifer are dominated by As(III) (Moore et al, 1988). 

Torreti o, P. et al. 1995. Soluhility and speciation results from over.saturation experiments on Np, Pu, and Am in a neutral elctrolyte with a total carbonate. similar to water from Yucca Mountain Region well UE-25it J. Los Alamos Natl. Lab., Report LA-I3018-MS. 

Methodological development focusing possible effect of storage and pretreatment conditions on speciation results. It was proposed that monome-thylseleninic acid observed in purified urine could be the oxidation product of Se-sugar... 

Table 3.4. Some of the speciation results for sample 912-18 (Merino, 1975), as produced by program solmin88. The original printout also includes columns PPM in the ANALYZED section and log 10 activity in the CALCULATED sections. These have been removed to allow the data to fit the page.

Analytical strategies ivhich employ combinations of various separation and/or detection methods are called orthogonal analytical concepts . They are an inevitable means for quality control in speciation, and provide the best chances to obtain correcf speciation results and even identification of heretofore unknoivn species. In analytical systems ivith only one separation and one detection system, the risk of coelution, impossibility of species identification or misidentification is high (e.g., McSheehy et al. 2002), but this problem can be solved by employing different systems in various ways. 

Speciation analysis has come a long way in the past 10 to 15 years with improvements in the instrumental and extraction hardware leading to faster methods with better accuracy and precision even at low analyte concentrations. The wide range of CRM and the greater availability of the standards and reagents commonly used for speciation analysis have helped to improve the results. Future advances are required in the provision of methods that provide quantitation with structural characterization simultaneously, which will improve confidence in the speciation results. A recent perspective article by one of the early pioneers in chemical speciation analysis discusses the future of the area, in the context of the initial work in the subject. 

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