Titration speciation analysis

IV. SPECIATION ANALYSIS OF ORGANOMAGNESIUM COMPOUNDS A. Titration Methods... 

Only slightly less accurate ( 0.3—0.5%) and more versatile in scale are other titration techniques. Plutonium maybe oxidized in aqueous solution to PuO " 2 using AgO, and then reduced to Pu" " by a known excess of Fe", which is back-titrated with Ce" ". Pu" " may be titrated complexometricaHy with EDTA and a colorimetric indicator such as Arsenazo(I), even in the presence of a large excess of UO " 2- Solution spectrophotometry (Figs. 4 and 5) can be utilized if the plutonium oxidation state is known or controlled. The spectrophotometric method is very sensitive if a colored complex such as Arsenazo(III) is used. Analytically usehil absorption maxima and molar absorption coefficients ( s) are given in Table 10. Laser photoacoustic spectroscopy has been developed for both elemental analysis and speciation (oxidation state) at concentrations of lO " — 10 M (118). Chemical extraction can also be used to enhance this technique. 

In another example, five test cases were computed by PHREEQE and EQ3/6 and the same thermodynamic database was run for each program (INTERA, 1983) to test for any code differences. The five examples were speciation of seawater with major ions, speciation of seawater with complete analysis, dissolution of microchne in dilute HCl, reduction of hematite and calcite by titration with methane, and dedolomitization with gypsum dissolution and increasing temperature. The results were nearly identical for each test case. Test cases need to become standard practice when using geochemical codes so that the results will have better credibility. A comparison of code computations with experimental data on activity coefficients and mineral solubilities over a range of conditions also will improve credibility (Nordstrom, 1994). 

Input the raffinate analysis into MINTEQA2 and let the program speciate the water as a means of determining the bisuifate, Compare this result to bisulfate computed above, and discuss the difference. Now calculate using the bisulfate and H -ion concentrations computed by MINTEQA2. Remember, the acidity is a sum of equivalent concentrations, not activities. Assume the raffinate will be completely oxidized during its titration. 

Proteins and Amino Acids Total protein in food and feed samples is commonly determined by Kjeldahl (acid digestion/titration) or Dumas (pyrolysis) or elemental analysis.14 FIPLC can separate major proteins and furnish protein profiles and speciation information. HPLC can be used to further characterize specific proteins via peptide mapping and amino acid sequence analysis. HPLC modes used for protein include IEC, SEC, RPC, and affinity chromatography with typical UV detection at 215 nm or MS analysis. Details on protein separations are discussed in the life sciences section. 

It is possible to analyse these titration curves quantitatively. The number of absorbing species in solution may be determined from the raw data by factor analysis, with evolving factor analysis often giving a good indication of the stoichiometry of the species [16]. If we have a model for the complexes formed, together with an estimate for the stability constant of each species, then we can calculate a speciation of the particles at any point in the titration from the known total concentrations of metal and ligand. This speciation may be used to obtain estimates of the molar extinction coefficients of the particles (if they are unknown), and calculate the absorbance [17] a non-linear least-squares refinement of the stability constants is then carried out to give the best fit of calculated and observed absorbance. 

As I see, an essential problem in this field is that the complex aspect of adsorption from electrolyte solutions shown in Fig. 1 has not been widely accepted. I have hardly found a systematic analysis of all probable simultaneous equilibria in a given adsorption system in the relevant literature. In most cases the solution condition (e.g., pH)-dependent dissolution of the solid phase, the surface precipitation, and the speciation in the aqueous phase are omitted in the evaluations either without mentioning them or with reference to some reasoning. To demonsteate some outcomes, it is worth inspecting a simple case of the surface-charge titration of a common aluminum oxide in detail. 

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