Citrate systems

J. B. Rosenbaum and co-workers. Sulfur Dioxide Emission Control hy Hydrogen Sulfide Eeaction inMqueous Solution—The Citrate System, PB221914/5, National Technical Information Service, Spriagfield, Va., 1973. 

The primary characteristic of an acid/base buffer affecting steam requirements is the temperature dependence of Pgc /P O-Since PSC /P O of the citrate system is independent of temperature, the ideal minimum steam requirement (moles H20/moles SO2) of a simple stripper is equal to the ratio, °f the... 

Iron(III) citrate, " " or iron(III) ammonium citrate, is the usual vehicle for administering supplementary iron to an iron-deficient patient, for inducing iron-overload in rats or other creatures prior to testing the efficacy of iron chelators, or for introducing the isotope Fe for metabolic tracer studies. Stability constants for the aqueous iron(III)-citrate system have been established. " The 2 1 complex is claimed to be the dominant species in iron(III)/citrate/DMF systems. " There has been a very qualitative study of the incorporation of iron into transferrin from iron citrate. " Iron(III) citrate reacts relatively slowly with the aluminum(III)-transferrin complex to give the thermodynamically strongly favored combination of iron(III)-transferrin with aluminum(lll) citrate. " The mechanism of iron uptake from citrate complexes in cells has been briefly discussed. An octa-iron citrate complex appears in Section 5.4.5.4.3 below. 

Hydrol5dic polymerization in the ferric citrate system can be prevented if sufficient excess citrate is present in solution 66). Approximately 20 millimolar excess citrate is sufficient to supress pol3mier-ization of 1 millimolar iron, as indicated by dialysis and spectrophotomet-ric measurements. From pH titration in high citrate solutions, it was concluded 66) that a dicitrate complex of iron is formed at high pH. Presumably formation of the dicitrate chelate is competitive with hydrolytic polymerization. The fraction of polymer formed in ferric citrate solutions was found to decrease smoothly as the citrate content was increased up to 20 millimolar. The nuclear relaxation rate of the water protons in ferric citrate solutions increases with the citrate concentration. 

Mehra, O.E and Jackson, M.L. (1960) Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate. Proc. 7th Natl. Conf. Clays,... 

TABLE 10.4. Chemical Models and the Conditional Formation Constants I log ( ff) at 25° C] That Have Been Developed to Describe the Aqueous Speciation of Al-Citrate Systems ... 

Many of the titration-based chemical models employed to describe Al-citrate speciation were validated usmg ancillary spectrometry data (Lakatos et al., 2001 Harris et al., 2003). Results from spectroscopic studies of Fe(III)-citrate systems do not support the titration-based models, which are defined by mononuclear monocitrate species. Instead, mononuclear dicitrate, dinuclear, and trinuclear Fe(III)-citrate species are observed. It may be concluded that the aqueous speciation of Fe(III)-citrate in soil solutions cannot be predicted. The current speciation models are not applicable to the pH range of soil solutions, or as in the case of the Essington et al. (2005) model, have not been validated. There is also evidence... 

Lakatos, A., Banyai, L, Decock, P., and Kiss, T. (2001). Time-dependent solution speciation of the Al -citrate system potentiometric and NMR studies. Eur. J. Inorg. Chem. 2001, 461-469. 

The first phase determined that the citrate system best met all of the critical requirements for an ideal sulfur dioxide absorption medium, including the system s capability for efficient removal of sulfur dioxide over a broad concentration range, e.g., the high levels in smelter waste gas, the sulfur dioxide-lean stack gas emitted by power plants, and the intermediate range represented by Claus plants. The results of the second phase of the program, dealing with the process chemistry, forms the basis for much of this paper. 

The results of some laboratory runs demonstrating the effect of pH and the oxidation inhibiting effect of citrate are given in Table I. These show that in going from pH 4 to 5 in the citrate system the oxidation approximately doubles. In a comparison run, using a different acid, much higher levels of oxidation were found. While citric acid does chelate the heavy metals that catalyze the oxidation, this was not a factor in the... 

W. I., Sulfur Dioxide Emission Control by Hydrogen Sulfide Reaction in Aqueous Solution—The Citrate System, U.S. Bur. Mines Rept. Invest. (1973) 7774. 

It is noteworthy that the spectrum shows two equivalent V nuclei with splitting half that of the V in V0(tartrate)2 at higher pH. This means that there is rapid electron exchange between the two vanadium nuclei and establishes the type of structure depicted above. This has since been proved by X-ray analysis and the V—V distance shown to be 4.06 A. Similar dimer formation has been postulated for the vanadyl-citrate system 190). Several mixed chelates which have two oxygen and two nitrogen-bonding atoms have been studied 101, 102, 464). Their ESR parameters are, in general, like those of VO(acac)2. 

ZA1 Zrfarani-Moattar, M.T., Emamian, S., and Hamzehzadeh, S., Effect of temperature on the phase equilibrium of the aqueous two-phase poly(propylene glycol) + tripotassium citrate system, J. Chem. Eng. Data, 53,456, 2008. 

Figure 5-1. The a fraction curves for the four species in citrate systems at ionic strength...

Figure 5-3. The equilibrium w (proton number dotted) for the citrate system at ionic strength 0.1 M, 25°. The solid lines are four material balance n lines for the solution of Example 1.

The equilibrium n curve for this citrate system is shown as the dotted plot in Figure 5-3. [This could be obtained from a values read from Figure 5-1 and used in the left expression of equation (5-7).] It shows the average number of protons per citrate, starting from three in acid solution, and falling toward zero in basic solution. If the approximate answer above is valid, we are at n = 2.00. This follows if a3 = a 1. Calculate n for our solutions with Ch = 2C, and C = C in equation (5-7) ... 

It is now a simple matter to use the same method to solve any problem in the citrate system, by moving the n fragment to the proper position in Figure 5-3. For example ... 

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