Oxidation buffer capacity

These measurements indicate that it is not possible to identify a single value of pe surrounding the O2/H2S interface in the environment. Redox couples do not respond to the pe of the environment with the same lability as hydrogen ion donors and acceptors. There is no clear electron buffer capacity other than the most general states of "oxygen containing" or "H2S containing." The reason for the vast differences in pec in the oxic waters is the slow oxidation kinetics of the reduced forms of the redox couples. The reduced species for which the kinetics of oxidation by O2 has been most widely studied is Mn. This oxidation reaction... 

If there is no buffering capacity [k - O and C(HA) - O] and if the diffusion away is very slow, the concentration of H+ ions at the interface will grow until the second term in Eq. (36) becomes equal to the first one. Substituting such a condition in Eq. (35), one can see that the rate of growth of the oxide becomes zero, i.e., the oxide attains a constant thickness. (In fact, some hydrogen ions will always escape by diffusion and, hence, complete equality of the two terms in Eq. (35) can never be attained so that some growth will have to continue.)... 

The compact, nonporous anodic alumina film is the most suitable for fundamental investigations. It is grown by anodization, mostly under constant-current (galvanostatic) conditions, in neutral solutions of borates, tartrates, citrates, and phosphates, all of which possess significant buffering capacity and hence do not allow significant dissolution of the oxide. 

One can see no way in which the halides could affect the buffering capacity of these electrolytes. There, indeed, seems to be little doubt that adsorption of the halides at the oxide surface takes place and plays a significant role. 

Recent studies demonstrated that the composition of the reaction mixture, and in particular the pH have significant effects on the kinetics of iron(III)-catalyzed autoxidation of sulfur(IV) oxides. When the reaction was triggered at pH 6.1, the typical pH profile as a function of time exhibited a distinct induction period after which the pH sharply decreased (98).The S-shaped kinetic traces were interpreted by assuming that the buffer capacity of the HSO3 / SO3- system efficiently reduces the acidifying effect of the oxidation process. The activity of the... 

The tailings comprise 5-10 wt. % pyrrhotite a highly reactive sulfide mineral that releases protons and Fe3+ into adjacent pore waters on oxidation. Further, the concentration of carbonate minerals in the tailings is low providing little buffering capacity above pH 5. Therefore, the tailings continued to acidify until they reach the pH of AI(OH)3 (pH 4-4.5) and Fe(OH)3 (pH 2.5-3.5) buffering. 

Minimal Interactions with Assay Components. If a buffer binds to or reacts with a component of the system, it should be avoided. For example, borate buffers can complex with alcohols and carbohydrates and great care should be exercised when utilizing these compounds. Some arsenate-based buffers have oxidizing potential with respect to thiols. Buffers should also have a low binding capacity with respect to divalent cations. 

Kuo, R.J. Matijevic, E. (1980) Particle adhesion and removal in model systems. III. Monodisperse ferric oxide on steel. J. Colloid Interface Sci. 78 407-421 Kuo, S. Jellum, E.J. (1994) The effect of soil phosphorus buffering capacity on phosphorus extraction by iron oxide-coated paper strips in some acid soils. Soil Sci. 158 124-131... 

Folate is a relatively unstable nutrient processing and storage conditions that promote oxidation are of particular concern since some of the forms of folate found in foods are easily oxidized. The reduced forms of folate (dihydro- and tetrahydrofolate) are oxidized to p-aminobenzoylglutamic acid and pterin-6-carboxylic acid, with a concomitant loss in vitamin activity. 5-Methyl-H4 folate can also be oxidized. Antioxidants (particularly ascorbic acid in the context of milk) can protect folate against destruction. The rate of the oxidative degradation of folate in foods depends on the derivative present and the food itself, particularly its pH, buffering capacity and concentration of catalytic trace elements and antioxidants. 

Buffer Capacities of Natural Waters. Natural waters are buffered in different ways and to varying degrees with respect to changes in pH, metal ion concentrations, various ligands, and oxidation-reduction potential. The buffer capacity is an intensive variable and is thermodynamic in nature. Hydrogen-ion buffering in natural waters has recently been discussed in detail by Weber and Stumm (38). Sillen (32) has doubted... 

Elements of /< greater than 3.2 form simple metallate anions in solutions of high pH—i.e., strongly alkaline solutions. As the pH of such solutions is lowered, isopolyanions are produced in many cases, ultimately yielding hydrous oxides, or salts of isopolymetallate ions as heterogeneous solid phases. Again, many of the isopolyanions exhibit buffer capacity. 

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