Optimum buffering capacity

Optimum buffering capacity occurs at a pH equal to the pA of the buffer. In general, you can expect most buffers to provide adequate buffering capacity for controlling mobile-phase pH only within +1 unit of their respective pA values. Beyond that, buffering capacity may be inadequate. 

H2P04, and in Equation 7.61, P04 is the salt of the acid HP04 . So each of these pairs constitutes a buffer system, and orthophosphate buffers can be prepared over a wide pH range. The optimum buffering capacity of each pair occurs at a pH corresponding to its Ka. The HP04 /H2P04 couple is an effective buffer system in the blood (see below). 

Another factor that can result in migration time variation is buffer electrolysis (buffer depletion). Several approaches have been used to reduce buffer depletion, such as the use of high concentration buffers with optimum buffer capacity, replenishment, changing the vials after a certain number of analyses, etc. During method development, buffer depletion should be investigated before the method is submitted to a validation procedure. ... 

Flue Ga.s Desulfuriza.tion. Citric acid can be used to buffer systems that can scmb sulfur dioxide from flue gas produced by large coal and gas-fired boilers generating steam for electrical power (134—143). The optimum pH for sulfur dioxide absorption is pH 4.5, which is where citrate has buffer capacity. Sulfur dioxide is the primary contributor to acid rain, which can cause environmental damage. 

Pancreatic secretions. In the acinar cells, the pancreas forms a secretion that is alkaline due to its HCOa content, the buffer capacity of which is suf cient to neutralize the stomach s hydrochloric acid. The pancreatic secretion also contains many enzymes that catalyze the hydrolysis of high-molecular-weight food components. All of these enzymes are hydrolases with pH optimums in the neutral or weakly alkaline range. Many of them are formed and secreted as proenzymes and are only activated in the bowel lumen (see p. 270). 

With these assumptions in mind, we now complete the outline of the solution of the diffusion-reaction problem as it applies to the most difficult case, the pH-based enzymatic sensors (potentiometric or optical). We assume only that there is no depletion layer at the gel/solution boundary (7), and that there is no fixed buffer capacity (4). The objective of this exercise is to find out the optimum thickness of the gel layer that is critically important for all zero-flux-boundary sensors, as follows from (2.26). 

Considerable difficulty was experienced throughout the entire period of plant-scale operation of the DBBP countercurrent extraction process in adjusting the CAW solution to the desired pH of 0.75. Several factors contributed to these difficulties. Lack of any buffering capacity in the CAW solution made it easy to overshoot or undershoot the desired pH. The two-step neutralization procedure and equipment aided considerably in achieving proper feed acidity. But, even with this approach, inadequate mixing coupled with unsophisticated and insensitive monitoring and control instrumentation made it impossible to routinely achieve reliable adjustment of feed acidity to its optimum range. 

Buffer solutions are widely used in pharmacy to adjust the pH of aqueous solutions to that required for maximum stability or that needed for optimum physiological effect. Solutions for application to delicate tissues, particularly the eye, should also be formulated at a pH not too far removed from that of the appropriate tissue fluid, as otherwise irritation may be caused on administration. The pH of tears lies between 7 and 8, with an average value of 7.4. Fortunately, the buffer capacity of tears is high and, provided that the solutions to be administered have a low buffer capacity, a reasonably wide range of pH may be tolerated, although there is a difference in the... 

Tears have some buffering capacity so, as we noted before, the pH-partition hypothesis has to be applied with some circumspection. The acid neutralising power of the tears when 0.1 cm of a 1% solution of a dmg is instilled into the eye is approximately equivalent to 10 fjL of a 0.01 mol dm strong base. The pH for either maximum solubility (see Chapter 5) or maximum stability (see Chapter 4) of a dmg may well be below the optimum in relation to acceptability and activity. Under these conditions it is possible to use a buffer with a low buffering capacity to maintain a low pH adequate to prevent change in pH due to alkalinity of glass or carbon dioxide ingress from the air. When such drops are instilled into the eye the tears will participate in a fairly rapid remm to normal pH. 

APase activity. The pH optimum of the enzyme is shifted to higher values with increasing substrate concentrations, whereas with increasing pK values of the substrate, the pH optimum tends to shift to neutrality. Addition of ions, such as Mg +, may significantly enhance enzyme activity in some buffers, (glycine buffers, which have insufficient buffering capacity for APase) but not in others (diethanolamine, Bergmeyer, 1974). Tris buffers produce a sharp increase in enzyme activity (Neumann et al., 1975). 

The desirable pH increment, ApH, can be decided on the basis of a function similar to that shown in Figure 5.5, which establishes for each soil how high the pH must be to eliminate A1 toxicity for a crop. Of course, the optimum pH varies for different crops because of plant-specific A1 tolerances and Ca requirements. The hme requirement of any soil can be calculated from the slope of the titration curve of that soil, as diagrammed in Figure 5.10. Conversely, the buffer capacity of the soil is the reciprocal of this slope that is, buffer capacity is the quantity of lime (alkali) added to the soil that achieves a unit change in pH. 

The peak capacity is not pertinent as the separation was developed by a solvent program. The expected efficiency of the column when operated at the optimum velocity would be about 5,500 theoretical plates. This is not a particularly high efficiency and so the separation depended heavily on the phases selected and the gradient employed. The separation was achieved by a complex mixture of ionic and dispersive interactions between the solutes and the stationary phase and ionic, polar and dispersive forces between the solutes and the mobile phase. The initial solvent was a 1% acetic acid and 1 mM tetrabutyl ammonium phosphate buffered to a pH of 2.8. Initially the tetrabutyl ammonium salt would be adsorbed strongly on the reverse phase and thus acted as an adsorbed ion exchanger. During the program, acetonitrile was added to the solvent and initially this increased the dispersive interactions between the solute and the mobile phase. 

O ring. At 20 min inhibition time the detection limits for malathion, parathion methyl and paraoxon were 3, 0.5 and 5pg I respectively. Although these bienzymatic systems look simple, it is difficult to provide optimal conditions for both enzymes. In general the optimum pH, temperature and buffer molarity for different enzymes are different. The experimental conditions are at the levels below the optimum capacity of both enzymes [14], This disadvantage can be minimized by use of a single enzyme system, which is readily inhibited by the pesticide. 

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