Buffering capacity maximum

The time interval between additions is selective, but is usually 300 ms. AH data is measured at the buffering capacity maximum, where the pH changes slowly and measurements are most accurate. 

Does not necessarily give better separations than TFA. Relatively slow to re-equilibrate. Good quality TEA preferable. Powerful buffering capacity. (Maximum CH3CN = 70—80%)... 

A solution containing equal concentrations of acid and its salt, or a half-neutralised solution of the acid, has the maximum buffer capacity . Other mixtures also possess considerable buffer capacity, but the pH will differ slightly from that of the half-neutralised acid. Thus in a quarter-neutralised solution of acid, [Acid] = 3 [Salt] ... 

Buffers resist a change in pH when protons are produced or consumed. Maximum buffering capacity occurs 1 pH unit on either side of pAl,. Physiologic buffers include bicarbonate, orthophosphate, and proteins. 

With a given weak acid, a buffer soiution can be prepared at any pH within about one unit of its p vaiue. Suppose, for exampie, that a biochemist needs a buffer system to maintain the pH of a soiution ciose to 5.0. What reagents shouid be used According to the previous anaiysis, the weak acid can have a p Z a between 4.0 and 6.0. As the p deviates from the desired pH, however, the soiution has a reduced buffer capacity. Thus, a buffer has maximum capacity when its acid has its p as ciose as possibie to the target pH. Tabie 18-1 iists some acid-base pairs often used as buffer soiutions. For a pH - 5.0 buffer, acetic acid (p Za — 4.75) and its conjugate base, acetate, wouid be a good choice. 

Thus, the buffering capacity depends on the composition of the buffer, i.e. on the concentration of the salt a or b. The maximum value found by differentiation of Eq. (1.4.27) with respect to a corresponds, for an acidic buffer, to b = s. 

Buffers are used mainly to control the pH and the acid-base equilibrium of the solute in the mobile phase. They can also be used to influence the retention times of ionizable compounds. The buffer capacity should be maximum and should be uniform in the pH range of 2-8 commonly used in HPLC. The buffers should be soluble, stable, and compatible with the detector employed, e.g., citrates are known to react with certain HPLC hardware components. 

Buffer solutions have two important characteristics. One of these characteristics is the pH of the solution. The other is its buffer capacity the amount of acid or base that can be added before considerable change occurs to the pH. The buffer capacity depends on the concentration of the acid/conjugate base (or the base/conjugate acid) in the buffer solution. When the ratio of the concentration of the buffer components is close to 1, the buffer capacity has reached its maximum. As well, a buffer that is more concentrated resists changes to pH more than than a buffer that is more dilute. This idea is illustrated in Figure 8.10, with buffer solutions of acetic acid and acetate of different concentrations. 

Although the condition is hypothetical, it can be calculated that if all of the skeletal muscles in the body degraded glycogen to lactic acid at the maximum rate and, if aU of the protons that were produced were transported into the blood, it would exceed the buffering capacity of the blood and the pH would fall dramatically (see below). This could soon result in death. Hence the inhibitory effect of protons... 

Figure 9-4b, which is the derivative of the upper curve, shows buffer capacity for the same system. Buffer capacity reaches a maximum when pH = pKa. That is, a buffer is most effective in resisting changes in pH when pH = pKa (that is, when [HAJ = [A-]). 

If you look back at Figure 9-4b, you will note that the maximum buffer capacity occurs when pH = pKa. That is, the solution is most resistant to pH changes when pH = pA., (and The buffer capacity measures the ability of the Vb = jV,) the slope (r/pH/4Vb) is therefore at its minimum. 

At what point in the titration of a weak base with a strong acid is the maximum buffer capacity reached This is the point at which a given small addition of acid causes the least pH change. 

Minor differences between the three electrolyte solutions are also observed. First, electrolyte number 3 only shows a peak maximum in the current-potential curves at potentials higher than 8 V. However, this is very clear because its pH value is smaller, indicating that this electrolyte solution possesses a higher buffer capacity against consumption of hydrogen ions in the vicinity of the fibre surface, avoiding hydrogen gas formation and Ni(OH)2 precipitation. Secondly, at a potential of 4V, no deposition occurred in electrolyte solution number 3, indicated by the absence of an increase in the measured electrical current and confirmed by XPS data. Additionally in this case, the lower pH plays an important role because of the lower pH value, the applied potential difference does not overlap with the potential window in which the reduction of Ni(II) occurs. Therefore no deposition is observed. 

Therefore, the maximum buffer capacity occurs at pH = pKa. The maximum buffer capacity is given by ... 

The maximum buffer capacity of the buffer in Example 2-9 is equal to 0.576(0.172 + 0.043) = 0.124. Therefore, it is recommended that a weak acid whose pKa is close to the required pH should be chosen for a buffer solution. 

Soil pH. This is only important when the pH buffering capacity of soil is very large (B approaches zero). Generally, when initial pH is high and soil B is very low, maximum NH3 is lost (Avnimelech and Laher, 1977). 

It follows, therefore, that the buffer capacity is a maximum when the hydrogen ion concentration of the buffer solution is equal to the dissociation constant of the acid. This condition, i.e., pH is equal to pka, arises when the solution contains equivalent amounts of the acid and its snlt such a system, which corresponds to the middle of the neutralization curve of the acid, has the maximum buffer capacity. The actual value of j3 at this point is found by inserting the condition given by (77) into equation (76) the result is... 

Preparation of Buffer Solutions.—The buffer capacity of a given acid-base system is a maximum, according to equation (77), when there are present equivalent amounts of acid and salt the hydrogen ion concentration is then equal to and the pH is equal to pfca. If the ratio of acid to salt is increased or decreased ten-fold, i.e., to 10 1 or 1 10, the hydrogen ion concentration is then lOfca or O.IAto, and the pH is pA a — 1 or pfca + 1, respectively. If these values for cn are inserted in equation (76), it is found that the buffer capacity is then... 

To make a buffer solution of a given pH, it is first necessary to choose an acid with a pfco value as near as possible to the required pH, so as to obtain the maximum buffer capacity. The actual ratio of acid to salt necessary can then be found from the simple Henderson equation... 

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