Buffers range

Remark The titration curve slope of an acid by a strong base is equal to dpWdC, that is, to the inverse of the buffer index (see Chaps. 9 and 10). 

In general, we may state, on experimental grounds, that the buffering capacity is maintained for mixtures within the range of concentrations ratios 1 acid/10 salt and 10 acid/1 salt. Hence, the approximate pH range of a buffer is 

In light of the guideline that the relative concentrations of acid and conjugate base should not differ by more than a factor of 10 in order for a buffer to be reasonably effective, we can calculate the pH range over which a particular acid and its conjugate base make an effective buffer. Since the pH of a buffer is given by the Henderson-Hasselbalch equation, we can calculate the outermost points of the effective range as follows  

Lowest pH for effective buffer occurs when the base is one-tenth as concentrated as the acid. 

A A concentrated buffer contains more of the weak acid and its conjugate base than a weak buffer does. It can therefore neutralize more added acid or added base. 

Which acid would you choose to combine with its sodium salt to make a solution buffered at pH 4.25 For the best choice, calculate the ratio of the conjugate base to the acid required to attain the desired pH. 

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Fig. 3. Effective buffer ranges for food acidulants piC values are given in parentheses.

Aqueous solutions of citric acid make excellent buffer systems when partially neutralized because citric acid is a weak acid and has three carboxyl groups, hence three p-K s. At 20°C pifj = 3.14, pi 2 4.77, and = 6.39 (2). The buffer range for citrate solutions is pH 2.5 to 6.5. Buffer systems can be made using a solution of citric acid and sodium citrate or by neutralizing a solution of citric acid with a base such as sodium hydroxide. In Table 4 stock solutions of 0.1 Af (0.33 N) citric acid are combined with 0.1 Af (0.33 N) sodium citrate to make a typical buffer solution. 

The buffer range is the pH range over which the buffer is effective. It is related to the ratio of concentrations of the weak acid and its conjugate. The further the ratio is from 1, the less effective the buffering action. Ideally, the acid/base ratio should be between 0.1 and 10. Since log10 10 = 1 and log10 0.1 = — 1, buffers are most useful within 1 pH unit of the weak acid s pfQ. 

De Vries, W, Posch, M, Kamari, J. (1989). Simulation of the long-term soil response to acid deposition in various buffer ranges. Water, Air and Soil Pollution, 48, 349-390. 

The set of buffers compiled by McLellan provides the simplest way to carry out the electrophoresis of proteins in their native state.25 McLellan s buffers range from pH 3.8 to pH 10.2, all with relatively low conductivity (Table 8.1). By using different buffers from the set it is possible to compare the effect of pH changes on protein mobility while maintaining similar electrical conditions. This is demonstrated... 

For an idea of buffering ranges. Fig. 7.6 shows these ranges for some... 

Some weak acids and bases have more than one buffer range, for example phosphoric acid has three ionisable protons with three different pA"a values and can be used to prepare buffers to cover three different pH ranges. The ionic species involved in the ranges covered by phosphate buffer are ... 

The buffering ranges of a weak electrolyte are only discrete if the pA a values of its acidic and/or basic groups are separated by more than 2 pH units. Some acids have ionisable groups with pKa values less than 2 pH units apart so that they produce buffers with wide ranges. For example, succinic acid, which has pA"a values of 4.19 and 5.57, can be considered to have a continuous buffering range between pH 3.19 and 6.57. 

Effective buffering ranges of several common buffers. 

Food acidulants -buffer ranges [HYDROXY DICARBOXYLIC ACIDS] (Vol 13) -lactic acid as [HYDROXYCARBOXYLIC ACIDS] (Vol 13)... 

In addition to considering an adjusted buffering range in mixed solvent systems, the effects of dilution on the pH of the formulation should also be considered (Rubino, 1987). As formulations containing mixed solvent systems are diluted, the solvent effects onWIievjil decrease. For example, the a of the buffer acid will decrease as the formulation is diluted due to the dilution of the cosolvent. The consequences of the pqbWnges on the physicochemical stability of the active compounds should be carefully studied. 

Table 6 Some Common Buffers and Their Buffering Ranges...

Data in Table 3.2 can be represented in graph form, the titration curve. This is shown in Figure 3.1, and it is generated by plotting NaOH added versus pH. It shows a plateau approximately between pH 3.7 and 5.7 and an inflection point at pH 4.7, the pK of acetic acid. pH 3.7-5.7 is considered the acetic acid buffer buffering range. 

Obtain 10 ml of sodium phosphate buffers ranging in pEl from 6.4 to 8.0 ... 

Solubility. A 1 g sample of protein was added to either 100 ml of 0.3 M citrate-phosphate buffer ranging from pH 2.0 to 8.5 or to 100 ml of pH 7.0 citrate-phosphate buffer extending in ionic strength from 0.005 to 1.00. The mixtures were blended... 

TABLE 21.8 Usefnl Buffering Range for Different Buffering Systems at 25 °C [21]. ... 

Tris(hydroxymethyl)aminomethane, commonly called TRIS or Trizma, is often used as a buffer in biochemical studies. Its buffering range is from pH 7 to 9, and Kb is 1.19 x 10-<5 for the reaction... 

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