Universal buffer mixture

The following table covering the pH range 2.6-12.0 (18°C) is included as an example of a universal buffer mixture. 

A 10 mM ionic strength universal buffer mixture, consisting of Good zwitterio-nic buffers, [174] and other components (but free of phosphate and boric acid), is used in the pION apparatus [116,556], The 5-pKa mixture produces a linear response to the addition of base titrant in the pH 3-10 interval, as indicated in Fig. 7.53. The robotic system uses the universal buffer solution for all applications, automatically adjusting the pH with the addition of a standardized KOH solution. The robotic system uses a built-in titrator to standardize the pH mapping operation. 

E. Solutions for the pH range 2-6-12-0 at 18°C - universal buffer mixture (Johnson and Lindsey, 1939) A mixture of 6 008 g of A.R. citric acid, 3-893 g of A.R. potassium dihydrogen phosphate, 1-769 g of A.R. boric acid and 5-266 g of pure diethylbarbituric acid is dissolved in water and made up to 1 litre. The pH values of mixtures of 100 ml of this solution with various volumes (Y) of 0-2m sodium hydroxide solution (free from carbonate) are tabulated below. 

Each buffer system is generally applicable over a limited range, viz., about 2 units of pH, but by making suitable mixtures of acids and acid salts, whose pfca values differ from one another by 2 units or less, it is possible to prepare a universal buffer mixture by adding a pre-deter-mined amount of alkali, a buffer solution of any desired pll from 2 to 12 can be obtained. An example of this type of mixture is a system of citric acid, diethylbarbituric acid (veronal), boric acid and potassium dihydrogen phosphate this is virtually a system of seven acids whose exponents are given below. 

Utilize the general form of the acetic acid-acetate buffer capacity curve obtained in Problem 11 to draw an approximate curve for the buffer capacity over the range of pH from 2 to 13 of the universal buffer mixture described on page 415. It may be assumed that the total concentration of each acid and its salt is always 0.2 molar. 

BRI/ROB] Britton, H. T. S., Robinson, R. A., The use of the antimony-antimonious oxide electrode in the determination of the concentration of hydrogen ions and in potentiometric titrations. The Prideaux-Ward universal buffer mixture, J. Chem. Soc., (1931), 458-473, Contains report of measurements by W. L. German. Cited on page 141. 

Replacement of the barbitone component of Britton and Robinson s (1931) universal buffer mixture with Tris gives buffers suitable for pH control in ultraviolet spectroscopy down to 230 nm (Davies, 1959). Details are summarized in Table 3.9. Dimethylglutarate buffers (pH 3—7) have been proposed for spectrophotometric enzyme studies (Stafford et al., 1955). Succinate buffers (below pH 6.1) and glycyl-glycine and glycine buffers (above pH 7.3) were used in the enzymic determination of purine nucleotides around 250— 290 nm (Kalckar, 1947). 

Buffer action 46 Buffer capacity 48 Buffer mixture universal, (T) 831 Buffer solutions 46, (T) 831 acetic acid-sodium acetate, 49 for EDTA titrations, 329 preparation of IUPAC standards, 569 Bumping of solutions 101 Buoyancy of air in weighing 77 Burette 84, 257 piston, 87 reader, 85 weight, 86... 

Fig. 3.3 Solubility profiles of sparingly soluble drugs, based on data taken from Avdeef et al. [20]. The solutions consisted of robotically adjusted universal buffers, based on a mixture of Good buffers (see text), and contained 0.2 M KCl. The dashed lines were calculated by the Henderson-Hasselbalch equation and, as can be seen, did not accurately describe the solubility profiles. The solid curves were...

The final fixative class that is becoming more significant is the combination fixative. These often combine alcohol with formalin, calcium or other heavy metals, and also with some kind of buffering mixture. Many are commercial, and as such their exact formulations are typically not disclosed by their manufacturers. Most are designed to address the search for a universal fixative that can standardize this element of IHC. To be truly universal, most of these fixatives also address RNA and DNA fixation, for genetic studies in fixed tissue (3, 4, 5). 

We have seen from Fig. 3.9 that the buffer capacity is at a maximum at a pH equal to the pK of the weak acid used in the formulation of the buffer system and decreases appreciably as the pH extends more than one unit either side of this value. If, instead of a single weak monobasic acid, a suitable mixture of poly-basic and monobasic acids is used, it is possible to produce a buffer which is effective over a wide pH range. Such solutions are referred to as universal buffers. A typical example is a mixture of citric acid (pJC i = 3.06, pK,2 = 4.78, pK,3 = 5.40), Na HPO (pK, of conjugate acid H2PO4 = 7.2), diethylbarbituric acid (pKji = 7.43) and boric acid (pK i = 9.24). Because of the wide range of pK, values involved, each associated with a maximum buffer capacity, this buffer is effective over a correspondingly wide pH range (pH 2.4-12). 

A solution of a weak acid and its salt (conjugate base) or a weak base and its conjugate acid acts as a buffer solution. The quantities of buffer components required to prepare buffers solutions of known pH can be calculated from the Henderson-Hasselbalch equation. The buffering capacity of a buffer solution is maximum at the pK of the weak acid component of the buffer. Universal buffers are mixtures of polybasic and monobasic acids that are effective over a wide range of pH. 

For routine work commercially available mixtures are useful. These contain several components and the addition of specified amovmts of a strong base is all that is required for the preparation of the buffer solution. Among these is Britton-Robinson buffer (Table 1), which contains acetic, phosphoric, and boric acids. Universal buffers for spectrophotometry may contain such components as chloroacetic, formic, acetic, phosphoric, succinic, citric, boric acids, tris(hydroxymethyl)aminomethane, and butylamine. These buffers are transparent at wavelengths at least down to 240 nm. 

If a buffer system has several successive pATg values which differ by about 2 pH units, approximately linear buffer capacity results. This property has been exploited in universal buffers having high buffer capacities over a wide pH range. Britton and Robinson (1931) used equimolar mixtures based on seven pK values of citric, phosphoric, boric and diethylbarbituric acids to cover the pH range 2.6—12, as listed in Tables 10.47 and 10.48 Coch Frugoni (1957) gave... 

DR. DAVID RORABACHER (Wayne State University) As Dr. Margerum has just pointed out, the increase in the number of experiments one needs expands dramatically as one encounters kinetic contributions from other species in the reaction mixture. We have recently encountered such a phenomenon in our laboratory which merits some comment within this context. This phenomenon involves an effect of so-called inert anions upon complex formation and dissociation kinetics which we find very disturbing. The implication of this phenomenon is that now, not only is it necessary to vary the concentration of the buffer along with the concentrations of reactants and products, but one must also vary the concentration of every other species in the system. 

A group of scientists from Peking University [44,45] proposed conducting CE-IA in a thermally reversible hydrogel added to the buffer as a replaceable packing material. Antibodies were immobilized in the gel and a mixture of tracer and analyte was injected. The presence of gel enhanced the peak shapes and resolution, whereas immobilized antibody suppressed dissociation during the CE run. The latter makes this assay a kind of a mixture between on-line and offline analysis modes. 

E. B. R. Prideaxjx and A. T. Ward have employed a mixture of several acids in order to obtain buffer solutions with a general applicability between pH s 2.0 and 12.0. The mixture used is 0.04 molar with respect to the following acids phosphoric, phenyl-acetic, and boric. The solution is neutralized with 0.2 N sodium hydroxide. The relatively small buffer action of such a universal solution decreases its general usefulness. 

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