Universal buffers

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. 

Concentration Control. Sequestration, solubilization, and buffering depend on the concentration control feature of chelation. Traces of metal ions are almost universally present in Hquid systems, often arising from the materials of the handling equipment if not introduced by the process materials. Despite very low concentrations, some trace metals produce undesirable effects such as coloration or instabiHty. 

In turbulent flow, the velocity profile is much more blunt, with most of the velocity gradient being in a region near the wall, described by a universal velocity profile. It is characterized by a viscous sublayer, a turbulent core, and a buffer zone in between. 

Beynon, R. J., and Easterby, J. S., 1996. Buffer Solutions The Basics. New York IRL Press Oxford University Press. 

Apparent partition coefficient (logZ)) at an ionic strength of / = 0.02M, log P value of the neutral microspecies and the acidic dissociation constant of 5 was calculated (97ANC4143). The distribution coefficient of 5 was determined between 1-octanol and universal buffer in the pH range 3-10 at a... 

In view of this, the properties of / films were examined after they had been subjected to increasing amounts of ion exchange . In order to do this, detached films were exposed at 65°C for 7 h to a universal buffer adjusted to a suitable pH and the resistance of the film measured at 25°C in 3 n and O OOlN potassium chloride. The results obtained with a pentaerythritol alkyd are shown in Fig. 14.4 from which it can be seen that as the pH of the conditioning solution increased, the resistance of the film fell, until at a pH of about 7.5 it suddenly dropped. The resistance of the film then followed that of the solution in which it was immersed, i.e. it became a D-type film. Similar results were obtained with films of a tung oil phenolic varnish, although in this case the change-over point occurred at a higher pH, i.e. about 9. 

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

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. 9.7 Bioluminescence of Panellus stipticus fruiting body (1) fluorescence of PM-2 in the presence of CTAB upon excitation at 440 nm (2) chemiluminescence of PM-2 in the presence of CTAB (3) chemiluminescence of PM-2 in the presence of 3-(dodecyldimethylammonio)propanesulfonate (SB3-12) (4) and chemiluminescence of the hot-water treatment product of PM-1 in the presence of SB3-12 (5). Curves 2-5 were measured in 2 ml of 50 mM Tris-HCl buffer (pH 8.0) containing 0.18 mM EDTA. Chemiluminescence was elicited by the addition of 5 p.1 of 50 mM FeSC>4 and 10 xl of 10% H2O2. From Shimomura, 1991b, with permission from Oxford University Press.

In the Taylor-Prandtl modification of the theory of heat transfer to a turbulent fluid, it was assumed that the heat passed directly from the turbulent fluid to the laminar sublayer and the existence of the buffer layer was neglected. It was therefore possible to apply the simple theory for the boundary layer in order to calculate the heat transfer. In most cases, the results so obtained are sufficiently accurate, but errors become significant when the relations are used to calculate heat transfer to liquids of high viscosities. A more accurate expression can be obtained if the temperature difference across the buffer layer is taken into account. The exact conditions in the buffer layer are difficult to define and any mathematical treatment of the problem involves a number of assumptions. However, the conditions close to the surface over which fluid is flowing can be calculated approximately using the universal velocity profile,(10)... 

In the Universal Velocity Profile , the laminar sub-iayer extends to values of y+ = 5 and the turbulent zone starts at y+ = 30 and the range 5 < y+ < 30, the buffer layer, is covered by a second linear relation between and In, y+. What is the maximum difference between the values of u+, in the range 5 < y4 < 30, using the two methods of representation of the velocity profile ... 

Avdeef and Bucher [24] investigated the use of universal buffers in potentiomet-ric titrations. Recently, such a buffer system, formulated with several of the Good components, has been designed specifically for robotic applications, where automated pH control in 96-well microtiter plates is required, with minimal interference to the UV measurement [48]. This universal buffer has a nearly perfectly linear pH response to additions of standard titrant in the pH 3-10 region [8, 48]. 

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...

Avdeef, A., Budier,).). Accurate measurements of the concentration of hydrogen ions with a glass electrode calibrations using the Prideaux and other universal buffer solutions and a... 

Apparently similar flowstream universal buffers have been developed by Alibrandi and others [128,129] for assessing kinetic parameters, such as the pH-dependent hydrolysis of acetylsalicylic acid. The pH-time curves are not as linear as in the SGA system. Other reports of continuous flow pH gradient spectrophotometric data have been described, with application to rank-deficient resolution of solution species, where the number of components detected by rank analysis is lower than the real number of components of the system [130]. The linear pH-time gradient was established in the flowstream containing 25 mM H3PO4 by the continuous addition of 100 mM Na3P04. 

CE determination of pKa is new, compared to the other techniques [144—147]. It has the advantage of being a rather universal method since different detection systems can be coupled to CE. Because it is a separation technique, sample impurities seldom are a problem. A fused-silica capillary, with an inner diameter of 50-75 pm and 27-70 cm in length is filled with a dilute aqueous buffer solution (ionic strength... 

A known quantity of sample is added to a known volume of a universal buffer solution of sufficient capacity and of known pH. The amount of sample must be sufficient to cause precipitation to occur in the formed saturated solution. After waiting for a period of time to allow the saturated solution to reach the desired steady state, the solution is filtered to remove the solid and obtain a clear solution, whose spectrum is then taken by the UV spectrophotometer. Mathematical treatment of the spectral data yields the area-under-the-curve of the filtered sample solution, AUQ. 

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. 

Pasek and Lauretta (University of Arizona, Tucson) point to a further important source of phosphate they studied the corrosion of phosphide minerals from iron meteorites under various conditions in aqueous solution, e.g., using NaHCCb as a buffer, or in solutions containing MgCh and CaCL, as well as in the presence of ethanol and acetic acid. 

Artemchenko et al. [25] used a spectrophotometric method with p-quinone chlor-imide in isopropanol in a pH 8 universal buffer for the determination of primaquine. 

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