PH buffer salts

Avdeef, A., Voloboy, D., Foreman, A. Dissolution-solubility of multiprotic drugs pH, buffer, salt, dual-solid, and aggregation effects. In ADME/Tox Approaches, Van de Waterbeemd, H ... 

Stewart and Tucker assert that hydrolysis is affected by pH, buffer salts, ionic strength, solvent, and other additives such as complexing agents, surfactants, and excipients, and each of these factors is discussed in some detail. Waterman et al. (31) provide a comprehensive treatment of hydrolysis as it relates to pharmaceuticals, with thorough discussions of mechanisms, formulation considerations, pH, ionic strength, buffers, solid-state considerations, hydrolysis of lyophiles, liquid dosage forms, packaging, etc. 

Make initial selection of mobile phase (pH, buffer, salt concentration) and method of delivery (isocratic or gradient elution). 

Degradation by hydrolysis is affected by a number of factors, of which solution pH, buffer salts and ionic strength are the most important. In addition, the presence of co-solvents, com-plexing agents and surfactant can also affect this type of degradation. 

The famous double helix, at the first glance, seems to be a comparably simple and rather uniform structure of a biopolymer. In fact however, not only may the double helix adopt several different conformations, the best known being the A-, B- and Z-types, but also single-stranded oligonucleotides, depending on their sequence and derivatization and conditions such as humidity, ion strength, counter ion charge, pH, buffer salts, solvent and last but not least temperature, display numerous types of polymorphism, the study of which has become an important field of biophysical research. 

The particular advantages of solution scattering for structural studies can be enumerated as follows (a) if the macromolecule is not crystallisable, structural parameters can nonetheless be obtained (b) structures are studied in the solution state, which is more relevant to physiological conditions than the crystal state or in vacuo (c) conformational changes (including denaturation and associative-dissociative processes) can be studied as a fimction of concentration, ligand, pH, buffer, salt... 

Sodium ions buffering the ionic strength and/or added as counterions of pH buffer salts compete with the analyte cations. Ion-exchange with micelles ... 

Direct Titrations. The most convenient and simplest manner is the measured addition of a standard chelon solution to the sample solution (brought to the proper conditions of pH, buffer, etc.) until the metal ion is stoichiometrically chelated. Auxiliary complexing agents such as citrate, tartrate, or triethanolamine are added, if necessary, to prevent the precipitation of metal hydroxides or basic salts at the optimum pH for titration. Eor example, tartrate is added in the direct titration of lead. If a pH range of 9 to 10 is suitable, a buffer of ammonia and ammonium chloride is often added in relatively concentrated form, both to adjust the pH and to supply ammonia as an auxiliary complexing agent for those metal ions which form ammine complexes. A few metals, notably iron(III), bismuth, and thorium, are titrated in acid solution. 

Another modification of this process was reported in 1988 (84). In this process, a precondensate of THPC and urea, plus excess urea, are neutralized to a pH of about 5.7, and the buffer salt is added. The fabric is then given a standard pad-dry-cure process followed by oxidation and laundering. The principal advantage of this modification is a reduction in both formaldehyde vapors and phosphine-like odors released during processing (84). 

Uses. The principal use of monosodium phosphate is as a water-soluble soHd acid and pH buffer, primarily in acid-type cleaners. The double salt, NaH2P04 H PO, referred to as hemisodium orthophosphate or sodium hemiphosphate, is often generated in situ from monosodium phosphate and phosphoric acid in these types of formulations. Mixtures of mono- and disodium phosphates are used in textile processing, food manufacture, and other industries to control pH at 4—9. Monosodium phosphate is also used in boiler-water treatment, as a precipitant for polyvalent metal ions, and as an animal-feed supplement. 

In many patent orHterature descriptions, a stabilized chlorine dioxide solution or component is used or described. These stabilized chlorine dioxide solutions are in actuaHty a near neutral pH solution of sodium chlorite that may contain buffer salts or additives to obtain chlorite stabiHty in the pH 6—10 range. The uv spectra of these solutions is identical to that of sodium chlorite. These pH adjusted chlorite solutions can produce the active chlorine dioxide disinfectant from a number of possible organic or inorganic chemical and microbiological reactions that react, acidify, or catalyze the chlorite ion. 

In preparing any of the above for use in columns, the dry powder is evacuated, then mixed under reduced pressure with water or the appropriate buffer solution. Alternatively it is stirred gently with the solution until all air bubbles are removed. Because some of the wet powders change volumes reversibly with alteration of pH or ionic strength (see above), it is imperative to make allowances when packing columns (see above) in order to avoid overflowing of packing when the pH or salt concentrations are altered. 

In addition, buffer salts such as disodium hydrogen phosphate may be used to prevent the pH of the aqueous phase falling during polymerisation. Small amounts of an anti-foam agent may be employed to reduce frothing when discharging from the vessel at the end of the polymerisation process. 

The optimum pH for the luminescence reaction is about 7.8, and the luminescence intensity is strongly affected by the buffer salt used... 

The kinetics of decarboxylation of 4-aminosalicylic acid in some buffer solutions at 50 °C were studied. The first-order rate coefficients increased with increasing buffer concentration, though the pH and ionic strength were held constant (Table 217). This was not a salt effect since the rate change produced by substituting potassium chloride for the buffer salt was shown to be much smaller. It follows from the change in the first-order rate coefficients (kx) with... 

Buffers are necessary to adjust and maintain the pH. Buffering agents can be salts of a weak acid and a weak base. Examples are ammonium, potassium, sodium carbonates (caustic soda), bicarbonates, and hydrogen phosphates [1345]. Weak acids such as formic acid, fumaric acid, and sulfamic acid also are recommended. Common aqueous buffer ingredients are shown in Table 17-8. 

Buffer Salt Solvent Strength and Selectivity Solvent strength and selectivity are influenced by the nature of the counterion i.e., its value. A change in buffer salt may also change the mobile phase pH. 

In many drug solutions, it is necessary to use buffer salts in order to maintain the formulation at the optimum pH. These buffer salts can affect the rate of drug degradation in a number of ways. First, a primary salt effect results because of the effect salts have on the activity coefficient of the reactants. At relatively low ionic strengths, the rate constant, k, is related to the ionic strength, p, according to... 

Flocculating agents can be simple electrolytes that are capable of reducing the zeta potential of suspended charged particles. Examples include small concentrations (0.01-1%) of monovalent ions (e.g., sodium chloride, potassium chloride) and di- or trivalent ions (e.g., calcium salts, alums, sulfates, citrates or phosphates) [80-83], These salts are often used jointly in the formulations as pH buffers and flocculating agents. Controlled flocculation of suspensions can also be achieved by the addition of polymeric colloids or alteration of the pH of the preparation. 

Dissolve the amine-containing molecule to be thiolated at a concentration of lOmg/ml in cold (4°C) 1M sodium bicarbonate (reaction buffer). For proteins, dissolve them in deionized water at a pH of 7.0-7.5, at room temperature. Note The presence of some buffer salts, like phosphate or carbonate, is incompatible with silver nitrate. 

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