Commonly Used Buffering Systems

For CMP related application, it is sometimes important to use a pH buffered system. Tables 21.8 and 21.9 show some of the commonly used buffering systems and their useful ranges. 

The interaction between aequorin and a chelator must be carefully considered when estimating Ca2+ concentrations with aequorin in a calcium buffer containing EDTA or EGTA. This is particularly crucial when using a common calcium buffer system that contains a constant total concentration of a chelator in the buffer solutions of various Ca2+ concentrations in such a buffer system, a buffer of lower Ca2+ concentration contains a higher concentration of the free form of the chelator, resulting in an increased inhibition. 

The use of buffers and pH adjustment is an important consideration in lens care products. It is a general practice that all products which are likely to come in direct contact with ocular tissues should be buffered for ocular comfort around physiologic pH and preferably in the range 6-8.0. The most commonly used buffers in contact lens care products are phosphates and borates. Buffers used occasionally are acetate, citrate, and others. Besides buffers, sodium hydroxide and hydrochloric acid are generally used to achieve a desirable pH in the final product. They are also used to adjust the final pH in products, which do not have any buffering system. The selection of an appropriate buffering system should consider the pH necessary for optimal performance of the product, as well as products... 

The solid-state and solution chemistry of triethanolamine complexes has been investigated. While the solid-state structure was maintained in organic solvent (38), a different structure was observed in aqueous solution.262 170 NMR spectroscopy was used to demonstrate that the two oxo groups were different and in combination with H and 13C NMR data, defined the structure as (39).262 Speciation studies and a detailed characterization of this class of compounds were important because the ligand is a commonly used buffer in biology and the complexes are model systems for interactions with proteins.61,263 The thermodynamic parameters were determined for several derivatized diethanolamine ligand-vanadium(V) complexes, and represent some of the few vanadium complexes for which such parameters are known.62 The structure of (nitrilotriacetato)dioxovanadate was reinvestigated.2 4... 

Experimental limitations of the absorption models include poor solubility of the drug candidate in the aqueous buffers used, non-specific binding, and the lack of physiological relevance of the commonly used buffers. To guarantee high-throughput, the solvent systems used should also not add challenges to the analysis of the samples. 

The buffer is used to carry the majority of the current, and it should be selected so that its components are significantly different from the analytes, and detection by difference is easier. Osmotic flow modifiers (OSM) are electrolyte additives that control the flow of buffer through the capillary. 0.5 mM concentrations are common. Some buffer systems that have been used are 10 mM mannitol, 0.05 M pH 7 phosphate, and a borate/gluconate mixture. 

Some titration curves have a long region of relatively flat slope. The addition of reagent in this portion of the titration cun e has little effect on the pH. Tliis flatness of the curve can be due to buffering, which occurs for mixtures of a weak acid or a weak base and its salt. It is also important for keeping solutions used for calibration at a known pH despite contamination from residue on the electrode. Some of the more commonly encountered buffer systems are acetic acid-acetate, carbonic acid-bicarbonates, and citric acid-citrates. 

The sensitivity of the equilibrium constant to temperature, therefore, depends upon the enthalpy change AH . This is usually not a serious limitation, because most reaction enthalpies are sufficiently large and because we commonly require that the perturbation be a small one so that the linearization condition is valid. If AH is so small that the T-jump is ineffective, it may be possible to make use of an auxiliary reaction in the following way Suppose the reaction under study is an acid-base reaction with a small AH . We can add a buffer system having a large AH and apply the T-jump to the combined system. The T-jump will alter the Ka of the buffer reaction, resulting in a pH jump. The pH jump then acts as the forcing function on the reaction of interest. 

While earlier papers cited buffer systems or aqueous o-phosphoric acid to achieve satisfactory peak resolution, most recent investigations involved acetic acid or formic acid systems. " Representative examples are 0.2% and 1% HCOOH for betacyanins and betaxanthins, respectively, the latter requiring a lower pH for chromatographic resolution. Methanol or acetonitrile are most commonly used as modifiers, either undiluted or diluted with purified water at ratios of 60 40 or 80 20 (v/v), respectively. - Typical HPLC fingerprints for yellow and red beet juice are shown in Figure 6.4.1. 

Buffer systems for parenterals consist of either a weak base and the salt of a weak base or a weak acid and the salt of a weak acid. Buffer systems commonly used for injectable products are acetates, citrates, and phosphates (see Table 2). Amino acids are being increasingly used as buffers, especially for polypeptide injectables. 

The most common buffering system containing a weak base together with its salt formed with a strong acid is ammonia with ammonium sulphate. Some useful buffers are obtained from combinations of unrelated acids or bases with salts. The following combinations find occasional use in textile coloration processes, but the acetates and orthophosphates are most frequently used ... 

Commonly used cells use Pt/C>2 or Pt/air as reference electrodes. At very low partial pressures of oxygen, care must be taken to avoid direct permeation of oxygen through stabilized zirconia from the air (or reference electrode) [74, 75]. The effect may be avoided by applying reference electrodes with activity near that observed at the working electrode. A well-defined buffer system like a metal-metal... 

The separation can be done in vertical or horizontal apparatus in rods or slabs. Because of the ease of use, horizontal slab electrophoresis systems are most commonly used in which the whole gel is submerged in buffer (Figure 13.8). 

While Franz-type diffusion cells are commonly used to assess in vitro penetration of compounds across the skin, they have also been used for the assessment of compound permeability across the buccal mucosa [19, 71, 104], In this system, buccal mucosa is sandwiched between two chambers, and compound solution is added to the donor chamber with compound-free buffer in the receptor chamber. The receptor chamber is then periodically sampled to assess the amount of compound that has permeated the tissue over time. 

For CE—MS, volatile buffers are common. To use MEKC systems combined with mass detection, volatile micelles have been tested.When using atmosferic pressure photo-inonization (APPI), non-volatile BGE constituents do not deteriorate the mass signal to... 

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