Commonly Used Buffers

Mix 14.95 ml glacial acetic acid or 261 ml 1M acetic acid with 7.875 g anhydrous sodium acetate or 96 ml 1M sodium acetate and fill up to 1000 ml. 

Dissolve 4.88 g barbital-sodium (Veronal, sodium diethylbar-biturate) and 3.23 g sodium acetate trihydrate in about 800 ml ddH20. Adjust pH to 8.6 with 0.1 N HCl (consumption about 30 ml), then fill up to 1000 ml. 

Dissolve 9.414 g citric acid and 18.155 g Na2HP04-2H20 in 900 ml ddH20, if necessary, correct pH by addition of diluted phosphoric acid or sodium hydroxide, then fill up to 1000 ml with ddH20. 

Alternatively, prepare the buffer by mixing 490 ml 0.1 M citric acid with 510 ml 0.2 M di-sodium hydrogenphosphate. 

---

In many cases, the analytical tasks are simply to detect and quantify a specific known analyte. Examples include the detection and quantification of commonly used buffer components (e.g., Tris, acetate, citrate, MES, propylene glycol, etc.). These simple tasks can readily be accomplished by using a standard one-dimensional NMR method. In other situations, the analytical tasks may involve identifying unknown compounds. This type of task usually requires homonuclear and heteronuclear two-dimensional NMR experiments, such as COSY, TOCSY, NOESY, HSQC, HMBC, etc. The identification of unknown molecules may also require additional information from other analytical methods, such as mass spectrometry, UV-Vis spectroscopy, and IR spectroscopy.14... 

Perhaps the most important parameter involved in aqueous-organic mixtures is their effective protonic activity (denoted by pH or pan). This parameter has been measured for most commonly used buffers in all selected mixtures down to their freezing point (Hui Bon Hoa and Douzou, 1975 Douzou ei al., 1976). Values of pH depend on solvent and temperature in a way that varies for different buffers, but with the data available a medium of known pH under any desired condition may be prepared. An example of the effect of solvent and temperature is provided by Tris-HCl buffer a solution of this at pH 8.0 in water at 20 C will be pH 10.5 in 50% (v/v) ethanediol at -40 C (Douzou et al, 1976). On the other hand, neutral buffers such as phosphate undergo... 

Ideally, other components in the reaction mixture should not absorb significantly at the monitored wavelength. In addition, colored impurities should be removed. For example, commercial imidazole, a commonly used buffer, contains a yellow impurity that can be easily removed upon recrystallization from ethyl acetate. 

Some commonly used buffers, such as sodium and potassium phosphate, are incompatible with ELSD, but there are ready alternatives. For example, ammonium acetate has similar buffering properties to potassium phosphate, and ammonium carbonate, ammonium formate, pyridinium acetate, and pyridinium formate are options for different pH ranges. Typical mobile phase modifiers that do not meet the volatility criteria can be replaced by a wide variety of more volatile alternates. For example, phosphoric acid, commonly used as an acid modifier fo control pH and ionization, can be replaced by trifluoroacetic acid other acids that are sufficiently volatile for use with FLSD include, acetic, carbonic, and formic acids. Triethylamine, commonly used as a base modifier, is compatible with FLSD other base modifiers that can be used are ethylamine, methylamine, and ammonium hydroxide [78]. 

Complexes with Acetate and Other Common Brensted Bases Many reactions of copper tend to be conducted in the range of pH 4.0-5.5 to avoid possible formation of hydroxycopper species. This is a range in which acetate is the most commonly used buffer. Unfortunately, acetate (Ac ) is a very poor choice as it forms stronger complexes with Cu(II) than with any other divalent metal ion except Hg(II). The stepwise equihhrium constants for the formation of Cu(Ac)+, Cu(Ac)2, Cu(Ac)3, and Cu(Ac)4 are 50, 10, 2.5, and 0.6, respectively [176]. 

Table 2. Commonly used buffers for cation-exchange chromatography...

Standard research-grade agarose is usually sufficient, but special agaroses may be used for specific applications (e.g. high-resolution gels). The electrophoresis buffer is usually prepared and stored as a 10 x concentrated stock. The most commonly used buffer is Tris-borate-EDTA (TBE), or alternatively, one may use Tris-acetate-EDTA (TAE) buffer ... 

Table 2 Commonly Used Buffering Agents and Their pA, Values...

Temperature Effects The pH of a buffer solution is influenced by temperature. This effect is due to a temperature-dependent change of the dissociation constant (pK ) of ions in solution. The pH of the commonly used buffer Tris is greatly affected by temperature changes, with a ApKa/C° of —0.031. This means that a pH 7.0 Tris buffer made up at 4°C would have a pH of 5.95 at 37°C. The best way to avoid this problem is to prepare the buffer solution at the temperature at which it will be used and to standardize the electrode with buffers at the same temperature as the solution you wish to measure. 

Nucleic acids catalyze many different types of reactions. Some RNA-catalyzed transformations show stereoselectivity [10,34]. The potential scope of organic reactions is quite broad, with a commensurate variability in reaction conditions. The essential components present in successful nucleic acid-catalyzed reactions are divalent metal ions such as Mg2+, Ca2+, Cu2+, Zn2+, as well as K+ [7,10,21,35,36]. A buffer is also required but should not contain functional groups that are reactive under the reaction conditions. A commonly used buffer is HEPES (2-[4-(2-hydroxyethyl)-l-piperazine]ethanesulfonic acid). These essential components are present to maintain the RNA s tertiary structure and prevent its aggregation. Because these reactions are carried out in aqueous solution, the addition of a co-solvent (e. g., DM SO or EtOH) may be necessary, depending on the solubility of the substrates. 

Note that in calculating this result we have set the equilibrium concentrations, (0.10 - x) and (0.10 + x), equal to the initial concentrations, 0.10, because x is negligible compared with the initial concentrations. For commonly used buffer solutions, Ka is small and the initial concentrations are relatively large. As a result, x is generally negligible compared with the initial concentrations, and we can use initial concentrations in the calculations. 

Resolution is optimized by adjusting the buffer pH and the amount of organic modifiers. The most commonly used buffers are perchlorate, acetate, and phosphate. The protocol of the selection and optimization of the mobile phase for the enantiomeric resolution of drugs on polysaccharide-based CSPs in reversed-phase mode is presented in Scheme 2. Table 4 correlates the effects of separation conditions for neutral, acidic, and basic drugs on polysaccharide-based CSPs. From Table 4, it may be concluded that a simple mixture of water and an organic modifier will produce chiral separation of a neutral molecule because there is no... 

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. 

TABLE 4-3. Commonly Used Buffers for Reversed-Phase HPLC... 

Table 4-3 in Chapter 4 lists some commonly used buffers for reversed-phase HPLC. In this table the buffers and their respective p/C values, and UV cutoffs are listed. Since it is becoming more common to find HPLC interfaced to mass spectrometers, volatile buffers for LC/MS applications are also indicated. 

Phosphate buffers Phosphate is one of the most commonly used buffers, because its pH range is very useful (pH 6.0-7.5) and phosphates are cheap, very soluble and chemically stable. However, phosphate is able to chelate Ca2+, and to a lesser extent Mg2+. Additionally, phosphate is toxic to mammalian cells, it inhibits many enzymes, and, at high concentration, it has an appredable UV absorbance. 

Fig. 7.4 Useful pH ranges of some commonly used buffers.

Table 1 Approximate pATa for commonly used buffers for parenteral administration...

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... 

Buffers are inherent constituents of all media formulations and can maintain the medium pH within an acceptable range. The most commonly used buffer is sodium bicarbonate and CO2, which is usually provided in air at 5%. Dissolved CO2 reacts with water to form carbonic acid, which dissociates into the bicarbonate ion [Eq. (1)] ... 

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. 

---