Anion buffers

An example of an anion buffer that may be suitable for standardizing an ion-selective electrode is based on the greater insolubility of silver iodide than silver chloride (Havas et al., 1971). This iodide ion buffer comprises a solution containing a high concentration of free chloride ion to which is added a small amount of silver ion and a smaller amount of iodide ion. The chloride ion activity determines the activity of silver ion (because of the solubility product of AgCl) and, in turn, the activity of silver ion determines the activity of the iodide ion in the buffer solution. For chloride ion concentrations of IM, O.lM, and O.OlM, pi is approximately 5.85, 6.85 and 7.85, respectively. 

Similarly, a pBr buffer should be formed by adding silver and bromide ions to a high concentration of chromate ion. 

For a chromate concentration of iM, O.lM and 0.01 M, pBr is approximately 6.4, 6.9 and 7.4, respectively. If iodate is used instead of chromate, pBr values become 4.8, 5.8 and 6.8. A pCr04 buffer might be obtained from a sulphate solution by adding lead and chromate ions. Sulphate concentrations of IM, O.lM and 0.0IM give pCr04 equal to 4.8, 5.8 and 6.8, respectively. 

Tanaka (1963) coined the term ligand buffers for systems containing a ligand and an excess of metal ion. He pointed out that where a stable 1 1 chelate is formed, pL is determined only by the ratio of the total metal ion and total ligand concentrations and is independent of pH. The relation is 

Although ligands are commonly anions, the treatment is a general one and applies equally to neutral ligands such as triethylenetetramine or tris(aminoethyl)amine. 

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Indeed, the equation is consistent with the observed experimental results, except in the case of [OH-]. They explained the discrepancy by the fact that the concentration of OH- is regulated by formate anion buffer via reaction with CO, thereby maintaining the overall water-gas shift reaction rate to be essentially independent of base. 

Deprotonation of the pyridinium ion (59) at positions to the heteroatom has been studied using neutral and anionic buffer bases in D2O. No catalysis other than by the deuteroxide ion was observed and once... 

In both of the above examples, we used an anionic buffer (MOPS or cacodylate). The buffer anions have only repulsive interactions with RNA and can be grouped with chloride ions when calculating mean ion activities. Thus, we apply mean ionic activity coefficients measured with KC1 solutions to solutions in which K+ ions are contributed both by KC1 and K-buffer salts. We strongly advise against the use of cationic buffers such as Tris, because of its idiosyncratic interactions with nucleic acids as compared to group I ions, and particularly against mixing KC1 with Tris buffer, which creates a cationic mixture of unknown activity. 

Over the last several decades, the decline in alkalinity in many streams in Europe and in northeastern USA as a result of acid deposition has been a subject of much concern (Likens et al., 1979). The concentration of bicarbonate, the major anion buffering the water chemistry of surface waters and the main component of dissolved inorganic carbon (DIC) in most stream waters, is a measure of the reactivity of the watersheds and reflects the neutralization of carbonic and other acids by reactions with silicate and carbonate minerals encountered by the acidic waters during their residence in watersheds (Garrels and Mackenzie, 1971). Under favorable conditions, carbon isotopes of DIC can be valuable tools by which to understand the biogeochemical reactions controlling carbonate alkalinity in groundwater and watersheds (MUls, 1988 Kendall et al., 1992 see Chapter 5.14). 

Alternatively, the delivery of the buffer ion can be largely eliminated by using cationic buffers in the cathode reservoir and anionic buffers in the anode reservoir, so that the buffer ion moves away from the skin when an electric field is applied. In addition to common weak acids such as citric and phosphoric, the use of amino acids in the anode formulation has been suggested. Amino acids such as cysteine and histidine would be incorporated at neutral or basic pH, where they are predominately anionic. ° ... 

For proteins, the variations of pKapp induced by cooling are very small in the acidic region (Tanford and Wagner, 1954). Moreover, the enthalpy of ionization is also practically zero for anionic buffers (Hui Bon Hoa and Douzou, 1973b). 

Use cationic buffers (Tris-HCI, piperazine-HC104, etc.) with anion resins and anionic buffers (phosphate, acetate, etc.) with cation exchange resins. 

The principle of this technique can be explained on the following example. Let us assume that there are three anions (A, B, C) sandwiched between anode and cathode. In the front, three zones will be formed after introducing the current, namely A, (A, B) and (A, B, C). Also at the other end there will be three zones, namely C, (B, C) and (A, B, C) (Fig. 6.9). The boundaries between the individual zones are determined by the concentration and effective mobilities of the sample constituents, the choice of the anodic and cathodic buffer and to a considerably lesser extent by viscosity, the nature of the solvent and temperature. The boundaries seen in both sides of the separation can be either zone or isotachophoretic boundaries. Thus, e.g., if the anion buffer has a lower electrophoretic mobility than the most... 

The dopant ion required for polymer conductivity is one of the most important components of a CP. Its structure, number of available balancing charges and interaction with the polymer backbone are key to the overall performance of the material. In biomedical applicaEons the dopant also needs to be nontoxic or restrained by the polymer matrix. A number of dopant types have been invesEgated for use in biomedical applicaEons, including small anions, polymeric anions, buffer salts, and biologically active anions. Table 18.1 summarizes various dopant types and solvents that have been reported in the... 

Wojciechowski K, Wroblewski W, Brzozka Z (2003) Anion buffering in the internal electrolyte resulting in extended durability of phosphate-selective electrodes. Anal Chem 75 3270-3273... 

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