Buffer solution definition

The preparation of a buffer solution of a definite pH is a simple process once the acid (or base) of appropriate dissociation constant is found smhll variations in pH are obtained by variations in the ratios of the acid to the salt concentration. One example is given in Table 2.2. 

Water soluble protein with a relative molecular mass of ca. 32600, which particularly contains copper and zinc bound like chelate (ca. 4 gram atoms) and has superoxide-dismutase-activity. It is isolated from bovine liver or from hemolyzed, plasma free erythrocytes obtained from bovine blood. Purification by manyfold fractionated precipitation and solvolyse methods and definitive separation of the residual foreign proteins by denaturizing heating of the orgotein concentrate in buffer solution to ca. 65-70 C and gel filtration and/or dialysis. 

Cu9ln4 and Cu2Se. They performed electrodeposition potentiostatically at room temperature on Ti or Ni rotating disk electrodes from acidic, citrate-buffered solutions. It was shown that the formation of crystalline definite compounds is correlated with a slow surface process, which induced a plateau on the polarization curves. The use of citrate ions was found to shift the copper deposition potential in the negative direction, lower the plateau current, and slow down the interfacial reactions. 

For the designation of pH in non-aqueous solvents, we use the forms described by Bosch and coworkers6 based on the recommendations of the IUPAC, In Compendium of Analytical Nomenclature. Definitive Rules 1997, 3rd edn, Blackwell, Oxford, UK, 1998. If one calibrates the measuring electrode with aqueous buffers and then measures the pH of an aqueous buffer solution, the term "pH is used if the electrode is calibrated in water and the pH of the neat buffered methanol solution then measured, the term, pH is used, and if the electrode is calibrated in the same solvent and the pH reading is made, then the term pH is used. 

Figure 6.8 Voltammograms of marmatite electrode activated by Cu in 0.1 mol/L KNO3 borate buffer solution ofpH= 9.18 by holding 2 minutes at a definite potential (scanning rate 50 mV/s). (a) from cathode to anode (b) from anode to cathode...

Total fluorine in fluoride supplements and dental products could be determined with minimal samples pre-treatment as for example by direct acid extraction or heating in TISAB buffer solution and subsequent determination of fluoride using fluoride ISE for the reason that entire fluorine, in these products, should be, by definition, available as free inorganic fluoride. 

As cell solution for this example one uses, in two different experiments, the unknown solution (x) and a standard buffer solution (s), whose pH (pH ) has been estimated so as to approach the second definition. Comparing the e.m.f. s gives... 

The International Union of Pure and Applied Chemistry (IUPAC) recommendation [3] for the definition of pH scales has formed the basis for the standardisation of pH measurements since 1985. IUPAC recommended two different approaches to derive the pH values of pH standard buffer solutions. They yield two different pH values for one solution [4],... 

For practical pH measurements, more convenient secondary standard - buffer solutions (SS) are recommended. Their secondary pH(SS) values are obtained by comparison with primary buffers in recommended cells with transference and have thus slightly larger uncertainties than pH(PS). pH(SS) can be traced back, again with stated uncertainties, to pH(PS) values and consequently to the definition of pH. 

To summarize pH measurement consists of a hierarchical system of three metrologically defined steps (1) the definition of pH by primary pH(PS) values assigned to primary buffer solutions (PS) in a Harned cell defined as a primary method of measurement, (2) the assignment of pH(SS) to secondary buffer solutions (SS) by tracing them back to pH(PS), and (3) measurement of pH(X) of unknown solutions (X) by comparison with... 

The complex results observed during the reactions of AN" with phenol prompted a reinvestigation of the protonation of 9,10-diphenylanthracene radical anion (DPA ) under the same conditions (Parker, 1981J). Kinetic results summarized in Table 5 give a clear indication that this reaction is more complex than previously believed as well. In unbuffered solution, showed a definite dependence upon [DPA] indicative that Raib is greater than 1 and close to 2. In buffered solution the substrate concentration dependence was less pronounced and in the opposite direction. Similar results were obtained for the reactions of 9-phenylanthracene radical anion. 

If the acid is too weak to yield an appreciable amount of A ions when dissolved in pure water, e.g., p-nitrophenol, it is necessary to employ a modified procedure which is probably less accurate. A definite quantity of the acid being studied is added to excess of a buffer solution (see Chap. XI) of known pH the pll chosen should be close to the expected pXo of the acid, for under these conditions the resulting solution will contain approximately equal amounts of the undissociated acid HA and of A ions. The amount of either HA or A , whichever is the more convenient, is then determined by studying the absorption of light of... 

Determination of pH With Buffer Solutions.—If a series of buffer solutions of known pH, which must lie in the region of the pH to be determined, is available the estimation of the unknown pH is a relatively simple matter. It is first necessary to choose, by preliminary experiments, an indicator that exhibits a definite intermediate color in the solution under examination. The color produced is then compared with that given by the same amount of the indicator in the various solutions of known pH. In the absence of a salt error, to which reference will be made later, the pH of the unknown solution will be the same as that of the buffer solution in which the indicator exhibits the same color. Provided a sufficient number of solutions of known pH are available, this method can give results which are correct to about 0.05 pH unit. 

When colored solutions are being studied, allowance must be made for the superimposition of the color on to that of the indicator this may be done by means of the arrangement shown in plan in Fig. 97. The colored experimental solution, to which a definite amount of indicator has been added, is placed in the tube A and pure water is placed in B the tube C contains the test solution without indicator, and D contains the buffer solution of known pH together with the same amount of indicator as in A, The solution in D is varied until the color of C and D superimposed is the same as that of A and B superimposed. The pH of the solution in A is then the same as that in D,... 

Histochemical techniques for detecting substrate before and after enzyme treatment are extremely useful in studies on cellular structure. One of the oldest histochemical tests utilized saliva to identify suspected glycogen or starch. More definitive results are obtained when thin sections of a tissue are incubated in a buffered solution of purified amylase and stained for poly-utc-glycols. Material stained by periodic acid-Schiff reagent in the control, but not in the section exposed to amylase, is assumed to be glycogen or starch. Two more of the numerous histochemical techniques associated with localization of substrate are—using hya-luronidase to locate hyaluronic acid and chondroitin 4- and 6-sulfates (179) and using neuraminidases to locate sialomucins (180). By use of electron microscopy in combination with the histochemical technique subcellular localization can be obtained. 

The pH-solubility profiles are very similar to the pH-log D profiles however, it is more difficult to estimate the solubility of the charged form of molecules. The reason for this is that the counter-ions in the aqueous solutions influence the solubility of the charged species so while we can estimate the partition for the charged species into octanol, we cannot make definitive predictions or estimations of the solubility of the charged species in the presence of various counter-ions in the aqueous buffer solution. 

Eq. (27) represents the so-called practical definition of the pH scale.f Evidently, in practice the voltage differences expressed in Eqs. (26) and (27) are not measured inasmuch as the meters provide direct pH readings. Hence, instead of the E(S) values, the pH(S) values are adjusted directly on the intrument scale. In the preparation of standard buffer solutions (Table 2), it is essential to use high-purity materials and carbon dioxide-free freshly distilled water, the specific conductance of which should not exceed 2 pS/cm. 

The reproducibility of the effective mobility is governed by temperature and pH effects. An acceptable run-to-run pH reproducibility can usually be assured, at least in equipment where the effects of possible electrode reactions can be avoided. Again, temperature plays a leading role The effective mobility has a temperature coefficient of 2-3% per degree. Most buffer solutions, incidentally, have a temperature-dependent pH value, so that changing the temperature in the capillary will, for weak ions, even lead to changing degrees of dissociation and, hence, effective mobility. These effects are, by definition, different for different buffers and different sample components. 

By definition, a buffer solution resists changes in pH with dilution or with addition of acids or bases. Generally, buffer solutions are prepared from a conjugate acid/base pair, such as acetic acid/sodium acetate or ammonium chloride/ammonia. Chemists use buffers to maintain the pH of solutions at a relatively constant and predetermined level. You will find many references to buffers throughout this text. 

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