Buffer mixture

Before leaving the subject of buffer solutions, it is necessary to draw attention to a possible erroneous deduction from equation (21), namely that the hydrogen-ion concentration of a buffer solution is dependent only upon the ratio of the concentrations of acid and salt and upon Ka, and not upon the actual concentrations otherwise expressed, that the pH of such a buffer mixture should not change upon dilution with water. This is approximately although not strictly true. In deducing equation (18), concentrations have been substituted for activities, a step which is not entirely justifiable except in dilute solutions. The exact expression controlling buffer action is ... 

Table 2.2 pH of acetic acid-sodium acetate buffer mixtures... 

Buffer mixtures are not confined to mixtures of monoprotic acids or monoacid bases and their salts. We may employ a mixture of salts of a polyprotic acid, e.g. NaH2P04 and Na2HP04. The salt NaH2P04 is completely dissociated ... 

This colour change can be observed with the ions of Mg, Mn, Zn, Cd, Hg, Pb, Cu, Al, Fe, Ti, Co, Ni, and the Pt metals. To maintain the pH constant (ca 10) a buffer mixture is added, and most of the above metals must be kept in solution with the aid of a weak complexing reagent such as ammonia or tartrate. The cations of Cu, Co, Ni, Al, Fe(III), Ti(IV), and certain of the Pt metals form such stable indicator complexes that the dyestuff can no longer be liberated by adding EDTA direct titration of these ions using solochrome black as indicator is therefore impracticable, and the metallic ions are said to block the indicator. However, with Cu, Co, Ni, and Al a back-titration can be carried out, for the rate of reaction of their EDTA complexes with the indicator is extremely slow and it is possible to titrate the excess of EDTA with standard zinc or magnesium ion solution. 

This is the basis of the indicator action in the EDTA titration. The pH of 10 is attained by the use of an aqueous ammonia-ammonium chloride buffer mixture. 

The following table covering the pH range 2.6-12.0 (18°C) is included as an example of a universal buffer mixture. 

Buffer action 46 Buffer capacity 48 Buffer mixture universal, (T) 831 Buffer solutions 46, (T) 831 acetic acid-sodium acetate, 49 for EDTA titrations, 329 preparation of IUPAC standards, 569 Bumping of solutions 101 Buoyancy of air in weighing 77 Burette 84, 257 piston, 87 reader, 85 weight, 86... 

Antonenko et al. [540] considered pH gradients forming in the UWL under bulk solution iso-pH conditions. They elegantly expanded on the buffer effect model and made it more general by considering multicomponent buffer mixtures. Direct measurements of the pH gradients (using wire-coated micro-pH electrodes) near the membrane-water interface were described. 

A 10 mM ionic strength universal buffer mixture, consisting of Good zwitterio-nic buffers, [174] and other components (but free of phosphate and boric acid), is used in the pION apparatus [116,556], The 5-pKa mixture produces a linear response to the addition of base titrant in the pH 3-10 interval, as indicated in Fig. 7.53. The robotic system uses the universal buffer solution for all applications, automatically adjusting the pH with the addition of a standardized KOH solution. The robotic system uses a built-in titrator to standardize the pH mapping operation. 

For practical purposes, a number of buffer mixtures have been proposed that are useful for various pH ranges. Procedures for their preparation and requirements on purity and definition of the chemicals used are given in laboratory manuals and tables. 

DPDPB is insoluble in aqueous solutions and should be initially dissolved in an organic solvent prior to addition of a small aliquot to a buffered reaction medium. Preparation of a stock solution in DMSO at a concentration of 25 mM DPDPB works well. The addition of an aliquot of this stock solution to the conjugation reaction should not result in more than about 10 percent organic solvent by volume in the buffered mixture or protein precipitation may occur. 

Since hematin inhibits Taq polymerase, it is absolutely essential to eliminate red blood cell contamination. Selective lysis of red blood cells can be accomplished with a buffer mixture consisting of 155 mM ammonium chloride, 10 mM potassium bicarbonate, and 0.1 mM EDTA adjusted to pH 7.4. Alternatively, the cytoplasmic membrane of all cells can be dissolved with a buffer mixture containing the non-ionic detergent Triton-X 100, leaving behind nuclei of white blood cells from which DNA can be extracted. However, this technique will result in the loss of cytoplasmic DNA to the supernatant, and hence will not be able to extract mitochondrial DNA (B11). 

Czamieki and Breslow (22) have studied the rate of acyl transfer from a substrate that is bound by the acyl part rather than by the leaving group. Having shown that ferrocene binds strongly to -cyclodextrin, Czamiecki and Breslow employed the p-nitrophenyl ester of ferrocinnamic acid in kinetic studies using DMSO-buffer mixtures. A rate acceleration of 51,000 times background was observed for acylation of /i-cyclodextrin. 

Polymers of 4(5)-vinylimidazole and copolymers containing this monomer are usually studied with ethanol-buffer mixtures as solvent because of their insolubility in water. Overberger and Smith (82) found that poly(l-Me-5-vinylimidazole) was soluble in water. Negatively charged substrates with long apolar side chains were bound very strongly to this polymer. A rate enhancement of 106 over the monomeric analog, 1,5-dimethylimidazole, was observed. 

A few common volative buffer mixtures, along with their respective pH range are pyridine-formic acid (2.3-3.5) trimethylamine-formic acid (or acetic acid) (3.0-6.0) triethanolamine-HCl (6.8-8.8) ammonia-formic acid (or acetic acid) (7.0-10.0). See Buffers... 

Add 5 pi of2-mercaptoethanol to 95 pi of SDS sample buffer stock solution to give a sample buffer mixture. (SDS may precipitate at room temperature. Warm up the SDS sample buffer stock solution before use) (see Note 8). 

Add the protein sample to the sample buffer mixture at 4 1 volume ratio. Heat the samples at 95°C for 10 min. The samples are now ready for SDS-PAGE. 

Acetonitrile shows in mixtnres with water, a better solnbility for salts. It is therefore recommended in ion-pair chromatography [52], Basic analytes also show better peak shapes in acetonitrile-buffer mixtures than with methanol. The proper selection, whether acetonitrile or methanol, should be used as the organic component in the mixtnre with a bnffer, however, the type of RP column used classical RP or a shielded RP column is also important. For demonstration with basic analytes, a standard mixture of anti depressives is used. Iso-eluotropic mixtures of methanol and acetonitrile are used. For standardization, the concentration of buffer components are also be kept constant. The analyte structures and the eluent mixtures are summarized in Table 2.2. As selectivity is worse in acidic eluents, a pH value of 7 has been used. Two phases... 

Predict the order of elution from first to last of the following morphinane compounds from an ODS column in an acetonitrile/buffer mixture pH 8.0 (10 90). Assume the ptCa values of the bases are all similar (Fig. 12.27)... 

On heating wood meal with a mixture of dioxane and phosphate buffer for 48 h at 150°C, 24% of the lignin dissolved, as shown in Figure 8. Most of this lignin is hydrophobic and eluted in the retention time range GO-GO minutes (Curve B). However, when the wood residue obtained after heating wood meal with phosphate buffer was heated with the dioxane-phosphate buffer mixture, only moderate further delignification was obtained (Curve C). 

Cells and organisms maintain a specific and constant cytosolic pH, keeping biomolecules in their optimal ionic state, usually near pH 7. In multicellular organisms, the pH of extracellular fluids is also tightly regulated. Constancy of pH is achieved primarily by biological buffers mixtures of weak acids and their conjugate bases. 

Payens, T. A. J. 1961. Zone electrophoresis of casein in urea-buffer mixtures. Biochim. Biophys. Acta 46, 441-451. 

Wood, J. Chem. Soc., 1908, 93, 411. This value agrees with that of Hughes (ibid., 1928, p. 491), who obtained i1=6xl0"10 from pH measurements of half-neutralised buffer mixtures. 

Kitada et al. (5,41) used a rapid method for TBZ and BP in citrus fruits. The crops were extracted with ethyl acetate and separated on a reverse-phase C8 column with UV and fluorometric detection, respectively. Methanol phosphate buffer mixture at a flow rate of 1.0 ml/min gave satisfactory results as the mobile phase. Recoveries of postharvest residue were greater than 93%. Carbendazim and thiophanate-methyl were determined in chicory, beans, lettuce, strawberries, and tomatoes (5,42). After extraction with methanol, the extract was cleaned up on a Sep-Pak C g cartridge. The rapid method gives recoveries of between 90 and 100%. 

Experiments were performed with mixtures of very low oxygen content. By analogy with the method of creation and maintenance of small concentrations of hydrogen ions in buffer mixtures and in electrochemistry, we used mixtures with a fuel surplus in which the small concentration of oxygen was determined by a mobile dissociation equilibrium 2H20 v= 2H20 + 02. The experiments showed with certainty the validity of the new expression for the reaction rate which follows from the chain mechanism. 

Prepare three nitrate standards at concentrations 1, 10, and 50 mg/L. To 10 mL of each standard in 40 mL beakers, add 10 mL buffer solution, respectively. Immerse the tip of the electrode in the solution while stirring. Record the stable millivolt reading for each standard. Prepare a calibration curve plotting N03-N concentrations in the abscissa and millivolts in the ordinate. The plot should be a straight line with a slope of 57 3 mV/decade at 25°C. After this, rinse and dry the electrode immerse in the sample-buffer mixture and record the stable potential reading. Determine the concentration of N03-N in the sample from the calibration curve. 

Buffer Mixtures Commonly Used for Polyacrylamide Gel Electrophoresis Proteins for Internal Standardization of Polyacrylamide Gel Electrophoresis Chromogenic Stains for Gels Fluorescent Stains for Gels... 

Buffer Mixtures Commonly Used for Polyacrylamide Gel Electrophoresis... 

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