Showing papers on "Buffer solution published in 1972"

Tris/Tris·HCl: A Standard Buffer for Use in the Physiologic pH Range

Abstract: A buffer solution containing tris(hydroxymethyl)-aminomethane (0.01667 mol/kg) and its hydrochloride salt (0.0500 mol/kg) is proposed as a pH standard for the physiologically important pH range of 7.3 to 7.5. Standard pH values were assigned to this reference solution at temperatures from 0° to 50°C by means of measurements with hydrogen/silver chloride cells without transference. At 37°C, the assigned pH of this buffer solution is 7.382, with a temperature coefficient of -0.026 pH unit per degree Celsius. This new standard is more compatible with biologic fluids than is the previously certified phosphate buffer.

Differential assays of folic acid in animal tissues

Abstract: Publisher Summary This chapter explains the evolution of folate assay procedures and use of combined criteria for differential assays of folates. The conjugase concept arose from ensuing experimentation in which various animal tissues were incubated with yeast extracts containing polyglutamate conjugates of folic acid but no endogenous enzyme to split them. In a study described in the chapter, a small amount of homogenized animal tissue incubated with a large amount of yeast extract led to a great increase in activity toward the folate assay organisms. A small sample of an extract of the tissue under study was adsorbed on the column from a buffer solution containing ascorbate. A standard amount of this same buffer was placed above the adsorbent and to this was added dropwise a phosphate–ascorbate buffer, pH 7.0, so as to gradually build up the phosphate content of the effluent as it ran through.

The determination of ammonia in boiler feed-water with an ammonium-selective glass electrode

Abstract: An investigation has been made into the accuracy of ammonium-selective (ammonium-responsive) glass electrodes for determining ammonia (10 to 1000 µg 1–1) in boiler feed-water and similar high-purity water samples from power stations. The electrode potential follows the Nernst equation in samples containing up to 10 000 mg 1–1 of ammonia, the pH of which is controlled between 8·0 and 8·4 by the addition of triethanolamine-hydrochloric acid buffer solution. However, interfering species in the buffer solution cause a detectable deviation from Nernstian response at low ammonia concentrations (less than 1000 µg 1–1). By use of a calomel-0·1 N hydrochloric acid reference electrode, reproducible results have been obtained in static buffered solutions containing 10 to 1000 µg 1–1 of ammonia. Of the other impurities likely to be present in power-station waters only sodium caused a serious effect (100 µg 1–1 of sodium is equivalent to 25 µg 1–1 of ammonia). The within-batch standard deviations of analytical results were 2, 7, 17 and 33 µg 1–1 at concentrations of 10, 100, 500 and 1000 µg 1–1 of ammonia, respectively. Details of a recommended analytical procedure for discrete samples are given, and the application of the ammonium-selective electrode to continuous on-stream analysis is briefly discussed.

The Rapid Analysis of Fluorine in Glass by the Use of Fluoride Ion Sensitive Electrode

Abstract: A rapid analysis for the direct determination of fluorine in glass using the Corning fluoride specific electrode without a prior separation of interfering ions is given. Among many buffer solutions, a 1M sodium citrate buffer solution was recommended for the analysis of fluorine in glass samples. Strong complexes of interfering ions such as Si6+, B3+, Al3+ with fluoride could be destroyed by an addition of the buffer solution to release the bound fluoride.Procedure: About 0.05∼0.4g of ground glass samples were accurately weighed into a platinum crucible. The sample was mixed with a 1.0g of sodium carbonate and fused. Distilled water was added and warmed on a steam bath to dissolve. The pH of the solution was adjusted to 6.0 using HCl solution and it was made up to 100ml. To ensure that the ionic strength and pH of the solution remained constant, 10ml of sample solution were mixed with 10ml of the buffer solution. The electrode were placed into the solution and the fluoride ion activity was measured. The concentration of fluorine ion was determined from the calibration curve obtained previously and the percentage of fluorine in the glass sample was calculated.The results of the proposed method were compared with the results obtained by the pyrohydrolysis-Th(NO3)4 titration method; these two results were in good agreement.The standard deviation of determination was about 0.009% for the fluorine 1.0% level.The time required for analysisis 20min.

Determination of Small Amounts of Monoguanylmelamine in Acetoguanamine by Cation Exchange Separation and Ultraviolet Spectrophotometry

Abstract: An ion-exchange chromatographic technique for the separation of small amounts of monoguanylmelamine in acetoguanamine by means of a stepwise elution from a 0.8 φ X 20 cm column of a strong-acid cation exchange resin, Dowex 50 WX4, in the sodium form is studied. As the eluant, Sφrensen's buffer solution consisting of glycine, sodium hydroxide and sodium chloride is used. An aqueous solution containing 100 mg of the sample is passed through the column. At first, acetoguanamine and its impurities are eluted with pH 9.9 buffer solution. The elution is continued until the absorption of the effluent at 255 nm is not appear. About 250 ml of the eluant is necessary for this. Then, monoguanylmelamine is eluted with pH 11.1-41.5 buffer solution as shown in Fig.3.150-250 ml of the effluent containing monoguanylmelamine is taken and adjusted to a certain volume by adding the buffer solution. The absorbance of the solution is measured at 255 nm. By this method, monoguanylmelamine in acetoguanamine can be determined down to 0.05%. This method is not interfered by the presence of diguanylmelamine, melamine, acetoguanamide, acetoguanide, cyanomelamine, ammeline and dicyandiamine which are present as impurities in the sample.

複核錯体[(CN)5FeII(CN)CoIII(CN)5]6-の光化学反応

Abstract: Photochemistry of, u-cyano-pentacyanoferrate Epentacyanocobaltate(111) ion, (CN), Fe(CN) Co(CN), re, has been studied in aqueous solutions using monochromatic light(313 nm, 366 nm, 435 nm) This complex ion has absorption maxima at 260 x 1O2- cm' (r =540) and at 310x IV cm' (e =830) The photochemical reaction proceeded only in aqueous acidic solutionsWith irradiation the absorption maxima of the complex ion shifted to longer wavelength and showed isosbestic point at 300O2- cm-1 in acetic acid-sodium acetate buffer solution (pH 40) Cyanide ion was detected in the solution and the concentration incerased with increasing irradiation time It was conchided from these facts that the primary reaction of the photochemical reaction was the release of CN- from the complex ionIn order to determine whether the cyanide ion was released from Fe(11) or from Co(E), the complex ion which had labeled CN-, (CN)5Fe(CN)Co(Cl5N)57-, was used The released cyanide ion was analyzed by a mass spectrometer and was found to be almost pure Ci4N at the conversion rate of 15, 30 or 50%So the primary reaction of the photochemical reaction was expressed as follows:[(CN)5Fe(CN)Co(CN)5]6- + H20 -0 (CN)4(H20)Fe(CN)Co(CN)05- CN- (5)In the case of the photochemical reaction in aircontaining solutions the primary reaction was followed by the secondary reaction That is, the colour of the solution changed from yellow to green and then to blue, and finally a blue precipitate was produced When an alkali was successively added to the solution, the precipitate disappeared, giving a precipitate of Fe(111) hydroxide This behavior is quite similar to the photochemical reaction of hexacyanoferrate (11), which supported the reaction scheme (5)Quantum yields of the primary reaction in a buffer solution (pH 40) were obtained from the determination of CN- Quantum yields obtained were dependent on irradiating wavelength, that is, 064 at 313 nm, 020 at 366 nm and 020 at 435 nm, and were independent of the reaction temperatureProduction of hydrated electron was not detected by the dissociation reaction of N20 Possible mechanisms of the photochemical reaction were discussed with relation to photochemical reaction of the mono-nuclear complex ion

Características de algumas soluções tampão utilizadas para avaliar a acidez do solo

Abstract: Buffer capacity or index was determined for SMP, - Woodruff, Woodruff (1 + 1), (1+2) and (1 + 3), 1,00 N, 0,50 N and 0,25 N calcium acetate solutions The data obtained showed that SMP solution presented a constant value for buffer capacity when 010 - 015 - 020 - 025 - 030 - 035 - 040 - 045 and 050 milliequivalents of HCl pointing out that the pH of all solutions decreased linearly water The equations were calculated by the method or least squares for the relationship between buffer solution pH and added amount of HCl pointing out that the pH of all solutions decrease linearly with respect to the quantity of HCl added

Binding of small molecules to lipoamide dehydrogenase

Abstract: The existence of a monomer-dimer equilibrium with lipoamide dehydrogenase is demonstrated. The equilibrium can be shifted to the monomer side at low ionic strength and low pH by removing the phosphate ions by extensive dialysis. At low ionic strength, I : 0.01 and 0.02, the enzyme precipitates while aggregation takes place. This aggregation seems to be due to changes in the activity coefficient of the enzyme. High phosphate concentrations, NADI and high temperatures favor association. Also bringing the enzyme in a more polar environment causes dissociation. Dioxan and 2-chloroethanol are used to decrease the dielectric constant of the buffer solution. Inactivation and dissociation of the enzyme is time- dependent in these solutions. High concentrations of dioxan and 2-chloroethanol cause denaturation and precipitation of the enzyme. High phosphate concentrations stimulate the denaturation and precipitation of the enzyme in dioxan and 2-chloroethanol.Dissociation of the enzyme is accompanied by loss in activity and decrease in apparent α-helix content. ORD and CD data show this decrease, however the possibility that this decrease is due to changes in shape and size of the protein molecule cannot be excluded. Fluorescence and CD experiments show that upon dissociation an amino acid, a tryptophan residue, moves to a more polar environment. Also by treating the enzyme with dioxan a tryptophan residue is pertubed.Dissociation of the enzyme can also be achieved by treating the enzyme with sodium dodecylsulfate. Hydrophobic and ionic interactions are observed. Binding to the hydrophobic sites, by sodium dodecylsulfate or Tween 80, has no influence on the lipoate activity and on absorption spectrum of the enzyme in the visible- region. Binding to the ionic sites causes loss in lipoate activity and affects the absorption spectrum. From the dependency on the pH and the ionic strength it is concluded that a group of the kind BH + = B + H + with a pK value around 6.6 is involved. At high SDS concentrations the binding of FAD to the enzyme is weakened and upon standing for long times the flavin dissociated off.Dimerization of the enzyme is favored by NAD + . Binding of NAD + to the enzyme yields a difference spectrum. From these spectral titration curves two pairs of NAD + -binding sites are calculated, the binding site with the highest affinity, K diss = 35 μM is assigned to the regulatory site while the binding site with K diss = 90-110 μM is assigned to the catalytic site. Upon NAD + binding to the regulatory site one proton per FAD is liberated. Comparision of the pH activity curves with computer models shows that the activating effect of NAD + in the lipoate activity can be explained by a shift in pK value of a group from pH 6.4-6.3 to 5.0-4.9 upon NAD + binding. Together with observations in the literature these results suggest that the pK value of a SH-group is shifted to lower pH upon NAD + binding. This SH-group is suggested to be functional in the S - state in the active center.

Specific solvation of carbanions of nitro compounds as the cause of their anomalous nucleophilicity in water

Abstract: 1. The kinetics of the reversible addition of the methyl ester ofα-nitropropionic acid (MNP) to acetaldehyde in dimethyl sulfoxide (DMSO) under the action of the components of a triethylammonium buffer solution were studied. 2. The equilibrium constant of the addition of MNP to acetaldehyde in DMSO was determined, and the value previously obtained for this constant in water was refined. 3. The rate constant of the nucleophilic addition of the carbanion of nitropropionic ester to acetaldehyde, catalyzed by the triethylammonium ion, was found. 4. The anomalous nature of the relationship of the basicity and nucleophilicity of the carbanions of the nitro compounds with respect to carbon, observed in water, is a consequence of solvation effects.