Sorensen buffer

The standard reaction mixture contained 0.20 mL of the enzyme source, 0.25 mL of NADPH (2.5 mg/mL), and 2.30 mL of Sorensen buffer (pH 7.4). The reaction was started by adding 0.05 mL of 5 bromouracil (0.9 mg/mL). At intervals, 50 /xL portions of the assay mixture were mixed with 150 /xL of 6% trichloroacetic acid. After centrifugation, the supemate was shaken with 200 /xL of 0.5 M trioctylamine solution in Freon and centrifuged again. Subsequently, 25 /xL of the upper phase was injected. When weak enzymatic activities were being measured, the volume of the reaction mixture was reduced to 1.0 mL. 

For bromthymol blue, J. T. Saunders finds, by comparison with Sorensen buffers, a salt error of — 0.19 when the medium is 0.6 N with respect to NaCl. The error becomes + 0.20 at a total electrolyte concentration of 0.003 N. The errors which Saunders finds for thymol blue, phenol red, cresol red, bromthymol blue, and bromcresol purple in salt concentrations below 0.1 N are in accord with the measurements of the author (cf. above pages 340 to 342). 

Mobile phase MeOH Sorensen buffer (67 mM KH2PO4) 15 85... 

This double spot formation is not observed on silica gel or alumina layers. The sensitivity to oxidation of the adrenaline derivatives is, however, increased by the metal or heavy metal impurities present in such layers. Adrenaline and noradrenaline have therefore been chromatographed on buffered silica gel layers (Sorensen buffer, pH 6.8), prepared with addition of sodium bisulphite and using 10% ethanol as solvent [163]. The sympathomimetics and the secondary products formed by oxidation tend moreover to form complex salts this manifests itself in elongated spots. Silica gel layers which had been prepared with O.IM EDTA have been used with the solvent acetone-formic acid-water (70 + 10 + 20) for the separation of adrenaline, noradrenaline and various substances of similar structure [110] silica gel HR (Krm 88) ought to be especially advisable for this purpose. On the other hand, Halmekoski [74] has made use of this very ability of the adrenaline-type of sympathomimetic to form complexes, in order to accomplish fractionation on buffered layers containing molybdate, tungstate or borax components... 

A. Potassium dihydrogen phosphate buffer (Sorensen buffer, pH 4.6, 0.067 M)... 

Sorensen s buffered solutions were adjusted by the mixture of 0.1 M NaCl, 0.1 M glycine, and 0.1 M NaOH solutions. Amount of Na+ transported was about zero in the all range... 

In 1909 Sorensen introduced the concept of pH, defined as pH = - log [H+]. He established a pH scale however, at a later date this scale was shown to be incorrect with respect to either - log [H+] or - log aH+, because it was simply based on the degree of dissociation according to conductivity measurements. The relation pHa = psH + 0.04 between the activity and the Sorensen scales appears to be a useful approximation for buffer solutions15. 

The determination of GSSGR activity is based upon Eq. (8) and can be followed spectrophotometrically by the decrease of NADPH2 absorbance at 340 or 366 mp. For the above-mentioned reasons phosphate buffer may be preferred. The typical reaction mixture contains in a final volume of 3.0 ml (H20) 1.6 to 2,4 ml phosphate buffer as described by Sorensen (0.076 M, pH 6.5) 0.2 ml NADPH2 (0.4 [junole per test volume) 0.2 ml GSSG solution (1.5 X 10 3M and equilibrated to pH 6.3-6.4 with NaOH) and 0.2-0.8 ml of serum. The blank contains water instead of substrate solution. Readings are taken at 340 or 366 mp at room temperature at one-minute intervals, the light path being 1.0 cm. The decrease in absorbance should not exceed 0.03 per minute. 

Figure 14. Effects of a group of clonidine derivatives on blood pressure in spinal rats and on heart rate in vagotomized rats. The distribution coefficient was measured with 0.1 m Sorensen phosphate buffer at a pH of 7.4.

Sorensen is usually considered to be the first to have realized the importance of hydrogen ion concentration in cells and in the solutions in which the properties of cell components were to be studied. He is also credited with the introduction of the pH scale. Electrochemistry started at the end of the nineteenth century. By 1909, Sorensen had introduced a series of dyes whose color changes were related to the pH of the solution, which was determined by the H+ electrode. The dyes were salts of weak acids or weak bases. He also devised simple methods for preparing phosphate buffer solutions covering the pH range 6-8. Eventually buffers and indicators were provided covering virtually the whole pH range. 

L. J. Henderson was a physician who wrote [H ] = /C0[acid]/[salt] in a physiology article in 1908, a year before the word buffer" and the concept of pH were invented by the biochemist S. R L Sorensen. Henderson s contribution was the approximation of setting [acid] equal to the concentration of HA placed in solution and [salt] equal to the concentration of A placed in solution. In 1916. K. A. Hasselbalch wrote what we call the Henderson-Hasselbalch equation in a biochemical journal.8... 

Electrochemical detection Potentiostat (ADInstruments, NZ) Ag/ AgCl reference electrode (BAS, USA) Pt wire auxiliary electrode (in-house) water jacketed cell for temperature control (Massey University, NZ) overhead stirrer (in-house) A/D converter (MacLab, ADInstruments, NZ) software (Chart, ADInstruments, NZ) Sorensen s buffer, pH 7.4 [2] butyryl thiocholine iodide (B-3128, Sigma). 

Prepare a stock solution of 100 mM BTCI in Sorensen s buffer, pH 7.4. 

Set up a controlled temperature cell at 37°C with a SPCE working electrode that has previously been exposed to standard or wool extracts, an Ag/AgCl reference electrode and a Pt wire auxiliary electrode in 10 ml Sorensen s buffer. 

Measure the background current of the SPCE in stirred Sorensen s buffer, pH 7.4, then add 25 pi BTCI stock to make the concentration in the cell 0.25 mM and measure the electrode response. The background current should be subtracted from the BTCI current for calculations. 

Preparation of browning product mixtures Xylose (15 g) and glycine (7.5 g) were dissolved in Sorensen s phosphate buffer (ji) (1/151 1 pH 8.2, 100 ml) and heated under reflux for 2 h. On 250-fold dilution with water, the absorbance at 450 nm was 0.75 i 0.05. The preparation was also carried out in the absence of buffer, initial pH 6.0. Larger amounts were prepared on 5 and 10 times this scale. 

Some kinetic data found in literature are referred to the conventional (Sorensen) pH scale [7] or, in a few cases, to the paH scale [7] (paH = —log aH). Application of the conventional pH scale is certainly useful in kinetic experiments which are done for practical purposes (such as stability studies of drugs in solution). Matters are different, however, if it is intended to determine well defined values of the catalytic coefficients fcH or ft oh As mentioned above, the pcH scale is most recommendable for an evaluation of the rate equation from experimental data — particularly if the dependence of the rate on [H+] is complicated. Only if the pcH scale is used, ftH and fcoH values (referred to concentrations) determined with dilute solutions of strong acids or strong bases will be identical with those measured in buffer solutions at the same ionic strength. ... 

This cell closely resembles the original Sorensen cell, with a glass electrode substituted for the hydrogen electrode. Since glass electrodes are subject to an unpredictable asymmetry potential, pH measurements are made in practice by substituting a standard buffer for the sample solution and then comparing the pH of the sample with the pH of the standard, pH, according to the equation... 

The degree and extent of precipitation will depend on the ability of a formulation to resist pH change when diluted. The pH change on dilution of one solution by another will depend on the initial pHs and buffer capacities of both solutions. Surakitbanharn et al. illustrated the affect of initial pH and phosphate buffer concentration on pH change when diluted with Sorensen s Phosphate Buffer. Myrdal et al. used the computational model of Surakitbanharn et al. as a means of selecting buffer concentration and initial pH to eliminate the precipitation potential of a weakly basic drug, levemopamil-HCl. Myrdal et al. showed that the unbuffered formulation precipitated upon dilution and resulted in phlebitis in vivo. 

Sorensen s glycine buffer 0.1 M glycine, 0.1 MNaCl adjusted to pH 10.5 with 1 M NaOH. 

Dopa, dopamine, and tyrosine have been the most common substrates in the preparation of synthetic eumelanins. In a typical experiment the enzyme (15 ml of solution of 30 mg of enzyme in 100 ml Sorensen s buffer, pH 7) and L-dopa (150 mg) in pH 7 buffer (500 ml) are kept with access to air for 2 weeks (755) stirring, bubbling air through the mixture, and raising the temperature up to 38°C accelerate the process. Melanin is separated by filtration, fractional sedimentation, or, more efficiently, by centrifuging (500 to 100,000 g), especially after acidification (pH < 3.5) (see Section IV) (251). Samples are further purified by repeated resuspension and centrifugation or dialysis (252). 

Sorensen citrate buffer (cf. page 249), citric acid and ... 

Sorensen citrate buffer, mono- and disodium citrate 18° 4.45... 

Although the SOrensen value is erroneous, it appears preferable, at least for the time being, to retain it because the pH of most buffer solutions described in the literature is calculated by Sorensen s equations. All Sorensen values will be readily convertible into poH, once the constant difference between pH (Sorensen) and paH has been established. At present, such a recalculation would merely add to the confusion already encountered, for various authors do not agree upon the value of this difference between pH (Sorensen) and paH. 

The buffer solutions of Clark and Lubs (biphthalate buffers) have an ionic strength of about 0.05-0.06, while the citrate mixtures of Sorensen have an ionic strength of 0.2. 

---