Clark and Lubs buffers

Four reagents are required for performance of this reaction. The first is a 0.1% ethanolic solution ofp-nitroso-A/iA -dimethylaniline. The second is pH 9.8 Clark and Lubs buffer, prepared by adding 40.8 mL of 0.2 M sodium hydroxide (carbon dioxide-free) to 50 mL of a 0.2M aqueous solution of both boric acid and potassium chloride. The third reagent is a 0.1% solution of phenol in ethanol, and the fourth reagent is a freshly prepared 1% aqueous solution of potassium ferricyanide. 

Millicoulometry is employed in Clarks and Lubs buffer of pH 2.00 to find out number of electrons in the electrode process. The results show that the number of electrons involved in the electrode process is four. The product of controlled potential electrolysis (carried out at -l.OV vs. SCE) in Clarks and Lubs buffer of pH 2.00 is identified as hydroxylamine. The number of protons involved in the rate determining step is evaluated as one from E1/2 vs. pH and Ep vs. pH plots. The electrochemical reaction order is shown to be one from log i vs. log C plots at constant E. 

CITR CL citrate Clark and Lubs (xxxx) (molecular weight) UB universal buffer... 

These solutions include the pH range from 1.0 to 10.0 (Fig. 14). Clark and Lubs have arranged their mixtures to cover the range from 2.0 to 10.0 in jumps of 0.2 unit of pH. Their buffers were prepared from the following solutions ... 

The mixtures of Clark and Lubs are very easy to prepare. The starting materials are readily obtained in the pure state, and the arrangement of solutions at pH intervals of 0.2 unit is very convenient. The biphthalate-hydrochloric acid buffers, however, have two disadvantages which detract somewhat from its usefulness. 

The buffer mixtures of Clark and Lubs are described in the following table. All data refer to 20° C. 

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. 

Many other buffers have been developed for various purposes. Generally, these alternate compositions are less stable or accurate than the primary buffers described the the National Bureau of Standards. They are often employed when special conditions must be met or when the buffer is more compatible with the sample. Some of these buffers are described in Section 4.4. One scheme of buffer compositions which cover the pH range 1-10 has been developed by Clark and Lubs. These are described in Table A.3 and, generally, with others listed in the Handbook of Biochemistry [5]. 

Green (1970) made further studies on the effect of pH on directly isolated algae of Xanthoria aureola. He used the buffer devised by Clark and Lubs (1916) rather than the citrate-phosphate buffers (Mcllvaine, 1921) which had been shown to affect the pattern of carbohydrate fixation. Green found that at any of the pH levels he used, very little fixed was released as sucrose in... 

Hiratsuka et al102 used water-soluble tetrasulfonated Co and Ni phthalocyanines (M-TSP) as homogeneous catalysts for C02 reduction to formic acid at an amalgamated platinum electrode. The current-potential and capacitance-potential curves showed that the reduction potential of C02 was reduced by ca. 0.2 to 0.4 V at 1 mA/cm2 in Clark-Lubs buffer solutions in the presence of catalysts compared to catalyst-free solutions. The authors suggested that a two-step mechanism for C02 reduction in which a C02-M-TSP complex was formed at ca. —0.8 V versus SCE, the first reduction wave of M-TSP, and then the reduction of C02-M-TSP took place at ca. -1.2 V versus SCE, the second reduction wave. Recently, metal phthalocyanines deposited on carbon electrodes have been used127 for electroreduction of C02 in aqueous solutions. The catalytic activity of the catalysts depended on the central metal ions and the relative order Co2+ > Ni2+ Fe2+ = Cu2+ > Cr3+, Sn2+ was obtained. On electrolysis at a potential between -1.2 and -1.4V (versus SCE), formic acid was the product with a current efficiency of ca. 60% in solutions of pH greater than 5, while at lower pH... 

Clark, W. M., and Lubs, H. A. Hydrogen electrode potentials of phthalate, phosphate and borate buffer mixtures. Jour. Biol. Chem., 26, 1916, 479. 

The following table of protein corrections is due to W. M. CiiAEK and H. A. Lubs. They made their comparisons with Clark buffers. 

Dissolve the sample in 25 ml. of a Clark Lubs pH 9 3 buffer and make up to 50 ml. Cool the solution so that the temperature is below 10°C, deoxygenate and after addition of 0-5 ml. of a 0-5 per cent solution of gelatin, titrate with 0-025 m p-diazobenzene sulphonic acid at —0-4 V. 

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