Acid buffer

Another level of regulatory significance is the toxic characteristic leach procedure (TCLP) limit of a characteristic waste. A material which is a waste because of the TCLP is ha2ardous if a Hquor resulting from an 18-h leach in an acetic acid buffer exceeds 5 ppm (mg/L) lead in the leach Hquor. 

The hberated iodine is measured spectrometricaHy or titrated with Standard sodium thiosulfate solution (I2 +28203 — 2 1 VS Og following acidification with sulfuric acid buffers are sometimes employed. The method requires measurement of the total gas volume used in the procedure. The presence of other oxidants, such as H2O2 and NO, can interfere with the analysis. The analysis is also technique-sensitive, since it can be affected by a number of variables, including temperature, time, pH, iodide concentration, sampling techniques, etc (140). A detailed procedure is given in Reference 141. 

In paints, zinc oxide serves as a mildewstat and acid buffer as well as a pigment. The oxide also is a starting material for many zinc chemicals. The oxide supphes zinc in animal feeds and is a fertilizer supplement used in zinc-deficient soils. Its chemical action in cosmetics (qv) and dmgs is varied and complex but, based upon its fungicidal activity, it promotes wound healing. It is also essential in nutrition. Zinc oxide is used to prepare dental cements in combination with eugenol and phosphoric and poly(acrylic acid)s (48) (see Dental materials). 

In Eq. (6-35), A/Z is the molar heat of ionization of the buffer acid at the conditions (temperature, solvent composition) of the kinetic studies. It happens that for many commonly used acidic buffers this quantity is small. Hamed and Owen give A//2 = —0.09 kcal/mol for acetic acid at 25°C, for example. The very important buffer of dihydrogen phosphate-monohydrogen phosphate is controlled by pK2 of phosphoric acid at 25°C its heat of ionization is —0.82 kcal/mol. 

That the methyl group in the less substituted isomer of the enamine (20) is axial was borne out by the work of Johnson et al. (18) in the total synthesis of the glutarimide antibiotic //-dehydrocycloheximide (24). The acylation of the morpholine enamine of 2,4-dimethylcyclohexanone (25) with 3-glutarimidylacetylchloride (26), followed by the hydrolysis of the intermediate product (27) with an acid buffer, led to the desired product in 35 % yield. The formation of the product in a rather low yield could most probably be ascribed to the relatively low enamine-type aetivity exhibited by the tetrasubstituted isomer, which fails to undergo the acylation reaction, and also because in trisubstituted isomer one of the CHj groups is axial. Since the methyl groups in the product are trans to each other, the allylic methyl group in the less substituted isomer of the enamine should then be in the axial orientation. 

Thus, in an acid buffer such as borax-boric acid or Na2HP04-NaH2P04 (p. 521) ... 

Fig. 2.12 Potential-time curves on mild steel in sodium borate/hydrochloric acid buffer solutions, pH 7-60, oxygen-saturated solution (after Ashworth )...

The ratio iff the concentrations or amounts ofHB and B. Small variations in pH can be achieved by adjusting this ratio. To obtain a slightly more acidic buffer, add more weak acid, HB addition of more weak base, B, will make the buffer a bit more basic. 

Lactic acid buffer from, 385-386 characterization, 385,471 enantiomers, 601... 

In general, we may state that the buffering capacity is maintained for mixtures within the range 1 acid 10 salt and 10 acid l salt and the approximate pH range of a weak acid buffer is ... 

The monoethanolamine-hydrochloric acid buffer has a buffering capacity equal to the ammonia-ammonium chloride buffer commonly employed for the titration of calcium and magnesium with EDTA and solochrome black (compare Section 10.54). The buffer has excellent keeping qualities, sharp end points are obtainable, and the strong ammonia solution is completely eliminated. 

Reagents. In view of the sensitivity of the method, the reagents employed for preparing the ground solutions must be very pure, and the water used should be re-distilled in an all-glass, or better, an all-silica apparatus the traces of organic material sometimes encountered in demineralised water (Section 3.17) make such water unsuitable for this technique unless it is distilled. The common supporting electrolytes include potassium chloride, sodium acetate-acetic acid buffer solutions, ammonia-ammonium chloride buffer solutions, hydrochloric acid and potassium nitrate. 

Hydroxylammonium chloride. 10 per cent aqueous solution, or benzene-1,4-diol (quinol), 1 per cent solution in an acetic acid buffer of pH ca 4.5 (mix 65 mL of 0.1M acetic acid and 35 mL of 0.1M sodium acetate solution). Prepare when required. 

Both HMR and MR have strong absorption peaks in the visible portion of the spectrum the colour change interval from pH 4 to pH 6 can be conveniently obtained with a sodium acetate-acetic acid buffer system. 

Sodium acetate-acetic acid buffer. Prepare a solution which is 0.2 M in sodium acetate and 0.8 M in acetic acid. The pH is 4.0. 

Sodium acetate-hydrochloric acid buffer. Add 1M hydrochloric acid to 350mL of 1M sodium acetate until the pH of the mixture is 2.2 (pH meter). 

Erythorbic acid is available as a 98+% Food Chemical Codex product (as per Pfizer sodium erythorbate FCC, although as Pfizer is now a pharmaceuticals company, much of the world s erythorbate is now supplied from China and other Asian countries) and in many diluted or blended forms, such as Nalco Sur-Gard . The ONDEO Nalco material is typical of products used within the industry, being based on erythorbic acid buffered with amine. A 1% solution of the product has a pH level of 6.3. 

Testing is undertaken by several methods, including chloroform extraction and use of a sulfonphthalein dye (absorbance of yellow-colored complex using bromophenol blue and bromocresol green) or the use of eosin (sodium tetrabromofluorescein) solution in acetone and tetrachloroethane solvent. After shaking with a citric acid buffer and eosin addition, upon standing the lower layer turns pink if filmer is present. Subsequent titration with Manoxol OT (sodium dioctyl sulfosuccinate) quantifies the filmer, with loss of the pink color indicating the end point. 

The ionization of alkyl (E)-arylazo ethers is subject to general acid catalysis when the reaction is carried out in the presence of carboxylic acid buffers (see Scheme 6-3), and the ionization is also subject to steric acceleration in the presence of bulky substituents ortho to the azo ether group (Broxton and Stray, 1980 Broxton and McLeish, 1983 a, and earlier work of Broxton s group). 

The Henderson-Hasselbalch Equation Describes the Behavior of Weak Acids Buffers... 

Whole cell OPH activity was measured by following the increase in absorbancy of p-nitrophenol from the hydrolysis of substrate (0.1 mM Paraoxon) at 400 nm (sm = 17,000 M cm ). Samples of culture (1 ml) were centrifuged at 10,000 g and 4 C for 5 min. The cells were washed, resuspended with distilled water, and 100 pi was added to an assay mixture containing 400 pi 250 mM CHES [2-(N-cyclohexylamino)ethane-sulfonic acid] buffer, pH 9.0, 100 pi 1 mM Paraoxon, and 400 pi distilled water. One unit of OPH activity was defined as pmoles Paraoxon hydrolyzed per min. Each value and error bar represents the mean of two independent experiments and its standard deviation. 

C18-0004. An acidic buffer solution can be prepared from phosphoric acid and dihydrogen phosphate. What is the pH of solution prepared by mixing 23.5 g NaH2 PO4 and 15.0 mL concentrated phosphoric acid (14.7 M) in enough water to give 1.25 L of solution ... 

Fig ure 3. Starch gel electrophoresis of hemoglobins. Tris-EDTA-boric acid buffer, pH 9.0. O-Dianisidine stain. 

The presence of Individual chains In a hemoglobin variant can also be demonstrated by electrophoresis at alkaline pH after the protein has been dissociated Into Its subunits through exposure to 6 M urea In the presence of 3-mercaptoethanol. The buffer is either a barbital buffer or a tris-EDTA-boric acid buffer, pH 8.0 - 8.6, and contains 6 M urea and 3-niercapto-ethanol. Dissociation of the hemoglobin Into subunits Is best accomplished In a mixture of 1 ml 10 g% Hb (or whole hemolysate), 4 ml 6 M urea barbital or tris-EDTA-boric acid buffer, and 1 to 1.5 ml 3-mercaptoethanol. After 30 minutes to 1 hour the sample Is subjected to cellulose acetate or starch gel electrophoresis. Each chain has a specific mobility and an alteration In electrophoretic mobility easily Identifies the abnormal chain. 

The soluble tryptic peptides of 130 mg a chain of Hb-St. Claude were separated on 0.9 x 60 cm columns of Chromobead resin type P (Technlcon Instruments, Dowex 50-X4) at 37°C using the procedure described earlier (16). The method uses a gradient of volatile pyrldlne-acetlc acid buffers of differing molarities and pH as follows first gradient, 666 ml 0.1 M, pH 3.1, and 333 ml 1.0 M, pH 5.0 and second gradient, 166 wl 1.0 M, pH 5.0, and 332 ml 2.0 M, pH 5.0. The amino acid composition of Isolated fragments was determined with a Splnco model 121 automated amino acid analyzer (Beckman Instruments)... 

The pectin/sucrose gels were characterized as follows (amounts per lOOg gel) 0.3 g AUA, 65% soluble solid substance, 0.01 mol sodium acetate / lactic acid buffer, pH 3.0 (20°C). The metal ions were added as combinations of chlorides according to a mixture design with constant amount of chloride ions (2.5 mmol / lOOg gel). Thus the total amount of metal ions... 

The PG activity was measured [10] by detecting the increase of reducing groups during the depolymerisation of 1 % (w/v) polygalacturonic acid buffered solutions, by a colorimetric method based on the 3,5-dinitrosalicylic acid. 

Pal, B., Sen, P.K. and Sen Gupta, K.K. (2001) Reactivity of alkanols and aryl alcohols towards tetrachloroaurate(lll) in sodium acetate-acetic acid buffer medium. Journal of Physical Organic Chemistry, 14, 284. 

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