Citric acid buffer mixture

To prepare the citric acid buffer, sodium hydroxide (NaOH) (16 g) is dissolved in a minimum amount of distilled water in a beaker, cooled, transferred to a 1 1 volumetric flask, and about 900 ml water is added. Citric acid (42 g) is dissolved in this solution, the pH adjusted to 5.0 first with 10 M abd then 1 M NaOH, and the volume adjusted to 1 1 with water. The mixture is then transferred to a reagent bottle and is stored at 5°C in the dark. Ethanol water is prepared by mixing 1 1 water and 1 1 95% ethanol in a 2.5 1 brown glass bottle. 

Biomimetic conversion of ferulic acid derivatives to phenylcoumarans was carried out by using a variety of oxidants, of which the oxidation system (H2O2-HRP) gave the best results. However, the enzyme did not effect any stereocontrol. To overcome this difficultly, enantiopure ferulic acid derivatives such a A-ferulyl (S)-alaninate (308) were synthesized. The substrate 308 was dissolved in dioxane and phosphate/citric acid buffer (pH 3.5) was added. Aqueous H2O2 and HRP were added over 20 min. The mixture was stirred at room temperature for 2.5 h to yield a mixture of two phenylcoumarans 309 and 310 (70%) with a 1 4 ratio (Scheme 66). In the case of a camphor sultan derivative 311, a mixture of two phenylcoumarans was also obtained in 40% yield (312/313 = 1 9). Furthermore, oxidation of 311 with Ag20 in CH2CI2 (room temp., 24 h) yielded the same phenylcoumarans (35%) in a 1 12 ratio. The observed enantioselectivity in the oxidation... 

Detection and Determination of Aldehyde. The amount of formaldehyde in methanolic reaction mixture was estimated quantitatively according to the procedure by Kolthoff (16). A series of solutions containing varying amounts (5 X 10" to 5 X lO M) of formaldehyde as well as the unknown sample, with pH adjusted to 3 by phosphate-citric acid buffer, was treated with 1.5 X lO M Schiff s reagent (3i). Thirty minutes later, the optical density at 5500 A. was determined by a Coleman Junior spectrometer. The unknown concentration of formaldehyde was estimated by interpolating the known values. This procedure was reproducible for autoxidation of ferrous chloride in methanol. However, in the presence of a reactive cosubstrate, such as benzoin, the color became unstable, and the analysis was only semiquantitative. It was possible to determine acetaldehyde quantitatively in ethanolic reaction mixtures by vapor chromatography using a decylphthalate column at 66°-68°C. 

The effective buffer range for a weak acid or base is approximately from pH = pATa + 1 to pH = pATa — 1. When two or more buffers are present, the effects are additive so that the buffering ability is spread over a wider pH range. Examples are Mcllvaine s (1921) citric acid-phosphate mixtures for pH 2.6—8 (Table 10.45) and Smith and Smith s (1949) piperazine-glycylglycine mixtures for pH 4.4—10.8 (Table 10.46). The pATa of ethanolamine (9.5) falls conveniently between two of the pATa values of phosphoric acid (7.2, 12.3) so that ethanolamine-phosphate mixtures provide almost uniform buffer capacity between pH 6.7 and pH 12.8 (Thies and Kallinich, 1953). 

The electrochemical behavior of the NO biosensor was studied in the pH range of 3.0—10.0. For the pH study, a mixture of disodium hydrogen phosphate and citric acid buffer was used. The current response was decreased from pH 7.0 to 3.0 and also from pH 7.0 to 10.0. This may be due to the denaturation of immobilized SODl. The maximum current response was observed at pH 7.0 as shown in Figure 3.39. 

Polymer Labs. PLRP-S Mixture of 0.1 M KH2P04, 0.01 M citric acid and 0.01 M EDTA UV 350 nm OTC, TC, CTC, and DMC in sheep liver and cattle kidney Extraction with succinate buffer, dilution with EDTA-pentanesulphonic buffer, cleanup with C8 or XAD-2 SPE cartridge and MCAC DL = 10 pg/kg (OTC) [81]... 

To a soln of aldehyde 41 xg (1.00 g, 3.97 mmol) in CH2C12 (27 mL) was added (.S )-2-phenylglycinol (0.65 g, 4.76 mmol) at rt. After being stirred at rt for 2h, the mixture was cooled to 0°C, and MeOH (3.3 mL) and TMSCN (0.79 mL, 5.96 mmol) were then introduced successively. After being stirred at 0°C for 1 h and at rt for 12 h, the mixture was carefully quenched by the addition of aq citric acid soln (CAUTION HCN perform in an efficient fume hood) and stirring was continued for another 30 min. The aqueous phase was then neutralized with pH 7 phosphate buffer and extracted with CH2C12. The combined... 

Buffered Indicator Solution Prepare a mixture consisting of 700 mL of 0.1 M citric acid (anhydrous, reagent grade), 200 mL of 0.2 M disodium phosphate, and 50 mL each of 0.2% bromophenol blue and of 0.2% bromocresol green in spectrograde methanol. 

Figure 23 Separation of a cytochrome c mixture on 50-pm-i.d. capillaries (A) bare capillary (B) etched cholesteryl-modified capillary (C) etched cyanopentoxy-modified capillary. Conditions V= 15 kV and mobile phase 100% aqueous pH 3.0 buffer (60 mM citric acid and 50 mM (f-alanine). Dimensions cholesteryl capillary, L= 70 cm and /= 45 cm. Bare and cyanopentoxy capillaries, Z.= 50 cm, and /= 25 cm. Solutes 1, chicken 2, tuna 3, horse 4, bovine. (Reprinted from Ref. 102, with permission.)...

E. Solutions for the pH range 2-6-12-0 at 18°C - universal buffer mixture (Johnson and Lindsey, 1939) A mixture of 6 008 g of A.R. citric acid, 3-893 g of A.R. potassium dihydrogen phosphate, 1-769 g of A.R. boric acid and 5-266 g of pure diethylbarbituric acid is dissolved in water and made up to 1 litre. The pH values of mixtures of 100 ml of this solution with various volumes (Y) of 0-2m sodium hydroxide solution (free from carbonate) are tabulated below. 

The reaction mixture contained 50 /xg to 1 mg of protein, 1 m M GMj in 200 ftL of 50 mM citric acid-100 mM sodium phosphate buffer (pH 4.4) containing 100 mM NaCl, and 0.5% sodium taurodeoxycholate. The mixture was incubated at 37°C for 1 hour, and the reaction was terminated by heating at 100°C for 2 minutes. Cooling in an ice bath was followed by addition of 200 /xL of the mobile phase solvent. The supemate obtained by centrifugation was filtered before analysis of an aliquot by HPLC. The reaction was linear for up to 1 hour with up to 0.7 mg protein added. 

Each buffer system is generally applicable over a limited range, viz., about 2 units of pH, but by making suitable mixtures of acids and acid salts, whose pfca values differ from one another by 2 units or less, it is possible to prepare a universal buffer mixture by adding a pre-deter-mined amount of alkali, a buffer solution of any desired pll from 2 to 12 can be obtained. An example of this type of mixture is a system of citric acid, diethylbarbituric acid (veronal), boric acid and potassium dihydrogen phosphate this is virtually a system of seven acids whose exponents are given below. 

Syn 3-(Ethylth(oniethyl)-4-hydroxy-6-phenyl>2-hexanone (4) and amt (5) 3 To emanethwi (to 0 mg 0 17 mmol) in the (2 mL) was added 1 54 M n butyliithwm in hexane (0 11 mU at 0°C under Ar Stannous Inflate (69 0 mg 0 17 mmol) was added and alter 20 mm the mixture was cooled to 45°C Methyl vinyl Ketone 1 (118 mg 1 98 mmol) m THE 1 5 mL) was added followed by 3 phenylpropanal 3 (350 mg 2 61 mmol) in THE (1 5 mL) Alter 12 h aq cilnc acid was added and the organic material extracted with CHjCia The resxlue after evaporation was dissolved in MeOH and treated with citric acid After 30 mm stimng. the mixture was quenched with pH 7 phosphate buffer extracted with CH2CI2, the solvent evaporated and the residue chromatographed to afford 336 mg of 4 (75%), syn anti (90 10)... 

The acrylamide concentration is chosen for the first dimension (acid gel), and may be 10% for fractionation of RNA mixtures containing maximum chain lengths of about 80 nucleotides (as applied by De Wachter and Fiers to a typical viral RNA partial digest), and is then made twice as high in the second (neutral) gel. The concentration of cross-linker (Bis) is 1/30 that of acrylamide. The buffer in reservoir and gel is 0.025 M citric acid, 6 M urea for the first dimension, and 0.04 M Tris-citric acid, pH 8, for the second dimension. Table 8.3 summarises the concentrations and amounts of stock solutions conveniently used for the preparation of each gel, as well as the catalyst, which is added iimnediately before the gel is poured. 

We have seen from Fig. 3.9 that the buffer capacity is at a maximum at a pH equal to the pK of the weak acid used in the formulation of the buffer system and decreases appreciably as the pH extends more than one unit either side of this value. If, instead of a single weak monobasic acid, a suitable mixture of poly-basic and monobasic acids is used, it is possible to produce a buffer which is effective over a wide pH range. Such solutions are referred to as universal buffers. A typical example is a mixture of citric acid (pJC i = 3.06, pK,2 = 4.78, pK,3 = 5.40), Na HPO (pK, of conjugate acid H2PO4 = 7.2), diethylbarbituric acid (pKji = 7.43) and boric acid (pK i = 9.24). Because of the wide range of pK, values involved, each associated with a maximum buffer capacity, this buffer is effective over a correspondingly wide pH range (pH 2.4-12). 

I) Whatman No.l, sheet (14 x 6 inches), buffered by dipping in 5% solution of sodium dihydrogen citrate, blotting and drying at 25 for one hour. It can be stored indefinitely. A solvent composed of 4.8 g of citric acid in a mixture of 130 ml of water and 870 ml of n-butanol was used (103). 

The following procedure is a typical example [152]. To a stirred solution of 1 mmol aldehyde in 1.7 ml of 0.1 mol 1 sodium citrate buffer (pH 4.5), 2000 lU of (S)-oxynitrilase (1000 lU/ml) were added and the mixture was cooled down to ice bath temperature. Subsequently, 2.5 mmole equivalents of potassium cyanide adjusted to pH 4.5 with cold 0.1 mol 1 citric acid (17 ml), were added in one portion. After stirring for 1 h at 0-5 °C, the reaction mixture was extracted with methylene chloride (3 X 50 ml). The combined organic layers were dried over anhydrous sodium sulfate and the solvent was removed by evaporation to give the crude cyanohydrin, which was purified by column chromatography using petroleum ether/ethyl acetate (5/1 or 9/1) acidified with trace amounts of anhydrous HCl as the eluent. 

A range of pH from 2 to 6 is possible with citric acid and sodium hydroxide. In order to obtain mixtures which have a high buffer capacity over a wide variation in composition, it is advisable to start with a mixture of acids of approximately similar dissociation constants. 

Figure 5 pH changes during the cooling (and freezing) and rewarming of an ice-seeded citric acid-sodium phosphate buffer mixture, illustrating the effects of delayed crystallisation of sodium phosphate reproduced from Pikal (unpublished)... 

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