Buffer mixtures, acetic acid-acetate

Table 2.2 pH of acetic acid-sodium acetate buffer mixtures... 

Buffer action 46 Buffer capacity 48 Buffer mixture universal, (T) 831 Buffer solutions 46, (T) 831 acetic acid-sodium acetate, 49 for EDTA titrations, 329 preparation of IUPAC standards, 569 Bumping of solutions 101 Buoyancy of air in weighing 77 Burette 84, 257 piston, 87 reader, 85 weight, 86... 

In the galvanic detector, the electrochemical detector consists of a noble metal like silver (Ag) or platinum (Pt), and a base metal such as lead (Pb) or tin (Sn), which acts as anode. The well-defined galvanic detector is immersed in the electrolyte solution. Various electrolyte solutions can be used, but commonly they may be a buffered lead acetate, sodium acetate and acetic acid mixture. The chemical reaction in the cathode with electrons generated in the anode may generate a measurable electrical voltage, which is a detectable signal for measurements of DO. The lead is the anode in the electrolyte solution, which is oxidised. Therefore the probe life is dependent on the surface area of the anode. The series of chemical reactions occurring in the cathode and anode is ... 

Mixture of acids and bases Various Phosphate buffer, 1% acetic acid (buffered to pH 3.0)... 

Several crown ethers that possess side chains with terminal mercapto groups enhance the rate of transesterification of amino-acid p-nitrophenyl esters. Matsui and Koga (1978) reported the reactions of a number of amino-acid p-nitrophenyl ester hydrobromides dissolved in mixtures of ethanol and dichloromethane (1 4) and buffered with acetic acid and pyridine (pH 4.60 in... 

A few common volative buffer mixtures, along with their respective pH range are pyridine-formic acid (2.3-3.5) trimethylamine-formic acid (or acetic acid) (3.0-6.0) triethanolamine-HCl (6.8-8.8) ammonia-formic acid (or acetic acid) (7.0-10.0). See Buffers... 

The reaction mixture included phosphate buffer, alcohol dehydrogenase, NAD+, substrates and internal standards, and mercaptoethanol in a final volume of 190 gtL. The enzyme preparation is preincubated with all components of the assay system except substrates, which are added to initiate the reaction. The reaction is terminated by adding 100 giL of the incubation mixture of 300 fiL of reaction-terminating solution containing acetate-perchlorate buffer and ascorbic acid. Samples could be stored up to 2 weeks at -80°C before thawing and filtering through 0.45 gm nitrocellulose filters. Flve-microliter aliquots were injected into the HPLC... 

Utilize the general form of the acetic acid-acetate buffer capacity curve obtained in Problem 11 to draw an approximate curve for the buffer capacity over the range of pH from 2 to 13 of the universal buffer mixture described on page 415. It may be assumed that the total concentration of each acid and its salt is always 0.2 molar. 

Bromcresol green (tetrabromo-m-cresolsulfonephthalein). A solution of 25 g. bromine in 150 c.c. of glacial acetic acid is added slowly to a suspension of 15 g. metacresolsulfonephthalein in 150 c.c. of glacial acetic acid. The stirred mixture is maintained at a temperature below 30°. The progress of the reaction is followed by observing the color produced by a drop of the solution in a buffer mixture with a pH of 7. When a maximum color... 

These figures permit us to calculate easily the influence of dilution upon the pH of a buffer mixture. For example, if we dilute ten-fold a mixture which is 0.1 normal with respect to both acetic acid and sodium acetate, the value of ju will change from 0.1 to 0.01 and — log/i will change from 0.11 to 0.04. This variation corresponds to a pH increase of 0.07. The influence of dilution upon the pH of a number of different buffer solutions is illustrated in the tables which follow. The calculated values of pH were checked by actual measurements with the hydrogen electrode (18°). 

Indicator papers serve the same purpose as do indicator solutions in that they reveal the reaction of a liquid. As we shall see farther on, the sensitivity of the papers depends on so many conditions that as a rule they do not permit a very precise measurement of the hydrogen ion concentration. It is true that the pH of buffer mixtures can be measured approximately with indicator papers. They may be employed to greater advantage, however, for qualitative purposes such as the testing of gases for acidic or basic constituents (ammonia, acetic acid, etc.). 

This is a time reaction and is very much influenced by the hydrogen ion concentration. The equation shows that H+ ions are removed from solution. Comparing the behavior of iodide-iodate paper in 0.0001 N HCl and in the acetic acid-acetate mixture, both reactions seem to be the same at first sight. The same brown or blue color appears. However, the paper treated with the buffer mixture gradually turns a deeper color because the hydrogen ions removed initially are replaced. This is not true of the hydrochloric acid. 

Electrolyte Acetic Acid (buffer) (reducing) Oxelic Acid (buffer) dil. Acid (cold) Acid (hot) Mixtures (fHF) Cheieting Agents Basic Soins Fusion (f Acid leach) MgCI2 HO Ac HOAc/OAc- m.mu ... 

If the chromatographic eluent is a mixture of organic modifier and water and contains no additives such as involatile buffers/acids, then product recovery can be effected simply by removing solvent, e.g., by rotary evaporation. Alternatively, if the solvent volumes are large, the organic modifier can be removed by rotary evaporation and the product recovered by adsorption/elu-tion from a suitable adsorbent such as a reverse phase silica or an organic copolymer resin. This is also a method of choice where additives such as involatile buffers (phosphates, acetates) and acids (orthophosphoric) are present in the fraction and need to be removed. 

What is the pH of a buffer mixture containing IM acetic acid and 0.5M sodium acetate ... 

Tetracyclines, nonsteroidal anti-inflammatory, antidepressants, " and mixtures of acidic drugs as well as veterinary drug residues have been determined by CZE (citric acid/citrate, borate, borate in MeOH, phosphate/MeOH, ammonium formate/formic acid/ACN, ammonium acetate, ammonium acetate/acetic acid/MeOH) and EKC (SDS/pH 2.5 phosphate buffer/ACN) methodologies in water samples from influent and effluent of sewage treatment plants as well as wastewater, river, surface and groundwater as compiled in Table 31.9. Estrogens have been receiving increased attention due to the already mentioned possible interference with the reproductive... 

An easy and efficient one pot synthesis of peracetylated glycals from unprotected sugars has been described. In this method the sugar was sequentially treated with acetic anhydride and catalytic hydrobromic acid-acetic acid (to effect per-acetylation), more hydrobromic acid-acetic acid (to form the glycosyl bromide), sodium acetate (to neutralize excess hydrobromic acid) and finally a buffered mixture of sodium acetate, acetic acid, zinc-copper sulfate and water (to effect a reductive-elimination). The method was applied to the syntheses of glycals derived from D-glucose, D-galactose, L-rhamnose, L-arabinose, maltose, lactose and maltotriose. ... 

This reaction changes some of the acetic acid to sodium acetate, but it does not change the hydrogen ion concentration much. If a small amount of hydrochloric acid is added to the buffer mixture of acetic acid and sodium acetate, some of the sodium... 

Buffers are typically mixtures of solids and or a liquid and a solid. Examples of buffers include acetate buffer (50 mM at pH 4.0), phosphate buffer (lOOmM at pH 7.0), and 0.1 % TEA/0.1 % TFA. Since the use of buffers in RP separations is commonplace, basic knowledge of the solubility of each buffer component in the mobile phase is critical. Consider the case of phosphoric acid and its series of conjugate acid/base pairs as the buffer for acetonitrile/water mobile phase. Phosphate has negligible UV absorbance down to 200 nm (see Fig. 1.5denature proteins, and has three effective buffer regions around the pH values of 2, 7, and 12. These properties make phosphate buffers very attractive for many HPLC separations. 

Living systems depend on buffers for pH control most of these are complex buffers that contain a mixture of various acids and bases. Buffers can be made from weak acids/bases and the salts of other weak acids/bases. For example, we could make an acidic buffer from acetic acid and sodium bicarbonate (NaHC03, a salt of the weak acid carbonic acid). Or, we could make a basic buffer from NH3 and NH2(CH3)2Br (the salt of the weak base di-methylamine, HN(CH3)2). But it is more difficult to calculate pH s or other concentration values from these mixed buffer systems. We have limited our discussion and detailed examples to buffers that contain a weak acid/base and the salt of icfiX. same acid/base. 

Amino acids (0.5 mg) are dissolved in 100 )il of triethylamine-acetic acid buffer (50 ml water -f 50 ml acetone + 0,5 ml triethylamine -i- 5 ml of 0.2 M acetic acid, pH 10.65) and treated with DABITC solution (50 pi, 4 nmole/pl in acetone). The mixture is heated at 54°C for 1 h, dried under vacuum, and then redissolved in water-acetic acid (40 pi + 80 pi) saturated with HCI (alternatively, 100 pi of 50% TEA can be used instead of this aqueous acid mixture). The acid solution is heated at 54°C for 45 min and then dried again under vacuum. The dried DABTH-amino acid (about 200 nmole) is dissolved in a suitable volume of 90% ethanol and stored at -20°C for TLC analysis. The presence... 

Formation of some unstable salts, through the reaction between urea and some of the initial formaldehyde, determines from the beginning an increased medium pH in the subsequent stages of the reaction, due to urea consumption, a reduction of medium pH takes place. This pH variation necessitates permanent control of reaction medium pH by the addition of buffers (sodium acetate, (H4N)2C03, citric acid, and sodium acetate mixture) or urotropine. The latter forms, with formic acid, medium-buffering compounds [21]. 

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