Sodium Acetate Electrode

Mercury electrode. Sodium acetate. Lithium perchlorate. According to other data, only up to 1.2 V. 

Row 45, item pH A value of 4.8 in a series of values around 6.2 is highly suspicious if the calibration of the electrode involves the use of an acetic acid/sodium acetate buffer (pK = 4.6)... 

This electrode filling is unsuitable with acetic acid or another related acid as the titration solvent, as in this medium possible leakage of sodium acetate would act as the inherent base. 

The electrochemical oxidation is often more sensitive to the reaction conditions than to the substituents. Platinum electrodes are recommended for methoxylation and the equivalent acetoxylation procedures.290 In acetonitrile buffered by hydrogen carbonate ion, 3,4-diethylfuran affords the 2,5-dihydroxy-2,5-dihydro derivative (84%) and Jones oxidation readily leads to diethylmaleic anhydride in what is claimed to be the best general method for such conversions.291 In unbuffered methanol and under current density control, the oxidation of 2-methylfuran appears to eliminate the methyl group since the product is the acetal-ester 111 also obtained from methyl 2-furoate.292 If sodium acetate buffer is used, however, the methyl group is retained but oxidized in part to the aldehyde diacetate 112 in a... 

The anodic oxidation of catechol in the presence of 1,3-dimethylbarbituric acid was carried out in aqueous solution containing sodium acetate in an undivided cell at graphite and nickel hydroxide electrodes [114]. The results did not fit with the expected structure (Scheme 47, path A) but a dis-piropyrimidine was isolated in 35% yield (Scheme 47, path B). It seems that the initial attack of 1,3-dimethylbarbituric acid on the anodically formed o-quinone does not occur through the carbon-oxygen bond formation but rather through the carbon-carbon bond formation, giving rise to the final product via several consecutive reaction steps. 

Reduction of substituted nitrobenzenes under alkaline conditions, usually with aqueous sodium acetate as electrolyte and a nickel cathode, is the classical method due to Elbs [45] for the formation of azo- and azoxy-compounds. Protons are used in the electrochemical reaction so that the catholyte becomes alkaline and under these conditions, phenylhydroxylamine reacts rapidly with nitrosobenzene to form azoxybenzene. Finely divided copper has long been known to catalyse the reduction of nitrobenzene to aniline in alkaline solution at the expense of azoxybenzene production [46]. Modem work confirms that whereas reduction of nitrobenzene at polycrystalline copper in alkaline solution gives mainly azoxybenzene, if the electrode is pre-oxidised in alkaline solution and then reduced just prior to the addition of nitrobenzene, high yields of aniline are obtained with good current efficiency... 

Corresponding to a cyclic voltammogram (CV), recorded at a glassy carbon electrode (GCE) immersed into a 1.0 mM Cu + solution in acetic acid/sodium acetate... 

Fig. 2.17 SQWVs of FTO electrodes modified with (a) saffron, and, (b) sample from Tibet temple immersed into 0.50 M acetic acid -I-0.50M sodium acetate aqueous buffer at pH 4.85. Potential scan initiated at —0.85 V in the positive direction potential step increment 4 mV square wave amplitude 25 mV frequency 2 Hz. Courtesy of the Philadelphia Museum of Arts...

The extract was then diluted with 0.5 mL with 0.2 M sodium acetate buffer, pH 4.7 and analyzed by HPLC. Chromatographic conditions were the same as for the determination of benzidine in hair dye formulations. For the particular lot of diarylide yellow studied 46 Ug/kg of DCB was found. In an attempt to confirm the identity of the chromatographic peak, its response as well as the response for the authentic DCB standard was determined at several different electrode potentials. These data, shown in Figure 7, illustrate the ability of HPLC/EC to yield qualitative as well as quantitative information for unknown components. 

Effect of pH on the addition reactions was studied from pH 4 to 10. For pH values below 7, the reaction was buffered with a 25 mM sodium acetate solution whereas for pH values above 7, a 25 mM disodium tetraborate solution was used the pH was adjusted by adding either HC1 or NaOH. The combination electrode used for the determination of experimental pH, was calibrated with National Bureau of Standards (NBS) buffers for Milli-Q water (36) and tris(hydroxymethyl)aminomethane (TRIS) buffers for seawater (37) and NaCl solutions (38) on the pHF (free proton) scale. Since the addition of reactants caused a small pH change in the buffered medium, the experimental pH values shown in the results were measured after the reactants were added to reaction bottle. Samples from low pH reaction series were adjusted topH 9 by addition of a strong borate buffer just prior to HPLC analysis. Inis was necessary because thiol analysis using o-phthalaldehyde requires this pH for optimum derivatization. 

Electrolytically initiated polymerization may either depend on a direct electron transfer between electrode and monomer, or on the formation of an intermediate which interacts with a monomer molecule in a fast chemical step, thus creating a chain initiator. As an example of the former type of process, the formation of a living polymer from the cathodic polymerization of a -methylstyrene by electrolysis in sodium tetraethylaluminate - tetrahydrofuran may be cited 639 whereas a typical case of the latter type is the anodic polymerization of vinyl monomers by electrolyzing them together with sodium acetate in aqueous solution 63 7,640) Here it is assumed that acetate ion is discharged to form an acetoxy or methyl radical which attacks the monomer molecule in a fast chemical step. 

Repeat the same procedures with 0.1 M sodium acetate, 0.1 M carbonic acid, 0.1 M sodium bicarbonate, and 0.1 M ammonia. Make certain that for each solution you use a dry and clean beaker, and before each measurement wash the electrode with distilled water and dry with Kimwipes. Record your data on the Report Sheet (2). 

Substrate Solution Transfer 4.0 g of the Hemoglobin into a 250-mL beaker, add 100 mL of water, and stir for 10 min to dissolve. Immerse the electrodes of a pH meter in the solution, and while stirring continuously, adjust the pH to 1.7 by adding 0.3 N hydrochloric acid. After 10 min, adjust the pH to 4.7 by adding 0.5 M sodium acetate. Transfer the solution into a 200-mL volumetric flask, dilute to volume with water, and mix. This solution is stable for about 5 days when refrigerated. 

Perbromic acid and perbromates are most readily assayed by determination of their oxidizing power after reduction with hydrogen bromide, as described earlier in this article. Traces of fluoride in the acid or salts may be determined potentio-metrically, using a fluoride-sensitive electrode (Orion Research, Inc.) and an expanded-scale pH meter. Acid or alkaline solutions should be neutralized or buffered with acetic acid and sodium acetate before the determination. The electrode response should be calibrated against similar solutions of known fluoride content. 

Dopamine was quantitated by high-performance liquid chromatography (HPLC) with electrochemical detection with a detection limit of approximately 5 fmol/sample. An HPLC pump (LKB, Pharmacia) was used in conjunction with an electrochemical detector (Antec, Leiden) working at 625 mV versus an Ag/AgCl reference electrode. The analytical column was a Supelco Supelcosil LC-18 Column (3 pm particle size). The mobile phase consisted of a mixture of 4.1 g/1 sodium acetate (Merck), 85 mg/1 octane sulphonic acid (Aldrich), 50 mg/1 EDTA (Merck), 1 mM tetramethylammonium chloride (ACROS), 8.5 % methanol (Labscan) and ultra pure water (pH=4.1 with glacial acetic acid). 

Figure 23-25 Cyclic voltammogram of the insecticide parathion in 0.5 M pH 5 sodium acetate buffer in 50% ethanol. Hanging mercury drop electrode. Scan rate 200 mV/s. (From W. R. Heineman and R T. Kissinger, Amer. Lab., 1982 (11), 34. Copyright 1982 by International Scientific Communications, Inc. Reprinted with permission.)...

The eluent was 0.1 M sodium acetate buffered to pH 6 in 70% methanol 30% water. The procedure was run in the isocratic mode at 1.0 mL/min with a nominal pressure of 700-800 psi. The applied potential to the working electrode was 0 V versus the Ag-AgCl reference electrode. Chloride and bromide did not interfere with the determination of thiosulfate and iodide because they are weakly electroactive at the applied potential. Retention times in minutes are 2.0 (Cl ), 3.9 (Br"), 8.4 (T), and 12.5 (S2 032 ). 

L. Michaelis has reported also a combination of veronal and acetate buffers which, due to the addition of an appropriate amount of sodium chloride, have the same ionic strength as a salt solution isotonic with blood. The original solution is 1/7 molar with respect to sodium acetate and the sodium salt of veronal, 500 c.c. of solution (in carbon dioxide-free water) containing 9.714 g.-of sodium acetate (CH3C00Na-3H20) and 14.714 g. of the veronal salt. Five c.c. portions of this solution are treated with 2 c.c. of an 8.5% NaCl solution, with a c.c. 0.1 N HCl, and with (18 — a) c.c. of water. The following table shows how o and pH (hydrogen electrode 25°) are related. 

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°). 

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