Methanol polarogram

Saber and Sidky [39] described polarographic estimations of Bayluscide (I) (niclosamide) or its ethanolamine salt (II). Solutions of I or II containing 80% by volume methanol (the rest was the buffer components in H20) yielded highly reproducible polarograms [39]. 

A complicated reaction pattern is also observed with dichlorotetraphenylditin87. The electrochemistry of this compound compound on Hg electrodes involves formation of intermediate SnHg compounds by reduction (see also Reference88). The polarogram of Ph2ClSn—SnClPh2 (in methanol/LiCl, on Hg) shows an anodic peak and two cathodic waves at —0.4, —0.55 and —1.35 (vs SCE). The oxidation involves between one and two electrons as determined by coulometry, and the proposed reactions are ... 

FIGURE 2.47. Polarograms obtained for the electrochemical reduction of the diphenyl-methyl radical produced by the reaction of diphenylmethyl chloride by photo-injected electrons in dimethylformamide are shown at two different measurements times (o, 7 ps , 500 pis) in the absence (a) and presence of 8.15 mM methanol (b). Adapted from Figure 1 of reference 50a, with permission from the American Chemical Society. 

Fig.3. Differential pulse polarograms of 0.1 mM glycerol trinitrate in water/methanol solutions, using 0.1 M ammonium acetate electrolyte. Methanol content a = 20 %, b = 40 %, c = 60 % and d = 80 %.

The composition of the solvent has an essential influence on the reversibility of the electrode reaction. From an analytical point of view, solvents giving reversible electrode reactions are to be preferred. The form of a differential pulse polarogram is dependent on the composition of the solution, which in turn will have an influence on the possibilty of getting a successful multi-component determination. As an example, the differential pulse polarograms for glycerol trinitrate (Fig.3) and 2,4,6-trinitrotoluene (Fig.4) in water/methanol solutions, are shown. 0.1 M ammonium acetate is used as the electrolyte. 

Fig.6. Differential pulse polarograms of 0.1 mM 2,4,6-trinitrotoluene in 60 % methanol, using a) 0.1 M ammonium acetate, b) 0.1 M tetram-ethyl ammonium bromide electrolyte.

To demonstrate the influence of buffered and non-buffered solutions differential pulse polarograms of glycerol trinitrate and 2,4,6-trinitrotoluene, are shown in Fig.5 and 6 respectively. The electrolytes are 60 % methanol solution with 0.1 M ammonium acetate (buffered solution) and 0.1 M tetramethyl ammonium bromide (non-buffered solution) electrolytes. 

Fig. 12. Differential pulse polarogram of 0.2 mM glycerol trinitrate, 0.67 mM nitroguanidine and 0.04 mM dibutylphthalate in 20 % methanol solution, using 0.1 M tetramethyl ammonium bromide electrolyte.

Nitrotoluenes and nitrate esters are reduced in the same potential range. By carefully selecting the methanol concentration of the solution, a mixture of two nitrotoluenes and one nitrate ester can be determined. The polarograms are influenced by the methanol content of the solution, and also by the fact that the nitrate ester group is reduced by 2 electrons and the nitro group by 6 electrons, and that the nitrate ester group reduction is strongly irreversible. 

Fig. 13. Schematic differential pulse polarograms of glycerol trinitrate (N), 2,4,6-trinitrotoluene (T) and 2,4-dinitrotoluene (D) in 60 % methanol solution, using 0.1 M ammonium acetate electrolyte. 

A polarogram of reagent-grade methanol is shown in trace a. Trace b shows reagent methanol with added 0.001 00 wt% acetone, 0.001 00 wt% acetaldehyde, and 0.001 00 wt% formaldehyde. Scales are the same in both panels. Solutions were prepared by diluting 25 mL of methanol up to 100 mL with water containing buffer and hydrazine sulfate, which reacts with carbonyl compounds to form electroactive hydrazones. An example is shown below ... 

From the two polarograms, estimate the wt% of acetone in reagent-grade methanol. 

Polarograms of (a) reagent grade methanol and (b) methanol containing added standards. [D. B. Palladino,/Am. Lab, August 1992, p. 56]. 

Studies of the oxidation of formaldehyde have been carried out primarily with nonstationary techniques, i.e., cyclic voltam-etry and chronopotentiometry. The polarograms obtained with formaldehyde show evidence of two oxidation peaks, which are shifted depending on the pH of the electrolyte. The peak currents which are not diffusion controlled, were found to be larger for formaldehyde than for methanol or formic acid. Plots of log i vs, V from the cyclic voltametric data for the oxidation... 

Budyina and Marinin [130] have described methods based on anodic voltammetry for the determination of lonol (2,6-di- -butyl-p-cresol) and quinol in polyester acrylates. To determine lonol the sample is dissolved in 25 ml of acetone and a portion (10 ml) is treated with 2.5 ml of acetone and 5 ml of methanol and diluted to 25 ml with a solution 0.1 M in lithium chloride and 0.02 M in sodium tetraborate. A polarogram is recorded with a graphite-rod indicator electrode. To determine quinol, the sample (1 to 3 g) is dissolved in 80 ml of methanol or methanohacetone (1 1) and the solution is diluted to 100 ml with the lithium chloride - sodium tetraborate solution. A polarogram is recorded under the same conditions. Concentrations are determined by the addition method. The values versus the SCE) are 0.25 V for lonol and 0.16 V for quinol. 

The differential pulse polarogram of a 10 ug/ml methanolic solution of acrylamide showed a well-defined and well-resolved peak. The differential pulse polarographic acrylamide reduction current is directly proportional to concentration as shown in Table 7.24. The polarographic detection limit for acrylamide is less than 1 pg acrylamide/cm. ... 

Acrylo-type compoimds, such as acrylic acid, acrylonitrile and acrolein can be present in polyacrylamides. Their unsaturated characteristics could cause them to interfere with the acrylamide analysis. Acrylic acid is electroreducible, but its anionic form, acrylate is not. A polarogram of acrylic acid and acrylamide in an 80 20 (v/v) methanol/water solution with tetra-/i-butylammonium chloride as the supporting electrolyte showed that the reduction of the associated acid occurs at ca. - 1.7 V vs SCE, 0.3 V more positive than the acrylamide reduction. The reduction peak of acrylic acid is easily resolved from acrylamide. Esters of acrylic acid are electroreducible and some, such as the alkyl esters (eg. ethyl acrylate) reduce in the same potential region as acrylamide and do constitute an interference. Acrylonitrile is also electroreducible at the same potential as acrylamide. However, the high volatility of acrylonitrile allows it to be readily purged from the analyte solution. The detection limit of acrylamide monomer by this technique is less than 1 ppm. 

The polarographic behavior and the form of the polarograms with many hydrazones are largely affected by the adsorbability of the molecules, at the surface of the dropping mercury electrode. At the limiting currents frequently more or less sharply defined decreases are observed, the magnitude of which depends on the concentration of depolarizer and methanol and also on the pH value of the solution. Furthermore it depends on the drop tiftie and on the buffer capacity. 

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