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... other values were reported by using pure mate-rials such as silver /31/, iodine /32/, benzoic and oxalic acids /33/, arsenic trioxide /34/ and 4-aminopyridine /35, 36/, and were summarized previously by Taylor et al. /37/ and also by Bishop /38/, and more recently by Cohen and Taylor /23/ and Koch and Diehl /35, 36/. They are shown in Table 1. All values which were obtained using chemical methods are more than 10 ppm higher compared with the value calculated by Lx e. ...Context 2
... and Taylor /33/ measured the Faraday constant with this acid, the purity of which was certified by potassium hydrogen phthalate prepared by Bates and Wichers /91/. (See Table 1). ...Context 3
... Pure Acids and Bases:-Pure adipic acid /22/ and potassium dihydrogen citrate /108/ were assayed at the NBS. Single crystals of oxalic acid /33/ and 4-aminopyridine /35, 36/ were used for the measurement of the Faraday Constant by Marinenko and Taylor and also by Koch et aL Their results were shown in Table 1. ...Citations
... e quantity of a substance produced at the electrode and the quantity of electric charge passed are linked with Faraday's laws of electrolysis. Many reports present coulometric methods of analysis of a variety of reagents [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. A number of original reports [3,4,11,[15][16][17] and reviews [1,2,[5][6][7][8][9][10][12][13][14] on coulometric methods were published over the past decades. ...
... Many reports present coulometric methods of analysis of a variety of reagents [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. A number of original reports [3,4,11,[15][16][17] and reviews [1,2,[5][6][7][8][9][10][12][13][14] on coulometric methods were published over the past decades. Coulometric method has been applied to analyze a large variety of inorganic and organic compounds [1,6,13]. ...
A gravimetric method for the quantitative assessment of the products of electrolysis of water is presented. In this approach, the electrolysis cell was directly powered by 9 V batteries. Prior to electrolysis, a known amount of potassium hydrogen phthalate (KHP) was added to the cathode compartment, and an excess amount of KHCO 3 was added to the anode compartment electrolyte. During electrolysis, cathode and anode compartments produced OH ⁻ (aq) and H ⁺ (aq) ions, respectively. Electrolytically produced OH ⁻ (aq) neutralized the KHP, and the completion of this neutralization was detected by a visual indicator color change. Electrolytically produced H ⁺ (aq) reacted with HCO 3⁻ (aq) liberating CO 2 (g) from the anode compartment. Concurrent liberation of H 2 (g) and O 2 (g) at the cathode and anode, respectively, resulted in a decrease in the mass of the cell. Mass of the electrolysis cell was monitored. Liberation of CO 2 (g) resulted in a pronounced effect of a decrease in mass. Experimentally determined decrease in mass (53.7 g/Faraday) agreed with that predicted from Faraday’s laws of electrolysis (53.0 g/Faraday). The efficacy of the cell was tested to quantify the acid content in household vinegar samples. Accurate results were obtained for vinegar analysis with a precision better than 5% in most cases. The cell offers the advantages of coulometric method and additionally simplifies the circuitry by eliminating the use of a constant current power source or a coulometer.
... Coulometry is one of the most precise and accurate techniques of chemical analysis [8,[20][21][22][23]. It was introduced in 1938 by Szebellédy and Somogyi [24], who are considered the pioneers of coulometry. ...
The use of pure materials in chemical analysis is currently in high demand due to the need to provide reliable measurement results. In the Electrochemistry Laboratory of the National Institute of Metrology from Brazil (Inmetro) is located the primary system of coulometry, which is considered the standard of the measurement for the amount of substance. The main function of this primary system is to certify primary reference materials to ensure reliability and metrological traceability for titration analyses. Some important certified reference materials (CRMs), homogeneous, stable, and characterized with an accurate property value have been developed. This work aims to present the stages for certifying the primary reference materials in a metrological approach: potassium hydrogen phthalate for acid-base titration, potassium chloride for precipitation titration, and potassium dichromate for redox titration. In addition, the key comparisons that were necessary to demonstrate the national traceability structure's equivalence for these CRMs' international recognition will be shown.
The electron transfer stoichiometry and principal oxidation products of the carbamate pesticide Aminocarb (3-methyl-4-dimethylaminophenyl N-methylcarbamate) were investigated in methanol + water and acetonitrile + water media, using flow injection coulometry,1H and 13C nuclear magnetic resonance spectrometry, and mass spectrometry. The four-electron oxidation was found to occur at aliphatic as opposed to aromatic sites, involving oxidation and nucleophilic attack at an N-methyl group to yield the hydroxy/methoxy analogs in water + methanol media, and yielding ultimately an aldehyde. The pathway in water + acetonitrile, as expected, was found to yield only the hydroxy analogs and the aldehyde.
Coulometric titrations of ammonia and sulphur dioxide can be implemented with an improved selectivity in a measuring cell combining a batch type titration cell with a gas diffusion separator. The supporting electrolyte is propelled through the coulometric titration cell and the acceptor side of the membrane separator by means of a magnetic centrifugal pump. The sample solution flows through the donor side of the membrane separator. Acceptor and donor side are separated by a microporous PTFE-membrane. The measuring cell assembly allows both selectivity enhanced coulometric titrations with enrichment of the sample substance to be determined and the continuous coulometric detection of volatile species.
The mass fraction of potassium hydrogen phthalate (KHP) from a specific batch was certified as an acidimetric standard. Two different analytical methods on a metrological level were used to carry out certification analysis: precision constant current coulometric and volumetric titration with NaOH. It could be shown that with a commercial automatic titration system in combination with a reliable software for the end-point detection it is possible to produce equivalent results with the same accuracy in comparison to a definite method handled by a fundamental apparatus for traceable precision coulometry. Prerequisite for titrations are that a high number of single measurement are applied which are calibrated with a high precision certified reference material.
