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Performance of a New Automatic Carbon Dioxide Coulometer

“Performance of a New Automatic Carbon Dioxide Coulometer” Microchemical Journal 22 (1977): 567-573.

Huffman, Edward W. D., Jr. and William A. Huffman.

INTRODUCTION

The analytical chemist has used a wide variety of methods for the determination of carbon dioxide. The classical gravimetric and volumetric methods, although somewhat tedious, have the distinct advantage of being based on theoretical considerations rather than empirical calibration with known amounts of CO2. Methods such as thermal conductivity, infrared absorption, electrical conductivity, conversion to methane, and detection with a flame ionization detector all require empirical calibration with known amounts of carbon dioxide and, at least under optimum conditions, are generally less accurate than the classical gravimetric approach. This paper describes a coulometric CO2, titrator that has the theoretical advantages of classical gravimetric and volumetric methods, nut, since the unit is fully automated with digital readout and is computer compatible, the analysis is much easier to perform and more reliable.

Direct titration methods for CO2 include absorption in non-aqueous or partially aqueous media, usually containing monoethanolamine for conversion of CO2 to the stronger acid hydroxyethylcarbamic acid. The absorbed CO2 is titrated with bases such as sodium methanolate (1, 2, 11) or tetrabutyl ammonium hydroxide (7). A problem with the titrimetric methods is that the titrant must be standardized regularly. The author has found that the titrant proposed by Merz (7) must be standardized at least daily. In performing large numbers of analyses, large volumes of absorbent and titrant must be dealt with.

If 100% coulometric efficiency can be obtained, coulometry can be used as a standard reference method without the necessity of empirical sample standardization. Several coulometric procedures which are basically extensions of some of the titrimetric procedures have been proposed. Nakamura et al. (9) used a coulometric generation of base in an aqueous barium perchlorate medium to maintain a pH of 10 as CO2 was absorbed. Boniface and Jenkins (3) developed a procedure for the determination of carbon in steel using a coulometric titration of CO2 in a dimethylformamide medium. Ottaway et al. (10) mention the use of pyridine-based was placed in the apparatus.