Continuous analyzer, coulometric

The continuous methods combine sample collection and the measurement technique in one automated process. The measurement methods used for continuous analyzers include conductometric, colorimetric, coulometric, and amperometric techniques for the determination of SO2 collected in a liquid medium (7). Other continuous methods utilize physicochemical techniques for detection of SO2 in a gas stream. These include flame photometric detection (described earlier) and fluorescence spectroscopy (8). Instruments based on all of these principles are available which meet standard performance specifications. 

Another example of the application of the principles of coulometric titrations to a continuous on-stream analyzer is the moisture analyzer developed by Kei-del.18 It illustrates one of the outstanding advantages of the coulometric generation of a titrant namely, an intermediate is produced as a titrant that would not be available in standard solutions. The principle of the moisture analyzer is to place a phosphoric acid solution between two closely spaced platinum electrodes (helically wound in a glass tube). When current is passed between the two electrodes, the water in the phosphoric acid is electrolyzed... 

The amount of some gases, such as SO2 [73], CO [74], can be automatically continuously measured by polarographic analyzers [75]. Measuring electrodes with a constant surface, e.g. carbon, platinum, gold disks or rods are most often used. Present research is concentrated on the so-called coulometric analyzers [73]. The analysed gas is brought by the shortest route directly to the measuring electrode. The substance to be determined is completely reduced or oxidized electrochemically at a large area electrode. 

Another broad field of applications involves continuous coulometric titrators which are employed in process stream analyzers. In these the generating current is continuously adjusted to maintain a small excess of electrogenerated titrant to react with material in the incoming liquid or gaseous sample stream. The level of generating current is a measure of the instantaneous concentration of the titrated substance (29, 30), Coulometric titration methods have also been used in chromatographic detectors and for determination of homogeneous reaction rates (31). 

There have since been many similar instruments, largely dedicated to measurement of mercaptans and other sufur compounds by reaction with generated bromine. An early example was the Titrilog, manufactured by Consolidated Electrodynamics Corporation in the 1950s. Others, produced by European or Japanese firms, are intended for the determination of SO2 or CO2 from combusion analyzers (47). Stock (48) has summarized the development and present status of continuous "coulometric" titrators. 

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