Chlorine ions, coulometric titration

During heat treatments, zinc and calcium stearates react with hydrogen chloride that has evolved from the polymer or with labile chlorine atoms to liberate zinc and calcium chlorides. These compounds are titrated by a coulometric method in tetrahydrofuran (7) using a generator of Ag+ ions that are precipitated in the presence of chloride ions. When zinc and calcium stearates are used together, both chlorides are titrated at the same time, and they are not differentiated. 

Some typical important industrial applications of coulometry include the continuous monitoring of mercaptan concentration in the materials used in rubber manufacture. The sample continuously reacts with bromine, which is reduced to bromide. A third electrode measures the potential of B12 vs. Br and, based on the measurement, automatically regulates the coulometric generation of the bromine. Coulometry is used in commercial instruments for the continuous analysis and process control of the production of chlorinated hydrocarbons. The chlorinated hydrocarbons are passed through a hot furnace, which converts the organic chloride to HCl. The latter is dissolved in water and the Cl titrated with Ag" ". The Ag" " is generated by coulometry from a sUver electrode, Ag°. It is necessary for the sample flow rate to be constant at all times. Integration of the coulometric current needed to oxidize the silver to silver ion results in a measurement of the Cl concentration. 

Test Method B, Combustion and Microcoulometry—The washed naphtha fiaction of a crude oil specimen is injected into a flowing stream of gas containing about 80 % oxygen and 20 % inert gas such as argon, helium, or nitrogen. The gas and sample flow through a combustion tube maintained at about 800 C. The chlorine is converted to chloride and oxychlorides whidi then flow into a titration cell where they react with the silver ions in the titration cell. The silver ions thus consumed are coulometrically replaced. The total current required to replace the silver ions is a measure of the chlorine present in the injected samples. 

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