Figure 1: Model CM5015S Coulomter
The UIC, Inc. Sulfur Coulometer quantitatively titrates SO2 and H2S. Typical applications include the determination of total sulphur (by combustion) and the determination of SO2 and H2S (by acid evolution).
PRINCIPLES OF OPERATION
The coulometer cell is filled with a solution which initially contains a slight excess of free iodine. When SOsub>2 or other reducing substances enter the cell, iodine is consumed. The amperometric-sensing circuit detects the deficiency of iodine in the solution and causes iodine to be electrically generated at a rate proportional to the sensed deficiency. When all of the substance has been titrated, the iodine is restored to its initial concentration, and the quantity of the titration is read directly on the display in user-selectable units. Since the coulometric efficiency is 100 percent, sample calibration is not necessary. The linear range and accuracy of the coulometric technique exceeds that obtained by other detection methods.
EASE OF OPERATION
The amount of cell titrating solution used on daily basis is dependent upon the amount of sulphur in the samples analyzed. It can be changed on a daily basis, or as seldom as once every few days. The cell is ruggedly constructed and refilling the cell is a fast and simple operation. The S Coulometer is factory calibrated and does not require daily field or lab calibration. All peripherals are designed for ease of operation.
RATE AND RANGE
The range of the S Coulometer is from 0.01 micrograms to over 100 milligrams S. At its maximum rate (240 mA), the Coulometer can titrate 2,400 microgram S per minute. The proportioning circuitry allows for fast and accurate completion of the titration. The S Coulometer has an accuracy of .15% +/-2 digits for standard range.
Any substance that reduces iodine will be determined by the Coulometer. Interfering substances are removed by scrubbing systems. Titration is normally used to determine SO2 or H2S, and the titration of either one involved a 2-electron transfer, giving the same titration in terms of quantity of S.
The most desirable systems are those which quantitatively convert all S to SO2, taking advantage of the absolute determination provided by the Sulfur coulometer. Two approaches to this idea have been used:
In both of the above systems, sulphur is quantitatively converted to SO2, which is titrated by the S Coulometer, giving a direct readout.
(It is interesting to note the S Coulometer could be used to titrate H2S from hydrogenation, and the titration factor is the same as for the SO2 titration.)