Graduate Thesis Or Dissertation
 

A continuous amperometric monitor for aqueous sulfite solutions using bipolar current readout

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  • A continuous amperometric monitor for aqueous sulfite solutions has been developed employing the electro-oxidation of sulfur (IV) in 0. 1 M sulfuric acid at a glassy carbon test electrode. The monitor employs a hydrodynamic flow cell, in which the solution stream enters the cell through an orifice impinging on the test electrode, and a potentiostat which gives a bipolar current readout, which is positive or negative depending on whether the sample concentration is greater than or less than a set-point concentration. A conventional reference electrode is used in this system, rather than a bipolar electrode, as has been used in some previously developed systems. The sulfur (IV) system was studied voltammetrically both with a rotating glassy carbon electrode, and with the flow cell. At a constant test electrode potential of +1. 50 volts vs. SCE it was found that the anodic limiting current was directly proportional to cell concentration of S (IV), and that the bipolar current was directly proportional to the deviation of that concentration from a set-point concentration, if the temperature and all flow rates remained constant. Significant errors were found to occur if temperature and flow rates were not held constant. In order to compensate for calibration changes caused by variations in temperature and flow rate, a pumping system involving two pumps and a mixing chamber was developed which allowed a standard addition procedure to be carried out with the flow cell. A standard addition equation was developed in which all of the instrumental parameters were eliminated, giving the concentration of a sample in terms of the concentration of a standard solution and two measurements of current. The standard addition procedure was evaluated experimentally, and was found to be effective in compensating for the calibration variations which occurred when the temperature and flow rates were changed. In order to improve the accuracy of the standard addition procedure, suggestions are made with regard to reducing the response time of the system. The merits of using the continuous monitor in the standard addition mode of operation are compared with the merits of a direct bipolar concentration readout.
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