Chlorine Detection With Pulsed Amperometric Detection

Abstract

A method of measuring oxidant in an aqueous composition using an electrode system comprising a membrane permeable to a species to be measured, a cathode situated behind the membrane, and an electrolyte between the membrane and cathode. Embodiments of the method may include contacting the membrane and an anode with the aqueous composition, and measuring the current between the cathode and anode in response to a first voltage applied between them. A pulse of a second voltage may be applied between the cathode and the anode, where the second voltage is different from the first voltage. Apparatus and computer program products which may perform the method, are also provided.

What is claimed is: 
     
         1 . An apparatus for measuring free chlorine in an aqueous composition, comprising:
 an electrode system comprising an electrolyte chamber defined at least in part by a hypochlorous permeable membrane and a cathode situated behind the membrane;   a power supply configured to apply a first voltage and a pulse of a second voltage between the cathode and an anode, where the second voltage is different from the first voltage; and   a current detector which measures the current between the cathode and the anode in response to the first voltage.   
     
     
         2 . An apparatus according to  claim 1  wherein the cathode is gold. 
     
     
         3 . An apparatus according to  claim 1  wherein the power supply is configured to apply repeatedly the pulse of the second voltage as a series of pulses. 
     
     
         4 . An apparatus according to  claim 1  wherein the second voltage comprises a voltage which is initially more negative than the first voltage. 
     
     
         5 . An apparatus according to  claim 3  wherein the second voltage comprises a voltage which is initially more negative than −100 mV. 
     
     
         6 . An apparatus according to  claim 1  wherein the second voltage comprises a voltage which is initially more positive than the first voltage. 
     
     
         7 . An apparatus according to  claim 2  wherein the power supply is configured to apply the second voltage at a frequency of no more than 10 Hz. 
     
     
         8 . An apparatus according to  claim 1  wherein a T 90  in response to the first voltage is less than 70% of the T 90  measured under the same conditions but without applying the pulse of the second voltage, the T90 being defined as the time needed to reach 90% of a steady state signal after a change in a concentration from 0 ppm to 1.1 ppm of the free chlorine. 
     
     
         9 . An apparatus according to  claim 1  wherein the power supply is configured to apply a sequence of alternating first and second voltages. 
     
     
         10 . An apparatus according to  claim 9  wherein the sequence of alternating first and second voltages is applied at a frequency of no more than 10 Hz.