What is the difference between colorimetric and amperometric chlorine analysers?

Document ID

Document ID CO199

Published Date

Published Date 27/02/2019
Question
What is the difference between colorimetric and amperometric chlorine analysers?
Summary
Brief overview of the difference between colorimetric and amperometric chlorine analysers
Answer
Chlorine can be measured colorimetrically using the N,N-diethyl-p-phenylenediamine (DPD) chemistry.  Chlorine oxidises DPD to produce a magenta coloured dye.  The intensity of the magenta colour is directly proportional to the concentration of chlorine in the sample.  The colour is determined photometrically by shining a specific wavelength of light through the coloured sample and measuring the amount of light absorbed.
  
Chlorine may also be measured amperometrically.  Amperometry is an electrochemical technique that measures the change in electrical current resulting from chemical reactions taking place at the electrodes as a function of the analyte concentration.  A typical amperometric sensor consists of two dissimilar electrodes – an anode and a cathode.  In an amperometric chlorine measurement the sensor measures the reduction of chlorine at the cathode and the oxidation of the anode.