What is the difference between colorimetric and amperometric chlorine analyzers?

Document ID

Document ID CO199

Version

Version 1.0

Status

Status Published

Published Date

Published Date 04/09/2018
Question
What is the difference between colorimetric and amperometric chlorine analyzers?
Summary
Brief overview of the difference between colorimetric and amperometric chlorine analyzers
Answer
Chlorine can be measured colorimetrically using the N,N-diethyl-p-phenylenediamine (DPD) chemistry.  Chlorine oxidizes DPD to produce a magenta colored dye.  The intensity of the magenta color is directly proportional to the concentration of chlorine in the sample.  The color is determined photometrically by shining a specific wavelength of light through the colored 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 chorine measurement the sensor measures the reduction of chlorine at the cathode and the oxidation of the anode.