ABSTRACT
Colorimetric detectors analyze the color change resulting from the reaction between the targeted chemical and reagents. This technique has been used in many different applications. Good examples of colorimetric detection are the use of litmus paper (or pH paper) to test the pH value of a solution, and the common water test kit used to analyze chlorine concentration in swimming pools. The litmus paper test is an example of a direct reading: the color is formed by the reaction with reagents impregnated on the paper, and no further manipulation occurs. As soon as the litmus paper is wetted with the solution, the pH of that solution causes the impregnated reagents to change color according to the solution’s pH value. Chlorine content testing of swimming pool water is based on the addition of reagent o-Tolidine to the solution to form the visible orange color that can be used for quantitative determination. Color intensity is related to the relative concentration of chlorine in the water. Colorimetric detectors using different methods are all easy to use, low cost, and provide relatively fast responses.
