Mobile-platform based colorimeter for monitoring chlorine concentration in water

Cost-effective monitoring concentration of residue chlorine in water can be simply accomplished via colorimetry where the selected indicating chemical material reacts with the chlorine in water to change its color. To suppress errors from reading the color level by naked eyes and from fluctuation of environmental illumination, this paper proposes a mobile-platform based colorimeter embedded with a self-referencing analysis for converting the color level of water to its corresponding chlorine concentration. The key idea relies on a two-dimensional (2D) color analysis in a portable closed chamber. Specifically, our 2D color analysis with self referencing is performed via the arrangement of both the reference material and the glass bottle in such a way that they both fit in the field of view of the mobile-device's camera. In this way, one color image inherently contains two image regions, one from the reference material and another from the glass bottle. Consequently, a specific color ratio from these two image regions is used for specifically converting the water color inside the glass bottle into its corresponding chlorine concentration. By using a chemical reaction between o-tolidine solution and chlorine dissolved in water and a smart mobile phone, the demonstration shows a very promising result in determining 0.06-2.0 ppm chlorine concentration in water. Other key features include cost effectiveness, compactness, portability, and ease of implementation.