Mobile device-based self-referencing colorimeter for monitoring chlorine concentration in water

Realizing that a widely-used and cost-effective method in determining the amount of chlorine in water is colorimetry, this paper proposes and experimentally demonstrates how a mobile device embedded with a digital camera can be used to function as a colorimeter for the analysis of chlorine concentration. Our key idea is to arrange both the reference material and the small transparent bottle such that they both fit in the field of view of the camera. In this way, one color image automatically contains two image regions, one from the reference material and another from the small transparent bottle, leading to a self-referencing configuration. Consequently, a specific color ratio from these two image regions is used for specifically converting the water color inside the small transparent bottle into its corresponding chlorine concentration. By using a chemical reaction between potassium–starch solution and chlorine dissolved in water, experimental demonstration shows a very promising result in determining 0.3–1.0 ppm chlorine concentration with <7% measurement errors. Other key features include low cost, portability, ease of implementation, and possibly large distribution via application markets.