Field analysis free chlorine in water samples by a smartphone-based colorimetric device with improved sensitivity and accuracy

Abstract

It is highly desirable to regularly monitor the concentration of free chlorine in water samples because residual free chlorine can greatly affect the health of human and the growth of aquatic baby animals. Visual colorimetry is a cost-effective method to monitor the concentration of residue chlorine in water. To reduce the errors from estimating the hue by naked eyes and to enhance the sensitivity, we propose a smartphone-based portable colorimetric device with long-path and self-calibration ability. The key idea relies on a flow colorimetric tube with the illumination in empty tube or at a low absorption wavelength as the internal references to correct the baseline drift due to light source intensity decay. The self-focusing ability in the round-bottom colorimetric tube is helpful to simplify the design of the portable device. The absorbance measured by proposed device obeyes the Lambert-Beer law in the range of 0–1. By using N,N‑diethyl‑p‑phenylenediamine as the colorimetric regent, the proposed method demonstrates a promising result for the determination of free chlorine with the linear range of 0.8–14 μM and the limit of detection of 0.23 μM. This simple colorimetric device offers the advantages of cost effectiveness, ease of implementation, portability, sensitivity and reliability for field analysis.