Smartphone colorimetric detection of calcium and magnesium in water samples using a flow injection system

Add time:08/11/2019    Source:sciencedirect.com

Water hardness has implications for both human health and industry. The main components that make water hard are calcium and magnesium. The magnesium in hard water may provide a moderate health benefit, but calcium can cause serious problems in industrial processes. This paper presents a rapid-response, reliable and convenient device developed to measure calcium and magnesium ion concentrations continuously in water samples by using a smartphone analysis of colorness change. The ion detection is based on phase extraction equilibria in a specific ion-exchange substance membrane that contains an ionophore (selectively binding to specific ions), a chromoionophore (a lipophilic pH indicator), an ionic salt (a cation exchanger), a polymer (PVC) and a plasticizer. The device is built on a PDMS fluidic layer with six parallel detection chambers that allows the water samples to flow through at a specific rate to these chambers. An Android smartphone App was developed to acquire the color images after the ions exchange across the membrane, and the analysis of target ion concentration can be realized by the pre-loaded calibration curves. The results show that the colorimetric sensor is capable of determining Ca2+ concentration in an acetate buffer solution (pH = 5.3) and total hardness in a Tris-HCl buffer solution (pH = 7.2), covering the range of normal water hardness (from soft to very hard). The measurements on real samples were analyzed by both Image J and the App and were compared with results from a commercial hardness kit and inductively coupled plasma mass spectrometry (ICP-MS), demonstrating the accuracy and precision of our colorimetric sensor compared to a commercial sensor. This cost-effective device and automatic analytical smartphone app can be combined easily as a ready-to-go sensor for monitoring Ca2+ and Mg2+ continuously and simultaneously, which is convenient for use in resource-limited areas.

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