The prolonged exposure to fluorides results in the development of several diseases, from dental fluorosis to crippling deformities of the spine and major joints. The population exposed to high fluoride concentration is located in developing countries where the assurance of water quality is difficult to perform. Addressing this challenge, an open-source system for the determination of fluoride in natural water was developed using the equilibrium between the red Fe–SCN complex and the colorless Fe–F. The reaction develops in cotton substrates to reduce the manipulation of liquid reagents and reduce the errors by nontrained operators. The system was optimized by image analysis and implemented in an open-source Arduino-based device and data was acquired through the serial port of a cell phone, which is also used as a power source, avoiding the use of a battery and reducing production costs. The device showed a detection limit of 0.7 mg L–1 and a linear range of up to 8 mg L–1. This extended detection limit makes the device useful for the application in regions where the fluoride concentration in drinking water is far higher than the United Nations limit (1.5 mg L–1), e.g., the United Republic of Tanzania, where the upper limit of F– was extended to 4 mg L–1 or in USA, where the Environmental Protection Agency established the Maximum Contaminant Level of F– in drinking water at 4 mg L–1. The method was tested with natural waters from the Arusha region in the northeast of Tanzania and validated against the results from ion chromatography showing a good correlation. The developed device exhibits chemical stability of 5 days, allowing it to be manufactured and distributed in local areas and, also, modified according to the requirements of the water composition due to Industry 4.0 concepts used in the design.
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acssensors.0c02273.
*Original abstract online at https://pubs.acs.org/doi/10.1021/acssensors.0c02273