Cost-effective smartphone-based method for low range chemical oxygen demand analysis *

Aiming the decentralization of monitoring policies and to facilitate the work of researchers, mainly in developing countries, the present method deals with the explanation of a simple and rapid protocol for chemical oxygen demand (COD) analysis through the use of digital smartphone devices coupled with a camera and a free app available for Android operating system that recog-nizes HSV (hue, saturation, value). The calibration of the method is done based on the theoretical values of potassium hydrogen phthalate for a proper and reliable build of the calibration curve by using the smartphone-based technique and the digested samples of COD. The coefficient of determination (R 2 ) attained a value upper than 0.99, providing a high confidence levels, and the method achieved 97% of average accuracy in samples with COD values ranging from 0 to 150 mg L -1. Finally, the procedure here presented can be a great support for scientific laboratories and monitoring policies, once it can efficiently substitute expensive spectrophotometers and can im-prove and ensure the sustainable management of water sanitation, which is one of the sustainable goals proposed by the United Nations. & BULL; COD measurements, based on the use of a simple smartphone with a camera, can be a promis-ing way for environmental analysis when spectrophotometers are not available, such as de-centralized approaches. & BULL; The use of smartphone protocol is a novel initiative to fulfill sustainable development goal 6 on clean water and sanitation. & BULL; The smartphone is capable to read the difference of HSV values efficiently and can substitute the use of expensive spectrophotometers.