Smartphone-based simultaneous pH and nitrite colorimetric determination for paper microfluidic devices López Ruiz, Nuria Curto, Vincenzo Erenas Rodríguez, Miguel María Benito Lopez, Fernando Diamond, Dermot Capitán Vallvey, Luis Fermín In this work, an Android application for measurement of nitrite concentration and pH determination in combination with a low-cost paper-based microfluidic device is presented. The application uses seven sensing areas, containing the corresponding immobilized reagents, to produce selective color changes when a sample solution is placed in the sampling area. Under controlled conditions of light, using the flash of the smartphone as a light source, the image captured with the built-in camera is processed using a customized algorithm for multidetection of the colored sensing areas. The developed imageprocessing allows reducing the influence of the light source and the positioning of the microfluidic device in the picture. Then, the H (hue) and S (saturation) coordinates of the HSV color space are extracted and related to pH and nitrite concentration, respectively. A complete characterization of the sensing elements has been carried out as well as a full description of the image analysis for detection. The results show good use of a mobile phone as an analytical instrument. For the pH, the resolution obtained is 0.04 units of pH, 0.09 of accuracy, and a mean squared error of 0.167. With regard to nitrite, 0.51% at 4.0 mg L−1 of resolution and 0.52 mg L−1 as the limit of detection was achieved. 2022-03-11T13:04:59Z 2022-03-11T13:04:59Z 2014 journal article Anal. Chem. 2014, 86, 19, 9554–9562 http://hdl.handle.net/10481/73337 dx.doi.org/10.1021/ac5019205 eng open access Royal Society of Chemistry