RESUMEN
The residual free chlorine concentration is an important parameter to evaluate the potability of water and the efficiency of disinfection in the water treatment system. As a restricted range of residual free chlorine concentration at all points of the distribution network is needed to ensure efficiency and to avoid deleterious effects, fast and in situ quantification of this specie is important. This work deals with the development and validation of two procedures based on DPD (N,N-diethyl-p-phenylenediamine) and OT (ortho-tolidine, 3,3-dimethylbenzidine) for the determination of residual free chlorine in water by exploiting a flow-based microdevice built with Low Temperature Co-Fired Ceramic (LTCC) technology. The analytical signal was monitored by a smartphone camera through RGB values obtained by a free application (Color Grab®). Under optimized conditions, linear ranges within 0.6-2.5 mg/L and 0.1-2.3 mg/L were obtained for DPD and OT methods, with limits of detection and quantification of 0.023 and 0.077 mg/L (DPD) and 0.026 and 0.089 mg/L (OT). Precision expressed as RSD (2.0 mg/L free chlorine, n = 10), was 1.3 % and 0.7 %, respectively. Both procedures were successfully applied to the analysis of samples from a water treatment plant. The flow-based microdevice coupled to digital-image colorimetry is an innovative, sustainable, and cost-effective analytical tool for in-field chemical analysis.