Chitosan-modified cotton thread for the preconcentration and colorimetric trace determination of Co(II) Suarez, Willian Toito Franco, Methewa O.K. Capitán Vallvey, Luis Fermín Erenas Rodríguez, Miguel María µTAD Thread-based microfluidic device Digital image analysis Cobalt determination In this work we propose a thread-based microfluidic device (μTAD) for the preconcentration and colorimetric determination of Co(II) in water using a digital image. The reaction is based on complexation of Co(II) by 4-(2- pyridylazo) resorcinol (PAR), which changes the detection zone from yellow to red. PAR is immobilized in a chitosan membrane to retain the complex in the detection zone. The designed μTAD makes it possible to pre- concentrate and determine cobalt between 25 and 600 µg·L−1 with a relative standard deviation of 4% (n = 5), and a detection limit of 6.5 µg·L−1. The device permits an enhancement factor of 11 by combining the use of a chitosan retention membrane and a sample volume of 50 µL. Recovery experiments were performed in tap water to evaluate the accuracy of the method, and the results obtained compared to a reference method presents an error no higher than 5.7% 2020-07-02T06:03:46Z 2020-07-02T06:03:46Z 2020-06-08 journal article Microchemical Journal 158 (2020) 105137 http://hdl.handle.net/10481/62815 https://doi.org/10.1016/j.microc.2020.105137 https://doi.org/10.5281/zenodo.3906816 eng http://creativecommons.org/licenses/by-nc-nd/3.0/es/ open access Atribución-NoComercial-SinDerivadas 3.0 España Elsevier