ORIGINAL PAPER Simple modeling of the physical sample dispersion process in rectangular meso (micro) channels with pressure-driven flows Mireia Baeza & José Luis Montesinos & Julián Alonso & Jordi Bartrolí Received: 29 August 2008 / Revised: 11 November 2008 / Accepted: 18 November 2008 / Published online: 9 December 2008 # Springer-Verlag 2008 Abstract The present paper reports the modeling and characterization of the physical sample dispersion process observed in rectangular microchannels when pressure-driven pumping is used. To explain experimental results provided by the silicon fluidic device constructed, two different mathe- matical models were tested. The first one is based on the diffusion–convection model, and the second one is based on the combination of ideal reactors. The silicon designed and constructed chip includes a microfluidic manifold with four inlet–outlet ports and a monolithically integrated optical flow cell. The microchannels, the optical flow cell, and the input– output ports were micromachined on a silicon wafer and then sealed with Pyrex glass anodically bonded. Optical windows were integrated in the chip, allowing simple absorbance– transmission measurements. Pressure-driven flows through fluidic channels were controlled via three-way solenoid valves and provided by an automatic microburette operating in aspiration mode. Experimentally obtained results demonstrate that the physical sample dispersion process can be easily modeled as a combination of a continuous stirred tank reactor and a plug-flow reactor. Keywords Hybrid system . μFIA . Modeling . Mixing . Diffusion–convection . CSTR . PFR Abbreviations μTAS micrototal analysis systems μFIA microflow injection analysis CSTR continuous stirred tank reactor PFR plug-flow reactor Introduction Miniaturization of conventional laboratory instrumentation has been at the center of research and development over the past 15 years [1]. Since Manz et al. [2] introduced the concept of micrototal analysis systems (μTAS) in 1990, remarkable efforts have been made towards the research and development of microsystems for fluid management [3–7]. In the last years, great efforts have been directed to the development of miniaturized active and passive elements to achieve automated fluid management within these structures. Unfortunately, only a reduced number of these key compo- nents are commercially available. This fact is the limiting factor in the development of μTAS and its application to solve real analytical problems. Meanwhile, the scaling down of total analysis systems using available components at the mesoscale is the most simple and reasonable option to design portable analytical instruments. Anal Bioanal Chem (2009) 393:1233–1243 DOI 10.1007/s00216-008-2532-8 M. Baeza (*) : J. Alonso : J. Bartrolí Grup de Sensors i Biosensors, Departament de Química, Facultat de Ciències, Edifici C-Nord, Universitat Autònoma de Barcelona, 08193 Bellaterra (Cerdanyola del Vallès), Spain e-mail: mariadelmar.baeza@uab.cat J. L. Montesinos Departament d’Enginyeria Química, Escola Tècnica Superior d’Enginyeria, Universitat Autònoma de Barcelona, 08193 Bellaterra (Cerdanyola del Vallès), Spain