Measurement of diffusion in gel is an essential task for pharmaceutic technology and biochemical engineering. In this work we investigate diffusion coefficients and release kinetics of colored substances loaded in polymeric thin strips, by extending a simple spectrophotometric technique from catalysis science to swellable polymer matrices. Absorbance can be a measure of the average solute concentration in the swollen gel so that the time decay of film absorbance can be a quantitative measure of the release kinetics and henceforth of the diffusion coefficient in the swollen gel. Thin film dissolution is carried out in a newly proposed microfluidic continuous flow-through device. Hydroxypropyl methylcellulose (HPMC) is used as filming polymer. Film thickness, uniformity of content and swelling time-scales are accounted for in the estimation of the effective diffusion coefficient. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.