<p>A method to improve the detection sensitivity and accuracy of paper-based microfluidic chips is proposed. By simply reconfiguring the detection cell without using complex equipment, the relative magnitudes of the evaporation rates at different positions of the detection pool were altered, which can direct the migration and enrichment of chromogenic molecules on a paper microfluidic chip. The chromatic intensity enhancement and distribution uniformity have been confirmed. As a demonstration, quantitative determination of iron and chromium in water were carried out. With the directed enrichment, the naked eye discernible concentration was decreased to 0.25-0.16 times the original level. This general method can be applied in most paper chip based studies, especially for the quantification of target material under resource limited settings.</p> Graphical Abstract <p></p>