An absorption cell for microfluidic chemical analysis made from tinted or coloured polymers, for example polymethylmethacrylate (PMMA), in which microfluidic channels are cut. Light is coupled into the absorption cell via two windows (typically 200 um thick) that are retained at either end of the channel. Absorption is measured using a light source, such as a light emitting diode (LED) and a photodiode butted against the windows. Spurious scattered and/or reflected light is absorbed by the coloured polymer over the length of the measurement cell, while very little light loss occurs at the coupling windows.