A differential viscosity detector for use in miniaturized chemical separation systems

We present a micromachined differential viscosity detector suitable for integration into an on-chip hydrodynamic chromatography system. The general design, however, is applicable to any liquid chromatography system that is used for separation of polymers. The micromachined part of the detector consists of a fluidic Wheatstone bridge and a low hydraulic capacitance pressure sensor of which the pressure sensing is based on optical detection of a membrane deflection. The stand-alone sensor shows a resolution in specific viscosity of 3/spl times/10/sup -3/, in which specific viscosity is defined as the increase in viscosity by a sample, relative to the baseline viscosity of a solvent.