Viscosity measurements of methanol–water and acetonitrile–water mixtures at pressures up to 3500 bar using a novel capillary time-of-flight viscometer

A new type of viscometer based on the Poiseuille flow principle has been developed that is capable of measuring solution viscosities at ultrahigh pressures. The capillary time-of-flight (CTOF) viscometer has been used to measure the viscosity of methanol–water and acetonitrile–water mixtures in decade volume% increments from atmospheric pressure to 3500 bar (50,000 psi), at 25 °C. This instrument works by utilizing a relatively small pressure drop (∼200 bar) across a capillary which has both inlet and outlet pressurized so that the average column pressure can be significantly elevated (up to 3500 bar). Measurements from the CTOF viscometer match high-pressure viscosity data collected previously using falling-body viscometers of the Bridgman design. This manuscript serves to bring viscosity data at ultrahigh pressures for the two most common liquid chromatographic mobile phases into the chromatographic literature.