High-temperature liquid chromatography. Part II: Determination of the viscosities of binary solvent mixtures—Implications for liquid chromatographic separations

This paper is the second in a series of consecutive publications, explaining the concept of high temperature liquid chromatography under various important aspects. The second publication deals with the determination of the viscosity of binary solvent mixtures used in reversed phase liquid chromatography in a temperature range between 25 and 250 °C. In literature, only limited data of the temperature dependent viscosities of liquid solvents or binary solvent mixtures can be found. Therefore, the viscosities of the pure solvents as well as the binary mixtures had to be determined experimentally up to 250 °C. The viscosity data were used to estimate the pressure drop in a capillary connecting a high-temperature HPLC system with a mass spectrometer. The solvent perturbation could be avoided by adjusting the diameter of the transfer capillary to the viscosity and vapour pressure of the mobile phase. The viscosity data were also used to show that a significant gain in analysis speed is theoretically feasible. This factor clearly depends on the nature of the solvent system, because for mixtures with a large viscosity maximum at ambient temperature, this effect is most pronounced.