High-throughput viscosity measurement using capillary electrophoresis instrumentation and its application to protein formulation

• Dynamic viscosity was measured using standard capillary electrophoresis equipment.
• Viscosities in the range of 5–40 mPa s were determined by the new method.
• Sample volumes were a few microliters and run times were 1–15 min.
• Viscosity data were compared to data obtained by plate/cone rheometry.
• Applicability was demonstrated by analysis of monoclonal antibody formulations.

Viscosity characterization of protein formulations is of utmost importance for the development of subcutaneously administered formulations. However, viscosity determinations are time-consuming and require large sample volumes in the range of hundreds of microliters to a few milliliters, depending on the method used. In this article, an automated, high-throughput method is described to determine dynamic viscosity of Newtonian fluids using standard capillary electrophoresis (CE) equipment. CE is an analytical method routinely used for the separation and characterization of proteins. In our set-up, the capillary is filled with the test sample, and a constant pressure is applied. A small aliquot of riboflavin is subsequently loaded into the capillary and used as a dye to monitor movement of protein samples. Migration time of the riboflavin peak moving through the filled capillary is converted to the viscosity by applying the Hagen–Poiseuille's law. The instrument is operated without using an electrical field. Repeatability, robustness, linearity, and reproducibility were demonstrated for different capillary lots and instruments, as well as for different capillary lengths and diameters. Accuracy was verified by comparing the viscosity data obtained by CE instrumentation with those obtained by plate/cone rheometry. The suitability of the method for protein formulations was demonstrated, and limitations were discussed. Typical viscosities in the range of 5–40 mPa s were reliably measured with this method. Advantages of the CE instrumentation-based method included short measurement times (1–15 min), small sample volumes (few microliters) for a capillary with a diameter of 50 μm and a length of 20.5 cm as well as potential to be suitable for high-throughput measurements.

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