Challenges in Determining Intrinsic Viscosity Under Low Ionic Strength Solution Conditions

Area of Science:

• Biochemistry
• Protein Chemistry
• Physical Chemistry

Background:

• Intrinsic viscosity is a key parameter for characterizing protein behavior in solution.
• Understanding solution conditions like pH and ionic strength is crucial for accurate viscosity measurements.
• Monoclonal antibodies (mAbs) are important biopharmaceuticals whose physical properties impact formulation and efficacy.

Purpose of the Study:

• To determine the intrinsic viscosity of monoclonal antibodies (mAbs).
• To investigate the impact of varying pH and ionic strength on mAb intrinsic viscosity.
• To assess the reliability of viscosity measurement techniques under different solution conditions.

Main Methods:

• Utilized an online viscosity detector coupled with HPLC (Viscotek®) for intrinsic viscosity determination.
• Employed the Ross and Minton equation for viscosity prediction at high protein concentrations.
• Measured bulk viscosity using a Cambridge viscometer.

Main Results:

• At 15 mM ionic strength, intrinsic viscosity of mAbs ranged from 5.6 to 6.4 mL/g, varying with pH.
• High ionic strength did not significantly affect intrinsic viscosity.
• A significant increase in intrinsic viscosity (up to 24.0 mL/g) was observed near zero mM ionic strength, indicating limitations of the single-point technique.

Conclusions:

• Intrinsic viscosity is valuable for modeling baseline viscosity but not predictive of solution non-ideality at higher concentrations.
• Experimental techniques face limitations near zero mM ionic strength due to breakdown of assumptions.
• The single-point approach yields reliable intrinsic viscosity results at 15 mM, but requires caution and data analysis near zero mM ionic strength.