The visual opacity of protein solutions, known as opalescence, is a phenomenon arising from molecular self-association. As a member of a group of concentration-dependent “colloidal properties”, also including high viscosity and aggregation, opalescence poses several challenges for the development of biologic drugs, particularly those intended for the high concentration formulations that are implicit in patient-centric products. Of significant concern is the relationship to the critical opalescence that accompanies phase separation.
Given the dependency of opalescence on factors such as concentration, pH, ionic strength, and temperature, it is important to incorporate measurement during the development of formulations and manufacturing unit operations in order to avoid conditions that induce phase separation. Moreover, such measurements are a valuable addition to developability screening workflows, helping to ensure that well-behaved lead candidate molecules are selected. The commercially available turbidimeters that are standard for measuring opalescence pose challenges for screening workflows because they generally require mL-scale quantities of sample.
As an alternative, we have evaluated the use of the 90o SLS channel of a microcuvette-based dynamic & static light scattering detector to enable ultra-low volume (<10 µL) opalescence measurements. These microscale nephelometric measurements afford stable performance across a broad dynamic range that covers a span of nephelometric turbidity unit (NTU) values relevant for mAb solutions. Such measurements are in good agreement with those made using a commercial turbidimeter, but with the low sample consumption required for screening paradigms. Turbidity measurements made with such an instrument are also suitable for small molecule formulations and other pharmaceutical development and QC applications.
- The importance of opalescence measurements in the development of biologic drugs
- Introduction to characterization of protein formulations by dynamic and static light scattering
- How opalescence and turbidity are measured in a microcuvette-based DLS/SLS instrument
- How ultra-low-volume opalescence characterization is implemented in screening workflows