A turbidimetric method to determine visual appearance of protein solutions.

An instrumental method to analyze protein solutions for visual appearance is described which is based on spectrophotometric comparison to reference suspensions with varying degrees of turbidity. This method provides a useful substitute for visual inspection of uniform opalescent suspensions in that it is more convenient and less time-consuming and has the potential to be more reproducible, accurate and objective. Established categories of opalescence based on European Pharmacopoeial reference suspensions were determined using turbidity measured as optical density in the 340-360 nm range. A comparison of the mean optical density of a protein sample to those of the reference suspensions allowed a more reproducible assignment of the sample's category of opalescence than that of visual inspection.