Determination of Protein Content in Alhydrogel^®-Based Vaccines by O-Phthalaldehyde Assay

The quantification of antigens adsorbed to aluminum-based adjuvants (alum) typically involves a method that first extracts antigen from the alum followed by the quantification of the antigen available in the extract. Extraction procedures often result in less than 100 % desorption of the antigen from the alum adjuvant and may alter the conformation of the antigen, reducing the accuracy of the subsequent method used for quantification. There is no generic method available for directly assessing the protein content when formulated on alum. Here we offer a method that can directly quantify protein adsorbed to Alhydrogel^® using a simple fluorescence assay that is highly accurate and reproducible for Alhydrogel^® formulations containing 25-400 μg/mL of antigen.