How are small and large test articles prepared for virus quantitation services?
The test article supernatant, whether from a large or a small test article, is clarified by filtration or centrifugation, then concentrated by density gradient ultracentrifugation techniques.
The concentrated test article is then prepared by mixing a known concentration of latex spheres with the unknown number of virus particles from the test article. This mixture is mounted onto grids, negatively stained, and examined in the transmission electron microscope. Both latex spheres and virus particles are enumerated, and the concentration of virus particles in the test article is determined by using ratio formulas.
