Physical fractionation methods ultracentrifugation

Painstaking attempts to identify the size of the infectious unit have in the past been necessitated for plant viruses, and also for animal viruses for which hitherto no method of assay for single virus particles has materialized. These include chemical fractionation, physical fractionation by means of separation cells in the ultracentrifuge and electrophoresis apparatus, and inactivation of the virus (Lauffer, 181,182,184,299). Because of electron microscopy and the excellent linearity of the plaque count, these methods have not proved necessary with the bacteriophages. 

Various technologies have been used to measure plasma lipids and lipoproteins and lipoprotein subfractions, including enzymatic, immunochemical, and chemical precipitation reagents, and physical methods, such as ultracentrifugation, electrophoresis, column chromatography, and others. Such methods have been reviewed extensively. As mentioned earlier, however, the cholesterol content of any particular lipoprotein class can vaiy somewhat from individual to individual. Moreover, although different methods of lipoprotein separation may produce similar lipoprotein fractions, they usually do not produce identical fractions, giving rise to systematic biases between methods that purport to measure the same component. The present discussion focuses primarily on methods and procedures commonly used in clinical practice for lipid and lipoprotein measurements. 

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