The determination of average molecular weights or particle sizes for polydispersed systems

✍ Scribed by Elmer O. Kraemer

• Publisher: Elsevier Science
• Year: 1941
• Tongue: English
• Weight: 919 KB
• Volume: 231
• Category: Article
• ISSN: 0016-0032
• DOI: 10.1016/s0016-0032(41)90354-x

✦ Synopsis

With the exception of certain well-defined, crystallizable proteins and some synthetic products prepared under quite special conditions (3), macromolecular substances are commonly non-homogeneous in molecular weight. Fine powders and colloidally dispersed materialare also typically polydispersed. The only generally applicable methods of determining the degree of heterogeneity of such materials without actually effecting a separation of the material into fractions depend upon sedimentation analysis. For the very finely divided dispersions and, particularly, for macromolecular substances, such analysis requires the application of the ultracentrifuge. Under the most favorable conditions, fractionation (e.g., by precipitation or solution methods) is relatively ineffective as well as laborious, and the results from the ultracentrifugal analysis of fractionated samples demonstrate that their degree of heterogeneity is quite pronounced (6, p. 353; 13, p. 437).

Owing to the highly specialized character of ultracentrifuge technic, the determination of an average molecular (Note--The Franklin Institute is not responsible for the statements and opinions advanced by contributors in the Joum~aL.