Numerical solutions of the Lamm equation. III. Velocity centrifugation

✍ Scribed by Menachem Dishon; George H. Weiss; David A. Yphantis

• Publisher: Wiley (John Wiley & Sons)
• Year: 1967
• Tongue: English
• Weight: 638 KB
• Volume: 5
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1967.360050804

✦ Synopsis

We have generated solutions to the Lamm equation to examine the effects of concentration dependence on velocity experiments. Two forms of c dependence are considered: s/so = 1kc and S / S O = (I + kc)-'. Features of these solutions are discussed. The magnitude of the errors resulting from the usual procedure of measuring the rate of movement of schlieren maxima or of the position a t which the concentration is one half the plateau value have been examined. These errors are usually negligible after sufficient centrifugation time. The errors in using the half-plateau concentration are less than those using the movement of the peak. We have also examined a technique due to Fujita for determining D from boundary spreading when s/so = 1kc.

This method is satisfactory when s/so is actually of this form, or under certain limitations when s/so = ( 1 + kc)-'. Creeth has shown that under certain conditions the concentration gradient curve remains virtually unchanged in shape after separating from the meniscus.

The condition for such a steady state is that kco be sufficiently large. Numerical confirmation of this method is presented in the final section. When this occurs it is possible to estimate s / D from the data.