The technique of self-beat or homodyne spectroscopy has been applied to the determination of the translational diffusion constant of human plasma low-density lipoproteins (LDL). Both power spectrum and autocorrelation methods give equivalent results, but with conventional equipment the power spectrum measurement takes on the order of hours while autocorrelation is accomplished in minutes. The effects of concentration of LDL, scattering angle of the light pH of the solution and buffer concentration were investigated. The diffusion constant obtained, D25,w = 2.14 ± 0.09 × 10-7 cm2/sec, was in good general accord with conventional measures. The equivalent spherical diameter, obtained from the Stokes-Einstein relationship, 229 ± 10 Å was within a broad band of values given by other techniques.
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