Electrophoretic mobility by electric field modulated forced Rayleigh scattering

By effecting the forced Rayleigh scattering measurements under an electric field with charged molecules that are either photochromic by themselves or labeled with photochromic dyes, we show here the electrophoretic mobilities as well as translational diffusion coefficients of such molecules can be determined under the identical conditions. To demonstrate how the technique works, we have chosen a photochromic azophenol dye dissolved in aqueous solutions at pH 6.9 and 10.7, and bovine serum albumin (BSA), labeled with an azobenzene moiety, at different pHs. For the labeled BSA the isoelectric point is determined as pH 4.5-4.7 from the observed pH profile of the mobility which is in accord with pH 4.7 reported in the literature.