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Capillary electrophoresis of small solutes in linear polymer solutions: Relation between ionic mobility, diffusion coefficient and viscosity
Author(s) -
Shimizu Tamo,
Kenndler Ernst
Publication year - 1999
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/(sici)1522-2683(19991101)20:17<3364::aid-elps3364>3.0.co;2-x
Subject(s) - viscosity , diffusion , polymer , chemistry , ethylene glycol , ionic strength , polyethylene glycol , reduced viscosity , analytical chemistry (journal) , thermodynamics , intrinsic viscosity , aqueous solution , relative viscosity , peg ratio , ionic bonding , chromatography , ion , organic chemistry , physics , finance , economics
Electrophoretic mobilities, μ, and diffusion coefficients, D , of a small ion (molecular weight 579) were determined in dependence on the viscosity, η, of aqueous buffer solutions containing ethylene glycol, or polyethylene glycol (PEG) with average molecular weights of 400, 20 000, 100 000 or 2 000 000, respectively, as additives. The values for μ and D are inversely proportional to the viscosity for the solutions with small‐sized additives (ethylene glycol and PEG400), in accordance to Walden's rule. In contrast, for the longest polymers the mobilities and the diffusion coefficients approximate the values observed for pure water, and are nearly independent of the viscosity. This result agrees with the model of fractional free volume and the obstruction theory. For solutions with equal viscosity, three ranges can be differentiated for μ and D in relation to the size of the additive: for small additives, on the one hand, and the long‐chained polymers, on the other hand, the values for μ and D are nearly independent of the size of the additive. In contrast, a pronounced increase of μ and D is found with increasing poly mer size in the molecular weight range between 20 000 and 100 000. The ratio μ/ D , occurring in a number of expressions for the plate height contributions, exhibits a remarkably small change over the entire polymer size and viscosity range (between 1 and 7 cP) under consideration. Consequently, the separation efficiency, expressed by the plate number, is found to be nearly constant, and is independent of viscosity.