title: The dependence of the electrophoretic mobility of small organic ions on ionic strength and complex formation.
abstract: The ionic strength dependence of the electrophoretic mobility of small organic anions with valencies up to -3 is investigated in this study. Provided the anions are not too aspherical, it is argued that shape and charge distribution have little influence on mobility. To a good approximation, the electrophoretic mobility of a small particle should be equal to that of a model sphere with the same hydrodynamic radius and same net charge. For small ions, the relaxation effect (distortion of the ion atmosphere from equilibrium due to external electric and flow fields) is significant even for monovalent ions. Alternative procedures of accounting for the relaxation effect are examined. In order to account for the ionic strength dependence of a specific set of nonaromatic and aromatic anions in aqueous solution, it is necessary to include complex formation between the anion with species in the BGE. A number of possible complexes are considered. When the BGE is Tris-acetate, the most important of these involves the complex formed between anion and Tris, the principle cation in the BGE. When the BGE is sodium borate, an anion-anion (borate) complex appears to be important, at least when the organic anion is monovalent. An algorithm is developed to analyze the ionic strength dependence of the electrophoretic mobility. This algorithm is applied to two sets of organic anions from two independent research groups.
authors.affiliation: Department of Chemistry, Georgia State University, Atlanta, GA 30302-4098, USA. sallison@gsu.edu
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Allison
authors.forename: Hongxia
authors.initials: H
authors.lastname: Pei
authors.forename: Saerom
authors.initials: S
authors.lastname: Baek
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Brown
authors.forename: Min Y
authors.initials: MY
authors.lastname: Lee
authors.forename: Vu
authors.initials: V
authors.lastname: Nguyen
authors.forename: Umar T
authors.initials: UT
authors.lastname: Twahir
authors.forename: Hengfu
authors.initials: H
authors.lastname: Wu
mesh_terms: D000085:Acetates / Q000737:chemistry; D000465:Algorithms; D000838:Anions / Q000737:chemistry; D001881:Borates / Q000737:chemistry; D004573:Electrolytes / Q000737:chemistry*; D019075:Electrophoresis, Capillary / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D008970:Molecular Weight; D009930:Organic Chemicals / Q000737:chemistry*; D009994:Osmolar Concentration; D010316:Particle Size; D012459:Salicylates / Q000737:chemistry; D013816:Thermodynamics; D014233:Tricarboxylic Acids / Q000737:chemistry
chemical_list: D000085:Acetates; D000838:Anions; D001881:Borates; D004573:Electrolytes; D009930:Organic Chemicals; D012459:Salicylates; D014233:Tricarboxylic Acids; C010634:sodium borate; C069849:trimesic acid