Mobility distribution of synthetic and natural polyelectrolytes with capillary zone electrophoresis

Parameters are proposed to describe the distribution of the effective electrophoretic mobilities of various anionic polyelectrolytes such as poly(styrene-4-sulfonates) and humic substances of different origins analyzed by capillary zone electrophoresis. The first step of the data treatment is a baseline correction and conversion of the electrophoretic raw time data to effective electrophoretic mobilities (μ-scale), taking into account the electroosmotic flow. With this new μ-scaling, the electropherograms are more representative of velocity-based separation phenomena than those using migration times, and a direct comparison of electropherograms is possible. Four different average electrophoretic mobilities were defined: the number-average effective mobility (μ_n), the weight-average effective mobility (μ_w), the z-average effective mobility (μ_z), and the peak-average electrophoretic mobility (μ_p). The polydispersity of the mobility of mixtures was described by the μ_w/μ_n, μ_z/μ_w, and μ_p/μ_w ratios. These parameters were used to describe the electrophoretic mobility distributions of different fractions of restricted molecular size: those obtained by ultrafiltration from a soil humic acid at neutral pH and reference humic substances of the International Humic Substances Society at different values of pH and ionic strength. The data clearly show the influence of both molecular size and charge distribution of the analyzed mixtures on the mobility distributions.