Separation of acidic and neutral compounds by strong anion-exchange capillary electrochromatography dynamically modified with sodium dodecylsulfate

Summary Acidic and neutral compounds have been separated by strong anion-exchange capillary electrochromatography (SAXCEC) dynamically modified by addition of sodium dodecylsulfate (SDS). It was found that separation of neutral solutes by SAXCEC without addition of SDS is difficult because of the weak interaction of the solutes with the hydrophilic packing surface. The hydrophobicity of the packing surface increases on addition of SDS to the mobile phase, however, and the capacity of separating neutral solutes increases. Acidic solutes are retained, mainly because of the ion-exchange properties of this system. The influence of mobile phase composition, e.g. SDS concentration, ionic strength, and organic modifier fraction, on the retention of acidic and neutral solutes was investigated. Three acids and five neutral solutes were separated in only 5 min under optimized conditions, because the direction of the strong electroosmotic flow (EOF) was the same as that of electrophoretic migration of the acids under the conditions used. The repeatability of this system in terms of migration time relative standard deviation (RSD) is good—less than 0.48% for 10 consecutive runs of all the solutes tested. Column efficiencies for acids were > 125000 plates m⁻¹; those for neutral solutes varied from 25000 to 100000 plates m⁻¹.