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

Acidic and neutral compounds have been separated by strong anion-exchange c apillary electrochromatography (SAXCEC) dynamically modified by addition of sodium dodecylsulfate (SDS). It was found that separation of neutral solut es by SAXCEC without addition of SDS is difficult because of the weak inter action of the solutes with the hydrophilic packing surface. The hydrophobic ity 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 thi s 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 direc tion of the strong electroosmotic flow (EOF) was the some as that of electr ophoretic migration of the acids under the conditions used. The repeatabili ty of this system in terms of migration time relative standard deviation (R SD) is good - less than 0.48% for 10 consecutive runs of oil the solutes te sted. Column efficiencies for acids were > 125000 plates m(-1); those for n eutral solutes varied from 25 000 to 100 000 plates m(-1).