Application of Nonaqueous Capillary Electrophoresis to the Separation of Long-Chain Surfactants

Abstract

The potential of nonaqueous capillary electrophoresis (CE) for the separation of hydrophobic solutes has been examined for a series of alkanesulfonates (C2−C16 ), alkyl sulfates (C8−C18), and linear alkyl benzenesulfonates. Sample loss and band broadening observed in aqueous CE separations was not observed in nonaqueous systems. Changes in separation selectivity induced by solvation and ion pair effects were examined. Separation selectivity was affected by changes in solvation and by a change from protic (methanol) to aprotic conditions (addition of acetonitrile). The addition of alkali metal ion caused changes in migration time via ion pairing but had only small effects on separation selectivity. However, the adjustment of the hydrophobicity of the electrolyte counterion was effective for separation optimization. The analytical features of these nonaqueous systems and applications to samples of shampoo, liquid detergent, and laundry detergents were also briefly examined. Alkanesulfonates and alkyl sulfates were separated in 0.01 mol/L sodium p-toluenesulfonate and 0.005 mol/L p-toluenesulfonic acid in methanol and in methanol/acetonitrile mixtures with indirect UV detection at 214 nm. Linear alkyl benzenesulfonates were separated in methanol and methanol/acetonitrile mixtures with tetramethylammonium as a counterion and direct detection at 214 nm.