Potential of long chain ionic liquids for on-line sample concentration techniques: Application to micelle to solvent stacking

The performance of micelle to solvent stacking (MSS) in capillary zone electrophoresis (CZE) was improved for anionic analytes using the long chain ionic liquid type cationic surfactant 1-dodecyl-3-methylimidazolium tetrafluoroborate (C₁₂-MIM-BF₄). The peak heights and corrected peak areas of the test profens and herbicides were enhanced up to 59 and 110-fold, respectively when compared to typical injection. These were up to 10 times better compared to the surfactant cetyltrimethyl ammonium bromide as MSS carrier. This performance was attributed to the properties of C₁₂-MIM-BF₄. MSS requires micelles in the sample for transport of bound analytes to a stacking boundary that contains an organic solvent for effective electrophoretic mobility reversal. The ionic liquid micelles provided better analyte transport properties that resulted from its hydrophobic and pi–pi interaction capabilities. The good solubility of the ionic liquid in high percentages of organic solvent also facilitated a more effective reversal of mobility. The LODs obtained for the test analytes were from 0.06 to 0.12 μg/mL. The linearity R² values in terms of peak height and corrected area were ≥0.99. The interday repeatabilities (%RSD, n = 10,) were 0.5–2.2% for retention time, 1.9–4.7% for corrected areas and 4.1–6.4% for peak heights.