Sample Stacking Coupled with Water-in-Oil Microemulsion Electrokinetic Chromatography for the Analysis of Inorganic Anions

For the first time, the study describes the potentialities of a powerful preconcentration technique called fieldenhanced sample injection (FESI) combined with water-in-oil microemulsion electrokinetic chromatography (W/O MEEKC) for the quantification of inorganic anions. Water-in-oil microemulsions as background electrolytes show unique selectivities of W/O MEEKC compared to the standard capillary-electrophoresis analysis of anions. The effect of a set of microemulsion parameters such as the concentration and type of the buffer solution, oil, and surfactant was attained using the separation of the test mixture. The combination of the FESI technique followed by optimized W/O MEEKC provided up to a 930-fold improvement in the detection sensitivity compared to the conventional sample injection. The potential of the developed method was demonstrated by the determination of iodide anions in hen eggs.