Nano-sized anion-exchangers as a stationary phase in capillary electrochromatography for separation and on-line concentration of carboxylic acids

Abstract

Nano-sized anion-exchangers (NSAE) are promising materials in electrophoretic separation methods due to their high ion-exchange capacity, large surface-to-volume ratios, high adhesion to the quartz surface and pH-independent positive charge. In current research we describe a simple approach for NSAE synthesis, which includes two-step grinding of macroanionite followed by centrifugation. The synthesized stable aqueous suspension of NSAE particles was applied as physically adsorbed modifier of fused-silica capillary walls for CEC separation of carboxylic acids. We proposed fast and simple approach to formation of NSAE-based stationary phase on the internal fused-silica surface, which included 15 min rinsing of the capillary with diluted water suspension of NSAE. Formed physically-adsorbed coating turned out to be extremely stable in a wide range of pH (from 2 to 10). NSAE modified capillaries provided high separation efficiency (N = 148-732 *10³ t.p./m) and selectivity (R_s = 1.2-5.7) of carboxylic acids. Simultaneous application of NSAE-modified capillaries with various on-line concentration techniques (such as field amplified sample stacking and field amplified sample injection) provided both low detection limits (up to 1-3 ng/mL) and high separation selectivity of carboxylic acids. It was useful for their quantitative determination in wines samples. Physically-adsorbed coatings based on NSAE exhibit higher selectivity and lower detection limits compared to commonly used dynamic modifier of fused-silica capillary walls - cetyltrimethylammonium bromide. NSAE-based coatings do not require equilibrium sustaining to maintain the surface coverage. It makes them appropriate for CE-MS application.

Keywords: Analysis of wine; Capillary electrochromatography; Carboxylic acids; Nano-sized anion-exchanger; Physically-adsorbed coating.