Reversed-phase capillary electrochromatography of aloins and related constituents of aloe

The separation of some anthrone-C-glucosyl constituents of aloe was carried out by isocratic capillary electrochromatography using a 50 μm l.D. column packed with 3 μm ODS silica gel. In comparison to HPLC mode, CEC resolution of aloins was obtained in a very short time with a high selectivity factor. The influence of mobile phase parameters (pH and ionic strength of the buffer, acetonitrile amount in the eluent etc.) on the retention of aloins was examined in order to improve the separation conditions and to study the retention mechanism. Efficiency was found to increase with decreasing the EOF up to a reduced plate height of about 2 at a reduced linear velocity of 0.3 mm s−1. This effect was ascribed to the fact that, under the buffer conditions used (pH 8), aloins are partially anionically charged, with a consequent low mass transfer between the mobile and stationary phases. However, resolution remains almost the same in a wide pH range permitting baseline separations of aloins in short analysis times. Since aloins are known to undergo fast degradation reaction dependent on pH, a kinetic study was also carried out. The method was extended to the analysis of aloins in food and cosmetic products.