Core-based hyperbranched polyethyleneimine coating in capillary electrophoresis

In capillary electrophoresis (CE), chemical and dynamic modification of a fusedsilica surface can be used to control the electroosmotic flow (EOF), to minimize the interaction of analytes with the capillary surface and to modify the selectivity. Polyvalent, core-based hyperbranched polyethyleneimine (CHPEI) polymer was utilized as either a static or dynamic coating in this study. A CHPEI-coated capillary was simply constructed in a rinsing fashion or by adding CHPEI in a running buffer. Two generations of CHPEI, CHPEI5 and CHPEI25, were investigated with the concentration ranges from 5-20% (w/v) for the static-coating method and 0.6-1.25% (w/v) for the dynamic-coating method.;In CHPEI static-coated capillaries, several parameters were studied as follows: (1) EOF as a function of buffer pH; (2) effect of coating media (NaCl solution) concentration; (3) effect of buffer concentration; and (4) stability and reproducibility of the coating. The performance of a static-coated capillary was investigated in the separation of a wide variety of compounds, such as phenols, basic amino acids, B vitamins, aniline and its derivatives. From these studies, CHPEI25 was selected as a dynamic coating. Performance of CHPEI25 dynamic-coated capillaries were investigated by varying the polymer concentration. Test analytes were B vitamins, aniline and its derivatives. Migration-time repeatability can be problematic in static-coated capillaries due to a coating depletion. Therefore, utilization of a hybrid-coating technique was proposed and examined.;Further investigation of the dynamic-coating method was undertaken with a 1.25% CHPEI25 dynamic-coated capillary and a commercial eCAP(TM) capillary from Beckman Coulter. Although primary-amine surface groups are predominant in CHPEI coating and tertiary amines are the major surface groups in eCAP(TM), the separation performance of both capillaries is comparable. For basic drugs and related compounds, as well as, with B vitamins analysis, it is evident that CHPEI25 dynamic-coated capillary provides significantly improved peak resolution under identical separation conditions compared to that in eCAP(TM).