FIELD AMPLIFIED SAMPLE INJECTION IN HIGH-PERFORMANCE CAPILLARY ELECTROPHORESIS

A simple on-column concentration technique in high-performance capillary electrophoresis (HPCE) is reported. In conventional electro-injection in HPCE, samples are prepared in a buffer solution which has the same concentration as that inside the capillary column. The amount of ions injected into the column under this condition is limited. By preparing samples in a low-conductivity solution, e.g., water, and injecting the sample solution electroosmotically into the column, one can achieve a field enhancement at the injection point. The amount of ions injected will then be proportional to this enhancement factor. However, if one samples by switching the column directly from the high-conductivity buffer reservoir to the low-conductivity sample solution, the buffer boundary at the end of the column is disturbed and the electric field at the injection point might not be amplified properly. By injecting a short plug of water before sample introduction, one can provide a high electric field strength from the beginning of the injection. Several hundred-fold enhancements in the amount of injection were confirmed experimentally.