Indirect Fluorescence of Amines in Capillary Electrophoresis, Using Cresyl Violet

Abstract

This paper describes the analysis of amines under acidic conditions by capillary electrophoresis (CE) in conjunction with indirect laser‐induced fluorescence (ILIF), using cresyl violet as a probe. In the system, a small pinhole (0.2 mm) and an interference filter (589 nm) were used to confine the light and to minimize the plasma interference from a He–Ne laser, respectively, improving the baseline stability. Adding lithium ions to the background electrolytes (BGEs) is effective to achieve narrower peak profiles, leading to better resolution. The analysis of six amines by CE–ILIF using an aqueous solution, pH 3.5, containing 5.0% methanol, 0.1 mM sulfuric acid, 0.1 mM cresyl violet, and 0.3 mM lithium was complete in 5 min, with the limits of detection (LOD) on the level of µM. Negative peak profiles are for amines with greater electrophoretic mobility than that of lithium ions, but positive peaks for the slower ones. To further improve the sensitivity, on‐line concentration based on pH junction has been demonstrated. When injecting the sample prepared in a solution of 0.2 mM sulfuric acid, pH 3.3, at 15 kV for 60 s, and conducting the separation using the above‐mentioned condition, the sensitivity improvements are greater than 10‐fold compared to that injecting at 15 kV for 5 s. With the advantages of rapidity, sensitivity, and low cost, this method has proven potential for the analysis of trace amines in biological samples.