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CE with sequential light‐emitting diode‐induced fluorescence and electro‐chemiluminescence detections for the determination of amino acids and alkaloids

This paper describes the determination of alkaloids and amino acids (AAs) using CE in conjunction with sequential light‐emitting diode‐induced fluorescence (LEDIF) and electrochemiluminescence (ECL) detections. In the CE‐LEDIF‐ECL system, the ECL detector was located in the outlet of the capillary, while the LEDIF detector was positioned 12 cm from the outlet. Naphthalene‐2,3‐dicarboxaldehyde (NDA) was used to form fluorescent AA–NDA derivatives from AAs possessing primary amino groups, while Ru(bpy)32+ was used to obtain ECL signals for analytes having secondary and tertiary amino groups. In the presence of poly(ethylene oxide), we accomplished the CE‐LEDIF‐ECL separation of a mixture of 12 AA–NDA derivatives, anabasine, nicotine, and proline within 11 min. This low‐cost CE‐LEDIF‐ECL system allows the analysis of these AA–NDA derivatives and alkaloids at concentrations in the ranges of 49 nM–0.2 μM and 0.66–4.7 μM, respectively. We applied our CE‐LEDIF‐ECL system to the analysis of a urine sample and also to tobacco extracts. We obtained good qualitative and quantitative results when using this method with these analytes: the RSDs were below 3.0 and 2.8%, respectively. This CE‐LEDIF‐ECL system provides the advantages of high efficiency, speed, and sensitivity for the analysis of analytes possessing amino groups.