Combining C4D and MS as a dual detection approach for capillary electrophoresis

The hyphenation of two detectors in combination with separation techniques is a powerful tool to enhance the analytical information. In this work, we present for the first time the coupling of two important detectors for capillary electrophoresis (CE), namely capacitively coupled contactless conductivity detection ((CD)-D-4) and electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). The elaborated experimental protocol took into account the requirements of separation aspects and the compatibility with both detectors. ESI-TOFMS requires background electrolytes (BGE) containing only volatile components such as ammonium acetate or formate. These, however, exhibit a rather high conductivity, which is disadvantageous for (CD)-D-4. Thus, the selection of the BGE in an appropriate concentration was undertaken for the determination of various phenolic compounds serving as a model system. The chosen BGE was a 10 mu M ammonium acetate/ammonia buffer with a pH of 9. This BGE was a compromise concerning the detection performance of both detectors. The LODs for m-cresol, m-and p-nitrophenol, and 2,4-dinitrophenol were 3.1 mu M ((CD)-D-4), 0.8 mu M (MS), 0.8 mu M (MS), and 1.5 mu M (MS), respectively. Moreover, the overall separation efficiency was excellent illustrating that detector-induced band broadening can be neglected in the CE-(CD)-D-4/MS system. The analytical characteristics for the determination of phenolic compounds show the suitability of this dual detection approach and demonstrate the complementary use of (CD)-D-4 and MS detection.