Experimental factors in pulsed electrochemical detection in capillary electrophoresis

• Published in: Journal of Chromatography A 1998-06, Vol.811 (1), p.181-192
• Main Authors: Wen, Jenny, Cassidy, Richard M., Baranski, Andrzej S.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Chemistry; Chromatographic methods and physical methods associated with chromatography; Exact sciences and technology; Metal cations; Other chromatographic methods
• ISSN: 0021-9673
• DOI: 10.1016/S0021-9673(98)00283-0

A number of experimental approaches that should offer improved S/ N in electrochemical detection were evaluated and compared. In addition, to evaluate and optimize the electrochemical response behavior of analytes under actual CE conditions, an on-line cyclic voltammetry (CV) system was developed. The experimental parameters examined included waveform shape, waveform frequency and various signal treatments, using a lock-in amplifier and Fourier analysis. A multiple-step pulse waveform provided the maximum S/ N enhancement [up to 10-fold relative to pulse amperometric detection (PAD)], with detection limits in the range of 2·10 −8 to 2·10 −7 mol/l. The use of the second harmonic from Fourier analysis offered the best improvement in baseline stability. Other approaches such as high pulse frequency (100 to 200 Hz), data collection over selected time windows, digital filters and average smoothing also enhanced S/ N 2- to 5-fold relative to PAD. On-line CV studies showed that the adsorption of organic electrolytes on electrode surfaces can inhibit O 2 reactions, and thus give low and stable background currents without O 2 removal. The CV studies also showed that detection of Pb 2+, Cu 2+ and Ag + affected subsequent electrode response, and that H + evolution contributed to the cathodic signals of the analytes Ni 2+, Co 2+ and Zn 2+.