Detection of Surface-active Compounds at Au and Pt Ultramicroelectrodes

Andrzej S. Baranski 

University of Saskatchewan, 110 Science Pl., Saskatoon S7N5C9, Canada

Abstract

In recent years in my laboratory a new detection method was developed, which takes advantage of changes in voltammograms (recorded with either Pt or Au electrodes) caused by the adsorption of inorganic and organic molecules. These changes may include reduction or oxidation of the adsorbate, inhibition of oxygen adsorption, inhibition of hydrogen adsorption and also changes in the charging current. Cyclic or square-wave voltammograms are periodically recorded (usually, 1 to 20 curves per second). The detection is carried out in a stripping mode after the accumulation of analyte on the electrode surface for 10 to 1000 ms. Typical scan rates are between 10 and 1000 V/s. Removal of oxygen from the studied solutions is unnecessary. Electrochemical conditioning of the working electrode is sufficient to ensure a stable response for a period of several hours. For strongly adsorbing molecules the linear dynamic range extends over two orders of magnitude from about 10-7 M to 10-5 M with the relative standard deviation for replicate determinations lower than 5%. The smallest discernable signal is associated with about 0.1 % surface coverage, which corresponds to the adsorption of about 10-18 mol of analyte on an electrode 5-μm in radius. The method was extensively tested under flow-injection and capillary electrophoresis conditions and HPLC. We also tested the usefulness of cyclic chronopotentiometry and the Cyclic Reciprocal Derivative Chronopotentiometry for the detection of surface-active compounds. The detection limits were similar to those obtained using square-wave voltammetry, however, the new techniques were particularly useful for end-column detection in capillary electrophoresis, because under controlled current conditions the detector response is unaffected by the offset voltage caused by the separation potential.

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Presentation: Tutorial lecture at SMCBS 2003 Workshop, by Andrzej S. Baranski
See On-line Journal of SMCBS 2003 Workshop

Submitted: 2003-09-16 04:44
Revised:   2009-06-08 12:55
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