VOLTAMMETRIC DETERMINATION OF SURFACE-ACTIVE COMPOUNDS AT AU AND PT ULTRAMICROELECTRODES IN FLOWING SOLUTIONS

A new detection method was developed that takes advantage of changes i n cyclic voltammograms (recorded with either a platinum or a gold ultr amicroelectrode) caused by the adsorption, of inorganic and organic mo lecules. These changes may include reduction or oxidation of the adsor bate, inhibition of oxygen adsorption, inhibition of hydrogen adsorpti on, and also changes in the charging current. The detection is carried out in a stripping mode after the accumulation of analyte on the elec trode surface for 50-1000 ms. Typical scan rates are between 10 and 10 00 V/s. Removal of oxygen from the solutions studied is not required. Electrochemical conditioning of the working electrode is sufficient to insure a stable response for a period of several hours. For strongly adsorbing molecules the linear dynamic range extends over two orders o f magnitude from about 10(-7) M to 10(-5) M with the relative standard deviation for replicate determinations lower than 5%. The smallest di scernable signal is associated with about 0.1% surface coverage, which corresponds to the adsorption of about 10(-18) mol of analyte on a ul tramicroelectrode 5 mu m in radius.