Background-current subtraction in voltammetric detection for flow-injection analysis

A new approach for background-current subtraction for flow-injection systems using potential-scanning voltammetric detection is described. The method is based on recording voltamperograms while the sample and carrier solutions flow through the cell, and taking the difference as the net response for the sample. Background currents due to hydrogen evolution, oxygen reduction, solvent oxidation or surface processes are thus compensated, and detection limits at submicromolar levels can be obtained. The compensation for oxygen reduction current means that samples do not need to be deaerated. The method has been evaluated for reproducibility, concentration dependence, detection limit, etc. A flow-cell with a stationary disk electrode, a 200-mul sample volume, and rapid differential pulse scanning are used. At a flow-rate of 0.3 ml min about 15 samples can be assayed per hour. Chlorpromazine, phenol, acetaminophen, norepinephrine, lead, cadmium, bismuth and zinc were used as test species.