Problems encountered during the application of anodic stripping voltammetry (a.s.v.) to the analysis of complex samples include the inadequacy of the sample solution as a medium for the stripping step, poor resolution of stripping peaks, and interferences resulting from the presence of macro constituents. Whenever possible, a solution is sought by choosing an appropriate medium for dissolving the sample or by introducing a separation step. Many workers prefer using some form of electrochemical separation (e.g. refs. 1-6). Although the method of medium exchange has been found a useful adjunct to anodic stripping 4-6.8, the following difficulties resulting from it cannot be disregarded.
During electrode transfer, following the prc-clectrolysis step, a little of the original sample solution adhering to the electrode is cotransferred into the stripping cell, and conversely, returning the electrode to the sample solution contaminates the latter with stripping medium.
During the transfer step, a break of the electrical circuit between the electrode and the reference electrode occurs, accompanied by the partial re-oxidation of metals (from the amalgam drop into the solution film enveloping it; this chemical oxidation may be caused either by substances present in the solution film and/or by atmospheric oxygen); 10 ~o losses have been reported in the case of tin 4. The transfer step is a cumbersome operation, often leading to the inadvertent shearing off the drop (whenever this occurs, complete repetition of the analysis is required).
The flow cell described in the present work was designed to overcome these difficulties 7.
EXPERIMENTAL
A. Flow cell construction