Computerized flow potentiometric stripping analysis with nafion-modified carbon fibre electrodes

Five to ten carbon fibres (10-μm diameter) are mounted perpendicularly to the flow direction in polyethylene tubes (0.8 mm inner diameter) and modified simultaneously by sucking five 10-μl portions of Nation dissolved in ethanol through the flow electrodes; after each portion, air is sucked through the tubes for some minutes. The modified electrodes can be used for several hundred electrolysis/stripping cycles in solutions containing albumin or Triton X-100. Analysis of a urine reference sample shows that zinc(II), cadmium(II) and lead(II) can be determined after acidification and electrolysis for 5, 35 and 100 s, respectively. For the determination of lead(II), 2 M hydrochloric acid is used as stripping medium but for the two other elements the sample itself is used. The electrochemically available fraction of the trace elements can be assessed by analyzing unacidified samples.