According to our knowledge, the detection limits obtained are the best reported in the literature. The methodology was successfully used in metal determinations in actual leaf samples.

A disposable screen-printed electrode was designed and evaluated for direct detection of chromium(VI) in batch and flow analysis. The carbon screen-printed electrode was modified with a graphite-epoxy composite. The optimal graphite-epoxy matrix contains 37.5% graphite powder, 12.5% diphenylcarbohydrazide, a selective compound for chromium(VI), and 50% epoxy resin. The principal analytical parameters of the potentiometric response in batch and flow analysis were optimized and calculated. The screen-printed sensor exhibits a response time of 20 +/- 1 s. In flow analysis, the analytical frequency of sampling is 70 injections per hour using 0.1 M NaNO(3) solution at pH 3 as the carrier, a flow rate of 2.5 mL.min(-1), and an injection sample volume of 0.50 mL. The sensor shows potentiometric responses that are very selective for chromium(VI) ions and optimal detection limits in both static mode (2.1 x 10(-7) M) and online analysis (9.4 x 10(-7) M). The disposable potentiometric sensor was employed to determine toxicity levels of chromium(VI) in mineral, tap, and river waters by flow-injection potentiometry and batch potentiometry. Chromium(VI) determination was also carried out with successful results in leachates from municipal solid waste landfills.

No abstract

A disposable dual screen-printed electrode was designed and evaluated for the direct and simultaneous determination of chromium(VI) and chromium(III) in batch and flow analysis. For this purpose a carbon screen-printed bielectrode was modified with a graphite-epoxy composite which contains diphenylcarbazide and another graphiteepoxy composite prepared with di(2-hydroxyphenylimino)ethane. The principal analytical parameters of the potentiometric responses in batch and flow analysis were optimized and calculated. The bisensor shows optimal detection limits of 7.7 10 À7 M and 7.9 10 À6 M in static mode, and 9.0 10 À7 M and 1.2 10 À5 M in flow analysis for hexavalent and trivalent chromium, respectively. This potentiometric device was employed with successful results to determine both chromium species in leachates from municipal solid waste landfills.

No abstract