RESUMO
A chemically modified electrode (CME) was prepared and studied as a potentiometric sensor for the end-point detection in the automatic titration of vanadium(V) with EDTA. The CME was constructed with a paste prepared by mixing spectral-grade graphite powder, Nujol oil and N-2-naphthoyl-N-p-tolylhydroxamic acid (NTHA). Buffer systems, pH effects and the concentration range were studied. Interference ions were separated by applying a liquid-liquid extraction procedure. The CME did not require any special conditioning before using. The electrode was constructed with very inexpensive materials and was easily made. It could be continuously used, at least two months without removing the paste. Automatic potentiometric titration curves were obtained for V(V) within 5 x 10(-5) to 2 x 10(-3)M with acceptable accuracy and precision. The developed method was applied to V(V) determination in alloys for hip prosthesis.
RESUMO
Bader indicated as the most convenient approaches for the determination of an element by atomic absorption spectrometry the (1) continuous variation of standard at constant total volume, and (2) continuous variation of the unknown analyte at constant total volume. Considering the relevance of the ease of atomization, Bader's statement were put to the test in the determination of copper, nickel, and chromiun in nodular iron by use of analysis of variance (ANOVA). The results presented here lead to the conclusion that Bader's modes (1) and (2) are not equivalent for all cases.