In the present paper a procedure for preconcentration and determination of vanadium and copper in seawater using inductively coupled plasma optical emission spectrometry (ICP OES) is proposed, which is based on solid-phase extraction of vanadium (IV), vanadium (V) and copper (II) ions as 1-(2-pyridylazo)-2-naphthol (PAN) complexes by active carbon. The optimization process was carried out using two-level full factorials and Doehlert matrix designs. Four variables (PAN mass, pH, active carbon mass and shaking time) were regarded as factors in the optimization. Results of the two-level full factorial design 2 with 16 runs for vanadium extraction, based on the variance analysis 4 (ANOVA), demonstrated that the factors pH and active carbon mass, besides the interaction (pH=active carbon mass), are statistically significant. For copper, the ANOVA revealed that the factors PAN mass, pH and active carbon mass and the interactions (PAN mass=pH) and (pH=active carbon mass) are statistically significant. Doehlert designs were applied in order to determine the optimum conditions for extraction. The procedure proposed allowed the determination of vanadium and copper with detection limits (3syS) of 73 and 94 ng l , respectively. The y1 precision, calculated as relative standard deviation (R.S.D.), was 1.22 and 1.37% for 12.50 mg l of vanadium and y1 copper, respectively. The preconcentration factor was 80. The recovery achieved for determination of vanadium and copper in the presence of several cations demonstrated that this procedure improved the selectivity required for seawater analysis. The procedure was applied to the determination of vanadium and copper in seawater samples collected in Salvador City, Brazil. Results showed good agreement with other data reported in the literature.

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In this research work, the effect of different concentrations of copper, iron, lead, zinc and nickel ions on the tendency for gum formation in gasohol fuel is investigated. For that purpose, a gasohol sample has been doped with these five metals ions at concentration levels of 0.25, 1.0, 2.0 and 3.0 μg ml − 1. Washed gum content tests have been carried out using ASTM D 381 on samples stored for 7, 14, and 28 days. The results show that gum formation is strongly affected by Cu and Fe, with a much weaker effect from Ni and Zn, and an almost negligible effect from Pb. A variance analysis (ANOVA) of the experimental results shows that an increase in metal concentration strongly increases the rate of gum formation for all metal ions investigated, particularly Cu and Fe, while an increase in storage time has only a much weaker effect, being negligible for Zn.