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.

Abstract. The present work describes the use of 2-(2-thiazolylazo)-p-cresol (TAC) as a spectrophotometric reagent for vanadium determination. TAC reacts with vanadium(IV) in the presence of ascorbic acid, forming a red complex with absorption maximum at 525 nm. The following parameters were studied: complex stability, pH effect, amount of TAC, amount of acetate buffer, HEDTA effect, order of addition of reagents and Beer's law validity. TAC can be used for vanadium determination in the pH range 4.6-6.0, with molar absorptivity of 2.11 x 104 L mole -1 cm -1 (at 525 nm). Beer's law is obeyed up to 2.0 pg mL -1. Many cation interferences can be easily eliminated by using HEDTA as a masking agent. Steel reference standards were used to test the proposed procedure and the accuracy and precision obtained were satisfactory.

O presente trabalho descreve o uso de 1-(2-thiazolylazo)-p-cresol (TAC) para separação, preconcentração e determinação de traços de ferro (ng g -1 ) em sais alcalinos usando a técnica ICP-AES. O método proposto é baseado na extração líquido-líquido do complexo formado entre o cátion ferro(III) e o 1-(2-thiazolylazo)-p-cresol (TAC). Foram estudados parâmetros tais como: quantidade de TAC, efeito de pH, influência do solvente orgânico, mineralização da fase orgânica e re-extração. Os resultados demonstraram que o complexo ferro(III)-TAC, formado na faixa de pH de 4,0 a 10,0, pode ser quantitativamente extraído de soluções salinas, usando como solvente extractor álcool isoamílico, tetracloreto de carbono, clorofórmio ou metil isobutil cetona. A solução para determinação de ferro pode ser obtida por uma re-extração usando soluções de ácido clorídrico 1 mol/L ou ácido nítrico 1 mol/L ou também por uma mineralização da fase orgânica, com uma evaporação do solvente orgânico e digestão do resíduo com ácido nítrico concentrado. O procedimento foi usado para determinação de ferro em amostras de vários sais alcalinos. A técnica da adição padrão foi aplicada e as recuperações obtidas revelaram que o procedimento proposto tem uma boa exatidão.The present paper describes the use of 1-(2-thiazolylazo)-p-cresol (TAC) for separation, preconcentration and determination of iron traces (ng g -1 ) in alkaline salts by the ICP-AES technique. The proposed method is based on the liquid-liquid extraction of the complex formed between iron(III) and 1-(2-thiazolylazo)-p-cresol (TAC). Parameters such as: TAC amount, pH effect, influence of the organic solvent on the extraction, back extraction and mineralization of the organic phase were studied. The results show that the iron(III)-TAC complex, formed in the pH range from 4.0 to 10.0, can be quantitatively extracted from saline solutions (up to 30% NaCl) using isoamyl alcohol, carbon tetrachloride, chloroform or methyl isobutyl ketone as extracting solvent. The solution for the iron determination can be obtained by a back extraction using 1 mol/L hydrochloric acid or 1 mol/L nitric acid solutions or also by mineralization of the organic phase, which was accomplished by evaporation of the organic solvent and digestion of the residue with concentrated nitric acid. The procedure was used for iron determination in several alkaline salt samples. The standard addition technique was applied and the recoveries obtained revealed that the proposed procedure has a good accuracy.

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