An on-line solid phase extraction system using polyurethane foam for the spectrophotometric determination of nickel in silicates and alloys

The present paper describes the use of a solid phase extraction system using a polyurethane foam (PUF) minicolumn, in order to separate nickel from interferences due to other elements and determine it by flow injection analysis with spectrophotometric detection. Separation is based on the retention of thiocyanate complexes of interferent ions in the PUF minicolumn. Nickel does not form complex with thiocyanate and pass through the minicolumn and then it can be determined by using 4-(2-pyridylazo)-resorcinol (PAR) as chromogenic reagent. So, parameters such as thiocyanate concentration and pH effects on the separation efficiency, sorption capacity of the polyurethane foam minicolumn, influence of the flow rates, PAR concentration, pH effect on the chromogenic reaction, minicolumn regeneration, analytical features and others were investigated. The results demonstrated that nickel (at concentration of 0.5 mg/ml) can be quantitatively separated from iron and copper (200 mg/ml), zinc and cobalt (100 mg/ml) by using a minicolumn containing 0.125 g of polyurethane foam. Nickel can be determined with great selectivity and sensitivity and the procedure was applied for nickel determination in brass, bronze, steel and rock certified reference materials. The results showed satisfactory accuracy and precision. The limit of detection was 77 ng/ml and the RSD was 2.63%. A dynamic range from 0.25 up to 5.00 mu g/ml and a sample throughput of 24 samples per hour were achieved. (C) 1999 Published by Elsevier Science B.V.