Selectivity enhancement in spectrophotometry: on-line interference suppression using polyurethane foam minicolumn for aluminum determination with Methyl Thymol Blue

A method is proposed for the determination of aluminum by flow injection spectrophotometry with Methyl Thymol Blue after separation of the interferent ions employing a polyurethane foam (PUF) minicolumn. The separation process is based on the retention of the interferents on the PUF minicolumn as thiocyanate complexes. In order to improve the performance of the system the effect of some chemical and flow variables were evaluated and under optimized conditions the system was able to determine aluminum at a concentration of 1.0 mu g mL(-1) in the presence of Fe(III) at 170 mu g mL(-1), Zn(II) at 100 mu g mL(-1) and Cu(II) and Co(II) at 50 mu g mL(-1), using a PUF minicolumn containing 200 mg of sorbent. The analytical procedure developed was successfully applied to several certified materials, including silicate materials and ores. Very good accuracy and precision was obtained. A limit of detection of 30 ng mL(-1) was achieved with RSD of 4.5% at 0.25 mu g mL(-1). A linear dynamic range from 0.25-2.0 mu g mL(-1) was observed and a sample frequency of 17 samples per hour was calculated.