Multivariate optimization of dual-bed solid phase extraction for preconcentration of Ag, Al, As and Cr in gasoline prior to inductively coupled plasma optical emission spectrometric determination

In this work, a dual-bed resin solid phase extraction (SPE) for preconcentration of Ag, Al, As and Cr prior to their inductively coupled plasma-optical emission spectroscopy (ICP-OES) determination has been developed. Dowex 50 W-x8 and Dowex 1-x8 packed in a column were used as metal ion sorbents. The optimization of the dual-bed SPE procedure was carried out using a two level full factorial design with three central points. Under optimized conditions, the limits of detection and quantification (n = 21) ranged from 0.16 to 0.22 and 0.52 to 0.76 μg L^-1, respectively. Enrichment factors of 100, 130, 130 and 150 and relative standard deviations (n = 15) of 1.2%, 2.0%, 1.8% and 1.3% were obtained in the determination of Ag, Al, As and Cr, respectively. The validity of the proposed method was checked by applying the standard addition method and the recoveries at the 20 μg L^-1level using both inorganic and organic metal standards ranged from 95% to 99%. The proposed method presented an analytical throughput of about 18 samples per hour and was applied for the determination of metal ions in ten gasoline samples. In addition, the accuracy of the method was evaluated using microwave-assisted digestion method and the results were not significantly different (at 95% confidence level).