Application of factorial design in optimization of preconcentration procedure for copper determination in soft drink by flame atomic absorption spectrometry

In the present paper, a procedure for preconcentration and determination of copper in soft drink using flame atomic absorption spectrometry (FAAS) is proposed, which is based on solid-phase extraction of copper(II) ions as its ion pair of 1,10-phenanthroline complexes with the anionic surfactant sodium dodecil sulphate (SDS), by Amberlite XAD-2 resin. The optimization process was carried out using 24-1 factorial and 22 factorial with a center point designs. Four variables (XAD-2 mass, copper mass, sample flow rate and elution flow rate) were regarded as factors in the optimization. Student's t-test on the results of the 24-1 factorial design with eight runs for copper extraction, demonstrated that the factors XAD-2 mass and sample flow rate in the levels studied are statistically significant. The 22 factorial with a center point design was applied in order to determine the optimum conditions for extraction. The procedure proposed allowed the determination of copper with detection limits (3α/S) of 3.9 μg l−1. The precision, calculated as relative standard deviation (R.S.D.) was 1.8% for 20.0 μg l−1 of copper. The preconcentration factor was 100. The robustness of this procedure is demonstrated by the recovery achieved for determination of copper in the presence of several cations. This procedure was applied to the determination of copper in soft drink samples collected in Campinas, SP, Brazil.