Multivariate optimization of a spectrophotometric method for copper determination in Brazilian sugar-cane spirits using the Doehlert design

This present work reports a multivariate optimization of a spectrophotometric method for copper determination in sugar-cane spirits, exploring the reaction of Cu(II) with phenylfluorone (PF) in the presence of cetylpyridinium chloride (CPC) and Triton X-100. The optimization strategy was based on the application of a two-level full factorial design for the screening of significant variables followed by a Doehlert design to determine the optimum conditions. The highest sensitivity was achieved when the pH was 8.0 and the PF and TX-100 concentrations were 6.2 × 10− 5 and 1.0 × 10− 2 mol L− 1, respectively. The optimized method presented a limit of detection of 3.4 μg L− 1 and a limit of quantification of 11 μg L− 1 and was applied in the determination of Cu in 17 samples. The obtained results were compared with those obtained by ICP OES and no statistical difference between the methods was observed.