Application of Simplex Optimization in the Development of an On-line Preconcentration System for the Determination of Cu in Human Hair Samples Using FAAS

Background: Hair provides important information that helps medicine with an early diagnosis of physiological disorders associated with metabolic alterations of essential and toxic elements. However, some metals are present in the hair sample in very low concentrations for some analytical techniques, such as flame atomic absorption spectrometry. This work aims to develop an on-line pre-concentration system for copper determination in trace levels from hair samples. Methods: A basic simplex algorithm was applied to the optimization of the on-line preconcentration system. The system is based on the solid phase extraction of copper in a mini-column packed with Amberlite XAD-4, functionalized with 3,4-dihydroxybenzoic acid, and metal elution with hydrochloric acid solution. The optimized variables were: pH, sample flow rate and HCl concentration. Results: The developed system presents limits of detection, quantification and enrichment factor of 1.1 μg L-1, 3.7 μg L-1 and 23.8, respectively, with a pre-concentration time of 120 s. The accuracy of the method expressed as relative standard deviation was 9.4% at the concentration of 10.0 μg L-1 and 8.5% for 40.0 μg L-1. The accuracy of the method was accessed by copper determinations in real hair samples, comparing the results of two analytical techniques, and there were no significant differences between the results at 95% confidence level. Conclusion: Simplex has been shown a simple, fast and efficient optimization method in the establishment of the optimum conditions for the developed of an on-line pre-concentration system for copper determination. Validation procedures has proved that, it presents analytical characteristics to allow trace levels determination from human hair.