Determination of copper total and speciation in food samples by flame atomic absorption spectrometry in association with solid-phase extraction with bamboo (Bambusa vulgaris) fiber loaded with bathocuproine

A bamboo fiber mini-column impregnated with bathocuproine is proposed as an off-line pre-concentration system for determination of copper speciation in food samples using flame atomic absorption spectrometry (FAAS). Sampling flow rate, elution flow rate, pH and buffer concentration were evaluated for their importance in the solid-phase extraction using a 24 full factorial design and were all found to be significant. Afterward, a Doehlert matrix was used to optimize the pre-concentration process. The experimental conditions established with this design were: 8.0 mL min− 1 sampling flow rate, 10.0 mL min− 1 elution flow rate and 0.02 mol L− 1 buffer at pH 5.5. This system allowed the determination of copper with a limit of detection (LOD) of 0.5 μg L− 1, a limit of quantification (LOQ) of 1.66 μg L− 1 and a precision expressed as relative standard deviation (RSD) of 2.70 and 2.79% for copper concentrations of 5.0 and 20 μg L− 1, respectively. A pre-concentration factor of 33 was achieved using a 50.0-mL sample volume. The accuracy was confirmed by analysis of a certified reference material (NIST SRM 1573a Tomato Leaves). Spike/recovery tests were performed with results ranging from 93 to 100%. The developed method was applied to determine copper in corn flour, cassava root flour, oregano leaves and cumin. In addition, a speciation strategy was used for wine samples, in which free copper was evaluated in 40.00-mL aliquots of undigested samples and total copper assessed in samples digested before the pre-concentration step.