Graphene-Based Preconcentration System Prior to Energy Dispersive X-Ray Fluorescence Spectrometric Determination of Co, Ni, and Cu Ions in Wine Samples

A combination of dispersive micro solid-phase extraction (DMSPE), based on graphene as a solid sorbent, with energy dispersive X-ray fluorescence spectrometry (EDXRF) is proposed for preconcentration and determination of Co(II), Ni(II), and Cu(II) ions in wine samples. In the developed procedure, cupferron complexes of metal ions are adsorbed on graphene dispersed in aqueous samples. After the adsorption process, aqueous samples are passed through a membrane filter with the use of filtration assembly, and then loaded filters are directly measured using EDXRF. In order to obtain high recovery of the metal ions, various analytical parameters influencing sorption were optimized, such as pH, amount of graphene, Triton X-100 and cupferron, sample volume, and sorption time. Under optimal conditions, the calibration plots cover the 2 to 100 ng mL(-1) range for Co(II) and Ni(II), and 2 to 150 ng mL(-1) for Cu(II). The detection limits of 0.08, 0.08, and 0.07 ng mL(-1) for Co(II), Ni(II), and Cu(II) were obtained using 50 mL sample volume and 200 mu g of graphene. The precision (at a 20 ng mL(-1) level for n = 10) is lower than 3.5 %. The proposed method was successfully applied to determination of Co, Ni, and Cu in wine samples.