Application of Graphene as a Sorbent for Simultaneous Preconcentration and Determination of Trace Amounts of Cobalt and Nickel in Environmental Water and Vegetable Samples

A new method using a column packed with graphene as adsorbent was developed for the preconcentration of trace amounts of cobalt (Co) and nickel (Ni) prior to their determinations by flame atomic absorption spectrometry. Several factors influencing the extraction efficiency of Co and Ni and their subsequent determinations, such as pH, amounts of the chelating agent, flow rates of sample and eluent solution, eluent type and its volume, breakthrough volume, and adsorption capacity were established. Under the optimum conditions, the calibration graphs were linear in the range of 4.0-200.0 mu g L-1 and 5.0-200.0 mu g L-1 with detection limits of 0.3614 mu g L-1 and 0.51 mu g L-1 for Co and Ni, respectively. Good relative standard deviations for ten determinations of 100.0 mu g L-1 of Co and Ni were 3.2 and 3.6%, respectively. The results for determination of Co and Ni in tap water, river water, sea water, vegetable and spiked samples have demonstrated the accuracy and applicability of the proposed method. To validate the proposed method, three certified reference materials of environment water (GSBZ 50030-94 and GSB 07-1186-2000) and tomato leaf (GSBZ 51001-94) were analyzed, and the determined values were in good agreement with the certified values.