Ligandless dispersive solid phase extraction of cobalt ion using magnetic graphene oxide as an adsorbent followed by its determination with electrothermal atomic absorption spectrometry

Abstract

ABSTRACT Ligandless dispersive solid phase extraction technique was used for preconcentration of cobalt ion (Co2+) followed by its determination using electrothermal atomic absorption spectrometry (ETAAS). Graphene oxide (GO) was synthesised from graphite by the Hummer method and chemically magnetised to synthesise of the magnetic graphene oxide (MGO). The synthesised MGO was characterised by the Fourier transform-infrared spectrophotometry (FT-IR), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) and then used as an adsorbent for solid phase extraction of Co2+. The main parameters affecting the extraction recovery of Co2+ including pH of sample solution, amounts of adsorbent, extraction time and type and concentration of desorption solvent were investigated and optimised. The calibration curve was plotted in the range of 0.08–1.2 µg L−1 Co2+ with a correlation coefficient of 0.9987. The intra-day precision based on six replicate analysis of 0.2 µg L−1 Co2+ was 3.8% and the limit of detection (LOD) was 0.023 µg L−1 Co2+ (n = 5). Also, the adsorption isotherms and adsorption kinetics were investigated and based on the obtained results, the adsorption of Co2+ onto the MGO nanocomposite followed by both Langmuir and Freundlich isotherms with a maximum adsorption capacity of 114.9 mg g−1 Co2+. The results of kinetic models also show that the adsorption of Co2+ followed by the pseudo second order kinetic model. The accuracy of the proposed method was successfully checked by the analysis of two certified reference materials including certified reference material-trace metals in drinking water (CRM-TMDW) and spinach leaves 1570a samples (Student t-test with 95% confidence limit, n = 5). Finally, the proposed rapid and efficient solid phase extraction technique was used for the determination of trace levels of Co2+ in the human saliva, urine and different real samples.