A graphene-based cobalt nanocomposite (G/Co3O4) was synthesized and used for the first time as an effective adsorbent for the preconcentration of the Pb(II), Cu(II) and Fe(III) ions in environmental water and food samples prior to flame atomic absorption detection. The properties of the graphene, Co3O4 and G/Co3O4 nanocomposite were characterized by X-ray diffraction, scanning electron microscopy, and thermal gravimetric analysis. The experimental parameters affecting the solid phase extraction efficiency for analyte ions including sample pH, adsorption and elution contact time, volume and concentration of eluting reagent, sample volume and interfering ions were examined. The adsorption capacity of the G/Co3O4 composite was found to be 58, 77 and 78 mg g(-1) for Pb(II), Cu(II) and Fe(III), respectively. The quantitative elution of the adsorbed metal ions was carried out by 2 mL of 2 mol L-1 HNO3. The preconcentration factor of the method was 175. The limit of detection was found to be <= 0.81 mu g L-1. The accuracy of the method was studied by analyzing certified reference material (RM 8704 Buffalo River Sediment, SRM 1568a Rice Flour and SPS-WW1 Batch 111-Wastewater) and spiked real samples. The method was applied for the separation and preconcentration of trace metal ions in tap water, wastewater, dam water, well water, kiwi and wheat samples.