Fe3O4-modified graphene oxide as a sorbent for sequential magnetic solid phase extraction and dispersive liquid phase microextraction of thallium

A combination of magnetic solid phase extraction (MSPE) and dispersive liquid phase microextraction (DLPME) was applied in a new method for preconcentration and extremely sensitive determination of thallium in aqueous samples. The first step of extraction uses a Fe3O4-graphene oxide conjugate whose surface was covalently linked to the chelator 4-methyl-2(2-pyrazinyl)-1,3-thiazole-5-carboxy acid. After completion ofMSPE, the nanoparticles were eluted with benzyl alcohol. In order to further enhance preconcentration, the benzyl alcohol phase containing the thallium chelate is used as a dispersing solvent for DLPME. After the elution, the preconcentrated thallium phase is transferred into a Rh/Pt/Pd-modified graphite tube and quantified via graphite furnace AAS. After optimization of the experimental conditions, the calibration plot is linear in the 0.015 to 4 mu g.L-1 thallium concentration range, and the detection limit (at an S/N ratio of 3) is 12 ng.L-1. An absolute detection limit of 120 fg was determined when injecting a 10 mu L volume into the graphite furnace. When using a 100 mL sample solution and 10 mu L of the extraction solvent, the enrichment factor is as large as 6500, with an overall 65% recovery if MSPE and DLPME are combined. Selectivity of the method is achieved by masking of possibly interfering ions with EDTA.