Hydrophobicity induced graphene oxide based dispersive micro solid phase extraction of strontium from seawater and groundwater prior to GFAAS determination

A novel graphene oxide (GO) mediated dispersive micro solid phase extraction method (D mu-SPE) is developed for the extraction of strontium (Sr) from seawater and groundwater. This method involves the quantitative sorption of Sr2+ ions from seawater onto the negatively charged surface of GO through electrostatic interactions. Notably, Sr was extracted directly from seawater without altering the inherent composition of the sample. After the sorption of Sr, the excess charge on GO was neutralized by the addition of an electrolyte, KCl. Following charge neutralization, attractive forces between discrete pi-electron networks of GO nano-sheets dominate and induce coagulation of GO, forming bulky GO aggregates with partial hydrophobicity. These aggregates were easily extracted into a small organic phase, CCl4, resulting in the separation and pre-concentration of Sr. The Sr present in the organic phase was back-extracted into dilute nitric acid and quantified using graphite furnace atomic absorption spectrometry (GFAAS). Under optimized conditions, a pre-concentration factor of 100, a limit of detection of 0.004 ng mL-1 for 50 mL seawater and recoveries ranging from 88% to 100% at concentrations of 0.2-2 ng mL-1 were achieved. The developed method was successfully applied to tap water, groundwater and seawater matrices.