Determination of Cobalt in Food and Water Samples by Ultrasound-assisted Surfactant-enhanced Emulsification Microextraction and Graphite Furnace Atomic Absorption Spectrometry

A novel method based on ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) has been developed for the preconcentration of cobalt prior to its determination by graphite furnace atomic absorption spectrometry. In the UASEME technique, chloroform was used as the extraction solvent, sodium dodecyl sulfate was adopted as emulsifier, and ultrasound was applied to assist emulsification. There is no need of using organic dispersive solvent which is typically required in conventional dispersive liquid–liquid microextraction method. Several parameters that affect the extraction efficiency, such as the kind and volume of the extraction solvent, the type and concentration of the surfactant, pH of sample solution, concentration of the chelating agent, and extraction time and temperature were investigated and optimized. Under the optimal conditions, the linearity of calibration curve was in the range of 0.1–5 ng mL−1 with a correlation coefficient (R2) of 0.9992. An enrichment factor of 58 was achieved with a sample volume of 5.0 mL. The detection limit of this method for Co was 15.6 ng L−1, and the relative standard deviation (RSD) was 4.3 % at 1.0 ng mL−1 concentration level of Co. The accuracy of the developed method was evaluated by analysis of the certified reference materials GBW07605 tea leaf and GBW10015 spinach. The method was successfully applied to determine trace cobalt in food and water samples with satisfactory results.