Syringe-to-syringe-dispersive liquid–phase microextraction combined with flame atomic absorption spectrometry for pre-concentration and determination of cobalt with the aid of experimental design

<p>A rapid and selective technique has been proposed for the extraction, pre-concentration and determination of trace amounts of cobalt in water and pharmaceutical samples by syringe-to-syringe-dispersive liquid–phase microextraction (SS-DLPME) combined with flame atomic absorption spectrometry (FAAS). In the developed method, 1-nitroso-2-naphthol was used as a selective complexing agent and 1-octanol was selected as the extraction solvent. Factors such as pH of the sample solution, concentration of the complexing agent, volume of the extraction solvent, number of injections and centrifugation time affecting the extraction efficiency were screened using a Plackett–Burman design (PBD) and optimised using a Box–Behnken design (BBD). Under optimum conditions, a dynamic linear range of 2.5–650 μg L⁻¹ with the coefficient of determination r² = 0.997 was obtained. The resultant limit of detection (LOD) was 0.68 μg L⁻¹, whereas the enrichment factor (EF), intraday precision and inter-day precision were 281, 1.43% and 1.93%, respectively. This method was used successfully for pre-concentration and determination of the analyte in environmental water and drug samples.</p