Ultrasound-Assisted Deep Eutectic Solvent-Based Liquid-Liquid Microextraction for Pre-Concentration and Determination of Trace Amounts of Cobalt in Real Samples

A green microextraction method entitled ‘ultrasound-assisted deep eutectic solvent (DES)-based liquid-liquid microextraction’ was devised for the pre-concentration of cobalt in water samples, with subsequent analysis performed via atomic absorption spectroscopy. Key extraction parameters were optimized, and the method was validated using central composite design for multivariate analysis. The DES was prepared by combining DL-menthol as a hydrogen bond acceptor and dodecanoic acid as a hydrogen bond donor in a 1 : 2 mass ratio. Under optimal conditions, pH of the solution, DES volume (µL), sonication time (min), and mass ratio of DES components were achieved, respectively: 5, 200, 9, and 1 : 2. The method demonstrated excellent linearity in the concentration range of 10–2000 µg/L, with a detection limit of 3.2 µg/L, quantification limits of 10 µg/L, relative standard deviations below 1.8%, and enrichment factors up to 234. The technique was successfully applied to determine cobalt concentrations in real samples.