For the separation, 100 μL sample was needed, and more than 50 × enrichment factor was achieved using up a sample volume of 5 mL. The applicability of the separation and preconcentration of Cr(VI) in complex sample matrix (seawater) was shown as well [28]. In our work, we used their optimized conditions. The carrier solution was an aqueous solution containing 0.1 mM NH4 acetate at pH 3.