The separation of metal ions by solvent-assisted dispersive solid phase extraction involves prior formation of a complex with sufficient hydrophobicity interacting and adsorbing with the fine particles of the sorbent. pH plays a unique role inmetal–PAN chelate formation and its subsequent extraction because the
existing form of metal ions and PAN is pH dependent. The effect
of pH on the extraction efficiency of Co(II) was evaluated in the pH
range of 1–10. The results shown in Fig. 5 indicate that the
complex of Co–PAN had a relatively wide range of solution acidity.
When the pH of the solution increased, the extraction recovery
increased in the pH range of 1–4 correspondingly. In the range of
pH 4–9, extraction recovery remained constant and the stronger
alkalescency induced a decrease in extraction recovery. Competition between protons and metal species could thus explain the weak extraction recovery in acid medium.On further increase in
pH, extraction recovery decreased probably due to the formation
of cobalt hydroxide. Hereby, a pH range from 4 to 9 could be
selected as the optimal condition in further experiments. A pH
value of 6.0 was chosen for further experiments and acetate/acetic
acid buffer was chosen for pH adjustment