Figure 2. Effect of DFID concentration on copper ion extraction by CPE. Conditions: 15 mL of 0.2 µ g mL -1 Cu 2+ ion at pH 5.7±0.3, 0.06% (w/v) Triton X-114, different concentration of DFID, 0.5% (w/v) NaCl, eluting solution 0.5 mL of 0.50 M HNO