The Effect of Amino Acids in the Aqueous Phase on the Extraction of Metal Ions with PC-88A

Abstract

The effect of amino acids in the aqueous phase on the extraction of divalent metal ions with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC-88A) was studied in order to evaluate the utility of amino acids as masking agents. The extraction of Cu(II) and Ni(II) significantly decreases in the presence of the amino acids examined, while that of Mn(II) and Cd(II) were unaffected. Extraction of Co(II) decreased only when histidine (His) was added. The extraction of Cu(II) and Co(II) using PC-88A in the presence of histidine derivatives were compared, in order to clarify the masking effect of each functional group in His. As the extraction of Co(II) significantly decreases only in the presence of His and histidine methyl ester (His-OMe), the imidazole group and the amino group are dominant for the complexation with Co(II), but the carboxyl group is not involved. In the presence of His, Mn(II) is selectively extracted using PC-88A from Cu(II) through the masking effect of Cu(II). The extraction reaction of Cu(II) with PC-88A in the presence of His was confirmed by slope analysis.