Solvent Extraction for Anion Species of Polyaminocarboxylic Acids with Triocthylmethylammonium Chloride in 1,2-Dichloroethane

Abstract

The Aliquat 336 (material of ISE) dissolved in 1,2-dichloroethan solvent was used for the solvent extraction of a anion species of triethylentetramine hexa acetic acid (TTHA, H₆X), diethylenetetraminepentaaceticacid (DTPAH₅X) and cyclohexanediaminetetraacetic acid (CyDTA). The extraction behavior was examined. The extraction efficiency (%E) was indicated in the enlarge order as CyDTA > EDTA > DTPA > TTHA in the pH range from 4.0 to 12.0. The extraction constants (K_n^ex) were calculated by using consecutive dissociation constant (k_m), overall acid formation constants of polyaminocarboxylic acid. (β_n). The extraction coefficients of all partitions of the extraction constants of anion species of TTHA are indicated as follows : K₂^ex = 3.6 × 10⁻⁵, K₃^ex = 5.49 × 10⁻⁶, K₄^ex = 9.08 × 10⁻⁶, K₅^ex = 1.15 × 10⁻⁵, K₆^ex = 1.81 × 10⁻⁵. All partitions of the extraction constants of the anion species of DTPA were also obtained as follows : K₂^ex = 1.25 × 10⁻³, K₃^ex = 9.26 × 10⁻⁵, K₄^ex = 3.11×10⁻⁴, K₅^ex = 5.22 × 10⁻⁴. All partitions of the extraction constants of CyDTA are also indicated as follows : K₂^ex = 0.043, K₃^ex = 0.014, K₄^ex = 0.02. The steric rearrangement by bonding between the aminocarboxylic acid anion in ligands and the triocthylmethylammonium cation species is important in solvent extraction. It was also found that the steric existence of cycloring in CyDTA affected the extraction.