A homogeneous liquid-liquid extraction method based on pH dependent phase separation phenomena in the water-acetic acid-chloroform ternary component system

Abstract

A new homogeneous liquid-liquid extraction method based on pH dependent phase separation phenomena was established using the water-acetic acid-chloroform ternary solvent system. The optimum conditions for each component at 25°C were determined as follows, i.e., in order to obtain the water-immiscible small phase (approximately 40 μl) of chloroform, sodium hydroxide solution ([NaOH] T= 1.03 mol dm-3) was added to a homogeneous aqueous solution which consisted of water, chloroform (230 μl: 0.66 vol.%) and acetic acid (2 cm3: 5.71 vol%), where the final total volume was 35 cm3. A concentration factor of 10000 (i.e. 35 cm3→3.5 μl) was achieved by adjusting the initial volume of chloroform. The compound α,β,γ,δ-tetrakis(4-pyridyl)porphine (TPyP) was selected as a model solute. In the extraction of TPyP, when the ratio (Vw/Vo) of the volume in the water phase (Vw) to that in the sedimented phase (Vo) was 700, the distribution ratio (D) and extraction percentage (E) were 5600 and 88.9%, respectively. The calibration graph was linear and passed through the origin over the concentration range of 10-9 mol dm-3 to 10-7mol dm-3. The detection limit (3σ) reached 1.67 × 10-10 mol dm-3, and the relative standard deviation was 2.17% for 5 × 10-8 mol dm-3 (5 determinations). Satisfactory results for the determination of iron in tap water was obtained by combination of this extraction method and the 8-quinolinol colorimetric method |iron(III)-8-quinolinol chelate: D = 1230, E = 63.7%, at Vw/Vo=700|. © 1994, The Japan Society for Analytical Chemistry. All rights reserved.