HPLC spectrophotometric determination of metal-porphyrin complexes following a preconcentration method by homogeneous liquid-liquid extraction in a water/pyridine/ethyl chloroacetate ternary component system

A new homogeneous liquid-liquid extraction method based on pH-dependent phase separation phenomena was developed using a water/pyridine/ethyl chloroacetate ternary solvent system. The optimum conditions in the procedure were determined as follows: in order to obtain the water-immiscible small phase (approximately 120 μl) of ethyl chloroacetate, hydrochloric acid ([HCl]T=1.44 mol dm-3) was added to a homogeneous aqueous solution which consisted of water, ethyl chlorolacetate (1 cm3: 2.0 vol%) and pyridine (5 cm3: 12.0 vol%), where the final total volume was 50 cm3. A concentration factor of 10000 (i. e. 50 cm3→ 5μl) was achieved by adjusting the initial volume of ethyl chloroacetate. The compound α, β, γ, δ-tetrakis(4-carboxyphenyl)porphine (TCPP) was selected as an extracting chelate reagent. In the extraction of TCPP and metal-TCPP complexes, when the ratio ( Vw/ Vo) of the volume in the water phase ( Vw) to that in the sedimented phase ( Vo) was 500, the distribution ratio (D) and extraction percentage (E%) were TCPP (14700, 96.7%), Cu-TCPP (7440, 93.7%), Zn-TCPP (22200, 97.8%), Mn-TCPP (1070, 68.1%) and Co-TCPP (8760, 94.6%), respectively. This extraction method was applied as preconcentration in HPLC. The simultaneous complex formation condition between TCPP and each metal ion { i.e., accelerator; [pyridine]T = 0.25 mol dm-3 and [Hg2+]T = 2×10-6 mol dm-3, pH; 9.3, reaction time; 30 min at room temperature} and The HPLC condition of the metal complexes { i.e., column; ODS (4.6 mm i.d.×250 mm), mobile phase; the mixture (50 w/w%) of acetonitrile and acetic acid-sodium acetate aqueous solution (pH 3.5), flow rate; 0.5 cm3/min, detection wavelength; 420 nm } were selected, respectively. All calibration graphs were linear and passed through the origin over the concentration range of 5×10-9 mol dm-3 to 10-7 mol dm-3. The detection limit (3σ) reached 1×10-10 mol dm-3 for Cu(II) and Mn(II) and 5×10-11 mol dm-3 for Zn(II) and Co(II), respectively. Satisfactory results for the determination of four kinds of metal in river water (standard material in the Japan Society for Analytical Chemistry: JAC 0032) was obtained.