Preconcentration of Cobalt(II) Using Synergistic Extraction with Dithizone and Tributylphosphine Oxide

Abstract

A simple preconcentration method for cobalt(II) in natural waters based on synergistic extraction is proposed. Cobalt(II) is extracted as the ternary complex, Co(I I )-dithizone-tributylphosphine oxide, from 300 cm3 of a water sample into 3 cm3 of carbon tetrachloride at pH 5. The method was applied to a river water sample. Using this method, cobalt(II) in natural waters with levels below µg dm-3 range could be determined by the atomic absorption spectrometry, an aliquot of the organic extract being injected into a graphite furnace.Keywords Preconcentration, cobalt(I I ), synergistic extraction, graphite furnace atomic absorption spectrometry, dithizone, tributylphosphine oxideRecently, there is an increasing interest in the concentration of trace metals in various water samples in relation to the environmental background. Since the concentrations of some metals in such samples are often very low, an appropriate preconcentration technique for a particular analyte is sometimes required prior to the determination. Cobalt(II) is one of such metals, whose concentration in river waters is reported to be below µg dm 3 level.l Solvent extraction, especially chelate extraction is a simple and highly selective method of concentration for metals, but the concentration factor by this method is not sufficient for a preconcentration purpose. However, the enhancement in the concentration factor could be expected by the use of a synergistic extraction system. Moreover, the synergism may accelerate the extraction, although the dithizone (H2dz, 3-mercapto-1,5-diphenylformazan) extraction of cobalt(II) is known to be slow.2The authors previously succeeded in the preconcentration of cadmium(II) by employing the synergistic extraction with dithizone and trioctylphosphine oxide (TOPO).3In that system, however, the phase separation was very time-consuming, and centrifugation was required occasionally. This was due to the high surface-activity of TOPO employed as a synergist. In the present paper, the preconcentration method for cobalt(II) by utilizing the synergistic extraction with dithizone and tributylphosphine oxide (TBPO), whose surface-activity is much lower than TOPO, is investigated. Experimental ApparatusA Hitachi Model 170-30 atomic absorption spectrometer and a Shimadzu Model 640-12 atomic absorption spectrometer equipped with a Model GFA-4 graphite furnace atomizer and a Model PCA-1 peak catcher were used for flame and flameless atomic absorption spectrometry(AAS), respectively. A singleelement cobalt hollow cathode lamp (Hamamatsu Photonics) was employed as a light source.All spectrophotometric measurements were carried out with Hitachi Model 200-10 and 101 spectrophotometers.A Horiba Model F-80 pH analyzer and a Iwaki KM type shaker were used for pH measurements and shaking of separatory funnels, respectively. ReagentsStandard cobalt(II) solution: A stock solution (1 mg cm-3) was prepared by dissolving 1.000 g of cobalt metal powder (Soekawa Chemicals Co. Ltd., 99.9% purity) in (1+1) nitric acid and then diluting to 1 d...

Preconcentration of Heavy Metal Ions Using Synergistic Extraction with Dithizone and Tributylphosphine Oxide on the Basis of HSAB Rule

“…Synergistic extraction with a mixture of dithizone and tributylphosphine oxide (TBPO) has been applied to the preconcentration of CoII and CdII in river waters.1'2 Chelate extraction constants (KeX) could be rationalized by HSAB (hard and soft acids and bases) rule3, into which a new dual parameter scale for strength (SA) and soft (QA) factors of a metal ion (Mr) was introduced:4 log KeX + ZPKa -SASB + QAQB (1) where the subscripts A and B denote Lewis acid and base, and pKa is the acid dissociation exponent of a chelating agent. In this work, a method for simultaneous preconcentration of CdII, CoII, Cu", Ni", Pb" and Zn" using dithizone extraction was designed based on the HSAB rule, and was applied to inductively coupled plasma atomic emission spectrometry (ICP-AES).…”