Koji Tohda

A sensitive and selective method for determination of gold(III) based on electrothermal atomic absorption spectrometry in combination with dispersive liquid-liquid microextraction using dicyclohexylamine.

A combined method with dispersive liquid-liquid microextraction (DLLME) and electrothermal atomic absorption spectrometry (ETAAS) has been developed for determining gold(III). Dicyclohexylamine, a new extractant for gold(III), showed excellent performance in DLLME. Acetone was indispensable to the quantitative extraction of gold(III), contributing to decrease in hydration, decrease in the difference in the dielectric constants between the supernatant phase and the sedimented phase, and dissolution of a part of chloroform as an extraction solvent to the supernatant phase as well as improvement of dipersibility. In DLLME using a mixture of 1.0mL of acetone and 100microL of chloroform containing 50mmolL(-1) of dicyclohexylamine, gold(III) could be extracted selectively and effectively from 8mL of a sample solution in the presence of iron(III), cobalt(II), nickel(II), copper(II), palladium(II), and platinum(IV) at pH 1. The extracted gold(III) was determinable by ETAAS; the detection limit was 0.002microgL(-1) (three times the standard deviation of the blank values, n=8) as a gold(III) concentration in 8mL of sample solution. The proposed method was applicable to the determination of gold in platinum metal and its alloy as well as effluent without any interference by the matrices.

A solid phase extraction using a chelate resin immobilizing carboxymethylated pentaethylenehexamine for separation and preconcentration of trace elements in water samples

A chelate resin immobilizing carboxymethylated pentaethylenehexamine (CM-PEHA resin) was prepared, and the potential for the separation and preconcentration of trace elements in water samples was evaluated through the adsorption/elution test for 62 elements. The CM-PEHA resin could quantitatively recover various elements, including Ag, Cd, Co, Cu, Fe, Ni, Pb, Ti, U, and Zn, and rare earth elements over a wide pH range, and also Mn at pH above 5 and V and Mo at pH below 7. This resin could also effectively remove major elements, such as alkali and alkaline earth elements, under acidic and neutral conditions. Solid phase extraction using the CM-PEHA resin was applicable to the determination of 10 trace elements, Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, V, and Zn, in certified reference materials (EnviroMAT EU-L-1 wastewater and ES-L-1 ground water) and treated wastewater and all elements except for Mn in surface seawater using inductively coupled plasma atomic emission spectrometry. The detection limits, defined as 3 times the standard deviation for the procedural blank using 500 mL of purified water (50-fold preconcentration, n=8), ranged from 0.003 microg L(-1) (Mn) to 0.28 microg L(-1) (Zn) as the concentration in 500 mL of solution.

Selective removal of mercury(II) from wastewater using polythioamides

The potential and feasibility of polythioamides as Hg(II) sorbents were evaluated. Powdered polythioamides quantitatively sorbed Hg(II) from an aqueous solution at pH 1-8. The sorption of Hg(II) on polythioamides obeyed the Langmuir adsorption isotherm; the sorption capacity was 0.70-0.85 g-Hgg(-1). Hg(II) was selectively separated from solutions containing 500 times larger amounts of Mn(II), Fe(III), Cu(II), Zn(II), and Pb(II) at pH 1. The tertiary polythioamide (PTA1) is soluble in chloroform and can be readily coated on a commercially available polymer resin, Amberlite XAD7HP. PTA1-coated resin as well as powdered PTA1 were applicable to the selective removal of Hg(II) from real wastewater.

Chelating fibers prepared with a wet spinning technique using a mixture of a viscose solution and a polymer ligand for the separation of metal ions in an aqueous solution

Chelating fibers containing polymer ligands such as carboxymethylated polyallylamine, carboxymethylated polyethyleneimine, and a copolymer of diallylamine hydrochloride/maleic acid were prepared with a wet spinning technique using mixtures of a viscose solution and the polymer ligands. The chelating fibers obtained effectively adsorbed various metal ions, including Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Ni(II), Pb(II), Ti(IV), and Zn(II). The metal ions adsorbed could be readily desorbed using 0.1 or 0.5 mol L(-1) HNO(3). The chelating fiber containing carboxymethylated polyallylamine was available for the separation of some metal ions in synthetic wastewater containing a large amount of Na(2)SO(4). The wet spinning technique using a solution containing a base polymer and a polymer ligand was quite simple and effective and would be applicable for preparing various chelating fibers.

Inductively coupled plasma atomic emission spectrometric determination of 27 trace elements in table salts after coprecipitation with indium phosphate

The coprecipitation method using indium phosphate as a new coprecipitant has been developed for the separation of trace elements in table salts prior to their determination using inductively coupled plasma atomic emission spectrometry (ICP-AES). Indium phosphate could quantitatively coprecipitate 27 trace elements, namely, Be, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, in a table salt solution at pH 10. The rapid coprecipitation technique, in which complete recovery of the precipitate was not required in the precipitate-separation process, was completely applicable, and, therefore, the operation for the coprecipitation was quite simple. The coprecipitated elements could be determined accurately and precisely by ICP-AES using indium as an internal standard element after dissolution of the precipitate with 5 mL of 1 mol L(-1) nitric acid. The detection limits (three times the standard deviation of the blank values, n=10) ranged from 0.001 microg (Lu) to 0.11 microg (Zn) in 300 mL of a 10% (w/v) table salt solution. The method proposed here could be applied to the analyses of commercially available table salts.

Modelling the response function of enzyme-based optical glucose-sensing capsules

A theoretical model for submillimetre-sized optical glucose sensors based on microscopic pH-sensitive optode beads and glucose oxidase (GOX) inside hydrophilic membrane capsules with ca. 12 μm thickness is presented. In this model, glucose influx and gluconic acid efflux across the capsule membrane are combined with enzymatic kinetics inside the capsule. Thereby, a simple model predicting the sensor responses with different permeabilities of the capsule membranes is obtained. The permeability of the capsule membranes for glucose and gluconic acid was successfully modified by changing the monomer ratio between 2-hydroxyethyl methacrylate (HEMA) and polyethylene glycol methacrylate (PEGMA) in the preparation of poly(HEMA-co-PEGMA)-based capsule membranes. Excellent agreements between the predicted sensor responses and the experimentally obtained ones were achieved in buffer solutions containing glucose at physiologically relevant concentrations. Consequently, this model can predict enhancement of the sensor response for glucose by reducing the gluconic acid efflux, and provides a general precept for the fabrication of enzyme-based optical sensors with enhanced responses.