Hirohiko Waki

Ion-exchanger colorimetry-I Micro determination of chromium, iron, copper and cobalt in water.

A new sensitive, colorimetric method based on the direct measurement of light-absorption by an ion-exchange resin phase, which has sorbed the sample complex species, has been developed. Determinations ofchromium(VI) with diphenylearbazide, iron(II) with 1,10-phenanthroline, copper with Zincon and cobalt with thiocyanate have more than ten times the sensitivity obtainable with conventional solution colorimetry. The present method can be applied to natural water samples containing very low levels of these metals.

Ion-exchanger phase absorptiometry for trace analysis

Ion-exchanger phase absorptiometry is based on the direct measurement of the degree of light-absorption by an ion-exchange resin phase which has sorbed a sample component. Direct application of the method makes it possible to determine trace elements in natural water samples without preconcentration. In this paper, all systems hitherto developed are reviewed and the theoretical background of solid-phase absorptiometry is described.

Donnan exclusion chromatography: I. Theory and application to the separation of phosphorus oxoanions or metal cations

Summary Donnan exclusion chromatography is a special type of ion-exchange separation method based on the electrostatic repulsion between the sample ions and fixed ionic groups of an exchanger. The elution behaviour in this chromatography is well explained by the Donnan equilibrium relation of ions between two phases. Practical separations for various oxoanions of phosphorus and for metal cations are reported. Possibilities of this chromatography in other applications are also discussed, as well as theoretical considerations.

Ion-exchanger colorimetry-III microdetermination of zinc in water.

An ion-exchanger colorimetric method for the determination of zinc(II) with Zincon has been developed. Zinc in a water sample can be determined by sorption onto an anion-exchange resin from 2M chloride solution followed by transformation into a coloured complex with Zincon. With use of a 1-litre sample the sensitivity is 10 times greater than that for conventional colorimetry. Most metals, except cadmium(II), lead(II) and bismuth(III), do not interfere when present in up to 100 times the concentration of zinc. The zinc: Zincon ratio of the complex in the resin phase was found to be 1 : 1 by the molar ratio method.

11B NMR studies on complexation of borate with linear and crosslinked polysaccharides

11 B NMR spectroscopy has been employed to elucidate the nature of the complexation of borate with crosslinked Dextran–containing glucopyranoside residues, and with linear Dextran and the monomer derivative, α-methyl-D-glucopyranoside. Well resolved 11B NMR spectra for Sephadex gel as well as for a solution of Dextran or α-methyl-D-glucopyranoside were observed. Four borate complexes with α,β-diols and α,γ-diols of glucopyranoside residues were present. The characteristic 11B chemical shift values were at δ–13 to –14 for the 1:1 complex with α,β-diol and at δca.–10 for the 1:2 complex with α,β-diols, and at δca.–18 for the 1:1 and 1:2 complexes with α,γ-diols, irrespective of the linear or crosslinked structure of the polysaccharide. The 1:1 complexes with the α,β-diols of Dextran and Sephadex gels have higher stability compared with those with α,γ-diols, whereas the complex with α,γ-diols is predominant for the α-methyl-D-glucopyranoside system. This indicates that the glucopyranoside residues of Dextran and Sephadex gels prefer the C1 conformation and the interconversion between the C1 and 1C conformers is restricted owing to the hydrodynamic and steric hindrance of the linear or crosslinked polymer in aqueous media. The formation of 1:1 complexes with α,γ-diol of the Dextran and Sephadex gels induces the conformational changes of the glucopyranoside residues from the C1 to 1C conformation in a part of the Dextran strands to create a domain of high local concentration of the α,γ-diol moiety, so that the α,γ-diols are located at a suitable position for 1:2 complexation.

The protonation constants and 31P NMR of tetra-, penta-, hexa- and heptapolyphospates

Abstract The first and second protonation constants of linear polyphosphates at 25°C and ionic strength 0.1 have been evaluated: log K 1 = 8.91, log K 12 = 6.13 for P 2 O 7 4− (P 2 ); log K 1 = 8.88, log K 12 = 5.86 for P 3 O 10 5− (P 3 ); log K 1 = 8.40, log K 12 = 6.58 for P 4 O 13 6− (P 4 ); log K 1 = 8.15, log K 12 = 7.03 for P 5 O 16 7− (P 5 ); log K 1 = 8.12, log K 12 = 7.16 for P 6 O 19 8− (P 6 ); log K 1 = 8.07, log K 12 = 7.18 for P 7 O 22 9− (P 7 ). The variations of these values with the polyphosphate chain length have been discussed. A simple identification for polyphosphate species utilizing 13 P NMR signal ratio of middle to end P has been proposed. By applying a micro ion-exchange technique, a rapid concentration of each polyphosphate and the subsequent preparation of the magnesium salt have been accomplished.

Separation of lower oxo acids of phosphorus by gradient elution chromatography using an anion exchange resin

Abstract A method has been proposed to predict the positions of the elution peaks of some lower oxo acids of phosphorus and orthophosphoric acid in gradient elution chromatography through an anion exchange resin. If the relation between lograrithms of the distribution ratios and of the concentration of ammonium acetate as eluent is linear, one can calculate the position of the elution peak by the method presented here. The calculated positions of the elution peaks of acid agreed approximately with the observed ones. The order of the sorbabilities of phosphate ions is dependent upon the concentrations of ammonium acetate as eluent.

Application of ion-exchanger phase spectrofluorimetry to the determination of micro-amounts of some rare earth elements by flow analysis

The fluorescence bands originating from d→f electron transitions, which can be used to determine europium, terbium, dysprosium or samarium selectively, were enhanced only if these elements were sorbed in a weak-acid cation-exchange gel, i.e., CM-Sephadex. After a sample solution had been introduced into a fused-silica tube (1.5 mm i.d.) packed with 1 mg of CM-Sephadex, the fluorescence intensity increase, resulting from the rare earth elements sorbed in the ion-exchange gel, could be measured directly with good precision. For europium, the detection limit was 22 ng with an 8.3 cm3 sample solution. The sensitivity of the proposed method depended on the sample volume introduced. The cell could be used repeatedly after desorbing the target element with a solution of nitric acid.

Determination of molybdenum(VI) in natural water and rock by ion-exchange absorptiometry combined with flow analysis

Abstract Ion-exchange absorptiometry combined with flow analysis has been applied to the determination of trace amounts of molybdenum(VI) in natural water and rock. By using a pretreatment column packed with Sephadex G-25 gel, molybdenum(VI) in a sample solution can be sorbed selectively on the gel at pH 3.5. The molybdenum(VI) in the column was desorbed with EDTA as the molybdenum(VI)-EDTA complex, and the solution was introduced into a Tiron solution stream. The yellow complex formed between molybdenum(VI) and Tiron in the flow system was then concentrated on a QAE-Sephadex A-25 anion exchanger packed in a flow-through silica micro-cell. The attenuation of incident light by the molybdenum(VI)-Tiron complex on the anion exchanger in the cell was continuously recorded with a spectrophotometer at 410 nm. The complex on the anion exchanger was easily desorbed with sodium nitrate, so the flow-through cell could be used repeatedly. The minimum amount that could be detected corresponded to 15 ng of molybdenum(VI). Molybdenum(VI) in three or four sample solutions could be determined within 1 h.

Enhancement of sensitivity of ion-exchanger absorptiometry by using a thick ion-exchanger layer

Enhancement of the sensitivity of ion-exchanger absorptiometry by the use of much thicker ion-exchanger layers than those previously employed has been investigated. Because the background attenuance due to light-scattering from the solid particle layer increases only moderately, whereas the net absorbance of the sorbed sample species increases greatly when the cell length is increased, a cell with at least 10-mm path-length may be effectively used without difficulty in most commercial spectrophotometers, giving at least ten times the sensitivity obtainable with a 1-mm cell. Since the background attenuance depends on the optical geometry, it can be lowered to some extent by using a particular type of spectrophotometer, and by placing a cylindrical mirror between the cell and the light-detector window or by setting the cell as close as possible to the window. The use of such long cells has been found to improve the sensitivity in the chromium-diphenylcarbazide, iron-1,10-phenanthroline, nickel-PAN, cadmium-PAR, bismuth-chloride and uranium-thiocyanate systems. Other methods may be similarly improved.