Etsuro Iwamoto

Selective determination of arsenic (III, V), antimony (III, V), selenium (IV, VI) and tellurium (IV, VI) by extraction and graphite furnace atomic absorption spectrometry

Abstract Parameters were investigated for the selective determination of arsenic (III, V), antimony (III, V), selenium (IV, VI) and tellurium (IV, VI) by graphite furnace atomic absorption spectrometry combined with extraction using an ammonium pyrrolidinedithiocarbamate and chloroform + carbon tetrachloride solvent mixture. Selenium (VI) and tellurium (VI) were not extracted over the entire range of pH studied, although the extraction conditions for the other species were not critical. It was found that the incorporation of titanium (III) chloride as a reducing agent in the extraction procedure made it possible to differentiate the above elements in the higher and lower oxidation states. The four elements at the low oxidation state were first extracted at pH 5 and after the addition of titanium chloride to the aqueous phase, the species in the high oxidation state were extracted at about pH 0.3. High sensitivity for the determination of the eight species was obtained. Interferences by many foreign ions have been studied.

Determination of tin by electrothermal atomic absorption spectrometry with a tungsten-coated tube

The W-coated tube was prepared, without soaking in the tungstate solution, and applied to the determination of tin in a fish sample. The coating process involved simply injecting 100 µl of a sodium tungstate solution (0.01 mol l–1) into a graphite tube [pyrolytic graphite (PG) and non-pyrolytic graphite (NPG) tubes], followed by heating according to a temperature programme similar to an atomization cycle for the determination of tin. This procedure for coating was repeated five times and the coated surface gave high stable signals for at least 100 firings. The W-coated NPG tube gave the highest and most stable absorption signal for tin in a sea bass sample.

Effects of Conditions for Pyrolysis of Ascorbic Acid as a Chemical Modifier on the Vaporization Mechanism of Gold in Electrothermal Atomic Absorption Spectrometry

The effect of the ramp and hold times and the temperature of the pyrolysis step of ascorbic acid as a chemical modifier on AA signals for gold have been investigated. Three methods of pyrolysis for ascorbic acid were used: (1) pyrolysis of ascorbic acid before deposition of a gold solution on the platform surface; (2) pyrolysis of ascorbic acid after ashing a gold solution; and (3) charring a solution containing both ascorbic acid and gold. Although pyrolysis methods (2) and (3) gave a delayed single absorption peak for gold compared with that in the absence of ascorbic acid, in pyrolysis method (1) a double peak appeared even at a high pyrolysis temperature of 1500 °C. However, as the ramp time increased from 5 to 80 s from a drying temperature of 120 up to 1500 °C, the first peak increased and concomitantly the second peak decreased with an isosbestic point; the integrated absorbance remained constant. The concentration dependence of the gold signals indicates that a fractional-order of release is shown for the first peak and a first-order process is obtained for the second, indicative of gold atoms adsorbed onto the active carbon surface. From inspection of a scanning electron micrograph and Raman spectra of the pyrolysed ascorbic acid, it was clear that a carbon film formed on the platform surface. It was concluded that use of a short ramp and hold time, even at 1500 °C, for the pyrolysis of ascorbic acid leads to the formation of active amorphous carbon enriched in micro-sized pores (r<25 nm), where adsorption of gold atoms that give rise to the second absorption signal occurs. Furthermore, the micro-sized pores are almost destroyed by treatment at temperatures higher than 1800 °C, resulting in graphitization of the carbon residue.

Strongly polarized water at the interfacial region in reversed micelles containing 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) as a probe

The change in the polarization of water in sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT) reversed micelles has been investigated spectrophotometrically using 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) cation, [Ni(tmc)]2+, as a probe of electron-pair acceptance. Although above a water-to-AOT molar ratio (R) of 10 the spectrum of [Ni(tmc)]2+ is very similar to that in bulk water, below R= 10 the peaks of the five-coordinated complex shift to longer wavelengths and at R≈ 1 the spectrum is very similar to that of the hydroxide ion-coordinated complex. This shows that a decrease in the R value obviously leads to a gradual increase in the polarization of water coordinated to [Ni(tmc)]2+ owing to the cooperative influence of the sulfo ion of AOT and [Ni(tmc)]2+ through hydrogen bonding at the water/surfactant interface.

Solute-solvent interactions with metal chelate electrolytes. Part III. Salting in of tris(acetylacetonato)cobalt(III) and benzene by aromatic and aliphatic ions

Salting effects of the metal chelate electrolytes, [Fe(phen)3]Br2, [Fe(bpy)3]Br2, [Co(phen)3]Br3, [Co(en)3]Br3, and [Co(pn)3]Br3 (where phen= 1,10-phenanthroline, bpy=2,2′-bipridyl, en=ethylenediamine, and pn=1,2-propanediamine), as well as the tetraalkylammonium bromides (Bu4NBr and Pr4NBr), tetraphenylphosphonium bromide (Ph4PBr), sodium tetraphenylborate (NaBPh4), and sodium halides on the solubility of benzene and tris(acetylacetonato) cobalt (III) [Co(acac)3, where acac=CH3·CO·CH·CO·CH3-] in water at 15, 20, 25, and 35°C were studied, and the transfer free energies of the nonelectrolytes from pure water to the electrolyte solutions were obtained. Co(acac)3 is strongly salted in by [Fe(phen)3]Br2, NaBPh4, and Ph4PBr with large positive transfer enthalpies and entropies, weakly salted in by Bu4NBr and Pr4NBr with much less positive enthalpies and entropies and is salted out by the other electrolytes. The differences between salting effects of aromatic and aliphatic ions are discussed using the transfer enthalpy-entropy relation.

Spectrophotometric determination of antimony (III) by solvent extraction with mandelic acid and malachite green

Abstract A sensitive and selective method has been developed for the spectrophotometric determination of antimony in the tervalent oxidation state. It was found that antimony (III) reacts with mandelic acid to form a complex anion extractable into chlorobenzene with malachite green in weak acidic media (pH 2.2 to 3.5) at room temperature and is determined indirectly by measuring the absorbance of malachite green in the extract at 628 nm. The calibration graph is linear for antimony (III) over the range 0.088–1.8 mg 1−1 (7.2 × 10−7–1.5 × 10−5 mol 1−1) with the apparent molar absorptivity e × 6.9 × 104 1 mol−1 cm−1. Antimony (V) was slightly extracted in the presence of phosphate buffer with e × 2.7 × 103 1 mol−1 cm−1.

Hydrophobic and charge-dipole interactions in aqueous solutions of highly charged metal chelate cations and nitrobenzene, dinitrobenzenes, and toluene at 25°C

Salting effects of metal chelate electrolytes Fe(phen)3Br2, Fe(bpy)3Br2, Co(phen)3Br2, Co(phen)3Br3, Co(en)3Br3, and Co(pn)3Br3 (where phen=1,10-phenanthroline, bpy=2,2′-bipyridyl, en=ethylenediamine, and pn=1,2-propylenediamine) on the solubilities of nitrobenzene,o-,m-,and p-dinitrobenzenes (DNB), and toluene were studied in water at 25°C and compared to the results for sodium bromide and tetrabutylammonium bromide (Bu4NBr). The Co(phen)33+, Fe(phen)32+, and Fe(bpy)32+ ions showed much stronger salting-in effects than did the Bu4N+ ion, while the effects of the Co(en)33+ and Co(pn)33+ ions are comparable with those of Bu4N+. A great dependence of salting-in on the polarity of dinitrobenzene isomers was found for Co(phen)33+ and Fe(phen)32+. The results were related to the partial molal volume of the respective cations. The very strong salting-in was considered to be mainly due to hydrophobic hydrations of the metal chelate cations and partly due to van der Waals interactions between the aromatic ligands and the nonelectrolytes. The small salting-in effects by Co(en)33+ and Co(en)33+ were interpreted in terms of hydrogen bonding between oxygen atoms of the nitro compounds or the solvent water molecules and hydrogen atoms attached to nitrogens in the complexes.

Periodic trends in sensitivity and its dependence on the properties of pyrolytic and non-pyrolytic graphite in graphite-furnace atomic-absorption spectrometry.

The sensitivities for metal determination by GFAAS in the peak-height and integration modes were examined with pyrolytic graphite (PG) and non-pyrolytic graphite (NPG) tubes for 34 elements. It was found that there are periodic trends of the mole sensitivity and the elements can be classified according to whether their sensitivity of determination is enhanced by use of (a) the PG tube (alkali, alkaline-earth and transition metals); (b) the NPG tube (semi-metals); about equally by both tubes (Mg, Zn, Cd, and Pb). The mole sensitivity pM for atomic-absorption spectrometry (AAS) was defined as pM = -log(m(h)/A(w)) where m(h) is the weight of an element corresponding to 1% absorption and A(w) is the atomic weight. It was found that the pM values for graphite furnace AAS have a periodic trend similar to that for flame AAS and atomic-fluorescence spectrometry.

Extraction of gold, silver, mercury, platinum(II) and palladium with O,O′-diisopropyl-S-benzylthiophosphate into molten diphenyl

Abstract Liquid-liquid distribution with O,O ′-diisopropyl- S -bebzylthiophosphate (DPBTP), tri-n-octylphosphine oxide, tri-n-butylphosphate, di-n-hexylsulfide (DHS) and O,O ′-dimethyl- O -(3-methyl-4-nitrophenyl)triophosphate (DMTP) into molten diphenyl was investigated for the extraction of metals from hydrochloric, nitric and sulfuric acid solution. Silver(I), gold(III), mercury(II), platinum(II) and palladium(II) can be selectively extracted with DPBTP, DHS and DMTP.

Stereospecific interaction between Cr(acac)3 or Co(acac)3 and Δ-(−)589-Ni(phen)32+ in aqueous solution

Abstract The salting effects of Δ-(−) 589 -Ni(phen) 3 2+ on the solubility of racemic M(acac) 3 (M = Cr and Co) were investigated. Δ-(−) 589 -Ni(phen) 3 2+ salts-in selectively the Δ-form of M(acac) 3 than the Λ-form. This stereospecificity was interpreted by the van der Waals attractive force through hydrophobic interactions.