BUNSEKI KAGAKU Abstracts

In the present study, all equilibria occurred upon shaking an aqueous solution containing Zn(II) and Eu(III) with an equal volume of chloroform containing Hpta (pivaloyltrifluoroacetone, HA), and H₂(salchn) {bis(salicylidene)cyclohexyldiamine, H₂B} were measured and analyzed in order to accumulate fundamental data to prepare a binuclear complex consisting of EuA₃ and ZnB. The results showed that H₂B formed a complex with ZnA₂ as well as EuA₃, but ZnB formed a more stable complex with EuA₃ than does H₂B. Although ZnB is less extractable than ZnA₂ in the presence of Zn(II) the dominant extracted species is EuA₃ZnB, because EuA₃ZnB is stable. From all of the constants determined, such as the extraction constants and the stability constants, it was estimated that the binuclear complex can be prepared when Eu(III) is extracted with Hpta and H₂(salchn) from an aqueous solution containing a sufficient amount of Zn(II) at a high pH ; e.g., at pH 5. The complex, ZnA₂H₂B, gives a weak fluorescence at around 470 nm, and ZnB shows blue fluorescence at 450 nm. When solutions of EuA₃ and ZnB were mixed, the blue fluorescence disappeared, and the red fluorescence at 612 nm was remarkably sensitized. When the fluorescence spectrum of the mixed solution dissolved, synthesized EuA₃ and ZnB were compared with that of the CHCl₃ extracted EuA₃ZnB at a similar composition and concentration of Eu(III) and Zn(II), the spectra were similar to each other.

The authors reported in a previous paper on the extraction and separation of divalent metals, such as Cd^2＋, Pb^2＋, Ni^2＋, and Zn^2＋, by using an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF₆]), including the extractant of 2-pyridinealdoxime (2-PA). However, the extraction equilibrium of Ni^2＋in the 2-PA/[Bmim][PF₆] extraction system remained unresolved. Then, the present study was undertaken to elucidate the extraction mechanism of Ni^2＋ in the 2-PA/[Bmim][PF₆] extraction system, as well as the effect of masking reagent on the metal extraction. The chemical form of the extracted Ni-complex was examined by analyzing the slope for the relationship between log D and the pH and between log D and log [2-PA] in [Bmim][PF₆]. Taking into account the facts that the slopes for the above-mentioned relationships were both close to 2.0 and the Ni^2＋ ion was mainly extracted in the acidic pH region in the vicinity of a pK_a1 of 2-PA (3.73) the extraction equilibrium of Ni^2＋ with 2-PA into [Bmim][PF₆] phase was concluded to be Ni^2＋_(aq)＋2H₂L^＋_(aq)＋2Bmim^＋・PF₆⁻_(org)⇌Ni(HL)₂^2＋・2PF₆⁻_(org)＋2H^＋＋2Bmim^＋_(aq), where HL and Bmim・PF₆ denote 2-PA and 1-butyl-3-methylimidazolium hexafluorophosphate and the subscript (org) and (aq) means the organic phase and aqueous phase, respectively. That is, the pyridinium form of 2-PA, H₂L^＋, in the aqueous phase reacted with the Ni^2＋_(aq) ion to form a nickel-2-PA complex cation, Ni(HL)^2＋_(aq), while repelling two H^＋ ions. Then, the formed Ni(HL)^2＋_(aq) ion was distributed into the organic phase by ion exchanging with the 1-butyl-3-methylimidazolium cation in the organic phase.

The behavior of the adsorption of inorganic and organic phosphorus compounds on zirconium-loaded activated carbon (Zr-C^＊) has been studied. A simple separation method using Zr-C^＊ for the determination of these phosphorus compounds in water has been developed, based on the adsorption behavior of these phosphorus compounds. Sample solutions containing inorganic and organic phosphorus compounds, which were adjusted to pH 2, were passed through Zr-C^＊ to collect them. The retained ionic phosphorus compounds were quantitatively eluted with a 1 mol/L sodium hydroxide solution as an eluent. However, the retained hydrophobic phosphorus compounds were not eluted with the eluent. Inorganic and organic phosphorus compounds in water could be separated into five fractions based on different analytical methods and different behaviors of adsorption and desorption using Zr-C^＊ among their compounds. Furthermore, from the results of applying this method to river-water samples, organic phosphorus compound fractions were found to be grouped into a readily degradable organic compound one and a slowly degradable organic compound one. The established method is applicable to brackish water and seawater as well as freshwater.

A new formaldehyde (HCHO) standard gas generation method based on gravitational dispensing-vaporization was developed, and an automated flow injection analysis (FIA) system coupled with a porous membrane-based diffusion scrubber (DS) is proposed for the determination of gaseous HCHO in human breath. An HCHO standard solution in a 2-mL Terumo^® syringe was dispensed gravitationally via a fused-silica capillary tip through a perpendicular arm of a tee heated at 40°C. The HCHO standard solution was delivered at a flow rate of 39.5 nL/min and completely vaporized by airflow through the tee-arm. The gaseous HCHO was collected into a water absorber in the DS. The solution dissolved sample gas was injected into the FIA system. The fluorescent derivative was produced by merging HCHO and 5,5-dimethylcyclohexane-1,3-dione at pH 5.0. The intensity was recorded at the excitation wavelength of 395 nm and the emission wavelength, 463 nm. In this manner, reliable instrument calibration of the FIA system could be carried out. Under the optimum condition, a linear calibration curve for HCHO was obtained in the range of 3.68 to 147 ppbv. The limit of detection (S/N＝3) was 0.16 ppbv. The collection of a gaseous sample and HCHO detection were automatically operated with a home-made protocol. The proposed method was applied to the determination of HCHO in exhaled human breath. The concentration range in 4 healthy volunteer subjects (nonsmoker) ranged from 5.8 to 11.8 ppbv. We also found that for another subject (smoker) smoking increased the breath HCHO concentration to approximately 1.5-fold, and then the concentration later returned to the initial level 30 min after the smoking.

A simple and sensitive voltammetric method for detecting 17β-estradiol (E2) was developed. The Nafion membrane dispersed multi-walled carbon nanotube (MWCNT) modified electrode was prepared by spin-coating a 1.5 wt％ Nafion ethanolic solution including 2 mg/mL MWCNT on glassy carbon (GC) at 2400 rpm. The voltammetric behavior of E2 was investigated with linear sweep voltammetry in an electrolyte including a hydrophobic cationic surfactant, such as Zephiramine, benzethonium chloride (BTC), and cethyltrimethylammonium bromide (CTAB). The peak current for the oxidation of E2 at the MWCNT-Nafion-GC electrode was enhanced by the presence of each hydrophobic cationic surfactant. The enhancement effect by Zephiramine was strongest when compared to the others. Although E2 below a concentration of 1×10⁻⁶ M at a bare GC electrode can not be measured, the peak current for the oxidation of 1×10⁻⁹ M E2 could be observed by using the MWCNT-Nafion-GC electrode in the presence of 6×10⁻⁵ M Zephiramine.

Plasticized poly(vinyl chloride) membranes containing an ionic liquid as the membrane solvent were prepared, and the ion-sensor properties of the ISEs were studied. When the ratio of ionic liquids to NPOE was less than 1, the ISEs showed near-Nernstian responses. However, as the ratio became higher than 1, the slope of the EMF responses became smaller. The selectivity for lithium ion was enhanced by the addition of ionic liquid into the membranes, when a polyether-amide derivative was used as the neutral carrier (lithium ionophore).

AC impedance spectra were measured for mediated bioelectrocatalytic systems containing PQQ-dependant glucose dehydrogenase, ferrocenecarboxylic acid and D-glucose. The catalytic system showed a circular arc in Nyquist plots, and its radius was inversely proportional to the mediator concentration. The kinetic parameters were evaluated with theoretical equations for the case in which the substrate concentration was sufficiently higher than the Michaelis constant, and the mediator concentration was sufficiently lower. The evaluated value of the kinetic parameter was comparable to that obtained by cyclic voltammetry, indicating the usefulness of AC impedance methods for bioelectrocatalysis systems.

A simple and rapid semi-micro column HPLC-fluorescence method for the determination of medium-chain fatty acids (MCFAs) is described. The MCFAs involving C₆, C₈, C₁₀, C₁₂, C₁₄ and C₁₆ were labeled with 2-(4-hydrazinocarbonylphenyl)-4,5-diphenylimidazole (HCPI). A simple deproteinization with a mixture of CH₃CN and dimethylformamide was employed for the extraction of MCFAs in plasma. The separation of HCPI-MCFAs was achieved within 35 min on a semi-micro ODS column (Daisopak-SP-120-5-ODS-BP, 250×2.0 mm, i.d.) by gradient elution with a mixture of H₂O and CH₃CN. The detection limits of MCFAs at a signal-to-noise ratio of 3 were in the range of 0.15〜0.26 pmol/5 μL injection. Furthermore, the proposed method was applied to determine MCFAs in human plasma. The relation between the levels of MCFAs and homocysteine, which is considered to be an independent risk factor for atherosclerosis, was estimated.

A spectrophotometric method was established for the determination of urinary protein with an o-sulfophenylfluorone-niobium(V) {SPF-Nb(V)} complex. This method is about 1.2-times more sensitive than the pyrogallol red-molybdenum(VI) method (PR method), and can determine trace amount of urinary protein. There was good for agreement between the results obtained for urinary protein by this method and those obtained by PR method (r＝0.914). The binding process between the {SPF-Nb(V)} complex and HSA was studied by determining the thermodynamic parameters. Moreover, upon application of this method to a protein assay kit, a mixed reagent was constructed and a simple sensitive method was developed for a visual detection of protein. The proposed method should be useful for a simple, rapid and sensitive determinations of urinary protein.

A sensitive preconcentration method for the spectrophotometric determination of trace thiamine and related compounds, which involves the filtration of a [thiamine - palladium(II) - Erythrosin] aggregate on a membrane filter, followed by its redissolution (Method A) or tristimulus colorimetry (Method B), was established. In the determination of thiamine, Beer’s law is obeyed in the range of 0.5〜7.0 ng/mL (Method A) and 1.3〜11 ng/mL (Method B), respectively. An appearent molar absorptivity of Method A was 4.7×10⁷ L mol⁻¹ cm⁻¹ at 550 nm, the relative standard deviation for 6 runs of 2.7 ng/mL thiamine being 4.1％. The method was successfully applied to assays of thiamine in pharmaceutical preparations (injection, tablet). The thermodynamic parameters (ΔG⁰＝−4.68 kJ mol⁻¹, ΔH⁰＝−18.28 J mol⁻¹, ΔS⁰＝15.37 J mol⁻¹ K⁻¹) and the binding parameters (n＝8.6, K＝9.9×10³ M⁻¹ at 30°C) suggest that the colored complex formed in this reaction system is an association complex between [thiamine - palladium] and Erythrosin.

A non-suppressed ion-exclusion/cation-exchange chromatography with conductimetric detection for the simultaneous determination of anions (SO₄²⁻, Cl⁻, NO₃⁻, I⁻, F⁻, HCOO⁻ and CH₃COO⁻) and cations (Na^＋, K^＋, NH₄^＋, Mg^2＋ and Ca^2＋) commonly found in a typical sub-urban river water and discharged water biologically treated by an activated sludge process for urban sewage was studied on a polymethacrylate-based weakly acidic cation-exchange resin column and a mixed eluent consisting of succinic acid, tartaric acids, and 18-crown-6 at pH 2.9. The separation mechanism is based on the ion-exclusion effect for the anions and the cation-exchange effect for the cations. Under the optimized eluent conditions (26 mM succinic acid/4 mM tartaric acid/1 mM 18-crown-6 at 0.6 mL/min), the simultaneous separation of anions and cations was achieved in ca. 20 min. The analytical performances, including calibration graph, detection limit, reproducibility, and recovery tests, were evaluated under the optimized chromatographic conditions. This simple and convenient non-suppressed ion-exclusion/cation-exchange chromatographic method could be successfully applied for evaluating the water quality of a sub-urban river watershed including sewage treated water, in terms of the biological oxidation reaction of NH₄^＋ to NO₃⁻.

A multielemental determination method for major-to-trace elements in sewage sludge has been developed by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) after microwave radiation assisted acid digestion or alkali fusion. A reference material of sewage sludge (BCR-144R) was analyzed to verify the determination method. The determined values of some elements such as Zn, Cu, Pb, Ni, Co and Cd by the alkali fusion were lower than the certified values. The analytical values of Cu and Ni obtained by the alkali fusion method with a platinum crucible was lower than those with a pyrolysis boron nitride crucible. From these results, it was suggested that the losses in the alkali fusion were due to volatilization among ignition for Zn, Pb, Co and Cd and alloy formation between Cu and Ni and platinum as crucible material. Furthermore, hydrofluoric acid was necessary to dissolve niobium, tantalum and hafnium in both decomposition processes for acid digestion and alkali fusion. The microwave radiation assisted acid digestion/ICP-MS and ICP-AES method was applied to the determination of major-to-trace elements in a sewage sludge sample collected at a sewage treatment plant in Tokushima. As a result, 44 elements could be determined.

A novel spectrophotometry for the determination of total free radicals and peroxides was developed using N,N,-dimethyl-p-phenylenediamine (DMPD) as a detection reagent. The stability of a DMPD aqueous solution was improved by dissolving DMPD in dimethyl sulfoxide (DMSO). The optimal conditions for the detection of free radicals in human serum were examined with DMPD. DMPD, the sample and 100 μmol L⁻¹ ammonium iron(II) sulfate were mixed in a 0.1 mol L⁻¹ acetate buffer solution (pH 5.0) containing 5％ DMSO and left standing at 40°C for 10 minutes, followed by a measurement of the absorbance at 550 nm. The calibration curves of free radicals (alkoxyl radical, hydroxyl radical and nitrogen monoxide) showed good linearity over the range of 2.9 nmol L⁻¹〜40 μmol L⁻¹ (r²＝0.995), 75.2〜500 nmol L⁻¹ (r²＝0.992) and 44.5〜300 mmol L⁻¹ (r²＝0.991), respectively. The detection limits of alkoxyl radical, hydroxyl radical and nitrogen monoxide were 0.9 nmol L⁻¹, 22.6 nmol L⁻¹ and 13.3 μmol L⁻¹, respectively. The recovery of 10 μmol L⁻¹ alkoxyl radical in human serum was 119％. The average of the total concentration for free radicals and peroxides as the concentration of tert-butyl hydroperoxide in human serum was 7.0 μmol L⁻¹ (n＝6).

Spectrophotometric determinations of heavy metal ions with xylenol orange (XO) have been carried out using cyclic flow injection analysis. A cation-exchanger mini-column (Amberlite IR124) was incorporated after a flow-through cell for the on-line regeneration of the used reagents and the accumulation of heavy metal ions. A solution of 1.0×10⁻⁵ M XO in 0.01 M acetate buffer (pH 5.0) in a single reservoir (100 mL) was continuously circulated, and sample solutions were injected into the stream. Cadmium(II), copper(II), iron(III), lead(II), zinc(II) and lanthanum(III) were sensitively monitored and determined. The regeneration and recycling of the XO reagent allowed as many as 50 repetitive determinations of heavy metal ions with the same 100 mL circulating reagent solution.

The atomization of various masses of gold deposited on a pyrolytic graphite furnace was observed between 0.02 and 0.20 ng. The process controlling function obtained indicated the formation of gold aggregates, such as droplets or clusters, and the desorption of gold atoms with the three-dimensional diffusion control. The value of activation energy (E_a) was decreased with decreasing in the mass of gold, indicating a decrease in the particle size. The size was calculated to be 0.34〜1.90 nm in the range 190〜300 kJ mol⁻¹, respectively. It was found that the first order reaction process was obtained and E_a＝88±13 kJ mol⁻¹ in the temperature range of 1162〜1436 K with the mass of 0.02 ng. The E_a value for the monoatomic state of gold dispersed on the conventional PG surface in electrothermal atomizer is discussed from the view point of a change in the degree of surface morphologies with basal plane, newly PG, aged PG, mechanically roughened PG, amorphous carbon and active carbon surfaces.

The liquid-membrane ion-selective electrode based on bis(pentafluorobenzyl)tin(IV) dibromide showed higher selectivities to α-hydroxycarboxylates than to other carboxylates without any hydroxyl group and those with a β-hydroxy group. The calibration curve for citrate was linear over a range of 10⁻⁴ to 10⁻² mol dm⁻³ with a potential slope of −60 mV/decade. The equilibrium study on the complexation between dimethyltin(IV) and a series of carboxylates indicates the formation of stable, neutral and dimeric complexes only with α-hydroxycarboxylates, [(Me₂Sn)₂(H₋₁hc)₂] {(H₋₁hc)⁻² : species formed by deprotonation of α-hydroxycarboxylates (hc⁻) at α-OH groups}. The corresponding species may be spontaneously formed as electroactive species in the liquid membrane containing bis(pentafluorobenzyl)tin(IV) dibromide and acquire the selectivity to α-hydroxycarboxylates.

As a prior oxidation procedure for the determination of total nitrogen in water based on an electrolytic reduction of nitrate to ammonia, the oxidation of 11 amino acids and 5 aminocarboxylic acids to nitrate with peroxodisulfate was studied spectrophotometrically. With 2 g of potassium peroxodisulfate and 0.8 g of sodium hydroxide, a 15 mL sample solution was heated to 200°C for 1 hour to oxidize these organic nitrogen compounds to nitrate, and to decompose any excess peroxodisulfate to sulfate. By the proposed method, except for histidine and CyDTA, individual amino acids and aminocarboxylic acids containing up to 3.2 mg of nitrogen (3.2 mgN/15 mL) were successfully oxidized to nitrate. Mixtures involving CyDTA or an amino acid having complicated structure were also found to be successfully oxidized to nitrate between 0.42 mgN/15 mL and 2.8 mgN/15 mL. These results suggest that the proposed method can be combined with the electrolytic reduction of nitrate to ammonia to establish an analytical system for the determination of total nitrogen in water.