Kunio Ohzeki

Enrichment of trace amounts of copper as chelate compounds using a finely divided ion-exchange resin

The enrichment of trace amounts of copper as complexes with various chelating agents was examined with the use of finely divided anion- and cation-exchange resins of the macroreticular type. Of the 16 chelating agents studied, bathocuproinedisulphonate (BCS) combined with the use of a finely divided anion-exchange resin was the most effective for the rapid enrichment of copper from large sample volumes. The resin particles holding the copper(I)-BCS complex were collected on a membrane filter and subsequently suspended in a small volume of 0.1 M hydrochloric acid. The resin suspension was then subjected to electrothermal atomisation atomic absorption spectrometry. The method was applied to the determination of copper in sea and river water samples and the results were compared with those obtained by densitometric measurement of the solid-state absorbance of the copper(I)-BCS complex in the resin phase.

Solid-phase extraction of trace amounts of beryllium(II) from natural water samples on a glass-fibre filter followed by solid-phase spectrophotometric determination using Chromazurol B

A selective and sensitive method for the determination of beryllium(II) is described, based on the combined use of solid-phase extraction on a glass-fibre filter (GFF) and solid-phase spectrophotometry using Chromazurol B (CAB). In solid-phase spectrophotometry, beryllium(II) is fixed and determined directly on a membrane filter as the BeII–CAB complex formed in the presence of hexadecyltrimethylammonium bromide. The detection limit is 0.4 ng for 30 cm3 of sample solution. Trace amounts of beryllium(II) in aqueous sample solutions are first extracted on a GFF from a solution containing ethylenediaminetetraacetic acid as a masking agent of co-existing ions at pH 9.5, then determined after desorption from the GFF with 30 cm3 of 0.1 mol dm–3 hydrochloric acid. A recovery of 96.3% is achieved. The proposed method was applied to river water and hot spring water samples with pH values in the range 1.6–3.6 using 3.0–50.0 cm3 of sample solution. The concentrations of beryllium(II) found were in the range 0.12–3.52 ppb.

Determination of molybdenum in sea water by solid-phase spectrophotometry

Abstract A simple and sensitive spectrophotometric method for the determination of molybdenum(VI) in sea water samples was developed. It is based on the extraction of the Mo(VI)-phenylfluorone complex on a membrane filter by simple filtration and direct measurement of the absorbance on the filter. The extraction was done in the presence of zephiramine and only 2–10 ml of sample solution was required. No preliminary treatment of the sea water sample was required to isolate molybdenum(VI) from the matrix. The absorbance was measured by the zero and first derivative modes. The tolerance limit for foreign ions was improved by measuring the first derivative absorbance.

Solid-phase spectrophotometric determination of germanium on a membrane filter after collection using phenylfluorone and Zephiramine

A highly sensitive and simple method for the determination of germanium(IV) has been developed. Germanium(IV) was extracted on a membrane filter as the phenylfluorone complex from a dilute hydrochloric acid (1 + 7) medium containing Zephiramine and the complex on the membrane filter was then determined by solid-phase spectrophotometry. A 1000-fold molar excess of Zephiramine over germanium(IV) at the nmol level was required for the formation of the germanium(IV)-phenylfluorone complex. The detection limit of germanium(IV) was found to be 1.9 ng for 40 ml of the sample solution. The method was applied to the determination of germanium(IV) in hot spring water and groundwater. The concentrations of germanium(IV) found were in the range 4.36–37.7 p.p.b. for hot spring water and 0–1.97 p.p.b. for groundwater.

Studies on the adsorption of trace amounts of beryllium(II) on the surface of silica fibres from an aqueous phase for the development of a novel enrichment technique for electrothermal atomic absorption spectrometry

Trace amounts of beryllium(II) were adsorbed on the surface of silica fibres from a weak alkaline solution. The distribution ratio depended on the pH of the solution; however, a constant value (log D= 5.1) was obtained at pH 9.5 in the concentration range 6.4–220 µmol kg–1 in the silica phase. From the pH versus D curve, it was deduced that the beryllium(II) species adsorbed was (—SiO)Be(OH)2– or (–SiO)2Be(OH)22–. Based on these phenomena a simple enrichment technique was developed for the determination of trace amounts of beryllium(II) by electrothermal atomic absorption spectrometry. A 50–500 ml portion of the sample solution (pH 9.5) containing up to 6 ng of beryllium(II) was passed through a stack of three sheets of silica-fibre filter to collect the beryllium(II), which was then desorbed using three 0.5 ml portions of 0.5 mol l–1 HCl containing 15 mg l–1 of silicon for electrothermal atomic absorption spectrometry. A concentration factor of over 300 was easily attained. The detection limit, based on three times the standard deviation of the blank, was 0.15 ng of beryllium(II) for 500 ml of solution. The method was applied to the determination of beryllium(II) in natural water samples. A quantitative recovery was obtained when 3.0 or 6.0 ng of beryllium(II) were added to 500 ml of sea-water.

Determination of trace amounts of cobalt(II) by thin-layer spectrophotometry after enrichment on a membrane filter as the PAN complex

A simple, selective and sensitive method for the determination of trace amounts of cobalt(II) has been developed. The method is based on the fixation of cobalt as the 1-(2-pyridylazo)-2-naphthol complex on a membrane filter and the direct determination of the reflection absorbance of the complex by densitometry. The working range of the calibration graph was 0.05–0.5 µg of cobalt(II). The recovery of cobalt(II) was not affected by the volume of sample solution up to 300 ml. The ligand buffer solution, composed of ethylenediaminetetraacetic acid and an excess of zinc(II), was found to be effective for masking interferences from foreign cations, especially from iron(III). The method was applied to the determination of cobalt(II) in white wine. The concentration of cobalt(II) found in four different wine samples was in the range 2.5–4.4 µg l–1.

Electrocatalysis for proton reduction by a coated Nafion® membrane dispersing ruthenium moieties

Electrocatalytic proton reduction was studied using Ru-red ([(NH3)5RuIIIORuIV(NH3)4ORuIII(NH3)5]Cl6) dispersed into a Nafion® membrane coated on a basal-plane pyrolytic graphite (BPG) electrode (denoted as BPG/Nf[Ru-red]) in a pH 1 electrolyte solution. It was found that the Nf[Ru-red] shows high activity in H+ reduction to produce H2. The electrocatalytic reaction by Ru-red embedded in the polymer membrane started to take place by forming catalytically active species after irreversible change of the complex under cathodic conditions. Electrochemical features of the Ru-red in the membrane as well as electrocatalysis by the Nf[Ru-red] for H+ reduction were discussed based on the results of CV measurement, UV–Vis spectroscopy before and after the electrochemical process and potentiostatic electrolysis.

Determination of trace amounts of aluminium in tap water by spectrophotometry after collection on a membrane filter using Chrome Azurol S and Zephiramine

A sensitive and selective spectrophotometric method for the determination of aluminium(III) using Chrome Azurol S and Zephiramine is described. The ion-pair precipitate formed between Zephiramine and perchlorate ions is effective for the enrichment of aluminium(III) on a membrane filter as its ternary complex with Chrome Azurol S and Zephiramine. The solid-state absorbance of the complex on the membrane filter is measured at 640 and 700 nm against a blank thin layer and the difference is calculated. Although the calibration graph does not obey Beers law good reproducibility is observed, the relative standard deviation for 0.10 µg of aluminium(III) in a 20-ml sample volume being 3.1%(n= 5). A ligand buffer solution, composed of trans-cyclohexane-1,2-diaminetetraacetic acid and an excess of zinc(II), is effective for masking interferences from foreign ions, particularly iron(III). The method has been applied to the determination of aluminium in tap water.

Determination of humic acid and iron(III) by solid-state spectrophotometry to study their interactions

A simple and sensitive method for the determination of humic acid has been developed. The method is based on the adsorptive enrichment of humic acid using a finely divided anion-exchange resin, collection of the resin on a membrane filter by filtration as a circular thin-layer, and direct measurement of the absorbance of the resultant thin-layer of resin by densitometry at 470 nm. Up to 80 µg of humic acid in 100 ml of sample solution can be determined, the limit of detection being 1.3 µg. The effect of iron(III) is masked with ethylenediaminetetraacetic acid (EDTA). Iron(III) is also determined by densitometry at 600 nm after enrichment on the thin-layer of resin as a complex with ammonium pyrrolidine dithiocarbamate (ammonium pyrrolidin-1-yldithioformate)(APDC), the limit of detection being 0.06 µg of iron(III). In the presence of humic acid, the blank value is obtained by masking the iron(III) as the EDTA complex, and calculating the net absorbance due to the APDC complex. The methods have been used to investigate the effect of humic acid on the formation of filterable iron(III) species, which can pass through a 0.45 µm membrane filter. The possibility of characterizing humic acid based on the formation of a complex with iron(III) has been shown.

Selective and sensitive spectrophotometric determination of copper in water after collection of its bathocuproine complex on an organic-solvent-soluble membrane filter

Abstract A rapid and simple preconcentration technique which can be used in place of solvent extraction, has been applied to the spectrophotometric determination of copper in water. Copper(II) is reduced to copper(I) by hydroxylammonium chloride and complexed with Bathocuproine (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline). The Bathocuproine complex is collected on a nitrocellulose membrane filter by passing the solution through the filter. The membrane filter and the complex are dissolved in a small volume of 2-methoxyethanol (Methylcellosolve) and the absorbance due to the complex in the solvent is measured at 477 nm. The proposed method is nearly specific to copper. It is less tedious than the conventional solvent extraction method and can be used by inexperienced workers. Enrichment factors as high as 100 can easily be attained, so that μg l −1 levels of copper in water can be determined precisely without using expensive apparatus such as a furnace atomic absorption spectrometer. The detection limit is 0.12 μg in 500 ml sample on a 3 σ b basis.