Masataka Hiraide

Flotation of traces of heavy metals coprecipitated with aluminum hydroxide from water and sea water

Abstract Microgram quantities of heavy metals in 1-l samples of water and sea water are quantitatively coprecipitated with aluminum hydroxide at pH 9.5. The precipitate is floated with the aid of sodium oleate and small nitrogen bubbles, separated and dissolved in 2 M nitric acid, and the heavy metals are determined by atomic-absorption spectrometry. The method is rapid and applicable to 9 heavy metals at the low p.p.b. level.

Collection of trace heavy metals complexed with ammonium pyrrolidinedithiocarbamate on surfactant-coated alumina sorbents

Surfactant aggregates were formed on alumina surfaces by mixing 100 mg of sodium dodecyl sulfate (SDS) and 1.5 g of gamma-alumina in 50 ml of water. The SDS-coated alumina incorporated water-insoluble metal-ammonium pyrrolidinedithiocarbamate complexes over the pH range 2-8 with a recovery of > 97%. The metals were quantitatively desorbed from the alumina with 4 mol 1(-1) nitric acid, leaving > 99% of SDS on the solid phase. They were determined by inductively coupled plasma mass spectrometry or graphite furnace atomic absorption spectrometry. The proposed method was successfully applied to the determination of traces of iron, cobalt, nickel, copper, cadmium and lead in high-purity alumina.

Separation and determination of traces of heavy metals complexed with humic substances in fresh waters by sorption on diethylaminoethyl-sephadex a-25

Abstract Copper(II), lead and cadmium complexed with humic and fulvic acids in filtered 1-l samples of fresh water are sorbed on a column containing 0.5 ml of the macroreticular weak-base anion exchanger, diethylaminoethyl-Sephadex A-25 at a flow rate of 20 ml min −1 . Simple metal cations are not sorbed at all. The sorbed trace metals are quantitatively desorbed with 4 M nitric acid batchwise and determined by graphite-furnace atomic absorption spectrometry. For synthetic aqueous solutions containing traces of heavy metals and humic acid, the results are in conformity with those obtained by cationexchange separation. About 80% of the sorbed humic substances are eluted with 0.5 M sodium hydroxide solution from the A-25 column and its quantity is estimated spectrophotometrically at 400 nm.

Concentration of heavy metal ions in water using thermoresponsive chelating polymer

Thermoresponsive polymers, poly(N-isopropylacrylamide) (PNIPAAm), having chelating functionalities were synthesized. PNIPAAm-imidazole (-Im) was precipitated and formed a gum-like aggregate in the neutral pH region at 50 degrees C, while PNIPAAm-carboxylic acid (COOH) and PNIPAAm-iminodiacetic acid (-IDA) remained soluble even at pH 7. An addition of a paired ion, dodecyltrimethylammonium ion, was effective for inducing the precipitation of those polymers. PNIPAAm-Im was useful for collecting copper(II), nickel(II), cobalt(II), and lead(II), but was ineffective for cadmium(II) recovery. In contrast, PNIPAAm-COOH collected cadmium(II), while insufficiently recovered cobalt(II) and nickel(II). PNIPAAm-IDA was the best choice for collecting all metal ions in neutral pHs. After 20-folds concentration, the metal ions in river and seawater were successfully determined by graphite furnace atomic absorption spectrometry (GFAAS).

Preconcentration of traces of cobalt, nickel, copper and lead in water by thermoresponsive polymer-mediated extraction for tungsten filament electrothermal vaporization-inductively coupled plasma mass spectrometry

A simple and rapid preconcentration method was developed for the determination of trace metals (Co, Ni, Cu, Pb) in water samples by electrothermal vaporization (ETV) inductively coupled plasma mass spectrometry (ICP-MS). The method is based on the thermoresponsive precipitation of a water-soluble polymer, poly(N-isopropylacrylamide) [PNIPAAm], from the aqueous sample solution and the simultaneous incorporation of hydrophobic metal chelates into the precipitate. To a 100 ml sample solution (pH 3) were added 20 mg of ammonium pyrrolidinedithiocarbamate (APDC), 60 mg of PNIPAAm, and 850 mg of NaNO3. When the solution was warmed at 50 °C, PNIPAAm precipitated to form a gum-like aggregate (polymer phase). Hydrophobic metal–APDC chelates were quantitatively incorporated into the polymer phase. The polymer phase was easily taken up and dissolved with N,N-dimethylformamide to prepare 1 ml of solution. A 5 µl aliquot of the resulting solution, containing palladium as a modifier, was placed onto a doubly coiled tungsten filament in an ETV system. Four metals (Co, Ni, Cu, and Pb) were simultaneously determined with ETV-ICP-MS, whereas Cd gave very small signals probably due to the volatile property of the Cd–APDC chelate. Because of the highly efficient concentration (100-fold), the determination of these heavy metal ions at pg ml−1 to ng ml−1 levels was successfully achieved. The precision and accuracy of the proposed method were evaluated by analyzing a certified water sample.

Immobilization of 1-nitroso-2-naphthol on surfactant-coated alumina for the collection of traces of cobalt(II) ions

Positively charged alumina surfaces were coated with sodium dodecyl sulfate, into which 1-nitroso-2-naphthol was immobilized. The alumina particles were effectively used for the collection of nanogram amounts of cobalt(II) from aqueous solutions of pH 1–2.5. The method has been applied to the electrothermal AAS determination of cobalt in high-purity zinc metal.

Separation and determination of chromium(VI) anions and chromium(III) associated with negatively charged colloids in river water by sorption on DEAE-Sephadex A-25

SummaryChromium(VI) anions, along with chromium(III) associated with negatively charged colloids, are sorbed on a macroreticular weak-base anion exchanger DEAE-Sephadex A-25 and then selectively desorbed by reduction with 5% (w/v) hydroxylammonium chloride solution for the determination by graphite-furnace atomic absorption spectrometry. The chromium concentration is increased 100-fold, allowing detection of chromium(VI) down to ca. 0.01 μg/l. Chromium(III) associated with negatively charged colloids is also determined after desorption with 4 mol/l nitric acid.

Aqueous size-exclusion chromatography of humic acids on a sephadex gel column with diluted phosphate buffers as eluents

Abstract The elution behavior of humic acids on a Sephadex gel column is senstive to the composition, concentration, and pH of the eluent. the concentrations of the eluent in the literature are too high to obtain the correct molecular size distribution of humic acids. By reducing the concentration of phosphate buffer eluents to about a hundredth of conventional concentrations, the correct distribution is obtained. In the proposed method, 1 ml of 0.1% sample solution is introduced into a Sephadex G-50 column (2.2-cm diameter, 55 cm long) and humic acids are eluted with a 10−3 M phosphate buffer solution (pH 7–9) at a flow rate of 1 ml min−1.

Preconcentration of trace heavy metals in large aqueous samples by coprecipitation—flotation in a flow system

Abstract In a stream (0.5 1 min−1) of sample solution, trace heavy metals are quantitatively coprecipitated with indium hydroxide and floated with sodium oleate and nitrogen bubbles. Indium and the surfactant are removed by solvent extraction. Cadmium at the ng l−1 level in 20 l of water is concentrated 2000-fold with recoveries of greater than 93%.

Humic and other negatively charged colloids of iron and copper in river water

Abstract Iron and copper present as humic and other negatively charged colloids are studied by sorption on indium-treated XAD-2 resin and DEAE-Sephadex A-25 anion exchanger and by filtration. The iron species include colloidal particles consisting of hydrated iron(III) oxide, clay and humic substances and smaller amounts of hydrated iron(III) oxide-clay or -silica aggregates, whereas most of the copper exists as humic complexes.