Mitsuko Oshima

Determination of total and dissolved amount of iron in water samples using catalytic spectrophotometric flow injection analysis.

A flow injection spectrophotometric method has been developed for the determination of dissolved and total amounts of iron in tap and natural water samples. The method for the determination of iron employs a sample acidification step in order to decompose iron hydroxide and iron-complexes into free iron, Fe(III) and Fe(II). The amounts of free iron were detected using a catalytic action of Fe(III) and Fe(II) on the oxidation of N,N-dimethyl-p-phenylenediamine in the presence of hydrogen peroxide. Increase in absorbance of oxidized product was detected spectrophotometrically at 514 nm. The proposed method allows 0.02 and 0.06 microg l(-1) of LOD and LOQ, respectively, with relative standard deviation (RSD) below 2%. The accuracy and the precision of the method were evaluated by the analysis of the standard reference material, river water. The developed method was successfully applied to real water samples.

Speciation of arsenic(III) and arsenic(V) by inductively coupled plasma-atomic emission spectrometry coupled with preconcentration system

A novel and simple flow-based method was developed for the simultaneous determination of As(III) and As(V) in freshwater samples. Two miniature columns with a solid phase anion exchange resin, placed on two 6-way valves were utilized for the solid-phase collection/concentration of arsenic(III) and arsenic(V), respectively. As(III) could be retained on the column after its oxidation to As(V) species with an oxidizing agent. The collected analytes were then sequentially eluted by 2M nitric acid and introduced into ICP-AES. Potassium permanganate was examined as potential oxidizing agent for conversion of As(III) to As(V). The standard deviation of the analytical signals (peak height) for the replicate analysis (n=5) of 0.5mugl(-1) solution were 3 and 5% for As(III) and As(V), respectively. The limit of detection (3sigma) for both As(III) and As(V) were 0.1mugl(-1). The proposed system produced satisfactory results on the application to the direct analysis of inorganic arsenic species in freshwater samples.

On-line preconcentration using dual mini-columns for the speciation of chromium(III) and chromium(VI) and its application to water samples as studied by inductively coupled plasma-atomic emission spectrometry

On-line preconcentration system for the selective, sensitive and simultaneous determination of chromium species was investigated. Dual mini-columns containing chelating resin were utilized for the speciation and preconcentration of Cr(III) and Cr(VI) in water samples. In this system, Cr(III) was collected on first column packed with iminodiacetate resin. Cr(VI) in the effluent from the first column was reduced to Cr(III), which was collected on the second column packed with iminodiacetate resin. Hydroxyammonium chloride was examined as a potential reducing agent for Cr(VI) to Cr(III). The effects of pH, sample flow rate, column length, and interfering ions on the recoveries of Cr(III) were carefully studied. Five millilitres of a sample solution was introduced into the system. The collected species were then sequentially washed by 1M ammonium acetate, eluted by 2M nitric acid and measured by ICP-AES. The detection limit for Cr(III) and Cr(VI) was 0.08 and 0.15mugl(-1), respectively. The total analysis time was about 9.4min. The developed method was successfully applied to the speciation of chromium in river, tap water and wastewater samples with satisfied results.

Synthesis of cross-linked chitosan possessing N-methyl-d-glucamine moiety (CCTS-NMDG) for adsorption/concentration of boron in water samples and its accurate measurement by ICP-MS and ICP-AES

A chitosan resin derivatized with N-methyl-d-glucamine (CCTS-NMDG) was synthesized by using a cross-linked chitosan (CCTS) as base material. The N-methyl-d-glucamine (NMDG) moiety was attached to the amino group of CCTS through the arm of chloromethyloxirane. The adsorption behavior of 59 elements on the synthesized resin was systematically examined by using the resin packed in a mini-column, passing water samples through it and measuring the adsorbed elements in eluates by ICP-MS. The CCTS-NMDG resin shows high ability in boron sorption with the capacity of 0.61mmolml(-1) (=2.1mmol g(-1)). The sorption kinetics of this resin was faster than that of the commercially available resins. Other advantages of the synthesized resin are: (1) quantitative collection of boron at neutral pH regions; (2) complete removal of large amounts of matrices; (3) no loss of efficiency over prolonged usage; (4) effective collection of boron in wide range concentration using a mini column containing 1ml resin; (5) complete elution of boron with 1moll(-1) nitric acid. The resin was applied to the collection/concentration of boron in water samples. Boron in tap water and river water was found to be in the range of 6-8microgl(-1). The limit of detection (LOD) of boron after pretreatment with CCTS-NMDG resin and measurement by ICP-MS was 0.07microgl(-1) and the limit of quantification (LOQ) was 0.14microgl(-1) when the volume of each sample and eluent was 10ml.

Synthesis of novel chitosan resin possessing histidine moiety and its application to the determination of trace silver by ICP-AES coupled with triplet automated-pretreatment system.

A novel chitosan resin, cross-linked chitosan functionalized with histidine moiety (histidine-type chitosan resin), was synthesized for the collection and concentration of trace silver in aquatic samples. A triplet automated-pretreatment system (Triplet Auto-Pret System) installed mini-columns packed with the synthesized histidine-type chitosan resin was coupled with an inductively coupled plasma-atomic emission spectrometry (ICP-AES) for a rapid and sensitive analysis. Adsorption behavior of 50 elements on the histidine-type chitosan resin was examined. A trace amount of Ag(I) was shown a good adsorption in wide pH regions (pH 5-9), and Ag(I) adsorbed was readily recovered with 1 M nitric acid solution. The limit of detection (3sigma) for silver was 0.03 microg L(-1). The system was successfully applied to river water and dipped water in silver coated container.

Simple flow-injection system for the simultaneous determination of nitrite and nitrate in water samples.

A novel spectrophotometric reaction system was developed for the determination of nitrite as well as nitrate in water samples, and was applied to a flow-injection analysis (FIA). The spectrophotometric flow-injection system coupled with a copperised cadmium reductor column was proposed. The detection was based on the nitrosation reaction between nitrite ion and phloroglucinol (1,3,5-trihydroxybenzene), a commercially available phenolic compound. Sample injected into a carrier stream was split into two streams at the Y-shaped connector. One of the streams merged directly and reacted with the reagent stream: nitrite ion in the samples was detected. The other stream was passed through the copperised cadmium reductor column, where the reduction of nitrate to nitrite occurred, and the sample zone was then mixed with the reagent stream and passed through the detector: the sum of nitrate and nitrite was detected. The optimised conditions allow a linear calibration range of 0.03-0.30mug NO(2)(-)-Nml(-1) and 0.10-1.00mug NO(3)(-)-Nml(-1). The detection limits for nitrite and nitrate, defined as three times the standard deviation of measured blanks are 2.9ng NO(2)(-)-Nml(-1) and 2.3ng NO(3)(-)-Nml(-1), respectively. Up to 20 samples can be analyzed per hour with a relative standard deviation of less than 1.5%. The proposed method could be applied successfully to the simultaneous determination of nitrite and nitrate in water samples.

Development of column-pretreatment chelating resins for matrix elimination/multi-element determination by inductively coupled plasma-mass spectrometry

Chelating resins, two kinds of iminodiacetate derivatives (IDA) of cross-linked chitosan (CCS) were synthesized and investigated for adsorption capacity, matrix elimination and collection/concentration of analytes by a column pretreatment in a multi-element ICP-MS determination method. The adsorption behavior of 54 elements at the 10 ng ml(-1) level on chitosan derivatives in a packed mini-column was systematically examined. Almost 30 kinds of metal ions were recovered quantitatively at pH 5 with CCS-HP/IDA (cross-linked chitosan possessing N-2-hydroxypropyl iminodiacetic acid groups) column. Compared with available chitosan-iminodiacetate resin, CHITOPEARL CI-03, the recovery of the metal ions such as Cu, Pb and La is satisfactory with CCS-IDA (cross-linked chitosan possessing N,N-iminodiacetic acid groups) and CCS-HP/IDA using 2 M nitric acid as an eluent, which may be attributed to the difference of cross-linking and macroporous structure. Compared with Chelex-100, the adsorption efficiency is in the order: Chelex-100 > CCS-IDA > CCS-HP/IDA, especially in the chelating ability for alkaline earth metals. The resin with a longer spacer (CCS-HP/IDA) showed higher adsorption selectivity between heavy metal ions and alkaline earth metals at pH < 7. The separation efficiency of the major matrix cations in seawater (Na. K, Mg, Ca) has also been investigated, and matrix interference was negligible even in a seawater sample at pH 5 with CCS-HP/IDA. The recoveries of Mn at pH 5 with CCS-HP/IDA or Chelex-100 were almost 100%. However, those of Mg with each resin were 4 or 98%, respectively. The adsorption capacities of synthesized CCS-HP/IDA for Cu(II), Pb(II) and La(III) were 0.90, 0.65 and 0.34 mmol g(-1), respectively. Therefore, the chelating chitosan resins developed are applicable to the pretreatment of trace amounts of elements in various kinds of water samples.

Sequential-injection on-line preconcentration using chitosan resin functionalized with 2-amino-5-hydroxy benzoic acid for the determination of trace elements in environmental water samples by inductively coupled plasma-atomic emission spectrometry

A new chelating resin using chitosan as a base material was synthesized. Functional moiety of 2-amino-5-hydroxy benzoic acid (AHBA) was chemically bonded to the amino group of cross-linked chitosan (CCTS) through the arm of chloromethyloxirane (CCTS-AHBA resin). Several elements, such as Ag, Be, Cd, Co, Cu, Ni, Pb, U, V, and rare earth elements (REEs), could be adsorbed on the resin. To use the resin for on-line pretreatment, the resin was packed in a mini-column and installed into a sequential-injection/automated pretreatment system (Auto-Pret System) coupled with inductively coupled plasma-atomic emission spectrometry (ICP-AES). The sequential-injection/automated pretreatment system was a laboratory-assembled, and the program was written using Visual Basic software. This system can provide easy operation procedures, less reagent consumption, as well as less waste production. Experimental variables considered as effective factors in the improvement sensitivity, such as an eluent concentration, a sample and an eluent flow rate, pH of samples, and air-sandwiched eluent were carefully optimized. The proposed system provides excellent on-line collection efficiency, as well as high concentration factors of analytes in water samples, which results in highly sensitive detection of ultra-trace and trace analysis. Under the optimal conditions, the detection limits of 24 elements examined are in the range from ppt to sub-ppb levels. The proposed method was validated by using the standard reference material of a river water, SLRS-4, and the applicability was further demonstrated to the on-line collection/concentration of trace elements, such as Ag, Be, Cd, Co, Cu, Ni, Pb, U, V, and REEs in water samples.

Adsorption behavior of uranium(VI) and other ionic species on cross-linked chitosan resins modified with chelating moieties.

Cross-linked chitosan resins with catechol (catechol-type chitosan, type 1 and type 2), iminodiacetic acid (IDA-type chitosan), iminodimetylphosphonic acid (IDP-type chitosan), phenylarsonic acid (phenylarsonic acid-type chitosan), or serine (serine-type chitosan) were prepared for the collection and concentration of uranium(VI). The adsorption behavior of U(VI) and other ionic species, such as metal ions and oxo-acid ions, on the cross-linked chitosan (base material) and chitosan resins modified with chelating moieties was examined using a column procedure. Especially, the catechol-type chitosan (type 2) adsorbed U(VI) at pH 2-7, and selectively collected U(VI) at acidic pH regions by forming a stable chelate with hydroxyl groups of catechol moiety introduced to the chitosan. Also, the adsorption properties of cationic and anionic species present in aquatic media were elucidated. The adsorption ability for U(VI) was in the order: catechol-type chitosan (type 2)>serine-type chitosan>phenylarsonic acid-type chitosan>the others. The catechol-type chitosan (type 2) was useful for the collection and concentration of uranium(VI).

Spectrophotometric determination of phosphorus as orthophosphate based on solvent extraction of the ion associate of molybdophosphate with malachite green using flow injection

Phosphorus as orthophosphate in water was determined by a spectrophotometric method involving flow injection coupled with solvent extraction. The ion associate formed between molybdophosphate and Malachite Green was extracted into benzene-4-methylpentan-2-one (1 + 2 V/V) and the absorbance was measured at 630 nm. The carrier stream was 0.005 M sulphuric acid and the reagent stream contained ammonium molybdate, Malachite Green and sulphuric acid. A newly designed phase separator was used to separate the organic phase. The sampling rate was 40 samples per hour. Calibration graphs were linear below 30 ng ml–1 and below 1 µg ml–1 of phosphorus on injecting samples of 300 and 10 µl, respectively. The detection limit was 0.1 ng ml–1 of phosphorus. Phosphorus in river water was determined satisfactorily by the proposed method.