Novel flow injection-fluorometric method for the determination of trace silicate and its application to ultrapurified water analysis

A highly sensitive fluorescence quenching method for the determination of silicate based on the formation of an ion associate between molybdosilicate and Rhodamine B (RB) in nitric acid medium was developed. A flow injection system coupled with a fluorescence detector was used for the measurement of fluorescence intensity at 560 and 580 nm as excitation and emission wavelengths, respectively. The calibration graph for Si showed a linear range of 0.1–5 ng cm⁻³ with correlation coefficient of 0.9999, and the detection limit of 0.06 ng cm⁻³. The proposed method was successfully applied to the determination of silicate in ultrapurified water with satisfactory results.     

Synthesis of chitosan resin possessing 3,4-diamino benzoic acid moiety for the collection/concentration of arsenic and selenium in water samples and their measurement by inductively coupled plasma-mass spectrometry

A chitosan resin functionalized with 3,4-diamino benzoic acid (CCTS-DBA resin) was newly synthesized by using a cross-linked chitosan (CCTS) as base material. The adsorption behavior of trace amounts of elements on the CCTS-DBA resin was examined by the pretreatment with a mini-column and measurement of the elements by inductively coupled plasma-Mass spectrometry (ICP-MS). Arsenic(V) could be retained on the CCTS-DBA resin at pH 3 as an oxoanion of H₂AsO₄⁻. Selenium(VI) is strongly adsorbed at pH 2 and pH 3 as an oxoanion of SeO₄²⁻, while selenium(IV) as HSeO₃⁻ is adsorbed on the resin at pH 3. The sorption capacities are 82, 64, and 88 mg g⁻¹resin for As(V), Se(IV), and Se(VI), respectively. The effect of common anions and cations on the adsorption of As(V), Se(IV), and Se(VI) were studied; there was no interference from such anionic matrices as chloride, sulfate, phosphate, and nitrate up to 20 ppm, as well as from such artificial river water matrices as Na, K, Mg, and Ca after passing samples through the mini-column containing the resin. The CCTS-DBA resin was applied to the collection of arsenic and selenium species in bottled drinking water, tap water, and river water.     

Functionalization of chitosan with 3-nitro-4-amino benzoic acid moiety and its application to the collection/concentration of molybdenum in environmental water samples

A chitosan resin functionalized with 3-nitro-4-amino benzoic acid moiety (CCTS-NABA resin) was newly synthesized for the collection/concentration of trace molybdenum by using cross-linked chitosan (CCTS) as base material. The carboxyl group of the moiety was chemically attached to amino group of cross-linked chitosan through amide bond formation. The adsorption behavior of molybdenum as well as other 60 elements on the resin was examined by passing the sample solutions through a mini-column packed with the resin. After the elution of the elements collected on the resin with 1 M HNO₃, the eluates were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) and atomic emission spectrometry (ICP-AES).

The CCTS-NABA resin can adsorb several metal ions, such as vanadium, gallium, arsenic, selenium, silver, bismuth, thorium, tungsten, tin, tellurium, copper, and molybdenum at appropriate pHs. Among these metal ions, only molybdenum could be adsorbed almost completely on the resin at acidic regions. An excellent selectivity toward molybdenum could be obtained at pH 3–4. The adsorption capacity of CCTS-NABA resin for Mo(VI) was 380 mg g⁻¹ resin. Through the column pretreatment, alkali and alkaline earth metals in river water and seawater samples were successfully removed.

The CCTS-NABA resin was applied to the adsorption/collection of molybdenum in river water and seawater samples. The concentrations of molybdenum in river water samples were found in the range of 0.84 and 0.95 ppb (ng g⁻¹), whereas molybdenum in seawater was about 9 ppb. The validation of the proposed method was carried out by determining molybdenum in the certified reference materials of SLRS-4, CASS-4, and NASS-5 after passing through the CCTS-NABA resin; the results showed good agreement with the certified values.     

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 1 M ammonium acetate, eluted by 2 M nitric acid and measured by ICP-AES. The detection limit for Cr(III) and Cr(VI) was 0.08 and 0.15 μg l⁻¹, respectively. The total analysis time was about 9.4 min.The developed method was successfully applied to the speciation of chromium in river, tap water and wastewater samples with satisfied results.     

Chitosan functionalized with di-2-propanolamine: Its application as solid phase extractant for the determination of germanium in water samples by ICP-MS

Cross-linked chitosan was chemically modified with di-2-propanolamine via an arm of chloromethyloxirane (CCTS-DPA resin). The adsorption behavior of the resin towards 62 elements was examined using a mini-column pretreatment method, and the collected elements were eluted with 1 mol L^− 1 nitric acid before measurement by inductively coupled plasma-mass spectrometry (ICP-MS).The CCTS-DPA resin can adsorb several metal cations and several oxoanionic elements at appropriate pH. However, di-2-propanolamine (DPA) attached to cross-linked chitosan (CCTS) showed excellent ability and selectivity for the adsorption of germanium at pH 6 to 9. The adsorption capacity of the resin for germanium (IV) was found to be 106 mg g^− 1 resin, whereas the adsorption rate constant was 9.82 × 10^− 2 min^− 1. Through the column treatment, alkali and alkaline earth matrices in river water and seawater matrices could be completely removed. The resin can also successfully remove chloride and selenium that can interfere with the direct determination of germanium by ICP-MS. The applicability of the CCTS-DPA resin was further demonstrated for the collection/preconcentration of germanium in environmental water samples and its determination by ICP-MS. The concentrations of germanium in tap water, river water and seawater samples were found in the range of 0.011 to 0.022 μg L^− 1.     

Speciation of chromium in seawater by ICP-AES with dual mini-columns containing chelating resin.

A method for the preconcentration and speciation of chromium in seawater was developed. On-line preconcentration and determination were carried out by using inductively coupled plasma atomic emission spectrometry (ICP-AES) with dual mini-columns containing a chelating resin. In this system, Cr(III) was collected on the first column. The effluent containing residual chromium from the first column was collected on the second column after passing through a reduction-switching unit, in which the reducing agent was introduced, or not, for the reduction of Cr(VI) to Cr(lII). Cr(VI) was determined as the difference between the concentration of pre-reduced Cr(VI) and Cr(III) in the effluent from the first column. The detection limits for Cr(III) and Cr(VI) were 0.04 and 0.09 microg l(-1), respectively.     

Trace and ultratrace analysis of purified water samples and hydrogen peroxide solutions for phosphorus by flow-injection method.

A highly sensitive fluorescence-quenching method for the determination of phosphorus based on the formation of an ion associate between molybdophosphate and Rhodamine B (RB) was developed. A simple flow-injection system coupled with a fluorescence detector was used to measure the fluorescence intensity at 560 nm and 580 nm as an excitation and an emission wavelength, respectively. The calibration graph for phosphorus showed a good linearity in the range of (0 - 1) x 10(-7) M (1 M = 1 mol L(-1)), and a detection limit of 1 x 10(-9) M (S/N = 3). The proposed method was successfully applied to the determination of ultratrace amounts of phosphorus in ultrapurified and purified water samples, and to the determination of trace amounts of phosphorus in commercially-available hydrogen peroxide solutions with satisfactory results.     

Ultratrace determination of phosphorus in ultrapurified water by a slope comparison method

The analytical method for the determination of phosphorus in ultrapurified water was developed. Ultrapurified water was evaporated to concentrate phosphorus and the final sample volume for analysis was 10 ml. In 0.55 mol l⁻¹ HCl, orthophosphate forms molybdophosphate, and then the molybdophosphate forms ion associate with Malachite Green (MG), which can be collected on a tiny membrane filter (diameter: 5 mm, and effective filtering diameter: 2 mm). After the ion associate on the membrane filter is dissolved together with the membrane filter in 1 ml of methyl cellosolve (MC), the absorbance of MC solution is measured at 627 nm by a flow injection-spectrophotometric detection technique. When 10 ml of the sample solution was used for the procedures and absorbance measurement, the calibration graph is linear up to about 500 ng l⁻¹ of phosphorus and the detection limit was 8 ng l⁻¹ (S/N=3). For the determination of phosphorus in an ultrapurified water, 10-40 ml of sample solutions were transferred into poly(tetrafluoroethylene) (PTFE) beaker and evaporated to 5 ml or to dryness. To them, 0.003 mol l⁻¹ HCl was added to get 10 ml of final solution, which was used as sample. Phosphate is determined by comparing the slope of the varied sample volume after evaporation/concentration with a slope of the standard calibration graph (a slope comparison method: SCM). The SCM enables to evaluate the concentration of phosphate in ultrapurified waters more sensitively and accurately.     

Synthesis of chitosan resin possessing a phenylarsonic acid moiety for collection/concentration of uranium and its determination by ICP-AES

A chitosan resin possessing a phenylarsonic acid moiety (phenylarsonic acid type chitosan resin) was developed for the collection and concentration of trace uranium prior to inductively coupled plasma (ICP) atomic emission spectrometry (AES) measurement. The adsorption behavior of 52 elements was systematically examined by packing it in a minicolumn and measuring the elements in the effluent by ICP mass spectrometry. The resin could adsorb several cationic species by a chelating mechanism, and several oxo acids, such as Ti(IV), V(V), Mo(VI), and W(VI), by an anion-exchange mechanism and/or a chelating mechanism. Especially, U(VI) could be adsorbed almost 100% over a wide pH region from pH 4 to 8. Uranium adsorbed was easily eluted with 1 M nitric acid (10 mL), and the 25-fold preconcentration of uranium was achieved by using a proposed column procedure, which could be applied to the determination of trace uranium in seawater by ICP-AES. The limit of detection was 0.1 ng mL⁻¹ for measurement by ICP-AES coupled with 25-fold column preconcentration.