Chemically modified silica gel with aminothioamidoanthraquinone for solid phase extraction and preconcentration of Pb(II), Cu(II), Ni(II), Co(II) and Cd(II)

Silica gel chemically bonded with aminothioamidoanthraquinone was synthesized and characterized. The metal sorption properties of modified silica were studied towards Pb(II), Cu(II), Ni(II), Co(II) and Cd(II). The determination of metal ions was carried out on FAAS. For batch method, the optimum pH ranges for Pb(II), Cu(II) and Cd(II) extraction were ≥3 but for Ni(II) and Co(II) extraction were ≥4. The contact times to reach the equilibrium were less than 10 min. The adsorption isotherm fitted the Langmuir's model showed the maximum sorption capacities of 0.56, 0.30, 0.15, 0.12 and 0.067 mmol/g for Pb(II), Cu(II), Ni(II), Co(II) and Cd(II), respectively. In the flow system, a column packed modified silica at 20 mg for Pb(II) and Cu(II), 50 mg for Cd(II), 60 mg for Co(II), Ni(II) was studied at a flow rate of 4 and 2.5 mL/min for Ni(II). The sorbed metals were quantitatively eluted by 1% HNO₃. No interference from Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻ and SO₄²⁻ at 10, 100 and 1000 mg/L was observed. The application of this modified silica gel to preconcentration of pond water, tap water and drinking water gave high accuracy and precision (%R.S.D. ≤ 9). The method detection limits were 22.5, 1.0, 2.9, 0.95, 1.1 μg/L for Pb(II), Cu(II), Ni(II), Co(II) and Cd(II), respectively.     

Determination of trace impurities in high-purity iron using salting-out of polyoxyethylene-type surfactants

To an iron sample solution was added polyoxyethylene-4-isononylphenoxy ether (PONPE, nonionic surfactant, average number of ethylene oxides 7.5) and the surfactant was aggregated by the addition of lithium chloride. The iron(III) matrix was collected into the condensed surfactant phase in >99.9% yields, leaving trace metals [e.g., Ti(IV), Cr(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II), and Bi(III)] in the aqueous phase. After removing the surfactant phase by centrifugation, the remaining trace metals were concentrated onto an iminodiacetic acid-type chelating resin. The trace metals were desorbed with dilute nitric acid for the determination by inductively coupled plasma-mass spectrometry or graphite-furnace atomic absorption spectrometry. The proposed separation method allowed the analysis of high-purity iron metals for trace impurities at low μg g⁻¹ to ng g⁻¹ levels.     

Determination of trace metals by ICP-OES in plant materials after preconcentration of 1,10-phenanthroline complexes on activated carbon

In this work, 1,10-phenanthroline was used as a complexing agent for the separation and preconcentration of Cd(II), Co(II), Ni(II), Cu(II) and Pb(II) on activated carbon. The metals were adsorbed on activated carbon by two methods: static (1) and dynamic (2). The optimal condition for separation and quantitative preconcentration of metal ions with activated carbon for the proposed methods was for (1) in the static methods in the pH range 7-9. The desorption was found quantitative with 8 mol dm⁻³ HNO₃ for Cd(II) (92.6%), Co(II) (95.6%), Pb(II) (91.0%), and with 3 mol dm⁻³ HNO₃ for Cd(II) (95.4%), Pb(II) (100.2%). The preconcentration factor was 100 with R.S.D. values between 1.0 and 2.9%. For (2), the dynamic method (SPE), the pH range for the quantitative sorption was 7-9. The desorption was found quantitative with 8 mol dm⁻³ HNO₃ for Cd(II) (100.6%), Pb(II) (94.4%), and reasonably high recovery for Co(II) (83%), Cu(II) (88%). The optimum flow rate of metal ions solution for quantitative sorption of metals with 1,10-phenanthroline was 1-2 cm³ min⁻¹ whereas for desorption it was 1 cm³ min⁻¹. The preconcentration factor was 50 for all the ions of the metals with R.S.D. values between 2.9 and 9.8%.The samples of the activated carbon with the adsorbed trace metals can be determined by ICP-OES after mineralization by means of a high-pressure microwave mineralizer. The proposed method provides recovery for Cd (100.8%), Co (97.2%), Cu (94.6%), Ni (99.6%) and Pb (100.0%) with R.S.D. values between 1.2 and 3.2%.The preconcentration procedure showed a linear calibration curve within the concentration range 0.1-1.5 μg cm⁻³. The limits of detection values (defined as “blank + 3s” where s is standard deviation of the blank determination) are 5.8, 70.8, 6.7, 24.6, and 10.8 μg dm⁻³ for Cd(II), Pb(II), Co(II), Ni(II) and Cu(II), respectively, and corresponding limit of quantification (blank + 10s) values were 13.5, 151.3, 20.0, 58.9 and 33.2 μg dm⁻³, respectively.As a result, these simple methods were applied for the determination of the above-mentioned metals in reference materials and in samples of plant material.     

Solid phase extraction of metal ions using carbon nanotubes

The sorption behaviour of carbon nanotubes (CNTs) toward some divalent metal ions such as Cu(II), Co(II), Ni(II), Zn(II), Pb(II), Mn(II) and Cd(II) has been investigated systematically. The affinity order of the metal ions towards CNTs at pH in the range of 7.0-9.0 was: Cu(II) > Pb(II) > Zn(II) > Co(II) > Ni(II) > Cd(II) > Mn(II). The experimental parameters for preconcentration of copper, which exhibits the highest affinity towards carbon nanotubes, on a microcolumn packed with CNTs prior to its determination by flame atomic absorption spectrometry have been investigated. Copper can be quantitatively retained at pH 8.2 from sample volume up to 150 mL and then eluted completely with 0.1 mol L^− 1 HNO₃. The limit of detection limit for Cu(II) determination with FAAS detection was 2.1 μg L^− 1, and the RSD was 3.5% at the 50 μg L^− 1 level. Under the optimal conditions for copper enrichment also Zn(II), Pb(II) and Ni(II) could be quantitatively preconcentrated from water samples. The method was validated using a certified reference materials BCR-610 and SRM 1640.     

4-{[(2-Hydroxyphenyl)imino]methyl}-1,2-benzenediol (HIMB) anchored Amberlite XAD-16: Preparation and applications as metal extractants

Amberlite XAD-16 was loaded with 4-{[(2-hydroxyphenyl)imino]methyl}-1,2-benzenediol (HIMB) via azo linker and the resulting resin AXAD-16-HIMB explored for enrichment of Zn(II), Mn(II), Ni(II), Pb(II), Cd(II), Cu(II), Fe(III) and Co(II) in the pH range 5.0-8.0. The sorption capacity was found between 56 and 415 μmol g⁻¹ and the preconcentration factors from 150 to 300. Tolerance limits for foreign species are reported. The kinetics of sorption is not slow, as t_1/2 is ≤15 min. The chelating resin can be reused for seventy cycles of sorption-desorption without any significant change (<2.0%) in the sorption capacity. The limit of detection values (blank + 3 s) are 1.72, 1.30, 2.56, 2.10, 0.44, 2.93, 2.45 and 3.23 μg l⁻¹ for Zn, Mn, Ni, Pb, Cd, Cu, Fe and Co, respectively. The enrichment on AXAD-16-HIMB coupled with flame atomic absorption spectrometry (FAAS) monitoring is used to determine the metal ion ions in river and synthetic water samples, Co in vitamin tablets and Zn in powdered milk samples.     

A new method for simultaneous determination of Co(II), Ni(II) and Pd(II) as morpholine-4-carbodithioate complex by SPME-HPLC-UV system

A new approach for the analysis of Co(II), Ni(II) and Pd(II) as morpholine-4-carbodithioate (MDTC) complexes in aqueous medium by using solid phase microextraction (SPME)-high performance liquid chromatography (HPLC)-UV has been developed. The method involves sorption of metal complexes on PDMS fiber from aqueous solution followed by desorption in the desorption chamber of SPME-HPLC interface using acetonitrile:water (60:40) as mobile phase. A good separation of metal complexes is achieved on C₁₈ column. The detection limits of Co(II), Ni(II) and Pd(II) are 0.17, 0.11 and 0.06 ng ml⁻¹, respectively. These can be determined by the proposed method without interference from other common metal ions such as Mo(VI), V(V), Ag(I), Sn(IV), Cd(II), Pb(II), Zn(II), Ag(I), Sn(II), Cr(III) and Cr(VI). The method was applied to the determination of these metals in different alloy samples and drinking water sample.     

2-{[1-(3,4-Dihydroxyphenyl)methylidene]amino}benzoic acid immobilized Amberlite XAD-16 as metal extractant

2-{[1-(3,4-Dihydroxyphenyl)methylidene]amino}benzoic acid (DMABA) was loaded on Amberlite XAD-16 (AXAD-16) via azo linker and the resulting resin AXAD-16-DMABA explored for enrichment of Zn(II), Mn(II), Ni(II), Pb(II), Cd(II), Cu(II), Fe(III) and Co(II). The optimum pH values for extraction are 6.5-7.0, 5.0-6.0, 5.5-7.5, 5.0-6.5, 6.5-8.0, 5.5-7.0, 4.0-5.0 and 6.0-7.0, respectively. The sorption capacity was found between 97 and 515 μmol g⁻¹ and the preconcentration factors from 100 to 450. Tolerance limits for foreign species are reported. The kinetics of sorption is fast as t_1/2 is ≤5 min. The chelating resin can be reused for 50 cycles of sorption-desorption without any significant change (<1.5%) in the sorption capacity. The limit of detection values (blank +3 s) are 1.12, 1.38, 1.76, 0.67, 0.77, 2.52, 5.92 and 1.08 μg L⁻¹ for Zn(II), Mn(II), Ni(II), Pb(II), Cd(II), Cu(II), Fe(III) and Co(II), respectively. The enrichment on AXAD-16-DMABA coupled with monitoring by flame atomic absorption spectrometry (FAAS) is used to determine all the metal ion ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples.     

Solid Phase Extraction of Trace Metals in Seawater Using Morpholine Dithiocarbamate‐Loaded Amberlite XAD‐4 and Determination by ICP‐AES

Abstract

Application of morpholine dithiocarbamate (MDTC) coated Amberlite XAD‐4, for preconcentration of Cu(II), Cd(II), Zn(II), Pb(II), Ni(II) and Mn(II) by solid phase extraction and determination by inductively coupled plasma (ICP) atomic emission spectrometry (AES) was studied. The optimum pH values for quantitative sorption of Cu(II), Cd(II), Zn(II), Pb(II), Ni(II), and Mn(II) were 6.5–8.0, 7.0–8.5, 6.0–8.5, 6.5–8.5, 7.5–9.0, and 8.0–8.5, respectively. The metals were desorbed with 2 mol L^?1. The t_1/2 values for sorption of metal ions were 2.6, 2.9, 2.5, 2.6, 3.0, and 3.8 min respectively for Cu(II), Cd(II), Zn(II), Pb(II), Ni(II) and Mn(II). The effect of diverse ions on the determination of the previously named metals was studied. Simultaneous enrichment of the six metals was accomplished, and the method was applied for use in the determination of trace metal ions in seawater samples.     

Sensitive electrochemical sensor using a graphene–polyaniline nanocomposite for simultaneous detection of Zn(II), Cd(II), and Pb(II)

This work describes the development of an electrochemical sensor for simultaneous detection of Zn(II), Cd(II), and Pb(II) using a graphene–polyaniline (G/PANI) nanocomposite electrode prepared by reverse-phase polymerization in the presence of polyvinylpyrrolidone (PVP). Two substrate materials (plastic film and filter paper) and two nanocomposite deposition methods (drop-casting and electrospraying) were investigated. Square-wave anodic stripping voltammetry currents were higher for plastic vs. paper substrates. Performance of the G/PANI nanocomposites was characterized by scanning electron microscopy (SEM) and cyclic voltammetry. The G/PANI-modified electrode exhibited high electrochemical conductivity, producing a three-fold increase in anodic peak current (vs. the unmodified electrode). The G/PANI-modified electrode also showed evidence of increased surface area under SEM. Square-wave anodic stripping voltammetry was used to measure Zn(II), Cd(II), and Pb(II) in the presence of Bi(III). A linear working range of 1–300 μg L⁻¹ was established between anodic current and metal ion concentration with detection limits (S/N = 3) of 1.0 μg L⁻¹ for Zn(II), and 0.1 μg L⁻¹ for both Cd(II) and Pb(II). The G/PANI-modified electrode allowed selective determination of the target metals in the presence of common metal interferences including Mn(II), Cu(II), Fe(III), Fe(II), Co(III), and Ni(II). Repeat assays on the same device demonstrated good reproducibility (%RSD < 11) over 10 serial runs. Finally, this system was utilized for determining Zn(II), Cd(II), and Pb(II) in human serum using the standard addition method.     

Effects of various competing ligands on the kinetics of trace metal complexes of Laurentian Fulvic Acid in model solutions and natural waters

The objective of this work was to study the effects of the following Ligands: Chelex-100, Dowex MAC-3 and Dowex 50WX-8 using Competing Ligand Exchange Method. This objective was achieved by investigating complex dissociation kinetics of trace metals: Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Mn(II) and Pb(II) of a well-characterized Laurentian Fulvic Acid (LFA) in model solutions and in a natural waters of Lake Heva (Québec, Canada). The effects of variation in the competing ligands (including their quantities) on the complex dissociation kinetics were quantitatively characterized by their first-order dissociation rate coefficients. The kinetic lability of the metal complexes varied with the metal-to-LFA ratio, as expected from the theory of metal complexes of the chemically and physically heterogeneous complexants, LFA. The general trend in the metal-binding by the above competing ligands was: Dowex 50WX-8 > Chelex-100 > Dowex MAC-3. However, no difference was found between the Dowex 50WX-8 and Chelex-100 for Cd(II), Zn(II), and Co(II). The results revealed the importance of the quantity of Chelex-100 as a competing ligand in the metal(II)-LFA complexation, on the dissociation kinetics of these complexes in model solutions. By developing Competing Ligand Exchange Method as an analytical technique, for studying the relative affinities of the above competing ligands for metals complexation in natural waters this work has made a substantial contribution to analytical chemistry.     

Spectrafluorimetric method for the rapid screening of toxic heavy metals in water samples

A fast and inexpensive sensitive screening test for recognising potential wastewater contamination by the presence of highly toxic heavy metals is described. The test is based on the reaction of the toxic heavy metals Hg(II), Cd(II), Pb(II) and Ag(I) with 6-mercaptopurine (6-MP) to produce highly fluorescent complexes.Optimum experimental conditions include a buffer of pH 7.2 (0.1 M citric acid/0.2 M Na₂HPO₄), a chelating reagent concentration of 6×10⁻⁴ M and the addition of 10⁻⁴ M of o-phenanthroline. The fluorescence emitted by the complexes was measured at 380 and 540 nm for excitation and emission wavelengths, respectively.Detection limits of 4, 3, 6 and 3 μg l⁻¹ were achieved for Hg, Cd, Pb and Ag. Relative standard deviation (R.S.D.) were between ±2 and ±6% of the fluorescence signals for five identical samples. Potential interference effects from other heavy metals (Zn, Mn, Co, Fe, Ni and Cu), which could affect the response of the proposed screening test was investigated. Results showed that none of these metals give rise to noticeable fluorescence signals under the above described experimental conditions.Finally, the capability of the proposed heavy metal screening test for the analysis of contaminated water samples is discussed.     

Potentiometric Studies of Some Bivalent Metal Ion Complexes of a New Ligand,o-(2-Thiazolylazo)-4-Ethylphenol

Abstract

The complexations of a new ligand, o-(2-thiazolylazo)-4-ethylphenol(TAEP) with Ca(II), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hq(II) and Pb(II) have been studied by potentiometric titrations, at 25.0 ± 0.2°C and an ionic strength of 0.1 in 30% v/v dioxane-water mixture. The dissociation constant and spectral data of TAEP and formation constants of the complexes containing various molar ratios of metal ion to ligand, are reported. It is observed that Ca(II) forms only an ML complex in any molar ratios, whereas other metal ions react in two steps forming ML and ML₂ complexes in a 1:3 molar ratio. In the case of 1:1 and 1:2 molar ratios, Mn(II), Co(II), Cd(II) and Hg(II) seemed to form bi- or poly-nuclear complexes because of slightly different formation curves from those of 1:3 molar ratio. The sequence of the first successive formation constant is Cu > Hg > Ni > Pb > Co > Zn > Cd > Mn > Ca, showing Mellor-Maley's order. Further correlation is shown between the formation constants and the second ionization potentials of the metals.     

Simultaneous determination of suspended particulate trace metals (Co, Ni, Cu, Zn, Cd and Pb) in seawater with small volume filtration assisted by microwave digestion and flow injection inductively coupled plasma mass spectrometer

A new technique for the determination of suspended particulate trace metals (P-metals >0.2 μm), such as Co, Ni, Cu, Zn, Cd and Pb, in open ocean seawater has been developed by using microwave digestion coupled with flow injection inductively coupled plasma mass spectrometry (FI-ICP-MS). Suspended particulate matter (SPM) was collected from 500 mL of seawater on a Nuclepore filter (0.2 μm) using a closed filtration system. Both the SPM and filter were completely dissolved by microwave digestion. Reagents for the digestion were evaporated using a clean evaporation system, and the metals were redissolved in 0.8 M HNO₃. The solution was diluted with buffer solution to give pH 5.0 and the metals were determined by FI-ICP-MS using a chelating adsorbent of 8-hydroxyquinoline immobilized on fluorinated metal alkoxide glass (MAF-8HQ). The procedure blanks with a filter were found to be 0.048 ± 0.008, 10.3 ± 0.3, 0.27 ± 0.05, 3.3 ± 1.8, 0.02 ± 0.03 and 0.85 ± 0.09 ng L⁻¹ for Co, Ni, Cu, Zn, Cd and Pb, respectively (n = 14). Detection limits defined as 3 times the standard deviation of the blanks were 0.023, 0.90, 0.14, 5.3, 0.078 and 0.28 ng L⁻¹ for Co, Ni, Cu, Zn, Cd and Pb, respectively. Accuracy was evaluated using certified reference materials of chlorella (NES CRM No. 3) and marine sediment (HISS-1). The method was applied to the determination of vertical distributions for P-Co, Ni, Cu, Zn, Cd and Pb in the Western North Pacific.     

Admicelle-mediated collection followed by flotation for the preconcentration of trace metals in fresh waters

Dithizone-impregnated admicelles were prepared by mixing silica particles with dithizone and cetyltrimethylammonium chloride in 0.1 mol L⁻¹ aqueous ammonia. The resulting admicelles were added to 1000 mL of sample solution and dispersed by stirring for 15 min. Traces of Ni(II), Cu(II), Ga(III), Cd(II), Pb(II) and Bi(III) in the solution were simultaneously incorporated into the admicelles at pH 7.5-9. With the aid of a rising stream of numerous tiny bubbles, the admicelles were floated on the solution surface and collected in a small sampling vessel by suction. The metals were desorbed from the admicelles with dilute nitric acid and determined by inductively coupled plasma-mass spectrometry. The proposed method offered a 100-fold multielement preconcentration and it was applicable to the analysis of river and pond waters.     

An off-line automated preconcentration system with ethylenediaminetriacetate chelating resin for the determination of trace metals in seawater by high-resolution inductively coupled plasma mass spectrometry

A novel automated off-line preconcentration system for trace metals (Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) in seawater was developed by improving a commercially available solid-phase extraction system SPE-100 (Hiranuma Sangyo). The utilized chelating resin was NOBIAS Chelate-PA1 (Hitachi High-Technologies) with ethylenediaminetriacetic acid and iminodiacetic acid functional groups. Parts of the 8-way valve made of alumina and zirconia in the original SPE-100 system were replaced with parts made of polychlorotrifluoroethylene in order to reduce contamination of trace metals. The eluent pass was altered for the back flush elution of trace metals. We optimized the cleaning procedures for the chelating resin column and flow lines of the preconcentration system, and developed a preconcentration procedure, which required less labor and led to a superior performance compared to manual preconcentration (Sohrin et al. [5]). The nine trace metals were simultaneously and quantitatively preconcentrated from ∼120 g of seawater, eluted with ∼15 g of 1 M HNO₃, and determined by HR-ICP-MS using the calibration curve method. The single-step preconcentration removed more than 99.998% of Na, K, Mg, Ca, and Sr from seawater. The procedural blanks and detection limits were lower than the lowest concentrations in seawater for Mn, Ni, Cu, and Pb, while they were as low as the lowest concentrations in seawater for Al, Fe, Co, Zn, and Cd. The accuracy and precision of this method were confirmed by the analysis of reference seawater samples (CASS-5, NASS-5, GEOTRACES GS, and GD) and seawater samples for vertical distribution in the western North Pacific Ocean.     

Spectral and Thermal Studies of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) Complexes with 3-methylglutaric Acid

Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) 3-methylglutarates were prepared as solids with general formula MC₆ H₈ O₄ ×n H₂ O, where n =0–8. Their solubilities in water at 293 K were determined (7.0×10⁻² −4.2×10⁻³ mol dm⁻³ ). The IR spectra were recorded and thermal decomposition in air was investigated. The IR spectra suggest that the carboxylate groups are mono- or bidentate. During heating the hydrated complexes lose some water molecules in one (Mn, Co, Ni, Cu) or two steps (Cd) and then mono- (Cu) or dihydrates (Mn, Co, Ni) decompose to oxides directly (Mn, Cu, Co) or with intermediate formation of free metals (Co, Ni). Anhydrous Zn(II) complex decomposes directly to the oxide ZnO. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb in seawater using high resolution magnetic sector inductively coupled mass spectrometry (HR-ICP-MS)

A novel method, combining isotope dilution with standard additions, was developed for the analysis of eight elements (Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb) in seawater. The method requires just 12 mL of sample and employs an off-line pre-concentration step using the commercially available chelating resin Toyopearl AF-Chelate-650M prior to determination by high resolution inductively coupled plasma magnetic sector mass spectrometry (ICP-MS). Acidified samples were spiked with a multi-element standard of six isotopes (⁵⁷Fe, ⁶²Ni, ⁶⁵Cu, ⁶⁸Zn, ¹¹¹Cd and ²⁰⁷Pb) enriched over natural abundance. In addition, standard additions of a mixed Co and Mn standard were performed on sub-sets of the same sample. All samples were irradiated using a low power (119 mW cm⁻²; 254 nm) UV system, to destroy organic ligands, before pre-concentration and extraction from the seawater matrix. Ammonium acetate was used to raise the pH of the 12 mL sub-samples (off-line) to pH 6.4 ± 0.2 prior to loading onto the chelating resin. The extracted metals were eluted using 1.0 M Q-HNO₃ and determined using ICP-MS. The method was verified through the analysis of certified reference material (NASS-5) and the SAFe inter-comparison samples (S1 and D2), the results of which are in good agreement with the certified and reported consensus values. We also present vertical profiles of the eight metals taken from the Bermuda Atlantic Time Series (BATS) station collected during the GEOTRACES inter-comparison cruise in June 2008.     

Thermodynamic characteristic of complex formation of some metals with 3-(4-chlorophenylazo)pentane-2,4-dione in aqueous ethanol

Effective charges of atoms in tautomeric forms (enol-azo, keto-azo, hydrazo) of 3-(4-chlorophenylazo) pentane-2,4-dione (L) have been determined by MO LCAO in the Hückel approximation. The complex formation of a series of metals with L in aqueous ethanol has been investigated by potentiometric and conductometric titration. Based on the results of potentiometric titration, the standard thermodynamic functions of complex formation have been established. They vary in the following order:

On-line preconcentration and separation of Co, Ni and Cd via capillary microextraction on ordered mesoporous alumina coating and determination by inductively plasma mass spectrometry (ICP-MS)

In this paper, an ordered mesoporous alumina coating was prepared and applied to capillary microextraction (CME) of trace Co, Ni and Cd for the first time. The coated capillary was used for on-line coupling CME with inductively plasma mass spectrometry (ICP-MS) for the determination of trace metals of Co, Ni and Cd. The porous structure of Al₂O₃ coating was examined by SEM and TEM. The effects of the extraction parameters including pH, sample flow rate and volume, elution solution and interfering ions on the recovery of analytes have been investigated and optimized. Under the optimized conditions, the limits of detection were 0.33, 1.5 and 1.4 ng L⁻¹ for Co, Ni and Cd, respectively, with a preconcentration factor of 10 times. The precisions for all investigated elements were 2.7, 4.1 and 2.5% (c = 0.05 ng L⁻¹, n = 7), for Co, Ni and Cd, respectively, and the sample frequency was 8 h⁻¹.The proposed method was successfully applied for the analysis of trace metals in water, rice and urine samples with the recovery of 94-105%. In order to validate the proposed method, two certified reference materials of GBW 0913 human urine and NIES No.10-b rice flour were analyzed, and the determination values are in good agreement with the certified values. The ordered mesoporous Al₂O₃ coated capillary can be used more than 20 times without decreasing the extraction efficiency.     

Thiacalix[4]arenetetrasulfonate as specific pre-column chelating reagent for nickel(II) ion in kinetic differentiation mode high-performance liquid chromatography

Thiacalix[4]arenetetrasulfonate (TCAS) has been examined as a pre-column chelating reagent for the determination of trace metal ions by kinetic differentiation mode (KD) ion-pair reversed-phase high-performance liquid chromatography (HPLC) with spectrophotometric detection. Among 14 kinds of common metal ions tested here, viz. Al(III), Ca(II), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Hg(II), Mg(II), Mn(II), Ni(II), Pb(II), V(V), and Zn(II) ion, only Ni(II) ion was detected as the TCAS chelate in the HPLC separation stage in spite of TCAS forming the chelates with various metal ions except for Al(III), Ca(II), and Mg(II) at the pre-column chelation stage. The undetected metal-TCAS chelates seemed to be dissociated on an HPLC column where no added TCAS was present in the mobile phase because of their kinetic unstability. The calibration graph for Ni(II) ion gave a wide linear dynamic range (40-20,000 nM) with the very low detection limit (DL) (3σ base-line fluctuation) to be 5.4 nM (0.32 ng ml⁻¹). The practical applicability of the KD-HPLC method with TCAS was demonstrated with the determination of trace Ni in coal fly ash.