Determination Of Trace Metal Ions Research Articles

Synthesis, characterization, and application of ZnO@SiO2-APTES core-shell composite for selective electrochemical detection of Pb2+ ions

This study focuses on improving the electrochemical performances for the detection of heavy metals such as Pb2+ by using a silica-based nanomaterial. In order to do this, ZnO nanoparticles (core) were used as a seed for the chemical deposition of a SiO2 shell. The nanomaterial was synthesized according to a core-shell configuration and the obtained particles were subsequently functionalized with (3-aminopropyl) triethoxysilane APTES to enhance their electrochemical sensing capabilities. The unique physical and chemical properties of these particles, such as their uniform porosity and their ability to detect Pb2+, were exploited. The resulting composite was characterized by scanning electron microscopy, X-ray diffraction, and infrared spectroscopy to analyze its morphology and chemical composition. An electrochemical characterization was also performed to evaluate the change in electrode properties with a ZnO@SiO2-APTES-modified glassy carbon electrode. The differential pulse voltammetry technique was used to determine the Pb2+ ion concentration. After optimization, the electrochemical sensor based on ZnO@SiO2-APTES showed significant sensitivity and exceptional performance in the detection of Pb2+ with a limit of detection of 0.1 nM. Moreover, the proposed electrochemical sensor was successfully applied in the determination of trace metal ions in real environmental samples.

Determination of trace metal ions in Gentiana rigescens by inductively coupled plasma-optical emission spectrometry after deep eutectic solvent-based digestion and related pharmacodynamic evaluation

A fast, simple and environmentally friendly method for the digestion of solid samples of Gentiana rigescens Franch. ex Hemsl. (G. rigescens) based on deep eutectic solvent (DES) was established, and inductively coupled plasma-optical emission spectrometry (ICP-OES) was used to quantify Ni, Zn, Co, Cr and Cu in DES digestion solution. Under optimized conditions, limits of detection (LOD) and limits of quantification (LOQ) ranged from 0.4 to 2.5 and 1.2–8.2 μg g-1, respectively. The intra-day and inter-day precision were carried out by relative standard deviation (RSD) ranged from 0.8% to 4.9% and 0.6%–1.4%, and the spiked recoveries ranged from 90.6% to 111.9%, respectively. The results of quantitative analysis by the developed method were in good agreement with those of microwave digestion. At the same time, the contents of the metal ions in the G. rigescens decoction liquid and freeze-dried powder solution of the decoction liquid of G. rigescens (crude extract) were determined by ICP-OES. The results showed that the contents of Ni, Zn, Co and Cu in the decoction liquid and crude extract were significantly lower than the contents in DES digestion liquid, and Cr was not detected. Then, the oxidative damage model of LO2 cells induced by H2O2 was established. The protective effect of crude extract of G. rigescens on damaged liver cells and the effect of metal ions with the same contents of decoction liquid on liver protection of G. rigescens were investigated for the first time. The results show that H2O2 could induce the decrease of LO2 cell viability and damage the cell morphology. GPS and crude extract could inhibit H2O2-induced liver injury by adjusting the antioxidant enzyme system. Metal ions corresponding to the content of the decoction liquid may weaken the hepatoprotective effect of GPS or crude extract by regulating the antioxidant enzyme system.

Magnetic porous coordination networks for preconcentration of various metal ions from environmental water followed by inductively coupled plasma mass spectrometry detection

Magnetic composites of Fe3O4@SiO2@PCN-224 (MPCN-224) was obtained by one-pot method with the interaction between PCN-224 monomer and silicon layer on magnetic core. MPCN-224 exhibited a core-shell structure with the specific surface area of 1114 m2 g−1 and good adsorption performance for various metal ions. With MPCN-224 used as the sorbent, a method combing magnetic solid phase extraction (MSPE) with inductively coupled plasma mass spectrometry (ICPMS) detection was established for the enrichment and determination of trace Cr(III), Zn(II), Pb(II) and Bi(III) in environmental water samples. Under the optimized conditions, the developed method exhibited low detection limits of 0.94–11.4 ng L−1 and wide linear range for target four metal ions. The analysis speed was fast (2/5 min for adsorption and desorption respectively). The MPCN-224 sorbent could be reused for at least 12 times, and the regeneration can be achieved easily by adjusting solution pH. The sorbent and the MSPE-ICPMS method have a great potential for adsorption and determination of trace metal ions in environmental water samples.

Preparation and Characterization of New Tetra-Dentate N<sub>2</sub>O<sub>2</sub> Schiff Base with Some of Metal Ions Complexes

This study describes preparation a new series of tetra-dentate N2O2 dinuclear complexes Cr(III), Co(II)and Cu(II) of the Schiff base 2-[5-(2-hydroxy-phenyl)-1,3,4-thiadiazol-2-ylimino]-methyl-naphthalen-1-ol], (LH2) derived from 1-hydroxy-naphthalene-2-carbaldehyde with 2-amino-5-(2-hydroxy-phenyl)-1,3,4-thiadiazole. These ligands were characterized by FT-IR, UV-Vis, Mass spectra, elemental analysis, and 1H-NMR. All prepared complexes have been characterized by conductance measurement, magnetic susceptibility, electronic spectra, infrared spectrum, thermal Analysis (TGA), and metal analysis by atomic absorption. The stoichiometry of metal to ligand, magnetic susceptibility, and electronic spectra measurements show an octahedral geometry for all (Cr3+, Co2+, Cu2+) complexes. Conductivity measurement shows that the prepared (Co2+, Cu2+) complexes were nonelectrolyte except (Cr3+). Studying the extraction efficiency such as ligand concentration, temperature and incubation time, centrifuge time, amount of surfactant were evaluated and optimized. The linear range of ions Cr(III), Co(II) and Cu(II) with ligand (0.2–3, 0.2–4, 0.2–3, µg mL–1), each individually, and relative standard deviation (0.15%, 0.34%, 0.46%). The successful method was applied for the determination of trace metal ions in the wastewater.

Graphene oxide lamellar membrane with enlarged inter-layer spacing for fast preconcentration and determination of trace metal ions.

We report a graphene oxide (GO) lamellar membrane with increased inter-layer spacing for efficient permeation of water molecules and heavy metal ions through nanoporous graphene oxide. The inter-layer spacing of the GO sheets in the lamellar structure was increased by introducing poly-aminophosphonic acid (APA) in between the GO sheets. We demonstrate experimentally, the use of a prepared membrane (GO–APA) by a SPE technique for the preconcentration and extraction of heavy metal ions by chelate formation and their determination by ICP-OES. We found that this sub-micrometer-thick membrane allows unimpeded permeation of water molecules through two-dimensional capillaries formed across the pores and by closely spaced graphene sheets. Compared to the bulk GO sorbent, GO–APA membrane offers enhanced sensitivity and permeability for heavy metal ions due to relatively large inter-layer spacing and high surface area (extraction phase) with a high number of active functional groups. The potential of this technique for the preconcentration and extraction of Pb(ii), Cd(ii) and Cu(ii) is illustrated with the contaminated ground water and industrial waste water analysis. The detection limit achieved for studied ions was 1.1 ng L−1, under optimized experimental conditions. The co-existing ions did not hinders the extraction of trace heavy metal ions. Accuracy of the developed method was assessed by analyzing Standard Reference Materials. The Student's t test values were found to less than the critical Student's t value of 4.303 at the 95% confidence level. The method shows good precision as coefficients of variation for five replicate measurements were found to be 4–5%.

Effective Enrichment and Quantitative Determination of Trace Hg2+ Ions Using CdS-Decorated Cellulose Nanofibrils.

Water pollution caused by metal contamination is of serious concern. Direct determination of trace metal ions in real water samples remains challenging. A sample preparation technique is a prerequisite before analysis. Herein, we report the facile water-based hydrothermal synthesis of cadmium sulfide nanoparticles on a cellulose nanofiber surface to prepare a new adsorbent material. Field emission scanning electron microscopy, high-resolution tunneling electron microscopy, elemental mapping and X-ray photoelectron microscopy were used to characterize the surface morphology, structural determination, elemental composition and nature of bonding. The nanoadsorbent (cadmium-sulfide-decorated cellulose nanofibrils (CNFs@CdS)) was employed for the solid-phase extraction and determination of trace Hg(II) from aqueous media. The experimental conditions were optimized systematically and the data show a good Hg(II) adsorption capacity of 126.0 mg g−1. The CNFs@CdS adsorbent shows the selective removal of Hg(II) accordingly to the hard and soft acid–base theory of metal–ligand interaction. A high preconcentration limit of 0.36 µg L−1 was obtained with a preconcentration factor of 580. The lowest level of trace Hg(II) concentration, which was quantitatively analyzed by the proposed method, was found to be 0.06 µg L−1. No significant interferences from the sample matrix were observed in the extraction of Hg(II). Analysis of the standard reference material (SRM 1641d) was carried out to validate the proposed methodology. Good agreement between the certified and observed values indicates the applicability of the developed methodology for the analysis of Hg(II) in tap water, river water and industrial wastewater samples.

Aminophosphonic Acid Functionalized Cellulose Nanofibers for Efficient Extraction of Trace Metal Ions.

Cellulose nanofibers were covalently functionalized using diethylenetriamine penta (methylene phosphonic acid) and studied for the extraction of heavy metal ions. The surface-functionalized nanofibers showed a high adsorption capacity towards heavy metal ions as compared to bare nanofibers. The elemental composition and surface morphology of the prepared bio-adsorbent was characterized by X-ray photoelectron spectroscopy, attenuated total reflectance infrared spectroscopy, field emission scanning electron microscopy, and energy dispersive spectroscopy. The prepared material was studied to develop a column-based solid phase extraction method for the preconcentration of trace metal ions and their determination by inductively coupled plasma optical emission spectroscopy. The batch experimental data was well fitted to Langmuir adsorption isotherms (R2 > 0.99) and follows pseudo-second-order kinetics. The experimental variables such as sample pH, equilibrium time, column breakthrough, sorption flow rate, the effect of coexisting ions, and eluent type were systematically studied and optimized accordingly. The detection limit of the proposed method was found to be 0.03, 0.05, and 0.04 µg L−1 for Cu(II), Pb(II), and Cd(II), respectively. Certified Reference Materials were analyzed to validate the proposed method against systematic and constant errors. At a 95% confidence level, the Student’s t-test values were less than the critical Student’s t value (4.302). The developed method was successfully employed for the preconcentration and determination of trace metal ions from real water samples such as river water and industrial effluent.

Detection of trace metal ions in high-purity boric acid by online two-dimensional valve switching coupled with ion chromatography-inductively coupled plasma mass spectrometry

In this paper, a two-dimensional valve switching technique was established to detect 10 trace metal ions in high-purity boric acid by ion chromatography-inductively coupled plasma mass spectrometry (IC-ICPMS). The system consisted of a quantitative loop, a matrix capture column, an iminodiacetic acid cationic chelating column, an ion chromatography column, two sample valves and an inductively coupled plasma mass spectrometer. The iminodiacetic acid cationic chelating column coupled the metal ions in the sample with its carboxyl functional groups to separate them from the matrix boric acid solution, and then eluted the chelated metal ions into the ion chromatographic column and inductively coupled plasma mass spectrometer. The proposed method feasibly achieved an online, rapid and efficient detection of 10 trace ions in high-purity boric acid with the optimized experimental conditions (1.0 mol/L HNO3), such as loading solution, loading flow rate, type of eluent, concentration of the eluent, sample matrix, etc. The experimental data showed that this method had good linearity in the range of 0.01–2.0 μg/L for 10 metal ions, such as Cr, Fe, Ni, Co, V, Mn, Cu, Zn, Cd and Pb in high-purity boric acid samples, with a correlation coefficient greater than 0.998. The limit of detection (LOD, S/N = 3) and the limit of quantitation (LOQ, S/N = 10) were 0.001–0.023 μg/L and 0.003–0.077 μg/L, respectively. The relative standard deviation (RSD) of each element was less than 3.0% (n = 6) and the spiked recoveries ranged between 83% and 110%. This method could be proposed to be suitable for determination of trace metal ions in real samples.

Simultaneous Determination of Cr, As, Se, and Other Trace Metal Elements in Seawater by ICP-MS with Hybrid Simultaneous Preconcentration Combining Iron Hydroxide Coprecipitation and Solid Phase Extraction Using Chelating Resin.

In the present study, ICP-MS with a new hybrid simultaneous preconcentration combining solid phase extraction using chelating resin and iron hydroxide coprecipitation in one batch at a single pH adjustment (pH 6.0) were developed for multielement determination of trace metal ions in seawater. In multielement determination, the present method makes it possible to determine Cr(III), As(V), Se (IV), and other 14 trace metal elements (Ti, V, Co, Ni, Cu, Zn, Zr, Ge, Cd, Sb, Sn, W, Pb, and U) in seawater. Moreover, for speciation analyses of Cr, As, and Se, the pH dependence on recovery for the different chemical forms of Cr, As, and Se was investigated. In speciation analyses, Cr, As, and Se were determined as the total of Cr (III) and a part of Cr (VI), total of As (III) and As (V), and Se(IV), respectively. Determination of total of Se and Cr(VI) remains as future task to improve. Nevertheless, the present method would have possibility to develop as the analytical method to determine comprehensively most metal elements in all standard and guideline values in quality standard in environmental water in Japan, that is, most toxic metal elements in environmental water.

Simultaneous determination of trace metal ions in industrial wastewater based on UV–vis spectrometry

A novel method combining with continuous wavelet transform and ratio spectra derivative is proposed for simultaneous determination of copper, cobalt and nickel in industrial wastewater by UV–vis spectrometry, without separation step. The derivative calculation by continuous wavelet transform (CWT) using Haar wavelet function is found suitable for noisy signals. The ratio derivative value is measured at zero-crossing wavelength. The linear ranges of calibration graphs are up to 3 mg /L for copper, cobalt and nickel. The root mean squared error of prediction (RMSEP) for copper, cobalt and nickel is 0.073, 0.064 and 0.131, respectively. The mean relative deviations of copper, cobalt and nickel are all less than 5%. The results indicate that the proposed method is rapid, inexpensive, and more accurate than partial least square method. Therefore, it is suitable for analyzing overlapping spectra in their mixtures.

Determination of trace elements in samples with high salt content by inductively coupled plasma mass spectrometry after solid-phase preconcentration

A method for solid-phase extraction (SPE) using nanometer-sized silica modified with N-[2-aminoethyl]-3-aminopropyltrimethoxysilane (AAPTS) coupled with inductively coupled plasma mass spectrometry (ICP-MS) was proposed in this work for analysis of Ni(II), Cu(II), Ga(III), Cd(II), Pb(II), and Bi(III). It was noted from zeta potentials that the absorptivity of the modified nanoparticles could be partially attributed to the electrostatic interactions of amino groups in alkaline conditions. Elemental ions were adsorbed at a pH of 9.0 and then eluted with 1 mol/L nitric acid and 0.5% citric acid. Effects of enrichment time, sample flow rate, and coexisting ions were also investigated. Using the same instrument conditions, higher recovery of elements in synthetic seawater after solid-phase extraction was achieved compared to directly diluting 50 times with 1% nitric acid. This method was successfully applied for the determination of trace metal ions (Ni, Cu, Ga, Cd, Pb, and Bi) in milk powder samples.

Investigation of adsorption mechanism of Fe, Cu, and Zn ions in extraction and preconcentration process on synthesized graphene oxide using an indole derivative

3-(chloro(2-methyl-1H-indol-3-yl)methyl)-2-methyl-1H-indole (MIMI) was chosen for separation and preconcentration of iron (III), copper (II), and zinc by solid-phase extraction (SPE). Ion–MIMI chelates are adsorbed onto synthesized graphene oxide (GO) as adsorbent, eluted with HNO3 and determined by flame atomic absorption spectrometry (FAAS). The adsorption mechanism of titled metal complexes on GO was investigated by using computational chemistry approach based on PM7 semi-empirical potential energy surface. The influences of analytical parameters were investigated. The interference effect of common cations tested did not interfere with the recovery of understudied ions. The preconcentration factor of 312.5 and the detection limits of 0.62, 0.28, and 0.05 ng mL−1 for iron (III), copper (II), and zinc, respectively, were obtained. The developed SPE method was successfully utilized for the determination of trace metal ions in different certified reference materials and real samples (including water, cheese, honey, tomato, leaves of spinach, and milk) by FAAS.

Development of Online Method for Simultaneous Preconcentration of Cd, Cu, Ni and Zn in Environmental Samples Using Modified Alumina

A sensitive and simple method for online simultaneous preconcentration of trace heavy metal ions in some of the environmental samples by flame atomic absorption spectrometry has been reported. In present study ammonium lauryl sulphate is used as a new surfactant for modification of alumina with dithizone as a adsorbent for simultaneous preconcentration of Cd, Cu, Ni and Zn. The adsorbed metals on modified alumina were eluted using 1 mL of 1 mol L-1 hydrochloric acid. The influences of the analytical parameters including pH, flow rate of sample, type and volume of eluent and sample volume were investigated. The calibration curve was linear in the range of 0.05–0.5 μg mL-1 for Cd, Cu, Ni and Zn. The limits of detection were 1, 0.5, 1.1 and 0.61 ng mL-1 for Cd, Cu, Ni and Zn respectively. The preconcentration factor of 100 for Cu and 150 for Cd, Ni and Zn was achieved. The developed method was successfully applied for the determination of trace metal ions in soil, water and plant samples.

High-sensitivity determination of Pb(II) and Cd(II) on a glassy carbon electrode modified with polypyrrole/sepiolite nanofibers

Polypyrrole-sepiolite (PPy/SPL) nanofibers were prepared by in situ chemical oxidation polymerization in the presence of sepiolite. A PPy/SPL composite modified glassy carbon electrode (PPy/SPL/GCE) was prepared and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and electrochemical methods. Differential pulse anodic stripping voltammetry for the simultaneous determination of trace Pb(II) and Cd(II) was carried out at the PPy/SPL/GCE. Operational parameters such as the deposition potential and time, the amount of modified suspension, and the pH values were optimized for the purpose of determination of trace metal ions in 0.10 M acetate buffer solution. Under the optimal conditions, the stripping peak currents showed good linear relationships with Pb(II) and Cd(II) at concentration ranges of 5.0 × 10–9‒1.2 × 10–6 M and 5.0 × 10–9‒1.2 × 10–7 M, and the detection limits were 1.2 and 1.5 nM, respectively. The proposed method is applicable to the simultaneous determination of trace Pb(II) and Cd(II) in real water samples with the relative standard deviations of less than 4.4% and the recovery rates of 97.9‒102.2%.

Bismuth-Activated Graphene Nanocomposite Modified Electrode for Electrochemical Determination of Trace Heavy Metals

Heavy metals, such as Pb2+, Cd2+, and Zn2+, cause major public-health concerns due to their high stability and bio-accumulation. These heavy metals affect several human organs even at very low concentrations. Accordingly, developing simple, robust and highly sensitive analytical methods for assessing environmental pollutants in soil, water, and air samples to improve the quality of environment and human life is very important. Graphene is an excellent nanomaterial for electrochemistry owing to its good electrical conductivity, low cost, excellent mechanical properties, and high specific surface area. To date, much research has been focused on their development for attractive applications in electroanalytical chemistry as a unique electrode material for manifolds. Moreover, chemical modification of graphene could further improve its electrochemical performance. The resultant activated graphene has a unique structure that makes it attractive as a potential material for the electrochemical determination of trace metal ions. In this work, we developed a facile method for the preparation of a new and enhanced sensing platform based on bismuth and activated graphene. The activated graphene was prepared through chemical activation of graphene oxide with KOH to create nanopores. The surface morphology of the bismuth-activated graphene nanocomposite film modified electrode was investigated by using scanning electron microscopy and transmission electron microscopy. The electrochemical properties of the nanocomposite electrode were evaluated to examine the effects of experimental variables, such as deposition potential, deposition time, bismuth concentration, and stirring speed during pre-concentration, on the determination of trace metal ions. The bismuth-activated graphene nanocomposite electrode was applied for the simultaneous determination of trace zinc, cadmium, and lead by differential pulse anodic stripping voltammetry. The composite film integrates the unique properties of activated graphene and the advantages of bismuth electrodes, leading to enhanced sensitivity towards trace metal ions, especially zinc. The appearance of a zinc stripping peak reveals its superior sensitivity as compared to previous bismuth electrodes. The bismuth-activated graphene nanocomposite was also used as an electrode material for the sensitive determination of metal ions in a real sample. The limits of detection achieved are much lower than the guideline for drinking water quality provided by the World Health Organization. Thus, the proposed method facilitates the monitoring of trace heavy metals and can be expanded to detect other environmental pollutants.

TiO2-coated Hollow Fiber Microextraction Combined with Electrothermal Vaporization-Inductively Coupled Plasma-Mass Spectrometry for Trace Elements Analysis in Environmental Water Samples

Abstract TiO2 coated hollow fiber (HF) was prepared by sol-gel method and characterized by X-ray powder diffraction and scanning electron microscope. The adsorption performance of the self-prepared TiO2 coated HF for interest metal ions was explored and a series of affecting factors including sample pH, extraction time, stirring rate and desorption condition were investigated and optimized. On basis of this, a method combining TiO2 coated HF micro-solid phase extraction with electrothermal vaporization (ETV)-inductively coupled plasma mass spectrometry (ICP-MS) was developed for the determination of trace metal ions in environmental water samples. Under the optimized conditions, the limits of detection obtained by the proposed method were 0.039, 0.021, 0.009 and 0.018 ng mL−1 for Cr(III), Cu(II), Cd(II) and Pb(II) with enrichment factors of 12.5, 11.7, 10.3 and 18.6, respectively. The preparation reproducibility of self-prepared TiO2 coated HF ranged from 4.5% to 6.8% (n = 9) in one batch, and from 7.7% to 9.6% (n = 7) in batch-to-batch. The developed method was validated by analyzing a certified reference material (GSBZ50009-88 200925) and also applied to the analysis of target metal ions in East Lake water and snow water successfully. Meanwhile, TiO2 coated HF stir bar was prepared for a comparison and it was demonstrated that TiO2 coated HF displayed higher extraction efficiency and adsorption capacity for the target ions.

Simultaneous Separation and Preconcentration of Trace Amounts of Cu(II), Ni(II), Zn(II), and Cd(II) with Modified Nanoporous Pumpellyite Zeolite.

A procedure for determination of trace levels of Cu(II), Zn(II), Ni(II), and Cd(II) by flame atomic absorption spectrometry using a preconcentration system has been proposed. In this system, we used modified nanoporous pumpellyite zeolite loaded with 2-phenyl-4-[1-(2-thienyl) methylidene]-5-oxazolone as a sorbent for extracting Cu(II), Zn(II), Ni(II), and Cd(II) ions from real samples. Several parameters such as pH of the sample solution, amount of nanoporous pumpellyite zeolite, amount of ligand, volumes of sample and eluent, type of eluent, flow rates of sample and eluent, and the effects of diverse ions on the preconcentration were investigated. The LODs for Cu(II), Zn(II), Ni(II), and Cd(II) in the original solution were 2.6, 1.3, 3.2, and 1.1 ng/mL, respectively. The preconcentration factor was 250 for Zn and Ni, 100 for Cd, and 125 for Cu. The developed method was applied to the determination of trace metal ions in certified reference material tea leaves and water samples with satisfactory results.

Flame Atomic Absorption Spectrometric Determination of Trace Metal Ions in Environmental and Biological Samples After Preconcentration on a Newly Developed Amberlite XAD-16 Chelating Resin Containing p-Aminobenzene Sulfonic Acid.

Amberlite® XAD-16 was functionalized with p-aminobenzene sulfonic acid via an azo spacer in order to prepare a new chelating resin, which was then characterized by water regain value, hydrogen ion capacity, elemental analyses, and IR spectral and thermal studies. The maximum uptake of Cu(II), Ni(II), Zn(II), Co(II), Cr(III), Fe(III), and Pb(II) ions was observed in the pH range 4.0-6.0 with the corresponding half-loading times of 6.5, 7.0, 8.0, 9.0, 11.0, 8.5, and 16.5 min. The sorption data followed Langmuir isotherms and a pseudo-second-order model. Thermodynamic quantities, ΔH and ΔS, based on the variation of the distribution coefficient with temperature were also evaluated. High preconcentration factors of 60-100 up to a low preconcentration limit of 4.0-6.6 μg/L have been achieved for the metal ions. The validity of the method was checked by analyzing standard reference materials and recoveries of trace metals after spiking. The analytical applications of the method were explored by analyzing natural water, mango pulp, mint leaves, and fish.

Restricted accessed nanoparticles for direct magnetic solid phase extraction of trace metal ions from human fluids followed by inductively coupled plasma mass spectrometry detection.

Herein, restricted accessed magnetic nanoparticles were synthesized by self-assembly of a non-ionic surfactant (Tween-20) onto the 4-(2-pyridylazo)resorcinol (PAR) functionalized magnetic nanoparticles (MNPs). A series of analytical techniques were employed for the characterization of the as-prepared restricted accessed Fe3O4@SiO2@PAR, and it was found that the as-prepared restricted accessed Fe3O4@SiO2@PAR nanoparticles have a porous structure with a BET surface area of around 99.4 m(2) g(-1), an average pore size of about 6.14 nm and a pore volume of 0.47 cm(3) g(-1). Besides, the prepared restricted accessed Fe3O4@SiO2@PAR showed good size exclusion properties toward proteins, providing application potential for the direct analysis of biological samples. Based on this, a novel method of restricted accessed magnetic solid phase extraction (MSPE) combined with inductively coupled plasma-mass spectrometry (ICP-MS) was developed for the direct determination of trace metal ions in human fluids. The parameters affecting the extraction of the target metals by MSPE were studied and the optimized conditions were established. Under the optimum conditions, the adsorption capacity of Cr(III), Cd(II), La(III), Nd(III) and Pb(II) on the as-prepared restricted accessed Fe3O4@SiO2@PAR was 62.9, 56.6, 33.7, 36.9 and 43.3 mg g(-1), respectively. With an enrichment factor of 30, the limits of detection for Cr(III), Cd(II), La(III), Nd(III) and Pb(II) were as low as 11.9, 0.8, 0.7, 1.6 and 4.1 ng L(-1), and the relative standard deviations were 7.6, 8.7, 8.4, 8.1 and 5.0 (C(Cr, Pb) = 0.05 μg L(-1), C(Cd, La) = 0.005 μg L(-1), C(Nd) = 0.01 μg L(-1), n = 7), respectively. The developed method was successfully applied for the direct analysis of free metal ions in human urine and serum samples, and has the advantages of good anti-interference ability, high sensitivity and exhibits great application potential in the direct analysis of trace metals in biological fluids.

Simultaneous Determination of Copper, Lead, and Cadmium Ions at a Mo6S9-xIx Nanowires Modified Glassy Carbon Electrode Using Differential Pulse Anodic Stripping Voltammetry

A novel electrochemical sensor based on a new kind of nanomaterials Mo6S9-xIx nanowires modified glassy carbon electrode (GCE) was constructed for simultaneous determination of cadmium(II), lead(II) and copper(II) using differential pulse anodic stripping voltammetry (DPASV). Various experimental parameters such as the modified amount, pH, deposition time and deposition potential were optimized. Under the optimal conditions, the stripping peak currents increase linearly with increasing concentrations of Cd(II), Pb(II) and Cu(II) ions in the ranges of 0.5∼150 μg · L−1, 1.5∼450 μg · L−1 and 0.8～240 μg · μg·L−1, 1.5∼450 μg·L−1 and 0.8∼240 μg·L−1, respectively. And the limits of detection (S/N = 3) are estimated to be 0.10 μg · L−1 for Cd (II), 0.45 μg·L−1 for Pb(II) and 0.20 μg·L−1 for Cu(II), which are two orders of magnitude lower than those obtained at the unmodified electrodes. Most importantly, the sensor has been successfully applied to the determination of trace metal ions in the tap water samples. This developed electrochemical sensor exhibits high sensitivity, good stability and reproducibility.