Determination Of Heavy Metal Ions Research Articles

Electrochemical Sensing of Heavy Metal Ions based on Monodisperse Single-crystal Fe3O4 Microspheres

Single-crystal Fe3O4 with monodisperse microspheres structure has been used for individual electrochemical detection of heavy metal ions. Morphology and structure of the as-prepared Fe3O4 microspheres were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Meanwhile the electrochemical properties of the Fe3O4 microspheres modified glass carbon electrodes (GCE) were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the enhanced electrochemical response in stripping voltammetry for individual detection of Pb(II), Hg(II), Cu(II), and Cd(II) was evaluated using square wave anodic stripping voltammetry (SWASV). With high specific surface area and excellent catalytic activity toward heavy metal ions, the as-prepared monodisperse and single-crystal Fe3O4 microspheres show a preferable sensing sensitivity (22.2 μA/μM) and limit of detection (0.0699 μM) toward Pb(II). Furthermore, the electrochemical sensor of Fe3O4 microspheres exhibits excellent stability and it also offers potential practical applicability for the determination of heavy metal ions in real water samples. This study provides a potential simple and low cost iron oxide for the construction of sensitive electrochemical sensors applied to monitor and control the pollution of toxic metal ions.

Screen‐printed Electrodes for the Determination of Iridium in Drugs

AbstractAmong the impurities that must be controlled in drugs and pharmaceuticals, metal ions are considered. These metal impurities appear in those products because of their use as catalysts. Although Pharmacopeias recommend ICP based methods for their determination, the use of electroanalytical techniques can be considered as a sensible, selective and non‐expensive alternative for the determination of heavy metal ions in general and metal impurities in particular. In the present work, we propose a differential pulse voltammetric method based on the use of carbon based‐screen‐printed electrodes (graphite, nanotubes or nanofibers) that allows the determination of iridium in drugs at the concentration limits recommended by official organisms. Carbon screen‐printed electrode modified with nanotubes (CNT‐SPCE) is the sensor that provided the best LOD and LOQ (0.03 and 0.10 mg L−1 respectively). Then, the proposed method was applied to the voltammetric determination of iridium in spiked drug samples purchased in local chemists using CNT‐SPCE.

A glassy carbon electrode modified with a bismuth film and laser etched graphene for simultaneous voltammetric sensing of Cd(II) and Pb(II)

Polyimide (PI) sheets were laser etched to obtain graphene-based carbon nanomaterials (LEGCNs). These were analyzed by scanning electron microscopy, X-ray diffraction and Raman spectroscopy which confirmed the presence of stacked multilayer graphene nanosheets. Their large specific surface and large number of edge-plane active sites facilitate the accumulation of metal ions. A glassy carbon electrode (GCE) with an in-situ plated bismuth film was modified with the LEGCNs to give a sensor with satisfactory response for the simultaneous determination of cadmium(II) and lead(II) by means of square wave anodic stripping voltammetry. It appears that is the first report on an electrochemical sensor based on the use of laser etched graphene for determination of heavy metal ions. Figures of merit for detection of Cd(II) include (a) a low and well separated working potential of -0.80V (vs. Ag/AgCl), (b) a wide linear range (from 7 to 120μg·L-1), and a low detection limits 0.47μg·L-1. The respective data for Pb(II) are (a) -0.55V, (b) 5 to 120μg·L-1, and (c) 0.41μg·L-1. The modified GCE displays remarkable repeatability, reproducibility, selectivity and stability. The sensor was applied to the simultaneous determination of Cd(II) and Pb(II) in spiked real water samples. The results confirm that the laser etching technique is an efficient tool for the preparation of carbon nanomaterials with high quality and great sensing performance. Graphical abstract Bismuth film and laser etched graphene-modified glassy carbon electrode (BF-LEGCN/GCE) for the simultaneous determination of cadmium(II) and lead(II) by square wave anodic stripping voltammetry.

Inherently fluorescent polystyrene microspheres as a fluorescent probe for highly sensitive determination of chromium (VI) and mercury (II) ions

Nowadays developing fluorescent probes that are cheaper, nontoxic, robust and easy to use for determination of heavy metal ions with high selectivity and sensitivity is still an ongoing challenge. In this paper, inherently fluorescent aminated polystyrene microspheres (PS-NH2) were fabricated from cross-linked polystyrene (PS) microspheres through acetylation, oximation and reduction, which can serve as a selective and sensitive fluorescence (FL) probe for the determination of chromium (VI) (Cr(VI)) and mercury (II) (Hg2+) ions. The photostability, selectivity and sensitivity of the fluorescent PS-NH2 microspheres were studied in detail. The feasibility of PS-NH2 microspheres as a fluorescent probe was conducted by determining Cr(VI) or Hg2+ in real water samples. Results revealed that no photoleaching or leaking issues were observed on PS-NH2 microspheres. The fluorescent probe could analyze Cr(VI) and Hg2+ separately in water samples with high sensitivity and good accuracy in the range of 0.01–1 μM. The detection limits for Cr(VI) and Hg2+ were 9.1 nM and 9.9 nM, respectively. Additionally, two possible FL quenching mechanisms were proposed for Cr(VI) and Hg2+. This work provides a new platform for accurate determination of Cr(VI) and Hg2+ in environmental fields.

Determination of heavy metal ions by an amperometric biosensor based on glucose oxidase immobilized onto single-walled carbon nanotubes/Nile blue nanocomposite

An enzymatic electrochemical biosensor was prepared based on glucose oxidase (GOD) immobilized on single-walled carbon nanotubes/Nile blue (Nb–SWCNTs) nanocomposite cross-linked with glutaraldehyde on graphite electrode. The function of glucose biosensor is based on the electrocatalytic reduction of H2O2 generated by the reaction of the enzyme with glucose molecules. The biosensor was characterized by Fourier transform infrared (FTIR) spectroscopy, emission scanning (FESEM), UV–Vis spectrometry, and voltammetric and amperometric methods. Parameters influencing the performance of the biosensor, namely pH and applied potential, were optimized. Inhibition was carried out for the detection of Hg2+ and Pb2+ species under optimized condition. Inhibition investigations showed that the type of inhibition for both the abov- mentioned heavy metal ions were reversible and competitive.

Progress on electrochemical sensors for the determination of heavy metal ions from contaminated water

With the development of modern industry, heavy metal pollution is increasingly becoming the focus of government and citizen concern around the globe. Some heavy metals such as Pb, Hg, As, Cr and Cd...

Electrochemical and density functional theory investigation on the differential behaviors of core-ring structured NiCo2O4 nanoplatelets toward heavy metal ions

In order to further improve the electroanalytical performance toward heavy metal ions, core-ring structured NiCo2O4 nanoplatelets were used to modify glass carbon electrode (GCE) for the determination of heavy metal ions in water. Owing to the high surface area of NiCo2O4 nanoplatelets, the Pb(II) sensitivity increased by a factor of 1.70, and the detection limit decreased by a factor of 2.64 as compared to solid NiCo2O4 nanoparticles modified GCE. Interestingly, NiCo2O4 nanoplatelets showed different sensitivities toward heavy metal ions with the same valence states, following the order Pb(II) > Cd(II) > Hg(II) > Cu(II). To better and scientifically understand the difference in sensitivity, adsorption and desorption abilities were integrated into account. Density functional theory calculations verified that the adsorption capability of NiCo2O4 toward Pb(II) was strongest among all heavy metal ions, thereby resulting in the largest sensitivity. Further desorption current measurements indicated the large desorption barrier of Cu(II) was another important factor leading to its lowest sensitivity. Finally, the applicability of the proposed method was demonstrated by the detection of heavy metal ions in real seawater.

Graphene Oxide Decorated with Cerium(IV) Oxide in Determination of Ultratrace Metal Ions and Speciation of Selenium.

Graphene oxide decorated with cerium(IV) oxide (GO/CeO2) was synthesized and applied in adsorption of several metal ions such as As(III), As(V), Se(IV), Cu(II), and Pb(II) from aqueous samples. The important feature of GO/CeO2 nanocomposite is also its selectivity toward selenite in the presence of selenate. The structure of GO/CeO2 has been proven by microscopic and spectroscopic techniques. The maximum adsorption capacities of GO/CeO2 calculated by Langmuir model toward arsenic, selenium, copper, and lead ions are between 6 and 30 mg g-1. An interesting feature of this adsorbent is its excellent dispersibility in water. Thus, GO/CeO2 nanocomposite is ideal for fast and simple determination of heavy metal ions using dispersive microsolid phase extraction (DMSPE). Moreover, coupling DMSPE with energy-dispersive X-ray fluorescence spectrometry (EDXRF) is extremely beneficial because it allows direct analysis of adsorbent. Thus, the analyte elution step, as needed in many analytical techniques, was obviated. The influence of sample volume and the sorption time as well as the influence of foreign ions and humic acid on the recovery of determined elements are discussed in the paper. The results showed that developed methodology provided low limits of detection (0.07-0.17 μg/L) and good precision (RSD < 4%). The GO/CeO2 nanocomposite was applied to analysis of real water samples and certified reference materials (CRM) groundwater (BCR-610) and pig kidney (ERM-BB186).

Determination of Heavy Metal Ions (As, Pb, Cd) and Zinc Mineral (Zn) in Humans and Cows Milk in Bitlis (Turkey)

Human�s milk and cow�s milk fed-infants, long before the mother is exposed heavy metals are potentially dangerous for both mother and baby. Concentrations of toxic heavy metals (Pb, Cd, As) and major nutritional trace element (Zn) which collected center Bitlis, Tatvan and various villages in the 75 volunteer nursing mothers received 6 months after the birth human�s milks and 75 cow milks were analyzed. This study was measured by Inductively Coupled Plasma-Mass Spectrometer. Work was measured in accredited laboratory. In the samples As and Cd were under detectable leves although Zn and Pb were measured. Survey conducted, Zn and Pb levels in the mother milk which collected Tatvan borough were determined the highest. The all metal levels in the mother milk and cow milk which collected Bitlis center higher than villages. Zn levels in the cow milks which collected Bitlis center the highest. As a results of analysis, the avarege values of the lead in the human milks respectively (Bitlis center, Tatvan borough and villages) were found 0.0003�0.00004 mg/kg, 0.00045�0.000052 mg/kg, 0.0002�0.00003 mg/kg; the avarege values of the zinc 3.2�0.64 mg/kg, 3.34�0.57 mg/kg, 2.5�0.37 mg/kg. The avarege values of the lead in the cow milks respectively (Bitlis center, Tatvan borough and villages) were found 0.002�0.0004 mg/kg, 0.003�0.0004 mg/kg, 0.001�0.0003 mg/kg; the avarege values of the zinc 3.7�0.51 mg/kg, 3.6�0.49 mg/kg, 3.0�0.41 mg/kg. As a results of analysis between groups weren�t found significant relationship (P]0.05).

Fe(III)-based metal–organic framework-derived core–shell nanostructure: Sensitive electrochemical platform for high trace determination of heavy metal ions

A new core–shell nanostructured composite composed of Fe(III)-based metal–organic framework (Fe-MOF) and mesoporous Fe3O4@C nanocapsules (denoted as Fe-MOF@mFe3O4@mC) was synthesized and developed as a platform for determining trace heavy metal ions in aqueous solution. Herein, the mFe3O4@mC nanocapsules were prepared by calcining the hollow Fe3O4@C that was obtained using the SiO2 nanoparticles as the template, followed by composing the Fe-MOF. The Fe-MOF@mFe3O4@mC nanocomposite demonstrated excellent electrochemical activity, water stability and high specific surface area, consequently resulting in the strong biobinding with heavy-metal-ion-targeted aptamer strands. Furthermore, by combining the conformational transition interaction, which is caused by the formation of the G-quadruplex between a single-stranded aptamer and high adsorbed amounts of heavy metal ions, the developed aptasensor exhibited a good linear relationship with the logarithm of heavy metal ion (Pb2+ and As3+) concentration over the broad range from 0.01 to 10.0nM. The detection limits were estimated to be 2.27 and 6.73 pM toward detecting Pb2+ and As3+, respectively. The proposed aptasensor showed good regenerability, excellent selectivity, and acceptable reproducibility, suggesting promising applications in environment monitoring and biomedical fields.

3D Printed Microfluidic Device with Microporous Mn2O3-Modified Screen Printed Electrode for Real-Time Determination of Heavy Metal Ions.

Fabricating portable devices for the determination of heavy metal ions is an ongoing challenge. Here, a 3D printing approach was adopted to fabricate a microfluidic electrochemical sensor with the desired shape in which the model for velocity profiles in microfluidic cells was built and optimized by the finite element method (FEM). The electrode in the microfluidic cell was a flexible screen-printed electrode (SPE) modified with porous Mn2O3 derived from manganese containing metal-organic framework (Mn-MOF). The microfluidic device presented superior electrochemical detection properties toward heavy metal ions. The calibration curves at the modified SPE for Cd(II) and Pb(II) covered two linear ranges varying from 0.5 to 8 and 10 to 100 μg L-1, respectively. The limits of detection were estimated to be 0.5 μg L-1 for Cd(II) and 0.2 μg L-1 for Pb(II), which were accordingly about 6 and 50 times lower than the guideline values proposed by the World Health Organization. Furthermore, the microfluidic device was connected to iPad via a USB to enable real-time household applications. Additionally, the sensing system exhibited a better stability and reproducibility compared with traditional detecting system which offered a promising prospect for the detection of heavy metal ions especially in household and resource-limited occasions.

A sensitive electrochemical sensor using an iron oxide/graphene composite for the simultaneous detection of heavy metal ions

We report an analytical assessment of an iron oxide (Fe2O3)/graphene (G) nanocomposite electrode used in combination with in situ plated bismuth (Bi) working as an electrochemical sensor for the determination of trace Zn2+, Cd2+, and Pb2+. The as-synthesized nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, thermo-gravimetric analyzer, and X-ray diffraction. The electrochemical properties of the Fe2O3/G/Bi composite modified electrode were investigated. Differential pulse anodic stripping voltammetry was applied for the detection of metal ions. Due to the synergetic effect between graphene and the Fe2O3 nanoparticles, the modified electrode showed improved electrochemical catalytic activity high sensitivity toward trace heavy metal ions. Several parameters such as the preconcentration potential, bismuth concentration, preconcentration time, and pH were carefully optimized to determine the target metal ions. Under optimized conditions, the linear range of the electrode was 1–100μgL−1 for Zn2+, Cd2+, and Pb2+, and the detection limits were 0.11μgL−1, 0.08μgL−1, and 0.07μgL−1, respectively (S/N =3). Repeatability (% RSD) was found to be 1.68% for Zn2+, 0.92% for Cd2+, and 1.69% for Pb2+ for single sensor with 10 measurements and 0.89% for Zn2+, 1.15% for Cd2+, and 0.91% for Pb2+ for 5 different electrodes. The Fe2O3/G/Bi composite electrode was successfully applied to the analysis of trace metal ions in real samples. The solventless thermal decomposition method applied to the simple and easy synthesis of nanocomposite electrode materials can be extended to the synthesis of nanocomposites and promising electrode materials for the determination of heavy metal ions.

Voltammetric Sensor Modified by EDTA-immobilized Graphene-like Carbon Nitride Nanosheets: Preparation, Characterization and Selective Determination of Ultra-Trace Pb (II) in Water Samples

A voltammetric sensor for selective determination of ultra-trace Pb (II) was prepared based on EDTA-immobilized graphene-like carbon nitride nanosheets (EDTA-CN-NS), which has been designed to improve the accumulation performance for Pb (II) onto the electrode surface. The EDTA-CN-NS was prepared through pre-oxidation by K2S2O8 and silanization by N-(trimethoxysilylpropyl) ethylene-diamine triacetic acid sodium salt. The crystalline structure, morphology and the added functional groups of EDTA-CN-NS were characterized by XRD, SAED, TEM, STEM mapping and FT-IR, which are quite in accord with the catalysis action in cyclic voltammetry test generated by improved accumulation performance of the immobilized EDTA for Pb (II). The detection limit of EDTA-CN-NS/Nafion modified sensor reached 5.7×10−13molL−1 with two linear ranges from 2.1×10−12∼1.3×10−9molL−1 and 1.3×10−9∼1.7×10−6molL−1. The sensor behaves acceptable immunity from common interferences in Pb (II) determination and was employed for analyzing the Pb (II) concentration in different water samples. This work gives new instructions in designing ultra-high sensitive sensors for determination of heavy metal ions using 2D functional materials.

Investigating film structure of membrane-based colorimetric sensor for heavy metal detection

A stable and relatively long lifetime optical membrane sensor for determination of heavy metal ions was prepared by covalent immobilization of dithizone (DTZ) on cellulose acetate membrane. Present work was aimed at gaining a quantitative understanding of the influence of membrane morphologies towards the immobilization of DTZ on the membrane surface. Experimental results indicated that the developed membrane by using 1wt.% chitosan and 17wt.% cellulose acetate showed to have the highest binding capacity and high binding stability up to 90 days of measurement. The prepared DTZ-membrane sensor exhibited quick (within 1min) color change and was found to be capable of displaying distinctive color changes responses to the presence of mercury, copper, and zinc in aqueous solutions. The color intensity increases with increasing metal ions concentration, showed the potential practical applications for on-site quick detection of metal ions.

Highly Sensitive and Selective In-Situ SERS Detection of Pb(2+), Hg(2+), and Cd(2+) Using Nanoporous Membrane Functionalized with CNTs.

Porous Anodic Alumina (PAA) membrane was functionalized with CoFe2O4 nanoparticles and used as a substrate for the growing of very long helical-structured Carbon Nanotubes (CNTs) with a diameter less than 20 nm. The structures and morphologies of the fabricated nanostructures were characterized by field emission- scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX), and Raman spectroscopy. By uploading the CNTs on PAA, the characteristic Raman peaks of CNTs and PAA showed 4 and 3 times enhancement, respectively, which leads to more sensitive Surface-Enhanced Raman Spectroscopy (SERS) substrates. For comparison, PAA and CNTs/PAA arrays were used as SERS substrates for the detection of Hg2+, Cd2+, and Pb2+. The proposed sensor demonstrated high sensitivity and selectivity between these heavy metal ions. CNTs/PAA sensor showed excellent selectivity toward Pb2+ over other metal ions, where the enhancement factor is decreased from ~17 for Pb2+ to ~12 for Hg2+ and to ~4 for Cd2+. Therefore, the proposed CNTs/PAA sensor can be used as a powerful tool for the determination of heavy metal ions in aqueous solutions.

Simultaneous determination of copper, cobalt, and mercury ions in water samples by solid-phase extraction using carbon nanotube sponges as adsorbent after chelating with sodium diethyldithiocarbamate prior to high performance liquid chromatography.

Recently, a sponge-like material called carbon nanotube sponges (CNT sponges) has drawn considerable attention because it can remove large-area oil, nanoparticles, and organic dyes from water. In this paper, the feasibility of CNT sponges as a novel solid-phase extraction (SPE) adsorbent for the enrichment and determination of heavy metal ions (Co(2+), Cu(2+), and Hg(2+)) was investigated for the first time. Sodium diethyldithiocarbamate (DDTC) was used as the chelating agent and high performance liquid chromatography (HPLC) for the final analysis. Important factors which may influence extraction efficiency of SPE were optimized, such as the kind and volume of eluent, volume of DDTC, sample pH, flow rate, etc. Under the optimized conditions, wide range of linearity (0.5-400μgL(-1)), low limits of detection (0.089~0.690μgL(-1); 0.018~0.138μg), and good repeatability (1.27~3.60%, n = 5) were obtained. The developed method was applied for the analysis of the three metal ions in real water samples, and satisfactory results were achieved. All of these findings demonstrated that CNT sponges will be a good choice for the enrichment and determination of target ions at trace levels in the future.

Exploring amide linkage in a polyviologen derivative towards simultaneous voltammetric determination of Pb(II), Cu(II) and Hg(II) ions

In this study, we report reductive electrosynthesis of a polyviologen derivative bearing amide linkage in its side chain, derived from a cyanopyridinium based monomer with amide functionality. The as grown film was characterized by cyclic voltammetry which displays a well-defined and reversible two step redox response characteristic of viologen. FTIR analysis show evidence of amide linkage and successful reduction of cyanopyridinium moieties to polyviologen. In situ multi ESR/UV-Vis-NIR spectroelectrochemistry show a single line in ESR signal, thereby suggesting polarons as the only charge carrier involved during charging/discharging process. Furthermore, a characteristic UV–Vis absorption spectra confirms viologen formation. Finally, the polyviologen film is subjected to simultaneous voltammetric determination of heavy metal ions, Pb(II), Cu(II) and Hg(II). The amide linkage in the polyviologen derivative is supposedly complexing these divalent metal ions, enabling their sensitive and simultaneous determination with low detection limits.

Screen-printed electrodes made of a bismuth nanoparticle porous carbon nanocomposite applied to the determination of heavy metal ions

This work reports on the simplified fabrication and on the characterization of bismuth-based screen-printed electrodes (SPEs) for use in heavy metal detection. A nanocomposite consisting of bismuth nanoparticles and amorphous carbon was synthesized by a combined one-step sol-gel and pyrolysis process and milled down to a specific particle size distribution as required for the preparation of an ink formulation to be used in screen printing. The resulting electrochemical devices were applied to the detection of Pb(II) and Cd(II) ions in water samples. The porous structure of carbon and the high surface area of the bismuth nanoparticles allow for the detection of Pb(II) and Cd(II) at concentration levels below 4 ppb. The application of the SPEs was demonstrated by quantifying these ions in tap drinking water and wastewater collected from an influent of an urban wastewater treatment plant.

Bis(spirolactam) 1,3-double-armed calix[4]arene compounds and their application as extractants for the determination of heavy metal ions

A number of double-armed calix[4]arene compounds, with proline-derived spirolactam ligating groups on the lower rim, have been synthesised and investigated as extractants of toxic heavy metal ions from aqueous solution. Pedersen’s extraction technique was employed to determine the capability of these new 1,3-distal derived calix[4]arene spiroalactams to extract selected heavy metal ions (e.g. Pb2+, Cd2+, Zn2+, Cu2+, Ni2+, Co2+) from an aqueous phase into an organic phase. The percentage extraction was calculated using UV–Vis spectroscopy. All of the compounds synthesised demonstrated good selectivity for the heavy metals selected over the alkali metal and alkaline earth metal ions, in particular for Pb2+. The level of selectivity observed was dependent on the N-substituent of the spirolactam moiety attached to alternate phenolic oxygens of the narrow calix[4]arene rim. Interestingly, higher sensitivity and lower selectivity was found when the two remaining –OH groups were replaced by –OCH3 groups.

Dispersive micro solid-phase extraction of heavy metals as their complexes with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol using graphene oxide nanoparticles

This article describes a new procedure for multi-element preconcentration of heavy metal ions, specifically of Cr(III), Co(II), Ni(II), Cu(II), Zn(II) and Pb(II) ions. The method is based on dispersive micro solid-phase extraction (DMSPE) of the metal complexes of 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) by graphene oxide nanoparticles prior to energy dispersive X-ray fluorescence spectrometric (EDXRF) determination. The effects of pH, amount of graphene oxide, concentration of complexing reagent, sample volume and sorption time were optimized. The influence of commonly encountered other ions was also investigated. Under optimal conditions, the calibration plots cover the 2 to 150 ng mL−1 range for each element. The precision (at a 20 ng mL−1 level for n = 10) is lower than 4.8 %, and the detection limits range is from 0.07 to 0.25 ng mL−1. The DMSPE-EDXRF procedure was successfully applied to the determination of heavy metal ions in water and spiked water samples with recoveries between 94.4 and 103.5 %.