Square wave anodic stripping voltammetric determination of lead(II) using a glassy carbon electrode modified with a lead ionophore and multiwalled carbon nanotubes

We report on a glassy carbon electrode (GCE) modified with a lead ionophore and multiwalled carbon nanotubes. It can be applied to square wave anodic stripping voltammetric determination of Pb(II) ion after preconcentration of Pb(II) at ?1.0?V (vs. SCE) for 300?s in pH?4.5 acetate buffer containing 400?μg?L^?1 of Bi(III). The ionophore-MWCNTs film on the GCE possesses strong and highly selective affinity for Pb(II) as confirmed by quartz crystal microbalance experiments. Under the optimum conditions, a linear response was observed for Pb(II) ion in the range from 0.3 to 50?μg?L^?1. The limit of detection (at S/N?=?3) is 0.1?μg?L^?1. The method was applied to the determination of Pb(II) in water samples with acceptable recovery.

Direct electrochemistry and electrocatalysis of hemoglobin on an indium tin oxide electrode modified with implanted carboxy ions

A flow injection on-line preconcentration system was developed for the determination of lead by hydride generation atomic fluorescence spectrometry (HG-AFS). It is based on a simple micro-column filled with multiwalled carbon nanotubes (MWCNTs). The preconcentration of lead on the MWCNTs was carried out based on the adsorptive retention of analyte via on-line introducing the sample into the micro-column system. A 0.3 mol L^?1 HNO₃ was introduced to elute the retained analyte and merged with KBH₄ solution for HG-AFS detection. Under the optimal experimental conditions, an enhancement factor of 26 was obtained with a sample consumption of 14.4 mL. The limit of detection was 2.8 ng L^?1 and the precision (RSD) of 11 replicate measurements of 0.2?μg L^?1 Pb was 4.4%. The method was validated by analyzing three certified reference materials, and was successfully applied to the determination of trace lead in natural water samples.     

Water hyacinth modified carbon paste electrode for simultaneous electrochemical stripping analysis of Cd (II) and Pb (II)

In this study, we demonstrated a highly sensitive electrochemical sensor for the simultaneous detection of Pb (II) and Cd (II) in aqueous solution using carbon paste electrode modified with Eichhornia crassipes powder by square wave anodic stripping voltammetry. The effect of modifier composition, pH, preconcentration time, reduction potential and time, and type of supporting electrolyte on the determination of metal ions were investigated. Pre-concentration on the modified surface was performed at open circuit. The modified electrode exhibited well-defined and separate stripping peaks for Pb (II) and Cd (II). Under optimum experimental conditions, a linear range for both metal ions was from 10 to 5000 μg L^?1 with the detection limits of 4.9 μg L^?1, 2.1 μg L^?1 for Cd(II) and Pb (II), respectively. The modified electrode was found to be sensitive and selective when applied to determine trace amounts of Cd (II) and Pb (II) in natural water samples.     

Flame atomic absorption spectrometric determination of trace amounts of Pb(II) and Cr(III) in biological, food and environmental samples after preconcentration by modified nano-alumina

A new solid-phase extraction sorbent was used for the preconcentration of Pb(II) and Cr(III) ions prior to their determination by flame atomic absorption spectrometry. It was prepared by immobilization of 2,4-dinitrophenylhydrazine on nano-alumina coated with sodium dodecyl sulfate. The sorbent was characterized by scanning electron microscopy, N₂ adsorption and Fourier transform infrared spectrometry, and used for preconcentration and separation of Pb(II) and Cr(III) from aqueous solutions. The ions on the sorbent were eluted with a mixture of nitric acid and methanol. The effects of sample pH, flow rates of samples and eluent, type of eluent, breakthrough volume and potentially interfering ions were studied. Linearity is maintained between 1.2 and 350???g?L^-1 of Pb(II), and between 2.4 and 520???g?L^-1 of Cr(III) for an 800-mL sample. The detection limit (3?s, N?=?10) for Pb(II) and Cr(III) ions is 0.43 and 0.55???g?L^-1, respectively, and the maximum preconcentration factor is 267. The method was successfully applied to the evaluation of these trace and toxic metals in various water, food, industrial effluent and urine samples.

LC Determination of Trace Amounts of Phenoxyacetic Acid Herbicides in Water after Dispersive Liquid–Liquid Microextraction

Dispersive liquid–liquid microextraction (DLLME) for extraction and preconcentration of phenoxyacetic acid herbicides in water samples is described. After adjusting the pH to 1.5, the sample was extracted in the presence of 10% w/v sodium chloride by injecting 1 mL acetone as disperser solvent containing 25 μL of chlorobenzene as extraction solvent. The effect of parameters, such as the nature and amount of extraction and disperser solvents, ionic strength of the sample, pH, temperature and extraction time were optimized. DLLME was followed by LC for the determination of 2,4-dichlorophenoxyacetic acid and 4-chloro-2-methyl phenoxyacetic acid. The method had good linearity and a wide linear dynamic range (0.5–750 μg L^?1) with a detection limit of 0.16 μg L^?1 for both the PAAs, making it suitable for their determination in water samples.     

Vergleichende atomabsorptionsspektrometrische untersuchungen zur elementspurenbestimmung in Urin

When using a direct determination procedure with graphite-furnace a.a.s. (e.t.a.a.s.), it is sufficient to make an addition of nitric acid in order to arrive at the optimal reduction of the spectral background. A “matrix modifier” (NH₄NO₃, (NH₄)₂HPO₄) produces a background which often cannot be compensated completely. Detection limits of the direct determination technique are: Cd 0.1, Co 8, Cu 4, Ni 5, Pb 2 and Tl 3 (μg l^?1). A similar power of detection can be achieved as with flame-a.a.s. due to a preceding preconcentration step (trace adsorption on highly dispersed silicic acid). After preconcentration and determination with e.t.a.a.s., the detection limits are: Cd 0.002, Co 0.1, Cu 0.05, Ni 0.09, Pb 0.09 and Tl 0.06 (μg l^?1). The trace concentrations in urine of healthy persons were found to be: Cd 0.2–0.8, Co ? 0.1, Cu 4–10, Ni 1–3, Pb 6–10 and Tl 0.7–1.3 (μg l^?1). Direct e.t.-a.a.s. is, therefore, found to be suitable for the determination of Cd, Cu and Pb. For the determination of Co, Ni and Tl concentrations, a preconcentration is required. Cobalt was not found in any of the urine samples at the limit of detection of 0.1 μg l^?1.     

Analysis of eight pyrethroids in water samples by liquid–liquid microextraction based on solidification of floating organic droplet combined with gas chromatography

A novel method was developed for the determination of eight pyrethroids in water samples by liquid–liquid microextraction based on solidification of floating organic droplets followed by gas chromatography with electron capture detection. The type and volume of the extraction solvents, extraction time, sample solution temperature, stirring rate and ionic strength were studied and optimized. Under the optimum conditions, enrichment factors ranged from 824 to 1,432, and the limit of detection range from 2.0 to 50 ng?L^?1. The calibration graph is linear from 0.15 to 80 μg?L^?1 for cyfluthrin, fenvalerate, fluvalinate and deltamethrin, 0.09 to 80 μg?L^?1 for fenpropathrin, 0.006 to 80 μg?L^?1 for lambda-cyhalothrin, 0.026 to 80 μg?L^?1 for permethrin, 0.01 to 80 μg?L^?1 for cypermethrin. The correlation coefficients (r) varied from 0.9961 to 0.9988. The method was successfully applied to the determination of pyrethroid pesticide residues in tap water, well water, reservoir water, and river water. Recoveries ranged from 79.0% to 113.6%, and relative standard deviations are between 4.1% and 8.7%.     

Solid phase extraction based on modified multi-walled carbon nanotubes packed column for enrichment of copper and lead on-line incorporated with flame atomic absorption spectrometry

A simple and rapid solid phase extraction?Cflow injection procedure is developed for on-line trace determination of Cu(II) and Pb(II) by flame atomic absorption spectrometry (FAAS). Multi-walled carbon nanotubes modified with a new Schiff??s base, 2,2??-(1E, 1E??)-(4-Methyl-1, 2-phenylene) bis (azen-1-yl-1-ylidine) bis (Methane-1-yl-1-ylidene) diphenol was used as a novel adsorbent material. Quantitative simultaneous extraction was obtained at pH 7.0. The retained metal ions were then eluted efficiently with 1.0?M HNO₃ into the nebulizer of FAAS for on-line determination. Different variables affecting the preconcentration efficiency, including pH, eluent concentration, sample and eluent flow rates and sample loading time, were optimized. Using 3?min preconcentration of sample solution at flow rate of 5?mL?min^?1 provided the enrichment factors of 20 and 21.5 for Cu(II) and Pb(II), respectively, at a sampling frequency of 17?h^?1. The detection limits (3??) were found to be 0.80 and 1.80???g?L^?1 for Cu(II) and Pb(II), respectively; and the relative standard deviations at 0.05???g?mL^?1 of these metal ions were 1.7 and 1.8% (n?=?8), respectively. The accuracy was assessed by analysis of a certified reference material NKK-916 and the obtained results are in good agreement with certified amounts of Cu(II) and Pb(II). The proposed method was successfully applied to the determination of target analytes in different real samples.     

Flow injection on-line spectrophotometric determination of thorium(IV) after preconcentration on XAD-4 resin impregnated with oxytetracycline

A very sensitive, selective and simple flow injection time-based method was developed for on-line preconcentration and determination of thorium(IV) at micro g L^–1 levels in environmental samples. The system operation was based on thorium(IV) ion retention at pH 4.0 in the minicolumn at a flow rate of 15.2 mL min^–1. The trapped complex was then eluted with 3.6 mol L^–1 HCl at a flow rate of 4.9 mL min^–1. The amount of thorium(IV) in the eluate was measured spectrophotometrically at 651 nm using arsenazo-III solution (0.05 % in 3.6 mol L^–1 HCl stabilized with 1 % triton X-100, 4.9 mL min^–1) as colorimetric reagent. All chemical, and flow injection variables were optimized for the quantitative preconcentration of metal and a study of interference level of various ions was also carried out. The system offered low backpressure and improved sensitivity and selectivity. At a preconcentration time of 60 s and a sample frequency of 40 h^–1, the enhancement factor was 97, the detection limit was 0.25 μg L^–1, and the precision expressed as relative standard deviation was 1.08 % (at 50 μg L^–1), whereas for 300 s of the preconcentration time and a sample frequency of 10 h^–1, the enhancement factor of 357, the detection limit (3σ) of 0.069 μg L^–1 and the precision of 1.32 % (at 10 μg L^–1) was reported. The accuracy of the developed method was sufficient and evaluated by the analysis of certified reference material IAEA-SL-1 (Lake Sediment) and spiked water samples.     

Graphene oxide-packed micro-column solid-phase extraction combined with flame atomic absorption spectrometry for determination of lead (II) and nickel (II) in water samples

A sensitive and simple method has been established for simultaneous preconcentration of trace amounts of Pb (II) and Ni (II) ions in water samples prior to their determination by flame atomic absorption spectrometry. This method was based on the using of a micro-column filled with graphene oxide as an adsorbent. The influences of various analytical parameters such as solution pH, adsorbent amount, eluent type and volume, flow rates of sample and eluent, and matrix ions on the recoveries of the metal ions were investigated. Using the optimum conditions, the calibration graphs were linear in the range of 7–260 and 5–85 μg L^?1 with detection limits (3S_b) of 2.1 and 1.4 μg L^?1 for lead and nickel ions, respectively. The relative standard deviation for 10 replicate determinations of 50 μg L^?1 of lead and nickel ions were 4.1% and 3.8%, respectively. The preconcentration factors were 102.5 and 95 for lead and nickel ions, respectively. The adsorption capacity of the adsorbent was also determined. The method was successfully applied to determine the trace amounts of Pb (II) and Ni (II) ions in real water samples. The validation of the method was also performed by the standard reference material.     

Solid-phase extraction system for Pb (II) ions enrichment based on multiwall carbon nanotubes coupled on-line to flame atomic absorption spectrometry

The present paper proposes the application of multiwall carbon nanotubes (MWCNTs) as a solid sorbent for lead preconcentration using a flow system coupled to flame atomic absorption spectrometry. The method comprises the preconcentration of Pb (II) ions at a buffered solution (pH 4.7) onto 30 mg of MWCNTs previously oxidized with concentrated HNO₃. The elution step is carried out with 1.0 mol L⁻¹ HNO₃. The effect of the experimental parameters, including sample pH, sampling flow rate, buffer and eluent concentrations were investigated by means of a 2⁴ full factorial design, while for the final optimization a Doehlert design was employed. Under the best experimental conditions the preconcentration system provided detection and quantification limits of 2.6 and 8.6 μg L⁻¹, respectively. A wide linear range varying from 8.6 up to 775 μg L⁻¹ (r > 0.999) and the respective precision (relative standard deviation) of 7.7 and 1.4% for the 15 and 200 μg L⁻¹ levels were obtained. The characteristics obtained for the performance of the flow preconcentration system were a preconcentration factor of 44.2, preconcentration efficiency of 11 min⁻¹, consumptive index of 0.45 mL and sampling frequency estimated as 14 h⁻¹. Preconcentration studies of Pb (II) ions in the presence of the majority foreign ions tested did not show interference, attesting the good performance of MWCNTs. The accuracy of the method was assessed from analysis of water samples (tap, mineral, physiological serum and synthetic seawater) and common medicinal herbs submitted to the acid decomposition (garlic and Ginkgo Biloba). The satisfactory recovery values obtained without using analyte addition method confirms the feasibility of this method for Pb (II) ions determination in different type of samples.     

Electrothermal atomic absorption spectrometric determination of cadmium in environmental samples with niobium wire preconcentration method

A preconcentration method by adsorption of cadmium on a niobium wire was developed for the environmental waters, followed by electrothermal atomic absorption spectrometry with a tungsten tube atomizer. After the preconcentration, the niobium wire was directly inserted into the tungsten tube atomizer. In the preconcentration (adsorption) process of cadmium, the optimal immersing time was 60?s. The effects of large amounts of concomitants on the preconcentration of cadmium were evaluated. When 10³–10⁴ fold excess of matrix elements existed in aqueous solution at pH 4 and 9, the cadmium response was profoundly affected by the matrix elements. However, the cadmium absorption signal was not significantly influenced at pH 7. Therefore, pH 7 was selected for the application into the real environmental samples. Under the optimal conditions, the detection limit (3S/N) for cadmium by the niobium wire preconcentration method was 7.0?pg?mL^?1 and the relative standard deviation was 6.8%. The method with preconcentration on a niobium wire was applied to the determination of cadmium in water and proved to be sensitive, simple and convenient. Because this preconcentration method can be utilized in the in situ treatment of trace cadmium in environmental water samples, it was unnecessary to carry the water samples to the analytical work place. The technique was shown to be useful for the determination of cadmium in environmental water samples at 0.1–1?µg?L^?1 levels.     

Determination of trace heavy metals in herbs by sequential injection analysis-anodic stripping voltammetry using screen-printed carbon nanotubes electrodes

A method for the simultaneous determination of Pb(II), Cd(II), and Zn(II) at low μg L⁻¹ concentration levels by sequential injection analysis-anodic stripping voltammetry (SIA-ASV) using screen-printed carbon nanotubes electrodes (SPCNTE) was developed. A bismuth film was prepared by in situ plating of bismuth on the screen-printed carbon nanotubes electrode. Operational parameters such as ratio of carbon nanotubes to carbon ink, bismuth concentration, deposition time and flow rate during preconcentration step were optimized. Under the optimal conditions, the linear ranges were found to be 2-100 μg L⁻¹ for Pb(II) and Cd(II), and 12-100 μg L⁻¹ for Zn(II). The limits of detection (S_bl/S = 3) were 0.2 μg L⁻¹ for Pb(II), 0.8 μg L⁻¹ for Cd(II) and 11 μg L⁻¹ for Zn(II). The measurement frequency was found to be 10-15 stripping cycle h⁻¹. The present method offers high sensitivity and high throughput for on-line monitoring of trace heavy metals. The practical utility of our method was also demonstrated with the determination of Pb(II), Cd(II), and Zn(II) by spiking procedure in herb samples. Our methodology produced results that were correlated with ICP-AES data. Therefore, we propose a method that can be used for the automatic and sensitive evaluation of heavy metals contaminated in herb items.     

Sensitive electrochemical detection of picloram utilising a multi-walled carbon nanotube/Cr-based metal-organic framework composite-modified glassy carbon electrode

This study describes the utilisation of a glassy carbon electrode modified with a composite of multi-walled carbon nanotube and Cr-based metal-organic framework (MIL-101, Cr-BDC, BDC = 1,4-benzenedicarboxylate) for the sensitive, simple and fast voltammetric determination of picloram in environmental samples. Under optimum conditions, additions of picloram using square wave voltammetry showed linear ranges of picloram concentrations from 24.15 to 3018 µg?L^?1 (0.1–12.5 μM) and from 3018 to 9658 µg?L^?1 (12.5–40 μM) with a detection limit of 14.49 µg?L^?1 (0.06 µM). The method was successfully applied to the determination of picloram in tap and river water samples spiked with picloram without any purification step by the standard addition method. The good recovery values obtained ranging from 97.5% to 105.0% revealed the reliability and accuracy of the method.     

Determination of lead and cadmium in tap water and apple leaves after preconcentration on a new acetylacetone bonded polyurethane foam sorbent

The present work describes a rapid, cost-effective analytical procedure for the determination of lead and cadmium in environmental samples by off-line preconcentration with polyurethane foam (PUF) functionalised with acetylacetone by covalent coupling through the–N=N–group. The optimum pH ranges for quantitative uptake were 5–7, 6–7 for lead and cadmium, respectively. The kinetics of metal uptake by the new foam was found to be fast, reaching equilibrium in a few minutes. Metal ions were sorbed in the minicolumn, eluted with acid solutions and determined by flame atomic absorption spectrometer (FAAS). Under the optimum conditions, the preconcentration factors obtained were 288 for Cd and 224 for Pb. The limits of detection of the proposed procedure were 0.09 and 0.07 µg L^?1 for Pb and Cd, respectively. The relative standard deviation (RSD) was less than 10%. The accuracy of the method was estimated by using environmental samples that were spiked with Cd and Pb ions. The capacity of the acetylacetone bonded PUF (AA-BPUF) sorbent at optimum conditions has been found to be 4.5, 6.9 µmol g^?1 of sorbent for Pb and Cd, respectively.     

Liquid-phase microextraction and gas-chromatographic determination of selenium(IV) in aqueous samples

A liquid-phase microextraction (LPME) method was employed for preconcentration of selenium as piazselenol complex in aqueous samples. The samples reacted with o-phenylenediamine in 0.1?M HCl at 90°C for 15?min, and then LPME was performed. A microdrop of carbon tetrachloride was applied as the extracting solvent. After extraction, the microdrop was introduced directly into the injection port of gas chromatography for analysis. Several important extraction parameters such as the type of organic solvent, sample and organic drop volumes, salt concentration, stirring rate, and exposure time were controlled and optimized. In the proposed LPME, the extraction was achieved by suspending a 3?µL carbon tetrachloride drop from the tip of a microsyringe immersed in 12.5?mL of aqueous solution. Under optimized conditions, a dynamic linear range was obtained in the range of 20–1000?µg?L^?1. The preconcentration factor and the limit of detection of selenium in this method were 91 and 0.9?µg?L^?1, respectively. The optimized procedure was successfully applied to the extraction and determination of selenium in different types of real samples. The relative standard deviations for the spiking levels of 50–100?µg?L^?1 in the real samples were in the range of 3.2–6.1%, and the relative errors were located in the range of ?5.4 to 5%.     

Solid phase extraction of trace amounts of Pb(II) in opium, heroin, lipstick, plants and water samples using modified magnetite nanoparticles prior to its atomic absorption determination

A new, simple, fast and reliable solid-phase extraction method has been developed for separation/preconcentration of trace amounts of Pb(II) using dithizone/sodium dodecyl sulfate-immobilized on alumina-coated magnetite nanoparticles, and its determination by flame atomic absorption spectrometry (FAAS) and graphite furnace atomic absorption spectrometry (GFAAS) after eluting with 4.0?mol?L^?1 HNO₃. Optimal experimental conditions including pH, sample volume, eluent concentration and volume, and co-existing ions have been studied and established. Under the optimal experimental conditions, the preconcentration factor, detection limit, linear range and relative standard deviation of Pb(II) using FAAS technique were 280 (for 560?mL of sample solution), 0.28?ng?mL^?1, 1.4?C70?ng?mL^?1 and 4.6% (for 10?ng?mL^?1, n?=?10), respectively. These analytical parameters using GFAAS technique were 300 (for 600?mL of sample solution), 0.002?ng?mL^?1, 0.006?C13.2?ng?mL^?1 and 3.1% (for 5?ng?mL^?1, n?=?10), respectively. The presented procedure was successfully applied for determination of Pb(II) content in opium, heroin, lipstick, plants and water samples.     

Determination of lead in water samples after its separation and preconcentration by 4,5-dihydroxy-1,3-benzenedisulfonic acid functionalised polyurethane foam

A new sorbent based on polyurethane foam functionalised with 4,5-dihydroxy-1,3-benzenedisulfonic acid (Tiron-PUF) was synthesised. This material was used in the development of a procedure for preconcentration of lead, with subsequent detection by flame atomic absorption spectrometry (FAAS). The influence of some variables involved in the extraction process was studied. Analytical parameters were evaluated using 50 and 500?mL of Pb (II) solution. Under optimum conditions, the system showed enrichment factors of 38 (50?mL) and 114 (500?mL). The detection limits obtained were 0.5 and 1.1?µg?L^?1 when volumes of 500 and 50?mL of Pb (II), respectively, were used. The method was applied to the determination of lead content in well water and drinking water samples collected in the town of Amelia Rodrigues, Bahia, Brazil.     

Development of carbon paste electrode modified with cadmium ion-imprinted polymer for selective voltammetric determination of Cd2+

A simple and fast voltammetric method based on a new electrode composed of carbon paste electrode/bifunctional hybrid ion imprinted polymer (CPE/IIP) was developed for the quantification of Cd²⁺ in water samples. The voltammetric measurements by Differential Pulse Voltammetry were performed by using CPE containing 11.0 mg of IIP under phosphate buffer solution at concentration 0.1 mol L^?1 and pH 6.5. The electrochemical method was carried out by Cd²⁺ preconcentration at ?1.2 V during 210 s, followed by anodic stripping. The performance of IIP towards Cd²⁺ determination was evaluated by comparison to non-imprinted polymer, whose detectability of IIP was much higher (45%). The sensitivity of the sensor was found to be 0.0105 µA/µg L^?1. The limits of detection and limits of quantification were found to be 4.95 μg L^?1 and 16.4 μg L^?1, respectively. The developed method was successfully applied to Cd²⁺ determination in mineral, tap and lake water samples, whose results are in agreement with thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) used as reference analytical technique. According to achieved results, the developed method can be used for routine analysis of quality control of water samples from different sources.     

Synthesis and characterisation of novel chelating resin for selective preconcentration and trace determination of Pb(II) ions in aqueous samples by innovative microsample injection system coupled flame atomic absorption spectrometry

Expanded polystyrene (EPS) foam waste (white pollutant) was utilised for the synthesis of novel chelating resin i.e. EPS-N = N-α-Benzoin oxime (EPS-N = N-Box). The synthesised resin was characterised by FT-IR spectroscopy, elemental analysis, and thermogravimetric analysis. A selective method for the preconcentration of Pb(II) ions on EPS-N = N-Box resin packed in mini-column was developed. The sorbed Pb(II) ions were eluted with 5.0 mL of 2.0 mol L^?1 HCl and determined by microsample injection system coupled flame atomic absorption spectrometry (MIS-FAAS). The average recovery of Pb(II) ions was achieved 95.5% at optimum parameters such as pH 7, resin amount 400 mg, flow rates 1.0 mL min^?1 (of eluent) and3.0 mL min^?1 (of sample solution). The total saturation capacity of the resin, limit of detection (LOD) and limit of quantification (LOQ) of Pb(II) ions were found to be 30 mg g^?1, 0.033 μg L^?1 and 0.107 μg L^?1, respectively with preconcentration factor of 300. The accuracy, selectivity and validation of the method was checked by analysis of sea water (BCR-403), wastewater (BCR-715) and Tibet soil (NCS DC-78302) as certified reference materials (CRMs). The proposed method was applied successfully for the trace determination of Pb(II) ions in aqueous samples.