Assessment of Lead and Cadmium in Canned Foods by Square-Wave Anodic Stripping Voltammetry

Abstract

This work reports the simultaneous determination of lead and cadmium in canned foods samples using square-wave anodic striping voltammetry (SWASV) on a bismuth film electrode (BiFE). The metal ions and bismuth were simultaneously deposited by reduction at ?1 V on a rotating carbon-paste disk electrode. Then, the preconcentrated metals were oxidized by scanning the potential of the electrode from ?1 to ?0.4 V using a square-wave waveform. The electrode displayed excellent linear behavior in the examined concentration range, from 5 to 150 µg/L of cadmium and lead (r² = 0.999 for both). Using the optimized conditions, the limits of detection were 0.27 µg/L for cadmium and 0.35 µg/L for lead. The reproducibility of the proposed sensor, evaluated in terms of relative standard deviation (RSD), were 5.8% and 3.7% of Cd and Pb, respectively for five measurements. Finally, the system based on BiFEs combined with rotating disk electrode was applied to determination of lead and cadmium in canned food samples. The results obtained were validated by inductively coupled plasma optical emission spectroscopy (ICP-OES).     

Simultaneous Determination of Cadmium,Copper, Lead and Zinc in Amino Acid Parenteral Nutrition Solutions by Anodic Stripping Voltammetry and Sample Digestion by UV Irradiation

Abstract

Irradiation with ultraviolet (UV) energy was investigated to assay cadmium, copper, lead, and zinc by anodic stripping voltammetry (ASV) in amino acid parenteral nutrition (PN) solutions. Sample digestion by UV irradiation showed the best performances to liberate the metals from the samples (metal recoveries between 90% and 102%) in comparison with classical oxidative wet digestion methods. The best UV digestion condition was obtained with 1:10 diluted PN samples irradiated during 10 h at 90±3°C with the addition of one aliquot of 50 µL concentrated H₂SO₄ and repeated additions of 50 µL 30% (v/v) H₂O₂ at each 60 min irradiation interval. By using the UV digestion procedure cadmium, copper, lead, and zinc were simultaneously assayed in commercial amino acid PN solutions by ASV. The metal concentrations ranged between 1.3 to 4.4 for cadmium, 2.9 to 40.8 for copper, 4.4 to 16.8 for lead, and 1.4 to 208.5 for zinc. The ASV method correlated well with atomic absorption spectrometry measurements to assay the investigated analytes in amino acid PN samples after the UV digestion.     

Ultratrace determination of lead,cadmium and copper in environmental and biological samples by atomic absorption spectrometry after their separation and preconcentration using octadecyl silica membrane disks modified with a new n–s schiff base

Pb(II), Cd(II) and Cu(II) ions were separated and preconcentrated by solid-phase extraction on octadecyl-bonded silica membrane disks modified with a new S–N-containing Schiff base (bis-2-thiophenal propandiamine) (BTPD) followed by elution and atomic absorption spectrometric detection. The method was applied as a separation and detection method for lead(II), cadmium(II) and copper(II) in environmental and biological samples. Extraction efficiency and the influence of sample matrix, flow rate, pH, and type and minimum amount of stripping acid were investigated. The maximum capacity of the membrane disks modified by 4?mg of BTPD was found to be 668 ± 10, 480 ± 8 and 454 ± 7?µg of lead, cadmium and copper, respectively. The limit of detection of the proposed method is 0.25, 0.01 and 0.02?ng/mL for lead, cadmium and copper, respectively.     

Flame Atomic Absorption Spectrometric Determination of Cu(II), Co(II), Cd(II), Fe(III) and Mn(II) in Ammonium Salts and Industrial Fertilizers after PrEconcentration/Separation on Diaion HP-20

A sensitive and simple separation-enrichment technique for the determination of trace amounts of Cu(II), Co(II), Cd(II), Fe(III) and Mn(II) was described. Metal ions were complexed with 1-nitroso-2-naphthol at pH 9. Following solid-phase extraction on Diaion HP-20 resin, metals were determined by flame atomic absorption spectrometry. The effect of the matrix ions were investigated. The recoveries of metal ions were greater than 95%. The detection limits of the analyte ions ( k = 3, N = 21) were varying 0.18 µg/l for Cd(II) to 0.44 µg/l for Fe(III). The method was applied to a stream sediment standard reference material (GBW7309), some ammonium salts and industrial fertilizer samples for the determination of copper, cobalt, cadmium, iron and manganese. The relative standard deviations (RSD) of the determinations for analyte ions at µg/g levels varied from 1 to 10%.     

Online Preconcentration Using Surfactant Coated Alumina Modified with 1,5-Diphenylthiocarbazone and Determination of Cadmium in Environmental Samples by Flame Atomic Absorption Spectrometry

A rapid and sensitive method for the determination of trace levels of cadmium in cigarettes, soil, and blood samples by flame atomic absorption spectrometry (FAAS) has been developed. It is based on the online sorption of Cd(II) ions on a minicolumn packed by sodium dodecyl sulfate–coated alumina modified with dithizone. The optimum experimental parameters for the adsorption and desorption of cadmium were investigated. The recovery obtained was found to be 96% with preconcentration factor of 150. The calibration curve was linear between 50–600 µg/L Cd with a detection limit of 3 µg/L, sample frequency of 30 h^?1 and reuse of column for 10 times without loss of sensitivity. The accuracy of the method was confirmed by applying the standard addition method and quantitative recoveries (95–99%) were obtained.     

Cloud point extraction for the determination of cadmium and lead employing sequential multi-element flame atomic absorption spectrometry

A cloud point extraction procedure for pre-concentration and determination of cadmium and lead in drinking water using sequential multi-element flame atomic absorption spectrometry is described. 4-(2-thiazolylazo)-orcinol (TAO) has been used as complexing agent and the micellar phase was obtained using the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) and centrifugation. The conditions for reaction and extraction (surfactant concentration, reagent concentration, effect of incubation time, etc) were studied and the analytical characteristics of the method were determined. The method allows the determination of cadmium and lead with quantification limits of 0.30?µg?L^?1 and 2.6?µg?L^?1, respectively. A precision expressed as relative standard deviation (RSD, n?=?10) of 2.3% and 2.6% has been obtained for cadmium concentrations of 10?µg?L^?1 and 30?µg?L^?1, respectively, and RSD of 1.3% and 1.7% for lead concentrations of 10?µg?L^?1 and 30?µg?L^?1, respectively. The accuracy was confirmed by analysis of a natural water certified reference material. The method has been applied for the determination of cadmium and lead in drinking water samples collected in the cities of Ilhéus and Itabuna, Brazil. Recovery tests have also been performed for some samples, and results varied from 96 to 105% for cadmium and 97 to 106% for lead. The cadmium and lead concentrations found in these samples were always lower than the permissible maximum levels stipulated by World Health Organization and the Brazilian Government.     

Simultaneous Determination of Tin,Nickel, Lead,Cadmium and Mercury in Tobacco and Tobacco Additives by Microwave Digestion and RP‐HPLC Followed by On‐Line Column Enrichment

A new method for the simultaneous determination of five heavy metal ions, tin, nickel, lead, cadmium and mercury ions as metal‐tetra‐(2‐aminophenyl)‐porphyrin (T₂APP) chelates was developed using reversed‐phase high performance liquid chromatography (RP‐HPLC) equipped with a photodiode array detector and combined with an on‐line enrichment technique. The tin, nickel, lead, cadmium and mercury ions were pre‐column derivatized with T₂APP to form color chelates. The Sn‐T₂APP, Ni‐T₂APP, Hg‐T₂APP, Cd‐T₂‐APP and Pb‐T₂APP chelates can be absorbed onto the front of the enrichment column when they are injected into the injector and sent to the enrichment column [Waters Xterra? RP₁₈(5μ, 3.9 × 20 mm)] with a buffer solution of 0.05 mol/L pyrrolidine‐acetic acid (pH = 10.0) as mobile phase. After the enrichment had finished, by switching the six‐port switching valves, the retained chelates were back‐flushed by mobile phase and traveling towards the analytical column. These chelates separation on the analytical column [Waters Xterra? RP₁₈ (5μ, 3.9 × 150 mm)] was satisfactory by gradient elution with methanol (containing 0.05 mol/L pyrrolidine‐acetic acid buffer salt, pH = 10.0) and acetone (containing 0.05 mol/L pyrrolidine‐acetic acid buffer salt, pH = 10.0) as mobile phase. The linearity range is 0.01?120 μg/L for each metal ion. The detection limits (S/N = 3) of tin, nickel, lead, cadmium and mercury are 4.0 ng/L, 3.5 ng/L, 2.5 ng/L, 3.0 ng/L and 3.0 ng/L, respectively. This method was applied to the determination of tin, nickel, lead, cadmium and mercury ions in tobacco and tobacco additives with good results.     

Starch coated titanium dioxide nanoparticles as a challenging sorbent to separate and preconcentrate some heavy metals using graphite furnace atomic absorption spectrometry

In this study, a challenging nanosorbent was described for preconcentration/separation method based on the sorption of cadmium, cobalt, copper, nickel, lead on starch coated titanium dioxide nanoparticles and its analysis by graphite furnace atomic absorption spectrometry. Optimum conditions were investigated for quantitative sorption. By using the proposed technique, the analyte elements were determined in spiked tap-water samples in the range of 95% confidence level. Limit of detection (3δ) was 0.05, 0.28, 1.90, 3.10 and 0.11 µg/L (3σ, N = 10) for cadmium, cobalt, copper, nickel and lead, respectively. The optimised technique is fast, easy handled, simple and environmental friendly.     

Rapid coprecipitation-separation and flame atomic absorption spectrometric determination of lead and cadmium in water with cobalt (II) and ammonium pyrrolidine dithiocarbamate

A coprecipitation technique which does not require complete collection of the precipitate was proposed for the determination of trace lead and cadmium in water with flame atomic absorption spectrometry (FAAS) after preconcentration of lead and cadmium by using cobalt (II) and ammonium pyrrolidine dithiocarbamate (Co-APDC) as coprecipitant and known amount of cobalt as an internal standard. Since lead, cadmium and cobalt were well distributed in the homogeneous precipitate, the concentration ratio of lead to cobalt, and cadmium to cobalt remained unchanged in any part of the precipitate. The amount of lead and cadmium in the original sample solution can be calculated respectively from the ratio of the absorbance values of lead and cadmium to cobalt in the final sample solution that is measured by FAAS and the known amount of the lead and cadmium in the standard series solutions. The optimum pH range for quantitative coprecipitation of lead and cadmium is from 3.0 to 4.5. The 16 diverse ions tested gave no significant interferences in the lead and cadmium determination. Under optimised conditions, lead ranging from 0 to 40?µg and cadmium ranging from 0 to 8?µg were quantitatively coprecipitated with Co-APDC from 100?mL sample solution (pH?～?3.5). This coprecipitation technique coupled with FAAS was applied to the determination of lead and cadmium in water samples with satisfactory results (recoveries in the range of 94.0–108%, relative standard deviations <6.0%).     

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.     

HPLC-spectrophotometric detection of trace heavy metals via ‘cascade’ separation and concentration

A cascade pre-concentration and separation system involving continuous solid-phase extraction and one-drop solvent concentration was developed to enable high-performance liquid chromatography (HPLC) determination of trace levels of Ni(II), Co(II), Cu(II), Se(IV) and Cr(VI) ions in aqueous solution via complexation with sodium diethyldithiocarbamate. The metal complexes were almost completely adsorbed on the solid phase (octadecylsilyl packed column). Ethyl acetate (eluent) containing the metal complexes was then placed in a centrifuge tube, to which a microvolume of dimethyl sulfoxide (DMSO) was added. Successful pre-concentration of the metal complexes into the DMSO phase was accomplished by removing the ethyl acetate using a compact evaporator in a water bath (40°C); 1000-fold concentration was achieved within 45 min. A portion of the residual DMSO phase was then subjected to HPLC analysis. The proposed method has high reproducibility and high sensitivity with detection limits (3σ) for Ni(II), Co(II), Cu(II), Se(IV) and Cr(VI) ions of 0.08, 0.11, 0.12, 0.44 and 0.20 µg/L, respectively. Relative standard deviations (RSDs) (n = 5) at Ni(II) 5.87 µg/L, Co(II) 5.89 µg/L, Cu(II) 6.35 µg/L, Se(IV) 7.90 µg/L and Cr(VI) 5.20 µg/L (1.0 × 10^?7 mol/L each) were 4.0%, 4.6%, 4.6%, 7.2% and 3.4%, respectively.     

Determination of Aluminium by Electrothermal Atomization Atomic Absorption Spectrometry in Serum to Characterize Hemodialysis Toxicity

A simple and cost-effective method is described for the determination of aluminum by electrothermal atomic absorption spectrometry (ET-AAS) in serum of hemodialysis patients and healthy subjects. The only preparative step required is the dissolution of the serum sample in 0.2% magnesium nitrate matrix modifier and separate diluents 0.01 M EDTA and 0.1% Triton X-100. The calibration curve was linear from 20 to 100 µg/L with correlation coefficients of 0.9993 and 0.9998 for EDTA and Triton X-100, respectively. The sensitivity of the method for aluminum at the 309.3 nm line was 74 pg. The instrumental and method limits of detection were 2.2 µg/L and 4.4 µg/L, respectively. The aluminum concentrations of forty serum samples from hemodialysis patients and healthy subjects were determined and the mean values were 170.9 ± 6.8 µg/L and 47.3 ± 9.3 µg/L, respectively, whereas the permissible limit for aluminum in blood serum is 10 µg/L. The high level of Al in serum was related to oral phosphate binding agents and dialysis treatment.     

Green synthesis and characterization of Tb-Fe-O-Cu ceramic nanocomposite and its application in simultaneous electrochemical sensing of zinc,cadmium and lead

In this work, a green technique for preparing TbFeO₃/CuO was reported by employing Crataegus and Lantana Camara leaves as fuel and alkalizing agents, respectively. The new sensor based on the perovskite-type nanocomposite was employed as a sensitive and selective platform to detect Pb(II), Zn(II) and Cd(II) simultaneously. TbFeO₃/CuO/Carbon paste electrode (CPE) exhibited a large specific surface area and great electrical conductivity, which enhanced electron transport in the electrochemical process considerably. Moreover, square wave anodic stripping voltammetry (SWASV) was used for the investigation of some factors influencing the sensor sensitivity like pH, modifier concentration, as well as accumulation time and potential. Therefore, the low detection limit (LOD) and a wide linear range were obtained at optimum conditions. In this study, a linear range between 0.9 and 110 µg/L for three ions and LOD of 0.48, 0.29 and 0.12 for zinc, cadmium and lead were achieved, respectively. Moreover, TbFeO₃/CuO/CPE was employed to detect zinc, cadmium and lead ions simultaneously in the real samples so that the results have shown consistency with a standard inductively coupled plasma (ICP).     

Sorption of arsenic, cadmium, and lead by chars produced from fast pyrolysis of wood and bark during bio-oil production

Bio-char by-products from fast wood/bark pyrolyses, were investigated as adsorbents for the removal of the toxic metals (As(3+), Cd(2+), Pb(2+)) from water. Oak bark, pine bark, oak wood, and pine wood chars were obtained from fast pyrolysis at 400 and 450 degrees C in an auger-fed reactor and characterized. A commercial activated carbon was also investigated for comparison. Chars were sieved (>600, 600-250, 250-177, 177-149, and <149 microm) and the particle size fraction from 600 to 250 microm was used without further modification for all studies unless otherwise stated. Sorption studies were performed at different temperatures, pHs, and solid to liquid ratios in the batch mode. Maximum adsorption occurred over a pH range 3-4 for arsenic and 4-5 for lead and cadmium. Kinetic studies yielded an optimum equilibrium time of 24 h with an adsorbent dose of 10 g/L and concentration approximately 100 mg/L for lead and cadmium. Sorption isotherms studies were conducted in broad concentration ranges (1-1000 ppb for arsenic, 1x10(-5)-5x10(-3) M for lead and cadmium). Oak bark out-performed the other chars and nearly mimicked Calgon F-400 adsorption for lead and cadmium. In an aqueous lead solution with initial concentration of 4.8x10(-4) M, both oak bark and Calgon F-400 (10 g/L) removed nearly 100% of the heavy metal. Oak bark (10 g/L) also removed about 70% of arsenic and 50% of cadmium from aqueous solutions. Varying temperatures (e.g., 5, 25, and 40 degrees C) were used to determine the effect of temperatures. The equilibrium data were modeled with the help of Langmuir and Freundlich equations. Overall, the data are well fitted with both the models, with a slight advantage for Langmuir model. The oak bark char's ability to remove Pb(II) and Cd(II) is remarkable when considered in terms of the amount of metal adsorbed per unit surface area (0.5157 mg/m(2) for Pb(II) and 0.213 mg/m(2) for Cd(II) versus that of commercial activated carbon.     

On-line simultaneous pre-concentration procedure for the determination of cadmium and lead in drinking water employing sequential multi-element flame atomic absorption spectrometry

An on-line pre-concentration system for the sequential determination of cadmium and lead in drinking water by using fast sequential flame atomic absorption spectrometry (FS-FAAS) is proposed in this paper. Two minicolums of polyurethane foam loaded with 2-(6-methyl-2-benzothiazolylazo)-orcinol (Me-BTAO) were used as sorptive pre-concentration media for cadmium and lead. The analytical procedure involves the quantitative uptake of both analyte species by on-column chelation with Me-BTAO during sample loading followed by sequential elution of the analytes with 1.0?mol?L^?1 hydrochloric acid and determination by FS-FAAS. The optimisation of the entire analytical procedure was performed using a Box–Behnken multivariate design utilising the sampling flow rate, sample pH and buffer concentration as experimental variables.

The proposed flow-based method featured detection limits (3σ) of 0.08 and 0.51?µg?L^?1 for cadmium and lead, respectively, precision expressed as relative standard deviation (RSD) of 1.63% and 3.87% (n?=?7) for cadmium at the 2.0?µg?L^?1 and 10.0?µg?L^?1 levels, respectively, and RSD of 6.34% and 3.26% (n?=?7) for lead at the 5.0?µg?L^?1 and 30.0?µg?L^?1 levels, respectively. The enrichment factors achieved were 38.6 and 30.0 for cadmium and lead, respectively, using a sample volume of 10.0?mL. The sampling frequency was 45 samples per hour. The accuracy was confirmed by analysis of a certified reference material, namely, SRM 1643d (Trace elements in natural water). The optimised method was applied to the determination of cadmium and lead in drinking water samples collected in Santo Amaro da Purificação City, Bahia, Brazil.     

Synthesis of 2-mercaptobenzothiazole/magnetic nanoparticles modified multi-walled carbon nanotubes for simultaneous solid-phase microextraction of cadmium and lead

This study describes the successful sequential modification of multi-walled carbon nanotube (MWCNT) by Fe₃O₄ magnetic nanoparticles and 2-mercaptobenzothiazole (MBT) followed by its application as a novel sorbent for simultaneous magnetic solid phase microextraction of lead and cadmium. Fourier transform infrared spectroscopy and scanning electron microscopy were employed to confirm the chemical surface modification of the MWCNT. The ions retained on the 2-MBT/magnetic nanoparticles modified MWCNTs were eluted with 1.0 mL of nitric acid (0.8 mol L^?1) in methanol solution and determined by the flame atomic absorption spectrometry. All parameters affecting the extraction condition were thoroughly investigated and optimised. Under the optimised condition preconcentration factor of 150.0, enhancement factors of 149.0 and 149.2 and limits of detection of 0.21 and 0.01 µg L^?1 were achieved for lead and cadmium, respectively. Using the prepared magnetic nanocomposite, the possible interference of other common ions associated with lead and cadmium determination was effectively avoided and the method was successfully applied to the simultaneous determination of the target ions in various environmental water samples.     

Potentiometric Titration of Trace Concentrations of Penicillamine Using Ion Selective Electrodes

Abstract

Penicillamine (PA) has shown promise as a therapeutic agent in the treatment of rheumatoid arthritis (RA), and a sensitive analytical procedure applicable to physiological fluids is needed. PA is a metal chelating agent which forms very strong complexes with heavy metal ions (e.g., Hg²⁺, Cu²⁺, Pb²⁺). This characteristic has been applied to the analytical problem presented. The method developed is based on potentiometric titration of the ligand with a metal ion solution utilizing for endpoint detection an indicator electrode selective for this metal ion. The procedure described used lead (II) as the titrant and a lead (II) selective electrode. Demonstrated precision was ±2.0% when 7.5 μg PA was determined in 50 ml solution.     

Adsorption of cadmium ions from aqueous solutions using nano-montmorillonite: kinetics,isotherm and mechanism evaluations

With increasing industrial development, heavy metal pollution, e.g., cadmium (Cd) pollution, is increasingly serious in soil and water environments. This study investigated the sorption performance of nano-montmorillonite (NMMT) for Cd ions. Adsorption experiments were carried out to examine the effects of the initial metal ion concentration (22.4–224 mg/L), pH (2.5–7.5), contact time (2–180 min) and temperature (15–40 °C). A simulated acid rain solution was prepared to study the desorption of Cd adsorbed on NMMT. After the adsorption or desorption process, the supernatant was analyzed using a flame atomic absorption spectrometry method. The Cd removal rate increased as the pH and contact time increased but decreased as the initial metal ion concentration increased. The maximum adsorption capacity was estimated to be 17.61 mg/g at a Cd²⁺ concentration of 22.4 mg/L. The sorption process can be described by both the Langmuir and Freundlich models, and the kinetic studies revealed that the pseudo-second-order model fit the experimental data. The Cd desorption rate when exposed to simulated acid rain was less than 1%. NMMT possesses a good adsorption capacity for Cd ions. Additionally, ion exchange was the main adsorption mechanism, but some precipitation or surface adsorption also occurred.     

Preconcentration and determination of lead, cadmium and nickel from water samples using a polyethylene glycol dye immobilized on poly(hydroxyethylmethacrylate) microspheres.

A simple and sensitive preconcentration analysis-atomic absorption spectrometric procedure is described for the determination of lead, cadmium and nickel. The method is based upon on-line preconcentration of metal ions on a minicolumn of Cibacron Blue F3-GA immobilized on poly(hydroxyethylmethacrylate), poly(HEMA). The enrichment factors obtained were 42 for lead, 52 for cadmium and 63 for nickel (sample volume 10 mL and sample flow rate 5 mL/min). The relative standard deviations (n = 10), in 10 mL sample solutions containing 100 microg/L Pb(2+), 10 microg/L Cd(2+) and 100 microg/L Ni(2+) were 8.9, 3.7 and 3.5%, respectively. The limits of detection (blank + 3s) (n = 10), were found to be 12.01 microg/L for Pb(2+), 1.34 microg/L for Cd(2+) and 28.73 microg/L for Ni(2+). The accuracy of the system was checked with certified and tap water samples spiked with known amounts of metal ions. No significant difference was found between the achieved results and the certified values.