Determination of Se, As, Cu, Pb, Cd, Zn and Mn by anodic and cathodic stripping voltammetry in marine environmental matrices in the presence of reciprocal interference. Proposal of a new analytical procedure

Arsenic(III), selenium(IV), copper(II), lead(II), cadmium(II), zinc(II) and manganese(II) have been determined in environmental matrices by differential pulse cathodic (DPCSV) and anodic (DPASV) stripping voltammetry. The voltammetric measurements were carried out using a conventional three-electrode cell and the ammonia–ammonium chloride buffer (pH 9.4) as the supporting electrolyte. The analytical procedure was verified by the analysis of the standard reference materials: Sea Water BCR-CRM 403; Lagarosiphon Major BCR-CRM 060; and Cod Muscle BCR-CRM 422. The precision, expressed as relative standard deviation, and the accuracy, expressed as relative error, were, in all cases, lower than 5%; the detection limits, for each element in the experimental conditions employed, was approximately 10⁻⁹ M. The standard addition technique significantly improved the resolution of the voltammetric method, even in the case of very high metal concentration ratios.     

Simultaneous determination of Cd, Pb, Cu, Sb, Bi, Se, Zn, Mn, Ni, Co and Fe in water samples by differential pulse stripping voltammetry at a hanging mercury drop electrode

A highly sensitive and selective voltammetric procedure is described for the simultaneous determination of eleven elements (Cd, Pb, Cu, Sb, Bi, Se, Zn, Mn, Ni, Co and Fe) in water samples. Firstly, differential pulse anodic stripping voltammetry (DPASV) with a hanging mercury drop electrode (HMDE) is used for the direct simultaneous determination of Cd, Pb, Cu, Sb and Bi in 0.1 M HCI solution (pH = 1) containing 2 M NaCl. Then, differential pulse cathodic stripping voltammetry (DPCSV) is used for the determination of Se in the same solution. Zn is subsequently determined by DPASV after raising the pH of the same solution to pH 4. Next, the pH of the medium is raised to pH 8.5 by adding NH3/NH4Cl buffer solution for the determination of Mn by DPASV. Ni and Co are determined in the same solution by differential pulse adsorptive stripping voltammetry (DPAdSV) after adding DMG (1 x 10(-4) M). Finally, 1 x 10(-5) M 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is added to the solution for the determination of Fe by DPAdSV. The optimal conditions are described. Relative standard deviations and relative errors are calculated for the eleven elements at three different concentration levels. The lower detection limits for the investigated elements range from 1.11 x 10(-10) to 1.05 x 10(-9)M, depending on the element determined. The proposed analysis scheme was applied for the determination of these eleven elements in some ground water samples.     

Metal analysis in real matrices. Simultaneous voltammetric determination of copper and antimony in alloys

This work addresses the simultaneous determination of copper(II) and antimony(III) in real matrices by differential pulse (DPASV) and fundamental harmonic alternating current anodic stripping voltammetry (ACASV). The voltammetric measurements were carried out using as supporting electrolyte the same acidic mixture (nitric, hydrochloric and perchloric acids) used in the dissolution of the real matrices with proper dilution. The procedure of the sample preparation is thus reduced to one step hence avoiding errors from long and complex sample handlings prior to the instrumental measurement. The results were verified by the analysis of the standard reference materials NBS-SRM 631 Spectrographic Zinc Spelter D-2 and BCS 207/2 Gunmetal. The precision, expressed as relative standard deviation, and the accuracy, expressed as relative error, were, in all cases, less than 5%; the detection limit, for each element and in the experimental conditions employed, was around 10⁻⁷ M. The standard addition technique improved the resolution of the voltammetric method, even in the case of very high metal concentration ratios.     

Heavy Metals in Matrices of Food Interest: Sequential Voltammetric Determination at Trace and Ultratrace Level of Copper,Lead, Cadmium,Zinc, Arsenic,Selenium, Manganese and Iron in Meals

The voltammetric methods are very suitable and versatile techniques for the simultaneous metal determination in complex matrices. The present work, regarding the sequential determination of Cu(II), Pb(II), Cd(II), Zn(II) by square‐wave anodic stripping voltammetry (SWASV), As(III), Se(IV) by square‐wave cathodic stripping voltammetry (SWCSV) and Mn(II), Fe(III) by square‐wave voltammetry (SWV) in matrices involved in foods and food chain as wholemeal, wheat and maize meal, are an interesting example of the possibility to sequentially determine each single element in real samples. Besides the set up of the analytical method, particular attention is aimed either at the problem of possible signal interference or to show that, using the peak area A_p as instrumental datum, it is possible to achieve lower limits of detection. The analytical procedure was verified by the analysis of the standard reference materials: Wholemeal BCR‐CRM 189, Wheat Flour NIST‐SRM 1567a and Rice Flour NIST‐SRM 1568a. Precision, as repeatability, and accuracy, expressed as relative standard deviation and relative error, respectively, were lower than 6% in all cases. In the presence of reciprocal interference, the standard addition method considerably improved the resolution of the voltammetric technique. Once set up on the standard reference materials, the analytical procedure was transferred and applied to commercial meals sampled on market for sale. A critical comparison with spectroscopic measurements is also discussed.     

Simultaneous voltammetric determination of toxic metals in sediments

Voltammetric methods are very suitable, versatile and rapid techniques for the simultaneous metal determination in complex matrices. The work, regarding the determination of As(III), Se(IV) and Mn(II), is a very interesting example of the possibility for simultaneously determining each single element in real samples in a wide range of concentration ratios. The differential pulse (DPV) measurements were carried out using a conventional three-electrode cell, while ammonia-ammonium chloride buffer (pH 9.6) was employed as the supporting electrolyte. The analytical procedure was verified by the analyses of standard reference materials: estuarine sediment BCR-CRM 277 and river sediment BCR-CRM 320. Precision and accuracy, expressed as relative S.D. and relative error, respectively, were in all cases of the order of 3-5%, while the detection limit for each element was around 10(-8) M. The standard addition technique improved the resolution of the voltammetric method, even in the case of very high element concentration ratios.     

Sensitive Quantification of Fe(III) in Food Samples at Screen Printed Carbon Electrode Modified with Graphene and Piroxicam by Catalytic Adsorptive Voltammetry

A new disposable sensitive voltammetric sensor for the determination of Fe(III) based on a graphene (G) and piroxicam (Pir) modified screen printed carbon electrode (Pir/G/SPCE) has been developed. The developed method is based on accumulation of Fe(III) on the surface of the prepared sensor strip, formation a complex with Pir and subsequent reduction the adsorbed chelated Fe(III) at ?0.03 V (vs. Ag/AgCl) coupled with the catalytic enhancement of bromate. Characterizations of the modified electrode surface were performed by field emission scanning electron microscopy (FE‐SEM), energy dispersive X‐ray spectroscopy (EDX) and electrochemical impedance spectroscopy (EIS). Electrochemical behavior of the modified SPCEs was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimum conditions, the catalytic voltammetric method exhibited linear calibration plot in the concentration ranges of 1–100 ng mL^?1 and 100–3500 ng mL^?1 Fe(III) with a limit of detection of 0.3 ng mL^?1. The sensor strip displayed good reproducibility with 1.7 % relative standard deviation (RSD%). The developed method was successfully applied for the determination of iron in food samples such as vegetables, fruit, and cereal.     

Extraction of PCDD/PCDF from soil with supercritical CO2: Optimization by a three-level factorial design approach

A highly sensitive and selective voltammetric procedure is described for the simultaneous determination of eleven elements (Cd, Pb, Cu, Sb, Bi, Se, Zn, Mn, Ni, Co and Fe) in water samples. Firstly, differential pulse anodic stripping voltammetry (DPASV) with a hanging mercury drop electrode (HMDE) is used for the direct simultaneous determination of Cd, Pb, Cu, Sb and Bi in 0.1 M HCl solution (pH = 1) containing 2 M NaCl. Then, differential pulse cathodic stripping voltammetry (DPCSV) is used for the determination of Se in the same solution. Zn is subsequently determined by DPASV after raising the pH of the same solution to pH 4. Next, the pH of the medium is raised to pH 8.5 by adding NH₃/NH₄Cl buffer solution for the determination of Mn by DPASV. Ni and Co are determined in the same solution by differential pulse adsorptive stripping voltammetry (DPAdSV) after adding DMG (1 × 10^–4 M). Finally, 1 × 10^–5 M 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is added to the solution for the determination of Fe by DPAdSV. The optimal conditions are described. Relative standard deviations and relative errors are calculated for the eleven elements at three different concentration levels. The lower detection limits for the investigated elements range from 1.11 × 10^–10 to 1.05 × 10^–9 M, depending on the element determined. The proposed analysis scheme was applied for the determination of these eleven elements in some ground water samples.     

Overlapping voltammetric peaks—an analytical procedure for simultaneous determination of trace metals. Application to food and environmental matrices

Voltammetric methods are very suitable, versatile and rapid techniques for simultaneous determination of metals in complex matrices. The present work, determination of Cu(II), Sn(II), Sb(III), Tl(I), and Pb(II) by square-wave anodic-stripping voltammetry and Cr(VI) by square-wave adsorptive-stripping voltammetry, is an interesting example of the possibility of simultaneous determination of each single element in food and environmental samples, even in the presence of reciprocal interference. Dibasic ammonium citrate, pH 6.3 or 8.2, was employed as supporting electrolyte. The voltammetric measurements were carried out using a stationary hanging mercury drop electrode as working electrode and a platinum electrode and an Ag|AgCl|KCl_sat electrode as auxiliary and reference electrodes, respectively. The analytical procedure was verified by analysis of standard reference materials—wholemeal BCR-CRM 189, wheat flour NIST-SRM 1567a, rice flour NIST-SRM 1568a, estuarine sediment BCR-CRM 277, river sediment BCR-CRM 320, and Montana soil with moderately elevated traces NIST-SRM 2711. Precision and accuracy, expressed as relative standard deviation and relative error, respectively, were generally below 6% whereas limits of detection for each element were below 0.069 g g^–1. In the presence of reciprocal interference the standard addition method considerably improved the resolution of the voltammetric technique, even for very high element concentration ratios. After being set up on the standard reference materials the analytical procedure was transferred and applied to commercial samples of meal and soil samples taken from sites devoted to agricultural practice. A critical comparison with graphite furnace atomic-absorption spectroscopy is also discussed. Work partially presented at Euroanalysis XIII, Salamanca, Spain, 5–10 September 2004     

Measurement of voltammetric peak area and resolution of overlapping peaks in the simultaneous determination of copper, lead, cadmium, and nickel in environmental matrixes

Peak area was used for the simultaneous determination of copper(II), lead(II), cadmium(II), and nickel(II) in environmental matrixes by differential pulse voltammetry. The voltammetric measurements were performed with a conventional 3-electrode cell and an ammonia-ammonium chloride buffer, pH 9.1, as the supporting electrolyte. The analytical procedure was verified first in aqueous reference solutions and later by analysis of the standard reference materials Estuarine Sediment BCR-CRM 277 and River Sediment BCR-CRM 320. The precision and accuracy of the method, expressed as the relative standard deviation and the relative error, respectively, were <5% in all cases; the detection limit for each element under the experimental conditions used was in the range 1-5 microg/L. In the case of mutual interference between neighboring elements, an analytical procedure is proposed that is based on the standard additions technique, which allows the resolution of the overlapping voltammetric peaks.     

Sequential voltammetric determination of trace metals in meals

An analytical procedure for the sequential determination of Zn(II), Cr(VI), Cu(II), Sb(III), Sn(II), Pb(II) by square wave anodic stripping voltammetry (SWASV) and Fe(III), Mn(II), Mo(VI) by square wave voltammetry (SWV) in matrices involved in foods and food chain as wholemeal, wheat and maize meal is described.The digestion of each matrix was carried out using a concentrated HCl–HNO₃–H₂SO₄ attack mixture, employing dibasic ammonium citrate buffer solution (pH 6.9 and 8.7) as supporting electrolytes. The analytical procedure was verified by the analysis of the standard reference materials Wholemeal BCR-CRM 189, Wheat Flour NIST-SRM 1567a and Rice Flour NIST-SRM 1568a.For all the elements in the certified matrix, the precision as repeatability, expressed as relative standard deviation (s_r) was of the order of 3–5%; the accuracy, expressed as relative error (e) was generally of the order of 3–6%.In presence of reciprocal interference, the standard addition method considerably improved the resolution of the voltammetric technique.Finally, the analytical procedure was transferred and applied to commercial meals sampled on market.A critical comparison with atomic absorption spectroscopic measurements is also discussed.     

Analysis of amino acids in complex samples by using voltammetry and multivariate calibration methods

A voltammetric method is proposed for the simultaneous determination of tryptophan, cysteine, and tyrosine using multivariate calibration techniques. Various electrodes and voltammetric techniques were explored to ascertain the optimum measurement strategy. Among them, differential pulse voltammetry (DPV) with a Pt electrode was selected as analytical technique since it provided a suitable compromise between sensitivity and reproducibility while allowing the oxidation peaks of the three compounds to be reasonably discriminated. The sensitivity of DPV with Pt electrode for Trp standards was 8.4×10⁻² A l mol⁻¹, the repeatability 3.7% and the detection limit below 10⁻⁷ M. The lack of full selectivity of the voltammetric data was overcome using multivariate calibration methods on the basis of the differences in the voltammetric waves of each compound. The accuracy of predictions was evaluated preliminarily from the analysis of three-component synthetic mixtures. Subsequently, this method was applied to the analysis of oxidizable amino acids in feed samples. Results obtained were in good concordance with those given by the standard method using an amino acid analyzer.     

Application of catalytic adsorptive stripping voltammetry of the cobalt-alpha-benzil dioxime complex to analysis of cobalt traces in metallic zinc

The catalytic adsorptive stripping voltammetric method with alpha-benzil dioxime and nitrite affords numerous advantages in cobalt determination. The detailed conditions of the determination of the cobalt traces in metallic zinc by catalytic adsorptive stripping voltammetry have been investigated. Both the linear sweep and the differential pulse stripping modes can be used with similar sensitivity. Possible interferences by Mn, Pb, Cu, Ni and Fe are evaluated. In the presence of 5 x 10(5) fold excess of Zn the linear dependence of the cobalt CASV peak current on concentration ranged from 0.05 mug/l to 3 mug/l. Optimal conditions include the accumulation potential of -0.65 V and the accumulation time of 10 sec. The results of the determination of 10(-5)% level of Co in the metallic zinc showed good reproducibility (relative standard deviation, RSD = 0.07) and reliability.     

Voltammetric determination of Cr(III) in plating baths containing Cr(III) salts as the main component

The differential pulse single-sweep voltammetric technique with hanging mercury drop electrode was used for the determination of Cr(III). The determination was carried out in 0.2 mol/l sodium acetate as supporting electrolyte. The reduction peak of Cr(III) was recorded at –1.5 V vs. Ag/AgCl reference electrode. The relative standard deviation was 3% for Cr concentrations in the range of 0.4 mol/l. The determination of impurities (Cd, Cu, Pb and Zn) in fresh and overworked galvanic baths using anodic stripping voltammetry in the differential pulse mode is also described.     

Voltammetric determination of imidacloprid insecticide in selected samples using a carbon paste electrode

The voltammetry of imidacloprid was investigated by using three kinds of carbon paste electrodes (CPEs) based on tricresyl phosphate, silicone oil, and n-tetradecane. The tricresyl phosphate-based carbon paste electrode exhibited the best analytical performance with respect to peak shape and signal intensity. The method, operated in the differential pulse voltammetric mode, was applied to the determination of imidacloprid in a river water sample and two commercial formulations and works in the concentration range from 1.7 to 30 μg mL⁻¹, with a relative standard deviation not exceeding 2.2%. This appears to be the first application of a CPE to the voltammetric determination of neonicotinoid insecticides.

     

Biomonitoring of essential and toxic metals in single hair using on-line solution-based calibration in laser ablation inductively coupled plasma mass spectrometry

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been established as a powerful and sensitive surface analytical technique for the determination of concentration and distribution of trace metals within biological systems at micrometer spatial resolution. LA-ICP-MS allows easy quantification procedures if suitable standard references materials (SRM) are available. In this work a new SRM-free approach of solution-based calibration method in LA-ICP-MS for element quantification in hair is described. A dual argon flow of the carrier gas and nebulizer gas is used. A dry aerosol produced by laser ablation (LA) of biological sample and a desolvated aerosol generated by pneumatic nebulization (PN) of standard solutions are carried by two different flows of argon as carrier or nebulizer gas, respectively and introduced separately in the injector tube of a special ICP torch, through two separated apertures. Both argon flows are mixed directly in the ICP torch. External calibration via defined standard solutions before analysis of single hair was employed as calibration strategy. A correction factor, calculated using hair with known analyte concentration (measured by ICP-MS), is applied to correct the different elemental sensitivities of ICP-MS and LA-ICP-MS. Calibration curves are obtained by plotting the ratio of analyte ion M⁺/³⁴S⁺ ion intensities measured using LA-ICP-MS in dependence of analyte concentration in calibration solutions. Matrix-matched on-line calibration in LA-ICP-MS is carried out by ablating of human hair strands (mounted on a sticky tape in the LA chamber) using a focused laser beam in parallel with conventional nebulization of calibration solutions. Calibrations curves of Li, Na, Mg, Al, K, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Sr, Mo, Ag, Cd, I, Hg, Pb, Tl, Bi and U are presented. The linear correlation coefficients (R) of calibration curves for analytes were typically between 0.97 and 0.999. The limits of detection (LODs) of Li, V, Mn, Ni, Co, Cu, Sr, Mo, Ag, Ba, Cd, I, Hg, Pb, Bi and U in a single hair strand were in the range of 0.001-0.90 μg g⁻¹, whereas those of Cr and Zn were 3.4 and 5.1 μg g⁻¹, respectively. The proposed quantification strategy using on-line solution-based calibration in LA-ICP-MS was applied for biomonitoring (the spatial resolved distribution analysis) of essential and toxic metals and iodine in human hair and mouse hair.     

Determination of heavy metals in TiO2 with isotope dilution mass spectrometry

An isotope dilution mass spectrometric (IDMS) method has been developed for the determination of trace impurities (Fe, Cu, Cr, Ni, Cd, Pb, Tl, and U) in TiO₂; this is of special interest for the quality control of this pigment substance. The measurement of the isotope ratios was carried out using a compact thermal ionization quadrupole mass spectrometer by producing positive thermal ions. For the dissolution of the sample, microwave digestion with HF was applied. Different separation techniques (ion exchange chromatography, extraction, electrolytic deposition) were used for the trace/matrix separation and the element specific isolation of the different trace elements to be determined. The detection limits obtained were (in ng/g): Fe=90, Cu=11, Ni=8, Cd=7, Pb=26, Tl=0.6, U=0.2. Because IDMS usually results in accurate analytical results, this method can best be used for calibration of other analytical methods, or for the certification of corresponding standard reference materials.     

Three-phase plasma arc atomic-emission spectrometric analysis of environmental samples using an ultrasonic nebulizer

Combination of an ultrasonic nebulizer and plasma excitation sources for spectrochemical analysis offers desirable features of low detection limits, high sample throughput, wide dynamic range of operation, acceptable precision and accuracy, and simultaneous quantitative analytical capabilities. Moreover, the ultrasonic nebulizer does not require sample preconcentration. Recently we have developed a three-phase plasma arc (TPPA) for atomic emission spectrochemical analysis. In the present work, to increase the analytical utility of the three-phase plasma system, an ultrasonic nebulizer was used for sample introduction. The effects of the argon gas flow rate, current, excitation temperature have been studied. The analytical calibration curves are obtained for Ca, Cr, Fe, Mg and Mn, and detection limits have been calculated. The present technique is used to determine the concentration of the elements Ca, Cr, Fe, Mg and Mn in airborne samples.     

Determination of nimesulide in human serum using a glassy carbon electrode modified with SiC nanoparticles

A glassy carbon electrode (GCE) was modified with silicon carbide nanoparticles and used to investigate the electrochemistry of the drug nimesulide via voltammetry and chronoamperometry. The structure of the modified electrode was studied by field emission scanning electron microscopy. Nimesulide undergoes electroreduction at pH 2 at a potential that is shifted from ?526 mV (at the bare GCE) to ?387 mV at the modified electrode. Simultaneously, sensitivity is increased by a factor of 5.8. The charge transfer coefficient, diffusion coefficient, standard heterogeneous rate constant and catalytic reaction rate constant were determined. A plot potential vs. pH revealed a voltammetric pKa value of about 6.5–7.0. The differential pulse voltammetric calibration plot for nimesulide is linear in 0.09–8.7 μM concentration range, and the detection limit and sensitivity are 30 nM and 512 nA.μM^?1, respectively. The modified electrode was applied to the determination of nimesulide in acidic solution and human blood serum samples without further pretreatment. The recoveries, as determined by the standard addition method, range from 95.7 to 98.7%, with an RSD of around 1.6%.

Cathodic stripping voltammetry of trace Mn(II) at carbon film electrodes

A sensitive voltammetric method is presented for the determination of tract levels of Mn (II) using carbon film electrodes fabricated from carbon resistors of 2 Ω. Determination of manganese was made by square wave cathodic stripping voltammetry (CSV), with deposition of manganese as manganese dioxide. Chronoamperometric experiments were made to study MnO₂ nucleation and growth. As a result, it was found to be necessary to perform electrode conditioning at a more positive potential to initiate MnO₂ nucleation. Under optimised conditions the detection limit obtained was 4 nM and the relative standard deviation for eight measurements of 0.22 nM was 5.3%. Interferences from various metal ions on the response CSV of Mn(II) were investigated, namely Cd(II), Ni(II), Cu(II), Cr(VI), Pb(II), Zn(II) and Fe(II). Application to environmental samples was demonstrated.     

Determination of heavy metals in TiO2 with isotope dilution mass spectrometry

An isotope dilution mass spectrometric (IDMS) method has been developed for the determination of trace impurities (Fe, Cu, Cr, Ni, Cd, Pb, Tl, and U) in TiO₂; this is of special interest for the quality control of this pigment substance. The measurement of the isotope ratios was carried out using a compact thermal ionization quadrupole mass spectrometer by producing positive thermal ions. For the dissolution of the sample, microwave digestion with HF was applied. Different separation techniques (ion exchange chromatography, extraction, electrolytic deposition) were used for the trace/matrix separation and the element specific isolation of the different trace elements to be determined. The detection limits obtained were (in ng/g): Fe=90, Cu=11, Ni=8, Cd=7, Pb=26, Tl=0.6, U=0.2. Because IDMS usually results in accurate analytical results, this method can best be used for calibration of other analytical methods, or for the certification of corresponding standard reference materials.