On-line preconcentration and speciation analysis of Cr(III) and Cr(VI) using baker's yeast cells immobilised on controlled pore glass

A study was undertaken to evaluate Saccharomyces cerevisiae as a substrate for the biosorption of Cr(III) and Cr(VI) aiming to the selective determination of these species in aqueous solutions. The yeast cells were covalently immobilised on controlled pore glass (CPG), packed in a minicolumn and incorporated in an on-line flow injection system. The effect of chemical and physical variables affecting the biosorption process was tested in order to select the optimal analytical conditions for the Cr retention by S. cerevisiae. Cr(III) was retained by the immobilised cells and Cr(VI) were retained by CPG. The speciation was possible by selective and sequential elution of Cr(III) with 0.05 mol L⁻¹ HCl and 2.0 mol L⁻¹ HNO₃ for Cr(VI). The influence of some concomitant ions up to 20 mg L⁻¹ was also tested. Quantitative determinations of Cr were carried out by means of inductively coupled plasma optical emission spectrometry (ICP OES). Preconcentration factors of 12 were achieved for Cr(III) and 5 for Cr(VI) when 1.7 mL of sample were processed reaching detection limits of 0.45 for Cr(III) and 1.5 μg L⁻¹ for Cr(VI). The speciation of inorganic Cr in different kinds of natural waters was performed following the proposed method. Spiked water samples were also analysed and the recoveries were in all cases between 81 and 103%.     

Facile preparation of glutathione-stabilized gold nanoclusters for selective determination of chromium (III) and chromium (VI) in environmental water samples

A novel method for selective determination of Cr(III) and Cr(VI) in environmental water samples was developed based on target-induced fluorescence quenching of glutathione-stabilized gold nanoclusters (GSH-Au NCs). Fluorescent GSH-Au NCs were synthesized by a one-step approach employing GSH as reducing/protecting reagent. It was found that Cr(III) and Cr(VI) showed pH-dependent fluorescence quenching capabilities for GSH-Au NCs, and thus selective determination of Cr(III) and Cr(VI) could be achieved at different pHs. Addition of EDTA was able to effectively eliminate the interferences from other metal ions, leading to a good selectivity for this method. Under optimized conditions, Cr(III) showed a linear range of 25–3800 μg L⁻¹ and a limit of detection (LOD) of 2.5 μg L⁻¹. The Cr(VI) ion demonstrated a linear range of 5–500 μg L⁻¹ and LOD of 0.5 μg L⁻¹. The run-to-run relative standard deviations (n = 5) for Cr(III) and Cr(VI) were 3.9% and 2.8%, respectively. The recoveries of Cr(III) and Cr(VI) in environmental water samples were also satisfactory (76.3–116%). This method, with its simplicity, low cost, high selectivity and sensitivity, could be used as a promising tool for chromium analysis in environmental water samples.     

Analysis of interferents by means a D-optimal screening design and calibration using partial least squares regression in the spectrophotometric determination of Cr(VI)

Using a central composite design, the signal of the process for the spectrophotometric determination of hexavalent chromium (λ = 543 nm) is maximised and its variability minimised using as complexing agent 1,5-diphenylcarbazide in sufficiently acid medium. To analyse the interference of various analytes (Mo(VI), V(V), Fe(III) and Mn(VII)) on the Cr(VI) as a function of concentration of interferent, a factorial design was prepared at three levels of each (zero, medium and high concentration), which implies performing 81 determinations. However, a D-optimal design with just nine experiments is sufficiently good to estimate the model proposed.The interference of these metals makes it impossible to determine Cr(VI) when they are present in the sample. To avoid prior separation steps, a multivariate regression by partial least squares, PLS, is proposed to calibrate the Cr(VI) in the presence of these analytes varying the concentration of the Cr(VI) between 0.1 and 0.9 μg ml⁻¹ and that of the interferents between 3 and 5 μg ml⁻¹. The average errors obtained were 4.5% and 3.29% fitted and in prediction, respectively, with a standard error in prediction (RMSEP) of 0.016% presenting absence of both constant and proportional bias.The detection limit with the PLS regression in the presence of interferents is 0.1 μg ml⁻¹ with a probability of false positive equal to 5% and less than 5% for false negative. The capability of detection is similar to that obtained with the univariate calibration (absorbance at 543 nm) in absence of interferents.With the PLS regression it is possible to discriminate 0.085 μg ml⁻¹ of Cr(VI) in a sample with 0.5 μg ml⁻¹ of Cr(VI) with probabilities of false compliance and false non-compliance equal to 0.05. For the univariate calibration without interferents, it was established at 0.0971 μg ml⁻¹ of Cr(VI) for the same nominal concentration.In relation to interference of V(V), Fe(III) and Mn(VII), the PLS calibration could be an efficient alternative to the separation step for Cr(VI) spectrophotometric determination using 1,5-diphenylcarbazide.     

Flow injection direct spectrophotometric assay for the speciation of trace chromium(III) and chromium(VI) using chromotropic acid as chromogenic reagent

A new rapid and sensitive FI assay is reported for the simultaneous direct spectrophotometric determination of trace Cr(VI) and Cr(III) in real samples. The method is based upon the reaction of Cr(VI) with chromotropic acid (CA) in highly acidic medium to form a water-soluble complex (λ_max = 370 nm). Cr(III) reacts with CA only after its on-line oxidation to Cr(VI) by alkaline KIO₄. The determination of each chromium species in the sample was achieved by absorbance differences. The calibration curves were linear over the range 3-4000 μg l⁻¹ and 30-1200 μg l⁻¹ for Cr(VI) and Cr(III), respectively, while the precision close to the quantitation limit was satisfactory in both cases (s_r = 3.0% for Cr(VI) and 4.0% for Cr(III) (n = 10) at 10 and 50 μg l⁻¹ level, respectively). The method developed proved to be adequately selective and sensitive (c_L = 1 and 10 μg l⁻¹ for Cr(VI) and Cr(III), respectively). The application of the method to the analysis of water samples (tap and mineral water) gave accurate results based on recovery studies (93-106%). Analytical results of real sample analysis were in good agreement with certified values.     

Speciated isotope dilution analysis of Cr(III) and Cr(VI) in water by ICP-DRC-MS

An isotope dilution method has been developed for the speciation analysis of chromium in natural waters which accounts for species interconversions without the requirement of a separation instrument connected to the mass spectrometer. The method involves (i) in-situ spiking of the sample with isotopically enriched chromium species; (ii) separation of chromium species by precipitation with iron hydroxide; (iii) careful measurement of isotope ratios using an inductively coupled plasma mass spectrometer (ICP-MS) with a dynamic reaction cell (DRC) to remove isobaric polyatomic interferences. The method detection limits are 0.4 μg L⁻¹ for Cr(III) and 0.04 μg L⁻¹ for Cr(VI). The method is demonstrated for the speciation of Cr(III) and Cr(VI) in local nullah and synthetically spiked water samples. The percentage of conversion from Cr(III) to Cr(VI) increased from 5.9% to 9.3% with increase of the concentration of Cr(VI) and Cr(III) from 1 to 100 μg L⁻¹, while the reverse conversion from Cr(VI) to Cr(III) was observed within a range between 0.9% and 1.9%. The equilibrium constant for the conversion was found to be independent of the initial concentrations of Cr(III) and Cr(VI) and in the range of 1.0 (at pH 3) to 1.8 (at pH 10). The precision of the method is better than that of the DPC method for Cr(VI) analysis, with the added bonuses of freedom from interferences and simultaneous Cr(III) determination.     

Hybrid mesoporous materials for on-line preconcentration of Cr(VI) followed by one-step scheme for elution and colorimetric determination at ultratrace levels

An hybrid mesoporous material synthesised in our laboratories for solid phase extraction (SPE) in flow through systems has been used for analytical purposes. The solid was obtained from mesoporous silica MCM-41 functionalized with 3-aminopropyltriethoxy silane by Sol-Gel methodology. In order to exploit the large sorption capacity of the material together with the possibility of modeling it for anions retention, a microcolumn (MC) filled with the solid was inserted in a flow system for preconcentration of Cr(VI) and its determination at ultratrace levels in natural waters. The analytical methodology involved a reverse flow injection system (rFI) holding a MC filled with the solid for the analyte extraction. Elution and colorimetric detection were carried out with 1-5 diphenylcarbazide (DPC) in sulfuric acid. DPC produced the reduction of Cr(VI) to Cr(III) together with the generation of a cationic red complex between Cr(III) and 1-5 diphenylcarbazone which was easily eluted and detected with a visible spectrophotometer. Moreover, the filling material got ready for the next sample loading remaining unspoiled for more than 300 cycles.The effect of several variables on the analytical signal as well as the influence of cationic and anionic interferences were discussed. Particular attention was given to sulfuric acid interference since it is the required media for the complex generation.Under optimal conditions, 99.8% of Cr(VI) recovery was obtained for a preconcentration time of 120 s (sample and DPC flow rates = 1 mL min⁻¹) and an elution volume of 250 μL. The limit of detection (3 s) was found to be 0.09 μg L⁻¹ Cr(VI) with a relative standard deviation (n = 10, 3 μg L⁻¹) of 1.8.Since no Cr(III) was retained by the solid material and Cr(VI) was completely adsorbed, electrothermal atomic absorption spectrometry (ET AAS) determinations of Cr(III) were also performed by simply measuring its concentration at the end of the microcolumn after Cr(VI) retention by the mesoporous solid.Applications to the determination of Cr(VI) and Cr(III) in natural waters and the validation of the methodology were also studied.     

Antimony-film electrode for the determination of trace metals by sequential-injection analysis/anodic stripping voltammetry

The possibility of applying antimony-film modified glassy carbon electrode in sequential-injection analysis (SIA) was investigated with the objective of determining Pb(II) and Cd(II) by anodic stripping voltammetry (ASV). The conditions of antimony-film deposition concerning composition of the plating/carrier solutions, concentrations of Sb(III) and hydrochloric acid, effects of different supporting electrolyte salts, and plating potential were optimized. It was found that the antimony-film deposition on glassy carbon substrate in a sample solution consisting of 750 μg L⁻¹ Sb(III), 0.5 mol L⁻¹ HCl at −1.5 V (vs. Ag/AgCl/3 mol L⁻¹ KCl) yielded a modified electrode suitable for the determination of Pb(II) and Cd(II) at the μg L⁻¹ level. The reproducibility of the analytical signals was characterized by a relative standard deviation lower than 2.8%, and the calculated values of detection limits were 1.2 μg L⁻¹ for Pb(II) and 1.4 μg L⁻¹ for Cd(II). The presence of KSCN in the sample solution offers the possibility of detecting ions with more negative oxidation potentials like Zn(II), Mn(II) or Cr(III). The developed SIA-ASV procedure was compared with the commonly used batch method, and its applicability was tested on a spiked tap water sample.     

Selective, peroxidase substrate based “signal-on” colorimetric assay for the detection of chromium (VI)

Due to the potentially adverse effects of the chromium (VI) on the human health and also on the environment, the quantitative determination of Cr(VI) is of particular interest. This work herein reports a facile, selective and rapid colorimetric determination of Cr(VI) based on the peroxidase substrate-2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS) as the color developing agent. ABTS, which was usually acted as peroxidase substrate for the enzyme linked immunosorbent assay, is used here for the first time to fabricate the “signal-on” colorimetric Assay for Cr(VI). The ABTS was chosen instead of the commonly used 1,5-diphenylcarbazide (DPC) due to its good solubility, stability, sensitivity and low background. This method provided a convenient colorimetric detection of Cr(VI) with a wider linear range from 8.33 μg L⁻¹ to 1.25 mg L⁻¹ by recording the absorption spectra at the wavelength of 419 nm and a low detection limit of 7.87 μg L⁻¹. In addition, the entire detection takes less than 10 min.     

A novel fiber-packed column for on-line preconcentration and speciation analysis of chromium in drinking water with flame atomic absorption spectrometry

A novel on-line preconcentration and determination system based on a fiber-packed column was developed for speciation analysis of Cr in drinking water samples prior to its determination by flame atomic absorption spectrometry (FAAS). All variables involved in the development of the preconcentration method including, pH, eluent type, sample and eluent flow rates, interfering effects, etc., were studied in order to achieve the best analytical performance. A preconcentration factor of 32 was obtained for Cr(VI) and Cr(III). The levels of Cr(III) species were calculated by difference of total Cr and Cr(VI) levels. Total Cr was determined after oxidation of Cr(III) to Cr(VI) with hydrogen peroxide. The calibration graph was linear with a correlation coefficient of 0.999 at levels near the detection limit and up to at least 50 μg L⁻¹. The relative standard deviation (R.S.D.) was 4.3% (C = 5 μg L⁻¹ Cr(VI), n = 10, sample volume = 25 mL). The limit of detection (LOD) for both Cr(III) and Cr(VI) species was 0.3 μg L⁻¹. Verification of the accuracy was carried out by the analysis of a standard reference material (NIST SRM 1643e “Trace elements in natural water”). The method was successfully applied to the determination of Cr(III) and Cr(VI) species in drinking water samples.     

Ligandless cloud point extraction of Cr(III), Pb(II), Cu(II), Ni(II), Bi(III), and Cd(II) ions in environmental samples with Tween 80 and flame atomic absorption spectrometric determination

A cloud point extraction (CPE) procedure has been developed for the determination trace amounts of Cr(III), Pb(II), Cu(II), Ni(II), Bi(III), and Cd(II) ions by using flame atomic absorption spectrometry. The proposed cloud point extraction method was based on cloud point extraction of analyte metal ions without ligand using Tween 80 as surfactant. The surfactant-rich phase was dissolved with 1.0 mL 1.0 mol L⁻¹ HNO₃ in methanol to decrease the viscosity. The analytical parameters were investigated such as pH, surfactant concentration, incubation temperature, and sample volume, etc. Accuracy of method was checked analysis by reference material and spiked samples. Developed method was applied to several matrices such as water, food and pharmaceutical samples. The detection limits of proposed method were calculated 2.8, 7.2, 0.4, 1.1, 0.8 and 1.7 μg L⁻¹ for Cr(III), Pb(II), Cu(II), Ni(II), Bi(III), and Cd(II), respectively.     

Indirect determination of hexavalent chromium ion in complex matrices by adsorptive stripping voltammetry at a mercury electrode

A sensitive method for the determination of chromium ion(VI) in complex matrices such as crude oil and sludge is presented based on the decreasing effect of Cr(VI) on cathodic adsorptive stripping peak height of Cu-adenine complex. Under the optimum experimental conditions (pH 7.5 Britton-Robinson buffer, 5 × 10⁻⁵ M copper, 8 × 10⁻⁶ M adenine and accumulation potential −250 mV versus Ag/AgCl), a linear decrease of the peak current of Cu-adenine was observed, when the chromium(VI) concentration was increased from 5 μg L⁻¹ to 120 μg L⁻¹. Detection limit of 2 μg L⁻¹ was achieved for 120 s accumulation time. The relative standard deviations (R.S.D., %) were 1.8% and 4% for chromium(VI) concentrations of 18 μg L⁻¹ and 100 μg L⁻¹, respectively. The method was applied to the determination of chromium(VI) in the presence of high levels of chromium(III), in various real samples such as crude oil, crude oil tank button sludge, waste water and tap water samples. Effects of foreign ions and surfactants on the voltammetric peak and the influences of instrumental and analytical parameters were investigated in detail. The accuracy of the results was checked by ICP and/or AA.     

Spectrofluorometric determination and chemical speciation of trace concentrations of chromium (III & VI) species in water using the ion pairing reagent tetraphenyl-phosphonium bromide

A highly selective, and low cost extractive spectrofluorometric method has been developed for determination of trace concentrations of chromium (III & VI) in water samples using the fluorescent reagent tetraphenylphosphonium bromide (TPP⁺·Br⁻). The method was based upon solvent extraction of the produced ion associate [TPP⁺·CrO₃Cl⁻] of TPP⁺·Br⁻ and halochromate in aqueous HCl and measuring the fluorescence quenching of TPP⁺·Br⁻ in chloroform at λ_ex/em = 242/305 nm. The fluorescence intensity of TPP⁺Br⁻ decreased linearly on increasing the chromium (VI) concentration in the range of 1-114 μg L⁻¹. The limits of detection (LOD) and quantification (LOQ) of chromium (VI) were 0.43 and 1.42 μg L⁻¹, respectively. Chromium (III) species after oxidation to chromium (VI) with H₂O₂ in alkaline solution were also determined. Chemical speciation of chromium (III & VI) species at trace levels was achieved. The method was applied for analysis of chromium in certified reference material (IAEA Soil-7) and in tap- and wastewater samples and compared successfully (>95%) with the inductively coupled plasma-mass spectrometry (ICP-MS) results.     

Electrochemical determination of arsenic(III) on mercaptoethylamine modified Au electrode in neutral media

A simple, rapid and sensitive sensing platform for the detection of As(III) has been fabricated in neutral media based on the mercaptoethylamine modified Au electrode. A wide detection range of 0.2–300 μg L⁻¹ and a low detection limit of 0.02 μg L⁻¹ were obtained with a preconcentration time of 100 s under optimal conditions. Compared with previous studies, this work shows obvious advantages that it not only suppresses the Cu(II) interference, but also can detect the As(III) in natural water samples at the original pH avoiding high concentration acidic media. Moreover, the practical application of the proposed method was verified in the lake water sample determination.     

Determination of chromium(VI) and lead in water samples by on-line sorption preconcentration coupled with flame atomic absorption spectrometry using a PCTFE-beads packed column

A new time-based flow injection on-line solid phase extraction method for chromium(VI) and lead determination using flame atomic absorption spectrometry was developed. The use of hydrophobic poly-chlorotrifluoroethylene (PCTFE)-beads as absorbent in on-line preconcentration system was evaluated. Effective formation of ammonium pyrrolidine dithiocarbamate complexes and subsequently retention in PCTFE packed column, was achieved in pH range 1.0-1.6 and 1.5-3.2 for Cr(VI) and Pb(II) ions, respectively. The sorbed analyte was efficiently eluted with isobutyl-methyl-ketone for on-line FAAS determination. The proposed packing material exhibited excellent chemical and mechanical resistance, fast kinetics for adsorption of Cr(VI) and Pb(II) permitting the use of high sample flow rates at least up to 15 mL min⁻¹ without loss of retention efficiency. For a preconcentration time of 90 s, the sample frequency was 30 h⁻¹, the enhancement factor was 94 and 220, the detection limit was 0.4 and 1.2 μg L⁻¹, while the precision (R.S.D.) was 1.8% (at 5 μg L⁻¹) and 2.1% (at 30 μg L⁻¹) for chromium(VI) and lead, respectively. The applicability and the accuracy of the developed method were estimated by the analysis spiked water samples and certified reference material NIST-CRM 1643d (Trace elements in water) and NIST-SRM 2109 (chromium(VI) speciation in water).     

Bismuth-dispersed xerogel-based composite films for trace Pb(II) and Cd(II) voltammetric determination

We report for the first time the synthesis of bismuth-modified (3-mercaptopropyl) trimethoxysilane (MPTMS) and its application for the determination of lead and cadmium by anodic stripping voltammetry. Xerogels made from bismuth-modified MPTMS and mixtures of it with tetraethoxysilane, under basic conditions (NH₃·H₂O), were characterized with scanning electron microscopy, energy dispersive spectroscopy, infrared spectroscopy and electrochemical methods. Bismuth-modified xerogels were mixed with 1.5% (v/v) Nafion in ethanol and applied on glassy carbon electrodes. During the electrolytic reductive deposition step, the bismuth compound on the electrode surface was reduced to metallic bismuth. The target metal cations were simultaneously reduced to the respective metals and were preconcentrated on the electrode surface by forming an alloy with bismuth. Then, an anodic voltammetric scan was applied in which the metals were oxidized and stripped back into the solution; the voltammogram was recorded and the stripping peak heights were related to the concentration of Cd(II) and Pb(II) ions in the sample. Various key parameters were investigated in detail and optimized. The effect of potential interferences was also examined. Under optimum conditions and for preconcentration period of 4 min, the 3σ limit of detection was 1.3 μg L⁻¹ for Pb(II) and 0.37 μg L⁻¹ for Cd(II), while the reproducibility of the method was 4.2% for lead (n = 5, 10.36 μg L⁻¹ Pb(II)) and 3.9% for cadmium (n = 5, 5.62 μg L⁻¹ Cd(II)). Finally, the sensors were applied to the determination of Cd(II) and Pb(II) ions in water samples.     

Voltammetric determination of Se(IV) and Se(VI) in saline samples—Studies with seawater, hydrothermal and hemodialysis fluids

Determination of Se(IV) and Se(VI) in high saline media was investigated by cathodic stripping voltammetry (CSV). The voltammetric method was applied to assay selenium in seawater, hydrothermal and hemodialysis fluids. The influence of ionic strength on selenium determination is discussed. The CSV method was based on the co-electrodeposition of Se(IV) with Cu(II) ions and Se(VI) determined by difference after sample UV-irradiation for photolytic selenium reduction. UV-irradiation was also used as sample pre-treatment for organic matter decomposition. Detection limit of 0.030 μg L⁻¹ (240 s deposition time) and relative standard deviation (RSD) of 6.19% (n = 5) for 5.0 μg L⁻¹ of Se(IV) were calculated. Linear calibration range for selenium was observed from 1.0 to 100.0 μg L⁻¹. Concerning the pre-treatment step, best results were obtained by using 60 min UV-irradiation interval in H₂O₂/HCl medium. Se(VI) was reduced to the Se(IV) electroactive species with recoveries between 91.7% and 112.9%. Interferents were also investigated.     

Modified mesoporous silica materials for on-line separation and preconcentration of hexavalent chromium using a microcolumn coupled with flame atomic absorption spectrometry

A modified SBA-15 mesoporous silica material NH₂-SBA-15 was synthesized successfully by grafting γ-aminopropyl-triethoxysilane. The material was characterized using transmission electron microscopy (TEM) and Fourier transform infrared/Raman (FT-IR/Raman) spectroscopy, and used for the first time in a flow injection on-line solid phase extraction (SPE) coupled with flame atomic absorption spectrometry (FAAS) to detect trace Cr (VI). Effective sorption of Cr (VI) was achieved at pH 2.0 with no interference from Cr (III) and other ions and 0.5 mol L⁻¹ NH₃·H₂O solution was found optimal for the complete elution of Cr (VI). An enrichment factor of 44 and was achieved under optimized experimental conditions at a sample loading of 2.0 mL min⁻¹ sample loading (300 s) and an elution flow rate of 2.0 mL min⁻¹ (24 s). The precision of the 11 replicate Cr (VI) measurements was 2.1% at the 100 μg L⁻¹ level with a detection limit of 0.2 μg L⁻¹ (3 s, n = 10) using the FAAS. The developed method was successfully applied to trace chromium determination in waste water. The accuracy was validated using a certified reference material of riverine water (GBW08607).     

Chemically modified silica gel with p-dimethylaminobenzaldehyde for selective solid-phase extraction and preconcentration of Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) by ICP-OES

Silica gel-bound amines phase modified with p-dimethylaminobenzaldehyde (p-DMABD) was prepared based on chemical immobilization technique. The product (SG-p-DMABD) was used as an adsorbent for the solid-phase extraction (SPE) Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). The uptake behaviors of SG-p-DMABD for extracting these metal ions were studied using batch and column procedures. For the batch method, the optimum pH range for Cr(III) and Ni(II) extraction was ≥ 3, for Cu(II), Pb(II) and Zn(II) extraction it was ≥ 4. For simultaneous enrichment and determination of all the metals on the newly designed adsorbent, the pH value if 4.0 was selected. All the metal ions can be desorbed with 2.0 mL of 0.5 mol L^− 1 of HCl. The results indicate that SG-p-DMABD has rapid adsorption kinetics using the batch method. The adsorption capacity for these metal ions is in the range of 0.40-1.15 mmol g^− 1, with a high enrichment factor of 125. The presence of commonly coexisting ions does not affect the sorption capacities. The detection limits of the method were found to be 1.10, 0.69, 0.99, 1.10 and 6.50 μg L^− 1 for Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II), respectively. The relative standard deviation (RSD) of the method under optimum conditions was 5.0% (n = 8) for all metal ions. The method was applied to the preconcentration of Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) from the certified reference material (GBW 08301, river sediment) and water samples with satisfactory results.     

Sequential injection anodic stripping voltammetry with monosegmented flow and in-line UV digestion for determination of Zn(II), Cd(II), Pb(II) and Cu(II) in water samples

A cost-effective sequential injection system incorporating with an in-line UV digestion for breakdown of organic matter prior to voltammetric determination of Zn(II), Cd(II), Pb(II) and Cu(II) by anodic stripping voltammetry (ASV) on a hanging mercury drop electrode (HMDE) of a small scale voltammetric cell was developed. A low-cost small scale voltammetric cell was fabricated from disposable pipet tip and microcentrifuge tube with volume of about 3 mL for conveniently incorporated with the SI system. A home-made UV digestion unit was fabricated employing a small size and low wattage UV lamps and flow reactor made from PTFE tubing coiled around the UV lamp. An in-line single standard calibration or a standard addition procedure was developed employing a monosegmented flow technique. Performance of the proposed system was tested for in-line digestion of model water samples containing metal ions and some organic ligands such as strong organic ligand (EDTA) or intermediate organic ligand (humic acid). The wet acid digestion method (USEPA 3010a) was used as a standard digestion method for comparison. Under the optimum conditions, with deposition time of 180 s, linear calibration graphs in range of 10-300 μg L⁻¹ Zn(II), 5-200 μg L⁻¹ Cd(II), 10-200 μg L⁻¹ Pb(II), 20-400 μg L⁻¹ Cu(II) were obtained with detection limit of 3.6, 0.1, 0.7 and 4.3 μg L⁻¹, respectively. Relative standard deviation were 4.2, 2.6, 3.1 and 4.7% for seven replicate analyses of 27 μg L⁻¹ Zn(II), 13 μg L⁻¹ Cd(II), 13 μg L⁻¹ Pb(II) and 27 μg L⁻¹ Cu(II), respectively. The system was validated by certified reference material of trace metals in natural water (SRM 1640 NIST). The developed system was successfully applied for speciation of Cd(II) Pb(II) and Cu(II) in ground water samples collected from nearby zinc mining area.     

FI automatic method for the determination of copper(II) based on coproporphyrin I-Cu(II)/TCPO/H(2)O(2) chemiluminescence reaction for the screening of waters

In this paper, an automatic method for the screening of water samples containing Cu(II) was proposed, based on peryoxalate chemiluminescence reaction using coproporphyrin I as fluorophor compound to provide selectivity and a simple flow injection (FI) chemiluminescence detector (CLD). FI system conditions were chosen in order to distinguish samples over or under legislation limit established (50 μg l⁻¹) with high reliability. The detection limit found was 9 μg l⁻¹ and the linear dynamic range was 15-125 μg l⁻¹ of Cu(II). Repeatibility and reproducibility studies gave good precision and accuracy with recovery near 100%. Under these conditions, the method resulted selective and only Fe(II), Fe(III) and Pb(II) could interfere, but at a concentration level higher than their normal concentration in waters. The proposed method was found to be highly reliable for screening purposes and it was successfully applied to the screening of a variety of real water samples.