Application of adsorptive cathodic differential pulse stripping method for simultaneous determination of copper and molybdenum using pyrogallol red

A reliable and sensitive procedure for the simultaneous determination of trace levels of copper and molybdenum is proposed. The complexing of copper(II) and molybdenum(VI) with pyrogallol red (PGR) is analyzed by cathodic stripping differential pulse voltammetry based on the adsorption collection of the complexes onto a hanging mercury drop electrode (HMDE). The effect of chemical and instrumental parameters on the sensitivity and selectivity were studied. Copper and molybdenum peaks potential were observed at about +0.13 and −0.22 V versus Ag/AgCl electrode, respectively. A standard addition method was utilized for the analysis of voltammogram data, under the optimum conditions and with accumulation time of 90 s. The measured peak current at about +0.14 and −0.22 V is proportional to the concentration of Cu(II) and Mo(VI) over the range of 2-70 and 0.8-80 ng ml⁻¹, respectively. The limit of detection are 0.3 and 0.1 ng ml⁻¹ for Cu(II) and Mo(VI), respectively. The capability of the method for the analysis of real samples was evaluated by determination of copper and molybdenum in river water, tap water and alloy. Atomic absorption spectrometry was applied as a reference method for determination of copper and molybdenum in water samples.     

Highly sensitive catalytic determination of molybdenum

A novel, highly sensitive, selective, and simple kinetic method was developed for the determination of Mo(VI) based on its catalytic effect on the oxidation of 1-amino-2-naphthol-4-sulfonic acid (ANSA) with H₂O₂. The reaction was followed spectrophotometrically by tracing the oxidized product at 465 nm after 30 min of mixing the reagents. The optimum reaction conditions were: 10 mmol l⁻¹ ANSA, 50 mmol l⁻¹ H₂O₂, 100 mmol l⁻¹ acetate buffer of pH 5.0 ± 0.05 and at 40 °C. Addition of 200 μg ml⁻¹ diethylenetriaminepentaacetic acid (DTPA) conferred high selectivity for the proposed method. Following the recommended procedure, Mo(VI) could be determined with a linear calibration graph up to 2.5 ng ml⁻¹ and a detection limit, based on the 3S_b-criterion, of 0.027 ng ml⁻¹. The unique sensitivity and selectivity of the implemented method allowed its direct application to the determination of Mo(VI) in natural and industrial waste water. The method was validated by comparison with the standard ETAAS method. Moreover, published catalytic-spectrophotometric methods for the determination of molybdenum were reviewed.     

Catalytic adsorptive stripping voltammetry determination of ultra trace amount of molybdenum using factorial design for optimization

A highly sensitive procedure is presented for the determination of ultra-trace concentration of molybdenum by catalytic adsorptive stripping voltammetry. The method is based on adsorptive accumulation of the molybdenum (Mo)-pyrocatechol violet (PCV) complex on to a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by chlorate. The influence of variables was completely studied by factorial design analysis. Optimum analytical conditions for the determination of molybdenum were established. Molybdenum can be determined in the range 1.0 × 10⁻³-100.0 ng ml⁻¹ with a limit of detection of 0.2 pg ml⁻¹. The influence of potential interfering ions on the determination of molybdenum was studied. The procedure was applied to the determination of molybdenum in mineral water and some analytical grade substances with satisfactory results.     

Determination of vanadium, molybdenum and tungsten in complex matrix samples by chelation ion chromatography and on-line detection with inductively coupled plasma mass spectrometry

In this work, two kinds of chelating resin, bis(2-aminoethylthio)methylated resin (BAETM) and γ-aminobutyrohydroxamate resin (γ-ABHX) were synthesized. Of these, the former has a hydrophobic skeleton, and the latter a hydrophilic skeleton. The functionalities of each were 0.91 and 2.21 mmol g⁻¹, respectively. The chelating behavior of these resins towards vanadium, molybdenum and tungsten as a function of pH was studied. To perform trace metals analysis in complex matrices, a hyphenated method-chelation ion chromatography (CIC) coupled on-line detection with inductively coupled plasma mass spectrometry (ICP-MS) was developed. With a BAETM resin column (5×0.4 cm i.d.) as the separator, a sample volume of 20 μl, nitric acid (pH 1.5) as the eluent and a flow rate of 1 ml min⁻¹, the detection limits for the determination of vanadium, molybdenum and tungsten were lower than 0.05 ng ml⁻¹and the linear ranges were up to 100 ng ml⁻¹ for each element. By increasing the injected sample volume to 250 μl, the resin concentrator improved the detection limit to 0.01 ng ml⁻¹. For the determination of these elements (5 ng ml⁻¹ for each) spiked in artificial sea water samples, γ-ABHX resin column (3×0.6 cm i.d.) demonstrated well resolved peak separation between the analytes and the matrix elements—calcium and magnesium, by using sodium nitrate (10 ml, 10⁻⁴ M) as the eliminator.     

Flow-injection catalytic spectrophotometic determination of molybdenum(VI) in plants using bromate oxidative coupling of p-hydrazinobensenesulfonic acid with N-(1-naphthyl)ethylenediamine

A novel flow-injection spectrophotometry has been developed for the determination of molybdenum(VI) at nanograms per milliliter levels. The method is based on the catalytic effect of molybdenum(VI) on the bromate oxidative coupling of p-hydrazinobenzenesulfonic acid with N-(1-naphthyl)ethylenediamine to form an azo dye (λ_max = 530 nm). Chromotropic acid (4,5-dihydroxy-2,7-naphthalenedisulfonic acid) acted as an effective activator for the molybdenum(VI)-catalyzed reaction and increased the sensitivity of the method. The reaction was monitored by measuring the change in absorbance of the dye produced. The proposed method allowed the determination of molybdenum(VI) in the range 1.0-20 ng mL⁻¹ with sample throughput of 15 h⁻¹. The limit of detection was 0.5 ng mL⁻¹ and a relative standard deviation for 10 ng mL⁻¹ molybdenum(VI) (n = 10) was 2.5%. The interfering ions were eliminated by using the combination of a masking agent and on-line minicolumn packed with cation exchanger. The present method was successfully applied to the determination of molybdenum(VI) in plant foodstuffs.     

Selective, sensitive and economical method for the adsorptive voltammetric determination of trace amounts of Mo(VI) in organic matter rich environmental samples

A differential pulse adsorptive stripping voltammetric method has been developed for molybdenum trace determination in environmental water samples containing organic compounds. It was proved that interferences from the organic matrix such as surface active substances and humic substances could be removed by the addition of resin to the analysed sample prior to voltammetric measurement. The parameters for Mo(VI) determination in the presence of resin, using a hanging mercury drop as the working electrode, were examined systematically for two complexing agents: cupferron and chloranilic acid. The detection limits estimated from 3 times the standard deviation for a low Mo(VI) concentrations were equal to 5 × 10⁻¹¹ and 3 × 10⁻¹⁰ mol L⁻¹ for cupferron and chloranilic acid, respectively. At the optimized conditions the quantitative Mo(VI) determination in the presence of even 50 mg L⁻¹ of surface active compounds can be performed. The proposed procedures were validated in the course of Mo(VI) determination in certified reference material NASS-5 and in the course of studying recovery of Mo(VI) from spiked river water samples.     

Group-specific enzyme-linked immunosorbent assay for fenitrooxon and 3-methyl-4-nitrophenol in water samples based on a polyclonal antibody

Fenitrooxon [O,O-dimethyl-O-(4-nitro-m-tolyl)phosphate] is the major metabolite of the organophosphorus insecticide fenitrothion, and 3-methyl-4-nitrophenol is its major degradation product. In the present study, we describe the development of an indirect competitive enzyme-linked immunosorbent assay (ELISA) for the detection of these compounds in water samples based on a group-specific polyclonal antiserum generated with a “bifunctional hapten”, which has two functions: the conventional function of producing an antibody against an antigen and a unique function of promoting the production of the antibodies in rabbit. For application to water samples, the influence of several factors such as organic solvent, pH, and detergent was studied. Under optimized conditions, the quantitative working range of the fenitrooxon ELISA was 0.71-27 ng ml⁻¹ with a limit of detection (LOD) of 0.32 ng ml⁻¹, and the fenitrooxon concentration giving 50% reduction of the maximum signal (IC₅₀) was 4.2 ng ml⁻¹. The quantitative working range of the 3-methyl-4-nitrophenol ELISA was 0.67-27 ng ml⁻¹ with a LOD of 0.38 ng ml⁻¹ and an IC₅₀ of 3.7 ng ml⁻¹. No significant matrix effect originating from the water sample (river water, tap water, purified water, and bottled water) was shown by addition of Tween 20 to the assay buffer. Water samples spiked with each of these compounds at 1, 5, 10, and 20 ng ml⁻¹ were directly analyzed without extraction and clean-up by the proposed ELISA. The mean recovery was 100.9%, and the mean coefficient of variation (CV) was 7.7% for the fenitrooxon ELISA and for the 3-methyl-4-nitrophenol ELISA, the mean recovery was 97.6%, and the mean CV was 7.2%. The proposed ELISA allows precise and accurate determination of these compounds in water at such low levels.     

Sensitive and selective determination of molybdenum by flow injection chemiluminescence method combined with controlled potential electrolysis technique

A sensitive and selective flow injection chemiluminescence (CL) method combined with controlled potential electrolysis technique was described for the determination of molybdenum. The method is based on the chemiluminescence reaction of luminol with unstable molybdenum(III) in alkaline solution. The molybdenum(III) was on-line reduced from molybdenum(VI) via controlled potential electrolysis technique using a homemade flow-through carbon electrolytic cell at the potential of −0.6 V (versus Ag/AgCl). The method allows the determination of molybdenum in the 5.0×10⁻¹⁰ to 5.0×10⁻⁷ g ml⁻¹ range with a limit of detection (3σ) of 5×10⁻¹¹ g ml⁻¹ molybdenum. The relative standard deviation is 2.6% for the 1.0×10⁻⁹ g ml⁻¹ molybdenum solution in 11 repeated measurements. This method was successfully applied to the determination of molybdenum in water samples.     

Adsorptive stripping voltammetric determination of trace concentrations of molybdenum at an in situ plated lead film electrode

An in situ plated lead film electrode has been applied for adsorptive stripping voltammetric determination of trace concentrations of molybdenum in the presence of Alizarin S. The procedure is based on the preconcentration of the molybdenum-Alizarin S complex at an in situ plated lead film electrode held at −0.6 V (versus Ag/AgCl), followed by a negatively sweeping square wave voltammetric scan. The peak current is proportional to the concentration of molybdenum over the range 2 × 10⁻⁹ to 5 × 10⁻⁸ mol L⁻¹, with a 3σ detection limit of 9 × 10⁻¹⁰ mol L⁻¹ with an accumulation time of 60 s. The measurements were carried out from underaerated solutions. The proposed procedure was validated in the course of Mo(VI) determination in water certified reference materials.     

Potassium permanganate-glyoxal chemiluminescence system for flow injection analysis of cephalosporin antibiotics: cefalexin, cefadroxil, and cefazolin sodium in pharmaceutical preparations

A sensitive flow injection chemiluminescence (FL-CL) method for the determination of cephalosporin antibiotics, was developed. The method was based on that cephalosporin antibiotics could enhance the CL reaction of glyoxal and KMnO₄ in sulfuric acid. Method development included the optimization of reagent concentrations and flow-rate. Under the optimized conditions, three cephalosporin antibiotics: cefalexin, cefadroxil, and cefazolin sodium, were determined. The detection limits of the method are 10 ng ml⁻¹ cefalexin, 2 ng ml⁻¹ cefadroxil, and 2 ng ml⁻¹ cefazolin sodium. The method was successfully applied to the determination of three cephalosporin antibiotics in pharmaceutical preparations.     

Electrochemical hydride generation atomic absorption spectrometry for determination of cadmium

An electrolytic hydride generation system for determination of another hydride forming element, cadmium, by catholyte variation electrochemical hydride generation (EcHG) atomic absorption spectrometry is described. A laboratory-made electrolytic cell with lead-tin alloy as cathode material is designed as electrolytic generator of molecular hydride. The influences of several parameters on the analytical signal have been evaluated using a Plackett-Burman experimental design. The significant parameters such as cathode surface area, electrolytic current, carrier gas flow rate and catholyte concentration have been optimized using univariate method. The analytical figures of merit of procedure developed were determined. The calibration curve was linear up to 20 ng ml⁻¹of cadmium. The concentration detection limit (3σ, n = 8) of 0.2 ng ml⁻¹ and repeatability (relative standard deviation, n = 7) of 3.1% were achieved at 10.0 ng ml⁻¹. It was shown that interferences from major constituents at high concentrations were significant. The accuracy of method was verified using a real sample (spiked tap water) by standard addition calibration technique. Recovery of 104% was achieved for Cd in the spiked tap water sample.     

Sensitive fluorimetric method for the determination of aniline by using tetra-substituted amino aluminium phthalocyanine

This is the first report of the determination of aniline with tetra-substituted amino aluminium phthalocyanine (TAAlPc) by a fluorimetric method. In KBr-HCl solution, nitrite ion diazotizes TAAlPc, thus, the fluorescence of TAAlPc is dramatically quenched. However, there is less quenching in the presence of aniline and the recovery in fluorescence intensity is linear with the concentration of aniline. Based on this, a novel method has been developed for the determination of aniline in aqueous solutions. Under the optimal conditions, the calibration graph for aniline is from 5 to 300 ng ml⁻¹ with a 3σ limit of detection of 1.8 ng ml⁻¹. The relative standard deviation for nine replicate measurements of 100 ng ml⁻¹ aniline is 1.7%. The method was applied to the analysis of water samples with satisfactory results.     

Speciation, liquid-liquid extraction, sequential separation, preconcentration, transport and ICP-AES determination of Cr(III), Mo(VI) and W(VI) with calix-crown hydroxamic acid in high purity grade materials and environmental samples

A new functionalized calix[6]crown hydroxamic acid is reported for the speciation, liquid-liquid extraction, sequential separation and trace determination of Cr(III), Mo(VI) and W(VI). Chromium(III), molybdenum(VI) and tungsten(VI) are extracted at pH 4.5, 1.5 M HCl and 6.0 M HCl, respectively with calixcrown hydroxamic acid (37,38,39,40,41,42-hexahydroxy7,25,31-calix[6]crown hydroxamic acid) in chloroform in presence of large number of cations and anions. The extraction mechanism is investigated. The various extraction parameters, appropriate pH/M HCl, choice of solvent, effect of the reagent concentration, temperature and distribution constant have been studied. The speciation, preconcentration and kinetic of transport has been investigated. The maximum transport is observed 35, 45 and 30 min for chromium(III), molybdenum(VI) and tungsten(IV), respectively. For trace determination the extracts were directly inserted into the plasma for inductively coupled plasma atomic emission spectrometry, ICP-AES, measurements of chromium, molybdenum and tungsten which increase the sensitivity by 30-fold, with detection limits of 3 ng ml⁻¹. The method is applied for the determination of chromium, molybdenum and tungsten in high purity grade ores, biological and environmental samples. The chromium was recovered from the effluent of electroplating industries.     

A novel kinetic determination of dissolved chromium species in natural and industrial waste water

A highly sensitive, selective and simple kinetic method was developed for the determination of dissolved chromium species based on the catalytic effect of Cr(III) and/or Cr(VI) on the oxidation of 2-amino-5-methylphenol (AMP) with H₂O₂. The fixed time and initial rate variants were used for kinetic spectrophotometric measurements by tracing the oxidized product at 400 nm for 10 min after starting the reaction. Boric acid and Tween-40 exerted pronounced activating and micellar sensitizing effects on the studied redox reaction, respectively. The optimum reaction conditions were: 3.0 mmol l⁻¹ AMP, 0.45 mol l⁻¹ H₂O₂, 0.50 mol l⁻¹ boric acid, 4 v/v% Tween-40, 10 mmol l⁻¹ phosphate buffer and pH 6.45 ± 0.02 at 35 °C. Both Cr(III) and Cr(VI) ions exerted the same catalytic effect on the studied reaction. Linear calibration graphs were obtained for the determination of up to 6.0 ng ml⁻¹ Cr with detection limits of 0.054 and 0.10 ng ml⁻¹ Cr; following the fixed time and initial rate methods, respectively. The proposed method was successfully applied to the speciation and determination of trace levels of dissolved Cr(III) and Cr(VI) in natural and effluents of industrial waste water. The total dissolved Cr(III) and Cr(VI) species was determined first. In a second run, Cr(VI) was determined alone after precipitation of Cr(III) ions in presence of Al(OH)₃ collector, where Cr(III) is then determined by difference. Moreover, published catalytic-spectrophotometric methods for chromium determination were reviewed.     

Determination of 4-nonylphenol and 4-tert.-octylphenol in water samples by stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry

A simple and highly sensitive method called thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS), which is used for the determination of trace amounts of 4-nonylphenol (NP) and 4-tert.-octylphenol (OP) in water samples, is described. NP and OP in samples are extracted from water samples and concentrated by the stir bar sorptive extraction (SBSE) technique. A stir bar coated with polydimethylsiloxane (PDMS) is added to a 2.0 ml water sample and stirring is carried out for 60 min at room temperature (25 °C) in a headspace vial. Then the extract is high sensitively analyzed by TD-GC-MS without any derivatization step. The optimum SBSE conditions are realized at an extraction time of 60 min. The detection limits are 0.02 ng ml⁻¹ for NP and 0.002 ng ml⁻¹ for OP. The method shows good linearity over the concentration range of 0.1-10 ng ml⁻¹ for NP and 0.01-10 ng ml⁻¹ for OP, and the correlation coefficients are higher than 0.999. The average recoveries of NP and OP are higher than 97% (R.S.D.: 3.6-6.2%) with correction using the added surrogate standards, 4-(1-methyl) octylphenol-d₅ and deuterium 4-tert.-octylphenol. This simple, accurate, sensitive and selective analytical method may be used in the determination of trace amounts of NP and OP in tap and river water samples.     

Determination of bismuth and copper using adsorptive stripping voltammetry couple with continuous wavelet transform

A new method is proposed for the determination of bismuth and copper in the presence of each other based on adsorptive stripping voltammetry of complexes of Bi(III)-chromazorul-S and Cu(II)-chromazorul-S at a hanging mercury drop electrode (HMDE). Copper is an interfering element for the determination of Bi(III) because, the voltammograms of Bi(III) and Cu(II) overlapped with each other. Continuous wavelet transform (CWT) was applied to separate the voltammograms. In this regards, wavelet filter, resolution of the peaks and the fitness were optimized to obtain minimum detection limit for the elements. Through continuous wavelet transform Symlet4 (Sym4) wavelet filter at dilation 6, quantitative and qualitative analysis the mixture solutions of bismuth and copper was performed. It was also realized that copper imposes a matrix effect on the determination of Bi(III) and the standard addition method was able to cope with this effect. Bismuth does not have matrix effect on copper determination, therefore, the calibration curve using wavelet coefficients of CWT was used for determination of Cu(II) in the presence of Bi(III). The detection limits were 0.10 and 0.05 ng ml⁻¹ for bismuth and copper, respectively. The linear dynamic range of 0.1-30.0 and 0.1-32.0 ng ml⁻¹ were obtained for determination of bismuth in the presence of 24.0 ng ml⁻¹ of copper and copper in the presence of 24.0 ng ml⁻¹ of bismuth, respectively. The method was used for determination of these two cations in water and human hair samples. The results indicate the ability of method for the determination of these two elements in real samples.     

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.     

Simultaneous determination of copper, zinc and lead by adsorptive stripping voltammetry in the presence of Morin

A sensitive and selective method for the simultaneous determination of copper, zinc and lead is presented. The method is based on the adsorptive accumulation of 2′,3,4′,5,7-pentahydroxyflavone (Morin) complexes of these elements onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. Optimal analytical conditions were found to be Morin concentration of 2.0 μM, pH of 4.0, and an adsorption potential at −500 mV versus Ag/AgCl. With an accumulation time of 60 s, the peak currents are proportional to the concentration of copper, lead and zinc over the 1 to 60, 0.3-80 and 1-70 ng ml⁻¹ range with detection limits of 0.06, 0.08 and 0.06 ng ml⁻¹, respectively. The procedure was applied to the simultaneous determination of copper, lead and zinc in some real and synthetic artificial real samples with satisfactory results.     

Determination of mercury species with a resin functionalized with a 1,2-bis(o-aminophenylthio)ethane moiety

A method for the simultaneous preconcentration and determination of Hg(II) and MeHg(I) at the ng ml⁻¹ level has been developed. This method is based on solid phase extraction using a newly synthesized chelating resin containing nitrogen and sulphur donor sites of the 1,2-bis(o-aminophenylthio)ethane moiety that is very selective for mercury. The characterization of the resin has been carried out by elemental analyses, infrared spectral data, thermogravimetric analysis and metal ion capacities. The resin is highly selective for Hg(II) and MeHg(I) with an exchange capacity of 0.38 and 0.30 mmol g⁻¹, respectively. Various parameters like pH, column flow rate, desorbing agents are optimized. Cold vapour atomic absorption spectrometry (CVAAS) was used to measure the concentration of both species of mercury. The calibration graph was linear upto 10 ng ml⁻¹ with a 3σ detection limit of 0.09 ng ml⁻¹. The recovery of Hg(II) and MeHg(I) was found to be 98.9±2.0 and 98.0±1.1%, respectively. The method has been used for routine determination of trace levels of mercury species in natural waters to comply with more stringent regulations.     

Hydride generation atomic fluorescence spectrometric determination of ultratraces of selenium and tellurium in cow milk

A sensitive procedure has been developed for selenium and tellurium determination in milk by hydride generation atomic fluorescence spectrometry (HG-AFS) after microwave-assisted sample digestion. The method provides sensitivity values of 1591 and 997 fluorescence units ng⁻¹ ml⁻¹ with detection limits of 0.005 and 0.015 ng ml⁻¹ for Se and Te, respectively. The application of the developed methodology to the analysis of cow milk samples of the Spanish market evidenced the presence of concentration ranges from 11.1 to 26.0 ng ml⁻¹ for Se, and from 1.04 to 9.7 ng ml⁻¹ for Te having found a good comparability with data obtained after dry-ashing of samples.