Showing papers in "Mikrochimica Acta in 2004"

Preconcentration and Separation Procedures for the Spectrochemical Determination of Platinum and Palladium

Abstract: Low concentrations of Pt and Pd in industrial (µg g−1 level) and environmental samples (ng g−1 level) together with the complexity of the matrix causing many interferences during the determination of noble metals often require elaboration and application of pre-concentration/matrix separation procedures before detection of the analyte. Different pre-concentration/matrix separation procedures applied prior to the determination of Pt and Pd by atomic spectrometric techniques are reviewed and critically compared taking into account potential interferences. The methods studied are divided into 5 groups including precipitation and coprecipitation, liquid–liquid extraction, solid phase extraction, electrochemical pre-concentration and biosorption. The main analytical problems occuring during sample preparation and storage are discussed.

Progress in Enzyme-Based Biosensors Using Optical Transducers

Abstract: Enzyme-based biosensors are well developed and relatively mature technique in the biosensing field. Biosensors that utilise enzymes as the recognition elements represent the most extensively studied area. The organisation of an enzyme-based biosensor requires the integration of the biocatalyst with the support or immobilised materials to the extent that the biocatalytic transformation is either optically or electronically transduced. Any optical or electrical changes at the support material as a result of the biocatalytic process, that is, depletion of the reactant or formation of the product, provide routes for the opto/electronic transduction of the biological process occurring at the sensing surface. This review focuses on the discussion of some enzyme immobilisation techniques including physical and chemical immobilisation. Enzyme-based biosensors using various optical detection methods such as absorptiometry, luminometry, chemiluminescence, evanescent wave, and surface plasmon resonance are also included. Finally, different types of enzyme-based optical biosensors for ascorbic acid, bilirubin, cholesterol, choline, ethanol, glucose, glutamate/glutamine, lactate, penicillin, urea, and uric acid determinations are presented.

Electrochemical Study and Selective Determination of Dopamine at a Multi-Wall Carbon Nanotube-Nafion Film Coated Glassy Carbon Electrode

Abstract: A homogeneous and stable suspension of multi-wall carbon nanotubes (MWNT) was achieved by dispersing MWNT into 0.1% Nafion ethanol solution. A uniform MWNT-Nafion cast film was obtained over a glassy carbon electrode (GCE) via solvent evaporation. The electrochemical behavior of dopamine (DA) was examined, and a reversible two-electron redox reaction was observed. In comparison with the bare GCE and the Nafion-modified GCE, the MWNT-Nafion modified GCE shows obvious electrocatalytic activity towards DA. Moreover, the MWNT-Nafion film coated electrode exhibits excellent selectivity towards DA even in the presence of high concentrations of ascorbic acid (AA) and uric acid (UA). The oxidation peak current was proportional to the concentration of DA over the range of 1 × 10−8 to 1 × 10−5 mol L−1, and a detection limit of 2.5 × 10−9 mol L−1 was obtained after 2 min. of open-circuit accumulation. The dispersion and morphology of MWNT-Nafion film were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transfer (FT) IR spectra.

Electrocatalysis of Tryptophan at Multi-Walled Carbon Nanotube Modified Electrode

Abstract: Acid-treated multi-walled carbon nanotubes (MWNTs) were immobilized on the surface of a glassy carbon electrode to form an MWNT-modified electrode. The electrocatalytic response of the modified electrode towards tryptophan (Trp) was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results demonstrated that the modified electrode exhibited a high degree of catalytic activity towards the oxidation of Trp. An oxidation peak was obtained in Trp solution at the MWNT-modified electrode. Compared with a bare electrode, the peak current had obviously increased, and the peak potential had shifted in a negative direction. However, under the same conditions, no response was observed for other amino acids. The oxidation peak currents were proportional linearly to the concentration of Trp, a property which could be utilized to detect Trp. The determination conditions, such as the concentration, the composition and the pH values of the supporting electrolyte, accumulation time, as well as scan rate etc. were optimized. Under the chosen conditions, the DPV peak current is linear to the concentration of Trp in the range of 2.5 × 10−7 to 1.0 × 10−4 mol L−1, and the detection limit is 2.7 × 10−8 mol L−1. Moreover, the detection is free of interference from other amino acids. The modified electrode has been successfully applied to determine the concentration of Trp in composite amino acid injections, and it displays excellent repeatability and higher sensitivity.

Electrochemical Determination of 4-Nitrophenol Using a Single-Wall Carbon Nanotube Film-Coated Glassy Carbon Electrode

Abstract: A single-wall carbon nanotubes (SWNT) film coated glassy carbon electrode (GCE) was fabricated for the direct determination of 4-nitrophenol (4-NP). The electrochemical behaviors of 4-NP at the SWNT-film coated GCE were examined. In 0.1 M phosphate buffer with a pH of 5.0, 4-NP yields a very sensitive and well-defined reduction peak at the SWNT-modified GCE. It is found that the SWNT film exhibits obvious electrocatalytic activity towards the reduction of 4-NP since it not only increases the reduction peak current but also lowers the reduction overpotential. Based on this, an electrochemical method was proposed for the direct determination of 4-NP. The reduction peak current varies linearly with the concentration of 4-NP ranging from 1 × 10−8 to 5 × 10−6 M, and the detection limit is 2.5 × 10−9 M after 3 min of open-circuit accumulation. The relative standard deviation at 2 × 10−7 M 4-NP was about 6% (n = 10), suggesting excellent reproducibility. This new method was successfully employed to determine 4-NP in several lake water samples.

Effect of Porogen Type on the Synthesis of Uranium Ion Imprinted Polymer Materials for the Preconcentration/Separation of Traces of Uranium

Abstract: Ion Imprinted Polymer (IIP) materials were prepared from different porogens by copolymerization of UO22+-5,7,dichloroquinoline-8-ol-4-vinylpyridine ternary complex in the presence of styrene as monomer, divinyl benzene as crosslinking agent and 2,2′-azobisisobutyronitrile as initiator The uranyl ion was removed on leaching with 50% (v/v) HCl, which leaves cavities in the polymer particles Of the various porogens tested, 2-methoxy ethanol gave a higher retention/adsorption capacity for uranium and better selectivity for uranium over thorium The optimum pH value for quantitative enrichment is 50–70, and desorption can be achieved with 5 mL of 1 M HCl The retention capacity of the uranyl ion imprinted polymer particles was found to be 340 mg g−1 for uranium, which is much higher than blank or ion recognition polymer More significantly, the selectivity coefficient (SU/Th) is much higher (∼990) with 2-methoxy ethanol as porogen The polymer particles obtained from this porogen have been characterized by IR, TGA, DTA, XRD, SEM and EDS analysis Five replicate determinations of 40 µg of uranyl ion present in 1000 mL of aqueous solution with Arsenazo III spectrophotometric method gave a mean absorbance of 0185 with a relative standard deviation of 246% The detection limit corresponding to 3 times the standard deviation of the blank was found to be 2 ng mL−1

Determination of Caffeine Using a Simple Graphite Pencil Electrode with Square-Wave Anodic Stripping Voltammetry

Abstract: A simple commercial graphite pencil electrode (GPE) was utilized for monitoring caffeine using the square-wave anodic stripping voltammetry (SWASV) method. This method was applied to determine the caffeine levels in several tea samples, which yielded a relative error of 1% in the concentrations. Caffeine was deposited at 0.0 V (vs. Ag/AgCl), then reduced at +1.40 V to strip it on the GPE. Optimal experimental conditions for the analysis were found to be as follows: pH value of 9 for the medium; deposition potential of 0.0 V; deposition time of 120 s; SW frequency of 25 Hz; SW amplitude of 45 mV, and step potential of 6 mV. Given these optimum conditions, a linear range was observed within the concentration of 0 ∼ 500 mg L−1. At caffeine concentrations of 50.0, 250.0, and 500.0 mg L−1, the relative standard deviations in measured concentrations (n = 12) were 0.19, 0.09, and 0.11%, respectively. The detection limit was found to be 9.2 mg L−1, which is comparable with the result obtained using a carbon paste electrode, equivalent to 8.2 mg L−1.

Re-Examination of the Cadmium Reduction Method and Optimisation of Conditions for the Determination of Nitrate by Flow Injection Analysis

Abstract: The present paper re-examines the widely used flow injection method for nitrate which is based on heterogeneous reduction of nitrate with copperized cadmium followed by spectrophotometric detection of nitrite formed. The thorough investigation presented here has shown that the reduction step is very critical as far as conversion rate, possible further reduction of nitrite and long-term stability of the reductor column is concerned. The reasons for inconsistent and irreproducible results mentioned in original papers and often obtained in routine applications could be traced back to the way the reductor material had been prepared, the chemical conditions under which reduction takes place (i.e. pH and concentration of complexing agents) and the poisoning of the cadmium surface by sample constituents. The concomitant reduction of dissolved oxygen has been identified as a potential problem causing loss of pH control (due to in-situ generation of hydroxide). De-oxygenation of the carrier solution was found to be a means to overcome this problem with the additional advantages of increasing the lifetime of the reductor column and significantly reducing the concentration of cadmium ions in the waste stream. The role of particle size and column dimension as well as sample residence time within the reductor column on reduction efficiency and sample dispersion has also been investigated.

Electrospray Ionization Mass Spectrometric Analysis of Aqueous Polysulfide Solutions

Abstract: The speciation of polysulfides in aqueous solutions was investigated by electrospray – ion trap and electrospray – time of flight mass spectrometry. The pH dependence of the observed total dissolved polysulfides’ concentration followed the trend calculated based on reported thermodynamic constants. However, the observed species’ distributions were substantially different from those calculated based on thermodynamic coefficients derived by UV spectroscopy. Notably, large abundances of heptasulfide, octasulfide and nonasulfide species were observed throughout the pH range 6 to 11. The large molecular weight anions had not been reported before in aqueous solutions although indirect evidence had suggested their existence.

Amperometric Detection of Dopamine in the Presence of Ascorbic Acid Using a Nafion Coated Glassy Carbon Electrode Modified with Catechin Hydrate as a Natural Antioxidant

Abstract: Catechin hydrate (trans-3,3′,4′,5,7-penta-hydroxyflavone) is a derivative of catechol, and it is one of the natural antioxidant and anticarcinogenic compounds found in many fruits and agricultural foods. A new electrode was prepared by electrodeposition of a catechin-hydrate film on the surface of an activated glassy carbon electrode, followed by coating with nafion layer. Cyclic voltammetry was used for the deposition process, and the resulting modified electrode was found to retain the activity of the quinone/hydroquinone group anticipated for a surface-immobilized redox couple. The cyclic voltammograms of the modified electrode indicated that the surface-confined catechin-hydrate was strongly dependent on the solution pH. The electrochemical behaviour and stability of the modified electrode were studied by cyclic voltammetry. The apparent charge transfer rate constant (k s ) and electron transfer coefficient (α) between the electrode surface and adsorbed catechin hydrate were calculated as 0.41 and 0.31 sz−1 0.31, respectively. The modified electrode exhibits an electrocatalytic effect on dopamine oxidation in the pH range of 2 to 7. The modified electrode was used for the electrocatalytic oxidation of dopamine in the presence of ascorbic acid and the elimination of the interference by ascorbic acid (AA) when present in a 200-fold concentration excess. A very large decrease (400 mV) in the overpotential for the oxidation of dopamine and current increase were observed on the surface of the modified electrode. Dopamine was determined amperometrically at the modified electrode in the concentration range of 100 nM to 0.1 mM. The detection limit (signal to noise is 3) and sensitivity are 11 nM and 16 nA/µM, respectively. The modified electrode was employed to determine DA in biological mediums.

Determination of Nitric Oxide in Biological Samples

Abstract: NO plays an important role in the regulation of physiological and pathophysiological mechanisms, and quite a lot of investigations have been focused on this kind of special molecule. It is difficult to achieve reliable ex vivo NO measurements with the existing analytical methods, and developing a reliable in vivo monitoring method for NO is still an urgent task. In this review, the techniques utilized for the determination of endogenous NO formed by enzymatic action and its reactions with other biological substances found in living organisms are discussed with respect to applications both in vivo or in vitro. In addition, various NO (micro)sensors and trap probes based on different principles are presented with their respective advantages and limitations. Finally, an NO monitoring system based on the combination of microdialysis sampling and chemiluminescence is introduced which is considered to be a prospective method for in vivo monitoring.

Silica Gel Loaded with o-Dihydroxybenzene: Design, Metal Sorption Equilibrium Studies and Application to Metal Enrichment Prior to Determination by Flame Atomic Absorption Spectrometry

Abstract: The aminopropyl silica gel (APSG) prepared by reaction of activated silica gel with 3-aminopropyltriethoxysilane on reaction with 3,4-dihydroxybenzaldehyde has resulted in a new chelating matrix, o-dihydroxybenzene (DHB) anchored silica gel, which is characterized by IR, TGA and elemental analyses. APSG is characterized with 13C CPMAS NMR spectroscopy. DHB anchored silica gel sorbs quantitatively (97.4–99.2% recovery) Cu(II), Pb(II), Fe(III), Zn(II), Co(II), Ni(II) and Cd(II) at pH 6.0–7.5, 5.0–7.0, 5.5–7.0, 6.0–8.0, 6.5–8.0, 5.5–7.0 and 6.5–7.5, respectively. The sorption capacity varies from 32 to 348 µmol g−1 and is highest for copper. Desorption was found to be quantitative with 1.0–3.0 mol L−1 HCl/HNO3 (for Pb). The optimum flow rate of the solution for quantitative sorption of metal ions on a column (10 cm × 10 mm) packed with 1 g of the modified silica gel is 1.0–4.0 mL min−1, whereas for desorption it is 2.0 −4.0 mL min−1. The tolerance limits for NaCl, NaBr, NaI, NaNO3, Na2SO4, Na3PO4, humic acid, EDTA, ascorbic acid, citric acid, sodium tartrate, Ca(II) and Mg(II) in the sorption of all the seven metal ions are reported. The preconcentration factors are between 100 and 300 and t1/2 values ≤17 min. The present matrix coupled with FAAS has been used to enrich and determine the seven metal ions in river and tap water samples (RSD 1.4–7.0%) and in synthetic certified water samples SLRS-4 (NRC, Canada) with an RSD of 2.73–2.83%. The cobalt present in pharmaceutical vitamin tablets and Zn in milk powder was preconcentrated on DHB anchored silica gel and determined by FAAS (RSD of 2.00 to 2.72%).

The uncertainty of weighing data obtained with electronic analytical balances

Abstract: Weighing is a common task in any chemical laboratory and weighing data are associated with some uncertainty, as this is common with all other working procedures and their data. This paper presents the influence factors which are part of the combined measurement uncertainty of a mass determination and their interplay, namely the technical specifications of the balance (repeatability, nonlinearity, sensitivity tolerance, and temperature coefficient of the sensitivity) and the effect of air buoyancy. Depending on the net and gross weight, the densities involved (density of air and of the weighing object in relation to the density of the reference weights) and the uncertainties of these densities the relative uncertainty of weighing data is often in the 10−5 to 10−4 range (10 to 100 ppm). It must be kept in mind that such low values can only be obtained with simple weighing goods, i.e. in the absence of disturbances such as electrostatic charges, air drafts, evaporation, or water adsorption phenomena.

Solid Phase Extraction of Cesium from Aqueous Solution Using Sol-Gel Encapsulated Cobalt Hexacyanoferrate

Abstract: The synthesis and evaluation of silica sol-gels doped with cobalt hexacyanoferrate (CoHCF) for solid phase extraction of Cs+ from aqueous solution is described. The CoHCF is formed by first introducing K4Fe(CN)6 (HCF) into the sol-gel and subsequently contacting the porous solid to a solution containing Co2+. Generally, sols contain alcohol as a co-solvent, which limits the solubility of HCF. Inclusion of generation-4 polyamidoamine (G4-PAMAM) dendrimer in the sol-gel increases the level of HCF and, in turn, the CoHCF. The uptake capacity of this composite was 0.43±0.01 mmol Cs+ g−1. A second approach to increasing the level of HCF silica is to exclude alcohol from the sol and use ultrasound to obtain a homogeneous suspension; HCF concentrations up to 0.17 M in the sol were thereby achieved. After gelation and reaction with Co2+, the resulting composite had a capacity of 0.61±0.01 mmol Cs+ g−1. With 0.5 mM Cs+ as the sample, the presence of either 0.5–100 mM Na+ or 10 mM Ca2+ did not change that value at the 95% confidence level.

Solid-Phase Extraction for Preconcentration and Separation of Vanadium Species in Natural Waters

Abstract: For selective preconcentration and separation of vanadium species, several conventional ion-exchange resins, functionalised cellulose sorbents and chelating resins were examined. Cellulose with phosphonic acid exchange groups (Cellex P) was found to be superior for enrichment of both vanadium(IV) and vanadium(V). Both species could be simultaneously eluted using EDTA solution with recoveries of 94–101% and determined by AAS method. An enrichment factor of 150 was obtained. The speciation study of vanadium ions has been tested using CDTA added to the sample or as a selective eluent for V(IV). Application of the proposed method to water analysis is discussed.

Application of Lanthanide-Sensitised Chemiluminescence to the Determination of Levofloxacin, Moxifloxacin and Trovafloxacin in Tablets

Abstract: A flow injection method including chemiluminescence detection has been developed and applied to the determination of fluoroquinolones levofloxacin, moxifloxacin and trovafloxacin in tablets. The proposed method is based on the luminescent properties of the system Ce(IV)–sulphite–fluoroquinolone and the addition of a trivalent lanthanide ion as emission-sensitizer. The optimum conditions for chemiluminescence emission were investigated for each fluoroquinolone. The best results were achieved when employing Eu(III) as lanthanide cation for levofloxacin and moxifloxacin, and Tb(III) for trovafloxacin. These fluoroquinolones were determined over the concentration range of 0.5–3.5 µg mL−1, 0.2–3.0 µg mL−1 and 0.008–0.400 µg mL−1, with detection limits of 0.100, 0.035 and 0.008 µg mL−1, respectively. The relative standard deviations were in the range of 1.0–2.5% for all three cases. The method was applied to the determination of three fluoroquinolones in their respective pharmaceutical preparations and compared with an independent UV-spectrophotometric method. The results were satisfactory.

Immobilization of Urease and Cholinesterase on the Surface of Semiconductor Transducer for the Development of Light-Addressable Potentiometric Sensors

Abstract: Various methods for the immobilization of urease and butyrylcholinesterase on the insulator surface of a laser-scanned semiconductor transducer (LSST) have been tested and compared for the development of an enzyme-based light-addressable potentiometric sensor (LAPS). The method of preparing photocurable membranes on LAPS is presented, and a new type of enzyme LAPS with photocurable polymeric enzyme membranes has been elaborated. It was found that sensors prepared by means of covalent bonding and cross-linking with inactive protein (type SIII) and with photocurable membrane matrices (type SIV) are more prospective. The enzyme LAPSensors with photocurable membranes demonstrate a degree of sensitivity close to the theoretical value and working ranges of 6.3·10−5−1.1·10−2 and 1·10−4−1·10−1 mol L−1 urea for acrylamide and acrylate-based membrane matrices, respectively, and 2.5·10−4−2·10−1 mol L−1 butyrylcholine for an acrylamide membrane matrix. It is shown that such sensors can be also used for the analysis of enzyme inhibitors.

Analysis of Toxic Aluminium Species in Natural Waters

Abstract: Aluminium is known to be toxic to a wide range of aquatic organisms under certain conditions. Monomeric hydroxy ions have been found to be primarily responsible for aluminium aquatic toxicity. A survey of aluminium toxicity and a brief discussion of speciation schemes are presented. The fast reaction of Al3+ with pyrocatechol violet (PCV) followed by spectrophotometric analysis is a frequently used method for aluminium speciation. By using a flow system, one obtains fairly exact and reproducible control of the reaction time, and as a result it provides a direct method of analysis for “free” aluminium (including inorganic monomeric aluminium). The PCV-method has been adapted for the determination of aluminium in carbonate-rich natural waters using an improved buffering system. Thus it is possible to monitor aluminium concentrations in lake water as well as in pore water of the sediments of eutrophicated hardwater lakes that has been treated with aluminium salts as a restoration measure.

SIMS Analysis of Uranium and Actinides in Microparticles of Different Origin

Abstract: In the framework of the projects “Environmental Sampling” and “High Performance Trace Analysis” in support to the International Atomic Energy Agency (IAEA) and the Euratom Safeguards Office (ESO), the research has been focused on the identification and characterisation of particles of interest containing mainly U and other actinides.

What Flow Injection has to Offer in the Environmental Analytical Field

Abstract: Flow injection analysis (FIA) is presented as a powerful tool to meet the analytical requirements of environmental and agricultural assays in terms of automation, monitoring, microsampling, speciation and sample processing. Its potentials and limitations are critically discussed and demonstrated in the body of the text with relevant examples devoted to water, air, soil and plant analysis. The features of this continuous flowing stream technique are classified according to the particular role that FIA plays as a universal handling system interfacing wet chemical reactions with analytical instrumentation. Special attention is paid to its assets as a liquid delivery system, chemical derivatization method as well as on-line sample pre-treatment tool.

Sensitive Method for Trace Determination of Mercury in Wines Using Electrothermal Atomic Absorption Spectrometry

Abstract: An accurate, simple and precise method for total mercury determination in wines is described Liquid/liquid extraction of inorganic and organic mercury species directly from untreated wine samples is recommended as a preconcentration procedure prior to determination by electrothermal atomic absorption spectrometry (ETAAS) Ammonium pyrrolidinedithiocarbamate was used as complexation agent The optimal instrumental parameters for ETAAS measurement of mercury species extracted are proposed The detection limit for total mercury determination is 02 µg L−1 The relative standard deviation is 15–22% for mercury in wine in the range of 02–5 µg L−1 The proposed procedure has been successfully applied to the determination of mercury in bottled wines in Bulgaria and Macedonia

Determination of Cationic Surfactants in Environmental Samples by Flow Injection Analysis

Abstract: A new simple flow injection analysis (FIA) procedure for the spectrophotometric determination of cationic surfactants (CSs), i.e. dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB), and cetylpyridinium chloride (CPC), is described. The method is based on absorptivity enhancement of the Bi(III)-I− complex in the presence of CSs. Among the investigated compounds, highest sensitivity is obtained with CPC, so it was selected for detailed study. The apparent value of molar absorptivity of the complex in terms of CPC is (6.00)×103 L mol−1 cm−1 at λmax 505 nm for FIA determination. The detection limit (3σ criterion) of the method for FIA determination is 110 µg L−1. The sample throughput is >140 samples h−1. The effect of analytical and FIA variables in the determination of CPC is described. The composition of the complex is discussed. The method is free from interferences of common ions. The method has been applied to the analysis of surfactant contamination in environmental samples, i.e. pond water, municipal/industrial wastewater, sewage, sediment and soil.

On-Line Separation and Preconcentration of Trace Metals in Biological Samples Using a Microcolumn Loaded with PAN-Modified Nanometer-Sized Titanium Dioxide, and Their Determination by ICP-AES

Abstract: A flow injection analysis system incorporating a microcolumn of nanometer-sized TiO2 loaded with 1-(2-pyridylazo)-2-naphthol (PAN) has been used for the development of an on-line multi-element method for simultaneous separation and preconcentration and subsequent determination of Cu2+, Co2+, Cr3+, Y3+, Yb3+ and Bi3+ by ICP-AES. Effects of pH, sample flow rate and volume, elution conditions, adsorption capacity and interfering ions on analyte recovery were examined. The adsorption capacity of nanometer-sized TiO2 loaded with PAN was 4.73, 18.57, 3.81, 6.14, 4.52 and 20.35 mg g−1 for Cu2+, Cr3+, Y3+, Yb3+, Co2+ and Bi3+, respectively. The method has been applied to the analysis of trace elements in standard reference biological samples, and the results are in good agreement with the certified values.

HPLC Determination of the Antiseptic Agent Chlorhexidine and its Degradation Products 4-Chloroaniline and 1-Chloro-4-Nitrobenzene in Serum and Urine

Abstract: Chlorhexidine (1,1′-hexamethylene-bis-[5-(p-chlorophenyl)-biguanide]-digluconate; CHD) is one of the most frequently used antiseptics. In spite of this, its resorption and elimination has hardly been investigated. One of the main reasons for this is the lack of suitable procedures for its analysis in biological materials. Samples of CHD also may contain the carcinogen 4-chloroaniline which also may be formed as a degradation product in preparations.

Electrocatalytic Reduction of Nitrite Using a Carbon Nanotube Electrode in the Presence of Cupric Ions

Abstract: A simple, inexpensive method for determining nitrite is presented. With a carbon nanotube modified glass carbon electrode (GC), the overpotential for reduction of nitrite decreased, and direct reduction could be achieved in acid solution. Sensitivity, however, was not very high. When cupric ions were added to the solution, the reduction peak current increased significantly, and in particular the presence of multiple nitrate did not interfere. Experimental conditions were optimized, and preliminary studies were performed on the electrochemical mechanism of nitrite reduction in the presence of cupric ions on the carbon nanotube modified electrode. Under optimized conditions, the peak current of reduction achieved with the differential pulse voltammetric method was proportional to the concentration of nitrite in the ranges of 2.0 × 10−6–1.0 ×thinsp;10−5 mol L−1 and 2.0 × 10−5–1.0 × 10−3 mol L−1. The detection limit reached 5.0 × 10−7 mol L−1, and most of the inorganic ions did not interfere. The determination of nitrite in samples of rain water and river water was satisfactory.

Electropolymerization of Azure B on a Screen-Printed Carbon Electrode and its Application to the Determination of NADH in a Flow Injection Analysis System

Abstract: The electrooxidation polymerization of azure B on screen-printed carbon electrodes in neutral phosphate buffer was studied. The poly(azure B) modified electrodes exhibited excellent electrocatalysis and stability for dihydronicotinamide adenine dinucleotide (NADH) oxidation in phosphate buffer (pH 6.9), with an overpotential of more than 400 mV lower than that at the bare electrodes. Different techniques, including cyclic voltammetry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy have been employed to characterize the poly (azure B) film. Furthermore, the modified screen-printed carbon electrodes were found to be promising as an amperometric detector for the flow injection analysis (FIA) of NADH, typically with a dynamic range of 0.5 muM to 100 muM.

Synthesis, Characterization and Selective Metal Binding Properties of Physically Adsorbed 2-Thiouracil on the Surface of Porous Silica and Alumina

Abstract: The physical adsorption of 2-hydroxy-2-mercaptopyrimidine (2-thiouracil) on the surface of porous silica gel and basic alumina is studied and described. Four silica and alumina materials were identified on the basis of surface coverage determination by thermal desorption method. Modified aluminas were found to be physically adsorbed with 2-thiouracil by 0.14, 0.54, and 0.43–1.63 mmol g−1. Modified silica materials (I–IV) were identified by adsorption of 2-thiouracil (0.344–0.446 mmol g−1). The metal sorption, binding and selectivity properties of these modified alumina and silica materials were studied and evaluated by a series of di- and trivalent metal ions. Aluminas (II–IV) were found to have high capacity in selective extraction of cadmium (II) from aqueous solutions compared to other tested metal ions. The highest metal capacity (1.0 mmol g−1) was found for cadmium (II) on modified aluminas (IV). Potential application of the modified aluminas (I–IV) for selective removal and extraction of 1.0 ng mL−1 of cadmium (II) from natural seawater samples was performed and compared with the modified silicas (I–IV). The modified aluminas (II–IV) showed a significantly higher capacity than the modified silicas for cadmium (II) with an average percentage recovery value of 97.8±0.4%. The matrix effect of seawater was found to play an insignificant role in the atomic absorption spectrophotometric analysis of cadmium (II).

Determination of Rare Earth Elements in Acid Mine Drainage by Inductively Coupled Plasma Mass Spectrometry

Abstract: A method was developed for the direct determination of 14 naturally occuring rare earth elements (REE, La–Lu) by means of inductively coupled plasma mass spectrometry in seepage waters caused by acid mine drainage The analytical procedure includes the additional determination of oxide and hydroxide formation by Ba and REE The determined polyatomic ion formation can be used to correct spectral interferences of oxides and hydroxides of Ba and the light REE on middle and heavy REE The total REE content in the acidic seepage waters investigated is up to 220 µg L−1 The concentration of the REE normalized to Post Archean Australian Shale (PAAS) is shown, and fractionation of the REE is discussed The PAAS-normalized REE-patterns feature an enrichment of middle and heavy REE as opposed to the light ones For one seepage water sampled over a period of about half a year, the REE patterns show very high reproducibility The accuracy of the method was demonstrated by the analysis of two water samples containing certified concentrations of REE

Characterisation of Sugar Cane Combustion Particles in the Araraquara Region, Southeast Brazil

Abstract: Biomass burning is an important primary and secondary source of aerosol particles. The presence of carbonaceous particles in the respirable size range makes the study of this fraction important in view of possible health and climatic effects. The annual burning of sugar cane plantations causes emission of huge amounts of pyrogenic particles. Aerosol samples were collected in Araraquara city, Sao Paulo state, Brazil, during the harvest season for fine and coarse particles and bulk; they were analysed by electron-probe microanalysis, including facilities for low-Z element determination (low-Z EPMA) and by energy-dispersive X-ray fluorescence (EDXRF), in order to investigate the elemental composition of individual particles and bulk samples, respectively. Numerical analysis of the EPMA results by hierarchical clustering shows high contributions of carbonaceous particles that can be distinguished mainly in two different types: biogenic and carbon-rich. Additionally, two significant contributions of aluminosilicate particles were identified: as rather pure aluminosilicates or mixed with carbonaceous species. The EDXRF results are compatible with those of aerosol particles in Amazon, which is nowadays one of the main sources of biogenic particles in the world.

Voltammetric Determination of Trace Amounts of Fenitrothion on a Novel Nano-TiO2 Polymer Film Electrode

Abstract: A novel nano-TiO2 polymer modified glassy carbon (GC) electrode was developed for the determination of an organophosphorous pesticide, fenitrothion (φ-NO2), in citrate buffer solution. The electrochemical behavior of fenitrothion was characterized by using cyclic voltammetry. An irreversible form, φ-NO2, was transformed into a reversible redox couple (φ-NHOH/φ-NO), and it can be used to determine trace fenitrothion by square wave voltammetry. The experimental parameters, such as film thickness, pH value, accumulation potential and time were optimized. Interestingly, a cyclic voltammetric scan was observed to be more effective than a constant potential for the accumulation of fenitrothion. A linear response over a fenitrothion concentration of 2.5 × 10−8 to 1.0 × 10−5 M was exhibited, with a detection limit of 1.0 × 10−8 M (S/N = 3). The high sensitivity and selectivity of this film electrode was demonstrated by its practical application to the determination of trace amounts of fenitrothion in lake water and apple samples.