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Analytica Chimica Acta (v.528, #2)
Electrochemical sensor for cinchonine based on a competitive host–guest complexation by Yu Yang; Xin Yang; Hai-Feng Yang; Zhi-Min Liu; Yan-Li Liu; Guo-Li Shen; Ru-Qin Yu (pp. 135-142).
An electrochemical sensor for cinchonine (CCN) using the β-cyclodextrin (β-CD) modified poly( N-acetylaniline) (PAA) electrode has been developed, in which 1,4-hydroquinone (HQ) was chosen as a probe. Complexation of HQ with β-CD modified on the glassy carbon electrode (GCE) was examined by cyclic voltammetry (CV). HQ was included in the cavity of β-CD and reversible voltammograms were observed. In the presence of CCN, a competitive inclusion equilibrium with β-CD was established between HQ and CCN, lowering the peak current of HQ. The decrease in the peak current of HQ is directly proportional to the amount of CCN. Linear calibration plot was obtained over the range from 4.0×10−6 to 8.0×10−5M with a detection limit (S/N=3) of 2.0×10−6M. From the inhibitory effect of CCN on the inclusion of HQ by β-CD, the apparent formation constant of CCN with the immobilized β-CD was estimated. This electrochemical sensor showed excellent sensitivity, repeatability, stability and recovery for the determination of CCN. The response mechanism of the sensor was discussed in detail. The optimum steric configuration of inclusion complex was presented by molecular dynamics simulation.
Keywords: Cinchonine; Poly(; N; -acetylaniline); 1,4-Hydroquinone; Molecular dynamics
Determination of mobile form contents of Zn, Cd, Pb and Cu in soil extracts by combined stripping voltammetry by T. Nedeltcheva; M. Atanassova; J. Dimitrov; L. Stanislavova (pp. 143-146).
The amount of mobile forms of Zn, Pb, Cd and Cu in extracts obtained by treating soil samples with ammonium nitrate were determined by an appropriate combination of anodic and cathodic stripping voltammetry with hanging mercury drop electrode. Every analysis required three mercury drops: on the first one, zinc was determined; on the second, cadmium and lead; on the third, copper was determined. Zinc, lead and cadmium were determined by conventional differential-pulse anodic stripping voltammetry. For copper determination, adsorptive differential-pulse cathodic stripping voltammetry with amalgamation using chloride ions as a complexing agent was applied. The standard deviation of the results was from 1 to 10% depending on the metal content in the sample. Voltammetric results were in good agreement with the AAS analysis. No microwave digestion of soil extracts was necessary.
Keywords: Stripping voltammetry; Mobile forms; Heavy metals; Soil analysis
Study of cork (from Quercus suber L.)-wine model interactions based on voltammetric multivariate analysis by Sílvia M. Rocha; Susana Ganito; António Barros; Helena M. Carapuça; Ivonne Delgadillo (pp. 147-156).
The cork from Quercus suber L. is the premium raw material used to produce wine-bottling stoppers; however, being a natural product, cork can be contaminated and attacked in different ways that could promote differences in its proprieties. A specific contamination is the defect known in the industry as “Mancha Amarela—Yellow spot� (MA). This cork shows modifications in its mechanical, structural and optical properties and is potentially able to cause off-flavours in wine. In this study, a new analytical approach is proposed for the rapid screening of cork-wine model interactions in order to determine if the cork were able to contaminate a wine. Cork samples classified as standard (S) and cork MA were put in contact with a wine model matrix. The model matrix was analysed by cyclic voltammetry and square wave voltammetry in function of different contact times. Considering that matrices in contact with cork S and MA exhibited different pH, the influence of this parameter on the distinction power was also evaluated. The data sets obtained from the different techniques were treated by principal component analysis (PCA) and PLS_Cluster. The major difference between samples S and MA is the occurrence of an important peak at ca. 580mV in the MA voltammograms. This more positive peak may be assigned to lignin related phenolics; therefore, it can be proposed as a possible marker to follow lignin degradation.
Keywords: Cork; Quercus suber; L; “Mancha Amarela—Yellow spot�; Voltammetric analysis; PCA; PLS_Cluster
Electrochemical studies and square wave stripping voltammetry of five common pesticides on poly 3,4-ethylenedioxythiophene modified wall-jet electrode by P. Manisankar; S. Viswanathan; A. Mercy Pusphalatha; C. Rani (pp. 157-163).
The cyclic voltammetric behavior of five common pesticides such as dicofol (DCF), cypermethrin (CYP), monocrotophos (MCP), chlorpyrifos (CPF) and phosalone (PAS) was investigated at a poly 3,4-ethylenedioxythiophene modified glassy carbon electrode (PEDOT/GCE). A method was developed for the detection and determination of these pesticides in trace level flowing stream, based on their redox behavior. The square wave stripping voltammetric principle was used to analyze the selected pesticides on PEDOT/GCE. Varying the accumulation potential and accumulation time, the best accumulation conditions were found out. Effects of initial scan potential, square wave pulse amplitude, step potential and frequency were examined for the optimization of stripping conditions. The peak current responses of analyte under optimum conditions were correlated over flow rate by using wall-jet PEDOT/GCE assembly. The calibration plots were linear over the pesticide's concentration range 0.10–72.60μgl−1 for DCF, 0.41–198.24μgl−1 for CYP, 0.22–220.95μgl−1 for MCP, 0.35–259.69μgl−1 for CPF and 1.07–141.46μgl−1 for PAS. The limit of detection was obtained between <0.09 and <1.0μgl−1 for five pesticides. It is low enough for trace pesticide determination in real samples. This method is applied for the determination of the five pesticides in soil samples. The recovery values obtained in spiked soil samples are 95.4 ± 5.4% for DCF, 93.7 ± 4.2% for CYP, 85.3 ± 8.4% for MCP, 94.6 ± 6.6% for CPF and 93.5 ± 4.9% for PAS.
Keywords: Stripping voltammetry; Pesticides; Modified electrode; Wall-jet electrode
Effects of an arginine-selective tagging procedure on the fragmentation behavior of peptides studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS) by Alexander Leitner; Wolfgang Lindner (pp. 165-173).
The presence of arginine as the naturally occurring amino acid with the highest gas-phase basicity strongly influences the fragmentation behavior of peptides undergoing collision-induced dissociation. Using a derivatization procedure recently developed in our group, based on a reversible reaction of the guanidino group with 2,3-butanedione and an arylboronic acid, we examined how this label affects the fragmentation patterns of labeled versus unlabeled peptides in MS/MS experiments. As part of this fundamental study, two groups of model peptides (angiotensins and bradykinins) as well as tryptic peptides were labeled according to our protocol and subjected to collision-induced dissociation (CID) in both a triple quadrupole and a quadrupole ion trap instrument. It was found that for angiotensins containing an AspArg sequence, C-terminal cleavage at Asp that occurs for native peptides was completely inhibited in Arg-labeled peptides. For bradykinins and peptides obtained from tryptic digests of standard proteins, some sample peptides were little affected by the tagging of arginine residues. Others, in contrast, exhibited an almost total loss of nonspecific backbone cleavage and their fragment ion spectra were dominated by loss of the arginine tag. These and other experimental results are discussed in view of the nature of the arginine tag and the concept of proton mobility.
Keywords: Mass spectrometry; Electrospray ionization; Peptides; Arginine tag; Fragmentation behavior
Micro-extraction procedures for the determination of Ra-226 in well waters by SF-ICP-MS by D. Larivière; V.N. Epov; K.M. Reiber; R.J. Cornett; R.D. Evans (pp. 175-182).
The radium-226 ( t1/2=1622 years) content of highly alkaline well water collected from the United Arab Emirates (UAE) was measured by double focusing sector-field inductively coupled plasma-mass spectrometry (SF-ICP-MS) after separation of the radium from other alkaline earth elements using a newly developed procedure. The results were comparable with those obtained by α-spectrometry for samples with concentrations ranging from 6.75 to 459pg/L (0.25 to 17Bq/L). Instrumental sensitivity on matrix-free samples was compared for two sample introduction systems, i.e. an Apex-Q high sensitivity system and a concentric nebulizer. A 12-fold improvement in sensitivity (instrumental detection limit=1.5pg/L or 55mBq/L) was found when the Apex-Q system was used. Two chromatographic methods were tested for the sequential separation of the alkaline earth elements contained in the well water samples in order to reduce matrix and polyatomic interference effects. Optimal elution parameters were determined and used for the separation and pre-concentration of Ra-226 in those samples. A method detection limit of 0.189pg/L (7mBq/L), which corresponds to a mass of 0.38fg of Ra-226 in the sample, was achieved. Only 2mL of sample is necessary when a combination of 50W-X8 and Sr*Spec resin, which are reusable, are utilized for the separation. This new analytical protocol significantly reduces sample preparation time resulting in a throughput rate of approximately 20 samples in only 8h; faster than the other published extraction procedures.
Keywords: Radium-226; Radionuclides; ICP-MS; Chromatography; Water; Alkaline earth elements
Metal-sulfide species in oxic waters by Katrina Sukola; Feiyue Wang; André Tessier (pp. 183-195).
Several analytical techniques were employed to characterize oxidation-resistant metal-sulfide species that have recently been suggested to be present in oxic waters. Sulfide in synthetic Cd-, Zn-, Pb-, Cu-sulfide solutions was found to persist in oxic waters for a prolonged period of time (2 to more than 10 weeks) whereas it was oxidized rapidly in Fe-, Mn- and Ni-sulfide solutions. Multiple lines of evidence did not support the presence of soluble molecular metal-sulfide clusters in these solutions as suggested previously. Instead, the metal-sulfide species resistant to oxidation in oxic waters were more likely a mixture of truly dissolved metal-sulfide complexes and dynamic metal-sulfide colloids. The morphology and size of the colloids, as monitored by transmission electron microscopy (TEM), changed significantly with time. Nanomolar to sub-micromolar levels of acid-volatile sulfide (AVS) and chromous-volatile sulfide (CVS) were measured in oxic surface waters of six lakes located on the Canadian Shield and in the nearby areas. Thermodynamic calculations indicated that at the AVS levels measured, the dissolved metal-sulfide complexes play a minor role in the speciation of Class B metal ions such as Pb, Cd, Cu, Hg. The relative importance of metal-sulfide colloids in these natural oxic waters remains unknown.
Keywords: Metal speciation; Oxic Water; Complex; Colloid; Nanocluster
Optical fibre reflectance sensor for the determination and speciation analysis of iron in fresh and seawater samples coupled to a multisyringe flow injection system by Carmen Pons; Rafael Forteza; Víctor Cerdà (pp. 197-203).
A novel optical fibre reflectance sensor coupled to a multisyringe flow injection system (MSFIA) for the determination and speciation analysis of iron at trace level using chelating disks (iminodiacetic groups) is proposed. Once iron(III) has been retained onto a chelating disk, an ammonium thiocyanate stream is injected in order to form the iron(III)–thiocyanate complex which is spectrophotometrically detected at 480nm. Iron(III) is eluted with 2M hydrochloric acid so that the chelating disk is regenerated for subsequent experiments. The determination of total iron is achieved by the on-line oxidation of iron(II) to iron(III) with a suitable hydrogen peroxide stream.A mass calibration was feasible in the range from 0.001 to 0.25μg. The detection limit (3 sb/ S) was 0.001μg. The repeatability (RSD), calculated from nine replicates using 1ml injections of a 0.1mg/l concentration, was 2.2%. The repeatability between five chelating disks was 3.6%. The applicability of the proposed methodology in fresh and seawater samples has been proved.The proposed technique has been validated by replicate analysis ( n = 4) of certified reference materials of water with satisfactory results.
Keywords: Optical fibre reflectance sensor; Multisyringe flow injection analysis (MSFIA); Chelating disk; Iron; Speciation analysis; Seawater
Complexation of Ni, Cu, Zn, and Cd by DOC in some metal-impacted freshwater lakes: a comparison of approaches using electrochemical determination of free-metal-ion and labile complexes and a computer speciation model, WHAM V and VI by J.W. Guthrie; N.M. Hassan; M.S.A. Salam; I.I. Fasfous; C.A. Murimboh; J. Murimboh; C.L. Chakrabarti; D.C. Grégoire (pp. 205-218).
Complexation of Ni(II), Cu(II), Zn(II), and Cd(II) by dissolved organic carbon (DOC) in some freshwater lakes in Rouyn-Noranda, Québec, Canada, where they were impacted by effluents from a nearby copper smelter, was measured by kinetic and equilibrium methods using cathodic and anodic stripping voltammetry. The measured free-metal-ion and labile metal-complex concentrations were compared with the predictions made by a widely-used computer speciation model, the Windermere Humic Aqueous Model (WHAM): WHAM V and its improved version WHAM VI. If it is assumed that 65% of the DOC is “active�, i.e. behaving as isolated humic substances such as fulvic acid, both versions of WHAM are able to predict the labile and free-metal-ion concentrations of Ni, Zn, and Cd reasonably well; however, both underestimate the free-copper-ion concentration by one to two orders of magnitude. WHAM VI is generally better than or equal to WHAM V for successfully predicting most of the free-metal-ion concentrations. The modelled competition by Al(III) and Fe(III) in the lake surface waters showed that in most cases Cu(II) was most affected by this competition. WHAM VI predicts a larger effect from the Al(III) and Fe(III) competition than does WHAM V.
Keywords: Windermere Humic Aqueous Model V and VI; Kinetic and equilibrium speciation; Freshwaters; Dissolved organic carbon; Free-metal-ion concentration; Cathodic and anodic stripping voltammetry
A novel capacitive immunosensor based on gold colloid monolayers associated with a sol–gel matrix by Zai-Sheng Wu; Ji-Shan Li; Ming-Hui Luo; Guo-Li Shen; Ru-Qin Yu (pp. 235-242).
A capacitive sensing method based on self-assembling gold nanoparticles to the surface of the sol–gel modified electrode has been developed for the direct detection of the human IgG in human serum. The capacitance of the immunosensor corresponding to the concentration of human IgG is investigated by alternating current impedance. The formed mercaptopropyltriethoxysilane (MPTS) film is ultrathin; the immobilization density of antibodies is high because of high surface-volume area of the assembled gold nanoparticles and the biological macromolecules when immobilized on gold nanoparticles can retain their bioactivity. This capacitive immunosensor prepared with present method can provide high sensitivity. The linear calibration curve was obtained in the range 8.3–2128ng/ml, with a detection limit of 3.3ng/ml when plotted versus the logarithm of the antigen concentration. After each immunoassay, the regeneration of the electrode could be performed through washing in basic solution without obvious decrease in response. No cross-reactivity was observed with other protein species. The dependence of sol–gel modified electrode stability on the pH value and ion strength was studied. The insulating properties of the different layers of the immunosensor were also investigated.
Keywords: Capacitive immunosensor; Sol–gel film; Gold nanoparticles; Human immunoglobulin G
Analytical performances of validated chemiluminescent enzyme immunoassays to detect N-methylcarbamate pesticides by Barbora Mickova; Tomas Kovalczuk; Pavel Rauch; María José Moreno; Antonio Abad; Angel Montoya; Elida Ferri; Fabiana Fini; Stefano Girotti (pp. 243-248).
In the present work, enzyme-linked immunosorbent assays (ELISAs) with chemiluminescent detection for the determination of carbofuran, carbaryl and methiocarb were developed and the analytical parameters of these assays were compared with those of ELISAs with colorimetric detection. Both were conjugate-coated formats based on identical monoclonal antibodies and homologous protein conjugates. In comparison with colorimetric ELISA, the ability of the chemiluminescent reagents to detect lower concentrations of horseradish peroxidase allowed to decrease the optimal antibody and conjugate concentrations and to reach better analytical parameters. The experimental comparison of the analytical performance of the ELISAs was carried out by analysing extracts of apple-strawberry baby food and simply diluted fruit juices, both spiked at different concentration levels with the above mentioned pesticides. Recovery values for both ELISAs were around 100% and no matrix effects were observed when fruit juices were diluted 1:20 or more. Results obtained by ELISAs correlated well, both in terms of accuracy and precision, with those obtained by a liquid chromatography–electrospray mass spectrometry (LC/ESI/MS/MS) analysis, used as reference method to validate the immunoassays results. The limits of detection reached by using the chemiluminescent assay were 0.03, 0.007 and 0.004ngml−1 for carbofuran, carbaryl and methiocarb, respectively.
Keywords: N; -methylcarbamate pesticides; Chemiluminescent and colorimetric enzyme-linked immunosorbent assay; Liquid chromatography–electrospray mass spectrometry; Baby foods; Fruit juices
Highly efficient approach for characterizing nanometer-sized gold particles by capillary electrophoresis by Fu-Ken Liu; Ying-Ying Lin; Chien-Hou Wu (pp. 249-254).
This paper demonstrates that capillary electrophoresis (CE) can be employed for characterizing the sizes of nanometer-scale gold particles. We characterized the gold nanoparticles by effecting CE separation using a buffer of SDS (70mM) and 3-cyclohexylamino-1-propanesulfonic acid (CAPS; 10mM) at pH 11.0 and an applied voltage of 18kV and obtained a linear relationship ( R2 > 0.99) between electrophoretic mobilities and size for nanoparticles whose diameters fall in the regime from 5.0 ± 0.5 to 41.2 ± 3.3nm; the relative standard deviations of these electrophoretic mobilities are <0.8%. We evaluated the feasibility of employing these separation conditions for the size characterization by of gold nanoparticle samples that were synthesized by a rapid microwave heating method. We confirmed that this CE method is a valid one for size characterization by comparing the results obtained by CE with those provided by scanning electron microscopy (SEM); a good correlation exists between these two techniques. Our results demonstrate that CE can be employed to accelerate the analysis of the sizes of nanomaterials.
Keywords: Capillary electrophoresis; Size characterization; Gold nanoparticles; Rapid microwave heating
Development and validation of an ion pair HPLC method for gemcitabine and 2′,2′-difluoro-2′-deoxyuridine determination by R. Losa; M.I. Sierra; C. Guardado; A. Fernández; M.O. Gión; D. Blanco; J.M. Buesa (pp. 255-260).
A reverse phase HPLC method based on ion-pair formation was set up for the simultaneous determination of gemcitabine and its metabolite 2′,2′-difluoro-2′-deoxyuridine (dFdU) in plasma samples obtained from cancer patients. The separation was performed on a μBondapack C18 (300mm×3.9mm i.d., 10μm particle size) column at room temperature. The mobile phase, 5mM pentane-1-sulfonic acid pH 3.1/methanol (96:4), was pumped at a flow rate of 1.5mLmin−1. Gemcitabine and dFdU eluted in less than 16min. Linearity, sensitivity, and reproducibility studies, which actual values met the demands for bioanalytical assays, validated the method. This assay provided pharmacokinetic data from patients treated with intravenous gemcitabine.
Keywords: Gemcitabine; dFdU; Ion-pair HPLC; Plasma; Pharmacokinetics
A single sorbent for tetracycline enrichment and subsequent solid-matrix time-resolved luminescence by LinShu Liu; Guoying Chen; Marshall L. Fishman (pp. 261-268).
The aim of this study was to search for a sorbent that could act as an extraction phase and as a support for solid-matrix time-resolved luminescence (SMTRL). Four potential sorbents were investigated for this purpose using tetracycline (TC) as a model analyte. Sorbents prepared from C18 silica gel or calcium cross-linked pectin gel were able to extract TC from dilute solutions. Europium(III)–TC complex adsorbed on the surface of C18 generated the most intense TRL signal when measured at λex=388nm and λem=615nm. This method achieved a 1ng/ml limit of detection (LOD) with a 100μl sample solution in a repeated spotting mode. Hyphenation of sorbent extraction and SMTRL was demonstrated using C18. This method is suitable for screening of TC in foods or aqueous solutions and can be extended to other luminescent lanthanide-chelating analytes in physiological or environmental samples.
Keywords: Time-resolved luminescence (TRL); Tetracycline; Europium; Sorbent; Pectin
Flow injection analysis–flame atomic absorption spectrometry system for indirect determination of cyanide using cadmium carbonate as a new solid-phase reactor by M. Noroozifar; M. Khorasani-Motlagh; S.-N. Hosseini (pp. 269-273).
A new and simple flow injection system procedure has been developed for the indirect determination of cyanide. The method is based on insertion of aqueous cyanide solutions into an on-line cadmium carbonate packed column (25% m/m suspended on silica gel beads) and a sodium hydroxide with pH 10 is used as the carrier stream. The eluent containing the analyte as cadmiumcyanide complexes, produced from reaction between cadmium carbonate and cyanide, measured by flame atomic absorption spectrometry. The absorbance is proportional to the concentration of cyanide in the sample. The linear range of the system is up to 15mgL−1 with a detection limit 0.2mgL−1 and sampling rate 72h−1. The method is suitable for determination of cyanide in industrial waste waters with a relative standard deviation better than 1.22%.
Keywords: Indirect determination; Cyanide; Cadmium carbonate; Flow injection analysis; Flame atomic absorption spectrometry
Artificial neural networks study of the catalytic reduction of resazurin: stopped-flow injection kinetic-spectrophotometric determination of Cu(II) and Ni(II) by Diana M. Magni; Alejandro C. Olivieri; Adrian L. Bonivardi (pp. 275-284).
An artificial neural network (ANN) procedure was used in the development of a catalytic spectrophotometric method for the determination of Cu(II) and Ni(II) employing a stopped-flow injection system. The method is based on the catalytic action of these ions on the reduction of resazurin by sulfide. ANNs trained by back-propagation of errors allowed us to model the systems in a concentration range of 0.5–6 and 1–15mgl−1 for Cu(II) and Ni(II), respectively, with a low relative error of prediction (REP) for each cation: REPCu(II)=0.85% and REPNi(II)=0.79%. The standard deviations of the repeatability ( sr) and of the within-laboratory reproducibility ( sw) were measured using standard solutions of Cu(II) and Ni(II) equal to 2.75 and 3.5mgl−1, respectively: sr[Cu(II)]=0.039mgl−1, sr[Ni(II)]=0.044mgl−1, sw[Ni(II)]=0.045mgl−1 and sw[Ni(II)]=0.050mgl−1. The ANNs-kinetic method has been applied to the determination of Cu(II) and Ni(II) in electroplating solutions and provided satisfactory results as compared with flame atomic absorption spectrophotometry method. The effect of resazurin, NaOH and Na2S concentrations and the reaction temperature on the analytical sensitivity is discussed.
Keywords: Artificial neural networks; Nickel; Copper; Catalytic reduction; Resazurin; Stopped-flow injection