Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Analytical and Bioanalytical Chemistry (v.381, #7)
H. Pasch, W. Schrepp: MALDI–TOF Mass Spectrometry of Synthetic Polymers
by Chrys Wesdemiotis (pp. 1317-1318).
Kinetic aspects of analytical chemistry: progress and emerging trends
by Stanley R. Crouch (pp. 1323-1327).
Using enzymes isolated from diverse sources to determine metal ion cofactors by Tatyana N. Shekhovtsova; Svetlana V. Muginova (pp. 1328-1335).
Oxidoreductases and hydrolases isolated from different sources (horseradish and peanut peroxidases, alcohol dehydrogenases from baker’s yeast and horse liver, and alkaline phosphatases from Escherichia coli, chicken and seal intestine) were used to determine their metal ion cofactors: Fe(III), Zn(II) and Mg(II), respectively. Studying the effects of the metal ion cofactors on the catalytic activity of the enzymes of different origin showed that the extent of their inhibition, activation, or reactivation of their apoenzymes depended on the structure and accessibility of the enzyme active site, which varies among the biocatalysts isolated from different sources. The developed procedures are based on the inhibiting (Zn(II)) or activating (Mg(II)) effects of the metal ions on the catalytic activity of the enzymes, or on reactivating effects (Fe(III) and Zn(II)) on the apoenzymes. The procedures are characterized by high sensitivity and selectivity; the detection limits of Fe(III) using horseradish peroxidase, Zn(II) using alcohol dehydrogenase from baker’s yeast, alkaline phosphatase from seal intestine and its apoenzyme, and Mg(II) using alkaline phosphatase from chicken intestine equal 10 ng L−1, 20 ng L−1, 3 μg L−1, 8 μg L−1 and 0.2 μg L−1, respectively.
Keywords: Enzymatic methods; Enzymes isolated from diverse sources; Determination of metal ion cofactors; Inhibition and activation of enzymes; Reactivation of apoenzymes
HPLC determination of residual monomers released from heat-cured acrylic resins by Afrodite Sofou; Irene Tsoupi; John Emmanouil; Miltiades Karayannis (pp. 1336-1346).
HPLC was used to examine the leachability of three non-phthalic and four phthalic post-polymerized residual monomers from three commercially available heat-cured acrylic resins. Specimens of equal dimensions were constructed from each brand of material by following the standardized procedure and were stored under three different conditions, namely, distilled water, artificial saliva, and a binary mixture of ethanol/water. The resulting liquids provided samples for analysis by HPLC. Three different experiments were performed for each brand of acrylic and each storage condition in order to examine the effects of parameters, particularly time and temperature. The results obtained from this study suggest that a wide spectrum of residues diffuse out of the three examined acrylic resin materials. The non-phthalic compounds were leached at high concentrations, whereas all the phthalates examined exhibited different degrees of elusion commensurate with the storage condition, brand of material, and type of experiment. It seems that a significant quantity of non-phthalic and phthalic residues diffuse out of the acrylic resin materials examined. The main component extracted was methyl methacrylate, the level of which seems to be time-dependent and decreases for a period of up to 5 days when resins are stored in distilled water at room temperature.
Keywords: Acrylic; Phthalic resins; Non-phthalic resins; Leachability
A kinetic study of trace element leachability from abandoned-mine-polluted soil treated with SS-MSW compost and red mud. Comparison with results from sequential extraction by C. Brunori; C. Cremisini; L. D’Annibale; P. Massanisso; V. Pinto (pp. 1347-1354).
The effect of adding treated red mud, a by-product of alumina production, to soil polluted by an abandoned mine and characterised by high concentrations of heavy metals, relatively low reaction grade, and low organic carbon content, was investigated. Also studied was addition of both red mud and compost (produced from source-separated municipal solid waste)—the synergistic action of red mud and compost could be exploited to achieve both metal trapping and an increase in organic carbon content. Leaching batch tests were performed on four different systems: soil, soil and treated red mud, soil and compost, soil and compost plus treated red mud. Dilute sulfuric acid and EDTA solution (liquid/solid ratio 10:1) were used in the tests—sulfuric acid to “mimic” acid rain and EDTA in accordance with general methods for estimating “plant-available” metals. Sequential extraction was also applied to the same samples. The use of relatively non-specific extractant reagents in the leaching tests led to a kinetic approach (already proposed in literature), because measurements of trace elements extracted at equilibrium cannot be related to their speciation. Comparison of information obtainable by the kinetic approach to evaluation of data from leaching tests with results from sequential extraction enabled evaluation whether the “kinetic fractionation method”, a relatively rapid and simple procedure, furnishes adequate information about the mobility and bioavailability of trace elements. Especially interesting results were obtained for Mn, Zn, and Ni, present in large amounts in the soil studied—their leachability was significantly reduced by addition of red mud and compost, suggesting interesting perspectives in soil-remediation activity.
Keywords: Compost; Red mud; Trace elements; Fractionation; Sequential extraction; Kinetic study
Electrocatalytic oxidation of NADH at single-wall carbon-nanotube-paste electrodes: kinetic considerations for use of a redox mediator in solution and dissolved in the paste by Riccarda Antiochia; Irma Lavagnini; Franco Magno (pp. 1355-1361).
Cyclic voltammetry has been successfully used to study the oxidation of nicotinamide adenine dinucleotide (NADH) at single-wall carbon-nanotube-paste (CNTP) electrodes modified with p-methylaminophenolsulfate (p-MAP) and 3,4-dihydroxybenzaldehyde (3,4-DHB). Diffusion-like behaviour was observed for p-MAP-modified electrodes, and a diffusion coefficient of 2.4×10−6 cm2 s−1 was calculated for p-MAP in the paste. The behaviour of 3,4-DHB-modified CNTP electrodes was typical of that of surface-confined mediators. p-MAP electrocatalytic activity was first checked in solution, and a rate constant of 9.2 mol−1 L s−1 was obtained for the reaction between NADH and the mediator. The p-MAP-modified electrode did not have significant electrocatalytic activity for electro-oxidation of NADH, probably because of the formation of a complex between NADH and the confined mediator. In contrast, the 3,4-DHB-modified electrode had very good NADH electrocatalytic activity, with a heterogeneous rate constant of approximately 20×102 mol−1 L s−1.
Keywords: NADH oxidation; Carbon-nanotube-paste electrodep-Methylaminophenolsulfate; 3,4-Dihydroxybenzaldehyde; Modified electrode
Potential application of the reaction between hydroquinone and chromate with respect to the kinetic determination of iron by D. Mihai; A. Rustoiu-Csavdari; I. Bâldea (pp. 1362-1366).
The analytical potential of the reaction between hydroquinone and chromate in acidic media is explored with respect to the kinetic determination of iron in water samples. The extent of the reaction is followed spectrophotometrically at 350 nm. The reaction occurs more quickly in the presence of the metal ion, but the values of absorbance at reaction initiation and completion are not altered. No other transitional metal ion affects the course of the reaction, regardless of its concentration. This fact represents the most eye-catching and analytically exploitable aspect of this indicator reaction. Three procedures used to obtain calibration graphs from the same kinetic data are discussed: slope, fixed and variable time techniques. The reaction follows a sequence of two consecutive steps, both of first-order with respect to the colored species. First-order kinetics is preserved in the presence of iron. Curve fitting is used to determine the corresponding rate coefficients. The slope method requires much data and uses plots of rate constants against analyte concentration for calibration purposes. In this case, the best detection limit (0.5 mg l−1) is given by the faster stage. On the other hand, the rate-determining step enables more precise results. The fixed and variable time methods rely on similar principles: they register either the value of absorbance achieved at a predetermined reaction time (here, 50 s) or the time interval required for the absorbance to drop to a predetermined value (here, 0.15 absorbance at 350 nm). In both cases, ratios between the average value from the blind runs and all individual values are plotted against the analyte concentration. The best results (detection limit of 0.3 mg l−1) are derived from the variable time procedure. Advantageously, neither of the techniques require the entire kinetic curve, and so sophisticated equipment is not needed.
Keywords: Kinetic methods; Slope technique; Fixed and variable time technique; Iron determination; Spectrophotometry
Determining pirimiphos-methyl in durum wheat samples using an acetylcholinesterase inhibition assay by Michele Del Carlo; Alessia Pepe; Marcello Mascini; Miriam De Gregorio; Angelo Visconti; Dario Compagnone (pp. 1367-1372).
An electrochemical assay used for detecting acetylcholinesterase (AChE) inhibitors has been optimised to detect pirimiphos-methyl in durum wheat. Pirimiphos-methyl is a phosphothionate insecticide and so it needs to be transformed into the corresponding oxo form to act as an effective AChE inhibitor. The inhibition assay was based on the electrochemical detection of the product of AChE, choline, via choline oxidase biosensors obtained with Prussian-Blue modified screen printed electrodes. The procedure for the oxidation of pirimiphos methyl via N-bromosuccinimide (NBS) and AChE inhibition was optimised for reagent concentrations and inhibition time in a buffer solution. A calibration of the pirimiphos-methyl (25–1,000 ng/ml) was obtained in the buffer. The intra-electrode CV ranged between 1.6 and 15.0, whereas the inter-electrode CV ranged between 4.6 and 16.0. The detection limit (LOD) was 38 ng/ml, and the I50% was 360 ng/ml. The assay conditions were then re-optimised to work with durum wheat extracts, and the calibrations were obtained under different experimental conditions, such as sample pretreatment (milled or whole grains) and extract concentration. The calibrations were slightly affected by the sample matrix, resulting in an increased LOD (65–133 ng/ml) and I50% (640–1,650 ng/ml). The LOD found for the sample, determined under optimal conditions, was 3 mg/kg. Spiked samples were prepared at the EU regulated level (5 mg/kg) and analysed with the optimised protocol, resulting in an average recovery of 70.3%.
Keywords: Pirimiphos-methyl; Whole grain; Acetylcholinesterase inhibition; Choline oxidase biosensor
Kinetic catalytic determination of trace Cu(II) in water samples with the thioglycolic/thiolactic acid–chromate reaction by A. Rustoiu-Csavdari; D. Mihai; I. Bâldea (pp. 1373-1380).
The use of two novel similar indicator reactions as applied to the kinetic determination of Cu(II) in water is investigated. The methods rely on the catalytic effect of the analyte on the oxidation of thioglycolic (TGA) and thiolactic (TLA) acids by chromate in acidic media. The extent of the reactions was followed spectrophotometrically at 345 nm. Pseudo-first-order rate coefficients, kobsd, were determined as a function of catalyst concentration. Interference of Fe(III) and Pb(II) was suppressed by complexation with pyrophosphate. For the reaction of TGA, a linear regression for kobsd versus [Cu(II)] was obtained for the entire concentration range considered. Although the plot corresponding to TLA oxidation exhibits a sharp change of slope at approximately 1.8×10−5 M Cu(II), it can still be described effectively by two linear regressions with different slopes. The reaction of TGA is more sensitive than that of TLA at low Cu(II) concentration. The opposite is true for higher catalyst contents. The detection limits were 65 μgL−1 for TGA and of 80 μgL−1 for TLA oxidation, respectively. The relative standard deviations, of 0.4% for TGA and 1.1% for TLA oxidation, respectively, were obtained for five replicate runs at 1000 μg L−1. Samples of river and wastewater from the mining region of Baia-Mare, Northern Romania were analyzed using the more sensitive reaction of thioglycolic acid. Results were compared to those obtained by the officially standardized methods. Good agreement was obtained, even for an untreated sample. Measurements did not require prior separation of interfering species.
Keywords: Kinetic catalytic method; Thiol oxidation; Cu(II) determination; Water analysis; Slope technique
Spectrofluorimetric determination of phenyl-β-naphthylamine used as rubber antioxidant by Zenovia Moldovan; Cristina Stoica; Mihaela Hillebrand; Laurenţia Alexandrescu; Gabriela Macovescu (pp. 1381-1386).
Phenyl-β-naphthylamine (PBN) used as rubber antioxidant was found to have native fluorescence. A spectrofluorimetric method for determination of PBN in multicomponent mixtures of polymer additives is described. The apparent excitation and fluorescence wavelengths used are 348 and 413.5 nm, respectively. Maximum fluorescence intensity is obtained by irradiating PBN dissolved in ethanol, at room temperature. The fluorescence varies linearly with the concentration of PBN in the range of 0.04–4 μg mL−1. The accuracy and precision of the method are reported.
Keywords: Phenyl-β-naphthylamine; Antioxidant; Polymer additive; Fluorimetry
Bioluminescence resonance energy transfer from aequorin to a fluorophore: an artificial jellyfish for applications in multianalyte detection by Sapna K. Deo; Mara Mirasoli; Sylvia Daunert (pp. 1387-1394).
In nature, the green light emission observed in the jellyfish Aequorea victoria is a result of a non-radiative energy transfer from the excited-state aequorin to the green fluorescent protein. In this work, we have modified the photoprotein aequorin by attaching selected fluorophores at a unique site on the protein. This will allow for in vitro transfer of bioluminescent energy from aequorin to the fluorophore thus creating an “artificial jellyfish”. The fluorophores are selected such that the excitation spectrum of the fluorophore overlaps with the emission spectrum of aequorin. By modifying aequorin with different fluorophores, bioluminescent labels with different emission maxima are produced, which will allow for the simultaneous detection of multiple analytes. By examining the X-ray crystal structure of the protein, four different sites for introduction of the unique cysteine residue were evaluated. Two fluorophores with differing emission maxima were attached individually to the mutants through the sulfhydryl group of the cysteine molecule. Two of the fluorophore-labeled mutants showed a peak corresponding to fluorophore emission thus indicating resonance energy transfer from aequorin to the fluorophore.
Keywords: Aequorin; Bioluminescence energy transfer; Site-directed mutagenesis
Determination of lead in bone tissues by axially viewed inductively coupled plasma multichannel-based emission spectrometry by Marco Grotti; Maria Luisa Abelmoschi; Simona Dalla Riva; Francesco Soggia; Roberto Frache (pp. 1395-1400).
A new procedure for determining low levels of lead in bone tissues has been developed. After wet acid digestion in a pressurized microwave-heated system, the solution was analyzed by inductively coupled plasma multichannel-based emission spectrometry. Internal standardization using the Co 228.615 nm reference line was chosen as the optimal method to compensate for the matrix effects from the presence of calcium and nitric acid at high concentration levels. The detection limit of the procedure was 0.11 μg Pb g−1 dry mass. Instrumental precision at the analytical concentration of ~10 μg l−1 ranged from 6.1 to 9.4%. Precision of the sample preparation step was 5.4%. The concentration of lead in SRM 1486 (1.32±0.04 μg g−1) found using the new procedure was in excellent agreement with the certified level (1.335±0.014 μg g−1). Finally, the method was applied to determine the lead in various fish bone tissues, and the analytical results were found to be in good agreement with those obtained through differential pulse anodic stripping voltammetry. The method is therefore suitable for the reliable determination of lead at concentration levels of below 1 μg g−1 in bone samples. Moreover, the multi-element capability of the technique allows us to simultaneously determine other major or trace elements in order to investigate inter-element correlation and to compute enrichment factors, making the proposed procedure particularly useful for investigating lead occurrence and pathways in fish bone tissues in order to find suitable biomarkers for the Antarctic marine environment.
Keywords: Inductively coupled plasma; Atomic emission spectrometry; Bone; Internal standardization; Matrix effects; Antarctica
Quantitative determination of cationic modified polysaccharides on hair using LC–MS and LC–MS–MS by Jan Ungewiß; Jens-Peter Vietzke; Claudius Rapp; Hartmut Schmidt-Lewerkühne; Klaus-Peter Wittern; Reiner Salzer (pp. 1401-1407).
Cationic polysaccharides containing N-hydroxypropyl-N,N,N-trimethylammonium substituents are widely used as conditioning agents for hair-care products. A sensitive method has been developed for the quantitation of these polymers. After acidic extraction from hair the polysaccharides are hydrolyzed using trifluoroacetic acid. The cationic monoglycosides are determined using liquid chromatography–tandem mass spectrometry (LC–MS–MS). The developed method is independent of hair treatment. Even hair cut from test persons after customary hair wash can be analyzed. After treatment of natural and bleached hair tresses using a real-life treatment procedure 180 μg and 300 μg of polymer per gram hair were quantified, respectively. Additionally the fragmentation mechanism of the cationic N-hydroxypropyl-N,N,N-trimethylammonium group during electrospray ionization was investigated. A mass loss of 60 Da in combination with loss of a single charge is observed and associated with cleavage of trimethylamine and a proton. It is assumed that this process is promoted by the anionic counter-ion which might be hydroxide in an aqueous environment.
Keywords: Cationic polysaccharides; Conditioning polymers; Hair; Quaternary ammonium; Cone-voltage fragmentation
Frequent analytical/experimental problems in lipase-mediated synthesis in solvent-free systems and how to avoid them by M. L. Foresti; M. L. Ferreira (pp. 1408-1425).
Compared with chemical catalysis, enzymatic catalysis is a relatively new topic. Experimental work involving lipases deserves careful attention and accurate procedures still need to be implemented. A rapid but careful survey of published data immediately demonstrates that experiments performed under similar conditions with similar reagents have led to very different results. The aim of this work is to point out the importance of accurate and systematic procedures in order to ensure the reproducibility of experimental data. We strongly believe that different results found by different labs are due to problems detected in the procedures used. Quantification of the immobilisation efficiency of lipase on several supports through UV/visible methods and sampling methods used to obtain correct enzymatic activity values are specifically analysed. After a brief review which demonstrates the big discrepancies found in the literature, original data from Candida rugosa lipase adsorption on polypropylene powder and its use in the solvent-free synthesis of ethyl oleate are introduced in order to exemplify the difficulties found in these kinds of systems. Several procedures described in the literature are assayed and the accuracy of the results obtained is carefully analysed. The aim of the whole analysis performed is that it would be useful for any powdered solid to be used as a support for a lipase in a solvent-free system for any synthesis reaction, especially for those involving a volatile reagent. Throughout this contribution, special emphasis is placed on how catalytic reaction results using enzymes (free and immobilised) are reported so as to allow comparison between published data, something which is usually difficult since very different units are used and often complementary data are not included.
Keywords: Enzymatic catalysis; Immobilisation efficiency; Sampling procedure; Solvent-free system
Peak parking technique for the simultaneous determination of anions and cations by Muhammad Amin; Lee Wah Lim; Toyohide Takeuchi (pp. 1426-1431).
An ion chromatography method is described for the simultaneous determination of anions (Cl−, NO3−, and SO42−) and cations (Na+, NH4+, K+, Mg2+, and Ca2+) using a single pump, a single eluent and a single detector. An anion-exchange column modified with chondroitin sulfate C facilitated the elution of the above three anions using 5 mM tartaric acid as the eluent in isocratic mode, whereas the same eluent facilitated the separation of the above five cations on a commercially-available cation-exchange column. The separation columns were connected in series via two six-port switching valves, so the required cation-exchange or anion-exchange separation could be carried out by selecting the appropriate positions for the switching valves. The separations were completed in 30 min.
Keywords: Ion chromatography; Column switching; Column modification; Peak parking
Reversed-phase liquid chromatography and argentation chromatography of the minor capsaicinoids by Robert Q. Thompson; Karen W. Phinney; Lane C. Sander; Michael J. Welch (pp. 1432-1440).
An investigation of the liquid chromatography of the minor capsaicinoids in a commercial capsaicinoid mixture is reported. Twelve stationary phases including C8, C18, C30, phenyl, and cation-exchange chemistries were examined in combination with isocratic aqueous methanol and aqueous acetonitrile mobile phases. A phenyl stationary phase and aqueous acetonitrile mobile phase baseline-resolved 7 of 11 capsaicinoids, and selected ion chromatograms (LC–ESI-MS) demonstrated this was the most effective reversed-phase separation. Argentation chromatography with an alkyl or phenyl column and aqueous silver nitrate–methanol mobile phase revealed the presence of the 6-ene-8-methyl and 6-ene-9-methyl homocapsaicin isomers and the absence of 7-ene-9-methyl homocapsaicin. A mixed phenyl–cation-exchange stationary phase (charged with silver ion) enabled unique and useful separations of the capsaicinoids.
Keywords: Capsaicinoids; Chili pepper; Reversed-phase liquid chromatography; Argentation Chromatography; Silver
Quantitative determination of capsaicinoids by liquid chromatography–electrospray mass spectrometry by Robert Q. Thompson; Karen W. Phinney; Michael J. Welch; Edward White V (pp. 1441-1451).
Eight naturally occurring capsaicinoids have been determined in Capsicum by use of high-purity standards, with norcapsaicin as an internal standard. The solid standards were rigorously checked for purity. The sensitivity of electrospray ionization (ESI), atmospheric-pressure chemical ionization (APCI), and coordination ion-spray (CIS; with silver) toward the capsaicinoids were measured and compared. The highest sensitivity was found for positive-ion ESI. Method validation of the liquid chromatography–ESI-mass spectrometry (LC–ESI-MS) determination is reported, including tests for repeatability (4%), detection limit (5 pg injected), linear range (20–6 ng injected), quantitation (excellent linearity; <2% relative standard deviation), and recovery (99–103%). The major and minor capsaicinoids in a commercial plant extract and in chili pepper fruits were quantified.
Keywords: Capsaicinoids; Chili pepper; LC–MS; Mass spectrometry; Electrospray ionization; Atmospheric-pressure chemical ionization
Determination of free copper concentrations in natural waters by using supported liquid membrane extraction under equilibrium conditions by Roberto Romero; Jan Åke Jönsson (pp. 1452-1459).
A method is described for measurement of freely dissolved copper concentrations in natural water samples using supported liquid membrane (SLM) extraction under equilibrium conditions, a technique denoted “equilibrium sampling through membranes” (ESTM). For this purpose, 1,10-dibenzyl-1,10-diaza-18-crown-6 as neutral carrier and oleic acid were used in the membrane phase. The main variables optimised were the carrier used to form the metal complexes, the organic solvent used in the membrane, the countercation, pH, the ligand used in the acceptor phase, the extraction time, and the flow rate of the donor phase. After the optimisation process an enrichment factor of 18.5 was obtained. Equilibrium conditions were reached after extraction for 60 min if a flow rate of 1.0 mL min−1 or greater was used. When different ligands such as humic acids, phthalic acid, and EDTA were added to the sample solution, and sample pH ranged from 6 to 8, the results obtained for freely dissolved copper concentrations were in a good agreement with results from speciation calculations performed with Visual Minteq V 2.30, Cheaqs V L20.1, and WinHumic V. The developed technique was applied to analysis of stream and leachate water.
Keywords: Supported liquid membrane; ESTM; Speciation; Copper; Diaza crown ether
Formic acid solubilization of marine biological tissues for multi-element determination by ETAAS and ICP–AES by Christine Scriver; Masahiko Kan; Scott Willie; Catherine Soo; H. Birnboim (pp. 1460-1466).
A simple, fast method is described for the determination of Ag, As, Cd, Cu, Cr, Fe, Ni, and Se in marine biological tissues by electrothermal atomic-absorption spectrometry (ETAAS) and Na, Ca, K, Mg, Fe, Cu, and Mn by inductively coupled plasma–atomic emission spectrometry (ICP–AES). Solubilization of the biological tissue was achieved by using formic acid with vortex mixing followed by heating to 50°C in an ultrasonic bath. Once solubilized, the tissues were diluted to an appropriate volume with water for analysis. Aliquots were sampled into a graphite furnace and ICP–AES using a conventional autosampler. The method was validated by use of biological certified reference materials from NRC, DORM-2, DOLT-2, DOLT-3, LUTS-1, TORT-2, and NIST SRMs 1566b and 2976. Simplicity and reduced sample-preparation time prove to be the major advantages to the technique.
Keywords: Trace metals; Biological tissues; Formic acid; ETAAS; ICP–AES
Underpotential deposition of tin(II) on a gold disc electrode and determination of tin in a tin plate sample by Zhiqing Qiao; Wei Shang; Xin Zhang; Chunming Wang (pp. 1467-1471).
This work describes a study of the underpotential deposition (UPD) of Sn2+ on a polycrystalline gold disc electrode using cyclic voltammetry (CV) and chronocoulometry (CC). Sn2+ ions showed well-defined peaks from UPD and UPD stripping (UPD-S) in 1 mol/L HCl solutions, while bulk deposition (BD) and BD stripping (BD-S) of the ions were also observed. The measured UPD shifts, ΔEUPD, between the UPD-S and the BD-S peaks were more than 200 mV. The UPD charge and the surface coverage of tin were measured by CC. A new method for determining Sn2+ was therefore developed, based on the excellent electrochemical properties of the Au/Sn UPD system. A plot of the UPD-DPASV (differential pulse anodic stripping voltammetry) signal versus the Sn(II) concentration was obtained for [Sn(II)] of 1.98×10−7 to 3.64×10−5 M. The method developed here has been applied to determine the tin in a tin plate sample.
Keywords: Tin(II); Underpotential deposition; Polycrystalline gold disc electrode; Cyclic voltammetry (CV); Chronocoulometry
Monitoring dioxins in food and feedstuffs using accelerated solvent extraction with a novel integrated carbon fractionation cell in combination with a CAFLUX bioassay by Malin Nording; Sune Sporring; Karin Wiberg; Erland Björklund; Peter Haglund (pp. 1472-1475).
The concentrations of dioxins in fish oil and fish meal were determined with accelerated solvent extraction, using a novel integrated carbon fractionation extraction cell followed by a miniturized multilayer silica column and bioanalysis on a recently-developed chemically-activated fluorescent gene expression cell bioassay. The developed method allows for simultaneous gravimetric lipid weight determination, which was shown for both matrices under study (about 100% lipid recovery of each sample). Initial results practically meet the quality criteria on screening methods for control of dioxins in food and feedstuffs laid down in the EU Commission Directives 2002/69/EC (food) and 2002/70/EC (feed). This demonstrates that the developed method can be used as a screening tool for monitoring dioxins in food and feed after some additional improvements and testing on a greater number of matrices.
Keywords: Dioxin; Accelerated solvent extraction; ASE; Cell-based bioassay; CAFLUX
Surface potential mapping of dispersed proteins by Dalila Laoudj; Cathy Guasch; Eric Renault; René Bennes; Jacques Bonnet (pp. 1476-1479).
We describe a method for detecting proteins after transfer to PVDF membranes, based on the surface potential attributed to each protein. Proteins separated by classical two-dimensional polyacrylamide gel electrophoresis could be detected by scanning the membrane surface with a vibrating capacitor (also called a Kelvin probe) on the basis of differences between their surface potential and that of the membrane. Coupled to colloidal gold staining, the technique enables detection of proteins previously undetectable by classical staining methods. Plotting variations of the surface potential in two dimensions visualizes proteins which migrate close together. Finally, we demonstrate that the Kelvin probe detects proteins over a concentration range from micro to sub-nanogram with increased sensitivity at lower concentrations, and unlike other methods, appears to be similar for all proteins tested so far. The method described is fast, reliable, and it can be automated for high throughput.
Keywords: Proteomics; Imaging; Biosensors; Nanotechnology
A microwave-assisted microassay for lipases by Parul Jain; Sulakshana Jain; M. N. Gupta (pp. 1480-1482).
A quick and efficient two-step assay for monitoring and screening lipase activity that uses a microtitre plate is described.
Keywords: Lipase assay; Microwave; Screening of lipases
Arsenic speciation in water samples containing high levels of copper: removal of copper interference affecting arsine generation by continuous flow solid phase chelation by Jessica Narváez; Pablo Richter; M. Inés Toral (pp. 1483-1487).
A simple continuous flow method is proposed to eliminate copper interference in arsenic speciation by hydride generation, based on the selective retention of this interfering ion in an iminodiacetate chelating resin previous to the hydride generation process. The arsines generated were cold trapped and measured by ICP/OES. The proposed method allows about 98% of the copper present in the samples to be removed. Minor co-retention of As(V) was observed as a result of electrostatic interaction between the arsenate anion and the nitrogen of the iminodiacetate group of the chelating resin Muromac A-1, the charge distribution of which is modified when copper is chelated. The species As(III), MMA and DMA were not retained in the microcolumn, probably because these species are mainly in the molecular form at the working pH value (4.5). In synthetic samples containing 50 μg l−1 of each arsenic species together with 100 mg l−1 copper, the recoveries obtained were: As(V) 97.6%, As(III) 100%, MMA 99.8%, and DMA 99.9%. The method was applied to arsenic speciation in river water samples containing high levels of copper.
Keywords: Copper removal; Arsenic speciation; Muromac A-1 chelating resin; Hydride generation; ICP/OES