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Analytical and Bioanalytical Chemistry (v.373, #8)
No Title by L. Micheli; S. Di Stefano; D. Moscone; G. Palleschi; S. Marini; M. Coletta; R. Draisci; F. delli Quadri (pp. 678-684).
In this paper the production of antibodies against saxitoxin (STX) is described, as is the optimization and comparison of two competitive ELISA formats (direct and indirect) for the detection of this toxin. Tests were performed in a 96-well microplate using the toxin-specific polyclonal antibodies produced in our laboratory, obtained from rabbits immunized with saxitoxin-keyhole limpet hemocyanin (STX–KLH). In indirect ELISA format saxitoxin, conjugated to bovine serum albumin (STX–BSA) was coated onto the microtitre plate and incubated with standard toxin and anti-STX antibody. A goat anti-rabbit IgG Peroxidase conjugate was used to enable detection. In the direct ELISA format, STX standard, STX conjugate to horseradish peroxidase (STX–HRP), and enzyme substrate/chromogen solution were sequentially added to the microplate after antibody coating.Results showed the saxitoxin detection limit to be 3 and 10 pg mL–1 for direct and indirect ELISA formats, respectively.The suitability of the assay for quantification of saxitoxin in mussels was also studied. Samples were spiked with saxitoxin before and after sample treatment to study the extraction efficiency and matrix effect, respectively. After treatment, samples were analysed at 1:1000 v/v dilution in PBS to minimize the matrix effect and to detect the regulatory limit of 40–80 µg saxitoxin per 100 g mussels as stipulated by the Food and Drug Administration. The efficiency of extraction of saxitoxin was from 72 to 102%. These data were confirmed by liquid chromatography coupled with fluorimetric detection, the technique currently used for quantitative determination of toxins in seafood.
Keywords: Enzyme immunoassay Saxitoxin Paralytic shellfish poisoning
No Title by An-Ping Deng; Vladimír Kolář; Robert Ulrich; Milan Fránek (pp. 685-690).
A direct competitive ELISA for determination of polychlorinated biphenyls (PCB) in soil samples was described. The standard calibration curve based on Delor 103 (Aroclor 1242) was constructed in the dynamic range of 10–1000 µg L–1 and a detection limit of 5.0–12.9 µg L–1 (or 0.5–1.29 µg g–1 soil) was achieved. When spiked soil samples were extracted with methanol recoveries were 90.6–106.3 %. The effect of methanol and DMSO on assay signal and sensitivity was established. Eight PCB-contaminated soil samples were analyzed by ELISA and gas chromatography (GC). The ELISA results from Soxhlet extraction were in a good agreement with those of GC (correlation coefficient 0.9866; n=8). Except for one soil sample the results from ELISA with methanol extraction were not significantly different from those from GC.
Keywords: Sheep antibody PCB Extraction Gas chromatography Correlation
No Title by G. Jeanty; A. Wojciechowska; J.-L. Marty; M. Trojanowicz (pp. 691-695).
Determination of the organophosphorus pesticides paraoxon, chlorpyrifos oxon, and malaoxon has been performed by a method based on inhibition of acetylcholinesterase (AChE) and amperometric detection in a flow-injection system with enzymes obtained from the electric eel (eeAChE) and Drosophila melanogaster (dmAChE) and immobilized on the surface of platinum electrode within a layer of poly(vinyl alcohol) bearing styrylpyridinium groups. dmAChE is more sensitive than eeAChE to inhibition by chlorpyrifos oxon and paraoxon. The sensitivity difference was largest for chlorpyrifos oxon (detection limit approx. 17 times lower), and practically none for malaoxon. Determination of the analytes in spiked river water samples by use of the dmAChE biosensor resulted in recoveries from 50 to 90 % for chlorpyrifos oxon at levels of 20 to 40 nmol L–1, 50 to 100 % for paraoxon at 0.6 to 0.8 µmol L–1, and 140 to 190 % for malaoxon at 0.6 to 1.2 µmol L–1.
Keywords: Biosensors Flow-injection analysis Amperometric detection Pesticides
No Title by M. Farré; C. Gonçalves; S. Lacorte; D. Barceló; M. Alpendurada (pp. 696-703).
Two different toxicity tests, an electrochemical biosensor Cellsense and a bioluminescence inhibition assay ToxAlert were performed in order to establish and compare the acute toxicity responses of different types of raw and spiked water for a selected group of pesticides. The selected compounds were endosulfan, chlorfenvinphos, dimethoate, fenamiphos, ametryn, deltamethrin and α-cypermethrin; all of them are used in large quantities for agricultural purposes. In the first step, the study of the toxicity responses for each individual pesticide with Milli-Q water was carried out. Next, the toxic responses of different mixtures of these pesticides in different water matrices, i.e., Milli-Q water, surface water, groundwater and wastewater were studied in order to evaluate (i) device advantages and limitations for the toxicity evaluation of real environmental samples, (ii) antagonistic or synergistic effects and (iii) the influence of the water matrices. The survey of pesticides in real samples was carried out using a combined method involving both chemical analysis and toxicity bioassays. Chemical analysis involved the use of solid-phase micro-extraction (SPME) followed by gas chromatography with electron capture detection (GC/ECD) or thermoionic specific detection (GC/TSD) with mass spectrometric confirmation (GC/MS).
No Title by M. Farré; J. Fernandez; M. Paez; L. Granada; L. Barba; H. Gutierrez; C. Pulgarin; D. Barceló (pp. 704-709).
The controlled biodegradation of ametryn and methomyl has been performed, in accordance with the OECD Zahn–Wellens/EMPA procedure, by use of an enriched mixture of activated sludge collected from three domestic waste-water-treatment plants (WWTP). During the process concentrations of ametryn and methomyl in the water samples were isolated by solid-phase extraction (SPE); recovery rates were 98.9 and 93.2 for methomyl and ametryn, respectively. Liquid chromatography–mass spectrometry (LC–MS) was used to determine final pesticide concentrations and for metabolite identification.The efficiency of aerobic biodegradation of ametryn and methomyl was evaluated by measuring both the decrease in the concentration of the pesticides and global properties such as the chemical oxygen demand (COD). The acute toxicity of ametryn and methomyl was evaluated by use of the ToxAlert100 biological test, which is based on inhibition of the bioluminescence of Vibrio fischeri. There was significant correlation between results from primary and ultimate biodegradation and those from determination of toxicity. Pesticide concentrations were always reduced to below the limit of detection in less than 17 days. High COD removal (90–96%) was achieved in 28 and 18 days for methomyl and ametryn, respectively.
Keywords: Methomyl Ametryn ToxAlert Sewage sludge
No Title by Pinar Kara; Dilsat Ozkan; Kagan Kerman; Burcu Meric; Arzum Erdem; Mehmet Ozsoz (pp. 710-716).
The electrochemical behavior of hemin, an iron complex of porphyrin, on binding to DNA at a glassy carbon electrode (GCE) and in solution, is described. Hemin, which interacts with covalently immobilized calf thymus DNA, was detected by use of a bare GCE, a double-stranded DNA-modified GCE (dsDNA-modified GCE), and a single-stranded DNA-modified GCE (ssDNA-modified GCE), in combination with differential pulse voltammetry (DPV). The structural conformation of DNA was determined from changes in the voltammetric signals acquired on reduction of hemin. As a result of its large steric structure and anionic substitution on its porphyrin plane, hemin intercalates between the base pairs of dsDNA. A scan-rate study for hemin and the dsDNA-hemin complex were also performed to determine the electrochemical behavior of the complex. The partition coefficient was obtained from the peak currents measured when different concentrations of hemin were in the presence of dsDNA. By observing the oxidation signals of guanine, damage to DNA after reaction with hemin at the GCE surface was also detected. The electrochemical detection of hybridization between the covalently immobilized probe and its target sequence was detected by use of hemin. These results demonstrate the use of DNA biosensors in conjunction with hemin for electrochemical detection of hybridization and damage to DNA.
Keywords: DNA biosensor Hemin Intercalator Damage Hybridization
No Title by Ana Oliveira-Brett; Luís da Silva (pp. 717-723).
An electrochemical DNA-biosensor has been used to investigate the interactions between DNA and members of a group of ten derivatives of 1,3,5-triazine herbicides: chloro-s-triazines (atrazine, propazine, terbutylazin, and cyanazin), thiomethyl-s-triazines (ametryn, prometryn, terbutryn, and simetryn), and methoxy-s-triazines (prometon and terbumeton). A UV spectrophotometric study of this group of herbicides was also undertaken. Of this group only cyanazin could be oxidized in aqueous solution using a glassy carbon electrode. Use of the electrochemical DNA-biosensor revealed the occurrence of a time-dependent interaction of all the herbicides with DNA, via the appearance of guanine, guanosine, and adenosine oxidation signals that correspond to DNA damage. Adduct formation between the herbicide and the DNA purine bases guanine and adenine is suggested as a mechanism.
Keywords: s-Triazine derivatives Interaction with DNA Voltammetric detection, DNA-electrochemical biosensor
No Title by Edyta Kosela; Hanna Elzanowska; Wlodzimierz Kutner (pp. 724-734).
Four different poly(pyridine) complexes of ruthenium, viz. RuII(trpy)(phen)(OH2)]2+ (1), trans-[RuIII(2,2'bpy)2(OH2)(OH)]2+ (2), [(2,2'bpy)2(OH)RuIIIORuIII(OH)(2,2'bpy)2]4+ (3), and [RuII(4,4'bpy)(NH3)5]2+ (4) (2,2'bpy=2,2'-bipyridine, 4,4'bpy=4,4'-bipyridine, trpy=2,2',2''-terpyridine, phen=1,10-phenanthroline), were tested as non-physiological charge mediators of 'second-generation' glucose biosensors. The membranes for these biosensors were prepared by casting anionic carboxymethylated β-cyclodextrin polymer films (β-CDPA) directly onto the Pt or glassy carbon (GC) disk electrodes. Simultaneously, glucose oxidase (GOD) was immobilized in the films by covalent bonding and the Ru complexes were incorporated both by inclusion in the β-CD molecular cavities and by ion exchange at the fixed carboxymethyl cation-exchange sites. The leakage of the mediator from the polymer has been minimized by adopting a suitable pre-treatment procedure. The biosensors catalytic activities increased in the order 1<2<3<4, as established by linear sweep voltammetry. In case of complexes 2–4, the enzymatic glucose oxidation was mediated by the Ru complexes at their redox potentials. However, this oxidation was mediated by oxygen in case of complex 1 where H2O2 was detected as the reaction product. The effectiveness of the mediators used in the presence of oxygen has been estimated using Pt and GC supports. The redox potential of the mediator does not depend on the support used, while the oxidation of H2O2 proceeds on GC at much higher positive potentials than on Pt. The sensitivity and the linear concentration range of the biosensor studied varied significantly. For complex 4, which forms stable inclusion complex with β-CD, the biosensor sensitivity was the highest and equal to 7.2 µA mM–1 cm–2, detectability was as low as 1 mM, but the linear concentration range was limited only to 4 mM. In contrast, for complexes 2 and 3 the sensitivity was 0.4 and 3.2 µA mM–1 cm–2, while the linear concentration range extended up to at least 24 and 14 mM glucose, respectively. Even though some common interfering substances, such as ascorbate, paracetamol or urea, are oxidized at potentials close to those of the Ru complex redox couples, their electro-oxidation currents at physiological concentrations are insignificant compared to those due to the biocatalytic oxidation of glucose. The biosensor response to glucose is reversible as demonstrated by the inhibition of GOD activity by Cu(II). That is, the Cu(II) concentration required to inhibit by half the response to glucose of the biosensor containing complex 2 was 1.0 mM. This inhibitory effect was fully reversed by addition of citrate, a ligand forming sufficiently stable complex with Cu(II).
Keywords: 'Second-generation' glucose biosensor Glucose oxidase Glucose oxidase inhibition Enzyme immobilization Polymer film modified electrode Carboxymethylated β-cyclodextrin polymer film Ru poly(pyridyl) complex mediator Cyclic voltammetry Linear sweep voltammetry
No Title by L. Svobodová; M. Šnejdárková; T. Hianik (pp. 735-741).
The properties of glucose biosensors based on dendrimer layers on a gold support, which depend on the method of immobilization of glucose oxidase (GOX), were studied by amperometry. The kinetic parameters of enzymatic reactions, response time, sensitivity, detection limit, linear range, and enzyme turnover were determined. We showed that a more stable and sensitive sensor was obtained when GOX was immobilized on the dendrimer by crosslinking with glutaraldehyde in vacuum. This biosensor was stable for at least eight weeks. The response time was approximately 1.3 min, the detection limit of glucose was 25 µM, and the apparent Michaelis-Menten constant was relative low (K m=1.1±0.1 mM) in comparison with that for GOX in solution. The reason for these differences is discussed. The example of the application of the developed biosensors for the detection of mercury is also presented. The inhibitory effect of mercury on GOX activity was observed at mercury concentration of 100 nM.
Keywords: Glucose sensor Glucose oxidase Dendrimers Amperometry Mercury
The electrochemical characterisation of benzyl mercaptan-modified Au(111): Structure and copper deposition by T. Baunach; D. Kolb (pp. 743-748).
The behaviour of benzyl mercaptan self-assembled monolayers on Au(111) in sulfuric acid solution was studied using cyclic voltammetry and in situ scanning tunnelling microscopy. Modification of the Au(111) surface in an ethanolic solution of benzyl mercaptan leads to a disordered monolayer. However, by partial reductive desorption a striped $$cleft( {15 imes sqrt 3 }
ight)$$ and a $$left( {2 imes sqrt 3 }
ight)$$ structure were obtained. The disordered benzyl mercaptan film was also used for the study of copper deposition. At –0.02 V versus SCE, that is in the underpotential deposition region, monoatomic high islands appear on the surface. Bulk deposition of copper starts at –0.08 V versus SCE with the growth of dendrites underneath the thiol film. At higher overpotentials, the growth of three-dimensional copper clusters commences.
Keywords: In situ STM Self-assembled monolayer Metal deposition
No Title by Thomas Nann; Udo Kielmann; Christoph Dietrich (pp. 749-753).
Multifunctional sensor systems are becoming increasingly important in electroanalytical chemistry. Together with ongoing miniaturization there is a need for micro- and nanopatterning tools for thin electroactive layers (e.g. self-assembling monolayers). This paper documents a method for production of a micro-array of different metal–porphyrin monolayers with different sensor properties. A new method has been developed for the selective and local metallization of bare porphyrin monolayers by cathodic pulsing and sweeping. The metal–porphyrin monolayers obtained were characterized by cyclic voltammetry. It was shown that porphyrin monolayers can be metallized with manganese, iron, cobalt, and nickel by use of the new method. It is expected that all types of metal–porphyrin monolayers can be produced in the same manner.
Keywords: Porphyrins Cyclic voltammetry Thiol-modified gold electrode Self-assembled monolayers (SAMs)
No Title by M. Roemer; T. Kurzenknabe; E. Oesterschulze; N. Nicoloso (pp. 754-757).
In this contribution we report the use of polyaniline and polypyrrole for miniaturized actuators fabricated by microstructural and electrochemical technologies. The potential necessary to drive the actuator is typically less than 1 V, i.e. 2–3 orders of magnitude lower than that necessary for the widespread piezoelectric actuator devices. This low voltage is imperative for future application of actuators of micrometer dimensions. The volume variation of polymers substantially exceeds that of piezoelectric materials. Different contributions to the actuator characteristics are discussed and evaluated semi-quantitatively.
Keywords: Conducting polymers Microactuators Electrochemistry Microstructure technology MEMS
No Title by Holger Ernst; Bernd Roß; Meinhard Knoll (pp. 758-761).
A continuous amperometric glucose monitoring system is presented. All analytically relevant units are integrated on a microchip (microreactor, control electrode, glucose oxidase based sensor electrode, reference electrode, counter electrode). The scavenging electrochemical microreactor pre-oxidises all interfering compounds enabling a reliable glucose determination. The reliability of the microreactor is demonstrated with the most important antioxidants, ascorbic and uric acids. The glucose sensor system operates at volumetric flow rates of common body interfaces (e.g. microdialysis, microperfusion).
Keywords: Glucose determination Glucose oxidase Ascorbic acid Uric acid Scavenging microreactor
No Title by Paul Dierkes; Philippe Coulon; Susanne Neumann; Wolf-Rüdiger Schlue (pp. 762-766).
Because changes in cell volume might disturb the normal function of animal cells, most cells are endowed with volume-regulating mechanisms. Experimentally induced changes in cell volume are often paralleled by changes in the membrane potential, which might affect a variety of transport processes across the cell membrane and, in turn, volume regulation [1, 2]. We have shown previously that multi-barrelled ion-selective microelectrodes are useful tools for measurement of cell volume and the intracellular concentrations of ions that might be relevant to volume regulation [1]. To investigate whether voltage-dependent transport processes are involved in cell-volume regulation we combined the potentiometric technique of ion-selective microelectrodes with the voltage-clamp technique. This combination enables simultaneous recording of cell volume, relevant intracellular ion concentrations, and ion currents across the cell membrane at a fixed membrane potential.
Keywords: Ion-selective microelectrodes Cell volume Voltage clamp Invertebrate nerve cells
No Title by Günther Weber; Günter Neumann; Volker Römheld (pp. 767-771).
Phytosiderophores of the mugineic acid family, and the respective iron species, have been separated by anion-exchange chromatography with NaOH gradient elution. Two different detection methods were used in parallel, pulsed amperometry (PAD) for phytosiderophores and atomic absorption spectrometry (AAS) for iron. This combination enables identification of separated iron species. Up to five different iron species were separated and detected within 30 min – two different phytosiderophore species, two amino acid species, and one species which has not yet been identified but which is most probably a decomposition product of phytosiderophores. The detection limit was in the low µmol L–1 concentration range, which is sufficiently low for determination in real plant samples, even after dilution. The method has been applied to root washings of iron-deficient wheat and barley plants and to a xylem exudate of non-deficient maize.
Keywords: Phytosiderophores Speciation HPLC Pulsed amperometry AAS
No Title by Christine Jeyaseelan; A. Joshi (pp. 772-776).
A simple and rapid differential pulse polarographic method has been developed for the trace determination of dexamethasone sodium phosphate. A well-defined single peak with an Ep value of –1.14 V is obtained in acetate buffer (pH 5.0). The linearity is valid in the range 0.2–1.2 mg/25 mL (r=0.9992) with minimum detection limit of 7.6×10–6 M. The precision of the method developed is implied from the values of relative mean deviation, standard deviation and coefficient of variation, which are 2.44%, 0.014 and 3.5% respectively. Marketed formulations of dexamethasone sodium phosphate have been analysed by calibration and standard addition methods. Recovery experiments were found to be quantitative, and analysis to determine the mass per tablet was obtained within ±0.2% of the expected market value. The studies have shown that the method is reproducible and accurate and can be used in the analysis of marketed formulations.
Keywords: Differential pulse polarography Dexamethasone sodium phosphate
No Title by Š Komorsky-Lovrić (pp. 777-780).
The standard redox reaction rate constant of cinnoline (1,2-benzodiazine) adsorbed to the mercury electrode in 0.9 mol L–1 KNO3 buffered to pH 7, 9.2, and 4.65 are ks=455±110 s–1, 65±25 s–1, and 300±75 s–1, respectively.
Keywords: Cinnoline Redox kinetics Square-wave voltammetry Benzodiazine
Reactant adsorption in cyclic staircase voltammetry on spherical microelectrodes. Reversible redox reactions by Milivoj Lovrić (pp. 781-786).
On spherical microelectrodes, cyclic staircase voltammograms of reversible redox reactions complicated by the reactant adsorption depend on lateral interactions in the monolayer. Attraction forces increase the separation between the main wave and the post-peak, while the repulsion prevents the resolution of responses of the surface and volume reactions. The theoretical relationships between the dimensionless responses and the dimensionless adsorption constant, the relative surface adsorption capacity, the Frumkin coefficient and the electrode sphericity are given.
Keywords: Cyclic staircase voltammetry Adsorption Microelectrode
No Title by Peter Fecher; Gisela Ruhnke (pp. 787-791).
Common white sugar was ashed in a muffle furnace under controlled heating at 450 °C. Together with these samples, sugar with added amounts of Pb and Cd (20, 50 µg) was mineralized in the same furnace. Depending on the absolute amount of Pb and Cd present in the furnace, an increase in the 'blank' values of the unspiked sugar samples was found. The same effect was observed when reference material containing natural amounts of Pb and Cd (TORT-1, Lobster) was present in the furnace. Although the results strongly depend on the blank levels of the muffle furnace, cross contamination effects could be demonstrated for both elements. The investigations demonstrate, that at a temperature of 450 °C, both Cd and Pb are lost during ashing of samples. The type of matrix in a sample with high contents of Pb and Cd has no significant effect on the volatility of these elements. The vapor lost from a sample containing high amounts of Pb and Cd will falsify the concentration in low level samples present in the furnace.
Keywords: Dry ashing Cross contamination Foodstuff Lead Cadmium
No Title by Keith J. Albert; Daljeet S. Gill; Tim C. Pearce; David R. Walt (pp. 792-802).
In this paper automatic sensor identification of sensor classes within a high-density randomized array, without a priori knowledge of sensor locations, is demonstrated. Two different fluorescence-based sensor types, with hundreds of replicates each, were randomly distributed into an optical imaging fiber array platform. The sensor element types were vapor-sensitive microspheres with the environmentally-sensitive fluorescent dye Nile Red adsorbed on their surface. Nile Red undergoes spectral changes when exposed to different microenvironmental polarity conditions, e.g. microsphere surface polarity or odor exposure. These reproducible sensor spectral changes, or sensor-response profiles, enable sensors within a randomized array to be grouped into categories by optical decoding methods. Two computational decoding methods (supervised and unsupervised) are introduced; equal classification rates were achieved for both. By comparing sensor responses from a randomized array with those obtained from known (control) arrays, 587 sensors were correctly classified with 99.32% accuracy. Although both methods were equally effective, the unsupervised method, which uses sensor response changes to odor exposure, is a better decoding model for the vapor-sensitive arrays studied, because it relies only on the odor-response profiles. Another decoding technique employed the emission spectra of the sensors and is more applicable to other types of multiplexed fluorescence-based arrays and assays. The sensor-decoding techniques are compared to demonstrate that sensors within high-density optical chemosensor arrays can be positionally-registered, or decoded, with no additional overhead in time or expense other than collecting the sensor-response profiles.
Keywords: Optical decoding Optical imaging fibers High-density sensor arrays Fluorescence Microscopy Imaging Cross-reactive vapor sensors PCA DFA.
No Title by Cunchang Wang; Hua Wang; Zhaoyang Wu; Guoli Shen; Ruqin Yu (pp. 803-809).
A piezoelectric immunosensor based on an improved immobilization strategy combining self-assembled monolayers (SAM) of cystamine (Cys) and polystyrene sulfonate (PSS) has been developed for the determination of Schistosoma japonicum antibodies (SjAb) in rabbit serum. Cys SAM were first applied to the gold electrode surface of the crystal, serving as a positively-charged base. Schistosoma japonicum antigen (SjAg) was then electrostatically immobilized on the crystal by means of a negatively-charged PSS layer. When sealed by use of an appropriately selected blocking reagent for BSA and normal rabbit serum (NRS), non-specific adsorption could be substantially reduced.The immunosensor was used to determine SjAb in optimized buffer medium with addition of poly(ethylene glycol) (PEG), which served as an immunoreaction enhancer. It was shown experimentally that SjAg immobilized by the Cys–PSS adsorption procedure had higher immunological activity or binding efficiency than those immobilized by the glutaraldehyde (GLU) binding or direct attachment procedures. The immunosensor developed had satisfactory sensitivity and detection limit, and regeneration of the piezoelectric quartz-crystal was easy. Analytical results obtained with infected rabbit serum samples indicated that the proposed immunosensor is a promising alternative for qualitative and quantitative determination of SjAb in clinical diagnosis of infection with Schistosoma japonicum.
Keywords: Cystamine SAM Polystyrene sulfonate Piezoimmunoassay Schistosoma japonicum antibodies
No Title by Hardy Weißhoff; Alfred Preiß; Irene Nehls; Tin Win; Clemens Mügge (pp. 810-819).
A hyphenated HPLC-1H NMR method for the identification and quantification of PAHs in soil samples has been developed and applied to a PAH reference sample provided by the Federal Institute for Materials Research and Testing (BAM, Berlin, Germany). The results were compared with those obtained by HPLC-DAD, HPLC-F, and GC-MS analyses of the same sample.
Keywords: Hyphenated techniques HPLC-NMR PAH analysis
No Title by Marit Langødegård; Grethe Wibetoe (pp. 820-826).
A graphite-furnace atomic-absorption spectrometric method, utilizing ultrasonic slurry-sampling has been developed for the determination of Ga in soils. Calibration with aqueous standards and with slurries prepared from a certified soil reference material were both employed. When calibration with soil slurries was used no modifier was needed. Because lower and more variable sensitivity was obtained for Ga in aqueous standards than for Ga in slurry soil samples, external calibration with aqueous Ga standards required a suitable chemical modifier to level out the sensitivity difference. Of the many potential modifiers tested, i.e. Al, As, Co, Mg, Mo, Ni, Pd, Pd+Mg, Se, and Te, Ni was found to be best. When Ni (1.0 mg mL–1, 10 µL) was injected to the graphite tube with the aqueous standards or slurry samples (10 µL) accurate results were obtained. Both methods of calibration gave acceptable accuracy and precision. The repeatability was ≤4.6% (RSD) for slurry sampling for both methods of calibration. The intermediate precision for analyses performed on three different days was 7.3% and 4.8% when using aqueous standards and slurry standards, respectively. The limit of detection for Ga was 3.0 µg L–1 in soil slurry solution, equivalent to 0.08 µg g–1 in the soil samples. Results from slurry sampling were compared with results from microwave-digested samples. Chemical interference was observed when the acid-mixture used to dissolve the samples contained HF. This interference was eliminated when Ni was added as chemical modifier. The repeatability was ≤7.2% (RSD) for analysis of decomposed samples.
Keywords: Graphite-furnace atomic-absorption spectrometry Ultrasonic slurry sampling Certified reference material Chemical modifier Soil Ga
No Title by M. Carvalho; L. Silveira; A. Casimiro (pp. 827-829).
Knowledge of the element content of biological systems is important in enabling understanding of uptake mechanisms and physiological response to stress conditions. In this work concentrations of mineral elements in sycamore (Acer pseudoplatanus L.) cells grown in the presence of cadmium have been analysed and compared with concentrations in control cells. Energy-dispersive X-ray fluorescence (EDXRF) was used to quantify the nutrients K, Ca, Mn, Fe, Cu, and Zn present in the cells. The reproducibility and accuracy of the technique were demonstrated by analysis of biological reference materials. Exposure of sycamore cells to cadmium had induced variation in the content of some elements. Mn, Cu, Zn, and, particularly, Fe concentrations in cells exposed to Cd were higher than those found in control cells. Ca is adsorbed on the cell walls and the concentration of K is not affected by the presence of Cd.
Keywords: Environment Biological samples Energy-dispersive X-ray fluorescence (EDXRF)
No Title by A. Gauthier; S. Derenne; L. Dupont; E. Guillon; C. Largeau; J. Dumonceau; M. Aplincourt (pp. 830-838).
.Ligno-cellulosic substrates (LCSs) isolated from wheat straw and bran exhibit high complexing capacities and may have important applications for metal removal from industrial effluents. These two LCSs were examined in the present work by spectroscopic and pyrolytic methods (solid state cross polarization magic angle spinning (CP/MAS) 13C NMR, XPS, conventional Curie pyrolysis (Cupy)/GC/MS, and TMAH thermochemolysis/GC/MS). This combined study highlighted the limitation of some of the above methods when applied to ligno-cellulosic materials and the resulting biases and the usefulness of TMAH thermochemolysis. A large difference in composition was observed between bran- and straw-LCS due to a much higher contribution of alkyl moieties in the former. These moieties correspond to fatty acids esterified to the ligno-cellulosic macromolecular structure and such carboxylic functions should play an important role for metal complexation.
Keywords: Ligno-cellulosic materials; Wheat Straw; Wheat Bran; Solid state CP/MAS 13C NMR; XPS; CuPy/GC/MS; TMAH pyrolysis, thermochemolysis
No Title by S. Yang; I. Smetena; C. Huang (pp. 839-843).
An improved method, gas chromatography (GC) with nitrogen–phosphorus detection (NPD), has been used for determination of alkaloids in green and cured tobacco. Tobacco alkaloids of interest included nicotine, nornicotine, myosmine, anabasine, and anatabine. Tobacco samples were treated with a small quantity of aqueous ammonia solution to "loosen" tobacco tissue and to adjust pH, then extracted with solvent. The composition of the extraction solvent solution affected recoveries of the alkaloids, particularly nornicotine, and also contributed to other phenomena such as carry-over in the injection liner and "quenching" of the nitrogen–phosphorus detector. Use of a packed injection liner (e.g. with Carbowax–KOH on Chromosorb) to reduce carry-over was studied. Quenching of the nitrogen–phosphorus detector was eliminated by reducing the injection volume (i.e. increasing the split ratio), by use of a packed injection liner, and by reducing the amount of pretreatment with aqueous ammonia. A narrow bore capillary column (i.e. 0.18 mm id) was used to improve sensitivity and resolution and to increase the speed of GC analysis. An internal standard, 2,4′-dipyridyl, was used for quantitative measurement of these tobacco alkaloids.
Keywords: Tobacco Minor alkaloids Gas chromatography analysis Nitrogen–phosphorus detector
No Title by Juan J. Pinto; Carlos Moreno; Manuel García-Vargas (pp. 844-848).
A sensitive spectrophotometric method for the direct determination of copper in aqueous samples without a preconcentration step has been developed. It is based on the formation of a yellow complex with the chromogenic reagent di-2-pyridyl ketone benzoylhydrazone (dPKBH) in an alkaline medium. The complex stoichiometry was 1:2 (Cu:dPKBH) and presents maximum absorbance at 370 nm. The influence of chemical variables affecting the behaviour of the system such as pH, concentration of dPKBH, buffer solution and ethanol, order of addition of the reagents and stability of the complex, were evaluated. The molar absorptivity (ε) was 3.92×104 L mol–1 cm–1, and Beer's law was obeyed up to 3 mg L–1 of copper. The relative standard deviation was 0.46% (n=11) for a sample containing 1 mg L–1 Cu(II). The limit of detection was 2.5 µg L–1 and was therefore more sensitive than the direct methods reported previously. Finally, the method was successfully validated by analysing several real samples with different matrices, such as tap water, natural water or copper alloys, with an average relative error of 2.46%.
Keywords: Copper determination Spectrophotometry Natural waters Trace metals dPKBH
No Title by Xuming Guo; Zoltán Mester; Ralph E. Sturgeon (pp. 849-855).
Chloride- and hydride-generation headspace solid-phase microextraction (SPME) techniques have been compared for the detection of trace amounts of germanium by inductively coupled plasma time-of-flight mass spectrometry (ICP–TOFMS). The conditions for generation of germanium chloride, including acid type and concentration, effect of sodium chloride and extraction time, were investigated. Detection limits of 20 and 92 pg mL–1 and precisions of 18% (n=11) and 9.7% (n=11) were achieved for chloride and hydride generation, respectively, at a concentration of 10 ng mL–1. The generated germanium chloride and hydride species identities were characterized and confirmed as GeCl4 and GeH4 by use of electron-impact ionization mass spectrometry. Chloride generation coupled with SPME sampling and ICP–TOFMS detection resulted in twofold enhancement of sensitivity compared to GeH4 and detection limits for continuous hydride generation were 20-fold better than reported atomic fluorescence data.
Keywords: Solid-phase microextraction (SPME) Germanium Chloride generation Hydride generation Inductively coupled plasma Time-of-flight mass spectrometry
No Title by Cristina T. Camagong; Takaharu Honjo (pp. 856-862).
Solvent extraction with 0.05 mol L–1 dicyclohexano-18-crown-6 (DC18C6) in 1,2-dichloroethane, coupled with flame atomic absorption spectrometry (AAS), has been investigated as a new method for separation of trace amounts of silver(I) from 0.05 mol L–1 potassium thiocyanate in 1.0 mol L–1 hydrochloric acid media and quantification of the amount of silver present. The method is based on the formation of an extractable ion-association product, [DC18C6·K]+[Ag(SCN)2]–, with a metal-to-crown ether ratio of 1:1 (as derived from slope analysis data). Stripping of the extracted silver(I) in the 1,2-dichloroethane phase was achieved within 5 min by use of 3.0 mol L–1 potassium thiocyanate. Reducing the concentration of acid in the sample solution to 0.1 mol L–1 improved the preconcentration factor severalfold. Excellent tolerance of the proposed method to the presence of foreign ions in solution with silver(I) was demonstrated. A detection limit of 13 ng mL–1 was derived from the mean value of the blank plus three times its standard deviation. The method was used to determine traces of silver(I) after separation from gold(III), platinum(IV), and palladium(II) matrices on the basis of extractability differences with 18-membered crown ethers under specified conditions. The efficiency of the adopted ion-association mechanism for silver(I) extraction was apparent from the average recovery of 96% for spiked standards by use of the back-washing technique. The proposed extraction procedure was applied to the determination of traces of silver(I) in a selection of chemical reagents.
Keywords: Silver Crown ether Ion-association Noble metals Solvent extraction
No Title by G. Heltai; B. Fehér; K. Percsich; B. Barabás; I. Fekete (pp. 863-866).
Results from use of a new isolation procedure based on sequential extraction with supercritical CO2, subcritical H2O, and an H2O/CO2 mixture in the same supercritical fluid extractor have been compared with results from the BCR-recommended three-step sequential extraction procedure. The new procedure gives more detailed information about environmentally mobile fractions (water-soluble, bicarbonate-forming), and in less time (5–6 h), than the BCR procedure.
Keywords: Heavy metal pollution Sequential extraction Heavy metal fractions Sediment analysis
No Title by Mary J. Gladis; T. Prasada Rao (pp. 867-872).
Amberlite XAD-4 has been functionalized by coupling it with 5-aminoquinoline-8-ol after acetylation. The resulting resin has been characterized by elemental analysis and IR spectra and has been used for preconcentrating uranyl ions prior to its determination by spectrophotometry. The optimum pH value for quantitative sorption is 4–6, and desorption can be achieved by using 5 mL of 1 mol L–1 HCl. The sorption capacity of the resin is 11.5 mmol g–1. The effect of various cations and anions on the preconcentration of uranium in conjunction with the determination procedure has been studied and we have found that none of the ions interfere except thorium. The enrichment factor for preconcentration of uranium was found to be 200. Ten replicate determinations of 40 µg of uranium present in 1 L of sample gave a mean absorbance of 0.185 with a relative standard deviation of 2.64%. The detection limit corresponding to three times the standard deviation of the bank was found to be 2 µg L–1. The validation of the developed preconcentration procedure was carried out by successfully analyzing standard marine sediment reference material. The uranyl content of sediment and soils is estimated by spectrophotometry after its preconcentration with the above chelating resin.
Keywords: Quinoline-8-ol Amberlite XAD-4 Synthesis Preconcentration Uranyl ion
No Title by H. Ernstberger; H. Zhang; W. Davison (pp. 873-879).
The techniques of diffusive gradients (DGT) and equilibration (DET) in thin-films have been combined in a single probe that can determine Cr(III) and Cr(VI) simultaneously in solution. The assembly has a layer of polyacrylamide hydrogel overlying a separate layer of resin embedded in gel. Cr(III) species accumulate exclusively and quantitatively in the resin layer, while Cr(VI) species equilibrate with both hydrogel and resin layers. The species are separated by peeling the two layers apart. Chromium is then eluted from each of the two layers. Cr(III) and Cr(VI) were determined quantitatively in standard, mixed solutions by in situ separation with DGT and detection by GF-AAS. With this method, Cr(III) is typically preconcentrated by a factor of 10 over a 24 h deployment, and limits of detection of 8 ng/L Cr(III) and 0.3 µg/L Cr(VI) were achieved. Due to the inbuilt preconcentration of Cr(III), the technique is particularly good at measuring low concentrations of Cr(III) in the presence of an excess of Cr(VI). Measurements were performed in three soils with various levels of chromium contamination. A concentration of 3 µg/L of labile Cr(III) was measured reproducibly in the presence of 290 µg/L of unreactive Cr species and 0.2 µg/L of labile Cr(III) was measured in the presence of 24 µg/L of unreactive Cr. The unique feature of the method is that the separation of Cr(III) from Cr(VI) occurs in situ. The Cr species are then stable in the resin and gel prior to analysis, eliminating the artefacts associated with sampling and storage, which are particularly prevalent for redox-sensitive elements. Therefore, it has great potential for assessing Cr(III) and Cr(VI) concentrations in situ in environments near redox boundaries where possible dynamic changes in Cr(III) and Cr(VI) concentrations are occurring.
Keywords: Chromium Speciation DGT waters Soils
No Title by G. Auffermann; U. Schmidt; B. Bayer; Yu. Prots; R. Kniep (pp. 880-882).
The nitrogen content of the binary compounds SrN = Sr4[N]2[N2], Sr[N2], and Ba[N2] (prepared by high-pressure syntheses) was determined analytically by using the carrier gas hot extraction method. For handling of the air- and moisture-sensitive samples, a transfer chamber was constructed to protect the compounds against decomposition before being analyzed. Additionally, it was necessary to develop a method allowing controlled and variable heating of the electrode furnace to get analytical results with high precision and accuracy. By means of a suitable temperature program it was possible not only to verify the existence but also to quantify the two different nitrogen species ([N3–] and [N2 2–]), and thus confirm the results of recent neutron diffraction studies.
Keywords: Carrier gas hot extraction Combustion method Diazenides Nitrogen Speciation
No Title by Xingguo Chen; Hongping Xu; Lijun Dong; Huitao Liu; Yibo Zeng; Zhide Hu (pp. 883-888).
A new rapid, selective and sensitive on-line microwave flow injection-kinetic method was developed for spectrophotometric determination of micro amounts of Ir(III), based on its catalytic effect on the m-acetylchlorophosphonazo (CPA-mA) and KIO4 reaction in NaOH media. An on-line microwave oven was employed to accelerate the reaction. The reaction was followed spectrophotometrically by measuring the decrease of the absorbance of CPA-mA at 580 nm. The effect of five variables for the determination of Ir(III) was optimized by means of a multilayer artificial neural network using extended delta-bar-delta (EDBD) algorithms. Under the optimum experimental conditions, Ir(III) could be determined in the range 0.060–0.60 µgZZZ;mL–1 with detection limit of 0.02 µgZZZ;mL–1 and the sampling frequency of 34 h–1. The proposed method was applied to the determination of micro amounts of Ir(III) in refined ore and secondary alloy with the recoveries from 91.4% to 109%.
Keywords: Microwave FIA Catalytic kinetics CPA-mA Iridium(III) Artificial neural network
No Title by I. Baranowska; M. Zydroń (pp. 889-892).
The structural descriptors with the best potential for predicting the reversed-phase retention of xanthines and their derivatives on the new Chromolith RP-18e columns have been examined, as has the molecular mechanism of the separation.QSRR analysis was performed by simultaneous solution of a set of linear equations. The logarithms of the capacity factors were the dependent variables. Structural descriptors calculated by means of semi-empirical methods of quantum chemistry were chosen as independent variables.
Keywords: QSRR RP HPLC Xanthines
No Title by S. Sánchez Ramos; F. Bosch Reig; J. Gimeno Adelantado; D. Yusá Marco; A. Doménech Carbó (pp. 893-900).
An in-depth chemical-analytical study has been performed on biscuit and mortar from 17th–18th century tiles from a mediaeval hermitage in the province of Valencia (Spain). Representative samples were chosen from the tile fragments available, using appearance, essentially color and consistency, as the criterion. The chemical composition was analyzed by X-ray fluorescence of the samples in the form of glass disks after a previous qualitative study to choose the standard materials for calibration and the experimental conditions used in the analysis. X-ray diffraction of the samples provided information about the mineralogical composition which was consistent with the firing of the original materials; it also gave information about the range of temperatures used in the firing. From thermal gravimetric analysis of the limestone, and from historical considerations, it was possible to deduce the raw materials used and their approximate composition in the tiles. In the same way it was possible to determine the nature of the mortars used to fix the tiles. Cyclic voltammetric study of the iron(II) and iron(III) system in the biscuit showed the simultaneous presence of both oxidation states, corroborating the results.
Keywords: Ancient ceramics XRF XRD Thermal analysis Iron(II) and Iron(III) voltammetry
Laboratory development and field evaluation of a new diffusive sampler to collect nitrogen oxides in the ambient air by F. De Santis; T. Dogeroglu; A. Fino; S. Menichelli; C. Vazzana; I. Allegrini (pp. 901-907).
Diffusive samplers for the determination of NOx and NO2 based on collection on a coated carbon paper filter have been developed. NO is first oxidized to NO2 and then collected on the reactive surface. When NO2 and NOx samplers are exposed simultaneously, NO can be calculated by difference. The sampler has been derived from a Palmes design as recently modified by Bertoni et al. for the determination of BTX (benzene, toluene, xylenes). Laboratory tests were conducted in controlled atmosphere to evaluate linearity, uptake rate, face velocity effects, sample stability, influence of relative humidity, precision and accuracy. The samplers are capable of reliable measurements of the two species at common levels of a polluted atmosphere in urban settings yielding average concentration levels over 1 month and beyond.The uptake rate of NO2 was found to be 11.7 mL/min in a very good agreement (within 5%) with the value calculated from theory. The measured uptake rate for NOx was determined in experiments involving sampling at different concentration levels in comparison to chemiluminescence (CL) measurements. The precision of the measurements for co-located passive samplers was better than 5%. The accuracy of the data collected is within ±20% of the actual value measured by CL. The laboratory and field results show that the NOx and NO2 samplers meet the data quality goal requested by the first EU Directive 1999/30/EU for these pollutants.
Keywords: Atmospheric pollution Diffusive sampling Nitrogen dioxide Nitrogen oxides