The usage of a bismuth film electrode as transducer in glucose biosensing

A second generation glucose biosensor was developed by using neutral red (NR) as a mediator and a bismuth film electrode (BiFE) as a transducer along with immobilized glucose oxidase. The linear range was between 0.2 and 2.5 mM, and a correlation coefficient of 0.999 was obtained with this electrode. The standard deviation (at 1 mM glucose for n = 4) and the coefficient of variation were calculated as ±8.07 μM and 3.4%, respectively. The biosensor was used for the determination of glucose in wine samples. Correspondence: ülkü Anık, Chemistry Department, Faculty of Arts and Science, Mugla University, TR-48000-K?tekli, Mugla, Turkey     

Energy Dispersive X-Ray Spectrometry by Microcalorimetry for the SEM

 Analytical X-ray spectrometry for electron beam instruments has advanced significantly with the development of the microcalorimeter energy dispersive X-ray spectrometer (μcal EDS). The μcal EDS operates by measuring the temperature rise when a single photon is absorbed in a metal target. A cryoelectronic circuit with electrothermal feedback and a superconducting transition edge sensor serves as the thermometer. Spectral resolution approaching 4.5 eV for high energy photons (6000 eV) and 2 eV for low energy photons below 2000 eV has been demonstrated in energy dispersive operation across a photon energy range from 250 eV to 8 keV. Spectra of a variety of materials demonstrate the power of the μcal EDS to solve practical problems while operating on a scanning electron microscope platform.     

An Electrode-Separated Piezoelectric Sensor as a Surface Monitoring Technique for Anionic Surfactant Adsorption on Quartz Surface

 In the configuration of an electrode-separated piezoelectric sensor (ESPS), the quartz crystal surface is in a direct contact with the liquid phase. With the pre-adsorption of Ca²⁺ as the ionic bridge, anionic surfactant can adsorb on the negatively charged quartz surface (pH > 2.0). The adsorption process of sodium dodecyl benzenesulfonate (SDBS) was monitored in real time with the ESPS method. It was shown that the adsorption of SDBS on quartz surface by Ca²⁺ inducement was reversible with respective to the dilution of solution phase. The adsorption behavior can be analyzed using Langmuir model. The adsorption and desorption rate constants were estimated to be k _a  = (108.4 ± 6.4) mol⁻¹L s⁻¹ and k _d  = (2.57 ± 0.32) × 10⁻³ s⁻¹, respectively. The observed adsorption densities in the ESPS method were significantly greater than the true ones. The influence on surface roughness of the quartz disc on adsorption densities should be corrected by adding a calibration coefficient in the Sauerbrey equation. The saturation adsorption density is 0.223 μg/cm² for SDBS on quartz surface. Double layer occurs for the adsorption of SDBS on quartz surface. Received July 25, 2001. Revision September 17, 2001.     

Determination of rhodium in water samples using cloud point extraction (CPE) coupled with flame atomic absorption spectrometry (FAAS)

Cloud point extraction was applied as a method for preconcentration of rhodium after formation of a complex with 2-propylpiperidine-1-carbodithioate (2-PPC), and later determined by flame atomic absorption spectrometry using TritonX-114 as surfactant. Rhodium was complexed with 2-PPC in an aqueous phase and kept for 15 min in a thermostatted bath at 40 °C. Separation of the two phases was accomplished by centrifugation for 15 min at 4000 rpm. The chemical variables affecting the cloud point extraction were optimized and successfully applied to rhodium determination in various water samples. Under optimized conditions, the preconcentration system (100 mL sample) permitted an enhancement factor of 50. The detection limits obtained under optimal conditions was 0.052 ng mL⁻¹. The extraction efficiency was investigated at different rhodium concentrations (7.0–42.0 μg mL⁻¹), and good recoveries (96.42–99.14%) were obtained using this method. It has been applied to the determination of rhodium in water and was compared with reported methods in terms of Student’s ‘t’-test and variance ratio ‘f’-test.     

Analysis of Laser Irradiated Organo-Platinum Films

 A study of the surface electronic configuration and surface morphology of excimer laser irradiated organo-platinum films [cis-dichlorobis(triphenylphosphine)platinum(II)] is presented. The films were deposited by thermal evaporation to a thickness of approximately 1 μm. The organo-platinum films were irradiated in air with 248 nm UV light in order to produce metallic deposits. The irradiation source used was a krypton fluoride excimer laser with a pulse length of approximately 20 ns. After irradiation, the surface morphology of the films was studied by atomic force microscopy, which yielded information concerning the effect of exposure dose on the surface roughness. The composition of the deposits was investigated using X-ray photoelectron and Fourier-transform infrared spectroscopy. The effect of annealing the deposits has also been studied. XPS analysis of the annealed samples has provided evidence for the formation of platinum silicide (PtSi).     

Synthesis and characterization of poly(styrene/α-t-butoxy-ω-vinylbenzyl-polyglycidol) microspheres

Polystyrene microspheres with polyglycidol (polyGL) in a surface layer were synthesized in batch radical emulsifier-free emulsion copolymerizations of styrene and surfmers, α-t-butoxy-ω-vinylbenzyl-polyGL macromonomers (VB-polyGL). Macromonomers with number-average molecular weight Mˉ _n=950 (VB-polyGL950) and Mˉ _n=2700 (VB-polyGL2700) were used for these polymerizations. In all syntheses the initial concentrations of styrene and initiator (K₂S₂O₈) were constant. The initial macromonomer-to-styrene ratios were varied from 1.10 × 10⁻³ to 1.64 × 10⁻² mol/mol and from 3.46 × 10⁻⁴ to 3.47 × 10⁻³ mol/mol for VB-polyGL950 and VB-polyGL2700, respectively. The diameters of microspheres obtained were smaller for the syntheses with higher concentrations of macromonomers. Syntheses with VB-polyGL950 yielded microspheres with number-average diameters (Dˉ _n) from 216 to 900 nm and with a bimodal diameter distribution. The number-average diameters of microspheres obtained with VB-polyGL2700 varied from 220 to 650 nm, depending on the initial concentration of macromonomer. Their diameter distributions were monomodal, with a diameter polydispersity parameter (ratio of weight-average and number-average diameters) in the range 1.007≤Dˉ _w/Dˉ _n≤1.022. For each type of microsphere the fraction of polyGL in a surface layer and the surface concentration of sulfate anions were determined. The fraction of polyGL in the surface layer was related to the initial monomer composition in the polymerizing mixture. Adsorption of human serum albumin onto surfaces of some poly(styrene/VB-polyGL) microspheres was up to 10 times lower than for the polystyrene microspheres obtained in a similar emulsifier-free emulsion polymerization of styrene. Received: 26 September 2000/Accepted: 19 February 2001     

Determination of trace amounts of cadmium and copper by atomic absorption spectrometry after simultaneous extraction and preconcentration using a new water-soluble polyacrylic acid/alumina sorbent

An analytical method using alumina modified with water-soluble polyacrylic acid polymer for the simultaneous separation and preconcentration of trace Cu and Cd in a column system, and their determination by flame atomic absorption spectrometry was developed. The conditions for coating Al₂O₃ with polyacrylic acid were optimized, then the column was packed with 50 mg of this sorbent. Cd and Cu solution was passed through a glass column at pH 4.5, and elution was carried out with 5 mL of 0.05 M HCl at a flow rate of 1 mL min⁻¹. A sorption capacity of 10 mg Cu and 12 mg Cd was obtained for 1 g sorbent. The detection limit was calculated as 4.5 μg L⁻¹ for Cu and 1.54 μg L⁻¹ for Cd in the final solution. Enrichment factors of 300 for Cd and 400 for Cu were obtained.     

Determination of atrazine, desethyl atrazine and desisopropyl atrazine in environmental water samples using hollow fiber-protected liquid-phase microextraction and high performance liquid chromatography

A new method based on hollow fiber-protected liquid-phase microextraction (LPME) was developed for the simultaneous determination of atrazine, desethyl atrazine and desisopropyl atrazine in environmental water samples. In LPME, analytes were extracted into 1-octanol immobilized in the micropores of a poly(vinylidene fluoride) porous hollow fiber membrane, and back extracted into the acceptor (4 M HCl) filled in the lumen of the hollow fiber. After LPME, the analytes trapped in the acceptor were analyzed with high-performance liquid chromatography after neutralization. The effect of extraction factors such as sample pH, acceptor pH, salinity, extraction time, stirring rate, and humic acid were studied. Under the optimized conditions, the limits of detection and relative standard deviations were respectively in the range of 0.5–1.0 μg L⁻¹ and 3.9–4.7% (n = 5). The proposed method was applied to determine atrazine, desethyl atrazine and desisopropyl atrazine in wastewater and groundwater samples. The three analytes were below the limits of detection, but good relative spiked recoveries over 90.1 ± 5.9% at 5 μg L⁻¹ spiked level were obtained.     

Development and prevalidation of a method for phenol determination by solid-phase spectrophotometry

A simple, sensitive and rapid solid-phase spectrophotometric procedure was developed for the determination of traces of phenol with 4-aminoantipyrine as a reagent (AAP-SPS), and the optimal experimental conditions were established. This method was performed by sorption and direct absorbance measurements of the product phenol-AAP sorbed on the anion-exchanger Dowex 1-X4 (0.2 g) at 495 nm (absorption maximum) and 700 nm (non-absorption wavelength). The sensitivity offered by the AAP-SPS procedure was higher by a factor of 40 compared with the respective conventional spectrophotometric method. Metrological characteristics were established using a prevalidation strategy. The AAP-SPS procedure is characterized by a linear calibration function in the working range of 0.05–0.50 μmol, low standard deviation of procedure (±0.012), low limit of determination (0.021 μmol), and favorable random (±0.85 to ±11.27%) and systematic deviations (−4.55 to +11.50%). Moreover, the accuracy of the system investigated by the recovery test is acceptable (99–102%). Favorable working and performance characteristics make the new SPS method ideal for phenol monitoring in pharmaceutical preparations as well as other matrices.     

Assessing the size-dependent chemical speciation of soil particles using electron probe X-ray microanalysis

Soils of the Pereemnaya river catchment, East Siberia, Russia, characterized by high percentage of particles under 10 μm size and the almost total absence of clay minerals, were studied using ultra-thin window electron probe X-ray microanalysis (EPMA). Three subfractions – 10–5 μm, 1–5 μm and <1 μm were distinguished within <10 μm fraction on the basis of mineralogical composition and chemistry peculiarities. Besides the single particles characterization, the bulk chemistry of specified subfractions and their contributions to the bulk soil chemistry were evaluated. It was shown that concentrations of alkali and alkaline-earth metals within <10 μm fraction increased in the row (5–10 μm) < (1–5 μm) < (<1 μm). The presence of two mica types – low-Fe and rich-Fe – was detected in all the subfractions. Being compared with the soil bulk chemistry, the data obtained for fraction <10 μm show that this fraction is the major source of alkali and alkaline-earth metals and consequently the main contributor to element release due to weathering.     

Oxidation of Steels and HgO Growth after 5000 Hours Exposure in Mercury at 573 K

 Corrosion tests on martensitic steels, F82H and MANET-II, were conducted in static Hg at 573 K in two batches: 1) the Hg covered with air for 5000 h, and 2) the Hg covered with Ar for 2000 h. Different techniques (EPMA, SEM, RHEED, XRD, SIMS) have been applied for surface analysis. The main results show that the surfaces of the samples are oxidized and covered with large amounts of red HgO single crystals (1 μm to 1 mm) under air atmosphere. The surface layers formed in the presence of air consist of oxides of types (Fe, Cr)₂O₃, Fe₃O₄, FeCr₂O₄ and have a thickness up to 680 nm for F82H and 310 nm for MANET-II. Replacing air with Ar in the containers reduces drastically the oxidation of the steels. In this case the maximum thickness of oxide film is of 10 nm and no HgO crystals form.     

Determination of trace rare earth elements in natural water by electrothermal vaporization ICP-MS with pivaloyltrifluoroacetone as chemical modifier

A novel method based on gaseous compounds introduction into the plasma as their pivaloyltrifluoroacetone (PTA) chelates was developed for electrothermal vaporization inductively coupled plasma mass spectrometry determination of trace rare earth elements (REEs) in natural water. The factors affecting formation of the chelates and their vaporization behaviors were studied in detail. Under the optimized conditions, the limits of detection (3σ) of REEs for this method were from 0.20 to 0.91 ng L⁻¹, the relative standard deviations for 0.1 μg L⁻¹ REEs were 2.5–9.1% (n = 9), and the linear ranges of calibration curve for REEs covered at least three orders of magnitude. The proposed method had been applied to the determination of trace REEs in water samples of Yangtze river, Han Shui river and East lake (Wuhan), and the recoveries for the spiked water samples were 93–105%.     

Kinetic Determination of Trace Amounts of Cu(II) in Water Based on its Catalytic Effect on the Reaction of Mercaptosuccinic Acid and Cr(VI)

 A kinetic method is presented for the determination of Cu(II) in water. It is based on the catalytic effect of Cu(II) on the oxidation of mercaptosuccinic acid by chromate in acidic media. The extent of the reaction is followed spectrophotometrically at 345 nm and pseudo-first order rate coefficients are determined as a function of catalyst concentration. The optimum operating conditions regarding ionic strength, temperature and concentration of reagents were established. Interference by several ionic species was studied and the effects of Fe(III) and Pb(II) were suppressed by complexation with pyrophosphate. Calibration lines were obtained for both low (30–640 μg · l⁻¹) and high (640–1500 μg · l⁻¹) catalyst concentrations. The relative standard deviation for 625 μg · l⁻¹ Cu(II) is 6.1% (n = 5). The detection limit is 22 μg · l⁻¹. The method was applied to real samples of river water of the mining region of Baia-Mare, Northern Romania. The results were compared to those obtained by an officially standardized AAS method. Good agreement was attained. The method is inexpensive, fairly rapid and sensitive. Moreover, its working range covers the exact range of concentrations usually encountered in the mentioned geographic area. Received July 28, 2000; accepted December 10, 2001; published online June 24, 2002     

Layer-by-layer immobilization of horseradish peroxidase on a gold electrode modified with colloidal gold nanoparticles

An amperometric biosensor, based on layer-by-layer self-assembly of colloidal gold nanoparticles, cysteine and horseradish peroxidase on Nafion modified electrode surface by electrostatic adsorption, has been used for the determination of hydrogen peroxide. The electrochemical behavior of the multilayer film was studied by cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The step layer-by-layer adsorption interface morphology was further characterized by means of electrochemical impedance spectroscopy and cyclic voltammetry. The performance and factors influencing the resulted biosensor were studied in detail. The sensor displayed an excellent electrocatalytic response to the reduction of H₂O₂ without the aid of an electron transfer mediator. Linear response to H₂O₂ was obtained for the concentration range from 1.6 μM to 2.4 mM under optimized conditions. The detection limit of the biosensor was 0.5 μM (S/N = 3), and the sensor achieved 95% of the steady-state current within 10 s. The sensor exhibited high sensitivity, selectivity and stability. Correspondence: Yan Liu, College of Chemistry, Chongqing Normal University, Chongqing 400047, P.R. China     

Evaluation of imaging plate technique coupled with activation detector as the passive neutron monitor

The spatial distribution of neutrons was measured at the muon science laboratory of KEK by the activation detector method using an imaging plate for the radioactivity measurement. It was confirmed that this method is highly sensitive to detect the average neutron dose of 10 μSv/h. The distribution of thermal and epithermal neutrons was also measured in the experimental room. The cadmium ratio inside the experimental room is one except for the neutron leakage point. The spatial distribution of neutrons inside the concrete shield of KENS was measured by the same method. Aluminum and gold foils were used for the measurement of fast and thermal neutrons, respectively. Two dimensional change of the reaction rate of the ²⁷Al(n,α)²⁴Na reaction shows a good agreement with the results calculated by the Monte Carlo simulation using MARS14 code. Thermal and epithermal neutron flux ratio on the beam axis was measured by the cadmium ratio method. The flux ratios were about 30 and almost constant for every slot except for the surface of the shield, because the cadmium ratio is 2. This method was very useful to measure the activity of many pieces of detector simultaneously without any efficiency and decay correction. Wide dynamic range and high sensitivity are also the merit of this method.     

Multi-syringe flow injection system for the determination of the scavenging capacity of the diphenylpicrylhydrazyl radical in methanol and ethanolic media

A multi-syringe flow injection system for the determination of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH^•) scavenging capacity using methanol or ethanolic solutions as reaction media is presented. A stopped flow approach was implemented in order to monitor the DPPH^• consumption using spectrophotometry at 517 nm. The kinetic profile for the first 3 min of reaction was determined for several antioxidant compounds and the number of DPPH^• molecules reduced by one molecule of antioxidant was calculated whenever the absorbance value was stable within the period of measurement. For ascorbic acid, trolox, isoeugenol and quercetin in methanol, the values obtained were similar to those reported in the literature. It was possible to perform 14 determinations per hour, consuming 0.34 μmol of DPPH^• per determination, which accounts for the application of this system as a screening tool for fast scavenger compounds.     

Introduction of unsaturated pendant groups to polyethylene by γ-ray irradiation under a 1,3-butadiene atmosphere

Ultra-high-molecular-weight polyethylene (Mˉ _v: 5 × 10⁶, 100-times elongated film) was irradiated with γ-rays under a 1,3-butadiene atmosphere at room temperature. Electron paramagnetic resonance (EPR) measurements indicated that the radicals formed on the polyethylene substrate during the irradiation were short-lived. EPR, Fourier transform IR spectroscopy, solid-state NMR, and differential scanning calorimetry of the as-irradiated materials indicated that butadiene molecules were covalently bound to the polyethylene chains as pendant groups bearing trans-vinylene and vinyl functions in a ratio of 3:1. Some crosslinks among the pendants, or between pendants and the main chains were produced. The number of unsaturated pendants introduced (including bridges) per carbon atom of the polyethylene main chain was dependent on the irradiation dose and the butadiene pressure, and was 0.096 butadiene units for 10 kGy irradiation under a 304 kPa butadiene atmosphere. The unsaturated pendants or bridges on the polyethylene chain thus introduced may be good targets to functionalize polyethylene by covalent modification. Received: 22 February 1999 Accepted in revised form: 30 June 1999     

Derivatization of Hydrophobic Amino Acids in Nonaqueous Media and Separation by Nonaqueous Capillary Electrophoresis with Laser-Induced Fluorescence Detection

A method of nonaqueous capillary electrophoresis was established for the separation and determination of alanine, phenylalanine, isoleucine and valine after derivatization with 4-chloro-7-nitrobenzo-2-oxa-1, 3-diazol in nonaqueous media. The derivatization and separation conditions were optimized. The optimum derivatization conditions were 70 min for the reaction time, 55 °C for the reaction temperature and 20 mM ammonium acetate in methanol for the derivatization buffer. The most suitable running buffer was composed of 60 mM ammonium acetate, 10% acetonitrile in methanol with a fused-silica capillary column (47 cm × 75 μm i.d.), 20 kV applied voltage and 20 °C capillary temperature. The correlation coefficients were better than 0.995 in the investigated concentration ranges. The relative standard deviation (R.S.D.) (n = 5) of the migration times and peak areas were 2.0–4.3% and 1.9–4.5%, respectively. The method was applied to the determination of four compounds in two compound amino acid injections, with the exception of phenylalanine, the recoveries for the other three compounds ranging between 88–116%.     

Interface of an Al–(Al2O3)p Composite Modified with Nickel

 A composite material with aluminium matrix and alumina particles coated with nickel was investigated. The nickel coating with thickness up to 1 μm formed by a chemical method consisted of a thin film directly on the alumina surface, porous zone of grains 100 nm size and discontinuous zone of grain agglomerates. As a result of the interaction between the alumina particles coated with nickel and the aluminium matrix, dissolution of nickel in aluminium occurred and reactive bonding took place. In the interface characterized by SEM and TEM methods nickel aluminide and locally nickel-iron aluminide were identified. The presence of complex aluminide was a result of local iron impurity in the aluminium powder.     

Determination of proteins in human serum by combination of flow injection sampling with resonance light scattering technique

A flow injection method combined with Resonance light scattering detection was developed for the determination of protein concentration in human serum samples. This method is based on the enhanced RLS signals of protein binding with the dye acid chrome blue K. The enhanced RLS intensities at 264 nm, in an acidic aqueous solution, were proportional to the protein concentration over the range of 2.0–40.0 μg·mL⁻¹ for human serum albumin (HSA) and the limit of detection (3σ) is 85 ng·mL⁻¹. This method was successfully applied to the quantification of total proteins in human serum samples. The maximum relative standard deviation is less than 2% and the recovery is between 97 and 103% for the standard addition method. The sample throughput was 60 h⁻¹.