Determination of Nucleic Acid at Nanogram Levels with Manganese-Tetrasulfonatophthalocyanine Sensitized by Cetyltrimethylammonium Bromide Using a Resonance Light-Scattering Technique

This is the first report on the determination of deoxyribonucleic acids based on the enhancement of resonance light-scattering (RLS) of manganese-tetrasulfonatophthalocyanine (MnTSPc) by DNA and cetyltrimethylammonium bromide (CTMAB). Under the conditions of pH 10.6011.85 and an ionic strength of 0.01molL^–1 (NaCl), the interaction of MnTSPc with DNA sensitized by CTMAB results in enhanced RLS signals at 314nm, 346.2nm, 452.6nm and 494.4nm in the enhanced regions. It was found that the enhanced RLS intensity at 346.2nm was proportional to the concentration of DNA in the suitable ranges. The limits of detection were 11.3ngmL^–1 for fsDNA and 22.9ngmL^–1 for ctDNA when the concentration of MnTSPc was chosen to be 2.0×10^–6molL^–1. This method was simple, rapid, and the dye (MnTSPc) was easily synthetized, inexpensive, and stable. We applied it to the determination of DNA in synthetic samples with satisfactory results.Received November 4, 2002; accepted January 18, 2003 Published online July 16, 2003     

Flow Injection Spectrophotometric Determination of Ferbam Based on a Photochemical Reaction

A flow-injection configuration for the spectrophotometric determination of ferbam is proposed. The procedure is based on the online decomposition of ferbam and complexation of the released Fe³⁺ with oxalate. The ferrioxalate formed is decomposed upon irradiation with visible light. The Fe²⁺ produced in the photochemical reaction was monitored by measuring the absorbance after complexation with ferrozine (_max=562nm). The method shows a linear range between 1.0 and 30µgmL^–1 (2.5×10^–6–7.2×10^–5molL^–1) with a limit of detection of 0.2µgmL^–1. Repeatibility was 0.53% expressed as relative standard deviation (n=10), and reproducibility, studied on five different days, was ±1.23%. The sampling frequency was about 45samplesh^–1. The applicability of the method was tested in the determination of ferbam in waters and grains.Received December 2, 2002; accepted April 13, 2003 Published online July 16, 2003     

Selective Extraction and Separation of Thorium from Monazite Using N-Phenylbenzo-18-crown-6-hydroxamic Acid

A method for the liquid–liquid extraction, separation, preconcentration and trace determination of thorium with N-phenylbenzo-18-crown-6-hydroxamic acid (PBCHA) is described. Thorium is extracted from the dichloromethane solution of PBCHA at pH 4.5 which gives a colourless extract (_max 375nm, =1.5×10⁴Lmol^–1 cm^–1, linear range following Beers law 0.77–18.48µgmL^–1). The extract is directly inserted into the plasma for ICP-AES measurements of thorium. A linear calibration graph was obtained between 10 and 130ngmL^–1 of thorium. The proposed method has been applied for the separation and determination of thorium in the presence of several ions in monazite sand, rare earths, sand and sea water samples. The thorium-PBCHA complexes are very stable, having the formation constant (log ₂) 13.45 compared to lanthanum (log ₂) 2.95, cerium (log₂) 2.95 and uranium (log ₂) 3.80. Hence, thorium can easily be separated and determined in monazite sand.Received October 31, 2002; accepted April 13, 2003 Published online July 16, 2003     

In Vitro Determination of Dobesilate in Medicine and Human Urine with Chemiluminescence Detection

A unique flow injection chemiluminescence (CL) method for the determination of calcium dobesilate in pharmaceutical preparations and human urine is presented in this paper. The analytical reagents involved in the CL reaction, luminol and ferricyanide, were both immobilized on an anion-exchange column in an FI system. The CL signal produced by the reaction of luminol with ferricyanide (the reagents had been eluted from the column through sodium phosphate injection) decreased in the presence of dobesilate. The decreased CL intensity was linear to the dobesilate concentration in the range 0.2100.0ngmL^–1. At a flow rate of 2.0mLmin^–1, one analytical cycle can be completed in 1.5min, including sampling and washing, resulting in a throughput of 40 cycles per hour. The proposed method was applied successfully to the determination of dobesilate in pharmaceutical preparations and human urine without any pre-treatment. It was found that, after oral administration, the dobesilate concentration reached its maximum after three hours, and the dobesilate metabolism ratio in 24 hours was 57.1% in the bodies of volunteers.Received September 14, 2002; accepted March 11, 2003 Published online July 16, 2003     

Electrochemical Behavior of Epinephrine at a Penicillamine Self-Assembled Gold Electrode,and its Analytical Application

The fabrication and electrochemical characteristics of a penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The self-assembled electrode shows obvious electrocatalytic activity for the oxidation of epinephrine (EP). In phosphate buffer (pH 7.73), a sensitive oxidation peak was observed at 0.190V with the PCA modified Au electrode. The peak current is proportional to the concentration of EP in the range of 2.0×10^–56.0×10^–4molL^–1 and 5.0×10^–6 2.0×10^–4molL^–1 for cyclic voltammetry (CV) and differential pulse voltammetry (DPV) with the detection limits of 1.8×10^–7 and 1.3×10^–7molL^–1, respectively. The possible reaction mechanism is also discussed. The PCA self-assembled monolayer modified gold electrode is highly stable and can be applied to the determination of EP in practical injection samples. Application is simple, rapid and produces accurate results.     

Photoluminescence of osmocene and decamethylosmocene

Osmocene (and decamethylosmocene) is characterized by a lowest-energy ligand field triplet which occurs at _max=372nm (374nm) in absorption and 567nm (572nm) in emission. This orange–yellow phosphorescence is rather intense at 77K but is also visible at r.t.     

Electrochemical Characterization of CoHP–Si Incorporated into a Carbon Paste Electrode

Reduction of dioxygen at a carbon paste electrode (CPE) modified with cobalt hematoporphyrin complex immobilized on silica gel (CoHP–Si) was studied by cyclic voltammetry and rotating disk electrode. In 0.5molL^–1 KCl solution, the supported complex showed significant catalytic activity towards four-electron reduction of O₂ to H₂O at a relatively high pH (5.4). The reduction of dioxygen proceeds at a more negative potential (–0.375V) than the redox reaction Co^III/Co^II (0.464V), indicating that the mechanism does not involve the complex as an electron transfer mediator. Catalytic activity of CoHP–Si towards reduction of H₂O₂ was tested, but no activity was observed.Received October 26, 2002; accepted March 10, 2003 Published online July 16, 2003     

Displacement of hydrogen from rhodium surface by carbon monoxide under conditions of pulsed-gas chromatography

Interaction of carbon monoxide with hydrogen on the surface of rhodium catalysts has been investigated under conditions of pulsed-gas chromatography within the temperature range of –80 to 500 °C. At temperatures up to about 180 °C adsorbed hydrogen was found to be displaced to the gaseous phase as a result of carbon oxide adsorption. At higher temperatures conversion of carbon monoxide and hydrogen to methane takes place.

---

–80 500 °C. 180 °C . .

     

Hydrogenation of CO2

The hydrogenation of CO₂ has been studied on three different series of catalysts: Fe/MgO, Ni/Ti, Cr/Zn doped with potassium. Reaction was carried out in a conventional flow microreactor system at 15 bar at 250–350°C. Three independent competing reactions: Reverse gas-water shift (RGWS), Fischer-Tropsch (FT) and methanol synthesis were observed.

---

CO₂ : Fe/MgO, Ni/Ti, Cr/Zn . 15 250–350°C. : RGWS, F.T. .

     

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

The synthesis and evaluation of silica sol-gels doped with cobalt hexacyanoferrate (CoHCF) for solid phase extraction of Cs⁺ from aqueous solution is described. The CoHCF is formed by first introducing K₄Fe(CN)₆ (HCF) into the sol-gel and subsequently contacting the porous solid to a solution containing Co²⁺. Generally, sols contain alcohol as a co-solvent, which limits the solubility of HCF. Inclusion of generation-4 polyamidoamine (G4-PAMAM) dendrimer in the sol-gel increases the level of HCF and, in turn, the CoHCF. The uptake capacity of this composite was 0.43±0.01mmolCs⁺g^–1. A second approach to increasing the level of HCF silica is to exclude alcohol from the sol and use ultrasound to obtain a homogeneous suspension; HCF concentrations up to 0.17M in the sol were thereby achieved. After gelation and reaction with Co²⁺, the resulting composite had a capacity of 0.61±0.01mmolCs⁺g^–1. With 0.5mMCs⁺ as the sample, the presence of either 0.5–100mM Na⁺ or 10mMCa²⁺ did not change that value at the 95% confidence level.     

Studies on catalytically active surface compounds, VIII. On the reaction of VCl4 with aerosil

The preparation and hydrolysis of silica supported vanadium catalysts have been investigated using VCl₄ as a paramagnetic probe. Chemical analysis shows the possibility of the VCl₄ molecule to react one, two, or three hydroxy groups of the surface. The type of reaction is influenced by the temperature of pretreatment of aerosil (TPA). ESR measurements show distortions of the tetrahedral coordination of the (SiO)_nVCl_4–n surface complex, which is strongest for the threefold attachment (n=3) of VCl₄ to the surface. Hydrolysis is accompanied by an increase of the coordination number and leads to highly mobile vanadium species.

---

, VCl₄ . , VCl₄ , . . (SiO)_nVCl_4–n, VCl₄ (n=3). .

     

Spectroscopic study of silver state in CaO

Electron spectra of the oxidized states of silver (Ag²⁺) in CaO have been identified by comparison of ESR and diffuse reflectance electron spectra.

---

Ag²⁺ CaO .

     

Catalysis by Pd(I) complexes in olefin isomerization and acetylene carbonylation

Carbonyl palladium(I) halide complexes have been tested as catalysts of olefin isomerization and acetylene carbonylation reactions. A new complex Pd(I)-MPdJ₂.2H₂O, where M=Li, Cs has been synthesized. It is shown that Pd(I) complexes are active catalysts in acetylene carbonylation.

---

. Pd(1) MPdJ₂·2H₂O, M=Li, Cs. , .

     

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

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

Solid-Phase Extraction with Slurry Injection of the Resin Into ETAAS for Trace Determination of Thallium in Natural Water

Thallium in natural water samples was determined by electrothermal atomic absorption spectrometry after 1000-fold enrichment by mini solid-phase extraction from a 100-mL sample solution. A Tl-pyrrolidine-1-carbodithioate complex formed in a sample solution of pH 1.6 was extracted on fine particles of a cellulose nitrate resin dispersed in the sample solution. The cellulose nitrate resin was then collected on a membrane filter (25mm^ø) by filtration under suction using a glass funnel with an effective filtration area of 0.64cm². As a result, a circular thin layer of the resin phase with a diameter of 9mm was obtained. Then the resin phase was carved out by an acrylate resin puncher with a 10-mm^ø hole to put it into a sample cup containing 100µL of 10mM HNO₃ containing 0.5mM NaCl. The resin phase was suspended in the solution by ultrasonication. 1000-fold enrichment was thus attained within 15min, and the suspension was delivered to electrothermal atomic absorption spectrometry. The linear calibration graph was obtained in the range of 0–4ng of Tl in 100mL of a sample solution. The detection limit obtained by 3 method was 0.19ng. The proposed method was applied to the determination of Tl in natural water samples. The results showed the concentration of Tl in seawater was 12.1±1.8pgmL^–1 for the calibration graph method and 12.6±1.4pgmL^–1 for the standard addition method. A snowmelt sample contained 20.7±1.0pgmL^–1 of Tl.     

A rapid method for catalyst activity measurements by combination of pulse reactor, mass spectrometer and process computer

The combination of a pulse reactor attached directly (without a separation column) to a mass spectrometer/process computer system is described. To obtain a conversion/temperature diagram for the dehydration and dehydrogenation of 2-butanol less than one hour is required. Therefore, the method can be used for rapid characterization or comparison of the activities of various samples.

---

, ( ) - . / 2- . .

     

Collisional energy transfer in the decomposition of 2-methyloxetane and 3-methyloxetane, II. Gas/wall collisions

The variable encounter method has been applied for the study of gas/wall vibrational energy transfer in the thermal decomposition of 2-methyloxetane and 3-methyloxetane. The average probability of reaction per collision was deduced from the data and was compared with stochastic calculations based on gaussian and exponential energy transfer probability models. The gaussian model fits the experimental data best. Using this model, the average down step energies were 2600 and 2690 cm^–1 for 2-methyloxetane and 3-methyloxetane, respectively, at 750 K, and they decreased with increasing temperature.

---

/ 2- 3-. , . . , 2600 2690 ^–1 750 K 2- 3-, . .

     

Development and Validation of Catalytic Kinetic Spectrophotometric Method for Determination of Copper(II)

A catalytic kinetic spectrophotometric method is developed for the determination of trace amounts of Cu(II). It is based on the catalytic effect of Cu(II) on the oxidation of cysteine (RSH) by hexacyanoferrate(III) in acidic medium. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of hexacyanoferrate(III) at 420nm. The optimum operating conditions regarding concentration of reagents, pH and temperature were established. The working curve is linear in the concentration range of 0–6.35ng·mL^–1. The maximum percentage error and standard deviation for determination of Cu(II) in the range of 1.27–6.35ng·mL^–1 have been calculated to be 3.9 and 0.4 respectively. The detection limit calculated was 0.15ng·mL^–1. The interference effect of several species was also investigated, and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cu(II) in various synthetic and real samples. The typical feature of this procedure is that determination can be carried out at 25°C and/or in the absence of any precision thermostatic bath in the very short analysis time of one minute. The newly developed method was found to have fairly good selectivity, sensitivity, simplicity and rapidity compared to other kinetic methods.Received October 8, 2002; accepted April 7, 2003 Published online July 16, 2003     

Reversible Optical Sensor Membrane for Hydrogen Peroxide Using an Immobilized Fluorescent Probe,and its Application to a Glucose Biosensor

An optical sensor for hydrogen peroxide (HP) based on the probe europium tetracycline (EuTc) incorporated into a polyacrylonitrile-co-polyacrylamide polymer matrix is described. Upon optical excitation with 400-nm light, the EuTc in the membrane displays fairly strong fluorescence peaking at 616nm. The fluorescence intensity increases up to 3-fold if the sensor is exposed to solutions containing HP. The effect is reversible and can thus be used for continuous sensing. The largest signal changes with HP are observed at pH levels between 6.5 and 7.5, and the range of the response is between 10 and 300ppm (w/w) of HP, equal to 0.3 to 10mmolL^–1). At concentrations above 0.3% of HP, decomposition of the EuTc in the membrane is observed. The limit of detection is 15ppm (0.45mmolL^–1). The response is fully reversible and rather slow (10min) in both directions, but the reverse response may be accelerated by addition of a reducing agent such as thiosulfate. Alkali ions and most anions remain inert, but phosphate and citrate interfere, as do Cu²⁺ ions, which quench fluorescence. In order to image the spatial distribution of HP concentrations, sensor membranes were placed on the bottom of the wells of a microtiter plate, and their fluorescence was imaged using an LED-based device based on the measurement of the luminescence decay time of EuTc. If glucose oxidase is immobilized on the sensor layer, a glucose sensor is obtained in which the HP sensor acts as the transducer and which can quantify glucose in concentrations between 0.1 and 5mmolL^–1. The limit of detection for glucose is 0.2mmolL^–1.     

2,3-Dihydroxypyridine Loaded Amberlite XAD-2 (AXAD-2-DHP): Preparation, Sorption–Desorption Equilibria with Metal Ions, and Applications in Quantitative Metal Ion Enrichment from Water, Milk and Vitamin Samples

2,3-Dihydroxypyridine loaded (via –N=N–linker) Amberlite XAD-2 (AXAD-2-DHP) was prepared and characterized by elemental analyses, TGA and FT-IR spectra. It (1g packed in a column of 1cm diameter; surface area 135.5m²g^–1) was found to be an effective solid phase sorbent for enriching Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺ at pH 3.5 to 7.0 using flow rates between 1.0–5.0mLmin^–1. For desorption (recovery 97.0–99.8%) of the metal ions, 8 to 10mL of 2.0molL^–1 HCl or 1.5molL^–1 HNO₃ at a flow rate of between 2.0 and 4.0mLmin^–1 were found most suitable. The t_1/2 (time for 50% sorption) is between 2 and 10min when a 50mL solution (containing a total amount of metal of 2mg) was equilibrated with 0.5g of resin. Sorption of all metal ions except Pb²⁺ follows the Langmuir model, whereas for Pb the data fits with the Freundlich model. The sorption capacity is between 60.7 (for Cd) and 406.7 (for Cu) µmolg^–1. The resin can withstand an acid concentration of 6molL^–1 and can be reused for thirty cycles of sorption–desorption. The preconcentration factor varies between 100 and 300. For Cd, Ni and Cu the sorption capacity of 2,3-dihydroxypyridine loaded cellulose is lower than that of the present resin. The tolerance limits of electrolytes, humic acid, complexing agents, Ca²⁺ and Mg²⁺ in the enrichment of all metal ions are reported. The limits of detection are 3.88, 5.37, 8.72, 13.88, 4.71, 1.24, 0.59 and 0.30µgL^–1 for Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺, respectively. The calibration curves for flame AAS determination were linear in the ranges 0.018–1.0, 0.067–5.0, 0.2–5.0, 0.9–20, 0.028–2.0, 0.077–5.0, 0.19–10 and 0.1–3.5µgmL^–1, respectively. All the eight metal ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples have been quantitatively enriched with Amberlite XAD-2-DHP and determined by flame atomic absorption spectrometry.