Determination of sulfanilamide based on the Mn(II)-catalyzed oscillating chemical reaction

A convenient and sensitive method for determination of sulfanilamide (SNA) was described based on the Mn(II)-catalyzed oscillating chemical reaction. Under optimum conditions, a linear relationship existed between the changes of oscillating period or amplitude and the negative of logarithm of SNA concentration in the range of 4.27 × 10⁻⁸ mol ·L⁻¹ ∼ 7.41 × 10⁻⁶ mol ·L⁻¹ (RSD, 0.85%) and 9.33 × 10⁻⁸ mol ·L⁻¹ ∼ 3.02 × 10⁻⁶ mol ·L⁻1 (RSD, 1.08%), respectively. The lower limit of detection was found to be 2.69 × 10⁻⁸ mol ·L⁻¹ and 6.03 × 10⁻⁸ mol ·L⁻¹, respectively.      

Determination of p-nitroaniline by the tartrate-acetone-Mn2+-KBrO3-H2SO4 double organic substrate oscillating system using non-equilibrium stationary state

This paper described the determination of p-nitroaniline in a double organic substrate oscillating system of tartrate-acetone-Mn²⁺-KBrO₃-H₂SO₄. Under the optimum conditions, temperature was chosen as a control parameter to design the bifurcation point and proposed a convenient method for determination of p-nitroaniline. Results showed that the system consisting of 3.5 mL 0.06 mol L⁻¹ tartrate, 4.0 mL 0.7 mol L⁻¹ H₂SO₄, 1.5 mL 1.5×10⁻⁴ mol L⁻¹ MnSO₄, 4.0 mL 0.4 mol L⁻¹ acetone and 7.0 mL 0.05 mol L⁻¹ KBrO₃ was very sensitive to the surrounding at 33.5°C. A good linear relationship between the potential difference and the negative logarithm concentration of p-nitroaniline was obtained to be in the range of 2.50×10⁻⁷∼3.75×10⁻⁵ mol L⁻¹ with a lower detection limit of 2.50×10⁻⁸ mol L⁻¹.      

Determination of ultra-trace amounts of inorganic selenium species in natural water by ion chromatography-inductively coupled plasma-mass spectrometry coupled with nano-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> solid phase extraction

This work presents a nano-Al₂O₃ solid phase extraction technique for the determination of ultra-trace amounts of inorganic selenium species in aqueous systems using ion chromatography inductively coupled plasma-mass spectrometry (IC-ICP-MS). In this experiment, the inorganic selenium species were successfully extracted on a nano-Al₂O₃ solid phase column and then quantitative eluted with a 100 mmol L⁻¹ NaOH solution. Extraction conditions such as solvent identity, solvent concentration, solvent volume, solvent pH and salt addition were optimized. Under the optimum extraction conditions (elute solvent: 100 mmol L⁻¹ NaOH, solvent volume: 4 mL, pH: 7.0), low detection limits (Se (IV): 6 ng L⁻¹, Se (VI): 11 ng L⁻¹; RSD<5.0%) and good linear range (0.5–100 ng mL⁻¹, R² > 0.999) were obtained for all of the analytes. Good spiked recoveries over the range of 80–98% were obtained by applying the proposed method on real environmental water samples. These results indicated that this method is very sensitive and reliable when monitoring trace levels of inorganic selenium species in aqueous samples.      

2-pyrrolidone - capped Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals

Water-soluble Mn₃O₄ nanocrystals have been prepared through thermal decomposition in a high temperature boiling solvent, 2-pyrrolidone. The final product was characterized with XRD, SEM, TEM, FTIR and Zeta Potential measurements. Average crystallite size was calculated as ∼15 nm using XRD peak broadening. TEM analysis revealed spherical nanoparticles with an average diameter of 14±0.4 nm. FTIR analysis indicated that 2-pyrrolidone coordinates with the Mn₃O₄ nanocrystals only via O from the carbonyl group, thus confining their growth and protecting their surfaces from interaction with neighboring particles.      

Determination of diclofenac in pharmaceuticals and urine samples using a membrane sensor based on the ion associate of diclofenac with Rhodamine B

The potentiometric response characteristics of a diclofenac selective electrode, based on ion association in different plasticizers, were compared. The sensitivity, working range, detection limit and selectivity of membrane sensors demonstrated significant dependence on the type of plasticizers. The potentiometric unit presented a linear response toward diclofenac concentrations between 1 × 10⁻⁵ − 5 × 10⁻² mol L⁻¹, with slopes of approximately 60 mV dec⁻¹, and exhibited a response time of 3 s. The potentiometric analysis of sodium diclofenac in pharmaceutical formulations was perfomed by the membrane electrode proposed and compared with the results of potentiometric titration given by the Pharmacopoeia of Ukraine.      

Cobalt(II) ion-selective electrode with solid contact

A new all plastic sensor for Co²⁺ ions based on 2-amino-5 (hydroxynaphtyloazo-1′)-1,3,4 thiadiazole (ATIDAN) as ionophore was prepared. The electrode exhibits a low detection limit of 1.5 × 10⁻⁶ mol L⁻¹ and almost theoretical Nernstian slope in the activity range 4.0 × 10⁻⁶–1 × 10⁻¹ mol L⁻¹ of cobalt ions. The response time of the sensor is less than 10 s and it can be used over a period of 6 months without any measurable divergence in potential. The proposed sensor shows a fairly good selectivity for Co(II) over other metal ions. The electrode was successfully applied for determination of Co²⁺ in real samples and as an indicator electrode in potentiometric titration of Co²⁺ ions with EDTA.      

Kinetic spectrophotometric determination of hydrazine

A kinetic spectrophotometric method for hydrazine determination in the range of 9.36×10⁻⁷ to 4.37×10⁻⁵ mol dm⁻³, based on the inhibitory effect of hydrazine on the oxidation of Victoria Blue 4- R by KBrO₃, was developed and validated. Kinetic parameters are reported for both the indicating and the inhibiting reaction. The detection limit was established as 9.98×10⁻⁸ mol dm⁻³. The selectivity of the proposed method was tested considering the influence of different ions that may be present in real samples. The method was successfully applied for hydrazine determination in various samples (very pure water from the water-steam system of a power plant and Isoniazid tablets, a pharmaceutical product).      

Properties of ibuprofen ion-selective electrodes based on the ion pair complex of tetraoctylammonium cation

Ibuprofen membrane electrodes based on different plasticizers: diisobutyl phthalate (DIBP), o-nitrophenyloctyl ether (o-NPOE), dioctyl sebacate (DOS) and tetraoctylammonium 2-(4-isobutylphenyl)propionate were prepared. All electrodes show: a near Nernstian slope of characteristic (58.3–60.9 mV decade⁻¹) in the measurement range (10⁻⁴–10⁻¹ mol L⁻¹), limit of detection (5.0×10⁻⁵ mol L⁻¹), really long lifetime (12 months), dependence of the electrode potential on pH (5.5–9.0), reproducibility of potential (0.6–1.2 mV) and selectivity coefficients in relation to some organic and inorganic anions. The electrodes were applied for the determination of ibuprofen in tablets by the calibration curve method and the standard addition method.      

Properties of naproxen ion-selective electrodes

Naproxen membrane electrodes based on different plasticizers and the quaternary ammonium salts (QASs) dimethyldidecylammonium bromide, methyltrioctylammonium chloride, or tetraoctylammonium chloride, were prepared. The following basic parameters were investigated for the optimal electrode: measurement range (10⁻⁴ − 10⁻¹ mol L⁻¹), slope of the linear range of the calibration curve (−58.3 mV decade⁻¹), limit of detection (6.0 × 10⁻⁵ mol L⁻¹), lifetime (2.5 months), dependence of the electrode potential on pH (5.5 − 9.0), reproducibility of potential (1.2 mV) and selectivity coefficients in relation to selected organic and inorganic anions. The electrode was utilized for determination of naproxen in tablets by the calibration curve method and the standard addition method.      

Determination of Alizarin Red S using a novel B-Z oscillation system catalyzed by a tetraazamacrocyclic complex

A new and convenient method for the determination of Alizarin Red S by the perturbations caused by different amounts of Alizarin Red S on a novel B-Z oscillating system is proposed. This new type Belousov-Zhabotinskii involves a macrocyclic copper(II) complex [CuL](ClO₄)₂ as catalyst and malic acid as the substrate. The ligand L in the complex is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. It is found that the relationship between the change in the oscillation amplitude and the logarithm of the Alizarin Red S concentration in the range of 1.5 × 10⁻⁷ to 1 × 10⁻³ M fits a polynomial model: ΔA = 659 + 184.2 log [Alizarin Red S]+ 12.9 log² [Alizarin Red S]. The RSD obtained with ten samples is 4.4%. The probable mechanism involving the perturbation of Alizarin Red S on the oscillating chemical system is also discussed.      

The crystal structure of Ho<Subscript>4</Subscript>Ni<Subscript>11</Subscript>In<Subscript>20</Subscript>

The polycrystalline Ho₄Ni₁₁In₂₀ was obtained by arc-melting of the elements. The subsequent high temperature procedure was used for single crystal growth. Crystal structure of the compound was investigated by X-ray single crystal method: U₄Ni₁₁Ga₂₀ type, C 2/m, a = 22.4528(17), b = 4.2947(3), c = 16.5587(13) Å, β = 124.591(5)°, R1 = 0.0276, wR2 = 0.0493 for 1989 independent reflections with [I>2σ(I)].The structure is composed of three-dimensional network from Ni and In atoms in which Ho atoms fill distorted pentagonal channels. Open image in new window     

Synthesis of functional magnetic porous SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/P(St-DVB-MAA) microspheres by a novel suspension polymerization

In this study, a novel and effective suspension polymerization has been employed to prepare functional magnetic porous SrFe₁₂O₁₉/P(St-DVB-MAA) microspheres in the presence of bilayer surfactants (sodium dodecyl benzene sulfonate (SDBS) and oleic acid (OA)) coated on micro-size magnetic SrFe₁₂O₁₉. This was achieved by pre-polymerizing the organic phase, which contained co-monomers, porogens and treated magnetic particles, at 65°C for 0.5 h under ultrasound conditions. Aqueous solutions containing a dispersion agent were then added to effect suspension polymerization. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and magnetic property measurement system (MPMS) were used to characterize the functional magnetic porous microspheres. The results show that the microparticles are well shaped with a uniform size distribution of about 0.5 ∼ 0.7 mm and the surfaces of the microspheres have many micro-pores with an average diameter of 0.533 μm. There are carboxyl groups (−COOH) on the surface of the microspheres to the extent of 0.65 mmol g⁻¹, as determined by conductometric titration. According to the XRD spectra, iron oxide consists mainly of SrFe₁₂O₁₉ which reveals hexahedral structure. The content of magnetic SrFe₁₂O₁₉ reaches 17.81% (by mass), and the microspheres have good heat resistance. The magnetic porous microspheres are ferromagnetic with high residual magnetization and coercivity, 21.59 emu g⁻¹ and 4.13 kOe, respectively. The saturation magnetisation is around 42.85 emu g⁻¹.      

Electrochemical oxidation of methylthiomethyleneisoquinolinium chloride — the first water soluble alkylthiomethylene substituted ammonium salt

Electrochemical oxidation of methylthiomethyleneisoquinolinium chloride (MTMIQ), the first alkylthiomethyl substituted ammonium salt, which is fully miscible with water has been investigated by voltammetric (SWV) method using glassy carbon electrode. On the electrode, MTMIQ undergoes oxidation at the potential near Ep = 0.07V (vs. Ag/AgCl/3 M KCl). The influence of the pH of buffers, amplitude, frequency, step potential on the received signal was studied. The best results were obtained with a citrate buffer at a pH of 5. The oxidation peak current used for MTMIQ voltammetric determination was in the range of 2–8×10⁻⁵ mol L⁻¹, LOD = 3.7×10⁻⁶, LOQ = 1.2×10⁻⁵. The product of the oxidation was accumulated at the working electrode and was investigated by spectroscopic method. Mechanistic pathways of the oxidation have been proposed.      

Calorimetric study of melts in the System KF - K<Subscript>2</Subscript>NbF<Subscript>7</Subscript>

The relative enthalpies of melts in the system KF - K₂NbF₇ were measured by drop-calorimetry at the temperatures 1058, 1140 and 1208 K as a function of composition. Heat capacities of melted mixtures and enthalpies of mixing were determined using the experimental data. The molar heat capacity of melts diverges slightly from additivity. The molar enthalpy of mixing of melts shows small negative deviation from ideality which decreases with decreasing temperature. The thermal effect at mixing was assigned predominantly to association reactions producing more complex fluoroniobate anions.      

Hydrogen sorption characteristics of magnesium-based composites with addition of Mg<Subscript>2</Subscript>Ni<Subscript>0.7</Subscript>Co<Subscript>0.3</Subscript> and graphite

Magnesium-based composites of 75 wt% Mg — (10, 15, 20) wt% Mg2Ni0.7Co0.3 — (15, 10, 5) wt% C mechanically activated for 30 min under argon in a planetary mill, were obtained. Their absorption-desorption characteristics were investigated under a pressure P = 1 MPa and temperatures of 623, 573, 473, 423 and 373 K. Desorption was carried out at 623 K and 573 K and a pressure of 0.15 MPa. All the three composites showed improved hydriding kinetics as compared to pure magnesium. However, the desorption temperature was somewhat higher than needed for practical application.      

Determination of submillimolar concentration of ferrate(VI) in alkaline solutions by amperometric titration

A new amperometric titration method was developed for quantitative determination of ferrate(VI) (Fe^VIO₄ ²⁻) in the 7.06×10⁻⁵−5.73×10⁻³ M concentration range. Chromium(III) hydroxide solution was used as the titrant. The diffusion current (Id) had a linear relationship with the concentration of ferrate(VI) and slopes were dependent on the concentration of NaOH. The amperometric titration could detect a lower concentration of ferrate(VI) than could potentiometric and colorimetric titrations. The method was applied successfully to determine concentrations of ferrate(VI), generated electrochemically, in strong alkaline solutions.      

Effect of the polymeric coating over Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> particles used for magnetic separation

In this work, the synthesis of magnetite nanoparticles by two variant chemical coprecipitation methods that involve reflux and aging conditions was investigated. The influence of the synthesis conditions on particle size, morphology, magnetic properties and protein adsorption were studied. The synthesized magnetite nanoparticles showed a spherical shape with an average particle size directly influenced by the synthesis technique. Particles of average size 27 nm and 200 nm were obtained. When the coprecipitation method was used without reflux and aging, the smallest particles were obtained. Magnetite nanoparticles obtained from both methods exhibited a superparamagnetic behavior and their saturation magnetization was particle size dependent. Values of 67 and 78 emu g⁻¹ were obtained for the 27 nm and 200 nm magnetite particles, respectively. The nanoparticles were coated with silica, aminosilane, and silica-aminosilane shell. The influence of the coating on protein absorption was studied using Bovine Serum Albumin (BSA) protein.      

Proposal for a mercury isolation procedure using cold vapor method in combination with voltammetric determination using a rotating gold electrode

The optimal process of pre-treatment and activation of gold rotating disc electrode (AuRDE) before voltammetric determination of mercury is proposed. This treatment encompasses polishing of the electrode surface, electrochemical cycling, and activation. This procedure both increases determination sensitivity as well as improves determination reproducibility. The detection limit on the working electrode achieved using this approach amounted to 8.26·10⁻¹⁰ mol L⁻¹for direct mercury determination in water solution (applying 200 s running accumulation). The procedure of the quantitative mercury isolation from complicated sample matrix was developed as well. It provides better selectivity and significant increase of sensitivity of mercury determination. In case of mercury isolation from one liter of water the detection limit is 6.23·10⁻¹¹ mol L⁻¹ (analyzing a greater sample volume the determined concentration could be lower).      

Controlled synthesis,characterization and thermal properties of Mg<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>

Optimum conditions for synthesizing monoclinic and triclinic Mg₂B₂O₅ compounds by high-temperature solid-state reactions were investigated. Mixtures composed of boric acid and magnesium oxide at MgO:B₂O₃ mole ratios of 1:0.25, 1:0.5 and 1:1.5 were heated for 1 hour at temperatures between 600–1050°C and the formed phases were identified by XRD analysis. Monoclinic Mg₂B₂O₅ was formed by heating at 850°C for 4 hours together with minimum amounts of triclinic Mg₂B₂O₅, while triclinic Mg₂B₂O₅ was formed as a single phase at 1050°C for the same reaction time. The products obtained at optimum conditions were subjected to a series of tests to determine their chemical compositions, particle size distributions, surface area values, IR spectra and TG/DTA patterns.      

Methylcellulose/SiO<Subscript>2</Subscript> hybrids: sol-gel preparation and characterization by XRD,FTIR and AFM

Methylcellulose (MC) / SiO₂ organic / inorganic hybrid materials have been prepared from MC and methyltriethoxysilane or ethyltrimethoxysilane, and characterized by XRD, FTIR and AFM. XRD showed peak shifts. FTIR shows intermolecular hydrogen bonding between MC and SiO₂. AFM depicts surface roughness which depends on the silica precursor and MC content.