Development of a PIXE method at high energy with the ARRONAX cyclotron

The high energy PIXE (HEPIXE) method is a multi-elemental non-destructive ion beam analysis technique. It is based on the detection of the X-ray emitted due to the interaction of high energy particle beam with a sample. This technique is fast and allows the analysis of heavy and medium elements in thin (μm), thick (mm) and multilayer samples. At the ARRONAX facility (Nantes, France), the HEPIXE method has been used to determine the composition of natural and synthetic sodalites. Photochromic properties of these samples are supposed to come from the trace elements (concentration in the ppm range) present in the samples. Taking advantage of the 70 MeV proton beam available at our facility, the HEPIXE method has been also used to study multilayer samples. It has been shown that it is possible to determine the composition of each layer, their thicknesses and their depth position by analyzing the recorded X-ray spectra.     

Use of hydroxylapatite composite membranes for analysis of bisphenol A

This study evaluates solid-phase micro-extraction (SPME) coupled with gas chromatography–mass spectrometry (GC–MS) to determine trace levels of bis-phenol A in water and leached from plastic containers. In our study, we used very thin composite membranes prepared in the laboratory. The extraction using headspace post-derivatization with bis(trimethylsilyl) trifluoroacetamide (BSTFA), containing 1 % trimethylchlorosilane (TMCS) vapor, following SPME was compared with extraction without derivatization. The SPME experimental procedures to extract bis-phenol A in water were optimized with a relatively polar polyacrylate (PA)-coated fiber, an extraction time of 50 min, and desorption at 300 °C for 2 min. Headspace derivatization following SPME was performed using 7 μL of BSTFA with 1 % TMCS at 65 °C for 30 s. The precision was 5.2 % without derivatization and 9.0 % headspace derivatization. The detection limit was determined to be at the nanogram per liter level. When SPME was used following headspace derivatization, the detection limit was one order of magnitude better than that achieved without derivatization. The results of this study reveal the adequacy of the SPME–GC–MS method for analyzing bisphenol A leached from plastic containers. The concentrations of bisphenol A leached from plastic containers into water ranged from 0.7 to 78.5 μg L^?1.     

Haloperidol imprinted polymer: preparation,evaluation, and application for drug assay in brain tissue

Several molecularly imprinted polymers (MIPs) were prepared in the present work, and their binding properties were evaluated in comparison with a nonimprinted polymer (NIP). An optimized MIP was selected and applied for selective extraction and analysis of haloperidol in rabbit brain tissue. A molecularly imprinted solid-phase extraction (MISPE) method was developed for cleanup and preconcentration of haloperidol in brain samples before HPLC-UV analysis. Selectivity of the MISPE procedure was investigated using haloperidol and some structurally different drugs with similar polarity that could exist simultaneously in brain tissue. The extraction and analytical process was calibrated in the range of 0.05–10 ppm. The recovery of haloperidol in this MISPE process was calculated between 79.9 and 90.4 %. The limit of detection (LOD) and the limit of quantification (LOQ) of the assay were 0.008 and 0.05 ppm, respectively. Intraday precision and interday precision values for haloperidol analysis were less than 5.86 and 7.63 %, respectively. The MISPE method could effectively extract and concentrate haloperidol from brain tissue in the presence of clozapine and imipramine. Finally, the imprinted polymer was successfully applied for the determination of haloperidol in a real rabbit brain sample after administration of a toxic dose. Therefore, the proposed MISPE method could be applied in the extraction and preconcentration before HPLC-UV analysis of haloperidol in rabbit brain tissue.     

Determination of methylisothiocyanate in soil and water by HS-SPME followed by GC–MS–MS with a triple quadrupole

Methylisothiocyanate (MITC) is the main degradation product of metam sodium, a soil disinfectant widely used in agriculture, and is responsible for its disinfectant properties. Because MITC is highly toxic and volatile, metam sodium has to be applied in a manner that tries to reduce atmospheric emissions but still maintains adequate concentration of MITC in soil to ensure its disinfectant effect. Thus, monitoring of MITC concentrations in soil is required, and to this end sensitive, fast, and reliable analytical methods must be developed. In this work, a headspace solid-phase microextraction (HS-SPME) method was developed for MITC determination in water and soil samples using gas chromatography-tandem mass spectrometry (GC–MS–MS) with a triple-quadrupole analyzer. Two MS–MS transitions were acquired to ensure the reliable quantification and confirmation of the analyte. The method had linear behavior in the range tested (0.026–2.6 ng mL^?1 in water, 1–100 ng g^?1 in soil) with r ² over 0.999. Detection limits were 0.017 ng mL^?1 and 0.1 ng g^?1 in water and soil, respectively. Recoveries for five replicates were in the range 76–92 %, and RSD was below 7 % at the two spiking levels tested for each matrix (0.1 and 1 ng mL^?1 for water, 4 and 40 ng g^?1 for soil). The potential of using multiple HS-SPME for analyzing soil samples was also investigated, and its feasibility for quantification of MITC evaluated. The developed HS-SPME method was applied to soil samples from experimental plots treated with metam sodium following good agriculture practices. Figure

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Interactions of collagen and cellulose in their blends with 1-ethyl-3-methylimidazolium acetate as solvent

Collagen/cellulose blended solutions with collagen/cellulose mass ratio (Col/Cel) of 0, 1/40, 1/20, 1/10 and 1/5 were prepared using [Emim]Ac as solvent. The interactions between the two polymers before and after regeneration were investigated. In steady shear flow, all of the experimental viscosity values were greater than those of the estimated values calculated from the log-additivity rule for each sample, suggesting interactions between the two polymers in solutions. All solutions exhibited shear thinning behavior and the flow curves could be described by Cross model. Zero shear viscosity (η ₀) versus Col/Cel was examined and a linear increase (from 8.73 to 16.39 Pa·s) can be observed for η ₀ as Col/Cel ≤ 1/10, while there was only a slight increase (from 16.39 to 18.42 Pa·s) in η ₀ as Col/Cel increased to 1/5. Dynamic rheology results suggested the existence of aggregates in solution with Col/Cel = 1/10. Furthermore, the activation energy of solution was 84.5 kJ mol^?1 as Col/Cel = 1/10, higher than that of cellulose solution (44.2 kJ mol^?1). Regenerated films were prepared and characterized to trace back the interactions between the two polymers in [Emim]Ac. Fourier transform infrared spectroscopy indicated the hydrogen-bond interaction between collagen and cellulose in films. The denaturation temperature of collagen in films with Col/Cel ≤ 1/10 could be improved, but it was decreased with the increase of collagen content, and finally was reduced to be close to that of collagen as Col/Cel = 1/5. The features of dynamic mechanical analysis for films were indicative of the lack of homogeneity between collagen and cellulose as Col/Cel = 1/5. Atomic force microscopy images further confirmed the phase-separation when Col/Cel = 1/5.     

Evaluation of natural gamma radiation and absorbed gamma dose in soil and rocks of Perambalur district (Tamil Nadu,India)

The activity concentrations and absorbed gamma dose of primordial radionuclides ²³⁸U, ²³²Th and ⁴⁰K were determined employing γ-ray spectrometry in 31 soil samples from the land area earmarked for house construction in Perambalur district and 14 rock samples from quarries that supply stones for the entire district. The soil samples registered relatively a higher mean value of 13.2 Bq kg^?1 for ²³⁸U, 66 Bq kg^?1 for ²³²Th and 340.3 Bq kg^?1 for ⁴⁰K as compared to mean values for rock samples (²³⁸U—8.0 Bq kg^?1; ²³²Th—65.1 Bq kg^?1; ⁴⁰K—199.1 Bq kg^?1). The mean absorbed gamma dose rate for soil (61.4 nGy h^?1) marginally exceeded the prescribed limit of 55 nGy h^?1 while, rocks registered the mean absorbed gamma dose rate of 10.4 nGy h^?1. The mean radium equivalent activity was distinctly higher in soil (130.6 Bq kg^?1) than in rock (20.0 Bq kg^?1). However, these values were lower than the limit (370 Bq kg^?1) set by OECD for building materials. It is evident from the data that the soil and rocks do not pose any radiological risk for house constructions in Perambalur district.     

Development of a certified reference material for the determination of perfluorooctanoic acid

A certified reference material (CRM) for the determination of perfluorooctanoic acid (PFOA) has been issued as NMIJ CRM 4056-a by the National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). Purity (kg kg^?1) based on a titration method was determined by subtracting the mass fractions of impurities measured using liquid chromatography/mass spectrometry (LC/MS) from those of acids expressed as PFOA measured by a neutralization potentiometric titration. To validate an obtained result, purity based on a mass balance method was determined by subtracting the mass fractions of impurities, measured using LC/MS, Karl-Fischer titration (KFT), and vacuum evaporation, from 1 kg kg^?1. Results from both titration and mass balance methods were in agreement within the accepted limits of uncertainty. The certified purity of NMIJ CRM 4056-a was determined to be 0.959 kg kg^?1, calculated as the mean of the results obtained with the two methods. The standard uncertainty of the certified purity was evaluated from purity evaluations as well as from sample homogeneity and stability obtained from LC/MS and KFT analyses. Consequently, the expanded uncertainty was estimated to be 0.005 kg kg^?1 with a coverage factor of k = 2.     

Rapid screening and detection of XOD inhibitors from S. tamariscina by ultrafiltration LC-PDA–ESI-MS combined with HPCCC

Xanthine oxidase (XOD) catalyzes the metabolism of hypoxanthine and xanthine to uric acid, the overproduction of which could cause hyperuricemia, a risk factor for gout. Inhibition of XOD is a major treatment for gout, and biflavonoids have been found to act as XOD-inhibitory compounds. In this study, ultrafiltration liquid chromatography with photodiode-array detection coupled to electrospray-ionization tandem mass spectrometry (UF-LC-PDA–ESI-MS) was used to screen and identify XOD inhibitors from S. tamariscina. High-performance counter-current chromatography (HPCCC) was used to separate and isolate the active constituents of these XOD inhibitors. Furthermore, ultrahigh-performance liquid chromatography (UPLC) and triple-quadrupole mass spectrometry (TQ-MS) was used to determine the XOD-inhibitory activity of the obtained XOD inhibitors, and enzyme kinetics was performed with Lineweaver–Burk (LB) plots using xanthine as the substrate. As a result, two compounds in S. tamariscina were screened as XOD inhibitors: 65.31 mg amentoflavone and 0.76 mg robustaflavone were isolated from approximately 2.5 g?S. tamariscina by use of HPCCC. The purities of the two compounds obtained were over 98 % and 95 %, respectively, as determined by high-performance liquid chromatography (HPLC). Lineweaver–Burk plot analysis indicated that amentoflavone and robustaflavone were non-competitive inhibitors of XOD, and the IC ₅₀ values of amentoflavone and robustaflavone for XOD inhibition were 16.26 μg mL^?1 (30.22 μmol L^?1) and 11.98 μg mL^?1 (22.27 μmol L^?1), respectively. The IC ₅₀ value of allopurinol, used as the standard, was 7.49 μg mL^?1 (46.23 μmol L^?1). The results reveal that the method for systematic screening, identification, and isolation of bioactive components in S. tamariscina and for detecting their inhibitory activity using ultrafiltration LC–ESI-MS, HPCCC, and UPLC–TQ-MS is feasible and efficient, and could be expected to extend to screening and separation of other enzyme inhibitors. Graphical Abstract

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Preparation,thermal property,and thermal stability of microencapsulated n-octadecane with poly(stearyl methacrylate) as shell

This study focused on preparation and thermal properties of poly(stearyl methacrylate) shell (PSMA) microcapsules containing n-octadecane as a phase change material (PCM). Pentaerythritol triacrylate (PETA) and divinylbenzene (DVB) were employed as crosslinking agents. The surface morphologies, particle sizes, and distributions of the microencapsulated phase change material (microPCM) were studied by scanning electron microscopy. The thermal properties, thermal reliabilities, and thermal stabilities of the microPCMs were investigated by differential scanning calorimetry and thermal gravimetric analysis. The microPCM with DVB exhibits higher phase change enthalpies of melting (87.9 J g^?1) and crystallization (94.8 J g^?1) and a greater thermal stability in comparison with the microPCM with PETA. The phase change temperatures and enthalpies of the microPCMs varied little after thermal cycles. Thermal images showed that the gypsum board with PSMA/n-octadecane microPCM possessed temperature-regulated property. Therefore, microencapsulated n-octadecane with PSMA as shell has good thermal energy storage and thermal regulation potential.     

A new ELISA for the quantification of equine procalcitonin in plasma as potential inflammation biomarker in horses

In human medicine, procalcitonin (PCT) is a very common and well-established biomarker for sepsis. Even though sepsis is also a leading cause of death in foals and adult horses, up to now, no data about the role of equine PCT in septic horses has been available. Based on monoclonal antibodies targeted against human PCT, we report here the development of a sandwich ELISA for the quantification of equine PCT in equine plasma samples. The ELISA was characterized for intra- and interassay variance and a working range from 25 to 1,000 ng mL^?1 was defined as within this range; both intra- and interassay variances were below 15 %. The target recovery ranged between 73 and 106 %. The ELISA was used to determine the equine PCT concentration in 24 healthy and 5 septic horses to show the potential for clinical evaluation of equine PCT. Significantly different (P?=?0.0006) mean equine PCT concentrations were found for the healthy control group and the sepsis group (47 and 8,450 ng mL^?1).     

Functional Microgels Assisted Tryptic Digestion and Quantification of Cytochrome c Through Internal Standard Mass Spectrometry

Quantitation of cytochrome c (Cyt c) in cell lysates through surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using gold nanoparticles (Au NPs) as the matrix and GR-10 peptide as an internal standard has been demonstrated. To shorten digestion time, temperature sensitive microgels containing trypsin (TR) and Au NPs have been employed. As-prepared functional microgels (TR/Au NPs/MGs) allow digestion of Cyt c within 15 s under microwave irradiation. The internal standard SALDI-MS approach provides linearity (R² = 0.98) of MS signal ratio (I _1168.6/I _1067.6) of the tryptic digested peptide (m/z 1168.6) to GR-10 peptide (m/z 1067.6) against the concentration of Cyt c ranging from 25 to 200 nM, with a limit of detection (at a signal-to-noise ratio of 3) of 10 nM. This approach has been validated by the analysis of the lysates of HeLa cells, with an average concentration of 13.7?±?3.5 μM for cytoplasmic Cyt c. Increased concentrations of Cyt c in the HeLa cells treated with etoposide (a commercial drug) or carbon dots (potential drug) have been revealed through this simple, sensitive, and rapid SALDI-MS approach, supporting the drugs induced Cyt c-mediated apoptosis of the cells. This study has shown that this internal standard SALDI-MS approach holds great potential for cell study. Graphical Abstract

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Biosorptive profile of synthetic and natural humiresin for the remediation of metallic water pollutants

To evaluate the bioremediation efficiency of natural humic substances, over it’s synthetic counterpart, a comparative batch equilibration biosorption assay have been carried out employing radiotracers on different humi-resins. The biosorptive profile of various humiresins as devised hereby, attempts to justify an innovative and concrete role of dry cow dung powder (DCP), in ‘as it is form’, for the bioremediation of metal pollutants such as Cr(III), Cr(VI), Cd(II), Hg(II) and Sr(II). Our comparative results conclude that, with all other optimized parameters as obtained 100 mg of DCP removes Cr(III) at pH 6, Cd(II) at pH 3 and Hg(II) at pH 3 to 70–75 and 80–85 % respectively. Also, at pH 1 with 250 mg of DCP 70–75 % Cr(VI) is removed. Similarly, 90–95 % of Sr(II) is sequestered at pH 6, with 350 mg of DCP. The study on thermodynamic, kinetic and isotherm modelling of DCP indicates feasible, eco-friendly and efficient process.     

Validation of an LC-MS/MS method for the quantitative determination of a novel fungicide: pyraoxystrobin in rat plasma and its application to a toxicokinetics study

A simple, sensitive, and reliable liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been developed for determination of pyraoxystrobin in rat plasma and applied to a toxicokinetics study. The separation was performed by gradient elution on a Luna 5 μ C18 (2) 100 Å column (50?×?4.6 mm I.D., 5 μm) with mobile phase: water (0.1 % formic acid, v/v)/acetonitrile (0.1 % formic acid, v/v), followed by quantification with a mass detector in multiple reaction monitoring (MRM) mode using ESI as an interface. The calibration curve was linear over a concentration range of 1.00–200 ng/mL. The recovery for pyraoxystrobin ranged from 101.4 to 108.2 %. The intraday bias and precision ranged from ?9.3 to 8.1 % and from 0.7 to 8.4 %, respectively, and the interday bias and precision ranged from ?0.3 to 4.0 % and from 4.4 to 7.2 %, respectively. The toxicokinetics of pyraoxystrobin after single 100 and 1,000 mg/kg oral doses were studied in rats. Figure

The chromatogram of pyraoxystrobin highest calibration standard (ULOQ) extract.     

The effect of the addition of polypropylene-grafted SiO2 nanoparticle on the thermal conductivity of isotactic polypropylene

The thermal conductivity of Isotactic polypropylene (iPP)/silica particle (SiO₂, 26 nm) nanocomposite has been investigated. The untreated SiO₂ and iPP grafted onto SiO₂ were dispersed in the iPP (M _w = 2.5 × 10⁵) matrix. The molecular mass of the iPP-grafted chain, M _n, was precisely controlled to be 5.8 × 10³, 1.2 × 10⁴, and 4.6 × 10⁴. It was found that the thermal conductivities of graft-treated nanocomposites were higher than that of untreated SiO₂ composites. This implied that it is possible to achieve even higher thermal conductivity using the graft treatment. A thermal conductivity analysis conducted using a three-phase model, with considerations for thermal conductivity at interfacial layers, showed that the thermal conductivity of the interfacial layer increased significantly when a graft chain was incorporated. Moreover, the thermal conductivity per graft chain was proportional to the 1/2 power of the molecular mass ( \( M_{\text{n}}^{0.5} \) ). The results strongly suggest that the thermal conductivity pathway of interfacial layer was the main chain direction of iPP-grafted molecular chains.     

Multiresidue Determination of Ten Nonsteroidal Anti-inflammatory Drugs in Bovine,Porcine, and Chicken Liver Tissues by HPLC-MS/MS

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the group of drugs having the therapeutic efficacy of analgesic and antipyretic. To detect health-threatening residues of NSAIDs, a fast and easy multiresidue method based on liquid chromatography tandem mass spectrometry (LC-MS/MS) was described. Ten NSAIDs were extracted from the tissues using 2 mL of acetonitrile and 0.1 mL of 2 mM ammonium formate in distilled water. After clean-up using C18 sorbent, it was evaporated under nitrogen, reconstituted with 1 mL distilled water and analyzed by LC-MS/MS. The method was validated based on guideline for residue testing laboratory. Furthermore, the method has also been applied successfully to detect ten NSAIDs from bovine, porcine, and chicken liver tissues. In a total of 315 liver samples tested, acetylic salicylic acid was detected from 28 porcine and 2 chicken liver tissues at levels of 13?～?576 and 50?～?53 ng/g, respectively. Subsequently, paracetamol was detected in 15 porcine liver tissues with a detection levels of 28?～?381 ng/g. Phenylbutazone and its metabolite, oxyphenylbutazone, were detected at 247 and 15 ng/g range in one of the bovine liver tissue, respectively.     

The Development and Validation of a Stability-Indicating UHPLC-DAD Method for Determination of Perindopril l-Arginine in Bulk Substance and Pharmaceutical Dosage Form

A stability-indicating ultra-high-performance liquid chromatography (UHPLC) method with a diode array detector was developed and validated for the determination of cis/trans isomers of perindopril l-arginine in bulk substance and pharmaceutical dosage form. The separation was achieved on a Poroshell 120 Hilic (4.6 × 150 mm, 2.7 µm) column using a mobile phase composed of acetonitrile–0.1 % formic acid (20:80 v/v) at a flow rate of 1 mL min^?1. The injection volume was 5.0 µL and the wavelength of detection was controlled at 230 nm. The selectivity of the UHPLC-DAD method was confirmed by determining perindopril l-arginine in the presence of degradation products formed during acid–base hydrolysis and oxidation as well as degradation in the solid state, at an increased relative air humidity and in dry air. The method’s linearity was investigated in the ranges 0.40–1.40 µg mL^?1 for isomer I and 0.40–2.40 µg mL^?1 for isomer II of perindopril l-arginine. The UHPLC-DAD method met the precision and accuracy criteria for the determination of the isomers of perindopril l-arginine. The limits of detection and quantitation were 0.1503 and 0.4555 µg mL^?1 for isomer I and 0.0356 and 0.1078 µg mL^?1 for isomer II, respectively.     

Synthesis,Crystal Structure and Magnetic Property of a New Binuclear Copper (II) Complex Containing Water Clusters

A new binuclear copper (II) complex {[Cu₂(phen)₂(tar)(H₂O)]·8H₂O}_n (1) has been synthesized and structurally characterized by single-crystal X-ray diffraction analysis. The complex crystallizes in monoclinic system, space group P2(1), with a = 7.1710(5), b = 22.0124(15), c = 10.6691(7) Å, β = 102.541(1)°, V = 1643.95(19) Å³, Z = 2. Compound 1 is further extended to a 2D supramolecular framework by hydrogen bonds and π–π stacking interactions. Especially, six of the eight uncoordinated water molecules are connected via hydrogen bonding interactions forming 1D chain, which play an important role in the stabilization of the crystal structure. Furthermore, magnetic susceptibility measurements of this complex shows weak antiferromagnetic exchange between the copper (II) ions (J = ?5.92 cm^?1).     

A polyaniline-magnetite nanocomposite as an anion exchange sorbent for solid-phase extraction of chromium(VI) ions

This work describes a novel polyaniline-magnetite nanocomposite and its application to the preconcentration of Cr(VI) anions. The material was obtained by oxidative polymerization of aniline in the presence of magnetite nanoparticles. The parameters affecting preconcentration were optimized by a Box-Behnken design through response surface methodology. Extraction time, amount of magnetic sorbent and pH value were selected as the main factors affecting sorption. The sorption capacity of the sorbent for Cr(VI) is 54 mg g^?1. The type, volume and concentration of the eluents, and the elution time were selected as main factors in the optimization study of the elution step. Following sorption and elution, the Cr(VI) ions were reacted with diphenylcarbazide, and the resulting dye was quantified by HPLC with optical detection at 546 nm. The limit of detection is 0.1 μg L^?1, and all the relative standard deviations are <6.3 %. The nanocomposite was successfully applied to the rapid extraction and determination of trace quantities of Cr(VI) ions in spiked water samples. Figure

A schematic procedure of magnetic solid phase extraction     

Simultaneous sensing of L-tyrosine and epinephrine using a glassy carbon electrode modified with nafion and CeO2 nanoparticles

An electrochemical sensor was developed and tested for detection of L-tyrosine in the presence of epinephrine by surface modification of a glassy carbon electrode (GCE) with Nafion and cerium dioxide nanoparticles. Fabrication parameters of a surfactant-assisted precipitation method were optimized to produce 2–3 nm CeO₂ nanoparticles with very high surface-to-volume ratio. The resulting nanocrystals were characterized structurally and morphologically by X-ray diffractometery (XRD), scanning and high resolution transmission electron microscopy (SEM and HR-TEM). The nanopowder is sonochemically dispersed in a Nafion solution which is then used to modify the surface of a GCE electrode. The electrochemical activity of L-tyrosine and epinephrine was investigated using both a Nafion-CeO₂ coated and a bare GCE. The modified electrode exhibits a significant electrochemical oxidation effect of L-tyrosine in a 0.2 M Britton-Robinson (B-R) buffer solution of pH 2. The electro-oxidation peak current increases linearly with the L-tyrosine concentration in the molar concentration range of 2 to 160 μM. By employing differential pulse voltammetry (DPV) for simultaneous measurements, we detected two reproducible peaks for L-tyrosine and epinephrine in the same solution with a peak separation of about 443 mV. The detection limit of the sensor (signal to noise ratio of 3) for L-tyrosine is ~90 nM and the sensitivity is 0.20 μA μM^?1, while for epinephrine these values are ~60 nM and 0.19 μA μM^?1. The sensor exhibited excellent selectivity, sensitivity, reproducibility and stability as well as a very good recovery time in real human blood serum samples.

Simultaneous electrochemical determination of L-tyrosine and epinephrine in blood plasma with Nafion-CeO₂/GCE modified electrode showing a 443 mV peak-to-peak potential difference between species oxidation peak currents.     

Non-isothermal reduction of silica-supported nickel catalyst precursors in hydrogen atmosphere: a kinetic study and statistical interpretation

A series of silica-supported nickel catalyst precursors was synthesized with different SiO₂/Ni mole ratios (0.20, 0.80 and 1.15). Non-isothermal reduction of Ni catalyst precursors was investigated by temperature-programmed reduction at four different heating rates (2, 5, 10 and 20 °C min^?1), in a hydrogen atmosphere. Kinetic parameters (E _a, A) were determined using Friedman isoconversional method. It was found that for all mole ratios, apparent activation energy is practically constant in conversion range of α = 30–70 %. In considered conversion range, the following values of apparent activation energy were found: E _a = 129.5 kJ mol^?1 (SiO₂/Ni = 0.20), E _a = 133.8 kJ mol^?1 (SiO₂/Ni = 0.80) and E _a = 125.0 kJ mol^?1 (SiO₂/Ni = 1.15). Using two special functions (y(α) and z(α)), the kinetic model was determined. It was established that reduction of Ni catalyst precursors with different SiO₂/Ni mole ratios is a complex process and can be described by two-parameter ?esták–Berggren (SB) autocatalytic model. Based on established values of SB parameters for each mole ratio, the possible mechanism was discussed. It was found that for all investigated ratios, the Weibull distribution function fits very well the experimental data, in the wide range of conversions (α = 5–95 %). Based on obtained values of Weibull shape parameter (θ), it was found that experimentally evaluated density distribution functions of the apparent activation energies can be approximated by the unbalanced peaked normal distribution.