Solubility of monazite chemical components in humic acid solutions

The α-factor is a measure of the epithermal neutron flux deviation from the ideal distribution 1/E, where E is neutron energy. It defends on the position of the irradiation channel in reactor. A determination method of the α-factors in irradiation channels of Dalat reactor is presented by fitting the epithermal neutron spectrum obtained from the calculation using MCNP code. The fitting α-values were compared to those by experiment used the “Cd-ratio” method with monitors ¹⁹⁷Au–⁹⁴Zr and ¹⁹⁷Au–⁶⁴Zn. It shows that the α-values calculated from neutron spectra agree well with experimental ones. The difference between both data is about 6%.     

Uneven Dielectric Barrier Discharge Reactors for Diesel Particulate Matter Removal

Uneven dielectric barrier discharge (DBD) reactors driven by positive–negative pulse plasma discharges were investigated for particulate matter (PM) removal from a diesel engine. Two kinds of uneven alumina plates and three kinds of uneven stainless steel plates were used to assemble six kinds of uneven DBD reactors of discharge gaps 0.4–1.0 mm. The experimental results show that PM from diesel engines can be removed using the uneven DBD reactors. The maximum PM removal was 67% at 300 W energy injections using the DBD reactor of 0.4 mm gap distance. PM removal increased with decreasing gap distance. The energy efficiency using the uneven DBD reactor of a shorter gap distance was higher than that using the uneven DBD reactor of a longer gap distance as the uneven DBD reactor of a shorter gap distance has a higher PM deposition rate. The energy efficiency was typically in a range of 3–10.6 g/kWh at an energy density of 2–16 J/L. A comparison of this study with reports given by other research groups is given.     

The effect of nanoparticle growth on rheological properties of silica and silicate dispersions

CdS and ZnS nanoparticles were prepared in the solid–liquid interfacial adsorption layer as a nanophase reactor. The substrates were hydrophilic and hydrophobic aerosils and hydrophilic layer silicates dispersed in ethanol–cyclohexane mixtures. The growth of particles at various surface concentration of precursor ions was monitored by absorption spectroscopy, band-gap-energy measurements and particle diameter measurements. Also, the rheological properties of nanoparticle–support composites in organic and aqueous dispersions were measured. The energy of separation between the nanoparticles depended on the particle diameter. The intercalation of nanoparticles in the layered silicates yielded a nanostructured two-phase system. The presence of semiconductive subcolloids was proven by transmission electron microscopy measurements, which offer an excellent possibility for the determination of the particle size distribution. Received: 20 July 1999/Accepted in revised form: 22 September 1999     

Theoretical treatment of first-order reversible reactions occurring in a chromatographic reactor, on the basis of consecutive reactions

Summary Analytical peak-shape equations were derived for first-order reversible reactions occurring in a chromatographic reactor by treating the reversible reactions as consecutive reactions with alternating products. The results of the analytical peak-shape equations were compared with those from a numerical solution of the partial differential equation system modeling the chromatographic reactor. For small to medium conversions the correspondence was found to be sufficiently close to enable substitution of the numerical solution in fitting procedures for the determination of rate constants. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Determination of boron range distribution in ion-implanted silicon by the10B(n, α)7 Li reaction

A measuring technique based on the alpha particles being released from the¹⁰B(n, α) nuclear reaction and using the time-of-flight technique at a periodically pulsing reactor was developed. Non-destructive determination for the range distribution of boron impurities in ion-implanted silicon have been performed. Projected ranges obtained in the energy region 20–80 keV are compared to calculated results and to other experiments. Examples are shown for some typical boron distributions before and after annealing the sample.     

Ion-exchange-membrane-based enzyme micro-reactor coupled online with liquid chromatography-mass spectrometry for protein analysis

In this article, we developed a membrane-based enzyme micro-reactor by directly using commercial polystyrene–divinylbenzene cation–exchange membrane as the support for trypsin immobilization via electrostatic and hydrophobic interactions and successfully applied it for protein digestion. The construction of the reactor can be simply achieved by continuously pumping trypsin solution through the reactor for only 2 min, which was much faster than the other enzyme immobilization methods. In addition, the membrane reactor could be rapidly regenerated within 35 min, resulting in a “new” reactor for the digestion of every protein sample, completely eliminating the cross-interference of different protein samples. The amount and the activity of immobilized trypsin were measured, and the repeatability of the reactor was tested, with an RSD of 3.2% for the sequence coverage of cytochrome c in ten digestion replicates. An integrated platform for protein analysis, including online protein digestion and peptide separation and detection, was established by coupling the membrane enzyme reactor with liquid chromatography–quadrupole time-of-flight mass spectrometry. The performance of the platform was evaluated using cytochrome c, myoglobin, and bovine serum albumin, showing that even in the short digestion time of several seconds the obtained sequence coverages was comparable to or higher than that with in-solution digestion. The system was also successfully used for the analysis of proteins from yeast cell lysate.     

Continuous Production of Thermostable α-Amylase by Immobilized Bacillus Cells in a Fluidized-Bed Reactor

The exponential cells ofBacillus cereus immobilized in calcium alginate and spun into microcylindrical particles were used in a fluidized-bed reactor for continuous synthesis of thermostable α-amylase. The reactor was operated over a period of 30 d with a dilution rate of 0.33 h^-1, producing 1000–1200 U/mL of enzyme. The productivity of the reactor was in the range of 330–396 kU/h. A 20-fold increase in the productivity with respect to batch fermentation with free cells was attained.     

Flow injection on-line sorption preconcentration of platinum in a knotted reactor coupled with electrothermal atomic absorption spectrometry

A flow injection on-line sorption preconcentration method for the electrothermal AAS determination of platinum has been developed. The pyrrolidine dithiocarbamate complexes of either Pt⁴⁺ or Pt²⁺, formed in 0.7 mol L^–1 HNO₃, are on-line adsorbed on the inner walls of a PTFE knotted reactor and subsequently eluted with methanol. An enhancement factor of 112 and a detection limit (3 σ) of 10 ng L^–1 along with a sampling frequency of 21 h^–1 are achieved with a 90 s preconcentration time at a sample flow rate of 8.8 mL min^–1. The relative standard deviation is 2.5% for 0.4 μg L^–1 Pt. The method has been applied to the determination of platinum in blood samples. Received: 6 October 1997 / Revised: 26 November 1997 / Accepted: 3 December 1997     

Determination of total iron in ground waters and multivitamin tablets using a solid-phase reactor with tiron immobilised on amberlite ion-exchange resin in a flow injection system

A method is described for the flow injection determination of total iron as Fe(III) using a solid-phase reactor containing disodium-1,2-dihydroxybenzene-3,5-disulphonate (tiron) as substrate. The iron(III) reacted with tiron to form a complex which absorbs strongly at 667 nm, where it was measured spectrophotometrically. The system has a linear range of 1 to 50 mg L^–1 with a detection limit of 0.67 mg L^–1. It is suitable for the determination of total iron in multivitamin tablets and iron-rich ground waters, with a relative standard deviation of better than 1.1%. The results obtained compared favourably with the certified values and a standard ICP-AES method. Received: 12 November 1997 / Revised: 9 March 1998 / Accepted: 15 March 1998     

Development of a combined SEM and ICP-MS approach for the qualitative and quantitative analyses of metal microparticles and sub-microparticles in food products

An integrated approach based on the use of inductively coupled plasma mass spectrometry (ICP-MS) and scanning electron microscopy (SEM) for the qualitative and quantitative analyses of metal particles in foods was devised and validated. Different raw materials and food products, like wheat, durum wheat, wheat flour, semolina, cookies, and pasta were considered. Attention was paid to the development of sample treatment protocols for each type of sample to avoid potential artifacts such as aggregation or agglomeration. The analytical protocols developed followed by ICP-MS and SEM investigations allowed us the quantitative determination and the morphological and dimensional characterization of metal nano- and microparticles isolated from the raw materials and finished food products considered. The ICP-MS method was validated in terms of linearity (0.8–80 μg/g and 0.09–9 μg/g for Fe and Ti, respectively), quantification limits (0.73 μg/g for Fe and 0.09 μg/g for Ti), repeatability (relative standard deviation (RSD) % equal to 10% for Fe and 20% in a wheat matrix as an example), and extraction recoveries (93 ± 2–101 ± 2%). Validation of the scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDS) measurements was performed working in a dimensional range from 1 to 100 μm with an estimated error in the size determination equal to 0.5 μm. ICP-MS data as well as SEM measurements showed a decrease in the concentration of metal particles from wheat to flour and from durum wheat to semolina samples, thus indicating an external contamination of grains by metal particles. These findings were confirmed by environmental SEM analysis, which allowed investigation of particles of lower dimensions. Generally, the largest number of particles was found in the case of iron and titanium, whereas particles of copper and zinc were only occasionally found without any possibility of quantifying their number.     

Optimisation of supercritical fluid extraction of polynuclear aromatic hydrocarbons from spiked soil and marine sediment standard reference material

 For the determination of 16 PAHs in soils and sediment samples by GC/FID and GC/MS, the dynamic off-line supercritical fluid extraction with both pure and modified carbon dioxide has been evaluated. The optimisation of extraction parameters was performed for four individual groups of PAHs according to their number of aromatic rings (2–3 rings, 4 rings, 5 rings and 6 rings) by varying pressure (200–510 bar), temperature (50–150 °C), extraction fluid volume (10–50 ml), and the methanol modifier concentration (0–10%). Using a five level spherical factorial experimental design the number of experiments required for optimisation was 45. In spiked soil samples extraction efficiencies of 80–100% were achieved for the individual groups of PAHs. At the optimal set of conditions 10–30% lower recoveries of PAHs were obtained for the standard reference material NIST SRM 1941a (marine sediment). The largest differences between extraction recoveries of native and spiked PAHs occurred at high molecular weight PAHs. Using SFE efficiency data for the standard reference material, cluster analysis proved that dividing the 16 PAHs into four groups according to their number of aromatic rings was appropriate and correct. Received: 2 February 1996/Revised: 26 November 1996/Accepted: 30 November 1996     

Trace analysis of high-purity graphite by LA–ICP–MS

Laser-ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) has been established as a very efficient and sensitive technique for the direct analysis of solids. In this work the capability of LA–ICP–MS was investigated for determination of trace elements in high-purity graphite. Synthetic laboratory standards with a graphite matrix were prepared for the purpose of quantifying the analytical results. Doped trace elements, concentration 0.5 μg g^–1, in a laboratory standard were determined with an accuracy of 1% to ± 7% and a relative standard deviation (RSD) of 2–13%. Solution-based calibration was also used for quantitative analysis of high-purity graphite. It was found that such calibration led to analytical results for trace-element determination in graphite with accuracy similar to that obtained by use of synthetic laboratory standards for quantification of analytical results. Results from quantitative determination of trace impurities in a real reactor-graphite sample, using both quantification approaches, were in good agreement. Detection limits for all elements of interest were determined in the low ng g^–1 concentration range. Improvement of detection limits by a factor of 10 was achieved for analyses of high-purity graphite with LA–ICP–MS under wet plasma conditions, because the lower background signal and increased element sensitivity. Received: 4 January 2001 / Revised: 27 March 2001 / Accepted: 28 March 2001     

Photoneutrons from a beryllium reflector: a potential source of problems with Zr–Au flux monitors in <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript> standardization based neutron activation analysis

The assumption that the shape of the epithermal neutron spectrum can be described, in any research reactor, by the 1/E ^1+α function is a fundamental starting point of the k ₀ standardization. This assumption may be questioned from a reactor physics viewpoint. The type of moderator, the existence of neutron reflectors, the additional production of (γ, n) neutrons and resonance capture by construction materials may be different for each reactor, with consequences for the shape of the neutron spectrum. This dependency may explain that various practitioners reported contradicting experiences with the use of Zr–Au flux monitors for the determination of the α-parameter. An objective view on the influence of the design of the reactor and irradiation facility on the shape of the neutron spectrum can be obtained by modeling. This has been applied in the Reactor Institute Delft for reactor configurations in which the irradiation facilities face the fuel elements with the presence of beryllium reflector elements. The Monte Carlo calculations indicate a distortion of the 1/E ^1+α relationship at the higher energy edge of the epithermal neutron spectrum. This distortion is attributed to the formation and thermalisation of both photoneutrons and (n, 2n) produced fast neutrons in the beryllium, and has a direct impact on the resonance activation of ⁹⁵Zr, other than represented by the 1/E ^1+α function. The obtained relationship between neutron flux and neutron energy was also used for estimating the f-value and compared with the value obtained by the Delft Cr–Mo–Au flux monitor.     

The Merrifield–Simmons index in (<Emphasis Type="Italic">n</Emphasis>, <Emphasis Type="Italic">n</Emphasis> + 1)-graphs

A (n, n + 1)-graph G is a connected simple graph with n vertices and n + 1 edges. In this paper, we determine the upper bound for the Merrifield–Simmons index in (n, n + 1)–graphs in terms of the order n, and characterize the (n, n + 1)–graph with the largest Merrifield–Simmons index.     

Ethanol Production from Wet-Exploded Wheat Straw Hydrolysate by Thermophilic Anaerobic Bacterium Thermoanaerobacter BG1L1 in a Continuous Immobilized Reactor

Thermophilic ethanol fermentation of wet-exploded wheat straw hydrolysate was investigated in a continuous immobilized reactor system. The experiments were carried out in a lab-scale fluidized bed reactor (FBR) at 70°C. Undetoxified wheat straw hydrolysate was used (3–12% dry matter), corresponding to sugar mixtures of glucose and xylose ranging from 12 to 41 g/l. The organism, thermophilic anaerobic bacterium Thermoanaerobacter BG1L1, exhibited significant resistance to high levels of acetic acid (up to 10 g/l) and other metabolic inhibitors present in the hydrolysate. Although the hydrolysate was not detoxified, ethanol yield in a range of 0.39–0.42 g/g was obtained. Overall, sugar efficiency to ethanol was 68–76%. The reactor was operated continuously for approximately 143 days, and no contamination was seen without the use of any agent for preventing bacterial infections. The tested microorganism has considerable potential to be a novel candidate for lignocellulose bioconversion into ethanol. The work reported here also demonstrates that the use of FBR configuration might be a viable approach for thermophilic anaerobic ethanol fermentation.     

Obtaining calcium carbonate in a multiphase system by the use of new rotating disc precipitation reactor

Rotating disc reactor (RDR) was constructed to conduct gas–liquid–solid reactions with controlled reagent transfer from gaseous to liquid phase. The concept is based on continuous formation of thin liquid films at a surface of rotating discs where the mass transfer proceed in diffusion–convective way. The reactor was employed to run precipitation reaction of CaCO₃ via carbon dioxide absorption in lime slurry. During each reaction pH changes and Ca²⁺ concentration in time were measured. Disc rotations and gas flows were changed during the experiment and their influence on the obtained CaCO₃ powders has been examined and fully discussed.     

Comparison of anoxic granulation in USB reactors with various inocula

Anoxic granulation process with four different inocula was monitored in a laboratory post-denitrification up-flow sludge bed (USB) reactor. Wastewater containing 20 mg L⁻¹ NO₃-N and methanol as an organic carbon source was used. Gradual increase of mass volumetric loading (B _v) and hydraulic loading (γ) resulted in spontaneous granulation of anoxic biomass both from flocculant activated sludge and from anaerobic granulated sludge. With flocculant activated sludge as the inoculum, anoxic granules sedimentation properties and maximum loadings of the USB reactor depended on the sludge volume index (SVI) of the inoculum. B _v,max achieved in the USB reactor with flocculant inoculum from a municipal wastewater treatment plant (SVI = 208 mL g⁻¹) was only 4.2 kg of COD per m³ per day and 0.7 kg of NO₃-N per m³ per day. B _v,max using flocculant inoculum from an industrial wastewater treatment plant (SVI = 170 mL g⁻¹) was 8.1 kg of COD per m³ per day and 1.35 kg of NO₃-N per m³ per day. With anaerobic granulated inoculum (SVI range 8–11 mL g⁻¹), markedly higher loadings in the USB reactor and lower SVI values of anoxic granulated biomass were achieved. Values of B _v,max were in the range of 16.1–22.4 kg of COD per m³ per day and of 2.7–3.7 kg of NO₃-N per m³ per day (depending on the inoculum and the granulation procedure). It was proved that anaerobic granulated sludge is not just an inoculum, it is also a carrier for new denitrification biomass.     

Biochemical properties of genetic recombinant xylanase II

An ultraviolet (UV) coil reactor was designed and used for the online sterilization of cheese whey. Its microbial destruction efficiency was compared to that of the conventionally used UV reactor. Both reactors have the same geometry (840 ml volume and 17 mm gap size) and were tested at 11 flow rates of 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, and 70 ml/min. The results obtained from this study showed that despite of its high turbidity, cheese whey could be sterilized using UV radiation if the proper reactor design and flow rate are used. The performances of the UV reactors were governed by the flow rate and the hydraulics of flow inside the reactor. The flow was laminar in both the reactors, as the Reynolds number was in the range of 1.39–20.10. The phenomenon of Dean Flow was observed in the coil reactor and the Dean number was in the range of 1.09–15.41. Dean vortices resulted in higher microbial destruction efficiency in the coil reactor in a shorter retention time. The rate of microbial destruction was found to be exponential in the conventional reactor and polynomial in the coil reactor. Increasing the flow rate from 5 ml/min to 70 ml/min decreased the microbial destruction efficiency of the conventional reactor from 99.40 to 31.58%, while the microbial destruction efficiency in the coil reactor increased from 60.77% at the flow rate of 5 ml/min to 99.98% at the flow rate of 30 ml/min and then decreased with further increases in flow rate reaching 46.2% at the flow rate of 70 ml/min. The maximum effluent temperatures in the conventional and coil reactors were 45.8 and 46.1°C, respectively. Fouling in the coil reactor was significantly less compared to the conventional reactor. The extent of fouling was influenced by flow rate and reactor’s hydraulics.     

Absorption spectra of carbohydrates and related compounds in H2SO4

The possibility of modifying the Dreywood anthrone method for spectrophotometric determination of carbohydrates in order to increase the accuracy and reproducibility of the results was examined. The classical method and a developed modification were compared. The relative uncertainty in a determination by the modified method was less than 4%. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 218–220, May–June, 2006.     

Electrochemical deposition and corrosion stability of Zn–Co alloys

Electrochemically deposited Zn–Co alloys under various deposition conditions were investigated using anodic linear sweep voltammetry for phase structure determination, scanning electron microscopy for surface morphology analysis, atomic absorption spectroscopy for determination of chemical composition, and polarization measurements and open circuit potential measurements for determination of corrosion properties. The influence of deposition current density, temperature, and composition of deposition solution on the phase structure and corrosion properties of Zn–Co alloys was studied. It was shown that the ratio of cobalt to zinc ions in the plating bath strongly affects the chemical content and phase structure, as well as corrosion stability, of Zn–Co alloys. Zn–Co alloys deposited from plating baths with the lowest and the highest ratios of cobalt and zinc ions exhibited the lowest corrosion rate.