Determination of total gas content and its composition in Indian PFBR blanket pellets

Total gas content and its composition are important specifications for sintered nuclear fuel pellets particularly in the case of fast breeder reactor fuels. Most commonly, total gas content and its composition is determined by hot vacuum extraction-quadrupole mass spectrometry (HVE-QMS). A number of parameters in this methodology such as temperature, duration of heating for quantitative extraction of evolved gases, total volume of the system, gas analysis conditions etc. need to be optimized for reliable measurements. In addition, sensitivity factors for various gases like H₂, CH₄, N₂, CO, O₂ and CO₂ in quadrupole mass spectrometry required for quantification of results have been determined and validated employing reference gas mixtures of known composition. Employing these optimized conditions total gas content and its composition in blanket pellets (uranium oxide pellets) of Indian prototype fast breeder reactor was determined employing HVE-QMS. The relative expanded uncertainty (at a coverage factor k = 2) in the measurement of total gas content excluding hydrogen was estimated as per ISO guidelines and it was found to be 9.2 %.     

A novel electrochemical method for efficient reduction of disulfide bonds in peptides and proteins prior to MS detection

A novel electrochemical (EC) method for fast and efficient reduction of the disulfide bonds in proteins and peptides is presented. The method does not use any chemical agents and is purely instrumental. To demonstrate the performance of the EC reactor cell online with electrospray mass spectrometry, insulin and somatostatin were used as model compounds. Efficient reduction is achieved in continuous infusion mode using an EC reactor cell with a titanium-based working electrode. Under optimized conditions, the presented method shows almost complete reduction of insulin and somatostatin. The method does not require any special sample preparation, and the EC reactor cell makes it suitable for automation. Online EC reduction followed by collision-induced dissociation fragmentation of somatostatin showed more backbone cleavages and improved sequence coverage. By adjusting the settings, the EC reaction efficiency was gradually changed from partial to full disulfide bonds reduction in α-lactalbumin, and the expected shift in charge state distribution has been demonstrated. The reduction can be controlled by adjusting the square-wave pulse, flow rate or mobile phase composition. We have shown the successful use of an EC reactor cell for fast and efficient reduction of disulfide bonds for online mass spectrometry of proteins and peptides. The possibility of online and gradual disulfide bond reduction adds a unique dimension to characterization of disulfide bonds in mid- and top-down proteomics applications.

Pepsin immobilized in dextran-modified fused-silica capillaries for on-line protein digestion and peptide mapping

On-line digestion of proteins under acidic conditions was studied using micro-reactors consisting of dextran-modified fused-silica capillaries with covalently immobilized pepsin. The proteins used in this study differed in molecular weight, isoelectric point and sample composition. The injected protein samples were completely digested in 3 min and the digest was analyzed with micro-high performance liquid chromatography (HPLC) and tandem mass spectrometry (MS/MS). The different proteins present in the samples could be identified with a Mascot database search on the basis of auto-MS/MS data. It proved also to be possible to digest and analyze protein mixtures with a sequence coverage of 55% and 97% for the haemoglobin β- and α-chain, respectively, and 35-55% for the various casein variants. Protease auto-digestion, sample carry-over and loss of signal due to adsorption of the injected proteins were not observed. The backpressure of the reactor is low which makes coupling to systems such as Surface Plasmon Resonance biosensors, which do not tolerate too high pressure, possible. The reactor was stable for at least 40 days when used continuously.     

Modeling of Fischer-Tropsch Synthesis in a Slurry Reactor with Water Permeable Membrane

Fischer-Tropsch synthesis is an important chemical process for the production of liquid fuels and olefins. In recent years, the abundant availability of natural gas and the increasing demand of olefins, diesel, and waxes have led to a high interest to further develop this process. A mathematical model of a slurry membrane reactor used for syngas polymerization was developed to simulate and compare the maximum yields and operating conditions in the reactor with that in a conventional slurry reactor. The carbon polymerization was studied from a modeling point of view in a slurry reactor with a water permeable membrane and a conventional slurry reactor. Simulation results show that different parameters affect syngas conversion and carbon product distribution, such as the hydrogen to carbon monoxide ratio, and the membrane parameters such as membrane permeance.     

Characterization of Gaseous Plasma Sustained in Mixtures of HMDSO and O2 in an Industrial-Scale Reactor

Optical emission spectroscopy and mass spectrometry was used to characterize gaseous plasma in an industrial reactor of volume 5 m³ during deposition of protective coatings. Plasma was created in mixtures of hexamethyldisiloxane (HMDSO) and oxygen at the powers between 1 and 8 kW. The plasma density was somehow below 10¹⁴ m^?3. The flows of both gases were varied up to 200 sccm while the effective pumping speed was adjusted by changing the roots pump rotation speed between 250 and 4000 rpm. At such conditions the HMDSO was only partially dissociated to fragments. The behaviour of optical emission lines and mass ion currents was well correlated indicating that even one single technique was sufficient to monitor the behaviour of plasma at various discharge conditions. The optical emission spectroscopy as a simple and economic method is therefore suitable for controlling key processing parameters in such a plasma reactor.

     

Rapid and Efficient Proteolysis for Protein Analysis by an Aptamer-Based Immobilized Chymotrypsin Microreactor

Efficient protein digestion is a key step for successful mass spectrometry identification. However, traditional in-solution digestion suffers some drawbacks, such as autolysis of protease, long analysis times and lack of control. Recently, specific single-stranded nucleic acids, aptamers, screened from random sequence pools, have been performed high affinity for targets. In this paper, we have developed a novel enzyme reactor, which immobilized chymotrypsin based on aptamer-grafted silica beads. Mixed proteins, which consist of bovine serum albumin, myoglobin, and cytochrome c, were used as samples, to evaluate the digestion performance of the enzymatic reactor. With the use of this novel tool, proteins were digested in 40 min to an extent similar to that achieved with soluble enzyme at 37°C after 16 h. Moreover, enzymatic reactor regeneration was carried out through chymotrypsin elution and re-immobilization. The advanced characteristics of the aptamer-based chymotrypsin reactor demonstrated that aptamers could serve as novel materials for rapid and efficient enzyme immobilization and application in protein studies.     

Direct study of the catalytic decomposition of chlorine and chloromethanes over carbon films

The decompositions of chlorine and chloromethanes over pyrolytic carbon surfaces have been studied by modulated beam mass spectrometry in a low-pressure flow reactor between 850–1280 K. Whereas CH₃Cl is thoroughly stable, molecular chlorine readily dissociates by a first-order process with an activation energy about a half of its bond energy. The decompositions of CH₂Cl₂ and CCl₄ over clean silica surfaces initially display marked autoacceleration associated with the formation of soot on reactor walls and reach limiting rates which are much faster than those predicted for their homogeneous pyrolysis under the same conditions.     

Comparison of radionuclide ratios in atmospheric nuclear explosions and nuclear releases from Chernobyl and Fukushima seen in gamma ray spectrometry

The Comprehensive Nuclear Test Ban Treaty has remote radionuclide monitoring followed by an On Site Inspection (OSI) to clarify the nature of a suspect event as part of its verification regime. An important aspect of radionuclide measurements on site is the discrimination of other potential sources of similar radionuclides such as reactor accidents or medical isotope production. The Chernobyl and Fukushima nuclear reactor disasters offer two different reactor source term environmental inputs that can be compared against historical measurements of nuclear explosions. The comparison of whole-sample gamma spectrometry measurements from these three events and the analysis of similarities and differences are presented. This analysis is a step toward confirming what is needed for measurements during an OSI under the auspices of the Comprehensive Test Ban Treaty.     

An emergency response intercomparison exercise using a synthetically generated gamma-ray spectrum

Although high resolution gamma ray spectrometry serves as the primary analytical technique in emergency response situations, chances for laboratories to practice analysing the type of spectra that may be expected in the early phase of such a situation are limited. This problem is more acute for laboratories in countries that have no nuclear facilities. The analysis of synthetically generated spectra may serve as a useful surrogate for actual spectra; this paper reports the results of a multilateral intercomparison exercise conducted using such a spectrum. Results indicate that the laboratories involved appear to have no problems identifying radioactive isotopes that regularly appear in national and international intercomparisons or exercises. However, some problems are evident for isotopes that are less often encountered which may, however, occur during the early phases of a nuclear accident. Isotopes prone to true coincidence summation proved also to be difficult with regard to correction of activities in some cases. The synthesized spectrum constituted a useful means of comparative analysis of complex spectra multilaterally without the impracticalities of using a sample drawn from a reactor.     

Removal properties of diesel exhaust particles by a dielectric barrier discharge reactor

The removal properties of diesel exhaust particles (DEP) were investigated using an engine exhaust particle size spectrometer (EEPS), field emission-type scanning electron microscopy (FE-SEM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). DEP were treated using a dielectric barrier discharge (DBD) reactor installed in the tail pipe of a diesel engine, and a model DBD reactor fed with DEP in the mixture of N(2) and O(2). When changing the experimental parameters of both the plasma conditions and the engine load conditions, we obtained characteristic information of DEP treated with plasma discharges from the particle diameter and the composition. In evaluating the model DBD reactor, it became clear that there were two types of plasma processes (reactions with active oxygen species to yield CO(2) and reactions with active nitrogen species to yield nitrogen containing compounds). Moreover, from the result of a TOF-SIMS analysis, the characteristic secondary ions, such as C(2)H(6)N(+), C(4)H(12)N(+), and C(10)H(20)N(2)(+), were strongly detected from the DEP surfaces during the plasma discharges. This indicates that the nitrogen contained hydrocarbons were generated by plasma reactions.     

A novel electrosynthetic system for anodic substitution reactions by using parallel laminar flow in a microflow reactor

We have developed a novel electrosynthetic system for anodic substitution reactions by using parallel laminar flow in a microflow reactor. This system enables nucleophilic reactions to overcome the restraint, such as the oxidation potential of nucleophiles and the stability of cationic intermediates, by the combined use of ionic liquids as reaction media and the parallel laminar flow in the microflow reactor. By using this novel electrosynthetic system, the anodic substitution reaction of carbamates, especially of cyclic carbamates, with allyltrimethylsilane were carried out to provide the corresponding products in moderate to good conversion yields in a single flow-through operation at ambient temperature (without the need for low-temperature conditions).     

On-line coupling of micro-enzyme reactor with micro-membrane chromatography for protein digestion, peptide separation, and protein identification using electrospray ionization mass spectrometry

To miniaturize high-performance membrane chromatography, a poly(vinylidene fluoride) membrane medium, employed as the stationary phase, is sandwiched between two poly(dimethylsiloxane) substrates containing the microchannels. The microchannels are fabricated by the capillary molding technique, involving the use of capillaries as the channel template and the fluid inlet/outlet. The micro(micro)-membrane chromatography system is coupled with a micro-enzyme reactor containing immobilized trypsins for performing rapid protein digestion, peptide separation, and protein identification using electrospray ionization mass spectrometry. Separation performance of cytochrome c digest in micro-membrane chromatography is compared with the results obtained from a regular reversed-phase micro-liquid chromatography. The efficacy and the potentials of micro-membrane chromatography in tryptic mapping are reported. On-line integration of the micro-enzyme reactor with micro-chromatographic separation techniques and electrospray ionization mass spectrometry clearly provides a microanalytical platform for automated sample handling, minimized sample loss, and reduced sample consumption. It also provides enhanced detection sensitivity and dynamic range for the analysis of complex protein mixtures such as cell lysates in proteomics research.     

Interference-free atomic spectrometric method for the determination of trace amounts of germanium by utilizing the vaporization of germanium tetrachloride

Trace amounts of germanium can be determined by atomic spectrometry by utilizing the vaporization of germanium tetrachloride at ambient temperature. Using an intermittent or continuous flow reactor, the sample solution was mixed with concentrated hydrochloric acid to form volatile germanium tetrachloride which can subsequently be determined by atomic spectrometry. The conditions for the volatilization of germanium chloride were investigated in detail and rapid method for the determination of trace amounts of germanium in real samples was proposed. A detection limit of 0.5 ng ml⁻¹ (3σ_n−1) was obtained by using atomic fluorescence spectrometric detection and the precision found was 0.8% for a germanium concentration of l00 ng ml⁻¹. Atomic emission and absorption spectrometric methods were also tested. Owing to the high selectivity of the reaction, no interference was found in the determination. The method was applied to the determination of germanium in several standard and certified reference materials; the results obtained were in good agreement with the certified values.     

Modeling the critical hydrogen concentration in the AECL test reactor

Hydrogen is added to a pressurized water reactor (PWR) to suppress radiolysis and maintain reducing conditions. The minimum hydrogen concentration needed to prevent radiolysis is referred to as the critical hydrogen concentration (CHC). The CHC was measured experimentally in the mid-1990s by Elliot and Stuart in a reactor loop at Atomic Energy of Canada (AECL), and was found to be approximately 0.5 scc/kg for typical PWR conditions. This value is well below industry-normal PWR operating levels near 40 scc/kg. Radiation chemistry models have also predicted a low CHC, even below the AECL experimental result. In the last few years some of the radiation chemical kinetic rate constants have been re-measured and G-values have been reassessed by Elliot and Bartels. These new data have been used in this work to revise the models and compare them with AECL experimental data. It is quite clear that the scavenging yields tabulated for high-LET radiolysis by Elliot and Bartels are not appropriate to use in the present context, where track-escape yields are needed to describe the homogeneous recombination kinetics in the mixed radiation field. In the absence of such data for high temperature PWR conditions, we have used the neutron G-values as fitting parameters. Even with this expedient, the model predicts at least a factor of two smaller CHC than was observed. We demonstrate that to recover the reported CHC result, the chemistry of ammonia impurity must be included.     

Chemical mechanisms in C3F8-H2 radiofrequency discharges

Discharges fed with C₃F₈-H₂ mixtures have been studied by means of mass spectrometry in a tubular reactor operated at 0.5 torr and 50 W. Comparison of the results with those obtained with emission actinometry give additional evidence that emission actinometry and mass spectrometry are powerful diagnostic tools to monitor stable and unstable species in discharges utilized for dry etching and polymer depositions. Mechanisms for end product formation and polymer deposition are also discussed.     

Immobilized enzyme reactor chromatography: optimization of protein retention and enzyme activity in monolithic silica stationary phases

Our group recently reported on the application of protein-doped monolithic silica columns for immobilized enzyme reactor chromatography, which allowed screening of enzyme inhibitors present in mixtures using mass spectrometry for detection. The enzyme was immobilized by entrapment within a bimodal meso/macroporous silica material prepared by a biocompatible sol-gel processing route. While such columns proved to be useful for applications such as screening of protein-ligand interactions, significant amounts of entrapped proteins leached from the columns owing to the high proportion of macropores within the materials. Herein, we describe a detailed study of factors affecting the morphology of protein-doped bioaffinity columns and demonstrate that specific pH values and concentrations of poly(ethylene glycol) can be used to prepare essentially mesoporous columns that retain over 80% of initially loaded enzyme in an active and accessible form and yet still retain sufficient porosity to allow pressure-driven flow in the low μL/min range. Using the enzyme γ-glutamyl transpeptidase (γ-GT), we further evaluated the catalytic constants of the enzyme entrapped in capillary columns with different silica morphologies as a function of flowrate and backpressure using the enzyme reactor assay mode. It was found that the apparent activity of the enzyme was highest in mesoporous columns that retained high levels of enzyme. In such columns, enzyme activity increased by ∼2-fold with increases in both flowrate (from 250 to 1000 nL/min) and backpressure generated (from 500 to 2100 psi) during the chromatographic activity assay owing to increases in k_cat and decreases in K_M, switching from diffusion controlled to reaction controlled conditions at ca. 2000 psi. These results suggest that columns with minimal macropore volumes (<5%) are advantageous for the entrapment of soluble proteins for bioaffinity and bioreactor chromatography.     

Recent Studies on the Decomposition of n-Hexane and Toluene in RF Thermal Plasma

Thermal decomposition of volatile organic compounds (VOCs) such as n-hexane and toluene has been studied in an inductively coupled thermal plasma reactor, at atmospheric pressure, in neutral and oxidative conditions, respectively. Thermodynamic calculations were performed for predicting the product distribution due to thermal decomposition. Based on these calculations formation of the products observed in the gas phase and in the extract of soot could be interpreted. In neutral conditions formation of soot and PAH was detected to different extent for the different models. The presence of oxygen in the plasma reactor depresses both soot and PAH formation. GC-MS analyses of the gaseous products and the extract of the soot, respectively, refer to as complex decomposition and recombination mechanism in given conditions.     

玉米秸秆催化液化制备生物油实验研究

以玉米秸秆为原料,添加分子筛催化剂在体积为500 mL的高温高压反应釜中进行催化液化制备生物油实验研究。选取反应温度、催化剂含量和反应时间三个主要因素为变量,探究其对玉米秸秆催化液化产物分布的影响。利用气相色谱-质谱联用仪(GC-MS)和傅里叶红外光谱仪(FT-IR)对玉米秸秆生物油的成分和官能团结构进行分析。结果表明,玉米秸秆的最佳催化液化条件为,反应温度为340 ℃,玉米秸秆15 g,FeHZSM-5催化剂含量为6.67%,反应时间为30 min。在此条件下,生物油产率为28.03%,催化液化整体转化率为81.73%。生物油的主要成分为酚类和长链酯类,生物油的热值达30.08 MJ/kg。     

电喷雾离子化飞行时间质谱研究鸡蛋清溶菌酶与β－环糊精 的新型复合物

运用电喷雾离子化飞行时间质谱分析鸡蛋清溶菌酶与β－环糊精的复合物。通过减少β－环糊精的配制浓度至原来的1/5,发现形成1:2和1:3复合比的溶菌酶-β-环糊精复合物的离丰度减弱,但化学计量比为1:1的复合物变化不大,证明该新型复合物为非特异性非共价复合物。此外还对质谱参数、分析条件对复合物离子化的影响作了详尽的考察,得出在nozzle电压为200V时复合物信号最强,在不影响生物分子高级结构的前提下添加少量的有机溶剂如甲醇、乙腈等能较明显地改善质谱信号。