Automated liner exchange— A novel approach in direct thermal desorption— gas chromatography

Summary A system was developed for fully automated liner exchange in direct thermal desorption— gas chromatography— mass spectrometry (DTD-GC-MS). Samples are put into a newly developed liner which is capped with a standard crimp cap. The liners are placed in a sample tray and transported to the thermal desorption device. Both liner transport and liner exchange (which can be performed after each analysis) are automated. The system was tested for spores and pollen, vegetable oil, wood (preservative), car exhaust (BTEX), and tobacco (nicotine) analysis to demonstrate the robustness and flexibility of the approach.     

S_2OF_(10)气体标准样品制备方法和测定方法研究

提出了一系列的安全、方便、可靠、在线和可连续操作的热解吸／色谱分析柱制备Ｓ２ＯＦ１０纯品、指数稀释法配制Ｓ２ＯＦ１０标准样品、应用定量校正系数测定样品中痕量Ｓ２ＯＦ１０的方法和技术。分别采用气相色谱、红外光谱、气相色谱／质谱等方法对色谱制备的Ｓ２ＯＦ１０纯品进行了纯度分析和测定。配制Ｓ２ＯＦ１０标准气体的体积分数范围为８．０×１０－７～２．６×１０－４。气相色谱测定Ｓ２ＯＦ１０的定量校正系数为０．１９７,测定方法的相对误差范围为１．８％～２０％。     

Uncertainty evaluation of the thermal expansion of simulated fuel

Thermal expansions of simulated fuel (SS1) are measured by using a dilatometer (DIL402C) from room temperature to 1900 K. The main procedure of an uncertainty evaluation was followed by the strategy of the UO₂ fuel. There exist uncertainties in the measurement, which should be quantified based on statistics. Referring to the ISO (International Organization for Standardization) guide, the uncertainties of the thermal expansion are quantified in three parts—the initial length, the length variation, and the system calibration factor. Each part is divided into two types. The A type uncertainty is derived from the statistical iterative measurement of an uncertainty and the B type uncertainty comes from a non-statistical uncertainty including a calibration and test reports. For the uncertainty evaluation, the digital calipers had been calibrated by the KOLAS (Korea Laboratory Accreditation Scheme) to obtain not only the calibration values but also the type B uncertainty. The whole system, the dilatometer (DIL402C), is composed of many complex sub-systems and in fact it is difficult to consider all the uncertainties of sub-systems. Thus, a calibration of the system was performed with a standard material (Al₂O₃), which is provided by NETZSCH. From the above standard uncertainties, the combined standard uncertainties were calculated by using the law of a propagation of an uncertainty. Finally, the expanded uncertainty was calculated by using the effective degree of freedom and the t-distribution for a given confidence level. The uncertainty of the thermal expansion for a simulated fuel was also compared with those of UO₂ fuel.     

Thermal risk assessment and grading of chemicals with instantaneous power density

The heat release behaviors of several chemical compounds were detected with C80 calorimeter. Furthermore, the thermodynamic and kinetic parameters of the chemicals were obtained based on the experimental data. Chemical thermal risk was simultaneously graded with combined use of instantaneous power density and the classification standard of thermal instability which was offered by the standard system for the identification of the hazards of materials for emergency response (NFPA704). The results show that the grading standard of thermal risk based on NFPA704 was reasonable and can be used as a preliminary thermal risk assessment for reaction hazards.     

Substoichiometric thermal neutron activation analysis determination of ruthenium in complex matrices

Complex matrices, namely ores and catalysts, have been analyzed for trace amount of ruthenium employing thermal neutron-activation analysis, involving substoichiometric solvent extraction of Ru/III/ with 2-mercaptobenzothiazole into chloroform. Three samples and a standard can be processed and counted within three hours.     

Terrylene in hexadecane revisited: a hole burning study

Holes burnt into the absorption spectrum of terrylene in hexadecane have quite unusual features: spectral diffusion behavior under thermal cycles shows a narrowing regime at very low temperatures (2-5 K) followed by a plateau region (up to about 13 K) and a broadening regime (T>13 K). Thermal line broadening (quasihomogeneous linewidth) shows a nonmonotonous behavior as a function of temperature: at around 4 K there is a maximum followed by a flat minimum and the onset of strong broadening at higher temperatures. Finally, the central hole shows one-sided narrowly spaced side features. This behavior is interpreted within the frame of a two-site model. One of the two sites can be well described by a standard two level system; the other, however, shows characteristic features of a multilevel system. The two sites are characterized by strongly different optical linewidths, phototransformation yields, and thermal stabilities.     

Thermal analysis of oxide-isolated stripe diode lasers

The finite-element thermal model of the oxide-isolated stripe geometry diode laser is presented in this work. The calculation procedure was carried out with a standard IBM PC/AT microcomputer. The ohmic contact heat generation and the thickness d_ox of the SiO₂ layer, as two parameters of OIS lasers crucial from a thermal aspect, were taken into account. The system of isotherms obtained for this laser allowed a discussion of the heat spreading process within the laser structure and a comparison of the relative contributions of all heat sources.This work was carried out in program CFRN 117/90 of the Polish Ministry of Education Research project P/04/142/90-2.     

A New Type of High Pressure System for a Tian-Calvet Calorimeter

A Tian-Calvet heat flux calorimeter has been modified for use with high pressures in measurements of thermal hazards of materials. The system comprising a specially designed high pressure vessel and an associated manifold is described. With this system, comparative measurements using both standard and high pressure vessels can be made, different materials and/or liners can be used for the high pressure vessel and an assessment of the influence of the gaseous environment on thermal behaviour can be made. Calibration was carried out in the range 25 to 300°C at different pressures and heating rates, using sapphire and the calibration results were verified with benzoic acid, both reference grade materials. With the new vessel, pressures up to about 70 MPa can be used or recorded during the thermal decomposition of energetic materials. The reproducibility of the baseline, as illustrated by standard error results, was about 0.02% compared with 0.13% for the standard vessel, over the entire temperature range. The corresponding results for the baseline of the pressure vessel at 5.5 MPa (in air and Ar) and in a calibration experiment with sapphire were 0.08%. Experimental data obtained for ammonium nitrate and 2,3-dimethyl-2,3-dinitrobutane in the standard and pressure vessels are compared and discussed. The effect of pressure and the nature of the gaseous environment (inert or oxidizing) on the results for these two materials will be described. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of nitroaromatic and nitramine explosives from a PTFE wipe using thermal desorption-gas chromatography with electron-capture detection

A method for the detection of nitroaromatic and nitramine explosives from a PTFE wipe has been developed using thermal desorption andgas chromatography with electron-capture detection (TD-GC-ECD). For method development a standard mixture containing eight nitroaromatic and two nitramine (HMX and RDX) explosive compounds was spiked onto a PTFE wipe. Explosives were desorbed from the wipe in a commercial thermal desorption system and trapped onto a cooled injection system, which was incorporated into the injection port of the GC. A dual column, dual ECD configuration was adopted to enable simultaneous confirmation analysis of the explosives desorbed. For the desorption of 50 ng of each explosive, desorption efficiencies ranged between 80.0 and 117%, for both columns. Linearity over the range 2.5-50 ng was demonstrated for each explosive on both columns with r2 values ranging from 0.979 to 0.991 and limits of detection less than 4 ng. Desorption of HMX from a PTFE wipe has also been demonstrated for the first time, albeit at relatively high loadings (100 ng).     

Substoichiometric determination of Hg by radiochemical neutron activation analysis

A rapid method has been developed for the determination of mercury in environmental samples by thermal neutron activation analysis. Radiochemical separation involves the extraction of Hg/II/ with substoichiometric amounts of 2-mercaptobenzothiazole /2-HMBT/ into chloroform¹. The time required for radiochemical purification and counting of two samples and a standard is about 2 h. Water, sludge and IAEA standard samples were analyzed for Hg concentration by this method.     

Automated high-speed analysis of selected organic compounds in urban air by on-line isotopic dilution cryofocusing gas chromatography/mass spectrometry

An automated environmental air monitor has been developed to measure selected organic compounds in urban air. The instrument is based on a cryofocusing-thermal desorption gas chromatographic mass spectrometry technique where the mass spectrometer is a slightly modified residual gas analyzer (RGA). The RGA was chosen as a detector because the whole system must be robust for long periods, with 24-h continuous air monitoring. RCA are extremely simple and seemed the most reliable mass spectrometers for this purpose. Moreover, because they have no physically limited ion source, contamination is considerably reduced, so maintenance intervals are longer. The gas chromatograph is equipped with a computer-controlled six-way sampling valve, with a 100-mL sampling loop and thermal desorption cold trap injector. Environmental air is enriched with an isotopically labeled internal standard in the sampling line. This internal standard is added with a validated, custom-made, permeation tube device. The “on-line” internal standard provides for high quality quantitative data because all variations in instrument sensitivity in cryofocusing or in thermal desorption efficiency are taken into account. High repetition rates (down to 5 min for a full analytical cycle) are obtained with the use of an isothermal gas chromatography program, microbore capillary column, and environmental air sampling during the gas chromatography run.     

CFD Simulation of a Hydrogen／Argon Plasma Jet Reactor for Coal Pyrolysis

A Computational Fluid Dynamics (CFD) model was formulated for DC arc hydrogen/argon plasma jet re-actors used in the process of the thermal H2/Ar plasma pyrolysis of coal to acetylene. In this model, fluid flow, convective heat transfer and conjugate heat conductivity are considered simultaneously. The error caused by estimating the inner-wall temperature of a reactor is avoided. The thermodynamic and transport properties of the hydrogen/argon mixture plasma system, which are usually expressed by a set of discrete da-ta, are fitted into expressions that can be easily implemented in the program. The effects of the turbulence are modeled by two standard k-ε equations. The temperature field and velocity field in the plasma jet reactor were calculated by employing SIMPLEST algorithm. The knowledge and insight obtained are useful for the design improvement and scale-up of plasma reactors.     

新型热量计的研制及其在吸热型碳氢燃料热沉测定中的应用

建立并完善了一套高温流动型热导式量热装置,实现了量热与色谱在线分析的有机结合。对该系统的仪器常数、热量常数、时间常数进行了精确的标定,并采用标准物质氮气、正庚烷等对仪器的准确性进行了考察,测量结果误差在2.2%～4.7%之间。同时还实测了吸热型碳氢燃料S-1,R-1等的热裂解热沉值。S-1在700℃时的热沉为2.99MJ/kg,而R-1的热沉为2.82MJ/kg。     

Construction of an automated gas chromatography/mass spectrometry system for the analysis of ambient volatile organic compounds with on-line internal standard calibration

An automated sampling and enrichment apparatus coupled with a gas chromatography/mass spectrometry (GC/MS) technique was constructed for the analysis of ambient volatile organic compounds (VOCs). A sorbent trap was built within the system to perform on-line enrichment and thermal desorption of VOCs onto GC/MS. In order to improve analytical precision, calibration accuracy, and to safe-guard the long-term stability of this system, a mechanism to allow on-line internal standard (I.S.) addition to the air sample stream was configured within the sampling and enrichment apparatus. A sub-ppm (v/v) level standard gas mixture containing 1,4-fluorobenzene, chloropentafluorobenzene, 1-bromo-4-fluorobenzene was prepared from their pure forms. A minute amount of this I.S. gas was volumetrically mixed into the sample stream at the time of on-line enrichment of the air sample to compensate for measurement uncertainties. To assess the performance of this VOC GC/MS system, a gas mixture containing numerous VOCs at sub-ppb (v/v) level served as the ambient air sample. Various internal standard methods based on total ion count (TIC) and selective ion monitoring (SIM) modes were attempted to assess the improvement in analytical precision and accuracy. Precision was improved from 7-8% RSD without I.S. to 2-3% with I.S. for the 14 target VOCs. Uncertainties in the calibration curves were also improved with the adoption of I.S. by reducing the relative standard deviation of the slope (Sm%) by an average a factor of 4, and intercept (Sb%) by a factor of 2 for the 14 target VOCs.     

单斜仲钨酸铵热分解的热化学测定

The heat of the thermal decomposition of monoclini c ammonium paratungstate, (NH4)10H2W12O42•4H2O, was measured in a HT-1000 microcalorimeter using three-step calorimetry and suitable thermochemical cycle. The standard enthalpy of the thermal decomposition reaction at 298.15 K and the standard enthalpy of formation at 298.15 K for monoclinic ammonium paratung-state were obtained to be (430.1± 10.2) kJ•mol－ 1 and－ (13 423.7±14.8) kJ•mol－ 1, respectively.     

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Decomposition of dichlorodifluoromethane in thermal plasma was investigated theoretically by computing the equilibrium composition of the gas mixtures involving carbon, chlorine and fluorine in presence of argon (which is assumed to be the main plasma gas) and/or in addition of hydrogen and calcium together with hydrogen. The calculations were carried out for the temperature range between 500 and 6000 K and for the total pressure of the system of 1 bar. Use is made of the fact that a thermal plasma is a plasma in (local) thermal equilibrium, which makes possible the theoretical determination of its equilibrium composition at definite temperature by employing Gibbs free energy data for the compounds present in the system and assuming that the equilibrium of the system corresponds to its minimum energy state. The results of calculations show that toxic molecules and radicals can be, under convenient conditions (appropriate temperature and amount of added substances), converted into stable non-toxic species like CaF₂ and CaCl₂.     

Strong rotating flow in stationary droplets in low power budget using wire electrode configuration

We explore a simple strategy of generating strong rotating flow in a stationary surface‐droplet, using an intricate interplay of local electrical and thermal fields. Wire electrodes are employed to generate on‐spot heating without necessitating any elaborate micro‐fabrication, which causes strong local gradients in electrical properties to induce mobile charges into the droplet. Applying a low voltage (～10 V), strong rotational velocity of the order of mm/s can be achieved in the system, within the standard operating ranges of operating and geometrical parameters. Further, altering the diameter of the electrode, vortices can be tuned locally or globally in low power budget, without incurring any droplet oscillations. These results may turn out to be of immense consequence in enhancing micromixing in a plethora of droplet based applications ranging from thermal management to medical diagnostics to be potentially employed in resource‐limited settings.     

Dielectric dispersion of polypeptide solutions. II. Helix-coil transition of poly(epsilon-carbobenzoxy-L-lysine) in m-cresol.

Dielectric dispersion measurements were made on dilute solutions of poly(epsilon-carbobenzoxy-L-lysine) in m-cresol; this system underwent a very sharp thermal helix-coil transition of inverse type around 30 degrees. Mean-square dipole moments "mu-2" and mean rotational relaxation times t were obtained as functions of molecular weight and helical fraction fN. It was found that "mu-2"-one-half varied almost linearly with fN-one-half over a substantial portion of the transition. The relaxation times corrected for solvent viscosity and temperature changed only slightly with fN except in the region of small fN, while, at fixed fN, they displayed molecular weight dependence characteristic of rod-like molecules. These results can be explained if the transition is assumed to proceed almost in all-or-none fashion. This assumption is consistent with the previous finding from statistical thermodynamic analyses that the transition of the system PCBL-m-cresol is highly cooperative, with standard deviation of population one-half being 0.0025 to 0.0027, where standard deviation of population is the cooperativity parameter. Application of Nagai's theory of "mu-2" for interrupted helices yielded the result that standard deviation of population-one-half was in the range 0.001 to 0.005 and the monomeric dipole moment in the helical conformation was 5.4 to 6.2 D.     

一次热解吸直接进样浓缩方法的研究--室内大气中挥发性有机化合物的分析

研制了新型的一次热解吸直接进样热解析仪．考察了新型热解吸仪热解吸定量的重复性、准确性、热解析率、线性等性能．通过实际采样分析证明,该方法提高了浓缩倍数,操作简单,易于掌握,定量重复性好、准确度高,分析结果可靠．适合大批量样品的分析测试．     

Utilization of standards generated in the process of thermal decomposition chemically modified silica gel for a single point calibration of a GC/FID system

The utilization of a multicomponent gaseous standard mixture, containing CO and CO(2) and obtained by thermal decomposition of a so-called immobilized compound, for a single point calibration of a GC/FID system are described. The generation of such a mixture takes place as a result of thermal decomposition of a sample of chemically modified silica gel placed in a heated chamber of thermal desorber coupled with the device being calibrated via a catalytic methanizer. The mean amount of the analyte librated from unit mass of the gel was 0.71 mg g(-1) (RSD = 3%) for carbon monoxide and 0.86 mg g(-1) (RSD = 3%) for carbon dioxide.