Interrupted thermal desorption of TiH2

Structural changes of commercial TiH₂ were studied using interrupted temperature desorption spectroscopy and X-ray diffraction techniques to understand the mechanism of its degradation under non-equilibrium conditions. Rapid cooling on different stages of temperature-programmed heating allowed to study the intermediate phase compositions that evolve upon cooling from the high-temperature phase βTi(H). The phase transformation sequence is described as a number of consecutive reactions corresponding to the observed desorption peaks. Phases δTiH_2−x, γTiH, and the solid solution αTi(H) were found to be intermediates in the TiH₂ → αTi transformation when the latter is interrupted. Additional evidence for the thermodynamic stability of γTiH is given.     

11种吸附剂上二噁英的热吸附/脱附性能评价

筛选在低温下高效捕集并在一定的高温下可以快速完全脱附二噁英的吸附/脱附材料是二噁英在线热捕集的关键.该研究以1,2,3,4-四氯代二苯并-对-二噁英(1,2,3,4-TCDD)和1,2,3,8,9-五氯代二苯并呋喃(1,2,3,8,9-PCDF)为二噁英模型物,以电子捕获检测器(ECD)作为检测器,利用填充柱气相色谱系...     

A study of the thermal cure of a phenylethynyl-terminated imide model compound and a phenylethynyl-terminated imide oligomer (PETI-5)

The kinetic mechanism of the thermal cure of a phenylethynyl-terminated imide model compound, 3,4′-bis[(4-phenylethynyl)phthalimido]diphenyl ether (PEPA-3,4′-ODA) and a phenylethynyl-terminated imide oligomer PETI-5 (MW 5000 g/mol) was studied. FTIR was used to follow the cure of the model compound, while thermal analyses (DSC) was used to follow the cure of the PETI-5 oligomer. The changes in IR absorbance of phenylethynyl triple bonds at 2214 cm⁻¹ of PEPA-3,4′-ODA as a function of cure time were detected at 318, 336, 355, and 373°C, respectively. The changes in the glass transition temperature, T_g, of PETI-5 as a function of time were measured at 350, 360, 370, 380, and 390°C, respectively. The DiBenedetto equation was applied to define the relative extent of cure, x, of the PETI-5 oligomer by T_g. For the model compound, the reaction followed first order kinetics, yielding an activation energy of 40.7 kcal/mol as determined by infrared spectroscopy. For PETI-5, the reaction followed 1.5th order, yielding an activation energy of 33.8 kcal/mol for the whole cure reaction, as determined by T_g using the DiBenedetto method. However, the cure process of PETI-5 just below 90% by this method followed first-order kinetics yielding an activation energy of 37.2 kcal/mol. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 461–470, 1998     

Sequential stir bar extraction,thermal desorption and retention time locked GC–MS for determination of pesticides in water

A method based on sequential stir bar sorptive extraction followed by automated thermal desorption–GC–MS for the determination of pesticides in underground and superficial water samples has been developed. Retention time locked GC–MS and deconvolution Automated Mass Spectral Deconvolution and Identification System software allows the use of pesticide databases for identification and quantification in routine applications. Quantitation limits and repetitivity using full scan mass spectrometric determination guarantee the applicability of the method, which enables considerable savings to be made in total analysis time, with data processing times of around 2 min/sample.     

Analysis of airborne substances by means of microwave thermal desorption

A method has been developed to enable thermal desorption of airborne substances from solid adsorbents based on active charcoal by means of microwave energy, followed by on-line GC-FID analysis. Ceramic traps were filled with 50 mg of commercially available graphitized carbon black. Adsorption efficiency and desorption conditions for three substances covering a broad range of vapor pressure were investigated. The recovery rate, breakthrough, and linearity of the system were determined by direct fortification with standard solutions, followed by microwave thermal desorption and gas chromatographic separation. The recovery efficiencies were 80–84 %, with a standard deviation of 3–6 %. The correlation coefficient of the linear range between 1 (10 for one of the compounds) and 1000 ng was > 0.999. Initial experiments were performed to investigate the enrichment of the standards from the gaseous state. The recovery rates of the most volatile compound was increased by optimizing the density of the packing.     

Rapid determination of methyl salicylate, a plant-signaling compound, in tomato leaves by direct sample introduction and thermal desorption followed by GC-MS

Many plants infested by herbivores or viruses can rapidly produce and accumulate a plant-signaling compound, methyl salicylate (MeSA), in their leaves to activate disease resistance. In the present work, a simple, rapid, and sensitive method was developed for the determination of MeSA in tomato leaves by direct sample introduction and thermal desorption followed by GC-MS. Results show that the proposed method has a low detection limit (0.08 ng mg(-1)) and good precision (RSD = 8.9%). The present method was applied to the investigation of tomato plant defense response to tobacco mosaic virus (TMV) by rapid analysis of volatile compounds in plant leaves. It was found that tomato plants can produce large amounts of MeSA as a defense response to TMV. This indicates that MeSA may be a plant-signaling compound in tomato plant defense response to TMV.     

Field sampling demonstration of portable thermal desorption collection and analysis instrumentation

The HAPSITE® (Hazardous Air Pollutants on Site) is a portable gas chromatography-mass spectrometry (GC–MS) unit designed to aid air sampling technicians by identifying and quantifying volatile organic compounds from occupational and environmental sampling. The main goal of the present study was to extend prior laboratory-based work with the portable HAPSITE® ER (extended range model) thermal desorption (TD) capability to real-world field samples from both indoor and outdoor environments using different types of active and passive sampling mechanisms. Understanding the performance of the HAPSITE® ER in a realistic field setting will allow air quality sampling technicians to make improved decisions related to sampling and analysis methods in the field. An important finding was that certain charcoal-based TD sorbents were contraindicated for the HAPSITE® ER because of a substantial hydrocarbon bleed which degraded system performance. A novel time series TD sampler (Logistically Enabled Sampling System-Portable [LESS-P]) was validated using Tenax TA TD tubes against standard active sampling across multiple field sampling sites, and the qualitative analytical trends and compound identities were similar between LESS-P replicates analysed via benchtop GC–MS and HAPSITE® ER. Once validated, the LESS-P was used to determine the reference concentrations for passive sampling calculations. The results confirmed the passive sampling methodology within the benchtop system, but highlighted some systemic sensitivity limitations that must be addressed in order for the HAPSITE® to be accurately applied to passive sampling. We propose that the LESS-P time-series sampler may help to alleviate the requirement for sampling technicians to be on-site during active sampling, allowing for automated sampling throughout the duration of a sampling event.     

室温下Pt电极上CO的脱附机理

利用流动电解池与电化学原位红外光谱技术研究了温度和阴离子竞争吸附等因素对室温下Pt电极上COad的脱附机理与动力学的影响.研究表明当溶液中有Cl-或硫酸根等离子时,室温下未观察到COad从电极表面脱附.但是当溶液相存在与COad的吸附能相当甚至比之更大的粒子如CO或CN-时,COad可以被取代而从电极表面脱附.红外光谱表明吸、脱附过程中CN-ad与COad的红外谱带强度存在反线性的关系,而且变温实验估算得到COad的脱附能垒小于40kJmol-1,该脱附能垒远比CO的吸附能（〉60kJmol-1）小.上述结果进一步验证了室温下COad在Pt电极上的脱附不是热激发脱附.据此结果,本文详细地讨论了我们早先提出的吸附驱动的脱附机理的历程与能量来源.     

Sensitive determination of polycyclic aromatic hydrocarbons in water samples using monolithic capillary solid-phase extraction and on-line thermal desorption prior to gas chromatography-mass spectrometry

A methacrylate-based monolithic capillary column has been evaluated for the preconcentration of polycyclic aromatic hydrocarbons (PAHs) from environmental water samples. For this purpose, the monolyte was in situ synthesized in a 6cm×0.32mm id fused-silica capillary. The microextraction unit was fitted to a micro-HPLC pump to pass 10mL of sample. The isolated pollutants were eluted by means of 10μL of methanol, the organic phase being directly collected in a specific interface that can be fitted to the injection port of the gas chromatograph without modification. The interface allows the on-line thermal desorption of the PAHs, avoiding the dilution and providing enough sensitivity to reach the legal limits established for these pollutants in the matrices selected. The limits of detection achieved for 10mL of water ranged between 2.8ng/L (indeno(1,2,3-cd)pyrene) and 11.5ng/L (acenaphthene) with acceptable precision (between 4.5 and 18.2% RSD). The method was applied to the determination of the selected PAHs in tap, river waters and sewage, being fluoranthene and pyrene detected in all of them at concentrations lower than the legal limits established for these compounds in the matrices assayed.     

Rapid and sensitive determination of morphine in street opium samples by thermal desorption gas chromatography using a microfurnace pyrolyzer

Thermal desorption of the alkaloids in opium samples at 300 degrees C using a vertical microfurnace pyrolyzer was followed by their on-line gas chromatographic (GC) analysis on a large-bore glass capillary column. This method permitted rapid and sensitive determination of the content of the main alkaloid, morphine, in the small (ca. 100 microg) opium samples with a relative standard deviation within 4% for 5 runs. The observed morphine contents of about 12 to 15 w/w% in the given opium samples were in fairly good agreement with those estimated by a conventional GC-MS method.     

Development of a sensitive thermal desorption method for the determination of trihalomethanes in humid ambient and alveolar air

A sensitive and reliable method has been developed for the determination of trihalomethanes (THMs) in air samples through adsorption in sorbent tubes and thermal desorption (TD) of the compounds, followed by gas chromatography (GC)–mass spectrometry (MS) analysis. Three commercial sorbent materials were compared in terms of adsorption efficiency and breakthrough volume, finding Chromosorb 102 to be the most appropriate adsorbent for air sampling. The method allows us to reach detection limits of 0.03 ng (0.01 μg m⁻³ for 3 l of air), linear ranges from 0.1 to 2000 ng and specific uncertainties of ca. 5.0 ± 0.2 ng for all THMs. Several salts were tested to reduce water retention (from the humid air of an indoor swimming pool) at the sampling stage, Na₂SO₄ being the one that provides optimum efficiency. The method was validated by a new recovery study in which several tubes with and without adsorbent were spiked with THMs and analyzed by TD-GC/MS, recoveries ranging from 92% to 97% for all the compounds. Finally, the performance of the method was evaluated through the analysis of ambient air samples from an indoor swimming pool and alveolar air samples from swimmers to assess their THM uptake. THMs were found to be stable in the sorbent tubes for at least 1 month when stored at 4 °C.     

Advances in the determination of volatile organic solvents and other organic pollutants by gas chromatography with thermal desorption sampling and injection

Summary The problem of the separation of 34 volatile organic chlorinated compounds is solved by using three different GC columns selected according to the needs of the particular separation required. The effect of water vapor contained as moisture in the trapped air on the retention of some characteristic compounds is studied. The influence of dead volumes on trap injection is also studied.Dedicated to Prof. Dr. A. Liberti on the occasion of his 70th birthday.     

Development of a novel solid-phase extraction element for thermal desorption gas chromatography analysis

A novel solid-phase extraction element is developed for sorptive enrichment of dilute analytes from liquid samples with high extraction efficiencies due to its larger amounts of polydimethylsiloxane (PDMS) absorbent than the conventional syringe type of solid-phase microextraction (SPME). The extraction element is made of titanium (Ti) open tubular tube (30 mm x 1.2 mm i.d. x 1.6 mm o.d.) coated with a chemically bonded layer of PDMS (500 microm in thickness). The extraction element combined with thermal desorption-gas chromatography-mass spectrometry using a pyrolysis-gas chromatography-mass spectrometry system was used to extract and analyze a typical herbicide, bethrodine in water samples over a concentration range from 2.5 to 2.5 x 10(4) ng/l. Thus obtained calibration curve showed good linearity for the tested whole concentration range with regression coefficient of 0.992. Detection limit of 0.5 ng/l level was achieved and the reproducibility of the measurements for bethrodine at 10 ng/l level was found to be fairly good with relative standard deviation below 7.5%.     

Automatic thermal desorption in GC analysis of dairy product volatiles

Summary Automatic thermal desorption (ATD) has been evaluated for the analysis of volatile components from dairy products. It has resulted in a fast and reproducible method which needs only a low amount of sample. Volatile components from milk are collected by off-line purging and trapped on cartridges packed which a suitable adsorbent. Cheese samples are submitted to the same process or directly introduced into the cartridges. The desorption step that follows is carried out automatically and on-line with the chromatographic analysis. Repeatability and sensitivity were satisfactory for both types of products.     

Multiphoton ionization spectroscopy in surface analysis and laser desorption mass spectrometry

The application of resonance-enhanced multiphoton ionization (REMPI) spectroscopy for the ultrasensitive detection of molecules originating from laser desorption experiments performed on a variety of substrates is reviewed. Laser-induced desorption from surfaces is capable of producing intact gas-phase molecules, even from polar, non-volatile, high-molecular-weight and thermally labile substances. REMPI is a highly efficient and optically selective ionization method, which, coupled with laser desorption allows the direct chemical analysis of complex mixtures, without the need for previous sample purification and separation steps. The use of REMPI spectroscopy is discussed in two contexts: (1) for the direct chemical analysis of complex mixtures, e.g., environmental samples, by laser desorption/laser postionization mass spectrometry and (2) for measurements of internal state distribution of molecules laser-desorbed from sub-monolayers surface films to gain insight into the laser desorption mechanism.Presented at the 13th International Symposium on Microchemical Techniques (ISM), held in Montreux, Switzerland, May 16–20,1994     

Application of a thermal desorption cold trap injector to multidimensional GC and GC-MS

The Thermal desorption Cold Trap injector (TCT) was used as a part of modified multidimensional GC (MDGC) or MDGC mass spectroscopy (MS) systems. These systems were based on a preparative GC (GC1), an analytical GC (GC2), or GC-MS and the TCT. The TCT was mounted on the GC2 or GC-MS. Analysis was carried out as follows: first, the volatile compounds heart-cut after separation on the GC1 column were adsorbed onto the Porapak Q column out of the GC1 oven. This Porapak Q column was then coupled to the TCT, and the volatile compounds adsorbed on the Porapak Q were thermally desorbed, cold trapped, and injected onto an analytical column in the GC2 or GC-MS. Repeatability of the retention time (RT) and area % of model samples consisting of citronellol, decanol, and geranyl acetate was examined. Also, the volatile compounds present at very low concentrations in ethanol solution were concentrated on the Porapak Q column. These were injected onto the analytical column by the same method as described above, and the repeatability of the RT and area % on the chromatogram was examined. In the two experiments, the standard deviation of the RT and area % for each compound was about 0.02 and less than 2.85, respectively. A commercial geranium oil was successfully analyzed by this technique. The results indicate that this modified MDGC and MDGC-MS system are very useful for detection and determination of compounds in complex mixtures.     

Analysis of volatiles and semivolatiles in drinking water by microextraction and thermal desorption

A new technique to analyze aqueous samples for nanograms per liter levels of volatile and semivolatile compounds using microextraction and thermal desorption into a gas chromatograph/ion trap mass spectrometer (GC/MS) is described. This method is inherently sensitive (50 mL of aqueous sample is extracted prior to each desorption), uses no solvents, and detects volatiles and semivolatiles in the same analysis. Aqueous standards and environmental samples are pumped through a length of porous-layer open-tubular capillary column, which is then thermally desorbed onto a 30 m × 0.25 mm i.d. analytical column interfaced to an ion trap mass spectrometer for subsequent separation and detection. Sharp chromatographic peaks and reproducible retention times (RT) were observed. Replicate injections of surrogates (n = 6) averaged 32.6% R.S.D. Analysis of domestic tap water detected 55 analytes, some at the low-nanograms per liter level, and detected 3 halogenated ethenes, not previously reported in drinking water. Analysis of an aqueous sample from a municipal ground water source detected the presence of numerous semivolatile compounds at trace-levels.     

Equilibrium adsorption data from temperature-programmed desorption experiments

This work describes a novel method that enables the calculation of a series of adsorption isotherms basically from a single Temperature-Programmed Desorption (TPD) experiment. The basic idea is to saturate an adsorbent packed in a fixed bed at a certain feed concentration and temperature and to subsequently increase its temperature linearly with time, while maintaining a constant feed concentration.We measured TPD response curves for carbon dioxide on activated carbon at different heating rates for various combinations of feed concentration, molar flow rate and particle size. Response curves from an axially dispersed plug flow model were fitted to experimental data by adjustment of the Langmuir parameters. Adsorption isotherms calculated with these fitted parameters are in good agreement with adsorption data obtained by other methods over the full temperature range.The influence of heating rate on intraparticle mass transfer resistance is discussed.     

On the thermal stability and thermal decomposition kinetics of some mono- and disubstituted furan-2,3-dions

The thermal behaviour of some compounds derived from 5-phenylfuran-2,3-dione was studied. The thermoanalytical data relating to the decomposition steps and intermediates were completed with mass spectrometric analysis and infrared spectroscopy results. For some of the investigated reactions, the kinetic and structural data correlated satisfactorily.     

二级热脱附-气相色谱-质谱联用测定大气可吸入颗粒物中的16种多环芳烃

建立了二级热脱附-气相色谱-质谱联用技术测定大气可吸入颗粒物PM10中16种多环芳烃的分析方法。对二级热脱附和色谱-质谱条件进行了优化。实验结果表明,方法的检出限为0.14～0.42 ng/m3,平均加标回收率为52.7%～97.9%,相对标准偏差(RSD)为8.0%～18.4%。与传统方法相比,该方法的样品前处理时间短、有机溶剂的使用量少,是对人体及环境友善的检测技术。该方法已应用于32份实际大气颗粒物样品的分析。