Preparation of poly(methyl methacrylate) particles by dispersion polymerization with organic peroxide in the presence of trimethylsiloxy terminated poly(dimethylsiloxane) in supercritical carbon dioxide

Dispersion polymerizations of methyl methacrylate (MMA) were conducted with various types of organic peroxides as radical initiator in the presence of trimethylsiloxy terminated poly(dimethylsiloxane) in supercritical carbon dioxide. Micron-sized, relatively “monodisperse” poly(MMA) particles were prepared by using benzoyl peroxide.Part CCLII of the series “Studies on Suspension and Emulsion”     

Dry ice-originated supercritical and liquid carbon dioxide extraction of organic pollutants from environmental samples

Packed in a high-pressure vessel and under calculated conditions, dry ice can be used as a source of carbon dioxide for supercritical CO₂ extraction or liquid CO₂ of organic compounds from environmental samples. Coupled with a fluid modifier such as toluene, dry ice-originated supercritical CO₂ (Sc CO₂) achieves quantitative extraction of many volatile organic compounds (VOCs) and semivolatile organic compounds (SOCs) including polycyclic aromatic hydrocarbons (PAHs), n-alkanes, and polychlorinated biphenyls (PCBs) from solid matrices. Compared to contemporary manual or automated supercritical fluid extraction (SFE) technologies, this novel technique simplifies SFE to a minimum requirement by eliminating the need of a high-pressure pump and any electrical peripherals associated with it. This technique is highly suitable to analytical areas where sample preservation is essential but difficult in the sampling field, or where sample collection, sample preparation, and analysis are to be done in the field.     

Interrelationship between total volatile organic compounds emissions,structure and properties of natural rubber/polycaprolactone bio-blends cross-linked with peroxides

Natural rubber/polycaprolactone (NR/PCL) bio-based blends with different organic peroxides were prepared using an internal batch mixer and subsequently cross-linked at 170 °C. Two types of commonly used organic peroxides, dicumyl peroxide and di(tert-butylperoxyisopropyl)benzene peroxide, were applied as free-radical initiator. Cross-linking efficiency of NR/PCL blends were investigated using oscillating disc rheometer measurements, followed by infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis and tensile testing. Total volatile organic compounds (TVOCs) emissions were determined using headspace analysis integrated with gas chromatography with flame ionization detector. Determined TVOCs emissions varying in range 21.6–52.1 μg/g and generally value of this parameter decreased with increasing content of PCL phase in studied blends or with application of more efficient di(tert-butylperoxyisopropyl)benzene peroxide as cross-linking agent. It was found that increasing of TVOCs parameter indicated deterioration of mechanical properties of NR/PCL blends, which corresponded with the changes in chemical structure and thermal properties of cross-linked NR/PCL. This confirms that evaluation of TVOCs parameter is interesting alternative for “conventional methods” to characterization of the studied bio-based blends.     

Application of thermal desorption to the development of a gas chromatographic/mass spectrometric method for the determination of toluene,chlorinated aromatic hydrocarbons,and 2,3,7,8-tetrachlorodibenzo-p-dioxin in combustion emissions

A fast and accurate analytical method, which uses commercially available adsorbents (Tenax TA, Carbotrap B and C, and Carbosieve S-III), was developed for the sampling and determination of aromatic hydrocarbons, chloroaromatic compounds, and 2,3,7,8-tetrachlorodibenzo-p-dioxin. The breakthrough volume data show that Carbotrap C has a good capacity for compounds of high molecular weight, whereas Carbosieve S-III and Tenax TA are efficient for volatile compounds. The organic components are thermally desorbed and transferred to a gas chromatograph/mass spectrometer. Importantly, thermal desorption avoids conventional solvent extraction procedures and also allows reuse of adsorbent tubes. Preliminary results for recovery of analytes from tubes packed with single adsorbent prove that a single-adsorbent bed is not capable of sampling a wide range of compounds. The best method to obtain the desired collection and desorption properties is to use adsorbent tubes containing several different materials. The results of optimization studies are summarized.     

Light emission on heating polymer networks formed by radical polymerization

Organic-inorganic hybrid monomers based on alkoxysilanes bearing methacrylate groups, or the pure organic dimethacrylate monomers were photo-polymerized to densely cross-linked networks. Storage of the polymer samples in nitrogen and at ambient laboratory temperature was associated with a slow decay of trapped free radicals and formation of new cross-links. In air, reactions with oxygen lead competitively to formation of peroxides due to easier diffusion in the polymer matrix. The formation and existence of peroxides in samples stored in air was shown by the chemiluminescence (CL) induced at elevated temperatures. The peroxide accumulation proceeds in three stages. At first, approximately up to 6 weeks, a high rate of accumulated peroxides activated by long living radicals is assumed. During the next 20 weeks a steady state oxidation stage is observed before another accumulation of peroxides occurs. The glass transition temperature (T_g) changes were used to estimate variation of cross-link density during ageing the networks. As far as the entirely organic network is concerned the main portion of precursors giving rise to cross-links in the post-curing period was deactivated within 9 weeks under the influence of oxygen. Contrary to this finding in networks based on organic-inorganic hybrid monomers and a copolymer of the inorganic and organic monomers the additional cross-linking is considerably less influenced by oxygen. It is anticipated that a pronounced network structure favours further cross-linking over oxygen addition.     

Determination of airborne methyl ethyl ketone peroxide

Summary A new method for the determination of airborne methyl ethyl ketone peroxide (MEKP) is based on the reaction of peroxides with 4-tert-butyl catechol, in which the peroxide radicals oxidize the catechol to the corresponding benzoquinone. The yellow colour generated is measured at 395 nm. Sampling from factory air can be performed by aluminium oxide sampling tubes. Glacial acetic acid is used as a solvent and for the desorption of the peroxide from the aluminium oxide. The detection limit (0.05 mg/m³ for 4 h samples) for the MEKP in air is well below the current hygienic reference value (1.5 mg/m³). The method was used for MEKP determinations during lamination applications in the production of reinforced unsaturated polyester plastics, where the airborne concentrations of the peroxide were well below the current hygienic reference values.     

Concentration and analysis of trace volatile organics in gases and biological fluids with a new solid adsorbent

Summary A new procedure for sampling, transfer, and analysis of volatile organic compounds by gas chromatography has been developed. An adsorbent trap ultimately becomes an insert for a modified injector port, and a valve system allows the sample to be transferred to a cooled precolumn and finally to the separating column. Several traps may be used for sampling (for multiple injections), and it has been established that such traps may be stored without loss of sample. The ease and reproducibility of this procedure is amenable for the investigation of volatile organic compounds involving air and water pollution, flavor, and aroma analyses, and body fluid metabolites.     

Sorbent-Based Method for the Analysis of Ambient Air Using Supercritical Fluid Desorption/Gas Chromatography

Abstract

The work described in this paper shows how we have investigated the utility of polar polyimide sorbents for the collection of polar and non-polar volatile organic compounds in ambient air. The results indicate that supercritical carbon dioxide can be used to recover a variety of compounds with a wide range of volatilities from polyimide sorbents and that these compounds can be effectively collected onto an adsorbent micro-trap after the expansion of the fluid prior to thermal desorption gas chromatographic analysis. Molecular sieve 3A was used and found to have a very high capacity for removal of water from the supercritical fluid extract stream. The sieve tended to adsorb polar compounds in the absence of water; the presence of water sometimes reduced analyte adsorption. The method was used to collect, recover, and analyze volatile organic compounds from the air of a laboratory building and was shown to be quite sensitive for appropriate compounds.     

超临界流体萃取分离离子液体与有机物及其相平衡的研究

离子液体具有一些优良的物理和化学性质,非常有希望成为传统有机溶剂的替代溶剂.但是如何从过程物流中分离和回收离子液体将是其工业化应用的一个很大挑战.蒸馏、液液萃取和超临界萃取是目前已知的三个可行的方法.其中超临界萃取可应用于离子液体与挥发的或相对不挥发的有机物的分离,而且不存在相间交叉污染.本文从二元体系相平衡、三元体系相平衡、模型化研究和萃取实验结果方面介绍了超临界萃取方法的最新研究进展,在此基础上提出了用超临界丙烷替代超临界二氧化碳作为萃取溶剂的新思路,并探讨了该领域今后的研究方向和工业化前景.     

Stability of reactive low boiling hydrocarbons on carbon based adsorbents typically used for adsorptive enrichment and thermal desorption

In the context of evaluating air sampling methods, laboratory experiments were performed to investigate the stability of eleven selected low boiling hydrocarbons (e.g. 1,3-butadiene, isoprene) adsorbed on four different carbon based adsorbents. The carbon molecular sieves Carboxen 569, Carboxen 1003, Carbosieve SIII and the graphitized carbon black Carbotrap X were tested. The influence of storage duration on the recovery of the analytes was examined by loading the adsorbent tubes with the test compounds via a sample loop under inert gas. Furthermore, the influence of sampling the hydrocarbons continuously from air on the recovery of the analytes was investigated using a simple experimental set-up providing a flow of synthetic air spiked with the hydrocarbons. Analysis of the loaded adsorbent tubes was performed by thermal desorption and capillary gas chromatography. Losses up to 80% of 1,3-butadiene and isoprene were observed for the carbon molecular sieves, occurring even immediately after the sampling step. In contrast, no significant losses of these reactive constituents were detected for Carbotrap X over a storage time of seven days. The laboratory investigations were confirmed in a field experiment.     

热解析-气相色谱法测定印刷品中总挥发性有机化合物释放量

建立用气袋法收集整册印刷品释放的挥发性有机化合物,热解析-气相色谱法检测总挥发性有机化合物(TVOC)的方法。将印刷品样品置入充满高纯氮气的密封PVF采样袋中,在35℃下放置12 h后,用采样器串联Tenax-TA采样管和采样袋,让袋内气体通过采样管,样品释放出的有机化合物被吸附到采样管的吸附剂上。用热解析-气相色谱法测试采样管中挥发性有机化合物的含量,其中苯、甲苯、邻二甲苯、间二甲苯、对二甲苯、乙苯、乙酸丁酯、苯乙烯和正十一烷按外标法定量,其它物质按甲苯标准曲线定量。该方法的加标回收率为74.4%~91.1%,测定结果的相对标准偏差不大于10%(n=9)。该方法的样品采集更贴近印刷品的实际生活场景,可以为评价印刷品挥发性有机物释放对人体健康的影响提供数据基础,为相关评价提供新思路。     

Effectiveness of Organic Peroxide Initiators in the High-Pressure Polymerization of Ethylene

The effectiveness of organic peroxides as initiators in the polymerization of high-pressure polyethylene has been studied in order to assess the most successful from a technical and economic view point. For this purpose polymerization experiments were carried out with ten different peroxides which are effective at various temperature ranges, e.g., 110 to more than 300° C. The organic peroxide consumption per kilogram of polyethylene produced was determined as a function of reaction temperature, pressure, organic peroxide concentration, and the mean residence time in the reactor. Also the dependence on the intensity of stirring inside the reactor was studied. The organic peroxide consumption initially decreases with increasing temperature, passes through a minimum, and then rises again. The minimum organic peroxide consumption and the related temperature are different for individual organic peroxides and are greatly influenced by the reaction conditions. From a study of the results, criteria to select the most suitable organic peroxide for certain reaction conditions including financial considerations are put forward.     

Stability of reactive low boiling hydrocarbons on carbon based adsorbents typically used for adsorptive enrichment and thermal desorption

In the context of evaluating air sampling methods, laboratory experiments were performed to investigate the stability of eleven selected low boiling hydrocarbons (e.g. 1,3-butadiene, isoprene) adsorbed on four different carbon based adsorbents. The carbon molecular sieves Carboxen 569, Carboxen 1003, Carbosieve SIII and the graphitized carbon black Carbotrap X were tested. The influence of storage duration on the recovery of the analytes was examined by loading the adsorbent tubes with the test compounds via a sample loop under inert gas. Furthermore, the influence of sampling the hydrocarbons continuously from air on the recovery of the analytes was investigated using a simple experimental set-up providing a flow of synthetic air spiked with the hydrocarbons. Analysis of the loaded adsorbent tubes was performed by thermal desorption and capillary gas chromatography. Losses up to 80% of 1,3-butadiene and isoprene were observed for the carbon molecular sieves, occurring even immediately after the sampling step. In contrast, no significant losses of these reactive constituents were detected for Carbotrap X over a storage time of seven days. The laboratory investigations were confirmed in a field experiment. Received: 28 June 1999 / Revised: 18 August 1999 / Accepted: 23 August 1999     

An adaptive breath sampler for use with human subjects with an impaired respiratory function

An adaptive sampler for collecting 2.5 dm(3) samples of exhaled air from human subjects with an impaired respiratory function is described. Pressure in the upper respiratory tract is continuously monitored and the data used to control an automated system to collect select portions of the expired breathing cycle onto a mixed bed Tenax(trade mark) and Carbotrap(trade mark) adsorbent trap for analysis by GC-MS. The sampling approach is intended for use in metabolomic profiling of volatiles in human breath at concentrations greater than microg m(-3). The importance of experimental reproducibility in metabolomic data is emphasised and consequently a high purity air supply is used to maintain a stable exogenous volatile organic compound profile at concentrations in the range 5 to 30 microg m(-3). The results of a 90 day stability study showed that exogenous VOCs were maintained at significantly lower levels (40 times lower for isopropyl alcohol) and with significantly higher reproducibility (80 times lower standard deviation for isopropyl alcohol) than would have been be the case if ambient air had been used. The sampling system was evaluated with healthy controls alongside subjects with chronic obstructive pulmonary disease. Subjects were able to breathe normally with control subjects observed to breathe at a rate of 9 to 17 breaths per minute, compared to 16 to 30 breaths per minute for subjects with COPD. This study presents, for the first time, observations and estimates of intra-subject breath sample reproducibility from human subjects. These reproducibility studies indicated that VOCs in exhaled breath exhibit a variety of dynamic behaviours, with some species recovered with a RSD <30%, while other species were observed to have significantly more variable concentrations, 30 to 130% RSD. The approach was also demonstrated to reliably differentiate the differences in the VOC profiles between alveolar and dead space air.     

Quantification of volatile PAHs present at trace levels in air flow by aqueous trapping—SPE and HPLC analysis with fluorimetric detection

In the context of a European project, a new approach of sampling of volatile polycyclic aromatic hydrocarbons (PAHs) from air was developed. In fact, the aim of this project was to test the efficiency of an air cleansing prototype reactor, which was operating by non-thermal plasmolysis. With an eye to model the atmosphere ejected by the prototype, we needed to vaporise the volatile PAHs in an air stream at concentrations as low as those recommended by European Directives (96/62/CE) for PAHs in ambient air (i.e. 1 ng m⁻³). Our strategy was based on the analysis of PAHs trapped in an aqueous medium, in order to avoid important losses of volatile compounds observed during the delicate desorption-concentration step when classical solid supports are used. Then a study was carried out to determine: the design of the collecting part, the flow-rate of the air sampling, the nature and concentration of chemical additives used to enhance PAH solubility in water. The very highly diluted aqueous media obtained after the bubbling step were concentrated by solid-phase extraction (SPE) on hydrophobic cartridges and analysed on-line by reversed-phase HPLC with UV and fluorimetric detections. Lastly, the sampling technique was directly applied to the outlet of the air cleansing prototype and the analysis after 3-6 h of non-thermal plasmolysis showed that the target volatile PAHs were not present in an air stream initially polluted by volatile organic compounds.     

Design and application of Hadamard-injectors coupled with gas and supercritical fluid sample collection systems in Hadamard transform-gas chromatography/mass spectrometry

A novel Hadamard transform-gas chromatography/mass spectrometry (HT-GC/MS) system equipped with on-line sample collection systems is described. A Hadamard-injector was successfully designed and then coupled with an on-line adsorption/desorption system for detecting volatile organic compounds (VOCs) and a supercritical fluid extraction (SFE) system, respectively, by HT-GC/MS. Six VOCs and three pesticides were used as model compounds. In the former case, an activated-charcoal trap was used to trap VOCs from the indoor air. After 10 L of indoor air had passed through the trap, the condensed components were heated and simultaneously injected into the GC column through the Hadamard-injector, based on Hadamard codes. In a second experiment, a sample of rice was spiked with three types of pesticides and the sample then extracted using a commercially available supercritical fluid extractor. After extraction, the extracted components were transferred to a holding tank and simultaneously injected into the GC column also using the Hadamard-injector. The findings show that, in both cases, the combination of on-line sample collection methods and the use of the Hadamard transform resulted in improved sensitivity and detection. Compared to the single injection used in most GC/MS systems, the signal-to-noise (S/N) ratios were substantially improved after inverse Hadamard transformation of the encoded chromatogram.     

Sorption Tubes Packed with Polydimethylsiloxane: A New and Promising Technique for the Preconcentration of Volatiles and Semi-Volatiles from Air and Gaseous Samples

This paper is concerned with the determination of volatile and semi-volatile organic components in air and gaseous (headspace) samples, focusing primarily on polar analytes. Samples were analyzed by preconcentration on different (ad)sorbents followed by thermal desorption and analysis by capillary gas chromatography. The performance of a cartridge filled with 100% polydimethylsiloxane (PDMS) particles was compared to that of adsorbents like Tenax TA and Carbotrap 300. Though the PDMS phase is non-polar it showed adequate retention for both polar and non-polar components. The blank runs of the PDMS trap were significantly better than those of most adsorbents and did not deteriorate, as was the case with all the conventional adsorbents investigated. With respect to trapping efficiencies, the PDMS phase performed better for most of the analytes under investigation compared to the adsorbents. For a range of analytes including triethylamine, butanone, diacetyl, nicotine, and acetic acid the PDMS phase performed exceptionally well whereas all adsorbents showed unsatisfactory performance. The packed PDMS traps were employed for the determination of organic acids, PAH's and nitro-PAH's in air and for the analysis of the headspace of cacao and hop.     

Application of a unique selective PLOT capillary column for the analysis of oxygenated compounds in ambient air

Summary A new PLOT column (CP-LOWOX) designed specifically for the analysis of oxygenated compounds has been used for the gas chromatographic determination of semi-volatile carbonyl compounds. The separation behavior of the new column was investigated by comparing it with the widely used non-polar polydimethylsiloxane and polar poly(ethylene glycol) columns. The CP-LOWOX column has unique selectivity for aldehydes and ketones enabling a selective separation of these analytes from predominating hydrocarbon matrices. Application of the CP-LOWOX column for the analysis of polar compounds in ambient air is demonstrated. Sampling was performed by adsorptive enrichment coupled with thermal desorption. The suitability of Tenax TA and a multi-bed adsorbent trap Carbotrap C and Carbotrap) was tested for the sampling of semivolatile carbonyl compounds. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Passive sampling application to control air quality in interior of new vehicles

The investigation of air pollution is a highly important field of research. Air quality in a vehicle’s interior has attracted growing attention since people spend much of their time in vehicles and those frequently travelling in new cars are exposed to harmful compounds. The main air pollutants inside new vehicles are volatile organic compounds (VOCs), present as a result of interior materials’ de-gassing. Among the sampling methods used in indoor air quality research, active sampling for VOCs collection is one method that has been extensively described and applied. The present study sought to implement passive sampling with Radiello® samplers to collect air samples directly in the car factory. The results from passive sampling were compared with results derived from active sampling using Carbograph 1TD and silicagel coated with 2,4-dinitrophenylhydrazine cartridges, based on previously validated methods. The identification and quantification of organic compounds was performed using gas chromatography with flame ionisation coupled with a mass spectrometer after thermal desorption. Aldehydes were determined by means of high-performance liquid chromatography. In the present study, the results obtained with the use of active and passive methods of air sampling were compared, correlations between the two sampling methods were designated and the repeatability of passive sampling was detailed.     

Advanced Methodologies for Sampling and Analysis of Toxic Organic Chemicals in Ambient Outdoor,Indoor, and Personal Respiratory Air

Many different kinds of sampling devices and analytical techniques are required to assess the potential adverse effects of toxic air pollutants on human health and the ecosystem. The U.S. Environmental Protection Agency has an on-going research and development program designed to provide the necessary tools to monitor air quality both outdoors and indoors and to measure personal respiratory exposures. Particular emphasis in recent years has been placed on real-time and integrative methods for neutral and polar volatile organic chemicals (e.g., chlorinated hydrocarbons, single-ring aromatics, alcohols, aldehydes, ethers, thiols, nitriles) and semi-volatile organics (e.g., polynuclear aromatics, nitrated aromatics, pesticides, phenols). Samplers capable of obtaining sufficient quantities of chemicals for ultratrace analyses and sometimes bioassay, that are also quiet, unobtrusive and user-friendly, are being developed and evaluated for indoor, outdoor, and personal monitoring. New analytical techniques such as matrix-isolation GC/FTIR, and supercritical fluid extraction and chromatography are being adapted to characterize collected samples.