Trace Determination of Organic Compounds in Water by Direct Enrichment in Multichannel Thick Film Silicone Rubber Traps with Capillary Gas Chromatography

The application of Multichannel Silicone Rubber Traps for the direct analysis of organic compounds in water was studied. The optimum collection flow rate for a 10 mL sample was found to be ca. 150 μL·min^–1. The effect of methanol on the retention power of the trap was evaluated. The addition of a methanol fraction of up to 40% to the water standards did not show any loss in collection efficiency. It was shown that the extraction of organic compounds from water with the multichannel trap is uncomplicated, i. e. methanol is not required to achieve accurate analyses, concentration of the sample onto the trap is by gravity flow, and excess water remaining in the multichannel trap after water extraction is removed by centrifugation. With the use of the multichannel silicone rubber trap a wide boiling point range of compounds were analyzed from aqueous samples at levels of 1–4 μg·L^–1.     

Trapping efficiency of aqueous pollutants in multichannel thick-film silicone-rubber traps for capillary gas chromatography

Established standard methods for analysing aqueous pollutants by capillary gas chromatography are cumbersome, time-consuming and expensive. With the aim of replacing the sample preparation procedures with direct concentrating and thermal desorption steps multichannel silicone-rubber traps were tested to determine breakthrough volumes and optimum accumulation conditions as a function of water flow-rate. Larger multichannel traps, consisting of 32 silicone tubes in parallel were made to increase the collection flow-rate through the trap with the same extraction efficiency of the initial smaller traps. It was shown that by increasing the number of parallel silicone tubes in the multichannel trap the breakthrough volume of benzene is 37 ml at a flow-rate of 75 microl/min and the trap displays 11 theoretical plates under these conditions.     

酸处理Silicalite—I沸石填充硅橡胶渗透蒸发分离膜

研究酸处理Ｓｉｌｉｃａｌｉｔｅ—Ｉ沸石对有机溶剂、水的吸附、脱附性质，酸处理Ｓｉｌｉｃａｌｉｔｅ—Ｉ填充硅橡胶膜对低浓度有机溶剂水溶液的渗透蒸发分离性能以及填充膜的力学性能。实验结果表明，在硅橡胶膜中填充酸处理Ｓｉｌｉｃａｌｉｔｅ—Ｉ沸石能改善膜对有机溶剂－水混合物的分离性能，且分离性能的改善与沸石在膜中的填充量以及硅橡胶的品种有关。另外，沸石的填充也有利于改善膜的力学性能。     

Determination of highly volatile organic contaminants in water by the closed-loop gaseous stripping technique followed by thermal desorption of the activated carbon filters

Very volatile organic contaminants in water were determined by using closed-loop gaseous stripping combined with thermal desorption from the activated carbon filter into a high-resolution gas chromatograph. The operating parameters for quantitative applications were evaluated. The solvent-free thermal desorption procedure permits the determination of compounds that normally elute under the gas chromatographic solvent peak (e.g., dichloromethane and Freons). Sixteen volatile compounds with boiling points in the range -30 to 120 degrees C were determined with an overall recovery of 12-52%. Qualitative determinations of volatiles from a secondary sewage effluent were in good agreement with the results found by two more established methods.     

A quantitative model for the surface restructuring of repeatedly plasma treated silicone rubber

Surface restructuring in ambient air of medical grade silicone rubber surfaces modified by repeated RF plasma treatments using various discharge gases including oxygen, argon, carbon dioxide and ammonia, was studied quantitatively. From advancing and receding water contact angle data, the fraction of the surface covered by mobile and immobile polar groups, and a characteristic time constant of the restructuring process were calculated. For argon plasma treated surfaces, the fraction of immobile polar groups increased with repeated plasma treatments, but remained relatively constant for samples repeatedly treated by an ammonia plasma. The use of an oxygen plasma only yielded incorporation of mobile polar groups but not of immobile polar groups. The increase in the restructuring time constants of argon and ammonia plasma treated silicone rubber with the number of plasma treatments suggested enhanced crosslinking of the silicone rubber by these plasmas. In contrast, when an oxygen plasma was repeatedly used, the restructuring time constant decreased suggesting chain cleavage by an oxygen plasma. Tentatively, the carbon dioxide plasma treatment of silicone rubber may initially (up to 3–4 repeated treatments) yield chain cleavage, while the occurrence of crosslinking is indicated after more repetitions.     

Extraction,confirmation, and screening of non-target compounds in silicone rubber teats by purge-and-trap and SPME combined with GC-MS

As a food contact material, the safety of silicone rubber teats for infants is very important. This analysis of non-target compounds in silicone rubber teats is a prospective work on the safety evaluation and early warning mechanism for similar polymer materials. In this study, two “green” analytical approaches were applied to extract non-target compounds in 30 silicone rubber teats based on the purge-and-trap method and solid phase microextraction. A total of 140 extracted compounds were separated and identified by gas chromatography-mass spectrometry, coupled with three qualitative methods, namely, matching with the mass spectra library, retention index (RI) and standard confirmation. Chromatographic peak area normalization was used to approximate the relative content of each component. A database containing 140 compounds in 12 categories was established. To identify the noteworthy compounds that could migrate and endanger infant health, all compounds were filtered by a three-step screening process based on the detection rate, RI and relative content. Finally, the 53 selected compounds included alkanes, siloxanes, aromatics, aldehydes, trimethylsilanol, butylated hydroxytoluene, N,N-dibutylformamide and benzothiazole. Given their higher detection rate, higher relative content or potential toxicity, these compounds should be further investigated for safety evaluation.     

Hydrophobic modification of poly(phthalazinone ether sulfone ketone) hollow fiber membrane for vacuum membrane distillation

New hydrophobic poly(phthalazinone ether sulfone ketone) (PPESK) hollow fiber composite membranes coated with silicone rubber and with sol–gel polytrifluoropropylsiloxane were obtained by surface-coated modification method. The effects of coating time, coating temperature and the concentration of silicone rubber solution on the vacuum membrane distillation (VMD) properties of silicone rubber coated membranes were investigated. It was found that high water permeate flux could be gotten in low temperature and low concentration of silicone rubber solution. When the coating temperature is 60 °C, the coating time is 9 h and the concentration of silicone rubber solution is 5 g L⁻¹ the water permeate flux of the silicone rubber coated membrane is 3.5 L m⁻² h⁻¹. The prepolymerization time influence the performance of polytrifluoropropylsiloxane coated membranes, and higher prepolymerization time decrease the water permeate flux of the membrane. The water permeate flux and the salt rejection was 3.7 L m⁻² h⁻¹ and 94.6%, respectively in 30 min prepolymerization period. The VMD performances of two composite membranes during long-term operation were studied, and the results indicated that the VMD performances of two composite membranes are quite stable. The salt rejection of silicone rubber coated membrane decreased from 99 to 95% and the water permeate flux fluctuated between 2.0 and 2.5 L m⁻² h⁻¹. The salt rejection of polytrifluoropropylsiloxane coated membrane decreased from 98 to 94% and the water permeate flux fluctuated in 1 L m⁻² h⁻¹ range.     

Trace-level determination of 1,4-dioxane in water by isotopic dilution GC and GC-MS

The volatile and polar solvent 1,4-dioxane has recently been reported as a contaminant of ground and surface waters, establishing the need to determine this substance in drinking water. This investigation established that 1,4-dioxane can be determined in water by various techniques including direct aqueous injection (DAI) gas chromatography (GC) and purge and trap GC-mass spectrometry (MS). Purge and trap GC-MS is limited by 1,4-dioxane's poor purge efficiency, resulting in detection limits up to 100 times greater than the efficiently purged volatile organic compounds. To attain the sensitivity required for drinking water monitoring, a method based on continuous liquid-liquid extraction with dichloromethane was developed. Isotope dilution was more accurate and reproducible than quantification with external standards, and the improvement in precision led to a lower method detection limit, 0.2 microgram L-1, using a quadrupole ion trap instrument in the electron ionization mode. Isotope dilution accuracy approached 100% in ppb determinations. Isotopic dilution quantification was also possible using a non-selective GC detector owing to the high efficiency of capillary GC columns that resolve the deuterium-labeled solvent from the natural isotopes.     

Pervaporation performance of oligosilylstyrene-polydimethylsiloxane membrane for separation of organics from water

A novel silicone rubber was prepared by crosslinking silylstyrene-oligomer containing -SiH groups with divinyl-polydimethylsiloxane using Karstedt's catalyst at room temperature. Membranes cast from this silicone rubber were found capable of separating chlorinated hydrocarbons and aromatics from water containing trace amount of the organics through pervaporation (PV). Synthesis of this silylstyrene-oligomer, crosslinking it to divinyl-polydimethylsiloxane to produce the silicone rubber and preparation of membranes from this rubber are discussed. PV test results are presented.     

The simultaneous determination of copper and nickel by solvent extraction and gas-liquid chromatography with bis (acetylpivalylmethane) ethylenediimine as reagent

The copper(II), nickel(II) and palladium(II) chelates of the bridged β-ketoamine, bis(acetylpivalylmethane) ethylenediimine, are described. The copper and nickel complexes are readily extracted by cyclohexane at pH 8.0 from aqueous solution. The gas chromatographic separation of the copper and palladium, the nickel and palladium, and the copper and nickel chelates is reported on a silicone gum rubber phase (E-350) supported on Universal B at 285°C. Optimal conditions for the complete separation of copper and nickel are reported; the solvent extraction—gas chromatographic procedures are applied to the determination of the individual metal ions (limit of detection, 1 ng) and to the simultaneous determination of copper and nickel in solution and in alloy samples. A rapid method for the determination of copper in domestic water samples is also described.     

硅橡胶/蒙脱土复合材料的制备、结构与性能

用溶液法和熔融法制备了硅橡胶／蒙脱土复合材料，测定了力学性能、耐热性、耐溶剂性等性能．并与通常采用的２＃气相法白碳黑填充补强硅橡胶的性能作了对比．实验表明，溶液法能使蒙脱土更好地分散在硅橡胶基体中，所得到的复合物的性能有了很大的提高，与２＃气相法白碳黑填充补强的硅橡胶性能相当．     

Hydrodistillation-adsorption method for the isolation of water-soluble, non-soluble and high volatile compounds from plant materials

Proposed method of hydrodistillation–adsorption (HDA) on activated carbon and hydrodistillation (HD) with solvent trap were compared for the isolation of water-soluble, non-soluble and high volatile compounds, such as acids, monoterpenes, isothiocyanates and others from carob (Certonia siliqua L.), rosemary (Rosmarinus officinalis L.) and rocket (Eruca sativa L.). Isolated volatiles were analyzed by GC and GC/MS. The main advantages of HDA method over ubiquitous HD method were higher yields of volatile compounds and their simultaneous separation in three fractions that enabled more detail analyses. This method is particularly suitable for the isolation and analysis of the plant volatiles with high amounts of water-soluble compounds. In distinction from previously published adsorption of remaining volatile compounds from distillation water on activated carbon, this method offers simultaneous hydrodistillation and adsorption in the same apparatus.     

硅橡胶复合材料阻燃研究进展

将功能填料引进到硅橡胶及其复合材料中可以获得特定功能的硅橡胶复合材料,已经成为近些年研究热点。目前阻燃剂种类繁多,但是性能比较单一,这已经不能满足人们的需要。人们在关注硅橡胶复合材料阻燃性能的同时,也考虑与其它性能兼备以及成本等问题。因此,本文综述了铂化合物、磷系阻燃剂、阻燃涂层、阻燃填料和微胶囊化阻燃剂等阻燃体系下硅橡胶复合材料的阻燃研究现状,总结了不同阻燃剂的阻燃机理,并且给出了其今后的改进方法,最后对硅橡胶复合材料阻燃研究的发展做了展望。     

Optimization of the Temperature for the Extraction of Pharmaceuticals from Wastewater by a Hollow Fiber Silicone Membrane

The influence of temperature on the extraction and selectivity of naproxen, ibuprofen, and triclosan by a thin-walled hollow fiber silicone rubber membrane was investigated. Determination of the diffusion coefficients and flux values at 25, 40, and 60 degrees Celsius was undertaken. The diffusion coefficient and flux were found to increase with temperature. It was also observed that at higher temperatures, mass transfer was influenced by the amount extracted in the acceptor phase. However, diffusion from the bulk donor phase through the hollow fiber silicone rubber membrane was shown to control the transport of analytes at lower temperatures. When applied to wastewater, the hollow fiber silicone rubber showed remarkable selectivity toward the analytes. However, at high temperatures, the amount of matrix components extracted also increased slightly. The amount extracted nearly doubled when extraction was performed at 40 degrees Celsius compared to 25 degrees Celsius, indicating that temperature increased the efficiency of the hollow fiber silicone rubber membrane. The application of the technique to municipal wastewater showed remarkable selectivity and reproducibility. The concentrations of these compounds were from 18.4 (1.37 percent) micrograms per liter for triclosan to 1.1 (0.16 percent) micrograms per liter for naproxen in the influent and 2.7 (0.29 percent) micrograms per liter for triclosan to 0.4 (0.01 percent) micrograms per liter for naproxen in the effluent.     

Rapid and sensitive determination of phenylurea herbicides in water in the presence of their anilines by extraction with a Carbopack cartridge followed by liquid chromatography

A rapid and sensitive method for determining phenylurea herbicides in environmental aqueous samples in the presence of their anilines is described. The water sample is preconcentrated by passage at a flow-rate of ca. 150 ml/min through a 250-mg graphitized carbon black (Carbopack B) cartridge. After washing with 0.6 ml of methanol, the Carbopack B trap is connected with a cartridge containing a strong cation exchanger. Organics trapped by the Carbopack cartridge are eluted by passage of 6 ml of methylene chloride-methanol (95:5, v/v). Anilines and other basic compounds are quantitatively subtracted from the solvent system while flowing through the cation-exchange cartridge. After evaporation and redissolution, the sample is subjected to reversed-phase gradient elution high-performance liquid chromatography with UV detection at 250 nm. Recoveries of phenylureas added to water at levels between 30 and 3000 ng/l were higher than 92%. The limit of detection was about 1 ng/l, for a 2-1 sample. With respect to an octadecyl (C18)-bonded silica cartridge, the Carbopack B cartridge had a far better extraction efficiency for polar phenylureas.     

Multi-channel open tubular traps for headspace sampling, gas chromatographic fraction collection and olfactory assessment of milk volatiles

A headspace sampling method is described for concentrating milk volatiles onto a multi-channel open tubular silicone rubber trap (MCT) for thermal desorption into a GC-FID. Sections of the chromatographic profile, single peaks or combinations of compounds are recaptured with secondary MCTs during a subsequent run. The recaptured aroma is released in a controlled manner by heating the MCT in a portable heating device. An aroma release window of several minutes allows up to six people the opportunity to sniff each aroma fraction more than once. Olfactory results suggest that a synergistic combination of 2-heptanone and 2-nonanone could be responsible for a pungent cheese, sour milk-like aroma. MCTs containing single components or fractions can be desorbed into a GC-MS for compound identification.     

Further development of a robust workup process for solution-phase high-throughput library synthesis to address environmental and sample tracking issues

During further improvement of a high-throughput, solution-phase synthesis system, new workup tools and apparatus for parallel liquid-liquid extraction and evaporation have been developed. A combination of in-house design and collaboration with external manufacturers has been used to address (1) environmental issues concerning solvent emissions and (2) sample tracking errors arising from manual intervention. A parallel liquid-liquid extraction unit, containing miniature high-speed magnetic stirrers for efficient mixing of organic and aqueous phases, has been developed for use on a multichannel liquid handler. Separation of the phases is achieved by dispensing them into a newly patented filter tube containing a vertical hydrophobic porous membrane, which allows only the organic phase to pass into collection vials positioned below. The vertical positioning of the membrane overcomes the hitherto dependence on the use of heavier-than-water, bottom-phase, organic solvents such as dichloromethane, which are restricted due to environmental concerns. Both small (6-mL) and large (60-mL) filter tubes were developed for parallel phase separation in library and template synthesis, respectively. In addition, an apparatus for parallel solvent evaporation was developed to (1) remove solvent from the above samples with highly efficient recovery and (2) avoid the movement of individual samples between their collection on a liquid handler and registration to prevent sample identification errors. The apparatus uses a diaphragm pump to achieve a dynamic circulating closed system with a heating block for the rack of 96 sample vials and an efficient condenser to trap the solvents. Solvent recovery is typically >98%, and convenient operation and monitoring has made the apparatus the first choice for removal of volatile solvents.     

Microextraction of volatile organic compounds using the inside needle capillary adsorption trap (INCAT) device

A novel method of solventless extraction has been developed based on a combination of solid phase micro extraction and purge and trap methods. In this technique, a hollow needle with either a short length of GC capillary column placed inside it, or an internal coating of carbon, is used as the preconcentration device. Sampling may be performed on ambient air, on solution, or the solution headspace, by passing the gas or liquid through the device either actively with a syringe, or passively via diffusion. The VOC are sorbed and concentrated onto either the carbon layer, or the liquid stationary phase of the capillary column, within the needle. Placing the needle into a heated GC injection port thermally desorbs the organic compounds directly into the GC without the need for solvent extraction. Results suggest that this procedure provides a rapid and sensitive alternative method to those currently available.     

Surface Modification of Nitrile Rubber by Plasma Polymerization

Radio frequency plasma polymerization of vinylidene fluoride was used to modify the surface properties of nitrile rubber. The chemistry and frictional properties of the plasma films were characterized. FTIR transmission spectra and EDX analysis of plasma polymer films deposited on NaCl windows showed that the degree of fluorination of the plasma polymers increased as plasma power was increased from 25 to 50 W, and then decreased monotonically at higher powers. An estimation of the actual F/C ratio from EDX data indicated that the plasma polymer films contained approximately one fluorine atom for every 2–5 carbon atoms. Sliding friction tests on a Delrin countersurface showed that the coefficient of friction of the plasma treated rubbers was lower than untreated rubber, but slighly higher than rubber coated with silicone oil. Repetitive sliding friction testing showed that silicone oil treated samples had a longer lubricating lifetime than plasma treated samples. However, cyclic friction tests conducted with nitrile rubber o-rings yielded similar frictional behavior and lubricating lifetimes for silicone oil and plasma treatments. There was no correlation between chemical composition and the frictional and wear properties of the plasma films. Environmental scanning electron micrographs showed that the plasma films were brittle and tended to crack and flake off during wear testing.     

Use of open-tubular trapping columns for on-line extraction–capillary gas chromatography of aqueous samples

The applicability of open-tubular trapping columns for on-line extraction–capillary GC analysis is evaluated. The extraction step involves sorption of the analytes from water into the stationary phase of an open-tubular column, removal of the water by purging the trap with nitrogen, and desorption of the analytes with an organic solvent. The effect of swelling of the stationary phase with organic solvents on the retention power of the trap is studied. When using pentane or hexane as swelling agent breakthrough volumes of at least 10 ml can easily be obtained for non-polar compounds. For a number of medium polarity compounds breakthrough volumes of 5 ml can be achieved when chloroform is used as the swelling agent. The required drying time is less than 1 minute. Quantitative desorption requires only 75 μl of organic solvent. Solvent elimination prior to transfer to the GC column is carried out using a PTV injector and a multidimensional GC system. The system is applied for the analyses of river water, urine, and serum samples.