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51.
Certain strained five-membered heterocycles undergo thermally-induced, carbon-carbon bond homolysis to generate diradicals capable of initiating vinyl polymerization. These compounds usually contain two oxygen atoms and a larger heteroatom (silicon, phosphorus, sulfur) in addition to carbon. If the heterocycle is suitably substituted with halogen (particularly bromine) containing moities it may function as a vehicle to permit incorporation of flame-retarding units into a polymer or oligomer. When an appropriate heterocycle is used as an initiator for radical polymerization each polymer chain formed contains at least one flame-retarding unit. One such heterocycle is 4,4,5,5-tetra(3,5-dibromophenyl)-2,2-diphenyl-1,3-dioxa-2-silole. In instances in which the heterocycle also acts as a monomer, i.e., it is reactive toward chain-propagating radicals, additional flame-retarding activity may be incorporated into the polymer. 相似文献
52.
53.
Humans are nowadays exposed to numerous chemicals in our day-to-day life, including parabens, UV filters, phosphorous flame retardants/plasticizers, bisphenols, phthalates and alternative plasticizers, which can have different adverse effects to human health. Estimating human’s exposure to these potentially harmful substances is, therefore, of paramount importance. Human biomonitoring (HBM) is the existing approach to assess exposure to environmental contaminants, which relies on the analysis of specific human biomarkers (parent compounds and/or their metabolic products) in biological matrices from individuals. The main drawback is its implementation, which involves complex cohort studies. A novel approach, wastewater-based epidemiology (WBE), involves estimating exposure from the analysis of biomarkers in sewage (a pooled urine and feces sample of an entire population). One of the key challenges of WBE is the selection of biomarkers which are specific to human metabolism, excreted in sufficient amounts, and stable in sewage. So far, literature data on potential biomarkers for estimating exposure to these chemicals are scattered over numerous pharmacokinetic and HBM studies. Hence, this review provides a list of potential biomarkers of exposure to more than 30 widely used chemicals and report on their urinary excretion rates. Furthermore, the potential and challenges of WBE in this particular field is discussed through the review of pioneer WBE studies, which for the first time explored applicability of this novel approach to assess human exposure to environmental contaminants. In the future, WBE could be potentially applied as an “early warning system”, which could promptly identify communities with the highest exposure to environmental contaminants. 相似文献
54.
建立了一种可同时测定锂离子电池电解液中13种有机磷阻燃剂含量的气相色谱-串联质谱分析方法,以乙酸乙酯为萃取溶剂,超声萃取锂离子电池电解液中的有机磷阻燃剂,萃取液经浓缩、定容、过滤后进行气相色谱-串联质谱分析,外标法定量。结果显示,13种有机磷阻燃剂在一定浓度范围内线性良好,相关系数不低于0.999 3,方法的检出限(S/N=3)为0.3~30μg/kg,定量下限(S/N=10)为1~100μg/kg。在低、中、高3个加标水平下的平均回收率为80.4%~94.6%,相对标准偏差(RSD)为3.8%~10%。该方法简单快捷,灵敏度高,定量下限低,可满足锂离子电池电解液中有机磷阻燃剂含量日常检测需要。 相似文献
55.
Maryam Shahbodaghi Hakim Faraji Hamidreza Shahbaazi Mohsen Shabani 《Journal of separation science》2020,43(2):452-461
Based on the solidification of a hydrophobic deep eutectic solvent in air‐assisted liquid phase microextraction combined with gas chromatography and mass spectrometry, a green and sustainable microextraction technique was developed for extracting, separating, and detecting organophosphorus flame retardants in aqueous samples. In this study, some strategies were considered for overcoming or improving the challenges of conventional solvent microextraction procedures. In addition, a hydrophobic deep eutectic solvent with a freezing point near the ambient temperature was employed as an extraction phase, the dispersive solvent was substituted by the syringe pump process, and the centrifugation step was omitted by using salting‐out phenomenon. Further, the effect of the main independent variables was evaluated by using the chemometric methods in order to maximize the extraction efficiency of the procedure. Under optimal conditions, the calibration model was linear in the range of 0.01–25.0 µg/L. Limits of detection and quantitation were assessed at the concentration levels of 2–23 and 9–65 ng/L, respectively. The precision involving repeatability and reproducibility was evaluated by estimating the relative standard deviation, the levels of which were <6.6 and <8.7%, respectively. The applicability of the method was successfully evaluated by analyzing the target analytes in real aqueous samples, which illustrated satisfactory recoveries (95–104.61%). 相似文献
56.
A procedure for the determination of 10 organophosphates, used as flame retardants and plasticizers, in sediment samples is presented. Microwave-assisted extraction (MAE) and gas chromatography with inductively coupled plasma mass spectrometry (GC-ICP-MS) were used for sample preparation and analytes determination, respectively. Influence of different variables on the performance of extraction and determination processes is thoroughly discussed. Temperature, type and amount of organic solvent showed a major effect on the yield of MAE. Regarding GC-ICP-MS detection, the combination of pulsed splitless injection with low radio frequency (rf) power, hard extraction conditions (referred to lens voltage) and addition of nitrogen (0.03 L min−1) to the argon plasma provided the best sensitivity. Under final working conditions, recoveries between 78% and 105%, for samples spiked at different concentration levels, and limits of quantification from 2 to 4 ng g−1 were achieved. Analysis of unspiked sediments confirmed the excellent selectivity of the proposed method for real-life polluted sample analysis. 相似文献
57.
The available investigations on the structure and properties of the enzyme organophosphate hydrolase exhibiting catalytic activity with respect to orthophosphates are reviewed. Recent data on the mechanism of enzymatic hydrolysis of paraoxon are surveyed. The role of two metal ions involved in the enzyme active site is considered. The substrate specificity and the influence of various inhibitors on the kinetic characteristics of the enzyme are discussed. 相似文献
58.
Marosi Gy. Csontos I. Ravadits I. Tohl A. Anna P. Sommer F. Botreau M. Tran M. D. 《Journal of Thermal Analysis and Calorimetry》1999,56(3):1071-1080
Pentaerythritol may react with tetraethoxy-silane and ammonium-polyphosphate in flame retarded polyolefins and an interfacial
layer can be formed around the ammonium-polyphosphate particles. It is advantageous to study such systems using methods of
thermal and surface analysis together.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
59.
Abstract Hydrolytic desulfonation, a general procedure for the replacement of an aromatic sulfonic group by a proton, has wide scientific and commercial utility:1 相似文献
60.
Summary A pressurised, hot-water extraction (PHWE) method was developed for brominated flame-retardants in sediments. The effect of
extraction time, temperature and pressure on PHWE recovery was investigated, together with solid-phase collection parameters
(trapping material, length of trapping column, eluent composition). The concentrated extracts were analysed by GC-MS. PHWE
recoveries were compared with those obtained by conventional Soxhlet-extraction. In general, recoveries were much higher with
PHWE than with Soxhlet. 相似文献