Development and optimisation of a novel three‐way extraction technique based on a combination of Soxhlet extraction,membrane assisted solvent extraction and a molecularly imprinted polymer using sludge polycyclic aromatic hydrocarbons as model compounds

A novel technique that integrates extraction and clean‐up into a single step format is reported as part of the search for new sample preparation techniques in the analysis of persistent organic pollutants from complex samples. This was achieved by combining the extraction efficiency of the Soxhlet extractor, the selectivity of a size exclusion membrane and the specificity of a molecularly imprinted polymer for the extraction of polycyclic aromatic hydrocarbons from wastewater sludge followed by quantitation using gas chromatography with time‐of‐flight mass spectrometry. The approach is described as the Soxhlet extraction membrane‐assisted solvent extraction molecularly imprinted polymer technique. This technique was optimised for various parameters such as extraction solvent, reflux time and membrane acceptor phase. The applicability of the developed technique was optimised using a wastewater sludge certified reference material and then tested on real wastewater sludge samples. The method detection limits ranged from 0.14 to 12.86 ng/g with relative standard deviation values for the extraction of the 16 US‐EPA priority polycyclic aromatic hydrocarbons from wastewater sludge samples ranging from 0.78 to 18%. The extraction process was therefore reproducible and showed remarkable selectivity. The developed technique is a promising prospect that can be applied in the analysis of organic pollutants from complex solid samples.     

Durable molybdenum oxide coated solid‐phase microextraction fiber for highly selective and efficient extraction of polycyclic aromatic hydrocarbons in water

A bonding method was developed for coating molybdenum oxides onto a steel wire substrate, which was used as a solid‐phase microextraction fiber, was coupled with gas chromatography. Based on the characterization, it is found that the as‐prepared molybdenum oxides material contained a nanobelt structure with a uniform size and good dispersibility. In addition, there were a large number of small protrusions on the surface of the nanobelts. These characteristics provided a large specific surface area for extraction. Molybdenum oxides exhibited a high extraction selectivity for polycyclic aromatic hydrocarbons owing to its moderate coordination. After the optimization of the factors, method detection limits of < 1.25 μg/L were achieved, and the calibration curves were linear within the range of 2–600 μg/L. In addition, repeatability was demonstrated, and the relative standard deviation < 6.4%. The molybdenum oxides coating had a high scratch resistance, which could effectively prevent coating wear and failure. Combined with the high thermal and chemical stability, the service life of the coating was improved and could be used 150 times without a significant reduction in the extraction performance. Finally, the as‐prepared fiber had a comparable extraction capacity and higher partition coefficients that those of commercial polyacrylate fibers.     

Polyaniline-coated magnetite nanoparticles incorporated in alginate beads for the extraction and enrichment of polycyclic aromatic hydrocarbons in water samples

A magnetic solid-phase extraction sorbent consisting of polyaniline-coated magnetite nanoparticles entrapped in alginate beads (PANI/alginate/Fe₃O₄) was successfully synthesised and applied for the extraction and preconcentration of polycyclic aromatic hydrocarbons (PAHs) in water samples. The magnetite nanoparticles helped to provide an easy and rapid isolation of the sorbent from the sample solution using an external magnet. The alginate beads helped to increase the surface area for polyaniline coating. The polyaniline-coated alginate/magnetite composite helped to increase the extraction efficiency due to the π–π interactions between the polyaniline and the PAHs. Various parameters that affected the extraction efficiencies were optimised including the polymerisation time, the amount of sorbent, sample pH, extraction time, ionic strength, and desorption conditions. Under the optimal conditions, a linear response was achieved in the concentration range of 0.040–50.0 µg L^?1, and the limit of detection was 0.010 µg L^?1. This simple, convenient, cost-effective, and environmentally friendly method was successfully applied for the extraction and enrichment of PAHs in water samples. The recoveries ranged from 86.0% to 97.8% with a relative standard deviation <10 %.     

Theoretical studies on the carcinogenicity of polycyclic aromatic hydrocarbons

The distinct molecular regions of a set of 28 polycyclic aromatic hydrocarbons (PAHs) showing varying degrees of carcinogenic activity (CA) have been analyzed on the basis of their calculated molecular electrostatic potential (MESP) at B3LYP/6-31+G(d,p) level of theory. The MESP, being a property directly related to electron density, clearly distinguishes the electron dense centers in the molecule into K, L, M, and newly defined N regions. Further, a quantitative structure activity relationship (QSAR) model of carcinogenicity is developed using the volume of MESP lobes at the named regions for a set of 17 carcinogenic molecules with experimentally known CA index. The QSAR equation suggested that all the geometrical regions are significant in determining the carcinogenic property of PAHs. The model clearly showed that K and M regions have activating carcinogenic effect whereas L and N regions have deactivating carcinogenic effect. The CA showed considerable enhancement when any three distinct regions are present in a PAH. On the other hand, all the PAH systems with only one type of region are inactive irrespective of whether the region is activating or deactivating. Similarly, molecules showing the presence of two types of regions are either inactive or weakly active. The essential features of both the "K, L region" and the "bay region" theories of carcinogenesis are well evident in the new QSAR model, as the former theory works on the basis of activating K and deactivating L regions whereas the latter theory is related with the activating M region.     

Efficient and selective separation of metronidazole from human serum by using molecularly imprinted magnetic nanoparticles

Magnetic molecularly imprinted nanoparticles were prepared through surface‐initiated reversible addition fragmentation chain transfer polymerization by using metronidazole as a template. The molecularly imprinted magnetic nanoparticles were characterized by attenuated total reflection Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy, X‐ray diffraction, and vibrating sample magnetometry. The adsorption characteristics were also investigated and the kinetics of the adsorption of metronidazole on the imprinted nanoparticles were described by the second‐order kinetic model with the short equilibrium adsorption time (30 min). The adsorption isotherm was well matched with the Langmuir isotherm in which the maximum adsorption capacity was calculated to be 40.1 mg/g. Furthermore, the imprinted magnetic nanoparticles showed good selectivity as well as reusability even after six adsorption–desorption cycles. The imprinted magnetic nanoparticles were used as a sorbent for the selective separation of metronidazole from human serum. The recoveries of metronidazole from human serum changed between 97.5 and 99.8% and showed similar sensitivity as an enzyme‐linked immunoassay method. Therefore, the molecularly imprinted magnetic nanoparticles might have potential application for the selective and reliable separation of metronidazole from biological fluids in clinical applications.     

Ultrasensitive separation of methylprednisolone acetate using a photoresponsive molecularly imprinted polymer incorporated polyester dendrimer based on magnetic nanoparticles

We developed an approach for the use of polyester dendrimer during the imprinting process to raise the number of recognized sites in the polymer matrix and improve its identification ability. Photoresponsive molecularly imprinted polymers were synthesized on modified magnetic nanoparticles involving polyester dendrimer which uses the reactivity between allyl glycidyl ether and acrylic acid for the high‐yielding assembly by surface polymerization. The photoresponsive molecularly imprinted polymers were constructed using methylprednisoloneacetate as the template, water‐soluble azobenzene involving 5‐[(4, 3‐(methacryloyloxy) phenyl) diazenyl] dihydroxy aniline as the novel functional monomer, and ethylene glycol dimethacrylate as the cross‐linker. Through the evaluation of a series of features of spectroscopic and nano‐structural, this sorbent showed excellent selective adsorption, recognition for the template, and provided a highly selective and sensitive strategy for determining the methylprednisoloneacetate in real and pharmaceutical samples. In addition, this sorbent according to good photo‐responsive features and specific affinity to methylprednisoloneacetate with high recognition ability, represented higher binding capacity, a more extensive specific area, and faster mass transfer rate than its corresponding surface molecularly imprinted polymer.     

Oxidation of polycyclic aromatic hydrocarbons catalyzed by soybean peroxidase

Soybean peroxidase (SBP) catalyzes the oxidation of a variety of polycyclic aromatic hydrocarbons (PAHs) in the presence of water-miscible organic cosolvents, including acetonitrile, tetrahydrofuran, and dimethylformamide (DMF). Oxidation was optimal at pH 2.0–2.5, with substantially lower reactivity at pH 1.5 as well as at pH > 3.0. Despite the low pH activity optimum, SBP had an observed half-life of 120 h at pH 2.5. Conversions of greater than 90% were observed with anthracene and 9-methylanthracene in the presence of 50% (v/v) DMF. Anthracene oxidation yielded exclusively anthraquinone, thereby demonstrating that SBP catalyzes a formal six-electron oxidation of the unactivated aromatic substrate to the quinone. A mechanism is proposed to account for this reaction that includes the initial one-electron oxidation of the PAH followed by addition of water to the oxidized PAH. 9-Methylanthracene was more reactive than anthracene, and its enzymatic oxidation yielded two products: anthraquinone and 9-methanol-9,10-dihydroanthracene. The former product indicates that loss of the methyl group occurs during enzymatic oxidation. These results suggest that SBP could be useful in the conversion of PAHs into more environmentally benign materials.     

Adsorption of polycyclic aromatic hydrocarbons onto graphyne: Comparisons with graphene

Density functional theory calculations were implemented to expand the knowledge about graphyne and its interaction with polycyclic aromatic hydrocarbons (PAHs). Due to the porous character of graphyne, the adsorption strength of PAHs onto graphyne surfaces is expected to be lower with respect to graphene (a perfect π‐extended system). However, there are not quantitative evidences for this assumption. This work shows that the adsorption strength of adsorbed PAHs onto γ‐graphyne nanosheets (GY) is weakened in 12 ? 23% with respect to the adsorption onto graphene, with a decrease of 10 ? 20% in the dispersive interactions. The adsorption energies (in eV) of the GY–PAH systems can be straightforward obtained as E _ads/eV≈0.033N _H + 0.031N _C, where N _H and N _C is the number of H and C atoms in the aromatic molecule, respectively. This equation predicts the binding energy of graphene–graphyne bilayers with a value of ～31 meV/atom. Analysis of the electronic properties shows that PAHs behaves as n‐dopants for GY, introducing electrons in GY and also reducing its bandgap in up to ～0.5 eV. Strong acceptor or donor substituted PAHs decrease the bandgap of γ‐graphyne in up to ～0.8 eV, with changes in its valence or conduction band, depending on the chemical nature of the adsorbate. Finally, these data will serve for future studies related to the bandgap engineering of graphyne surfaces by nonaggressive molecular doping, and for the development of graphyne‐based materials with potential applications in the removal of persistent aromatic pollutants.     

Effects of spin contamination on estimating bond dissociation energies of polycyclic aromatic hydrocarbons

The objective of this work is to investigate the impact of spin contamination on the prediction of the enthalpies of formation of Polycyclic Aromatic Hydrocarbon (PAH) radicals and of the bond dissociation energies of their precursor molecule. These PAH radicals play a major role in the mass growth of soot precursors leading ultimately to the first soot particles. In this work, we highlights the errors due to spin contamination by comparing spin‐unrestricted open‐shell calculations (UHF, UMP2, and Quadratic CI singles and doubles [QCISD(T)]) with spin‐restricted open‐shell calculations (ROHF, ROMP2, and ROCCSD(T)). The results suggest that one should be very careful using any of the spin‐unrestricted methods (even QCISD (T)) unless the values are extremely close to the theoretical value. Following these observations, we propose a new set of best‐estimates for the enthalpies of formation of these critical PAH radicals using spin‐restricted open‐shell ROMP2 and RCCSD(T) calculations. © 2015 Wiley Periodicals, Inc.     

Retention behavior of large polycyclic aromatic hydrocarbons on cholesteryl 10-undecenoate bonded phase in microcolumn liquid chromatography

Summary The retention behavior of large polycyclic aromatic hydrocarbons (PAH) in reversed-phase microcolumn liquid chromatography has been found to depend primarily on the inherent planarity of the molecules, the degree of orderliness of the bonded phase, and the concentration of solvent. The planarity recognition capability of cholesteryl 10-undecenoate bonded phase for large PAH is comparable with that of monomeric ODS phases. During solvation, however, the phase characteristics seemed to suggest a fairly rigid structure (an ordered phase), i.e. increased selectivity for non-planar molecules which approaches that of polymeric ODS rather than that of other phases with similarly bulky groups, e.g. naphthylethyl and pyrenylethyl bonded phases.     

Differential scanning calorimetry to measure the purity of polycyclic aromatic hydrocarbons

The application of differential scanning calorimetry (DSC) for purity determination is well documented in literature and is used amongst others in the analysis of pure organic crystalline compounds. The aim of this work is to examine whether the DSC method for purity determination consistently produces values for the purity of polycyclic aromatic hydrocarbons (PAHs) which are sufficiently accurate as required for the certification of reference materials. For this purpose, 34 different existing PAH certified reference materials were tested. The DSC results are shown to be consistent with the results obtained by other methods assessing the organic impurities content in PAHs, like gas chromatography (GC), high performance liquid chromatography (HPLC) and mass spectrometry. Significant differences between the measured values and the certified purity values were observed only in a limited number of cases.     

Determination of average molecular polarizabilities of polycyclic aromatic hydrocarbons directly from retention indices

Summary A significant correlation has been found between the retention indices of polycyclic aromatic hydrocarbons on non-polar stationary phases and the average molecular polarizabilities of the molecules separated on these phases. Equations have been derived for the determination of the average molecular polarizabilities, directly from the retention indices.     

A new strategy based on cholesterol-functionalized iron oxide magnetic nanoparticles for determination of polycyclic aromatic hydrocarbons by high-performance liquid chromatography with cholesterol column

This study reported for the first time the use of cholesterol-functionalized magnetic nanoparticles (Fe₃O₄@SiO₂@Chol) for the determination of polycyclic aromatic hydrocarbons (PAHs) in traditional Chinese medicine samples (TCMs) by high performance liquid chromatography (HPLC) coupled with fluorescence detection. The method was efficient, environmentally friendly, and fast. The solvent consumption of the proposed column is only half of the conventional column but with higher efficiency. Influencing factors, including sorbent amount, desorption solvent, sample volume and extraction time, were investigated in detail. Under the optimum conditions, good linearity (R² > 0.991) was obtained over the range of 5–400 ng g⁻¹, with limits of detection (LOD) 0.75, 0.50, 1.0, 0.56, 0.60, 0.84 and 0.80 ng g⁻¹ for anthracene, fluoranthene, pyrene, chrysene, benzo[a]anthracene, benzo(b)fluoranthene and benzo(k)fluoranthene, respectively.     

Colorimetric test-systems for creatinine detection based on composite molecularly imprinted polymer membranes

An easy-to-use colorimetric test-system for the efficient detection of creatinine in aqueous samples was developed. The test-system is based on composite molecularly imprinted polymer (MIP) membranes with artificial receptor sites capable of creatinine recognition. A thin MIP layer was created on the surface of microfiltration polyvinylidene fluoride (PVDF) membranes using method of photo-initiated grafting polymerization. The MIP layer was obtained by co-polymerization of a functional monomer (e.g. 2-acrylamido-2-methyl-1-propanesulfonic acid, itaconic acid or methacrylic acid) with N, N′-methylenebisacrylamide as a cross-linker. The choice of the functional monomer was based on the results of computational modeling. The creatinine-selective composite MIP membranes were used for measuring creatinine in aqueous samples. Creatinine molecules were selectively adsorbed by the MIP membranes and quantified using color reaction with picrates. The intensity of MIP membranes staining was proportional to creatinine concentration in an analyzed sample. The colorimetric test-system based on the composite MIP membranes was characterized with 0.25 mM detection limit and 0.25–2.5 mM linear dynamic range. Storage stability of the MIP membranes was estimated as at least 1 year at room temperature. As compared to the traditional methods of creatinine detection the developed test-system is characterized by simplicity of operation, small size and low cost.     

Reduction of polycyclic aromatic hydrocarbons promoted by cobalt or manganese nanoparticles

A new methodology for the partial reduction of polycyclic aromatic and heteroaromatic hydrocarbons under mild reaction conditions is presented, the process being a reasonable alternative to the catalytic hydrogenation or the Birch reaction. The reduction protocol described is based on the use of cobalt or manganese nanoparticles generated in situ in a simple and economic way, by reduction of commercially available CoCl₂·6H₂O or MnCl₂·2H₂O in the presence of lithium sand and the corresponding PAH, acting itself as an electron carrier. The use of a deuterium-oxide-containing cobalt(II) salt allows the simple preparation of deuterium labeled products. The regiochemistry and degree of reduction in the case of 1-substituted naphthalene derivatives markedly depends on the nature of the metal-NPs used.     

Carbon nanospheres as solid‐phase microextraction coating for the extraction of polycyclic aromatic hydrocarbons from water and soil samples

A solid‐phase microextraction with carbon nanospheres coated fiber coupled with gas chromatographic detection was established for the determination of eight polycyclic aromatic hydrocarbons (naphthalene, biphenyl, acenaphthene, fluorine, phenanthrene, anthracene, fluoranthene, and pyrene) in water and soil samples. The experimental parameters (extraction temperature, extraction time, stirring rate, headspace volume, salt content, and desorption temperature) which affect the extraction efficiency were studied. Under the optimized conditions, good linearity between the peak areas and the concentrations of the analytes was achieved in the concentration range of 0.5‐300 ng/mL for water samples, and in the concentration range of 6.0‐2700 ng/g for soil samples. The detection limits for the analytes were in the range of 0.12‐0.45 ng/mL for water samples, and in the range of 1.53‐2.70 ng/g for soil samples. The method recoveries of the polycyclic aromatic hydrocarbons for spiked water samples were 80.10‐120.1% with relative standard deviations less than 13.9%. The method recoveries of the analytes for spiked soil samples were 80.40‐119.6% with relative standard deviations less than 14.4%. The fiber was reused over 100 times without a significant loss of extraction efficiency.     

Theoretical study concerning the reactivity of imine derivatives of polycyclic aromatic hydrocarbons

The opening reaction of N-protonated polycyclic aromatic hydrocarbon imines has been computed by means of ab initio, density functional, and semiempirical methods of calculation. Imines are predicted to be more stable than the corresponding O-protonated derivatives, epoxides and diol epoxides. On the other hand, the activated N-methanesulfonylbenzene imine presented more favorable DeltaE( not equal ) and DeltaE(r) for ring opening due to the effect of hydrogen-bond interactions. Anti and syn trans-diol benzene imines did not show a different behavior from the unsubstituted imine. According to these calculations, bay-region, fjord-region, and bay-region methyl-substituted compounds opened more easily among the imine derivatives, following the same reactivity pattern as the oxygen analogs. The exothermicity of the opening process correlated with the charge delocalization in the resulting carbocation.     

咪草烟分子印迹聚合物的制备及其选择性吸附性能的研究

以丙烯酸为聚合单体,TMPTA为交联剂,AIBN为引发剂,咪草烟为模板分子,采用在低温光聚合的方法,制备了对咪草烟分子具有选择性识别能力的分子印迹聚合物．通过IR和HPLC表征,咪草烟分子印迹聚合物对咪草烟分子具有良好的识别作用．     

气相色谱-质谱法测定热塑性弹性体中的多环芳烃

建立了一种简单、准确的测定热塑性弹性体中16种多环芳烃(PAHs)的气相色谱-质谱(GC-MS)方法。考察了样品制备、萃取溶剂、萃取方法、时间以及温度对厂家制备的阳性热塑性弹性体样品中PAHs提取效率的影响,确定了萃取条件和方法。样品经甲苯超声萃取、浓缩后用环己烷溶解、二甲亚砜液液萃取净化后采用GC-MS进行分析,内标法定量。通过对不同材质阳性热塑性弹性体样品的加标回收、精密度试验等对建立的方法进行评价,16种PAHs的平均回收率为70%～117%,精密度为0.2%～10.8%。该方法适合于热塑性弹性体中PAHs的测定。