Analysis of perfluorinated compounds in sewage sludge by pressurized solvent extraction followed by liquid chromatography-mass spectrometry

Perfluorinated compounds (PFCs) are widely used in everyday life and one of the main recipients of these compounds is waste water treatment plants (WWTPs). Due to the structure and physicochemical properties of PFCs, these compounds could be redistributed from influent water to sludge. This work reports a new validated protocol for the analysis of 13 perfluorinated acids, 4 perfluorosulfonates and the perfluorooctanesulfonamide. The present work has been focused to develop a sensitive and robust method for the analysis of 18 PFCs in sewage sludge, based on pressurized solvent extraction (PSE) followed by solid phase extraction (SPE) clean-up, analytes separation by liquid chromatography and analysis in a hybrid quadrupole-linear ion trap mass spectrometer (LC-QLiT-MS/MS) working in single reaction monitoring (SRM) mode. The final methodology was validated using a blank sewage sludge fortified at different concentration levels. The method limits of detection were ranging in general from 15 to 79 ng/kg. These values were comparable to the decision limit (CCα) and the detection capability (CCβ), which were 17-1134 ng/kg and 18-1347 ng/kg, respectively. The percentage of recovery was from 79 to 111% in the most cases at different spiked levels. Finally, the repeatability of the method was in the range 4% (PFOS and PFOA) to 25% (RSD %). In order to evaluate the applicability of the method, 5 sludge samples were analyzed. The results showed that the 18 PFCs were present in all samples. However, the concentrations for most of them were below the limits of quantification. The compound present at higher concentrations was perfluorooctanesulfonate (PFOS), which was in concentrations from 53.0 to 121.1 μg/kg. The other PFCs were at concentrations between 0.3 and 30.3 μg/kg.     

Sensitivity Analysis Using Adjoint Parabolized Stability Equations for Compressible Flows

An input/output framework is used to analyze the sensitivity of two- and three-dimensional disturbances in a compressible boundary layer for changes in wall and momentum forcing. The sensitivity is defined as the gradient of the kinetic disturbance energy at a given downstream position with respect to the forcing. The gradients are derived using the parabolized stability equations (PSE) and their adjoint (APSE). The adjoint equations are derived in a consistent way for a quasi-two-dimensional compressible flow in an orthogonal curvilinear coordinate system. The input/output framework provides a basis for optimal control studies. Analysis of two-dimensional boundary layers for Mach numbers between 0 and 1.2 show that wall and momentum forcing close to branch I of the neutral stability curve give the maximum magnitude of the gradient. Forcing at the wall gives the largest magnitude using the wall normal velocity component. In case of incompressible flow, the two-dimensional disturbances are the most sensitive ones to wall inhomogeneity. For compressible flow, the three-dimensional disturbances are the most sensitive ones. Further, it is shown that momentum forcing is most effectively done in the vicinity of the critical layer. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of extraction techniques for the isolation of explosives and their degradation products from soil

A comparison of four extraction techniques used for the isolation of 14 explosive compounds (Method 8330-Explosives) from spiked soil samples is described. Soxhlet warm extraction (SWE), pressurized solvent extraction (PSE), microwave assisted extraction (MAE) and supercritical fluid extraction (SFE) were included. The effects of basic extraction conditions – i.e. type of extraction solvent, temperature, pressure, and extraction time – were investigated. The best extraction recovery of the monitored compounds from spiked soil was obtained using pressurized solvent extraction. Recoveries of explosives using the PSE technique were in the range from 65 to 112%. Extraction recoveries by Soxhlet warm extraction and supercritical fluid extraction reached 65–99% and 52–75%, respectively. The lowest extraction recoveries (28–65%) were obtained using microwave assisted extraction. A very low extraction recovery for tetryl was observed in all cases but the best results were achieved by pressurized solvent extraction (58%).     

Nonparallel stability of the flow in an axially rotating pipe

The linear stability of the developing flow in an axially rotating pipe is analyzed using parabolized stability equations (PSE). The results are compared with those obtained from a near-parallel stability approximation that only takes into account the axial variation of the basic flow. Though the PSE results obviously coincide with the near-parallel ones far downstream, when the flow has reached a Hagen-Poiseuille axial velocity profile with superimposed solid-body rotation, they differ significantly in the developing region. Therefore, the onset of instability strongly depends on the axial evolution of the perturbations. The PSE results are also compared with experimental data from Imao et al. [Exp. Fluids 12 (1992) 277], showing a good agreement in the frequencies and wavelengths of the unstable disturbances, that take the form of spiral waves. Finally, a simple method for detecting one of the conditions to characterize the onset of absolute instability using PSE is given.     

Structural and electronic properties of single-walled carbon nanotubes adsorbed with 1-pyrenebutanoic acid, succinimidyl ester

The adsorption of a 1-pyrenebutanoic acid, succinimidyl ester (PSE) interacting with metallic armchair (n, n) carbon nanotubes (CNTs) (n= 3-13) was investigated by using a density-functional tight-binding method with an empirical van der Waals force correction. In this study of large systems involving weak interactions, our calculations showed that the pyrene ring of PSE could be spontaneously absorbed onto the CNTs surface through π-π stacking at the physisorption distances. Increasing of the CNTs diameter leads to a higher adsorption energy. After adsorption of PSE on its sidewall, the geometric and electronic structures of CNTs are basically undamaged. CNTs contribute to the main peak of the electron excitation procedure in the UV/vis spectrum, with a slight red shift after adsorption of PSE.     

Applications of parabolized stability equation for predicting transition position in boundary layers

The phenomenon of laminar-turbulent transition exists universally in nature and various engineering practice.The prediction of transition position is one of crucial theories and practical problems in fluid mechanics due to the different characteristics of laminar flow and turbulent flow.Two types of disturbances are imposed at the entrance,i.e.,identical amplitude and wavepacket disturbances,along the spanwise direction in the incompressible boundary layers.The disturbances of identical amplitude are consisted of one two-dimensional(2D) wave and two three-dimensional(3D) waves.The parabolized stability equation(PSE) is used to research the evolution of disturbances and to predict the transition position.The results are compared with those obtained by the numerical simulation.The results show that the PSE method can investigate the evolution of disturbances and predict the transition position.At the same time,the calculation speed is much faster than that of the numerical simulation.     

Dramatic effect of PSE clamping on the behaviour of d-glucal under Ferrier I conditions

Clamped by the acid-resistant phenylsulfonylethylidene (PSE) acetal, d-glucal privileged the additive pathway over the Ferrier I rearrangement when confronted with protic nucleophiles.     

Determination of 41 polybrominated diphenyl ethers in soil using a pressurised solvent extraction and GC-NCI-MS method

A rapid and reliable analytical method based on pressurised solvent extraction (PSE) and GC-NCI-MS was developed for the determination of 41 different PBDEs in soil. All PBDEs, including mono- to hepta-BDEs (sum of 39 congeners), one nona-BDE and deca-BDE, were efficiently extracted from soil samples using the extraction technology of PSE. The extract was then cleaned up on a florisil column. Satisfactory separation of 41 PBDE congeners was obtained on a 15-m DB-5MS capillary column, saving the use of another 30-m column specific for the separation of mono- to hepta-BDEs. PBDEs were identified and quantified by GC-MS in negative chemical ionisation (NCI) mode, and further confirmed in semi electron impact (SEI) mode when the ion source was also NCI. The method detection limits ranged from 0.01 to 0.03?ng?g^?1?dw for mono- to hepta-BDEs, 1.43?ng?g^?1?dw for the nona-BDE and 0.20?ng?g^?1?dw for deca-BDE. The applicability of the method was tested in soil samples collected from an e-waste recycling site at Guiyu. Twenty-one PBDEs (mono- to deca-) were detected, and eighteen congeners were quantified. The concentration range of PBDEs was 0.78–436?ng?g^?1?dw. BDE-47, BDE-99, BDE-153, BDE-183, BDE-206 and BDE-209 were the dominant congeners, and BDE-209 accounted for 62% of the total PBDEs. The congener profiles of PBDEs in soil samples were similar to those in three commercial PBDE products (Penta-, Octa- and Deca-BDE), and Deca-BDE product was the most important contributor.     

Extracting and trapping biogenic volatile organic compounds stored in plant species

Biogenic volatile organic compounds (BVOCs), released by practically all plants, have important atmospheric and ecological consequences. Because BVOC-emission measurements are especially tedious, complex and extremely variable between species, two approaches have been used in scientific studies to try to estimate BVOC-emission types and rates from plant species. The first, which has known little success, involves grouping species according to plant-taxonomy criteria (typically, genus and family). The second involves studying the correlation between BVOC content and emission (i.e. how leaf content could be used to estimate emissions). The latter strategy has provided controversial results, partly because BVOCs are amazingly chemically diverse, and, as a result, techniques used to study plant BVOC content, which we review, cannot be equally adequate for all analytes.In order to choose an adequate technique, two patterns must be distinguished. Specifically stored compounds - mainly monoterpenes and sesquiterpenes that dominate the essential oil obtained from a plant - are permanently and massively present in specific storage structures (e.g., secretory cavities, trichomes) of the order of μg/g-mg/g and usually allow emissions to occur during stress periods when terpenes are weakly synthesized. These BVOCs can be studied directly through traditional extraction techniques (e.g., hydrodistillation) and novel techniques (e.g., application of microwaves and ultrasound), and indirectly by trapping techniques involving the collection, within adsorbent material, of BVOCs present in the headspace of a plant.Non-specifically stored compounds (e.g., isoprene, 2-methyl-3-buten-2-ol, and, in species without storage structures, monoterpenes and sesquiterpenes) can only be temporarily accumulated in leaf aqueous and lipid phases in small concentrations of the order of ng/g. As a result, studying their concentration in leaves requires the use of trapping techniques, more sensitive to trace amounts. Unlike for specifically stored BVOCs, knowledge of the concentration of non-specifically stored BVOCs cannot provide any information regarding the emission potential of a species but, instead, provides crucial information to understand why BVOC emissions may be uncoupled from the physiological processes that drive their synthesis.We describe both extracting and trapping techniques and discuss them in terms of the technical choices that may cause losses of thermolabile constituents, chemical transformations, different volatile recoveries and suitability to represent plant content of BVOCs faithfully. The second part of this review addresses technical shortcomings and biological and environmental factors that may alter the correlations between BVOC content and emission from plants.     

Improvement for expansion of parabolized stability equation method in boundary layer stability analysis

An improved expansion of the parabolized stability equation(iEPSE) method is proposed for the accurate linear instability prediction in boundary layers. It is a local eigenvalue problem, and the streamwise wavenumber α and its streamwise gradient dα/dx are unknown variables. This eigenvalue problem is solved for the eigenvalue dα/dx with an initial α, and the correction of α is performed with the conservation relation used in the PSE. The i EPSE is validated in several compressible and incompressible boundary layers. The computational results show that the prediction accuracy of the i EPSE is significantly higher than that of the ESPE, and it is in excellent agreement with the PSE which is regarded as the baseline for comparison. In addition, the unphysical multiple eigenmode problem in the EPSE is solved by using the i EPSE. As a local non-parallel stability analysis tool, the i EPSE has great potential application in the eNtransition prediction in general three-dimensional boundary layers.