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71.
Marta Llorca Marinella Farré Yolanda Picó Damià Barceló 《Analytical and bioanalytical chemistry》2010,398(3):1145-1159
The analytical suitabilities of three different liquid chromatography–tandem mass spectrometry (LC-MS/MS) systems, (1) triple quadrupole (QqQ), (2) conventional 3D ion trap (IT), and (3) quadrupole–linear IT (QqLIT), to determine trace levels of perfluorinated compounds (PFCs) in fish and shellfish were compared. Sample preparation was performed using alkaline extraction and solid-phase-extraction cleanup. This evaluation was focused on both quantitative (sensitivity, precision, and accuracy) and qualitative (identification capabilities) aspects. In the three instruments, the former facet was evaluated using selected reaction monitoring (SRM), which is the standard mode for quantitative LC-MS/MS analysis. Accuracy was similar in the three systems, with recoveries always over 70 %. Precision was better for the QqLIT and QqQ systems (7–15%) than for the IT system (10–17%). The QqLIT (working in SRM mode) and QqQ systems offered a linear dynamic range of at least 3 orders of magnitude, whereas that of the IT system was 2 orders of magnitude. The QqLIT system achieved at least 20-fold higher sensitivity than the QqQ system, and this was at least tenfold higher sensitivity than for the IT system. In the IT system, identification was based on sensitive full mass range acquisition and MS n fragmentation and in the QqLIT system, it was based on the use of an information-dependent-acquisition scan function, which allows the combination of an SRM or MS full scan acting as the survey scan and an enhanced product ion scan followed by MS3 as the dependent scan in the same analysis. Three instruments were applied to monitor the content in fish and shellfish (anchovies, swordfish, tuna, mussels, and oysters) obtained from Valencia and Barcelona markets (Spain). The eight target PFCs were detected at mean concentrations in the range from 10 ng ?kg-1 (perfluoro-7-methyloctanoic acid and perfluoro-1-decanesulfonate) to 4,200 ng ?kg-1 (perfluoropentanoic acid). Furthermore, perfluoroheptanoic and perfluoroundecanoic acids (not covered as target analytes) were identified in some samples. Figure
PFCs in the environment 相似文献
72.
We present a class of cosmological solutions of Einstein equations, with matter and electromagnetic field, which are anisotropic and spatially homogeneous of Bianchi types VIII and IX. 相似文献
73.
Renato Spigler Damián H. Zanette 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1993,44(5):812-827
A BGK-type model is derived to describe the interaction between transport and chemical reactions in multispecies gas mixtures, at the kinetic level. The underlying kinetic process is modelled by a Fokker-Planck-type equation, in the Kramers-Smoluchowski limit. When the reaction terms in the kinetic equation are properly scaled, an expansion in powers of a small parameter related to the mean collison time yields a reaction-diffusion equation for the densities of the chemical species involved. For different scalings of the reaction terms, the related macroscopic equations describe the prevailing of transport processes on chemical reactions, orvice versa. The spatially homogeneous case with its own peculiarities is addressed, and the Selkov model is considered as an example. 相似文献
74.
Gros M Pizzolato TM Petrović M de Alda MJ Barceló D 《Journal of chromatography. A》2008,1189(1-2):374-384
This paper describes the development of an analytical methodology to determine eight beta-blockers in waste waters using molecularly imprinted polymers (MIPs) as extraction and pre-concentration material, followed by liquid chromatography-quadrupole-linear ion trap mass spectrometry (LC-QqLIT MS). The advantages offered by MIPs, in terms of selectivity and specificity, were compared with the most commonly polymeric materials used (the lipophilic-hydrophilic balanced Oasis HLB cartridges). Even though recoveries achieved with both sorbents were similar, ranging from 50 to 110% for sewage treatment plant (STP) effluent and 40-110 for STP influent, respectively, MIPs provided lower method detection limits than Oasis HLB, due to their specificity for target analytes and closely related analogues. Method detection limits (MDL) achieved using MIPs ranged from 0.2 to 6.4 ng/L for STP effluent and from 0.4 to 6.5 ng/L for STP influent. To highlight the advantages of MIPs against conventional polymeric cartridges, a detailed matrix effects study as well as cross reactivity tests were performed. For the latter purpose, the extraction efficiency of some pharmaceuticals and pesticides belonging to different therapeutic classes was assessed. LC-QqLIT MS, used for quantification and confirmation, proved to be a powerful analytical tool, as instrumental detection limits (IDL) achieved ranged from 0.2 to 2.7 pg injected (in multiple reaction monitoring mode (MRM)). In addition the inclusion of high sensitive MS/MS scans for each compound when working in Information Dependent Acquisition mode (IDA) provided extra confirmation for unequivocal identification of target compounds in complex environmental matrices. 相似文献
75.
Terrado M Kuster M Raldúa D Lopez de Alda M Barceló D Tauler R 《Analytical and bioanalytical chemistry》2007,387(4):1479-1488
Data sets obtained from quantitative analysis of seventeen pesticides in water samples from a network of irrigation and drainage
channels in the Ebro river delta (Catalonia, NE Spain) have been analysed by chemometric and geostatistical methods. Samples
were taken at fourteen locations during the main rice-growing season, from May to August 2005. Principal-component analysis
enabled investigation of the spatial and temporal distribution of the main pollution patterns caused by application of pesticides
in the region under study. A first pesticide-contamination pattern from the Ebro river was differentiated from a second more
specific pattern from the water-drainage channels of the delta, collected from the rice fields. The seasonal peak in this
more specific rice pesticide source was observed in July. Coupling the results from chemometric data analysis with use of
geostatistical methods was shown to be a useful procedure for discovery of the most significant spatial and monthly variations
of the main pesticide-contamination patterns, taking into account the particular geographical structure of the area under
study. 相似文献
76.
Carlos Henrique Marchi Leandro Alberto Novak Cosmo Damião Santiago Ana Paula da Silveira Vargas 《Applied Mathematical Modelling》2013,37(12-13):7386-7397
A theoretical basis is presented for the repeated Richardson extrapolation (RRE) to reduce and estimate the discretization error of numerical solutions for heat conduction. An example application is described for the 2D Laplace equation using the finite difference method, a domain discretized with uniform grids, second-order accurate approximations, several variables of interest, Dirichlet boundary conditions, grids with up to 8,193 × 8,193 nodes, a multigrid method, single, double and quadruple precisions and up to twelve Richardson extrapolations. It was found that: (1) RRE significantly reduces the discretization error (for example, from 2.25E-07 to 3.19E-32 with nine extrapolations and a 1,025 × 1,025 grid, yielding an order of accuracy of 19.1); (2) the Richardson error estimator works for numerical results obtained with RRE; (3) a higher reduction of the discretization error with RRE is achieved by using higher calculation precision, a larger number of extrapolations, a larger number of grids and correct error orders; and (4) to obtain a given value error, much less CPU time and RAM memory are required for the solution with RRE than without it. 相似文献
77.
We define a probability measure on the space of polynomials over ? n in order to address questions regarding the attainment of the norm at given points and the validity of polynomial inequalities.Using this measure, we prove that for all degrees k ≥ 3, the probability that a k-homogeneous polynomial attains a local extremum at a vertex of the unit ball of ? 1 n tends to one as the dimension n increases. We also give bounds for the probability of some general polynomial inequalities. 相似文献
78.
We have produced single-crystal spheres and spherical disks of photorefractive barium titanate (BaTiO(3)) . The spheres and disks allow direct fiber-to-fiber two-beam coupling without additional optical elements. We also investigate the spontaneous oscillation of triangles and other whispering-gallery modes in these spherical structures. 相似文献
79.
80.
Wamberto J. L. Queiroz Danilo B. T. Almeida Francisco Madeiro José V. de M. Cardoso Damião F. L. Pereira Marcelo S. Alencar 《Telecommunication Systems》2018,69(3):321-333
Method of moments has been a parameter estimation technique appropriate to calculate signal-to-noise ratio (SNR) estimates in fading channel models in which an optimal technique like maximum likelihood estimation is not mathematically tractable. In this article, the ratio of the second moment squared to the fourth moment of the received signal envelope is considered to calculate an exact expression for the SNR estimate in Nakagami-m fading channel for M-QAM and \(\theta \)-MQAM modulations as well as expressions to evaluate the variance and the mean of the estimate. The paper presents two useful contributions for SNR estimation theory on Nakagami fading. Besides the exact algebraic expression for the estimate for a generalized QAM modulation scheme, its performance is evaluated through a statistical linearization argument. 相似文献