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排序方式: 共有272条查询结果,搜索用时 13 毫秒
31.
An automated direct sample introduction technique coupled to comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (DSI-GC x GC/TOF-MS) was applied for the development of a relatively fast and easy analytical screening method for 17 polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and 4 non-ortho polychlorinated biphenyls (PCBs) in fish oil. Comparison of instrumental performance between DSI-GC x GC/TOF-MS and the traditional gas chromatographic high resolution mass spectrometric (GC-HRMS) method showed good agreement of results for standard solutions analyzed in blind fashion. Relatively high tolerance of the DSI technique for lipids in the final extracts enabled a streamlined sample preparation procedure that only required gel permeation chromatography (GPC) and solid-phase extraction (SPE) cleanup with graphitized carbon black. The sample size for the method was 2g of cod liver oil, which achieved limits of quantitation (LOQs) of 0.019-7.8 pg/g toxic equivalent quotients for the individual PCDD/Fs. Lower detection limits can be achieved by using larger sample size and scaling up the sample preparation procedure, but this adds to the labor, time, solvent consumption, and expense of the approach. However, the streamlined method yielded 0.94 pg/g and 2.3 pg/g LOQs for 2,3,7,8-tetrachloro dibenzofuran (TCDF) and 3,3',4,4',5-pentachloro biphenyl (CB126), which were sufficiently low for regulatory monitoring of 2g samples. Therefore, instead of congener specific analysis, this streamlined analytical screening method for TCDF and CB126 has the potential to monitor fish oil contaminated with dioxin and dioxin-like PCBs at or above current food safety limits. Acceptable recoveries for nearly all analytes at three different spiking levels in fish oil samples were achieved with good repeatability. 相似文献
32.
Development of mass spectrometric methods for detecting arsenic-glutathione complexes 总被引:1,自引:0,他引:1
It has been suggested recently that arsenic-glutathione (As-GSH) complexes play an important role in the methylation of arsenic. The present study describes the development of high-performance liquid chromatography (HPLC)-electrospray tandem mass spectrometry (ES-MS/MS), operated in the selected reaction monitoring (SRM) mode, and HPLC-inductively coupled plasma mass spectrometry (ICP-MS) methods suitable for the sensitive and selective identification of four As-GSH complexes. Method optimization was carried out using a series of synthetically prepared standards, i.e., three As-GSH species containing trivalent arsenic: tri(glutamyl-cysteinyl-glycinyl)trithio-arsenite (ATG), di(glutamyl-cysteinyl-glycinyl)methyl-dithio-arsonite (MADG), and (ã-glutamyl-cysteinyl-glycinyl) dimethyl-thio-arsinite (DMAG), as well as one As-GSH species containing pentavalent As: dimethylthioarsinic acid-glutathione (DMTAV-GSH). The collision induced dissociation behavior of these compounds was investigated in detail to identify optimum SRM transitions for each complex. Both methods were based on reversed-phase chromatography using gradient elution with methanol, formic acid, and water as solvents. The amount of methanol that was used with this HPLC method (up to 12% vol/vol) was compatible with ICP-MS, without the need of a specially adapted interface. Subsequently, these analytical methods were applied to carry out a preliminary investigation about the role of As-GSH complexes in the methylation of arsenite by methylcobalamin (CH3B12) in the presence of glutathione (GSH). For the first time, the complexes ATG, MADG, and trace amounts of DMAG were detected as products of this reaction. 相似文献
33.
Catherine P. Raptopoulou Athanassios K. Boudalis Katerina N. Lazarou Vassilis Psycharis Nikos Panopoulos Michael Fardis George Diamantopoulos Jean-Pierre Tuchagues Alain Mari George Papavassiliou 《Polyhedron》2008,27(18):3575-3586
The use of salicylaldehyde oxime (H2salox) in manganese(III) carboxylate chemistry has yielded new members of the family of hexanuclear compounds presenting the [Mn6(μ3-O)2(μ2-OR)2]12+ core, complexes [MnIII6(μ3-O)2(O2CPh)2(salox)6(L1)2(L2)2] (L1 = py, L2 = H2O (1); L1 = Me2CO, L2 = H2O (2); L1 = L2 = MeOH (3)). Addition of NaOMe to the acetonitrile reaction mixture, afforded the 1D complex [MnIII3Na(μ3-O)(O2CPh)2(salox)3(MeCN)]n (4), whereas addition of NaClO4 to the acetone reaction mixture afforded an analogous 1D complex [MnIII3Na(μ3-O)(O2CPh)2(salox)3(Me2CO)]n (5). The structures of 1–3 present the [Mn6(μ3-O)2(μ2-OR)2]12+ core and can be described as two [Mn3(μ3-O)]7+ triangular subunits linked by two μ2-oximato oxygen atoms of the salox2− ligands, which show the less common μ3-κ2O:κO′:κN coordination mode. The benzoato ligands are coordinated through the usual syn,syn-μ2-κO:κO′ mode. The 1D polymeric structures of 4 and 5 consist of alternating [Mn3(μ3-O)]7+ subunits and Na+ atoms linked through two μ3-κ2O:κO′:κN and one μ4-κ2O:κ2O′:κN salox2− ligands as well as one syn,anti-μ2-κO:κO′ benzoato ligand. DC and AC magnetic susceptibility studies on 1 revealed the stabilization of an S = 4 ground state, and indications of single-molecule magnetism behavior, whereas the DC experimental data from polycrystalline sample of 5 are indicative of antiferromagnetic interactions within the [Mn3] subunit. Solid state 1H NMR data of 1 were used to probe the spin-lattice relaxation of the system. 相似文献
34.
Hopley C Bristow T Lubben A Simpson A Bull E Klagkou K Herniman J Langley J 《Rapid communications in mass spectrometry : RCM》2008,22(12):1779-1786
Product ion spectra produced by collision-induced dissociation (CID) in tandem mass spectrometry experiments can differ markedly between instruments. There have been a number of attempts to standardise the production of product ion spectra; however, a consensus on the most appropriate approach to the reproducible production of spectra has yet to be reached. We have previously reported the comparison of product ion spectra on a number of different types of instruments - a triple quadrupole, two ion traps and a Fourier transform ion cyclotron resonance mass spectrometer (Bristow AWT, Webb KS, Lubben AT, Halket JM. Rapid Commun. Mass Spectrom. 2004; 18: 1). The study showed that a high degree of reproducibility was achievable. The goal of this study was to improve the comparability and reproducibility of CID product ion mass spectra produced in different laboratories and using different instruments. This was carried out experimentally by defining a spectral calibration point on each mass spectrometer for product ion formation. The long-term goal is the development of a universal (instrument independent) product ion mass spectral library for the identification of unknowns.The spectra of 48 compounds have been recorded on eleven mass spectrometers: six ion traps, two triple quadrupoles, a hybrid triple quadrupole, and two quadrupole time-of-flight instruments. Initially, 4371 spectral comparisons were carried out using the data from eleven instruments and the degree of reproducibility was evaluated. A blind trial has also been carried out to assess the reproducibility of spectra obtained during LC/MS/MS.The results suggest a degree of reproducibility across all instrument types using the tuning point technique. The reproducibility of the product ion spectra is increased when comparing the tandem in time type instruments and the tandem in space instruments as two separate groups. This may allow the production of a more limited, yet useful, screening library for LC/MS/MS identification using instruments of the same type from different manufacturers. 相似文献
35.
Husáková L Cernohorský T Srámková J Hubácková K Dolezalová I 《Analytica chimica acta》2008,614(1):38-45
The mixture of palladium (chloride) with citric acid and lithium is proposed as a new chemical modifier for the elimination of interference occurred during the determination of Tl in aqua regia extracts from rocks, soils and sediments by electrothermal atomic absorption spectrometry using instrumentation with deuterium-lamp background correction (D2-ETAAS). Palladium was preferred to rhodium and platinum as to analyte stabilization, citric acid served as an effective reducing agent facilitating formation of Pd-Tl stable covalent bonds playing an important role in the analyte stabilization. Citric acid in addition helps to remove most of interfering chloride at low temperature. The further addition of Li increased significantly the robustness of chemical modifier against strongly interfering ZnCl2 matrix by binding free chlorine into a more stable LiCl molecule. In the presence of the proposed chemical modifier the temperature for the final step of pyrolysis was adjustable up to 1000 °C, without any noticeable loss of volatile Tl species and the interference of the rest chloride matrix was significantly reduced. The application of the modifier to direct determination of Tl in aqua regia extracts from rocks, soils and sediments has ensured the characteristic mass and LOD value for the original sample 13 pg and 0.043 μg g−1, respectively (10-μL aliquots of sample) and has enabled the use of matrix-free standard solutions for attaining accurate analysis. The accuracy was verified by the analysis of certified reference samples and by the comparison of results with those found by an inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometer (ICP-oa-TOFMS) method. 相似文献
36.
Magnetically Induced Continuous CO2 Hydrogenation Using Composite Iron Carbide Nanoparticles of Exceptionally High Heating Power
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Alexis Bordet Dr. Lise‐Marie Lacroix Dr. Pier‐Francesco Fazzini Dr. Julian Carrey Dr. Katerina Soulantica Dr. Bruno Chaudret 《Angewandte Chemie (International ed. in English)》2016,55(51):15894-15898
The use of magnetic nanoparticles to convert electromagnetic energy into heat is known to be a key strategy for numerous biomedical applications but is also an approach of growing interest in the field of catalysis. The heating efficiency of magnetic nanoparticles is limited by the poor magnetic properties of most of them. Here we show that the new generation of iron carbide nanoparticles of controlled size and with over 80 % crystalline Fe2.2C leads to exceptional heating properties, which are much better than the heating properties of currently available nanoparticles. Associated to catalytic metals (Ni, Ru), iron carbide nanoparticles submitted to magnetic excitation very efficiently catalyze CO2 hydrogenation in a dedicated continuous‐flow reactor. Hence, we demonstrate that the concept of magnetically induced heterogeneous catalysis can be successfully applied to methanation of CO2 and represents an approach of strategic interest in the context of intermittent energy storage and CO2 recovery. 相似文献
37.
Voltammetric determination of aminobiphenyls at a boron-doped nanocrystalline diamond film electrode
Voltammetric behavior of 2-aminobiphenyl, 3-aminobiphenyl, and 4-aminobiphenyl at a boron-doped nanocrystalline diamond film electrode was investigated using cyclic voltammetry and differential pulse voltammetry. Optimum conditions have been found for the determination of those genotoxic substances by differential pulse voltammetry at the above given electrode in the concentration range of 2 × 10−7 to 1 × 10−5 mol/L. 相似文献
38.
A reversed-phase high performance liquid chromatographic method for the successful separation and determination of 13 synthetic food colorants (Tartrazine E 102, Quinoline Yellow E 104, Sunset Yellow E 110, Carmoisine E 122, Amaranth E 123, Ponceau 4R E 124, Erythrosine E 127, Red 2G E 128, Allura Red AC E 129, Patent Blue V E 131, Indigo Carmine E 132, Brilliant Blue FCF E 133 and Green S E 142) was developed. A C18 stationary phase was used and the mobile phase contained an acetonitrile-methanol (20:80 v/v) mixture and a 1% (m/v) ammonium acetate buffer solution at pH 7.5. Successful separation was obtained for all the compounds using an optimized gradient elution within 29 min. The diode-array detector was used to monitor the colorants between 350 and 800 nm. The method was thoroughly validated. Detection limits for all substances varied between 1.59 (E 142) and 22.1 (E 124) μg L−1. The intra-day precision (as R.S.D.r) ranged from 0.37% (E 122 in fruit flavored drink at a concentration of 100 mg L−1) to 4.8% (E 142 in icing sugar at a level of 0.9 mg kg−1). The inter-day precision (as R.S.D.R) was between 0.86% for E 122 in fruit flavored drink at 100 mg L−1 and 10% for E142 in jam at a concentration of 9 mg kg−1. Satisfactory recoveries, ranging from 94% (E 142 in jam) to 102% (E 131 in sweets), were obtained. The method was applied to the determination of colorants in various water-soluble foods, such as fruit flavoured drinks, alcoholic drinks, jams, sugar confectionery and sweets, with simple pre-treatment (dilution or water extraction). 相似文献
39.
40.
Theocharakis P Glotsos D Kalatzis I Kostopoulos S Georgiadis P Sifaki K Tsakouridou K Malamas M Delibasis G Cavouras D Nikiforidis G 《Magnetic resonance imaging》2009,27(3):417-422
In this study, a pattern recognition system has been developed for the discrimination of multiple sclerosis (MS) from cerebral microangiopathy (CM) lesions based on computer-assisted texture analysis of magnetic resonance images. Twenty-three textural features were calculated from MS and CM regions of interest, delineated by experienced radiologists on fluid attenuated inversion recovery images and obtained from 11 patients diagnosed with clinically definite MS and from 18 patients diagnosed with clinically definite CM. The probabilistic neural network classifier was used to construct the proposed pattern recognition system and the generalization of the system to unseen data was evaluated using an external cross validation process. According to the findings of the present study, statistically significant differences exist in the values of the textural features between CM and MS: MS regions were darker, of higher contrast, less homogeneous and rougher as compared to CM. 相似文献