Inductively coupled plasma mass spectrometric determination of molybdenum in urine

A method was developed for the determination of molybdenum (Mo) in human urine by direct dilution of the sample in doubly distilled water with 1% HNO3 (v/v) and inductively coupled mass spectrometry (ICP-MS). In and Y were used as internal standards. Since (98)Mo provides a higher sensitivity, it was chosen as the reference isotope. The influence of different factors, such as sample dilution, HNO3 concentration and the stability of the analyte were evaluated. The detection limit (LOD) was assessed at 0.2 microg/L Mo, while the lower limit of quantification (LOQ) was 0.6 microg/L. Recoveries ranged between 97.2 and 100.7% from solutions containing from 10 to 50 microg/L Mo. Linear calibration curves were generated from 2.1 and 52.1 microg/L with coefficients of variation (CV ) ranging from 1.62 to 3.56%. In order to establish reference values (RV) for molybdenum, the procedure presented here was used to determine Mo in the urine of a population group living in Tuscany, Italy.     

Determination of coplanar and non-coplanar polychlorinated biphenyls in human serum by gas chromatography with mass spectrometric detection: electron impact or electron-capture negative ionization?

A time- and cost-saving method for the congener-specific analysis of polychlorinated biphenyls (PCBs) in human serum has been developed and validated. After two fast extraction and clean-up steps, analyses were performed using gas chromatography coupled with mass spectrometry with single ion monitoring (GC/SIM-MS), either in electron impact (EI) or electron-capture negative ionization (ECNI) mode. For the determination of dioxin-like congeners, an improvement in EI-MS sensitivity is desirable and use of NI is thus preferred. The procedure was validated for 12 dioxin-like congeners by analyzing spiked samples on three different days and using (13)C(12)-labelled analogues as internal standards. When using an NCI source, the limit of quantification was assessed at 0.01 microg/L, except for PCBs #77 and #81, which cannot be reliably detected below 0.05 microg/L. For the lower chlorinated non-dioxin-like congeners, NI offers less selectivity because of limited fragmentation. Electron impact ionization and electron-capture negative ionization mode can therefore be considered to be complementary for the determination of PCB congeners in the general population.     

Controlling chaos in a satellite power supply subsystem

In this work, we show that chaos control techniques can be used to increase the region that can be efficiently used to supply the power requests for an artificial satellite. The core of a satellite power subsystem relies on its DC/DC converter. This is a very nonlinear system that presents a multitude of phenomena ranging from bifurcations, quasi-periodicity, chaos, coexistence of attractors, among others. The traditional power subsystem design techniques try to avoid these nonlinear phenomena so that it is possible to use linear system theory in small regions about the equilibrium points. Here, we show that chaos control can be used to efficiently extend the applicability region of the satellite power subsystem when it operates in regions of high nonlinearity.     

直接键连原子间的NMR偶合常数的自然杂化轨道研究V.~(13)C-~(13)C和~(13)C-~(31)P核自旋偶合常数~1J_(CC)和~1J_(CP)

在前文工作的基础上，结合ＭＮＤＯ／ＥＨＭＯ分子轨道方法和自然杂化轨道方法，具体计算了ＣＣ键和ＣＰ键的核自旋偶合常数．计算结果表明，１ＪＣＣ和１ＪＣＰ主要由成键原子的轨道杂化作用和键极性这两种结构因素所决定．为从简单价键理论角度解释和计算１ＪＣＣ和１ＪＣＰ值提供了简便直观的方法．     

A biomimetic approach to the chemical inactivation of chrysotile fibres by lichen metabolites

Some lichens were recently reported to modify the surface state of asbestos. Here we report some new insight on the physico-chemical modifications induced by natural chelators (lichen metabolites) on two asbestos samples collected in two different locations. A biomimetic approach was followed by reproducing in the laboratory the weathering effect of lichen metabolites. Norstictic, pulvinic and oxalic acid (0.005, 0.5 and 50 mM) were put in contact with chrysotile fibres, either in pure form (A) or intergrown with balangeroite, an iron-rich asbestiform phase (B). Mg and Si removal, measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), reveals an incongruent dissolution for pure chrysotile (A), with Mg removal always exceeding that of Si, while chrysotile-balangeroite (B) follows a congruent dissolution pattern in all cases except in the presence of 50 mM oxalic acid. A much larger removal of Mg than Si in the solutions of 0.5 and 50 mM oxalic acid with chrysotile (A) suggests a structural collapse, which in the case of chrysotile-balangeroite (B) only occurs with 50 mM oxalic acid; in these cases both samples are converted into amorphous silica (as detected by X-ray diffraction (XRD)). Subsequent to incubation, some new phases (Fe(2)O(3), CaMg(CO(3))(2), Ca(C(2)O(4)) x H(2)O and Mg(C(2)O(4))2 x H(2)O), similar to those observed in the field, were detected by XRD and micro-Raman spectroscopy. The leaching effect of lichen metabolites also modifies the Fenton activity, a process widely correlated with asbestos pathogenicity: pure chrysotile (A) activity is reduced by 50 mM oxalic acid, while all lichen metabolites reduce the activity of chrysotile-balangeroite (B). The selective removal of poorly coordinated, highly reactive iron ions, evidenced by NO adsorption, accounts for the loss in Fenton activity. Such fibres were chemically close to the ones observed in the field. Chrysotile-rich rocks, colonised by lichens, could be exposed to a natural bioattenuation and considered as a transient environmental hazard.     

Determination of dichloroanilines in human urine by gas chromatography/mass spectrometry: validation protocol and establishment of Reference Values in a population group living in central Italy

3,4- and 3,5-Dichloroanilines (DCAs) are common markers of some non-persistent pesticides, e.g. linuron, diuron, vinclozolin, and iprodione. The general population may be exposed to these DCAs and/or their precursors mainly through diet. Since adverse effects on human health, such as endocrine disruption, have been reported, biological monitoring is essential for exposure assessment both of occupationally exposed subjects and of the general population. A highly sensitive and selective gas chromatography/mass spectrometry (GC/MS) method has been developed for the determination of 3,4- and 3,5-DCAs in urine using 4-chloro-2-methylaniline as an internal standard. The selected ion monitoring (SIM) mode was employed for quantitation of the analytes. The sample treatment procedure is simple and fast and no derivatization is required. The overall method was validated including uncertainty measurement. The limit of detection (LOD) and the lower limit of quantitation (LLOQ) were determined to be 0.005 and 0.010 microg/L for both analytes. The method was then applied to the establishment of reference values for a population group living in a rural area of central Italy (Novafeltria, Marche). A total of 151 out of 153 samples were found to be positive for 3,5-DCA, and 81.7% were positive for 3,4-DCA. For this group, 3,4-DCA levels ranged from 0.01 to 6.19 microg/L, while 3,5-DCA urinary concentrations were between 0.02 and 6.71 microg/L.     

Critical evaluation of a high‐throughput analytical method for polychlorinated biphenyls in human serum: which detector for the establishment of the reference values?

A rapid screening method, previously developed and validated for the determination of 60 PCB congeners in human serum by using high-resolution gas chromatography coupled with low-resolution mass spectrometry, was applied to the establishment of the reference values in the general population. The reliability of this method was further confirmed by analyzing ten serum samples, obtained from the same population group involved in the original study, by electron impact ionization with either low- or high-resolution mass spectrometry. Analyses in electron capture negative ionization mode were also performed for the determination of 'dioxin-like' isomers. The data were found to be in good accordance with one another, especially for the congeners of highest environmental significance. Then, 162 real serum samples were analyzed for the presence of PCBs. Comparison with the results from other studies reported in the literature showed that a similar profile was observed; the most abundant congeners were #153, #180, #138 and #170. A statistical analysis was performed to determine whether there were significant correlations between PCB concentrations and specific variables such as age, gender, and dietary habits.     

Rapid and sensitive determination of paclitaxel (Taxol(R)) in environmental samples by high-performance liquid chromatography tandem mass spectrometry

A new, rapid and sensitive method for the quantitative determination of paclitaxel (Taxol(R)) in environmental samples is developed and validated. This highly sensitive and specific method was successfully applied to an environmental monitoring study for identifying occupational exposure situations to anticancer drugs. After addition of an internal standard, 2'-methylpaclitaxel, aqueous extraction of wipe samples or air filters followed by a single-step liquid-liquid extraction with ethyl acetate was performed. Extraction efficiency averaged 90%. The method is based on analysis by liquid chromatography with tandem mass spectrometry in selected reaction monitoring mode of environmental samples from the preparation and administration of cytostatic agents. The assay is linear (r = 0.998) in the range 2-64 ng on filters (air samples), and 20-320 ng on wipe samples. The accuracy of the assay is always 相似文献