Fully automated standard addition method for the quantification of 29 polar pesticide metabolites in different water bodies using LC-MS/MS

A reliable quantification by LC-ESI-MS/MS as the most suitable analytical method for polar substances in the aquatic environment is usually hampered by matrix effects from co-eluting compounds, which are unavoidably present in environmental samples. The standard addition method (SAM) is the most appropriate method to compensate matrix effects. However, when performed manually, this method is too labour- and time-intensive for routine analysis. In the present work, a fully automated SAM using a multi-purpose sample manager “Open Architecture UPLC®-MS/MS” (ultra-performance liquid chromatography tandem mass spectrometry) was developed for the sensitive and reliable determination of 29 polar pesticide metabolites in environmental samples. A four-point SAM was conducted parallel to direct-injection UPLC-ESI-MS/MS determination that was followed by a work flow to calculate the analyte concentrations including monitoring of required quality criteria. Several parameters regarding the SAM, chromatography and mass spectrometry conditions were optimised in order to obtain a fast as well as reliable analytical method. The matrix effects were examined by comparison of the SAM with an external calibration method. The accuracy of the SAM was investigated by recovery tests in samples of different catchment areas. The method detection limit was estimated to be between 1 and 10 ng/L for all metabolites by direct injection of a 10-μL sample. The relative standard deviation values were between 2 and 10 % at the end of calibration range (30 ng/L). About 200 samples from different water bodies were examined with this method in the Rhine and Ruhr region of North Rhine-Westphalia (Germany). Approximately 94 % of the analysed samples contained measurable amounts of metabolites. For most metabolites, low concentrations ≤0.10 μg/L were determined. Only for three metabolites were the concentrations in ground water significantly higher (up to 20 μg/L). In none of the examined drinking water samples were the health-related indication values (between 1 and 3 μg/L) for non-relevant metabolites exceeded.     

Determination of organic priority pollutants in the low nanogram-per-litre range in water by solid-phase extraction disk combined with large-volume injection/gas chromatography–mass spectrometry

Polybrominated diphenyl ethers, polychlorinated biphenyls, polycyclic aromatic hydrocarbons and organochlorine pesticides in the low nanogram-per-litre range in water were enriched by solid-phase extraction (SPE) disks and their concentration determined by large-volume injection/gas chromatography–mass spectrometry (LVI/GC-MS). One advantage of using SPE disks in comparison with SPE cartridges is that suspended particulate matter (SPM) does not have to be separated prior to the enrichment step, which saves time and effort. To increase the sensitivity of the method, the SPE disk procedure was combined with LVI/GC-MS, which has not been reported so far for water analysis. The method was calibrated in ranges from 0.25 to 2.5 ng/L and from 2.5 to 25 ng/L. The average recovery was 76 % at an analyte concentration of 2.5 ng/L. The limits of quantification, defined at a signal-to-noise ratio of 6:1, reach from 0.1 to 24.0 ng/L and are up to 400 times lower than previously reported in water analysis. By the developed SPE/LVI/GC-MS method, it is possible to investigate the whole water sample without prior separation of the SPM within 2 h including GC-MS analysis.     

Periodic mesoporous hydridosilica--synthesis of an "impossible" material and its thermal transformation into brightly photoluminescent periodic mesoporous nanocrystal silicon-silica composite

There has always been a fascination with "impossible" compounds, ones that do not break any rules of chemical bonding or valence but whose structures are unstable and do not exist. This instability can usually be rationalized in terms of chemical or physical restrictions associated with valence electron shells, multiple bonding, oxidation states, catenation, and the inert pair effect. In the pursuit of these "impossible" materials, appropriate conditions have sometimes been found to overcome these instabilities and synthesize missing compounds, yet for others these tricks have yet to be uncovered and the materials remain elusive. In the scientifically and technologically important field of periodic mesoporous silicas (PMS), one such "impossible" material is periodic mesoporous hydridosilica (meso-HSiO(1.5)). It is the archetype of a completely interrupted silica open framework material: its pore walls are comprised of a three-connected three-dimensional network that should be so thermodynamically unstable that any mesopores present would immediately collapse upon removal of the mesopore template. In this study we show that meso-HSiO(1.5) can be synthesized by template-directed self-assembly of HSi(OEt)(3) under aqueous acid-catalyzed conditions and after template extraction remains stable to 300 °C. Above this temperature, bond redistribution reactions initiate a metamorphic transformation which eventually yields periodic mesoporous nanocrystalline silicon-silica, meso-ncSi/SiO(2), a nanocomposite material in which brightly photoluminescent silicon nanocrystallites are embedded within a silica matrix throughout the mesostructure. The integration of the properties of silicon nanocrystallinity with silica mesoporosity provides a wealth of new opportunities for emerging nanotechnologies.     

Biosynthesis and Ether‐Bridge Formation in Nargenicin Macrolides

The nargenicin family of antibiotics are macrolides containing a rare ether‐bridged cis‐decalin motif. Several of these compounds are highly active against multi‐drug resistant organisms. Despite the identification of the first members of this family almost 40 years ago, the genetic basis for the production of these molecules and the enzyme responsible for formation of the oxa bridge, remain unknown. Here, the 85 kb nargenicin biosynthetic gene cluster was identified from a human pathogenic Nocardia arthritidis isolate and this locus is solely responsible for nargenicin production. Further investigation of this locus revealed a putative iron‐α‐ketoglutarate‐dependent dioxygenase, which was found to be responsible for the formation of the ether bridge from the newly identified deoxygenated precursor, 8,13‐deoxynargenicin. Uncovering the nargenicin biosynthetic locus provides a molecular basis for the rational bioengineering of these interesting antibiotic macrolides.     

Analytic atomic gradients in the fermi-löwdin orbital self-interaction correction

We derived, implemented, and thoroughly tested the complete analytic expression for atomic forces, consisting of the Hellmann-Feynman term and the Pulay correction, for the Fermi-Löwdin orbital self-interaction correction (FLO-SIC) method. Analytic forces are shown to be numerically accurate through an extensive comparison to forces obtained from finite differences. Using the analytic forces, equilibrium structures for a small set of molecules were obtained. This work opens the possibility of routine self-interaction free geometrical relaxations of molecules using the FLO-SIC method. © 2018 Wiley Periodicals, Inc.     

Conversion of Methane and Carbon Dioxide in a DBD Reactor: Influence of Oxygen

A continuous plug flow reactor supported by a dielectric barrier discharge (DBD) is used to study the conversion of methane, carbon dioxide, and oxygen at different compositions. The three studied gases were diluted with helium to 3 % with an overall flow rate of 200 sccm. The 13.56 MHz plasma was ignited at atmospheric pressure. The product stream and the inlet flow were analyzed by a FTIR spectrometer equipped with a White-cell and by a quadrupole mass spectrometer. The DBD reactor generates hydrogen, carbon monoxide, ethane, ethene, acetylene, formaldehyde, and methanol. Additional oxygen in the feed has positive effects on the yield of methanol, formaldehyde and carbon monoxide and reduces the total consumed energy. The hydrogen yield reaches its maximum at medium amounts of oxygen in the inlet flow. The conversion of methane increases to a limiting value of about 35 %. Methane rich feeds increase the yield of hydrogen, ethane and methanol. On the other hand, additional oxygen has a negative influence on the produced amount of C2 hydrocarbons. The conversion of methane and carbon dioxide as well as the yield of synthesis gas components and C2 hydrocarbons increases by changing the plasma power to higher values.     

ChemInform Abstract: Infrared Spectroscopy of Hydrated Bicarbonate Anion Clusters: HCO3‐(H2O)1‐10.

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