The ethyl halides: Stable neutral and radical cation isomers [C2, H2, X] where X = F,Cl, Br,I

The following isomers of the ethyl halide molecular ions have all been shown to be stable species in the gas phase: [CH₂CH₂FH]⁺˙; [CH₃ClCH₂]⁺˙ (ΔH_f° = 1012 kJ mol^?1); [CH₃CHClH]⁺˙ (ΔH_f° = 971 kJ mol^?1); [CH₂CH₂ClH]⁺˙; [CH₃BrCH₂]⁺˙ (ΔH_f° = 1058 KJ mol^?1); [CH₃CHBrH]⁺˙ (ΔH_f° = 995 kJ mol^?1) and [CH₂CH₂BrH]⁺˙. Neutralization–reionization mass spectrometry, employing Xe as the electron transfer target gas and O₂ as the target gas for reionization, indicated that the ylides CH₃ClCH₂ and CH₃BrCH₂ could not be generated by such means. However, the species CH₃CHClH, CH₂CH₂ClH and CH₂CH₂BrH (and possibly CH₃CHBrH) were unambiguously identified.     

High trans selectivity in the copper bis(oxazoline)-catalyzed asymmetric cyclopropanation of olefins by (trimethylsilyl)diazomethane

Copper(I) bis(oxazoline) species are among the most enantioselective cyclopropanation catalysts that have been reported, although these catalysts generally give low diastereoselectivities. We have observed greatly improved diastereoselectivities using (trimethylsilyl)diazomethane as the carbon source. We have also identified several bis(oxazoline) species that also give comparable or higher enantioselectivities with (trimethylsilyl)diazomethane compared to the more readily available ethyl diazoacetate. The application of this methodology to several olefins has been explored.     

Selective molecularly imprinted polymer combined with restricted access material for in-tube SPME/UHPLC-MS/MS of parabens in breast milk samples

A new molecularly imprinted polymer modified with restricted access material (a hydrophilic external layer), (MIP-RAM) was synthesized via polymerization in situ in an open fused silica capillary. This stationary phase was used as sorbent for in-tube solid phase microextraction (in-tube SPME) to determine parabens in breast milk samples by ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Scanning electron micrographs (SEM) illustrate MIP surface modification after glycerol dimethacrylate (hydrophilic monomer) incorporation. The interaction between parabens and MIP-RAM was investigated by Fourier-transform infrared (FTIR) spectroscopy. The Scatchard plot for MIP-RAM presented two linear parts with different slopes, illustrating binding sites with high- and low-affinity. Endogenous compounds exclusion from the MIP-RAM capillary was demonstrated by in-tube SPME/LC-UV assays carried out with blank milk samples. The in-tube SPME/UHPLC-MS/MS method presented linear range from 10 ng mL⁻¹ (LLOQ) to 400 ng mL⁻¹ with coefficients of determination higher than 0.99, inter-assay precision with coefficient of variation (CV) values ranging from 2 to 15%, and inter-assay accuracy with relative standard deviation (RSD) values ranging from −1% to 19%. Analytical validation parameters attested that in-tube SPME/UHPLC-MS/MS is an appropriate method to determine parabens in human milk samples to assess human exposure to these compounds. Analysis of breast milk samples from lactating women demonstrated that the proposed method is effective.     

Noncovalent Functionalization of Black Phosphorus

Black phosphorus (BP) was functionalized with organic moieties on the basis of liquid exfoliation. The treatment of BP with electron‐withdrawing 7,7,8,8‐tetracyano‐p‐quinodimethane (TCNQ) led to electron transfer from BP to the organic dopant. On the other hand, the noncovalent interaction of BP with a perylene diimide was mainly due to van der Waals interactions but also led to considerable stabilization of the BP flakes against oxygen degradation.     

Production of Ethyl Esters by Direct Transesterification of Microalga Biomass Using Propane as Pressurized Fluid

Applied Biochemistry and Biotechnology - This work aimed to produce ethyl esters from Chlorella vulgaris microalgae biomass, using an immobilized enzymatic catalyst associated with pressurized...     

Determination of cadmium and lead in plastic material from waste electronic equipment using solid sampling graphite furnace atomic absorption spectrometry

The European initiatives to minimize waste electric and electronic equipment (WEEE) and the restriction of hazardous substances (RoHS) had a major impact on the routine control of hazardous substances, including toxic trace metals, such as cadmium and lead, in all kinds of materials that are used in electric and electronic equipment. Instead of analyzing a whole computer, cell phone or television set, individual parts are normally investigated in order to simplify the analytical task. Plastic components are important constituents of electronic equipment, and a potential source of toxic trace metals that are added as catalysts, stabilizers or colorants. As high-tech plastic materials are designed to be resistant against chemical attack, they are usually difficult to bring into solution. A procedure is proposed in the present work that uses direct solid sampling graphite furnace atomic absorption spectrometry and calibration against aqueous standards. The method is sensitive, fast, and it does not require any sample preparation. The limits of detection of 0.1 mg kg^− 1 for Cd and 0.6 mg kg^− 1 for Pb are more than adequate for the purpose. Additional means are presented for reducing the sensitivity in order to cope with high analyte concentration. The method has been tested analyzing two certified reference materials, and good agreement with certified values has been obtained.     

Simultaneous speciation of arsenic (As(III), MMA, DMA, and As(V)) and selenium (Se(IV), Se(VI), and SeCN−) in petroleum refinery aqueous streams

High-performance liquid chromatography (HPLC) coupled to an ICP-MS with an octapole reaction system (ORS) has been used to carry out quantitative speciation of selenium (Se) and arsenic (As) in the stream waters of a refining process. The argon dimers interfering with the ⁷⁸Se and ⁸⁰Se isotopes were suppressed by pressurizing the octapole chamber with 3.1 mL min⁻¹ H₂ and 0.5 mL min⁻¹ He. Four arsenic species arsenite—As(III), arsenate (As(V)), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA)—and three inorganic Se species—selenite Se(IV), selenate Se(VI), and selenocyanate (SeCN⁻)—were separated in a single run by ion chromatography (IC) using gradient elution with 100 mmol L⁻¹ NH₄NO₃, pH 8.5, adjusted by addition of NH₃, as eluent. Repeatabilities of peak position and of peak area evaluation were better than 1% and about 3%, respectively. Detection limits (as 3σ of the baseline noise) were 81, 56, and 75 ng L⁻¹ for Se(IV), Se(VI), and SeCN⁻, respectively, and 22, 19, 25, and 16 ng L⁻¹ for As(III), As(V), MMA, and DMA, respectively. Calibration curve R ² values ranged between 0.996 and 0.999 for the arsenic and selenium species. Column recovery for ion chromatography was calculated to be 97 ± 6% for combined arsenic species and 98 ± 3% for combined selenium species. Because certified reference materials for As and Se speciation studies are still not commercially available, in order to check accuracy and precision the method was applied to certified reference materials, BCR 714, BCR 1714, and BCR 715 and to two different refinery samples—inlet and outlet wastewater. The method was successfully used to study the quantitative speciation of selenium and arsenic in petroleum refinery wastewaters.