Developments in the use of chromatographic techniques in marine laboratories for the determination of halogenated contaminants and polycyclic aromatic hydrocarbons

Chromatography has been an important tool in marine laboratories. Since the 1960s, marine laboratories have been involved in the analysis of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), and brominated flame retardants (BFRs). Column chromatography and liquid chromatography (LC) techniques have been used, mainly in the clean-up phase, while gas chromatography (GC) has been used extensively in the final determination of these contaminants. Developments have been observed from the use of packed GC columns, via capillary columns to the use of heart-cut multi-dimensional GC and comprehensive multi-dimensional GC. The progress made in interlaboratory studies and the availability of certified reference materials are discussed.     

Hydrogen sulphide doping of GaAs and AlxGa1−xAs grown by molecular beam epitaxy (MBE)

H₂S gas has been used during molecular beam epitaxy (MBE) growth of GaAs and Al _x Ga_1–x As as sulphur vector forn-type doping. Doping efficiencies are less than 10^–3 at usual growth temperatures, and are limited by an incorporation competitive surface process, probably 2Ga+H₂SGa₂S+H₂. In Al_xGa_1–x As forx0.2 the doping efficiency is further reduced by carrier freeze-out at deep levels. Measured thermal activation energies depend on growth conditions and remain relatively low even up to the direct-indirect bandgap crossover for substrate temperatures in the 585–645 C range.     

Silica-Supported Tantalum Catalysts for Asymmetric Epoxidations of Allyl Alcohols

Tantalum good, titanium bad: This appears to be the case for silica-supported catalysts for the asymmetric epoxidation of allyl alcohols. Complexes such as [SiO-Ta(OEt)(4)] were prepared from silica and [Ta(=CHCMe(3))(CH(2)CMe(3))(3)], and in the presence of a tartrate and an alkyl hydroperoxide, these surface tantalum compounds lead to efficient and convenient catalysts for the asymmetric epoxidation of 2-propen-1-ol (R=H) and trans-2-hexen-1-ol (R=nPr; see reaction).     

Comparative study of reflectance cells for PLS-FTIR determination of sugars in soft drinks

A comparative study has been carried out between a horizontal Attenuated Total Reflectance (h-ATR) cell and a Cylindrical Internal Reflection (CIR) cell (CIRCLE cell). Both cells were employed for the determination of glucose, fructose, sucrose and total sugar in soft drinks and fruit juices using absorbance measurements at two resolution values (4 and 8 cm^–1). Data were processed by Partial Least Squares regression (PLS). Using a resolution of 4 cm^–1, mean relative errors of prediction from 0.6% to 1.3% were obtained using the horizontal-ATR and from 0.6% to 2.8% using the CIRCLE cell resulting in a limit of detection from 0.03% in the case of sucrose to 0.21% for total sugar for the h-ATR and from 0.06% for sucrose to 0.13% for glucose using the CIRCLE cell. Both cells provided appropriate figures of merit, but the analytical sensitivity obtained using the h-ATR cell was three times higher than that obtained using the CIRCLE cell.     

Influence of the reduction of iodate ion by hydrogen peroxide on the model of the Bray-Liebhafsky reaction

The reduction of iodate ion by hydrogen peroxide, originally postulated by Liebhafsky, is considered as a possible step in the kinetic model proposed by Kolar-Ani and G. Schmitz for the overall Bray-Liebhafsky oscillatory process.     

Hydrogen isotope effects in electron donor-acceptor systems

The charge-transfer (CT) transition of complexes involving alkylated aromatic electron donors shifts hypsochromically upon benzylic deuteration. This is attributed to hyperconjugative effects.     

Thermal decomposition of novel rare-earth selenites

TG and DTA have been carried out on new anhydrous rare-earth selenites R₂Se_aO_3+2a (a=3.5,4) in order to establish their stability. Decomposition occurs in three steps attributed to successive losses of SeO₂. The first process gives rise to other new group of selenites of composition R₂Se₃O₉, which crystallize in two different forms depending on the rare-earth element. The second process leads to isomorphous compounds R₂SeO₅. The final product of thermal degradation is R₂O₃. All products were characterized by chemical analysis and X-ray powder diffraction methods.     

二茂钛含氟有机酸衍生物的质谱研究

本文研究了二茂钛含氟长链有机酸衍生物(1～3)和具有环状结构的新型二茂钛全氟有机酸(4～7)的电子轰击质谱(EIMS)和负离子化学电离质谱(NICIMS)。在EI谱中出现弱的或不出现M~+,1～7均以CpTiF_2离子为基峰。高质量区的主要特征碎片离子有[M-·cp]~+、[M-R]~+(1～3)和氟重排离子。在低质量区出现一系列二茂钛及茂钛氟重排离子。 1、4～7的NICI(CH_4)质谱中,4、5出现强的M~-离子峰,1出现[M-1]-离子峰,有两个钛的环状结构化合物6和7出现双电荷M~=离子峰,而不出现M~-。