Selenium in environmental waters: Determination, speciation and concentration levels

This article reviews the different methods used for the determination of selenium species in all types of environmental waters. Basic difficulties are discussed and the efficiency of the methods is explained in view of the sub-mug/1. concentration levels. Special attention is paid to preconcentration steps. Published data on speciation and concentration levels in various water samples are critically reviewed.     

Conversion of diaryliodonium salts to aryl fluorides

The preparation of aryl fluorides by the reaction of diaryliodonium salts with KF is discussed. Generally, best results were obtained when the salt Ar₂I⁺X^? was heated with KF in the absence of solvent. The counterion, X^?, must be non-nucleophilic.     

Anomalous vibrational relaxation of a hot S*1 state of 3,4-benzpyrene in 2-methylpentane

Two anomalous emission bands in the fluorescence spectrum of 3,4-benzpyrene, dissolved in 2-methylpentane, have been studied as a function of temperature. These emissions originate from the second excited singlet state S₂, and from a vibrationally excited S₁ (S^*₁) respectively. From the temperature dependence of the relative yield and the decay time of the S^*₁ emission it can be concluded that the vibrational relaxation of this state is hampered. The rate constant for this relaxation process is smaller that 4 > 62;x 10⁷ sec^?1.     

Differentiation between dexamethasone and betamethasone in a mixture using multiple mass spectrometry

Direct gas chromatographic methods to analyse phenylurea pesticides are discouraged by the thermal instability of these compounds, that in conventional hot splitless inlet systems leads to extensive and irreproducible formation of isocyanates and amines. However a careful control of the operating conditions, like the inlet temperature, the pressure and the presence of suitable chemical additives (as acetic acid, low-molecular-mass amines, organic anhydrides) can either: (i) minimise the thermal decomposition enabling the direct GC-MS analysis of phenylureas, or (ii) lead to reproducible conversion to isocyanates. Experimental design was employed to study the effect of the experimental variables on the thermal transformation of phenylurea pesticides in splitless inlet system. Two strategies were alternatively optimised: (i) the minimisation of degradation reactions to increase the signal of phenylureas; (ii) the maximisation of the degradation to isocyanates that are in turn determined. The maximal yields in isocyanate were obtained with high inlet temperatures, low carrier flows in the injection phase and the presence of acetic anhydride. By contrast, the use of relatively low inlet temperatures, high carrier flows during the injection and the presence of an amine maximise the response of the parent compounds.     

Comparison of experimental and calculated relative sensitivity coefficients for spark-source mass-spectrometry of metals

Sensitivity calibration has been performed for the spark-source mass-spectrometric analysis of iron, copper and aluminium matrices, with standard reference materials. The experimental relative sensitivity coefficients, corrected for discrimination effects in the mass spectrometer, are compared with values obtained with various empirical approaches to calculate relative sensitivity coefficients for an r.f. spark. The best correlation found is only of the order of 50%.     

Synthesis of N-(tosyl)azetidin-2-imines

A synthetic route for N-(tosyl)azetidin-2-imines $\text{6}$, a novel class of derivatives of β-lactams, has been developed. The procedure is applicable to the synthesis of azetidin-2-imines related to penicillins and cephalosporins.     

Stability study and quantitative determination of mebeverine hydrochloride in tablets by means of reversed-phase high-performance liquid chromatography

Summary A rapid and specific reversed-phase high-performance liquid chromatographic method (RPHPLC) is described for the determination of mebeverine hydrochloride in tablets. Elution was performed on an octyl silane column with a methanol-water mixture (75-25), containing 0.05% hexylamine as silanol-blocking agent, adjusted to pH 5.0 with phosphoric acid. The method gave accurate, precise and reproducible results. The mean recovery of the drug from six synthetic tablet mixtures was 100.0% with a relative standard deviation (RSD) of 0.94%. In order to test the specificity of the method, the interference of the degradation compounds of mebeverine hydrochloride and of the intermediates from the synthesis was investigated. None of them did interfere. By means of mass spectrometry and UV-spectrophotometry, the degradation compounds of mebeverine were identified as veratric acid and as 4-|ethyl-[2-(4-methoxyphenyl)-1-methylethyl]amino| 1-butanol. The stability study proved that mebeverine hydrochloride is very stable in tablets; the tablets still contain more than 95% of the declared drug potency after storage for more than one year at 50°C.Colofac; Duspatal; Duspatalin     

TEQ-value determinations of animal feed; emphasis on the CALUX bioassay validation

Polyhalogenated aromatic hydrocarbons, such as polychlorinated dibenzo-p-dioxins are a large and diverse group of environmental pollutants. Their tendency to accumulate in the food chain and their toxicity make monitoring necessary. The reference analysis method is laborious and very expensive, therefore cheap and rapid bioassays have been developed. The chemical-activated luciferase bioassay (CALUX) bioassay uses a recombinant cell line, which responds to dioxins and dioxin-like molecules with Ah receptor (AhR)-dependent induction of firefly luciferase in a dose related response. The CALUX was tested for its use in the screening of feed. Aliquots of 20 g of enriched feed were extracted with a toluene:methanol mixture (20:4 v/v) and extracts were defatted on 33% H₂SO₄ silica columns and purified on carbon columns. Only the dioxin and furan fraction was analysed, the PCB fraction was discarded. The precision of the method is acceptable and in compliance with an R.S.D. <30% as suggested for cell-based bioassays in the Commission Directive 2002/70/EC of July 2002. The results evidence good agreement between TEQ-values obtained by either CALUX or GC–HRMS. The method is now routinely in use for a feed screening programme designed by the Federal Agency for the Safety of the Food chain. Approximately, 25 samples are analysed weekly. From the obtained results approximately 10% was confirmed by GC–HRMS. The false positive ratio is 1% and no false negatives were found, making the use of the CALUX technology advantageous.     

Quantitative High Resolution Electron Microscopy

 With the resolution becoming sufficient to reveal individual atoms, HREM is now entering the stage where it can compete with X-ray methods to quantitatively determine atomic structures of materials without much prior knowledge, but with the advantage of being applicable to aperiodic objects such as crystal defects. In our view the future electron microscope will be characterised by a large versatility in experimental settings under computer control such as the illumination conditions (TEM-STEM), CBED, detecting conditions (diffraction, image, ptychography) and many other tunable parameters such as focus (g), voltage, spherical aberration (C _s ), beam tilt, etc. Since modern detectors can detect single electrons, also the counting statistics is known. The only limiting factor in the experiment will be the total number of electrons that interact with the object during the experiment due to the limitations in the exposure time or in the object damage. However, instrumental potentialities will never be exploited fully if not guided by an experimental strategy. Here intuitive guidelines can be very deceptive. For instance an image made with the best electron microscope (C _s  = 0) at the best focus (g = 0) from the best object (phase object) would show no contrast at all. Hence, questions such as what is the best C _s , focus, object thickness, etc. can only be answered properly if done using a method of experiment design.     

Micro-structural characterization of black crust and laser cleaning of building stones by micro-Raman and SEM techniques

Research concerning the formation and removal of black crusts on various historical objects is approached from many different angles. The so-called "yellowing effect", observed after laser treatment for cleaning purposes, has also received a lot of attention. Evidence regarding this phenomenon differs considerably and the actual mechanisms are still speculated on by researchers. In an attempt to elucidate the processes involved in the yellowing effect associated with laser cleaning, a new analytical technique has been used to investigate the black crust, a region of the sample cleaned by laser irradiation at 1064 nm and another region of the same sample subjected to further laser irradiation at 355 nm, on a limestone sample from the cathedral of Seville in Spain. Micro-Raman spectrometry offers the advantage of spatial chemical characterization of the stone, based upon its molecular makeup and was performed on the bulk body of the stone. Raman and scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDXS) results indicate that the surfaces cleaned by irradiation at 1064 nm and by double irradiation at 1064 and 355 nm differed in terms of their calcium sulphate, calcium oxalate and iron oxide content, and that this could contribute to the difference in colour observed.