Quantitative determination of specified chlorobiphenyls in fish with capillary gas chromatography and its use for monitoring and tolerance purposes

A gel permeation (GPC) clean-up procedure of fish samples in combination with capillary gas chromatography is used for the determination of individual chlorobiphenyls. The described method is compared with a more universal method based on saponification. Starting from a tolerance for PCB's expressed as a technical Aroclor, tolerance for some specified individual chlorobiphenyls are derived. It is shown that these tolerances for specified individual chlorobiphenyls can be used for monitoring and tolerance purposes. Rejection obtained with the Dutch PCB tolerance agree with rejections obtained with individual tolerances.     

Determination of soil fumigants in air using tandem capillary gas chromatography after charcoal trapping

Soil fumigants, like 1,3-dichloropropene and metham-sodium (forming methyl isothiocyanate) diffuse into the atmosphere, thus presenting a hazard to people in the surroundings. A method is described in which a large volume (50 μl) of extractant, used to desorb the compounds from charcoal, is injected into a GC, equipped with two capillary columns. By way of Deans switching, the solvent is separated from the compounds of interest. Modification of a GC sampler makes unattended analyses possible.     

A Facile Diagnostic 1H NMR Method for Syn and anti Hydroxy Systems

In diastereomeric hydroxyl-containing systems, the relative ¹H-NMR chemical shift of the carbamate NH of the in situ generated trichloroacetylisocyanate derivatives appear to be diagnostic for the syn and anti stereochemistry.     

An analytically oriented discretization technique for boundary value problems

Dedicated to ProfessorJ.W. Schmidt on the occasion of his 60 ^th birthday     

Electronic conductivity in La1−xBaxF3−x crystals

The electronic conductivities of solid solutions La_1?xBa_xF_3?x (0 ? x ? 0.0952) were investigated up to 533 K using the Hebb-Wagner dc polarization technique. The electrochemical cell (-)La|La_1?xBa_xF_3?x|Pt(+) has been utilized with Pt as the ion-blocking electrode. Under steady-state conditions the La_1?xBa_xF_3?x solid solutions exhibit electronic conductivity. The electronic conductivity vanishes in pure LaF₃. Together with ac conductivity measurements it appears that the ionic transference number for La_1?xBa_xF_3?x (0 ? x ? 0.0952) is essentially unity over the temperature range studied.     

On the existence of certain generalized Moore geometries,part II

The existence of generalized Moore geometries of type GM_m(s,t,s+1),with st>1, is investigated. In a previous paper it was shown that if the diameter m is odd such a geometry can exist only if m?7; as a consequence of the main result of the present paper the restriction ‘m is odd’ has become superfluous.     

Toward the enantioselective total synthesis of lyngbyatoxin A: on the stereocontrolled introduction of the quaternary stereogenic centre

This paper deals with an approach to the enantioselective total synthesis of Lyngbyatoxin A, with focus on the stereocontrolled introduction of the quaternary stereogenic centre. The key step in the synthesis involves an enantiospecific Lewis-acid mediated rearrangement of chiral vinyl epoxides carrying a 7-substituted indole moiety.     

Ionic conductivity in tysonite-type solid solutions La1−xBaxF3−x

The ionic conductivity of single crystals of tysonite-type solid solutions La_1?xBa_xF_3?x(0?x?0.095) has been studied parallel and perpendicular to the crystallographic c axis in the temperature range 293–1300 K. Three regions can be discerned in the compositional dependence of the ionic conductivity: (i) the “pure” crystal, in which at room temperature no exchange occurs between different types of anion sites in the tysonite structure; (ii) an intermediate region(0 < x < 7 × 10^-2) which reveals changes in both the conductivity activation enthalpy and the magnitude of the conductivity; (iii) a concentrated solid-solution region (x > 7 × 10^-2), where fluoride ions interchange easily among the different anion sublattices. Diffusion coefficients calculated from ionic conductivity results, are in good agreement with those calculated from ¹⁹F NMR measurements. Using the present data, along with ¹⁹F NMR data, dielectric relaxation data and structural considerations, mechanisms governing the ionic conductivity are proposed.