Performance-improvement in57Fe-DCEMS by an optimized scintillation counter

Applications of DCEMS or ICEMS for UHV studies of surfaces and interfaces are often severely limited by long recording times. To clarify the practical means to shorten this time, we introduce the “statistical utility rate” α characterizing the statistical quality of a given measurement. By improving detection efficiency and reducing background contribution simultaneously, we have developed an extremely low-noise scintillation detector (Hamamatsu R1635-02 or R2557 photomultiplier with P-47 thin-layer phosphor). Performance comparison with a channeltron by⁵⁷Fe-DCEMS measurements on an 90% enriched⁵⁷Fe foil with 7.2 keV electrons reveals a measuring time gain over an order of magnitude in favour of the scintillation e-detector. Improvements achievable for samples with normal isotope abundance are higher than for enriched ones.     

Surface analysis using ultrashort laser pulses and time-of-flight mass spectrometry

An all-optical mass spectrometric system is presented which combines the advantages of picosecond-laser desorption and post-ionization with the high performance of a time-of-flight mass-spectrometer. System studies show directly that the ionization process is saturated at focal power densities of about 10¹²W/cm². The saturated ionization is used to quantificate the amount of desorbed particles. Typical desorption rates far below one single monolayer per laser pulse could been achieved.     

Isomer-specific determination of 79 polychlorinated diphenyl ethers (PCDE) in cod liver oils, chlorophenols and in a fly ash

The occurrence of polychlorinated diphenyl ethers (PCDEs) has been investigated in two different cod liver oils produced in 1985 and 1993, respectively, from North-Atlantic fish. These samples mirror the distribution of PCDEs among other persistent organochlorine compounds in the marine environment. To elucidate the input of PCDEs in the environment, five possible sources of PCDEs have been analyzed, namely two wood preserving formulations containing approximately 10% pentachlorophenol, two technical chlorophenol products, and one fly ash from a municipal waste incinerator. The determination has been based on 106 available PCDE congeners. During sample preparation a 2-(l-pyrenyl)ethyldimethylsilylated silica column has been used in the normal phase mode to separate the PCDEs from possible PCDF interferences. The PCDEs have been quantified by high resolution gas chromatography/mass spectrometry on a SE 54 capillary column using electron ionization and selected ion monitoring. The total amount of PCDEs in 2,3,4,6-tetrachlorophenol have been determined to be 213 mg/kg. The lowest concentrations of PCDEs have been found in the more recently produced cod liver oil (sum PCDEs: 49 g/kg) and in the fly ash sample (sum PCDEs: 93 µg/kg), respectively. The isomer-specific analysis has been employed to characterize the relationship between possible sources and the PCDEs found in the environment. PCDEs, like PCBs, can be indicator molecules for the global pollution of the environment.Dedicated to Professor Dr. Dieter Klockow on the occassion of his 60th birthday     

Radical cyclization of sugar-derived beta-(alkynyloxy)acrylates: synthesis of novel fused ethers

[formula: see text] Tributyltin radical mediated cyclization of carbohydrate-derived beta-(alkynyloxy)acrylates leading to highly functionalized cis- and trans-fused bicyclic ethers of various ring sizes is described. The efficacy of the radical cyclization is nicely illustrated in the iterative construction of a trans-fused tricyclic tetrahydropyran.