A novel method of sample introduction into an isotope ratio mass spectrometer (IRMS) is described. The technique uses the chemical reaction interface (CRI) to convert samples coming from a gas chromatograph (GC) or high-performance liquid chromatograph (HPLC) into CO2 using a microwave-induced helium plasma. Optimization parameters for both GC/CRI/IRMS and HPLC/CRI/IRMS are described. In both modes of operation, it was possible to obtain 13CO2/12CO2 ratios with standard deviations less than 1%. Investigation of HPLC/CRI/IRMS performance at low and high concentrations (0.5-10 micrograms) resulted in no significant deviations of the isotope ratios. The ability to differentiate samples of different biological origins was illustrated using chlorophyll a from spinach and algae, where a large difference was observed but good precision was maintained (SD < 0.60%).
Abstract The cuticular hydrocarbons of the Colorado beetle Leptinotarsa decemlineata say consist of 2-methylalkanes, internally branched monomethylalkanes, dimethyl-, trimethyl-and tetramethyl-alkanes. The hydrocarbons differ from those of most of the other insects so far investigated. The major components were found to be the dim ethyl branched alkanes, 2,6-and/or 7,22-dimethyl-octacosane and the tetram ethylalkane, 3,10,16,23-tetram ethyltritriacontane. The hydrocarbons identified are members of homologous series which differ by two m ethylene groups. The identification of hydrocarbons was achieved by mass spectrom etry and gas chromatographic determination of Kovats retention indices on two high efficiency capillary columns coated with Dexsil 300 and OV-1.
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