Plasma chromatography of heroin and cocaine with mass-identified mobility spectra.

Plasma chromatography detects and identifies compounds in trace quantities at atmospheric pressure through characteristic positive and negative mobility spectra. To facilitate use of the technique to detect gas chromatographic effluents, a number of reference mobility spectra for different classes of compounds have been reported. Reference spectra for two more compounds, heroin and cocaine, are presented in this study. The primary ions found in these mobility spectra were determined to be M+, (M - H2)+, and (M - CH3CO2)+ for heroin and M+, (M - C6H5CO2)+ and (M - C6H5CO2 - CO2CH3)+ for cocaine using a directly interfaced plasma chromatograph-mass spectrometer. The identified ions agree closely with those predicted in the ion mobility spectra using mass-mobility correlation data coupled with chemical ionization mass spectrometry data. Also, an independent check demonstrating the reliability of reduced mobility values reported in earlier reference spectra was made.     

Photon-induced dissociation with a four-sector tandem mass spectrometer

The feasibility of using photodissociation of protonated peptide molecules to sequence specific fragment ions with a 193-nm pulsed laser beam in a magnetic deflection tandem mass spectrometer of EBEB configuration was demonstrated. Although the short pulse (15 ns) and low repetition rate (100 Hz) of the excimer laser permitted the irradiation of only ～ 0.02% of the (M + H)⁺ ions exiting MS-1, a photon-induced decomposition spectrum of the heptapeptide angiotensio III (M _r 930.5) was produced that was practically the same (but with better signal-to-noise ratio) as that generated by collision-activated dissociation at the same low duty cycle. Because of the low and pulsed fragment ion currents, an array detector was used to record the spectra. A dependence between laser power and abundance of fragment ions was observed (increased power increases the relative abundance of ions of low mass). Laser power was varied from 6 to 80 mJ. Formation of fragment ions from a large peptide (melittin, M, 2844.75) was also observed. The results permit the design of modifications that may increase the fragment ion yield to 10% or higher, which would make photon-induced decomposition a useful method for magnetic deflection mass spectrometers.     

Selectivity enhancement of a metal-sensitive flame ionization detector for capillary gas chromatography

A novel modification of a hydrogen-atmosphere flamo ionization detector (HAFID) is presented which attenuates response to hydrocarbon compounds, significantly enhancing selectivity towards organometallic compounds by more than an order of magnitude. Chromatograms of an organometallic compound test mixture and regular leaded gasoline are presented to depict the specificity of the response.     

Exploring CH-activation pathways in bifunctional zirconocene/borane systems

The dimethylsilanediyl-bridged ansa-zirconocene dichloride 1, that contains a pendent allyl substituent at a Cp-ring, adds HB(C(6)F(5))(2) to the vinyl group to yield the bifunctional zirconocene/borane complex 2. Substituted benzimidazoles were added to the strongly electrophilic borane moiety as protective groups, which allowed subsequent chloride versus -CH(2)SiMe(3) exchange at zirconium to take place by treatment with the respective alkyllithium reagent. Alternatively, the introduction of active sigma-ligands at zirconium is carried out first, followed by the hydroboration reaction. This route was followed for the synthesis of the diphenyl-ansa-zirconocene/borane complex 12. Complex 12 reacts slowly in solution by intramolecular electrophilic attack of the borane at its adjacent Cp-ring, followed by deprotonation using a [Zr]-Ph group to yield the zwitterionic complex 14 featuring a borata-tetrahydroindenyl moiety as part of the ansa-metallocene framework. Complex 14 was characterized by X-ray diffraction. It adds PMe(3) at zirconium to yield 15. Thermolysis of 12 with excess PMe(3) leads to the formation of the (aryne)zirconocene complex 18, which is stabilized by PMe(3) coordination to zirconium and PMe(3) addition to boron. N-Methylbenzimidazole adds to the -B(C(6)F(5))(2) unit of 12 to give the 1:1 adduct 19. Thermolysis of 19 at 80 degrees C in benzene solution in the presence of one additional equivalent of N-methylbenzimidazole results in deprotonation of the substrate to yield the sigma-N-methylbenzimidazolyl zirconium complex 20 (as a mixture of two diastereoisomers). An additional N-methylbenzimidazole ligand is bonded to the B(C(6)F(5))(2) unit in this product.     

Synthesis and structural characterization of [Au2Pd14(μ3-CO)7(μ2-CO)2(PMe3)11](PF6)2—An icosahedrally-based high nuclearity mixed metal cluster

[Au₂Pd₁₄(₃-CO)₇(₂-CO)₂(PMe₃)₁₁](PF₆)₂ has been synthesized from [Pd₈(CO)₈(PMe₃)₇] and AuCl(PCy₃) in the presence of TIPF₆. It has been characterised on the basis of mass spectrometry, infrared and NMR spectroscopy, and a single crystal X-ray diffraction study. The structure is based on a palladium-centered Au₂Pd₁₁ icosahedron which shares an edge with a Pd₅ trigonal bipyramid.This paper is dedicated to Larry Dahl on his 65th Birthday—his enthusiasm and achievements in cluster chemistry have inspired us all for more than 30 years.