A preconcentrator coupled to a GC/FTMS: Advantages of self-chemical ionization,mass measurement accuracy,and high mass resolving power for GC applications

Coupling of a cryogenic preconcentrator (PC) to a gas chromatograph/Fourier transform ion cyclotron resonance mass spectrometer (GC/FT-ICR MS) is reported. To demonstrate the analytical capabilities of the PC/GC/FT-ICR MS, headspace samples containing volatile organic compounds (VOCs) emitted from detached pine tree twigs were analyzed. Sub-ppm mass measurement accuracy (MMA) for highly resolved (m/Deltam(50%) > 150 k) terpene ions was achieved. Direct PC/GC/FT-ICR MS analyses revealed that detached twigs from pine trees emit acetone, camphor, and four detectable hydrocarbon isomers with C(10)H(16) empirical formula. The unknown analytes were identified based on accurate mass measurement and their mass spectral appearances. Authentic samples were used to confirm initially unknown identifications. Self-chemical-ionization (SCI) reactions furnished an additional dimension for rapid isomer differentiation of GC eluents in real time.     

Distorted Molecules: Perturbation Design,Preparation and Structures

The structure of a molecule can change considerably as its energy and thus its electron distribution within the time-domain of dynamic relaxation varies. Based on comparison of approriate measured data of related compounds and supported by quantum chemical calculations, therefore, charge-perturbed and/or sterically overcrowded molecules can be designed. Their preparation, handling, and structural characterization, frequently under extreme and especially largely aprotic conditions, provides some surprises. New structural principles become evident and old-fashioned ones are confirmed. Thus the contact-ion aggregates that form on ultrasonically supported reduction of unsaturated hydrocarbons with sodium metal partly contain dibenzene sodium sandwiches. Vicinal dimethylamino substituents or isoelectronic isopropyl groups cause steric overcrowding and facilitate oxidation to molecular cations by energetically favorable delocalization of the generated positive charge. Molecules and molecular ions in which an even number of π electrons are distributed over a σ skeleton containing an odd number of centers preferentially form cyanine subunits. This is demonstrated by the novel ethene dication and dianion salts with central C? C single bonds and molecular halves twisted relative to each other. Altogether in two years well over 50 structures have been determined. Much has been learned from them, especially about electron transfer and contact ion-pair formation in aprotic solvents. Nevertheless, we had to realize that answers to many questions, above all “what crystallizes, how, and why”, are still out of reach.     

Photoelektronen-Spektren und Moleküleigenschaften. 132 [1, 2]. Trifluormethylsulfan und Derivate F3CSX (X  CF3, Cl,Br, I)

Photoelectron Spectra and Molecular Properties. 132. Trifluoromethylsulfane and Derivatives F₃CSX (X ? CF₃, Cl, Br, I) The He(I) photoelectron spectra of trifluoromethylsulfane F₃CSH and its derivatives F₃CSX (X ? CF₃, Cl, Br, I) are assigned by Koopmans' correlations, IE = ?ε, with MNDO eigenvalues, by radical cation state comparison and based on resolved vibrational fine structures, which can' be discussed by MNDO FORCE calculations. The spin/orbit splitting in F₃CSI can be approximated by additional ITEREX-85 calculations. Gasphase thermolysis of the trifluoromethylhalogensulfanes F₃CSX at 10^?4 mbar yields decomposition temperatures, which decrease from X ? Cl to I, and as fragmentation products of presumably radical intermediates, in addition to the respective halogens X₂ and F₂C?S, also F₃CX as well as S₂ and CS₂ (X ?Cl, Br) are PE spectroscopically detected.     

Tellurocarbonyldifluorid und seine Derivate: (HeI)-Photoelektronen-Spektren und HF-, GF- sowie DFT-Berechnungen

Tellurocarbonyldifluoride and its Derivatives: (HeI)-Photoelectron Spectra and HF, GF as well as DFT Calculations The He(I) photoelectron spectra of tellurocarbonyldifluoride F₂C=Te, its trifluormethyl derivative F₃C(F)C=Te and of the ditelluretanes: 2,2,4,4-tetrafluor-1,3-ditelluretane, 2,4-difluoro-2,4-bis(trifluormethyl)-1,3-ditelluretane und und 2,4-dichloro-2,4-bis(trifluormethyl)-1,3-ditelluretane are assigned by ab initio calculations, radical cation state comparison and based on resolved vibrational fine structures.     

Evidence for Sequence Scrambling and Divergent H/D Exchange Reactions of Doubly-Charged Isobaric b-Type Fragment Ions

To date, only a limited number of reports are available on structural variants of multiply-charged b-fragment ions. We report on observed bimodal gas-phase hydrogen/deuterium exchange (HDX) reaction kinetics and patterns for substance P b₁₀ ²⁺ that point to presence of isomeric structures. We also compare HDX reactions, post-ion mobility/collision-induced dissociation (post-IM/CID), and sustained off-resonance irradiation-collision induced dissociation (SORI-CID) of substance P b₁₀ ²⁺ and a cyclic peptide with an identical amino acid (AA) sequence order to substance P b₁₀. The observed HDX patterns and reaction kinetics and SORI-CID pattern for the doubly charged head-to-tail cyclized peptide were different from either of the presumed isomers of substance P b₁₀ ²⁺, suggesting that b₁₀ ²⁺ may not exist exclusively as a head-to-tail cyclized structure. Ultra-high mass measurement accuracy was used to assign identities of the observed SORI-CID fragment ions of substance P b₁₀ ²⁺; over 30 % of the observed SORI-CID fragment ions from substance P b₁₀ ²⁺ had rearranged (scrambled) AA sequences. Moreover, post-IM/CID experiments revealed the presence of two conformer types for substance P b₁₀ ²⁺, whereas only one conformer type was observed for the head-to-tail cyclized peptide. We also show that AA sequence scrambling from CID of doubly-charged b-fragment ions is not unique to substance P b₁₀ ²⁺.

Collisional relaxation of metastable electronic states of Fe+

The overall rate constants for collisional relaxation of metastable excited states of Fe⁺ by He, Ar, Kr, H₂, ²H₂, CO, N₂, NO, CH₄, and CH₃OH have been studied by using charge-exchange ion-molecule reaction chemistry. The rate constants vary according to the nature of the quenching reagent as well as the energy level and electron configuration of the Fe⁺ ions. In general, NO, CH₄, and CH₃OH are the most efficient quenching reagents with rate constants that approach the Langevin collision rate, whereas the reaction rates for the rare gas atoms are slow and vary depending upon the specific electron configuration of the Fe⁺ ion. The mechanism of collisional relaxation is discussed with emphasis on a curve-crossing. mechanism for the rare gas atoms. An electron-transfer mechanism is described for the relaxation of high lying (Fe⁺)*.