Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.     

Extended-ion approximation and pressure shifts inF-band energies

Pressure variation of maximumF-band absorption energies in the halides of lithium, sodium and potassium has been investigated employing the extended-ion approximation for the calculation of theF-electron energy eigenvalues and using values of local compressibility in the neighbourhood of theF-centres which include the effect of vacancy and pressure. The results obtained agree with the experimental results.     

Podophyllotoxin from suspension culture of Linum album

Callus and suspension cultures of Linum album as an Iranian species for synthesis of aryltetralin lactone were used. After cultivation period; we can isolate and characterize podophyllotoxin as glycosides compounds. Maximal product yield is 0.5% of the dry weight in dark grown cultures.     

High-performance liquid chromatography/mass spectrometric identification of dibenzylbutyrolactone-type lignans: insights into electrospray ionization tandem mass spectrometric fragmentation of lign-7-eno-9,9'-lactones and application to the lignans of Linum usitatissimum L. (Common Flax)

In continuation of our studies into the mass spectrometric detection of natural lignans and their identification in complex mixtures such as crude plant extracts, the electrospray ionization tandem mass spectrometric (ESI-MS/MS) fragmentation of Delta(7,8)-unsaturated dibenzylbutyrolactone-type lignans (lign-7-eno-9,9'-lactones) was studied in detail. It is demonstrated that the characteristic fragmentation allows unambiguous identification including distinction between constitutional isomers. These lignans containing an alpha,beta-unsaturated lactone structure exist as equilibrium mixtures of E- and Z-isomers indistinguishable by mass spectrometry, but it is shown that chromatographic retention time can be used to distinguish between the isomeric forms. Based on these observations, re-analysis of the dichloromethane extract obtained from flowering aerial parts of Linum usitatissimum L. by high-performance liquid chromatography (HPLC)/ESI-MS/MS led to the identification of eighteen lignans of these types (five lignano- and one lignenolactone previously reported along with five further lignano- as well as seven lignenolactones hitherto unreported for this plant). The simultaneous identification of eighteen different lignans in the complex matrix of a crude plant extract by a single analysis demonstrates the potential of this method, which will certainly lead to new insights into the lignan composition and metabolism of different Linum species and many other plants.     

Diagrammatic structure of the general coupled cluster equations

The general formula for the number of diagrammatic terms occurring in the T_n equation within a particular coupled cluster model is derived. Both the antisymmetrized and Goldstone diagrams are considered. In addition to the full coupled cluster equation approximate approaches are discussed, and for each the general formula for the number of terms is given. Analogous expressions are presented for the number of diagrammatic terms contributing to the elements of the transformed Hamiltonian [Hbar] = e^?T He^T .     

Plane Sources of Waves in the Presence of Magnetic Field

In this paper the generation of harmonic waves in an elastic magneticmaterial, which is a perfect conductor of electricity, isconsidered. It has been assumed that an infinite body is subjected tothe action of an initially constant magnetic fieldH = (H,0,0) and in the plane ax+by=0 acts a source ofdistortion. It has been shown that this source may produce bothtransverse and longitudinal waves and each of them consists of two parts,which propagate with different speeds. The amplitudes and speeds in dependence on theangle between the direction of wave propagation and the magnetic fieldintensity H have been discussed.