Calibration of mass selective detector in non-target analysis of volatile organic compounds in the air

Volatile organic compounds (VOCs) play an important role in the chemistry of the atmosphere and in biogeochemistry. They contribute to the oxidative capacity of the atmosphere, particle and air pollutants, as well as to the production of greenhouse gases (for instance ozone). Among analytical techniques for their determination in the atmosphere gas chromatography coupled with mass spectrometry (GC-MS) offers several advantages. However, for an accurate quantification calibration with standard substances is necessary. A quantitative structure-property relationship (QSPR) model for the prediction of MS response factors was developed on basis of our experimental measurements for the quantification of ozone precursors present in the atmosphere. A linear correlation between chemical structures and response factors was established by using a 7-parameter MLR model. The average error in the prediction of response factors was calculated by cross-validation procedure and was below 20%, which is sufficient for the determination of VOCs in the air. The proposed procedure is time consuming so it is more suited for the quantification of tentatively identified organic compounds during the reprocessing of MS chromatograms in cases when the original sample is no longer available.     

Wet mineralization of organic matrices in glassy carbon vessels in a pressure-bomb system for trace element analysis

Glassy carbon (Sigradur G(R)) is thermally stable up to 600 degrees under atmospheric conditions and has proved to be substantially resistant to many decomposition agents at temperatures up to 250 degrees . It can, therefore, substitute for PTFE vessels in a pressure-bomb device for the wet decomposition of organic and inorganic substances with, e.g., nitric, chloric or hydrofluoric acid or mixtures thereof, in the determination of trace elements. The mineralization can be carried out at temperatures up to 50 degrees higher than with PTFE vessels, which are limited to a maximum of 170 degrees . The higher decomposition temperature, which results in a higher oxidation potential, considerably shortens the decomposition time. On account of the lower content of impurities, particularly of Hg, Ag, Bi, Cd, Se, Te and Sb, the results are more accurate than those obtained with PTFE vessels, if these elements are to be determined in the ng/g range in the resulting solution.     

Solid-phase synthesis of a combinatorial array of 1,3-bis(acylamino)-2-butanones, inhibitors of the cysteine proteases cathepsins K and L

To more rapidly prepare members of the 1,3-bis(acylamino)-2-butanone class of cysteine protease inhibitors, a solid-phase synthesis was developed. 1-Azido-3-amino-2,2-dimethoxybutane (4), which has the two amino groups differentiated and the ketone protected as a a ketal, served as a surrogate for the 1,3-diamino-2-butanone core. Amine (4) was coupled to the BAL-resin-linked carboxylic acids derived from alpha-amino acid esters. Evaluation of a small combinatorial array by measuring inhibition constants (Ki,appS) against cathepsins K, L, and B provided some structure-activity relationship trends with respect to selectivity and potency. Novel, potent inhibitors of cathepsins K and L were identified.     

The application of ETAAS to the determination of Cr,Pb and Cd in samples taken during different stages of the winemaking process

Chromium, cadmium and lead were determined in different fractions of the winemaking process such as in grape, pressed pomace, must deposit, deposit of lees, must and wine. Grape, pressed pomace, must deposit and deposit of lees were digested by a high-pressure microwave-assisted digestion system with a mixture of nitric acid and hydrogen peroxide, while for must and wine no special treatment was required. The temperature programs of the graphite furnace were optimised and different matrix modifiers were applied: Mg(NO3)2, NaVO3 for Cr and NH4H2PO4, Pd(NO3)2 for Pb and Cd determinations. Mg(NO3)2 and NaVO3 thermally stabilized Cr and enabled the increase of pyrolysis temperatures up to 1500 degrees C. NH4H2PO4 and Pd(NO3)2 are suitable modifiers for Pb and allowed pyrolysis temperatures up to 800 degrees C in grape, pressed pomace and wine samples, 1100 degrees C in must samples and 1200 degrees C in deposit of lees. The non-specific background absorption of NH4H2PO4 was 1.5-2 orders of magnitude higher than that of the Pd(NO3)2.     

Formation of anions of nitroaromatic compounds in gases during UV laser irradiation

The mechanism of formation of negative ions of trinitrotoluene, dinitrotoluene, and para-nitrotoluene in the gas phase under the action of laser irradiation was studied using ion mobility spectrometry. The gas mixture was ionized by the fourth harmonic radiation of a YAG:Nd³⁺ laser. The irradiance was varied within 2–5 MW/cm². It was demonstrated that, although the test compounds are characterized by a high cross section of absorption of laser radiation the formation of their anions occurs largely through the multiphoton ionization of organic admixtures present in the gas mixture with the subsequent attachment of electrons formed. In a nitrogen medium, the attachment of electrons occurs directly, whereas in air, the O ₂ ^? immediate plays an important role. Laser radiation causes the dissociation of the molecules under study, especially marked for para-nitrotoluene.     

Temperature-dependent exchange interaction in molecular magnets Cu(hfac)2L(R) studied by EPR: methodology and interpretations

Exchange-coupled spin triads nitroxide-copper(II)-nitroxide are the key building blocks of molecular magnets Cu(hfac)(2)L(R). These compounds exhibit thermally induced structural rearrangements and spin transitions, where the exchange interaction between spins of copper(II) ion and nitroxide radicals changes typically by 1 order of magnitude. We have shown previously that electron paramagnetic resonance (EPR) spectroscopy is sensitive to the observed magnetic anomalies and provides information on both inter- and intracluster exchange interactions. The value of intracluster exchange interaction is temperature-dependent (J(T)), that can be accessed by monitoring the effective g-factor of the spin triad as a function of temperature (g(eff)(T)). This paper describes approaches for studying the g(eff)(T) and J(T) dependences and establishes correlations between them. The experimentally obtained g(eff)(T) dependences are interpreted using three different models for the mechanism of structural rearrangements on the molecular level leading to different meanings of the J(T) function. The contributions from these mechanisms and their manifestations in X-ray, magnetic susceptibility and EPR data are discussed.     

Hyper‐Raman and Raman scattering in paratellurite TeO2

Raman spectra of the tetragonal structure of paratellurite TeO₂ have been revisited avoiding anomalous polarization‐selection‐rules violations previously observed and due to optical activity. We present a complementary hyper‐Raman scattering study of paratellurite. Wavenumber and symmetry assignments are given for all expected 21 Raman active optical branches, except one LO component (out of the eight expected TO–LO pairs) of the polar doublet E modes. Also, the four expected hyper‐Raman active A₂ (TO) modes have been observed. Moreover, we have observed a strong Kleinman‐disallowed hyper‐Rayleigh signal, which is tentatively assigned as a first evidence of hyper‐Rayleigh optical activity. Copyright © 2013 John Wiley & Sons, Ltd.     

Wavelength dependence of the orientation of optic axes in KGW

We report on the wavelength dependence of the orientation of the optic axes in monoclinic crystals using undoped and neodymium-doped KGd(WO₄)₂ (KGW) samples. Measurements have been performed over a wide wavelength range from 420 up to 1,580 nm with more than 70 measurement points. This provides the widest measurement range of the optic axis variation ever reported in literature for KGW crystals. With such a measurement, which can be performed in principle in all biaxial crystals, the refractive indices values can be checked with a precision down to 10^?3.