T. Welsch
Leipzig University
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Featured researches published by T. Welsch.
Chromatographia | 1987
W. Engewald; U. Billing; T. Welsch; G. Haufe
SummaryThe retention indices of cycloalkenes and cycloalkadienes with C6–C13 rings are determined by gas-liquid chromatography (GLC) on glass capillary columns coated with OV-1 and Ucon LB 550X and by gas-solid chromatography (GSC) on a microcolumn packed with uncoated graphitized thermal carbon black (GTCB). Structure — retention correlations are derived on using index differences such as HOV, HGTCB and ΔI values, considering the differences in the stereochemistry of these compounds. It is shown that the combined application of index increments obtained in GLC and GSC provides more detailed structure informations. The value of the retention index units agree with the most stable conformations of the alicyclic compounds.The high value for the energy equivalent to an index unit (ΔGI.U.=4.18kJ/mol) confirmes that graphitized thermal carbon black causes much stronger dispersive interactions than any nonpolar liquid phase.
Chromatographia | 1984
T. Welsch; H. Frank; H. Zwanziger; S. Liebisch; W. Engewald
SummaryUsing n-heptane as eluent a direct linear correlation was found between the logk’ values of various polar test compounds and the silanol content determined by the methyllithium method. The peak asymmetries pass through a maximum at a medium silanol content. Peak asymmetries and logk’ values depend also on the chain length of the bonded alkyl group. A computer program was used to classify 25 home-made RP materials, 7 commercial products and the starting silica to achieve a hierarchical classification of them. The arrangement provides some detailed information about the presence and the effect of silanol groups.
Chromatographia | 1990
W. Engewald; J. Pörschmann; T. Welsch
SummaryThe adsorption of moelcules on the nonspecific and nonporous adsorbent graphitized thermal carbon black (GTCB) is mainly determined by their intermolecular dispersion interaction with the flat graphite surface. Since the retention values strongly depend on the geometrical configuration and shape of the investigated molecules and their arrangement on the graphite plane, it is possible to separate compounds with only small differences in their molecular shape on short columns packed with particles of pure or modified GTCB.The outstanding shape-selectivity of GTCB toward isomeric hydrocarbons is demonstrated by some examples.In most cases the elution sequences of isomeric compounds differ from that obtained in GLC using nonpolar stationary liquids. Moreover, the well defined relationship between retention data and molecular structure by adsorption on a flat and homogeneous surface give useful information for the identification of separated compounds or for the investigation of the molecular structure.
Fresenius Journal of Analytical Chemistry | 1991
E. Stottmeister; H. Hermenau; P. Hendel; T. Welsch; W. Engewald
SummaryA high-resolution gas-chromatographic (HRGC) method with electron capture detection is described for the sensitive determination of PCBs and toxaphene in water in the lower ng/l range. The required low detection limits are guaranteed by isolation of the target compounds and concentration from the filtered water sample by solid phase extraction with specific C18 silica gel (200–250 μm) alone or combined with the injection of larger extract volumes into a programmed temperature vaporizer (PTV) operating in the solvent venting mode. The bonded silica gel was prepared by reaction of the surface silanol groups with octadecyltrichlorosilane. A C18 silica of reproducible coverage was received. Practical aspects of the use of the solid phase extraction in combination with the PTV injection technique are discussed. The recoveries for toxaphene and PCBs were 85 and 78%.
Hrc-journal of High Resolution Chromatography | 1991
T. Welsch; Ute Teichmann
Hrc-journal of High Resolution Chromatography | 1985
T. Welsch; H. Frank
Fresenius Journal of Analytical Chemistry | 1987
H. Frank; Heinz Zwanziger; T. Welsch
Hrc-journal of High Resolution Chromatography | 1988
T. Welsch
Hrc-journal of High Resolution Chromatography | 1982
Gy. Vigh; J. Hlavay; Z. Varga-Puchony; T. Welsch
Hrc-journal of High Resolution Chromatography | 1984
J. Pörschmann; T. Welsch; W. Engewald; Gy. Vigh