Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where T. Welsch is active.

Publication


Featured researches published by T. Welsch.


Chromatographia | 1987

Structure-retention correlations of hydrocarbons in gas-liquid and gas-solid chromatography. Cycloalkenes and cycloalkadienes

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

Classification of reversed-phase materials by means of selected chromatographic data

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

Graphitized thermal carbon black as a shape-selective stationary phase in GC

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

Solid phase extraction/programmed temperature vaporizer (PTV) injection in GC-analysis of toxaphene and PCBs in aqueous samples

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

The thermal immobilization of hydroxy-terminated silicone phases in high-temperature-silylated glass capillaries. A study of reaction mechanisms

T. Welsch; Ute Teichmann


Hrc-journal of High Resolution Chromatography | 1985

A study in high-temperature silylation of silica

T. Welsch; H. Frank


Fresenius Journal of Analytical Chemistry | 1987

Zur fraktalen Oberflächendimension chromatographisch relevanter Kieselgele

H. Frank; Heinz Zwanziger; T. Welsch


Hrc-journal of High Resolution Chromatography | 1988

High-temperature silylation in the production of inert glass capillary columns. From the first experiments to the chemical mechanism

T. Welsch


Hrc-journal of High Resolution Chromatography | 1982

Preparation and use of high temperature silylated capillary columns coated with a mixture of OV‐1 and FFAP for the analysis of volatile carboxylic acids

Gy. Vigh; J. Hlavay; Z. Varga-Puchony; T. Welsch


Hrc-journal of High Resolution Chromatography | 1984

Characterization of OV‐1/FFAP‐mixture coated glass capillary columns used for the separation of free fatty acids

J. Pörschmann; T. Welsch; W. Engewald; Gy. Vigh

Collaboration


Dive into the T. Welsch's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Researchain Logo
Decentralizing Knowledge