Th. Welsch

Zur Desaktivierung von Glaskapillaren mittels Silanisierung

SummaryThe deactivation of glass capillaries by silanization with different agents under various reaction conditions has been investigated. It was found the effectiveness of the silanization procedure can be improved if the treatment is performed with pure hexamethyldisilazane for a period of about 20 hours at temperatures approaching 300°C.ZusammenfassungDie Desaktivierung von Glaskapillaren duch Silanisierung mit verschiedenen Reagenzien bei unterschiedlichen Reaktionsbedingungen wurde untersucht. Es zeigte sich, daß die Wirksamkeit der Silanisierung wesentlich verbessert werden kann, wenn die Behandlung der Glaskapillaren mit reinem Hexamethyldisilazan etwa 20 Stunden lang bei 300°C erfolgt.

Surface modification of glass capillaries by high-temperature silylation

Abstract High-temperature silylation (HTS) on leached glass capillaries is highly effective deactivation method for preparing neutral and inert surfaces. Several silylating agents such as disilazanes and disiloxanes containing different alkyl groups and phenyl groups were prepared and investigated for their usefulness in HTS. The conditions of the procedure, especially the influence of the amount of silylating agent, were examined. It was found that most of the reagents are suitable for use in HTS in achieving very low adsorption activities of the treated glass surface. With increasing chain-length or number of phenyl groups in the reagent, not only was a change of critical surface energy of the treated glass capillaries effected but also a better wettability for numerous stationary phases was observed.

Characterization of a new dehydroxylated reversed-phase material

Abstract Reversed-phase (RP) silicas prepared by reacting silica with disilazanes or disiloxanes at temperatures of about 350°C under so-called high-temperature silylation conditions were compared with RP silicas prepared under “normal” conditions, at 139°C, and with commercially available materials, by determining the surface concentration of organic and hydroxyl groups and also their properties in liquid chromatography using both n -heptane and methanol—water mixtures as eluents. Relative to the conventional RP materials, the RP silicas prepared at 350°C show no marked differences in the surface concentration of the organic groups, but their hydroxyl group content is greatly reduced. This results in a different chromatographic behaviour for solutes with different polarities.

Properties of micro-packed columns and of porous-layer open-tubular columns with graphitized thermal carbon black

Abstract The properties of porous-layer open-tubular (PLOT) colums and of so-called micro-packed columns with grahitized thermal carbon black not coated with a liquid phase were compared by means of characteristic parameters such as HETP, permeability, capacity ratio and the C term in the Van Deemter equation. It was found that micro-packed columsn with graphitized thermal carbon black are useful for efficient and rapid separations and for the determination of the retentioon data of low-boiling isomers.

Analysis of fatty acids by combined application of chemical, chromatographic and spectroscopic methods

Abstract By combined application of chemical pretreatments, and chromatographic and spectroscopic methods, it is possible to coordinate individual species of a complex lipid extract with high safety. In the sample studied, besides a high content of palmitic and cis -vaccenic acid, small amounts of unusual fatty acids containing hydroxy groups and cyclopropane rings were detected. The presence of polyunsaturated fatty acids was excluded by structure-retention relationships, which were obtained on phases of different polarity. On the basis of these studies, and without the use of reference substances, a routine analysis of these unusual fatty acids in biological materials is possible.

Molekülstruktur und retentionsverhalten : II. Retentionsverhalten cycloaliphatischer kohlenwasserstoffe bei der gas-adsorptions- und gas-verteilungschromatographie☆

Abstract Molecular structure and retention behaviour. Retention behaviour of cycloaliphatic hydrocarbons in gas—solid chromatography and in gas—liquid chromatography The retention indices of cycloalkanes, cycloalkenes, and some cycloalkadienes of the ring size C 6 C 13 have been determined on a column packed with graphitized thermal carbon black, and compared with the corresponding data on squalane. The relationships between molecular structure and retention indices as well as homomorphism factors are discussed. According to the different separation principles of gas—solid chromatography and gas—liquid chromatography, respectively, the homomorphism factors are negative on graphitized thermal carbon black, but positive on squalane.

Molekülstruktur und retentionsverhalten : VI. Retentionsverhalten von bicyclo[n.m.0]alkanen bei der gas-adsorptions- und gas-verteilungs-chromatographie☆

Abstract The retention indices of bicyclo[n.m.0]alkanes with 6–13 carbon atoms have been determined by gas-solid chromatography (GSC) on a column packed with graphitized thermal carbon black (GTR) and by gas-liquid chromatography (GLC) on glass capillaries coated with squalane (S), and Ucon 50 HB 280X polar, respectively. The relationships between the retention behaviour and the structure of the hydrocarbons are discussed by means of homomorphic factors (HGTR, HS) and index differences (ΔI). Like corresponding data of cycloalkanes and cycloalkenes, the homomorphic factors of bicyclo[n.m.0]alkanes are positive on polar and non-polar liquid phases (GLC), but negative on graphitized carbon black (GSC).

Molekülstruktur und retentionsverhalten : VIII. Zum gaschromatographischen retentionsverhalten von dicyclopentadienderivaten

SummaryThe retention indices and homomorphic factors of alkylbenzenes with 9–14 carbon atoms have been determined by gas-solid chromatography on a column packed with graphitized thermal carbon black. The homomorphic factors are positive for benzene derivatives with several methyl groups and negative for alkyl benzenes and dialkylbenzenes. The relationships between retention behaviour and structure of the hydrocarbons are discussed and the results are compared with corresponding data from gasliquid chromatography. The advantages of this adsorbent for the separation of alkyl benzenes with branched side chains are demonstrated.ZusammenfassungDie Retentionsindices von Alkylbenzolen der C-Zahlen 9 bis 14 wurden bei der GAC an einer mit graphitiertem thermischem Ruß gepackten Säule gemessen. Die daraus abgeleiteten Homomorphiefaktoren sind für Benzolderivate mit mehreren Methylgruppen positiv, für die übrigen Alkyl-und Dialkylbenzole negativ. Es werden Zusammenhänge zwischen Molekülstruktur und Retention diskutiert und die Ergebnisse mit entsprechenden Resultaten in der GVC verglichen. Die Vorteile dieses Adsorbens zur Trennung von Alkylbenzolen mit verzweigten Seitenketten werden demonstriert.Abstract Molecular structure and retention behaviour. VIII. Gas chromatographic retention behaviour of dicyclopentadiene derivatives The retention indices of exo—endo isomeric dicyclopentadienes, dihydrodicyclopentadienes and tetrahydrodicyclopentadienes have been determined by gas—liquid chromatography (GLC) on glass capillaries coated with squalane, Ucon LB 550X and Ucon 50HB 280 X polar, and by gas—solid chromatography on graphitized thermal carbon black. The influence of exo - and endo -configuration of the carbon skeleton and of the position of the double bond on retention is discussed by means of homomorphic factors and index differences. In the same manner the relationships between retention and configuration of the carbon skeleton and of the substituent are elucidated from the retention indices of 9-hydroxy-, 9-acetoxy-, 9-ketodihydrocyclopentadienes and substituted tetrahydrodicyclopentadienes, respectively, obtained by GLC on capillary columns with different polarity.

Molekülstruktur und Retentionsverhalten I. Strukturelle Zuordnssung von thermischen Umlagerungsprodukten der Cyclododecatriene (1.5.9) mittles Gas-Adsorptions-Chromatographie

SummaryIn the present paper, retention data on graphitized thermal carbon black were determined for some hydrocarbons obtained by thermal rearragement of 1.5.9-cyclododecatrienes, and their hydrogenation products. Thus, by semiempirical calculations and by comparison with retention data on open tubular columns coated with squalane or Ucon 50 HB 280×polar respectively, an assignment of configuration was possible.ZusammenfassungIn der vorliegenden Arbeit wurden für einige durch thermischen Umlagerung von cyclododecatrien-(1.5.9) erhaltene Kohlenwasserstoffe und ihre Hydrierungs-produkte Retentionsdaten an graphitiertem thermischen Ruß bestimmt. In Verbindung mit semiempirischen Berechnungen und durch Vergleich mit Retentionsdaten, die an Squalan-bzw. Ucon 50 HB 280×polar-Trennkapillaren gemesen wurden, konnte aus diesen, Werten eine konfigurative Zuordnung getroffen werden.

Desorptions- und eichvorrichtung zur spurenanalyse von organischen luftinhaltsstoffen mittels adsorptiver anreicherung und kapillar-gaschromatographie

Abstract For capillary gas chromatographic determination of organic air pollutants at ppb (10 9 ) levels being based on adsorptive sampling a desorption device were constructed permitting a substance trasfer from adsorption tubes to glass capillary columns. The gas chromatograph was additionally equipped with an arrangement of capillary columns which allows a controlled dosage of very small amounts of substances onto adsorption tubes with respect to identification and calibration. The performance of the technique reported was characterized by means of the reproductibility of the recoveries and retention data. On the basis of two air samples of different origin the practical applicability of the method was discussed.