Gabriella Garzó

Method for preparing glass capillary columns for gas chromatography

Abstract A method is given to prepare glass capillary columns with almost any stationary phase. The method is based on etching the soda-lime glass capillary tubing by dry gaseous hydrochloric acid. Coating the columns by the static method resultsin high-performance apolar and polar columns. The polar columns can be used even for the analysis of highly polar solutes. Studying the etched surface of soda-lime glass, the presence of a uniform layer of microcrystalline NaCl was found.

Gaschromatographische und 29Si‐NMR‐spektroskopische Untersuchungen an Kieselsäuretrimethylsilylestern

Kieselsauretrimethylsilylester unterschiedlicher Konstitution werden mit Hilfe der Gaschromatographie hinsichtlich ihres Retentionsindex und der Retentionstemperatur charakterisiert. Es wird gezeigt, das die Retentionsdaten der Ester im wesentlichen von der Anzahl der Trimethylsilylgruppen im Molekul abhangen und nur wenig von der Konstitution des Kieselsauregerustes beeinflust werden. Die 29Si-NMR-Spektren von neun Kieselsaure-TMS-Estern unterschiedlicher Konstitution wurden aufgenommen und die Zuordnung der Signale zu den einzelnen Baugruppen der Ester diskutiert. Auf der Grundlage dieser Ergebnisse wurden Konstitutionsuntersuchungen an hexameren Kieselsaure-TMS-Estern durchgefuhrt, die zur Identifizierung von zwei Isomeren des Bicyclohexakieselsaureesters [(CH3)3Si]10[Si6O17] fuhrten.

Gas chromatography of trimethylsilylated silicate anions : separation with glass capillary columns and new aspects in derivatization

Abstract The advantages of capillary-column gas chromatography (GC) in the analysis of trimethylsilylated silicate systems are demonstrated and separation parameters and measurement and calculation methods for the qualitative and quantitative analysis of different silicic acid solutions are outlined. The problems of the trimethylsilylation procedures are discussed. Results obtained by GC after derivatization with bistrimethylsilylacetamide (BSA) as the trimethylsilylating agent indicate that both the unwanted condensation and hydrolysis during silylation are suppressed if the proton-trimethylsilyl is accelerated e.g. , by a powerful trimethylsilyl donor such as BSA, and if the pH of the silylation reaction mixture is controlled. Chromatograms of some silicic acid samples are compared with those of identical samples silylated according to Lentz and Gotz-Masson, respectively. Comparison of both the qualitative and quantitative results indicates that the compositions of the original silicic acid solutions are best reflected in the chromatograms after silylation with BSA. The effect of the after-treatment of the silylated silicic acid solution with Amberlyst 15 cation-exchange resin is disscussed separately.

Gas chromatographic retention characteristics of trimethylsilylated silicate anions

Abstract Pure volatile trimethylsilylated silicates of well-defined structures were prepared from different synthetic and natural silicates. Thin-layer chromatography followed by mass spectrometry was used for the separation and identification of the pure compounds. Eleven standard substances were chromatographed on gas chromatographic columns, having programmed temperatures, using four phases of different polarity. For the gas chromatographic characterization of the title compound, isothermic retention indices were also measured. The retention of the trimethylsilylated silicates depended mainly on the number of trimethylsilyl groups present in the molecule. This resulted in similar retentions for molecules with rather different molecular weights and structures. Homologue rules make possible the prediction of the identity of unknown peaks appearing in the chromatograms of natural and synthetic trimethylsilylated silicates.

Reactions of trimethylsilylated silicate anions in acidic medium. Part 1. Effect of Amberlyst 15 cation-exchange resin on the products of trimethylsilylation of hexameric ring silicates

Chemical and structural transformations induced by proton–donor catalysts (Amberlyst 15 cation-exchange resin and trichloroacetic acid) have been studied using the silicate derivatives Si6O15(SiMe3)6 and Si6O18(SiMe3)12 as model compounds. The experiments were performed in hexamethyldisiloxane solutions using a standard quality Amberlyst 15. Gas chromatography with a glass capillary column was used for detection of the composition changes in the reaction mixtures. Present and former results have permitted a probable structural presentation of the reaction pathways to be made. The transformations tend to produce structures containing only tetrameric siloxane rings when starting from cyclic and polycyclic silicate derivatives containing trimeric, (pentameric), or hexameric siloxane rings. Three different reaction types are suggested for the interpretation of the transformations. Amberlyst 15 was found to contribute significantly to side reactions during the Amberlyst treatment following the trimethylsilylation of silicates under the usual conditions employed.

Reactions of trimethylsilylated silicate anions in acidic media. Part 2. The influence of reaction parameters

It is shown that the ion-exchange resin Amberlyst 15 acts as a powerful proton donor for SiO bond cleavages and rearrangements of trimethylsiloxysiloxanes. In the presence of hexamethyldisiloxane, transformations of trimethylsiloxysiloxanes of different structure show a dual effect: highly caged structures are loosened, while very loose structures become more rigid. Tetrameric ring structures predominate in the reaction products. The transformation reactions are controlled by the acid to hexamethyldisiloxane ratio in the reaction mixture. In the absence of hexamethyldisiloxane trimethylsiloxysiloxanes are highly degraded.

Thermal decomposition of cyclo-linear methylsiloxane polymers

Abstract The pyrolysis products from two cyclo-linear methylsiloxane polymers have been analysed, and formation of the important products interpreted in terms of a simple decomposition mechanism. This mechanism is very similar to that of the polydimethylsiloxane degradation; thus cyclic oligomers are formed from the linear segments, and polycyclic compounds from the cyclic segments of the cyclolinear methylsiloxane polymers.

Thermal degradation of poly[alkenebis(dimethylsiloxanes)]. I. By pyrolytic gas chromatography

Abstract The results of pyrolytic gas chromatographic experiments performed with poly[ethylenebis(dimethylsiloxane)] and poly[propylenebis(dimethylsiloxane] samples have been utilized for the evaluation of the mechanism of the thermal degradation of these polymers. All the significant peaks on the pyrograms have been identified and the relative amounts of the pyrolysis products have been determined at different pyrolysis temperatures. According to the experimental results, two types of decomposition reactions occur during pyrolysis, (a) a siloxane-type degradation leading to the elimination of cyclic monomers from the polymer chain and (b a radical-type splitting of the Cue5f8C or Siue5f8C bond in the hydrocarbon segment followed by an intramolecular radical transfer and subsequent β-scission. These two processes occur simultaneously.

Gas chromatographic determination of 5-alkyl-uracils and 5-alkyl-deoxyuridines using flash methylation and glass capillary columns

Abstract A sensitive analytical method has been developed for 5-alkyl-substituted deoxy-uridines and their main metabolites, the corresponding uracils in body fluids. The compound to be determined is methylated by the “flash” methylation technique, i.e., by injecting a mixture of the compounds and trimethylanilinium hydroxide (TMAH) into the hot injector of a gas chromatograph, followed by separation of the derivatives with a suitably deactivated glass capillary column. The optimal conditions for methylation were found by studying the effect of injector temperature, residence time and TMAH/compound molar ratio on the yield of the reaction. The optimal residence time of the sample in the injector could be set by a “semi-splitless” injection method.

Pyrolysis gas chromatography of branched-chain methylsiloxane polymers

Abstract The catalyzed and non-catalyzed thermal degradation of a branched-chain methyl siloxane polymer system has been investigated by pyrolysis gas chromatography measurements using the pyrolysis unit described in a previous paper. The effects of the catalysts KOH, DMSO and KOH+DMSO, in addition to that of the pyrolysis time, upon the nature and distribution of the products has been examined. The pyrolysis products have been identified and it has been shown that during the course of thermal treatment slow processes occur in the presence of DMSO. for this reason, the mechanism of thermal degradation in the presence of DMSO is different from that of the non-catalyzed and KOH-catalyzed pyrolysis. The slow processes mentioned above are most probably related to the migration of the CH3 groups along the Si-O-Si skeleton.