Preparation of thermally stable phenylpolysiloxane fused silica capillary columns : optimization and evaluation of the deactivation by capillary GC and solid state 29Si NMR

The deactivation of fused silica capillary columns with a laboratory-made poly-diphenylvinylmethylhydrosiloxane copolymer has been investigated. The deactivation obtained at different temperatures and reaction times is characterized with a dual column capillary GC system [1]. In parallel, the effect of the silylation temperatures and reaction times on the nature, the structure, and the chemical properties of the deactivation layer has also been studied by solid-state 29Si NMR spoctroscopy. A fumed silica, Cab-O-Sil M5, was used as a model substrate for these spectroscopic studies. The deactivated fused silica capillaries show an excellent thermal stability (up to 400°C), a high resistance to solvolysis, and a minimal interaction to various critical test components. A good wettability of the fused silica capillary columns deactivated with this reagent was confirmed by successful subsequent coating with polysiloxanes with different phenyl content

Inzicht in de verouderingsprocessen leidt tot stabielere fasen voor RP-HPLC

Gebruik van agressieve eluentia verkort de Ievensduur van chemisch gemodificeerde stationaire fasen in gepakte kolommen. Het is een uitdaging voor fabrikanten stabielere stationaire fasen te ontwikkelen. Een beter inzicht in de verouderingsprocessen helpt hierbij. De vakgroep Instrumentele Analyse van de TU Eindhoven, heeft een aantal modeme 'reversed phase'-HPLC stationaire fasen uitgebreid getest voor en na specifieke verouderingsprocedures. Bij het onderzoek is naast chromatografie ook een aantal fysisch-chemische karakteriseringsmetboden toegepast, zoals vaste stof kernspinresonantiespectrometrie. De resultaten bieden aanbevelingen voor syntbese van betere stationaire fasen

Estimation of the instrumental band broadening contribution to the column elution profiles in open tubular capillary liquid chromatography

In comparison with conventionally packed HPLC columns, from a theoretical point of view, open capillary liquid chromatography (OTLC) systems offer a number of advantages like high plate numbers and short analysis times. On the other hand, drastic changes have to be made to the instrumentation. In particular, the contribution to band broadening by the chromatographic equipment must be considerably reduced. In the present study an OLC system was developed and evaluated, which yields satisfactory results for 26 pm i.d. columns. The determination of the contribution of the chromatographic equipment to the total band broadening is discussed

Effect of acid pretreatment of the silica substrate on the stability of octadecyl modified reversed phases

Two stationary phases, identically modified and derived from the same experimental Chromspher substrate, but one of which has been pretreated with a hydrofluoric acid solution, are compared after ageing with various eluents under simulated routine conditions. The hydrothermal hydrofluoric acid treatment of the silica substrate prior to modification with dimethyloctadecyl-silane improved both the surface coverage and the stability of the resulting stationary phase compared to those of the original substrate. The stability of the silica-to-silane bonding after modification was characterized by means of chromatographic techniques and elemental analysis. Changes in the rigidity of the substrate were studied by means of solid state29Si NMR. The effect of the hydrothermal acid treatment on relevant substrate parameters, including formation of crystalline regions at the surface, is also discussed

Characterization of polymers by multi-step thermal desorption/programmed pyrolysis gas chromatography using a high temperature PTV injector

Thermal treatment hyphenated with gas chromatography is a versatile and powerful tool in the study of polymer characterization. An inexpensive system where thermal treatment at different temperatures occurs inside a Programmable Temperature Vaporization injector (PTV) is described. The samples investigated, commercial plastics, are complex mixtures that contain several polymers and additives. These plastics as well as their pure constituents are subjected to multi-step thermal treatment. The individual chromatograms of the various constituents of the polymeric sample are correlated with those of the final material in order to identify additives (thermal desorption) and degradation products (pyrolysis). Results obtained with the new method indicate the interesting potentials of the technique for the characterization of polymer compositions. Reproducibility of absolute and relative peak areas has been considered and found to be acceptable. The absence of a heated transfer line and switching valves, which are always present in conventional set-ups, eliminates the risk of losses of high molecular weight components. Further advantages of the technique proposed are simplicity, versatility, and its inexpensive nature

Effect of acid pretreatment of the silica substrate on the stability of octadecyl modified reversed phases

Two stationary phases, identically modified and derived from the same experimental Chromspher substrate, but one of which has been pretreated with a hydrofluoric acid solution, are compared after ageing with various eluents under simulated routine conditions. The hydrothermal hydrofluoric acid treatment of the silica substrate prior to modification with dimethyloctadecyl-silane improved both the surface coverage and the stability of the resulting stationary phase compared to those of the original substrate. The stability of the silica-to-silane bonding after modification was characterized by means of chromatographic techniques and elemental analysis. Changes in the rigidity of the substrate were studied by means of solid state29Si NMR. The effect of the hydrothermal acid treatment on relevant substrate parameters, including formation of crystalline regions at the surface, is also discussed

Preparation of thermally stable phenylpolysiloxane fused silica capillary columns : optimization and evaluation of the deactivation by capillary GC and solid state 29Si NMR

The deactivation of fused silica capillary columns with a home made polydiphenylvinylmethylhydrosiloxane copolymer is investigated. The deactivation performance obtained at different temperatures and reaction times is characterized with a dual column capillary GC system. In parallel the effect of the silylation temperatures and reaction times on the nature, the structure and the chemical properties of the deactivation layer is investigated with solid-state 29Si NMR spectroscopy. A fumed silica, Cab-O-Sil M5, was used as a model substrate for this spectroscopic studies. The deactivated fused silica capillaries show an excellent thermal avalability (up to 400"C), a high resistance to solvolysis and a minimal interaction to various critical test components. An improved wettability of the fused silica capillary columns deactivated with this reagent was confirmed through successful subsequently coating with polysiloxanes with different phenyl contents