Herstellung, Funktionalisierung und Charakterisierung von monolithischen Kapillarsäulen für die Hochleistungs-Flüssigkeitschromatographie

Abstract

Monolithic silica columns for high performance liquid chromatography (HPLC) were fabricated in fused-silica capillaries with inner diameters between 25 and 100 micrometers and lenghts up to 150 cm. High permeability and chromatographic activity is provided by a bimodal pore structure resulting from a sol-gel-process. Well-known shrinkage during preparation, aging and drying could be avoided completely. Scanning electron microscopy showed a variety of morphologies ranging from sponge-like to sintered-particle-like micro-structures. This material was used to carry new selectivities. Brush-type phases containing polar-embedded groups with different terminating groups were synthesised. For lack of suitable investigation methods due to the small amounts of material, characterization was carried out by investigating column properties like permeability, silanophilic activity, hydrophobic character and selectivity, efficiency and steric selectivity. Especially a phenyl-functionalised phase showed excellent selectivity and efficieny in separating mixtures of common analytes like nitroaromatic compounds, hormones or polyaromatic hydrocarbons. Due to the high number of theoretical plates that can be achieved with long monolithic columns, a 70-cm monolithic column functionalised with RP18 properties was used to separate a complex mixture of peptides. A further enhancement in efficiency and peak capacity was achieved by increasing operating temperature. Therefore, a fully temperature-controlled HPLC-system was built up and it was applied for separation of the same peptide mixture at 70 °C. Analysis time could be reduced by 45%. Finally, a monolithic capillary column was coupled to a flame ionization detector (HPLC-FID). The coupling was suitable for UV-inactive, volatile and water-soluble analytes. A homologous series of n-alcohols could be separated on a monolithic column and detection was performed with a commercial flame-ionisation-detector for gaschromatography.