Development of techniques and methods for drug analysis by packed capillary liquid chromatography with octadecylbonded silica and porous graphitic carbon columns
Abstract: Packed capillary liquid chromatography in combination with ultraviolet and mass spectrometric (MS) detection was explored as an analytical tool for drug analysis. The focus was put on column and sample preparation techniques as well as on fundamental aspects and development of chromatographic separations. Both octadecylbonded (C18) silica and porous graphitic carbon (PGC) was used as stationary phases.Supercritical carbon dioxide was used as the packing carrier to pack silica based C18 particles in 0.2 mm internal diameter fused silica capillaries. A factorial design was used to examine the influence of selected factors on packing performance. The model obtained indicated that the best packing conditions would include the use of a pressure ramp, a high final pressure and a long restrictor.The retention behaviour of sulphated heparin and chondroitin disaccharides of different charge levels was studied on PGC capillary columns. It was found that the retention was strongly dependent on the choice of buffer and number of sulphate groups on the disaccharides. An increase in retention was observed when the temperature or the concentration of the organic modifier was increased.A packed capillary PGC column was also used to separate the polar drug L-DOPA and four of its metabolites in plasma. The mobile phase contained no ion-pairing agents and relatively high concentrations of organic modifier, which makes it suitable for e.g. MS detection.A method was developed to determine the free concentration of the drug tolterodine at pM-nM levels in microliter plasma volumes. Ultrafiltration was used as the sample preparation method. For the analyses, packed capillary C18 columns in a column-switching system coupled to MS detection was used.Finally, the two sample preparation methods ultrafiltration and microdialysis were compared with regard to the determination of the free concentration of ropivacaine in plasma. Both methods gave a free fraction of 6 %.
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