Showing papers by "Stig Pedersen-Bjergaard published in 2000"

Liquid-phase microextraction and capillary electrophoresis of acidic drugs.

Abstract: Vial liquid-phase microextraction (LPME) combined with capillary electrophoresis (CE) was evaluated for the determination of the acidic drugs ibuprofen, naproxen, and ketoprofen present in water samples and in human urine. The 2.5 mL samples containing the drugs were filled into conventional vials and subsequently acidified by 250 microL of 1-10 M HCl. Porous hollow fibers of polypropylene containing 25 microL of an aqueous solution of 0.01-0.1 M NaOH (acceptor solution) and with dihexyl ether immobilized in the pores of the wall were placed into each of the samples. The acidic drugs were extracted from the acidified sample solutions into the dihexyl ether phase, in the pores of the hollow fiber, and further into the alkaline acceptor solution forced by high partition coefficients. The drugs were extracted almost quantitatively (75-100% extraction efficiency) from the 2.5 mL samples and into the 25 microL acceptor solutions, providing 75-100 times preconcentration. The acceptor solutions were collected for automated CE analysis, which enabled the drugs to be detected down to the 1 ng/mL level.

Analysis of Pharmaceuticals by Microemulsion Electrokinetic Chromatography in a Suppressed Electroosmotic Flow Environment

Abstract: Microemulsion electrokinetic chromatography (MEEKC) in a suppressed electroosmotic flow environment has been evaluated for the separation of compounds of pharmaceutical interest. The separation medium was 0.8% (w/w)n-octane, 6.0% (w/w) sodium lauryl sulphate (SDS), 6.6% (w/w) 1-butanol, 20.0% (w/w) 2-propanol, and 66.6% (w/w) 25 mM phosphate buffer pH 2.5. The electroosmotic flow was effectively suppressed by use of this acidic microemulsion. The separation voltage was reversed, with the anode placed at the capillary outlet, and the negatively charged microdroplets ofn-octane migrated towards the detector. Several steroids, benzodiazepines, antidepressants, antipsychotic drugs, and antiepileptic drugs were effectively separated on the basis of their different interactions with the migrating microdroplets ofn-octane. The MEEKC system was briefly validated for the determination of the antidepressant citalopram in commercial tablets; quantitative data were in accordance with the label claim (5.5% deviation) and intra-day and inter-day variation were 1.63%RSD and 3.54%RSD, respectively.

Capillary gas chromatography coupled with negative ionization microplasma mass spectrometry for halogen-selective detection

Abstract: Gas chromatography was coupled with plasma mass spectrometry with a microplasma ion source for negative ion detection. The ion source, which was kept inside the high vacuum chamber of the mass spectrometer, was a rigid fused silica capillary tube containing a capacitively coupled radiofrequency helium plasma. This made the setup quite simple: eliminating the sampler–skimmer pressure-reducing interface traditionally used in plasma mass spectrometry. The present study describes the utilization of halogen-selective negative ion detection. A high selectivity of fluorine to hydrocarbon compounds (3 × 103), and a highly sensitive detection for F, Cl, Br, and I (0.13–12 pg s−1), were obtained. The mechanisms of negative ion formation and breakdown were discussed in conjunction with the results that were achieved.