Biomedical subjects

Gerd Vanhoenacker

Publications and source records attributed to Gerd Vanhoenacker.

6 recordsLinked to original sources

PubMed2006

Elevated temperature and temperature programming in conventional liquid chromatography--fundamentals and applications.

Temperature, as a powerful variable in conventional LC is discussed from a fundamental point of view and illustrated with applications from the author's laboratory. Emphasis is given to the influence of temperature on speed, selectivity, efficiency, detectability, and mobile phase composition (green chromatography). The problems accompanying the use of elevated temperature and temperature programming in LC are reviewed and solutions are described. The available stationary phases for high temperature operation are summarized and a brief overview of recent applications reported in the literature is given.

Chromatography, Liquid↗

PubMed2005

High temperature liquid chromatography and liquid chromatography-mass spectroscopy analysis of octylphenol ethoxylates on different stationary phases.

Temperature was investigated as active parameter in the liquid chromatography (LC) analysis of octylphenol ethoxylates. Significant differences in selectivity were observed when the oligomers were analyzed by reversed phase LC (RPLC) on silica-, zirconia- and polystyrene/divinylbenzene based stationary phases at low (ambient), medium and elevated temperature with acetonitrile/water as mobile phase. As ascertained by LC-mass spectroscopy (MS), in most cases the elution order of the oligomers was completely reversed comparing ambient and high temperature separations. On a graphitized carbon type column, the selectivity remained unchanged, regardless the analysis temperature. Also in normal phase LC, the elution order remained unaffected by temperature variations both for acetonitrile/water and methanol/water mixtures as mobile phase. Surprisingly, when reversed phase LC on a octadecylsilicagel column at different temperatures was repeated with methanol instead of acetonitrile as mobile phase ingredient, the reversal of elution order did not take place. Results are evaluated in terms of thermodynamic parameters.

Chromatography, Liquid↗

PubMed2004

Dynamic coating for fast and reproducible determination of basic drugs by capillary electrophoresis with diode-array detection and mass spectrometry.

The double coating principle of CEofix buffers was evaluated for the analysis of some basic drugs by capillary electrophoresis-diode-array detection (CE-DAD) and capillary electrophoresis-mass spectrometry (CE-MS). The involatile phosphate present in original low pH CEofix, was replaced with formic acid for hyphenation of CE with MS. The double coating produces a substantial and highly reproducible electroosmotic flow (EOF), even at low pH. The rinsing procedure and electrolyte composition were optimized for both CE-DAD and CE-MS. The system was evaluated with the analysis of a mixture of basic drugs and a spiked urine sample enriched by solid-phase extraction (SPE). The R.S.D. values on the migration time and peak area measured for 28 analyses with CE-DAD were below 0.25 and 2.40%, respectively. For CE-MS, the R.S.D. on the migration time was 0.85% or less and the area precision ranged from 5.65 to 14.33% (for seven injections). The LOD with the developed CE-MS method was below 50 ppb for all five drug standards tested.

Electrophoresis, Capillary↗

PubMed2004

Stir bar sorptive extraction-liquid desorption applied to the analysis of hop-derived bitter acids in beer by micellar electrokinetic chromatography.

Stir bar sorptive extraction-liquid desorption (SBSE-LD) has been applied as an efficient sample preparation method for the analysis of beer bitter acids. Extracts free of almost all interfering compounds were obtained, allowing simultaneous analysis of iso-alpha-acids and reduced iso-alpha-acids. A robust micellar electrokinetic chromatography (MEKC) method was developed that enables fast separation of iso-alpha-acids and reduced iso-alpha-acids. Quantitative data are in good agreement with results obtained by high-performance liquid chromatography (HPLC) using direct beer injection.

Acids↗

PubMed2002

Chemotaxonomic features associated with flavonoids of cannabinoid-free cannabis (Cannabis sativa subsp. sativa L.) in relation to hops (Humulus lupulus L.).

The major flavonoids present in the leaves and flowers of the cannabinoid-free cannabis (Cannabis sativa subsp. sativa L.) cultivars Felina and Futura are orientin (1), vitexin (2), luteolin-7-O-beta-D-glucuronide (3), and apigenin-7-O-beta-D-glucuronide (4), while prenylated flavonoids, to which the potent estrogenicity of hops (Humilus lupulus L.) is associated, are absent. The different composition of flavonoids has chemotaxonomic value.

Apigenin↗

PubMedDate not supplied

Evaluation of a two-stage screening procedure in the combinatorial search for serine protease-like activity.

A series of peptidosteroid derivatives containing two independent peptide chains in which Ser and His are incorporated were synthesized by solid-phase peptide synthesis. The activity of the different compounds in the hydrolysis of the activated substrate NF31 was assessed in a stepwise fashion. First, the different resin-bound derivatives 6a-l and 6x-z were individually assayed for serine esterification in the absence of water. The use of a colored substrate allowed for a visual identification of the most active compounds. Through the inclusion of control substances, the involvement of histidine in the mechanism for serine acylation was shown. Second, the hydrolysis and methanolysis of the different acylated derivatives 8a-l and 8x were evaluated using UV spectroscopy, again indicating the involvement of histidine. The feasibility of applying the above procedures in a combinatorial context was proven via the screening of artificial libraries, created by mixing the different resin-bound peptidosteroid compounds. In this respect, the use of a photocleavable linker allowed for the unambiguous structural characterization of the selected members via application of single-bead electrospray tandem mass spectrometry.

Combinatorial Chemistry Techniques↗