Koen Desmet

Analysis of 1-hydroxypyrene in urine as PAH exposure marker using in-situ derivatisation stir bar sorptive extraction-thermal desorption-capillary gas chromatography-mass spectrometry

SummaryA fast and rabust method for the determination of 1-hydroxypyrene (OH-pyrene) and other hydroxylated PAHs in urine by stir bar sorptive extraction (SBSE) combined with thermal desorption-capillarygas chromatography-mass spectrometry (TD-CGC-MS) is described. After enzymatic hydrolysis, in-situ derivatisation with acelic acid anhydride precedes SBSE sampling to improve the chromatographic behavior of the analytes. The performance of the method has been evalucted by the quantitative determination of OH-pyrene in some certified samples. Detection limits as low as 2ngL1(ppt) can be obtained. The procedure is illustrated with the analysis of a urine sample of a firefighter.

Determination of the enantiomerization energy barrier of some 3-hydroxy-1,4-benzodiazepine drugs by supercritical fluid chromatography

The first-order kinetic equation for irreversible reactions was used to determine the enantiomerization barrier of some of 3-hydroxy-1,4-benzodiazepine enantiomers by supercritical fluid chromatography (SFC). The racemates of lorazepam, oxazepam and temazepam were separated by SFC on chiral (R,R)-Whelk-O1 column with supercritical carbon dioxide containing 12.5% methanol and 0.5% diethylamine as a mobile phase. Peak areas of enantiomers prior to (A(A0), A(B0)) and after the separation (A(A), A(B)), used for calculation of the enantiomerization barrier, were determined by computer-assisted peak deconvolution of peak clusters from the chromatograms. It was demonstrated for the first time that using a model for a four-peak cluster produces height precise results, and most closely approximates the published results. The kinetic equation for irreversible reactions was used to determine apparent enantiomerization rate constants. The dependence of the apparent enatiomerization barrier (deltaG(app)(A-->B), deltaG(app)(B-->A)) on temperature was used to determine apparent activation enthalpy (deltaH(app)(R-->S), deltaH(app)(S-->R)) and entropy (deltaS(app)(R-->S), deltaS(app)(S-->R)) for all studied benzodiazepines.

A simple approach to on-line oxidative pyrolysis-capillary gas chromatography—Mass spectrometry

SummaryA simple and robust approach to on-line oxidative pyrolysis-capillary gas chromatographymass spectrometry (OxPYR-CGC-MS) analysis is presented. Only minor adaptations on a conventional filament pyrolysis unit are required. Air is introduced into the pyrolyzer through a bypass-valve during pyrolysis and the degradation products are focused in a cryo-cooled programmed temperature vaporization (PTV) injector. Before GC analysis, the system is switched back to helium and after equilibration PTV injection is carried out. The potential of the system is illustrated with normal and oxidative pyrolyses of polystyrene (PS) and polyethylene (PE).

Evaluation of the suitability of sampling on Tenax TA and polydimethylsiloxane for the analysis of combustion gases

Two sorbents commonly employed for air sampling were selected for the evaluation of their suitability for the analysis of combustion gases namely Tenax TA as adsorbent and polydimethylsiloxane (PDMS) as absorbent. Target compounds were selected among the gaseous combustion products of polyurethane foam and fire-retarded polystyrene. The combustion gases were generated by burning test materials in the flame of a Bunsen burner. Gaseous combustion products were sampled simultaneously with the two sorbents using a two-way adapter, thereby exposing each sorbent to the same combustion gas atmosphere. Special attention was given to the deterioration encountered in the Tenax TA performance upon repeated combustion gas exposure, limiting its use for sampling reactive atmospheres.

Profiling the spatial concentration of allethrin and piperonyl butoxide using passive sorptive sampling and thermal desorption capillary GC-MS.

Spatial concentration distribution of a chemical in an indoor environment is an important factor in the evaluation of chemical nuisances. However, straightforward techniques for the determination of this distribution are not very common and usually limited in their application. Sorptive sampling using polydimethylsiloxane-coated stir bars and the combination of active and diffusive sampling were shown to allow uncomplicated spatial concentration profiling of multiple compounds in an indoor environment. The validity of the approach was demonstrated in the analysis of the spatial concentration distribution of a pyrethroid insecticide in a common bedroom. The relative concentrations of allethrin and piperonyl butoxide were profiled throughout the room upon the application of an insecticide vaporizer.