Towards automated, miniaturized and solvent-free sample preparation methods.
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Journal Article↗
Biomedical subjects
Frank David
Publications and source records attributed to Frank David.
Evaluation of ultra performance liquid chromatography. Part I. Possibilities and limitations.
A practical evaluation of the possibilities and limitations of ultra performance liquid chromatography (UPLC) is presented. Acquity BEH columns packed with 1.7 microm particles are evaluated by means of van Deemter and Knox plots. The columns are characterised by high optimal velocities (3.7 mm/s) and low plate heights (4.4 microm). Minimum plate heights of 2d(p) were, however, not reached and reasons are presented and discussed. Furthermore, the use of 1.7 microm particles at 1000 bar is compared, from a theoretical viewpoint, to conventional LC (3.5 and 5 microm particles at 400 bar) in terms of analysis speed and practical maximum efficiency. Experimental data are used to construct kinetic- or "Poppe-plots", which facilitate investigation of the effect of pressure and particle size on speed and efficiency. It is found that UPLC conditions hold advantages in terms of speed of analysis, for required theoretical plate counts up to approximately 80,000.
Acetophenones↗
High-efficiency liquid chromatography on conventional columns and instrumentation by using temperature as a variable I. Experiments with 25 cm x 4.6 mm I.D., 5 microm ODS columns.
High plate numbers were obtained in conventional LC by coupling columns and by using temperature to reduce the viscosity of the mobile phase. At 80 degrees C up to eight columns of 25 cm x 4.6 mm I.D. packed with 5 microm ODS particles could be coupled generating 180,000 effective plates while the pressure drop was only 350bar. For routine work, a set of four columns is preferred. The analysis times on one column operated at 30 degrees C and 1 mL/min flow rate and on four columns at 80 degrees C and 2 mL/min flow rate are the same in isoeluotropic conditions while the resolution is doubled. Multicolumn systems were successfully applied in isocratic and gradient mode for the analysis of pharmaceutical and environmental samples.
Chromatography, Liquid↗
Determination of suspected allergens in non-volatile matrices using PTV injection with automated liner exchange and GC-MS.
A method is described for the analysis of suspected volatile allergens in products containing high molecular weight or non-volatile compounds such as plant extracts, solid and liquid detergents, shampoos, etc. The method is based on dissolution/extraction of the sample followed by direct injection in a programmed temperature vaporizing inlet, the liner of which contains PDMS foam to retain the high molecular weight non-volatile material. The liner is automatically replaced after each injection, by an automated liner exchange device. Analysis is done by GC-MS operated in the retention-time locked mode. The figures of merit are illustrated with the analysis of some real samples.
Allergens↗
Fast capillary GC using a low thermal mass column oven for the determination of residual solvents in pharmaceuticals.
A low thermal mass column oven was used for fast capillary GC analysis (high throughput) of residual solvents in pharmaceutical products. A dedicated capillary column, 20 m L x 180 microm ID x 1 microm DB-624 was programmed from 35 degrees C (30 s) to 150 degrees C at 100 degrees C/min and to 250 degrees C (30 s) at 200 degrees C/min, resulting in a total GC cycle time of less than 4 min. Complete separation of a target 20-component mixture was achieved, while method performance in terms of repeatability, sensitivity, and linearity was maintained in comparison to the generic method currently applied in our laboratories.
Chromatography, Gas↗
Dual-phase twisters: a new approach to headspace sorptive extraction and stir bar sorptive extraction.
The fields of applicability of headspace sorptive extraction (HSSE) and stir bar sorptive extraction (SBSE) using polydimethylsiloxane (PDMS) as sorbent have been intensively discussed and widely described. One of the limits of sorptive extraction is that PDMS (i.e. an apolar phase) is the only polymer currently in use making it difficult to recover polar analytes from complex or multi-ingredient matrices and those with very volatile components (C1-C4 analytes). Dual-phase twisters are here introduced as new tools for HSSE and SBSE to overcome the above limits. Dual-phase twisters combine the concentration capabilities of two or more sampling materials operating in different ways (in this case sorption and adsorption). The new twisters consist of a short PDMS tube the ends of which are closed with two magnetic stoppers, thus creating an inner cavity that can be packed with different types of adsorbents like activated carbons. The concentration capability of dual-phase twisters was evaluated by using them for the HSSE and SBSE sampling of a number of matrices in the vegetable, food and environmental fields. The contributions made by different carbons to recovery, repeatability and intermediate precision were also investigated.
Chromatography, Gas↗
Automated headspace-solid-phase micro extraction-retention time locked-isotope dilution gas chromatography-mass spectrometry for the analysis of organotin compounds in water and sediment samples.
An automated method for the simultaneous determination of six important organotin compounds namely monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), monophenyltin (MPhT), diphenyltin (DPhT) and triphenyltin (TPhT) in water and sediment samples is described. The method is based on derivatization with sodium tetraethylborate followed by automated headspace-solid-phase micro extraction (SPME) combined with GC-MS under retention time locked (RTL) conditions. Home-synthesized deuterated organotin analogues were used as internal standards. Two high abundant fragment ions corresponding to the main tin isotopes Sn118 and Sn120 were chosen; one for quantification and one as qualifier ion. The method was validated and excellent figures of merit were obtained. Limits of quantification (LOQs) are from 1.3 to 15 ng l(-1) (ppt) for water samples and from 1.0 to 6.3 microg kg(-1) (ppb) for sediment samples. Accuracy for sediment samples was tested on spiked real-life sediment samples and on a reference PACS-2 marine harbor sediment. The developed method was used in a case-study at the harbor of Antwerp where sediment samples in different areas were taken and subsequently screened for TBT contamination. Concentrations ranged from 15 microg kg(-1) in the port of Antwerp up to 43 mg kg(-1) near a ship repair unit.
Automation↗
Optimization of a multi-residue screening method for the determination of 85 pesticides in selected food matrices by stir bar sorptive extraction and thermal desorption GC-MS.
A multi-residue method to determine 85 pesticides, including organochlorine pesticides, carbamates, organophosphorus pesticides, and pyrethroids, in vegetables, fruit, and green tea, has been developed. The method is based on stir bar sorptive extraction (SBSE) coupled to thermal desorption (TD) and retention time locked (RTL) GC-MS operating in the scan mode. Samples are extracted with methanol and diluted with water prior to SBSE. Dilution of the methanol extract before SBSE was optimized to obtain high sensitivity and to minimize adsorption onto the glass wall of the extraction vessel as well as to minimize sample matrix effects (particularly for the pesticides with high log K(o,w) values). The optimized method consists of a dual SBSE extraction performed simultaneously on respectively a twofold and a fivefold diluted methanol extract. After extraction, the two stir bars are placed in a single glass thermal desorption liner and are simultaneously desorbed. The method showed good linearity (r2 > 0.9900) and high sensitivity (limit of detection: < 5 microg kg(-1)) for most of the target pesticides. The method was applied to the determination of pesticides at low microg kg(-1) in tomato, cucumber, green soybeans, spinach, grapes, and green tea.
Food Analysis↗
Stir bar sorptive extraction: a new quantitative and comprehensive sampling technique for determination of chemical signal profiles from biological media.
Various applications of a novel sampling procedure in chemical ecology are outlined. The stir bar extraction method features the analytical reproducibility needed in recording the analytical profiles of volatile and semivolatile components of biological mixtures. This methodology has been demonstrated here through the examples of small volume urine samples, glandular tissue volatiles, and the air blown through animal cages. Its analytical merits are compared with those of the previously established purge-and-trap (dynamic headspace) technique.
Animals↗
Kinetics of orally administered di(2-ethylhexyl) phthalate and its metabolite, mono(2-ethylhexyl) phthalate, in male pigs.
Di(2-ethylhexyl) phthalate (DEHP) is used as a plastic softener in the polymer industry and is widespread in medical devices. DEHP has been incriminated as an endocrine-disrupting chemical, and the effects of DEHP in various species have included disturbances in the reproductive system. The effects of the chemical have varied, depending upon exposure routes and species. This study was performed in order to characterise the kinetics of DEHP and its metabolite mono(2-ethylhexyl) phthalate (MEHP) in the young male pig, an omnivore model-species for research in reproductive toxicology. Eight pigs were given 1000 mg DEHP/kg bodyweight by oral gavage. The concentrations of DEHP and MEHP were then measured in the plasma and tissues of the pigs at different time points after administration. There was no consistent rise above contamination levels of concentrations of DEHP in the plasma of the pigs. However, the metabolite MEHP reached the systemic blood circulation. The half-life of MEHP in the systemic blood circulation was calculated to be 6.3 h. Absorption from the intestine was biphasic in six of the eight pigs and the mono-exponential elimination-phase started 16 h after the after the administration of DEHP. To conclude, MEHP consistently reaches the systemic circulation in the pig when DEHP is administered orally. The kinetic pattern of the parent substance on the other hand is more difficult to characterise.
Administration, Oral↗
Multi-residue screening of pesticides in vegetables, fruits and baby food by stir bar sorptive extraction-thermal desorption-capillary gas chromatography-mass spectrometry.
The performance of stir bar sorptive extraction (SBSE) for the enrichment of pesticides from vegetables, fruits and baby food samples is discussed. After extraction with methanol, an aliquot is diluted with water and SBSE is performed for 60 min. By applying a new thermal desorption unit (TDU), fully automated and unattended desorption of 98 stir bars is feasible, making SBSE very cost-effective. The presence of pesticide residues is elucidated with the retention time locked gas chromatography-mass spectroscopy method (RTL-capillary GC-MS). With SBSE-RTL-capillary GC-MS operated in the scan mode, more than 300 pesticides can be monitored in vegetables, fruits and baby food. The multi-residue method (MRM) described provides detectabilities from the mg/kg (ppm) to the sub-microg/kg (ppb) level, thereby complying with the maximum residue levels (MRLs) set by regulatory organizations for pesticides in different matrices. Several examples, i.e. pesticide residues in lettuce, pears, grapes and baby food, illustrate the potential of SBSB-RTL-capillary GC-MS.
Fruit↗
High-throughput capillary gas chromatography for the determination of polychlorinated biphenyls and fatty acid methyl esters in food samples.
High-throughput capillary gas chromatography (CGC) methods, developed during the Belgian 1999 "dioxin" food crisis, for the determination of the contaminating polychlorinated biphenyls (PCBs) and the fatty acid composition of the lipids are described. For PCB analysis, the fat obtained by ultrasonic extraction is fractionated by matrix solid-phase dispersion, and the PCBs are analyzed by CGC-electron capture detection on a 10-mL x 100-microm-i.d. HP-5MS column. Analytical conditions for the high-speed column are deduced from analyses on conventional CGC columns using the method translation software. The concept of retention time locking is implemented to facilitate the elucidation of the PCB markers. The fatty acid methyl esters (FAMEs) are prepared by the sodium methylate procedure on part of the ultrasonic extract followed by analysis on 10-mL x 100-microm-i.d. HP-WAX or BPX-70 capillary columns. By optimizing both the sample preparation and CGC analysis, the throughput is more than fifty PCB and FAME samples per day with the same robustness as conventional methods.
Chromatography, Gas↗