Biomedical subjects

Pat Sandra

Publications and source records attributed to Pat Sandra.

At least 37 records · Page 2Linked to original sources

PubMed2005

On the capillary gas chromatographic separation of enantiomers of N-trifluoroacetyl-O-alkyl esters of selected amino acids on 2,3-di-O-pentyl-6-O-acyl cyclodextrins.

In this work, the separation of enantiomers of N-TFA-O-alkyl amino acids on the 2,3-di-O-pentyl-6-O-acyl alpha-, beta- and gamma-cyclodextrin stationary phases has been studied. The influence of structure differences in the alkyl substituents bonded to the stereogenic carbon atom (R1), as well as in the ester group (R2) of the selected amino acid derivatives, and the selectivity of modified alpha-, beta- and gamma-cyclodextrin phases in gas chromatographic separation of derivatized amino acid enantiomers was studied in detail. A model set of N-TFA-alkyl esters of four amino acids was separated on five columns. The separation of enantiomers was evaluated in terms of the interactions of the alkyl substituents bonded to the stereogenic carbon (R1) and/or the ester group (R2) of the N-TFA-O-alkyl amino acid derivatives as well as the nature of the 3-O-acyl group in the 2,6-di-O-pentyl-3-O-acyl alpha-, beta- and gamma-cyclodextrins. It was shown that the variation in the enantiomeric separation with temperature and the retention order of enantiomers on a given cyclodextrin capillary column depends both on the nature of the bonded R1 and R2 alkyl groups. It was found that the temperature dependencies of selectivity factors, ln alpha on 1/T, were mostly non-linear. The thermodynamic data [delta(deltaS) and [delta(deltaH)] which characterize the chiral recognition were used to gain more insight into the mechanistic aspects of enantio separation of the N-TFA-O-alkyl amino acid derivatives on 2,6-di-O-pentyl-3-O-acyl-alpha-, beta- and gamma-cyclodextrins.

Amino Acids↗

PubMed2005

Determination of bromophenols as dioxin precursors in combustion gases of fire retarded extruded polystyrene by sorptive sampling-capillary gas chromatography-mass spectrometry.

Extruded polystyrene (XPS) is often treated with hexabromocyclododecane (HBCD) as fire retardant (FR). Because of its aliphatic structure, HBCD is not suspected to cause formation of polybrominated dioxins upon combustion. Precursors of polybrominated dioxins, namely bromophenols, were detected during tubular furnace combustion experiments of FR-XPS in combination with sorptive enrichment on polydimethylsiloxane followed by on-line thermal desorption-capillary GC/MS. The highest concentration of mono- and tribromophenols detected were 85.9 and 3.7 mg kg(-1), respectively, at a temperature of 700 degrees C, while a temperature of 500 degrees C yielded the highest concentration of dibromophenols namely 10.4 mg kg(-1). At a combustion temperature of 900 degrees C no bromophenols were detected.

Dioxins↗

PubMed2005

Determination of the acaricide fenbutatin oxide in water samples by automated headspace-SPME-GC/MS.

The analysis of the acaricide fenbutatin oxide (FBTO) having a molecular weight of 1052.66 g mol(-1) in water samples by capillary GC/MS after in-situ derivatization with sodium tetraethylborate (NaBEt4) and headspace-SPME enrichment is described. Automated SPME is performed at 80 degrees C for 30 min. Detection is carried out in the ion monitoring mode with deuterated triphenyltin (TPhTd15) as internal standard. Good linearity (R2 = 0.9993) was obtained in the dynamic range 20 to 1000 ng L(-1) with a limit of detection of 16 ng L(1) (LOD at 3 S/N) and a limit of quantitation of 50 ng L(-1) (LOQ at 10 S/N). Intra-day RSD% for n=6 was 8.9 at the LOQ level.

Animals↗

PubMed2005

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↗

PubMed2005

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↗

PubMed2004

Combining gel and capillary electrophoresis, nano-LC and mass spectrometry for the elucidation of post-translational modifications of Trichoderma reesei cellobiohydrolase I.

N-Glycosylation of cellobiohydrolase I from the fungus Trichoderma reesei (strain Rut-C30) is studied using a combination of electrophoretic, chromatographic and mass spectrometric techniques. As four potential N-glycosylation sites and several uncharged and phosphorylated high-mannose glycans are present, a large number of glycoforms and phospho-isoforms can be expected. Isoelectric focusing both in gel and in capillary format was successfully applied for the separation of the phospho-isoforms. They were extracted in their intact form from the gel and subsequently analysed by nanospray-Q-TOF-MS, thereby making use of a powerful two-dimensional technique. Nano-LC/MS/MS on a Q-Trap MS further allowed the determination of the glycosylation sites. As a novel approach, an oxonium ion was used in precursor ion scanning for selective detection of glycopeptides containing phosphorylated high-mannose glycans.

Amino Acid Sequence↗

PubMed2004

Characterization of cellobiohydrolase I N-glycans and differentiation of their phosphorylated isomers by capillary electrophoresis-Q-Trap mass spectrometry.

A capillary electrophoresis-mass spectrometric (CE-MS) method is described for the simultaneous analysis of uncharged and charged glycans. The glycans were labeled with the negatively charged tag 8-aminopyrene-1,3,6-trisulfonate by reductive amination and separated in an ammonium acetate buffer. A Q-Trap instrument was used for mass spectrometric detection. The CE-MS method was first optimized using maltooligosaccharides and ribonuclease B N-glycans and then applied to the characterization of enzymatically released N-glycans from the glycoprotein cellobiohydrolase I. The method, as developed, allowed differentiation of phosphorylated isomers and MS/MS provided useful structural information. Further structural evidence was obtained by studying the methylated glycans in off-line ESI-MS/MS experiments and by using a combination of chemical and enzymatic sequencing.

Carbohydrate Conformation↗

PubMed2004

Use of headspace solid-phase microextraction and headspace sorptive extraction for the detection of the volatile metabolites produced by toxigenic Fusarium species.

An efficient methodology was developed to determine the growth of toxigenic Fusarium spp., based on headspace solid-phase microextraction (SPME) and stir bar sorptive extraction of the fungal volatile metabolites produced. SPME and headspace sorptive extraction (HSSE) were used to monitor the de novo production of sesquiterpene hydrocarbons, such as trichodiene, a volatile marker and intermediate in the biosynthesis of trichothecenes. On growth media such as malt extract agar and potato dextrose agar, it was found that trichodiene was produced by toxigenic strains of Fusarium sambucinum and Fusarium sporotrichioides. It was the main volatile metabolite in the headspace extract of the cultures. On the other hand, deoxynivalenol producing Fusarium graminearum showed a completely different pattern of volatile sesquiterpenes and could easily be distinguished from a zearalenone producing strain of F. graminearum based on the headspace profile. Hence, it can be concluded that headspace analysis of volatile fungal metabolites by SPME and HSSE in combination with gas chromatography/mass spectrometry is a suitable monitoring technique to differentiate toxigenic strains of Fusarium.

Fusarium↗

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↗

PubMed2004

Analysis of gums by capillary electrophoresis with laser induced fluorescence.

Gums were derivatised with the fluorescence reagent, 9-aminopyrene-1,4,6-trisulfonic acid followed by microcentrifuge filtration. The resulting high mass fractions were analysed by capillary electrophoresis (CE) on a polyacrylamide coated capillary with laser induced fluorescence (LIF) detection. A wide pH range of electrolytes was used to study the influences on the electrophoretic mobilities and on the peak shapes of the gums. In this way, the separation of a mixture of five commercial gums, namely iota carrageenan, kappa carrageenan, alginic acid, xanthan and carboxymethyl cellulose (CMC), could be achieved at pH 3.2 with a 25 mmol/L trisodium citrate buffer. It is also shown that a mixture of Arabic gum, Karaya gum and CMC could be separated at pH 7.8 in a similar buffer.

Acrylic Resins↗

PubMed2003

Stir bar sorptive extraction-thermal desorption-capillary GC-MS for profiling and target component analysis of pharmaceutical drugs in urine.

Stir bar sorptive extraction (SBSE) in combination with thermal desorption (TD) on-line coupled to capillary gas chromatography-mass spectrometry (CGC-MS) was applied to the analysis of pharmaceutical drug compounds and metabolites in urine. SBSE implies stirring of the aqueous sample (urine, blood, etc.) with a glass stir bar coated with a thick layer (24 microl) of polydimethylsiloxane (PDMS) for sorptive enrichment of the analytes of interest. In combination with quantitative TD, on-line coupled with CGC-MS, the technique showed to be very versatile and sensitive for the analysis of a wide range of drug substances. Moreover, the relative high enrichment efficiencies of SBSE allow to use mass spectrometric detection (MSD) in the full scan mode. In situ derivatization of polar compounds before SBSE is demonstrated for the analysis of paracetamol and this resulted in both improved chromatographic behavior and higher sensitivity. The quantitative performance of SBSE-TD-CGC-MS is illustrated with the analysis of some barbiturates in urine.

Electrophoresis, Capillary↗

PubMed2003

Rapid method development for chiral separation in drug discovery using sample pooling and supercritical fluid chromatography-mass spectrometry.

A novel strategy for rapid chiral method development has been implemented using sample pooling and supercritical fluid chromatography-mass spectrometry (SFC-MS) on four chiral stationary phases, namely Chiralpak AD and AS, and Chiralcel OJ and OD, and eight different modifier concentrations (5 to 40% methanol-0.2% isopropylamine). The screening is performed under an outlet pressure of 110 bar at 35 degrees C, and at a flow-rate of 2.5 ml/min for the initial 20 min and then ramped up to 4 ml/min and held for 4.5 min to elute all solutes from the column. The entire process is fully automated from injection to data processing, and operates unattended for 15 h overnight to obtain optimal chiral separation for multiple compounds. A unique feature of using SFC-MS to monitor chiral synthesis is the negligible interferences from achiral impurities. In addition, with SFC-MS, enantiomeric excess can be determined with much lower detection limits than UV and much shorter analysis times compared to normal-phase/reversed-phase liquid chromatography.

Amylose↗

PubMed2003

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↗

PubMed2003

Considerations on ultra trace analysis of carbamates in water samples.

A new routine method for the ultra trace analysis of carbamates in water samples is presented, using solid-phase extraction followed by high-performance liquid chromatography coupled to atmospheric pressure electrospray ionisation mass spectrometry (SPE-LC-ESI-MS). Instrumental conditions of LC-ESI-MS in the selected ion monitoring (SIM) mode, showed excellent linear response for the six N-methyl carbamates studied (aldicarb, carbaryl, carbofuran, methomyl, oxamyl and pirimicarb) in the range from 1 to 50 microg/l and a precision having a relative standard deviation below 7.8% was achieved. Instrumental limits of detection of 0.10 microg/l were found for these carbamates, with the exception of methomyl for which 0.50 microg/l was measured. The SPE assays were shown to be easy, fast, very sensitive, requiring a low volume (50 ml) of water sample. For laboratory-spiked water samples having 0.03 and 0.30 microg/l of individual N-methyl carbamates, higher selectivities were achieved in cartridges having octadecylsilica, polystyrene-divinylbenzene and N-vinylpyrrolidane-divinylbenzene as solid phases, for which reasonable average recoveries were obtained. Ten replicates using octadecylsilica SPE cartridges, showed average recoveries between 73.7 and 92.6% with a relative standard deviation lower than 14.7%. The present methodology evidences good robustness, accuracy and precision for monitoring of N-methyl carbamates in water samples, and is shown to be a suitable alternative to replace the currently dedicated analytical systems. The limits of detection for the analysis of N-methyl carbamates in water samples reached in the present methodology (0.5 to 3 ng/l), clearly cover the maximum concentration admissible for pesticides, established by the European Union directive on water quality.

Aldicarb↗

PubMed2003

Monitoring and fast detection of mycotoxin-producing fungi based on headspace solid-phase microextraction and headspace sorptive extraction of the volatile metabolites.

Solid phase microextraction in combination with capillary GC-MS was used as monitoring technique for the collection and detection of the fungal volatile metabolite (+)-aristolochene by sporulated surface cultures of Penicillium roqueforti. A comparison was made between different toxigenic and nontoxigenic strains of P. roqueforti. Different growth conditions and media, such as malt extract agar, potato dextrose agar and sabouraud dextrose agar were compared. Whereas toxigenic strains produced large amounts of (+)-aristolochene, beta-elemene, valencene and germacrene A, nontoxigenic P. roqueforti strains showed a remarkably different headspace profile, in which ethyl-2-hexenoate, E-beta-caryophyllene, aromadendrene and beta-patchoulene were the predominant volatiles, apart from other sesquiterpene hydrocarbons present at lower concentrations. Stir bar sorptive extraction, was also applied in the headspace sampling mode, i.e. headspace sorptive extraction (HSSE) for the enrichment of fungal volatiles from sporulated surface cultures to differentiate between toxigenic and nontoxigenic fungi. Hence, it can be concluded that headspace analysis of volatile fungal metabolites by SPME and HSSE in combination with capillary GC-MS is a suitable monitoring technique for the fast detection of mycotoxin producing fungi.

Gas Chromatography-Mass Spectrometry↗

PubMed2003

Flavour analysis of Greek white wine by solid-phase microextraction-capillary gas chromatography-mass spectrometry.

Solid-phase microextraction (SPME) was optimised for the qualitative determination of the volatile flavour compounds responsible for the aroma of Greek Boutari wine. Several factors influencing the equilibrium of the aroma compounds between the sample and the SPME fiber were taken into account, including the extraction time, the extraction temperature, the sampling mode (headspace and direct immersion or liquid SPME), and the presence of salt. Four different SPME fibers were used in this study. namely poly(dimethylsiloxane) (PDMS), poly(acrylate), carbowax-divinylbenzene and divinylbenzene-carboxen on poly(dimethylsiloxane). The best results were obtained using the PDMS fiber during headspace extraction at 25 degrees C for 30 min after saturating the samples with salt. The optimised SPME method was then applied to investigate the qualitative aroma composition of three other Greek wines, namely Zitsa, Limnos and Filoni.

Flavoring Agents↗

PubMed2003

Analysis of volatiles of malt whisky by solid-phase microextraction and stir bar sorptive extraction.

Blended Scotch whisky was analysed by solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE) to study the composition of the volatiles. For SPME analysis, three different fibres were compared, poly(dimethylsiloxane) (PDMS) (100 microm). poly(acrylate) (PA) (85 microm) and divinylbenzene-Carboxen on poly(dimethylsiloxane) (DVB-CAR-(PDMS) (50/30 microm). It was found that the PDMS and DVB-CAR-PDMS fibres showed a higher enrichment capacity than PA as well as a better reproducibility. The influence of sampling time, temperature and salt addition on the enrichment of volatiles as well as the difference between liquid and headspace SPME were studied. An optimum SPME method was developed. Finally a more recent sample preparation technique, namely SBSE was evaluated to extract whisky volatiles.

Alcoholic Beverages↗