Biomedical subjects

Pat Sandra

Publications and source records attributed to Pat Sandra.

44 records · Page 3Linked to original sources

PubMed2003

SBSE-GC-ECD/FPD in the analysis of pesticide residues in Passiflora alata Dryander herbal teas.

Stir bar sorptive extraction (SBSE) in combination with GC-ECD/FPD analysis is here applied to the determination of the residues of 11 pesticides (hexachlorobenzene, lindane, chlorothalonil, parathion methyl, parathion ethyl, fenitrothion, malathion, dieldrin, alpha- and beta-endosulfan, and tetradifon) in herbal teas prepared with Passiflora alata Dryander spiked leaves. The method was optimized using spiked herbal teas in a range from 0.05 to 1 pg/microL for organochlorine pesticides and from 0.15 to 3 pg/microL for organophosphorus pesticides. The method is reproducible and repeatable with recoveries calculated from herbal teas prepared with spiked plant material versus spiked herbal teas, varying from about 30% for tetradifon to about 90% for parathion methyl and malathion. The limits of quantitation (LOQs) ranged from 0.017 pg/microL for lindane to 0.117 pg/microL for malathion.

Beverages↗

PubMed2003

Photolysis of hop-derived trans-iso-alpha-acids and trans-tetrahydroiso-alpha-acids: product identification in relation to the lightstruck flavour of beer.

The photolysis of hop-derived trans-iso-alpha-acids (2a-c; naturally occurring bitter compounds present in beer) and of trans-tetrahydroiso-alpha-acids (5a-c; semi-synthetic advanced hop products) was investigated at 300 nm in methanol. The complex photoreaction mixtures were separated by high-performance liquid chromatography (HPLC) using diode array detection and the major photoreaction products were identified by HPLC-mass spectroscopy. The main part of the mixture consisted of compounds, which originated from recombination of radicals derived from Norrish Type I photocleavage of the acyloin moiety in both trans-iso-alpha-acids and trans-tetrahydroiso-alpha-acids. The results confirm the intermediacy of radicals that were previously identified by time-resolved electron paramagnetic resonance and they bear relevance to the formation of the lightstruck flavour that is generated when beer is exposed to light. Additionally, new photoproducts were found that are formed by photochemical reactions hitherto undiscovered in hop chemistry, including photoenolization of trans-isohumulone (2a) leading to trans-alloisohumulone (13a) and a retro oxa-di-pi-methane rearrangement in trans-isohumulone (2a) and trans-tetrahydroiso-alpha-acids to humulone (1a) and tetrahydro-alpha-acids (23a-b), respectively.

Journal Article↗

PubMed2002

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.

Benzodiazepines↗

PubMed2002

Headspace sorptive extraction (HSSE), stir bar sorptive extraction (SBSE), and solid phase microextraction (SPME) applied to the analysis of roasted Arabica coffee and coffee brew.

Headspace sorptive extraction (HSSE) and stir bar sorptive extraction (SBSE), two recently introduced solventless enrichment techniques, have been applied to the analysis of the headspace of Arabica roasted coffee and of the headspace of the brew and of the brew itself. In both HSSE and SBSE enrichment is performed on a thick film of poly(dimethylsiloxane) (PDMS) coated onto a magnet incorporated in a glass jacket. Sampling is done by placing the PDMS stir bar in the headspace (gas phase extraction or HSSE) or by immersing it in the liquid (liquid phase extraction or SBSE). The stir bar is then thermally desorbed on-line with capillary GC-MS. The performance of HSSE and SBSE have been compared through the determination of the recoveries and relative abundances of 16 components of the coffee volatile fraction to classical static headspace (S-HS) and to headspace and in-sample solid phase microextraction (HS-SPME and IS-SPME, respectively) applying the fibers PDMS 100 microm, Carbowax/divinylbenzene 65 microm (CW/DVB), Carboxen/PDMS 75 microm(CAR/PDMS), polyacrylate 85 microm(PA), PDMS/divinylbenzene 65 microm(PDMS/DVB), and Carboxen/divinylbenzene/PDMS 50-30 microm(CAR/PDMS/DVB). In all cases, HSSE and SBSE gave higher recoveries, and this is entirely due to the high amount of PDMS applied.

Chromatography, Gas↗

PubMed2002

Capillary gas chromatography inductively coupled plasma mass spectrometry (CGC-ICPMS) for the enantiomeric analysis of D,L-selenomethionine in food supplements and urine.

Capillary gas chromatography inductively coupled plasma mass spectrometry (CGC-ICPMS) was applied to the determination of D- and L-selenomethionine in food supplements and in urine. Derivatization was performed with ethylchloroformate (ECF) offering the advantage that the reaction can be carried out in aqueous medium i.e. urine. The derivatives were separated on the chiral stationary phase (CSP) Chiralsil-L-Val. The method was validated with D- and L-seleno-ethionine as internal standard (IS) and the linearity for a seven point calibration from 12.5 pg to 2.5 ng per enantiomer was excellent (R(2) 0.9997). Repeatability of injection (n=3) was <1.8%. The limit of detection (LOD) and quantification (LOQ) were 4 and 12 pg, respectively. Food supplements presently on the market contain L-selenomethionine for at least 90%. Repeatability of the whole procedure (n=6) was tested on one L-selenomethionine formulation and was 3.8 (R.S.D.%). Data for urine samples after a daily intake of L-selenomethionine or the racemate D,L-selenomethionine corresponding to 100 microg selenium indicate that the D-enantiomer is not metabolized.

Dietary Supplements↗

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↗

PubMedDate not supplied

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↗