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Results for “Solid Phase Microextraction”

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PubMed2002

Identification of dimethylchloroarsine near a former herbicide factory by headspace solid-phase microextraction gas chromatography-mass spectrometry.

The application of an improved method based on multidetector gas chromatography to the determination of trace levels of organoarsines in complex matrices is described. The method using headspace-mode solid-phase microextraction (SPME) was applied to a carefully sampled and preserved freshwater sediment core obtained from central Green Bay, Lake Michigan. The sediment core was collected and fractionated in an inert atmosphere. A carboxen/ polydimethylsiloxane-coated SPME fiber (85 microm film thickness) was equilibrated (n = 4) for 60 min at 25 degrees C in the headspace of the sample vessel before introduction to the chromatograph. Conventional quadrupole ion trap mass spectrometry (electron impact ionization), electron capture detection, and pulsed flame photometric detection (arsenic mode) were employed for structure elucidation. A heretofore unidentified species in this region, dimethylchloroarsine (DMCA). was identified. The mass spectrum for DMCA is interpreted based on the observed fragmentation pattern. A bimodal vertical distribution of DMCA in the sediment core sample was observed and its interpretation based on Pb-210 dating is reported.

Arsenicals↗

PubMed2003

Solid-phase microextraction liquid chromatography/tandem mass spectrometry to determine postharvest fungicides in fruits.

A method to determine five postharvest fungicides (dichloran, flutriafol, o-phenylphenol, prochloraz, tolclofos methyl) in fruits (cherries, lemons, oranges, peaches) has been developed using solid-phase microextraction (SPME) coupled to liquid chromatography (LC) with photodiode array (DAD), mass spectrometry (MS), or tandem mass spectrometry (MS/MS) with ion trap detection. Extraction involved sample homogenization with an acetone/water solution (5:1), filtration, and acetone evaporation prior to fiber extraction. The pesticides were isolated with a fused-silica fiber coated with 50-microm Carbowax/template resin. The effects of pH, ion strength, sample volume, and extraction time were investigated, and their impact on the SPME-LC/MS was studied. Dynamic and static modes of desorption were compared and the variables affecting desorption processes in SPME-LC optimized. Static desorption provided the best recoveries and peak shapes. Recoveries at the limit of quantification (LOQ) levels were between 10% for prochloraz and 60% for o-phenylphenol, with relative standard deviations from 13.6% for prochloraz to 3.1% for o-phenylphenol. The versatility of the method was also exhibited by its excellent linearity in the concentration intervals between 0.0005 and 5 mg kg(-1) for dichloran and 0.01-10 mg kg(-1) for tolclofos methyl and prochloraz. LOQs ranged from 0.25 to 1 microg g(-1) using DAD, from 0.002 to 0.01 microg g(-1) using LC/MS, and from 0.0005 to 0.01 to microg g(-1) using LC/MS/MS. LOQs obtained in the present study using LC/MS and LC/MS/MS are lower than maximum residue limits established for all the fungicides in any matrix studied. The method enables to determine polar pesticides at low-microgram per gram levels in fruits.

Calibration↗

PubMed2006

Comparison of solid-phase microextraction and stir bar sorptive extraction for the quantification of malodors in wastewater.

Malodors in wastewater from animal-rearing facilities are due to the presence of characteristic polar compounds. The efficiency and reproducibility of three solid-phase microextraction (SPME) fibers (Carboxen-PDMS, polyacrylate, and PDMS) as well as PDMS-coated stir bars for the measurement of some of these compounds in the liquid phase were compared. In initial experiments, the SPME fibers and stir bars were exposed to a standard water solution containing a mixture of 18 compounds with a range of octanol-water partition coefficients. The polyacrylate SPME fibers and PDMS-coated stir bars, having been found to possess the best combination of extraction efficiency and reproducibility of measurement, were compared for the extraction of a high-strength swine wastewater. Ten compounds, which are known contributors to malodors in wastewater, were quantified by both methods of extraction. For most compounds, greater levels were estimated by the PDMS-coated stir bars than by SPME, and measurement reproducibility was also greater. For both methods of extraction, there was greater variation in the measurement of volatile fatty acids than there was for aromatics.

Adsorption↗

PubMed1999

Comparison of solid-phase microextraction and dynamic headspace methods for the gas chromatographic-mass spectrometric analysis of light-induced lipid oxidation products in milk.

A sensitive, rapid procedure for testing lipid oxidation products in milk is developed using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry. SPME is as sensitive as dynamic headspace (DH) analysis for measuring the pentanal and hexanal produced in milk after exposure to light. Furthermore, compared with DH, SPME is less expensive and demonstrates better precision and accuracy. In addition, SPME does not exhibit carryover or septa artifact peaks. The linearity of calibration curves (based on the method of additions technique with an internal standard) is consistently better for SPME than for DH. Furthermore, replicate analyses of pentanal and hexanal spiked in skim milk and 2% milk at 2 ng/mL demonstrate significantly lower coefficients of variation using SPME. To further test the practicality of SPME for measuring light-induced chemical changes in milk, 2% milk and skim milk samples are exposed to fluorescent light (200 foot-candles) for 0, 3, 6, 9, 12, 17, 24, and 48 h and analyzed by SPME and DH. Pentanal and hexanal in all samples are measured by SPME and DH. Correlation coefficients of resulting plots indicate that SPME is more accurate than DH in measuring the quantity of lipid oxidation products in milk.

Aldehydes↗

PubMed2005

Molecular characterisation of birch bark tar by headspace solid-phase microextraction gas chromatography-mass spectrometry: a new way for identifying archaeological glues.

To develop an analytical methodology, as non-destructive as possible, suitable for the identification of natural substances from archaeological origin, we studied the potentiality of solid-phase microextraction (SPME) for analysing birch bark tar, an adhesive commonly used during ancient times. First of all, birch bark tars were produced by a controlled heating of birch bark. The two kinds of samples obtained using different processes of fabrication, one at liquid state, the second one at solid state, were then analysed by headspace HS-SPME-GC-MS. Different conditions of sample treatment were tested (two different fibre coatings, various times and temperatures of extraction) in order to suggest optimal conditions for the analysis of birch bark tar. Both samples were shown to be rich in volatile organic components. Two main groups of constituents, namely phenolic compounds issued from lignin or tannin known to be present in bark and sesquiterpenoid hydrocarbons, secondary metabolites largely distributed in the plant kingdom, were detected for the first time in birch bark tar. HS-SPME-GC-MS appears thus to be a very efficient method for investigating the volatiles emitted by plant tars and could be further used for the study of birch bark tar samples issued from archaeological context.

Adhesives↗

PubMed2004

Solid-phase microextraction with on-fiber derivatization for the analysis of anti-inflammatory drugs in water samples.

A sensitive and solvent-free procedure for the determination of non-steroidal acidic anti-inflammatory drugs in water samples was optimized using solid-phase microextraction (SPME) followed by on-fiber silylation of the acidic compounds and gas chromatography-mass spectrometry (GC-MS) determination. Microextraction was carried out directly over the filtered water samples using a polyacrylate fiber. Derivatization was performed placing the SPME fiber, loaded with the extracted analytes, in the headspace of a vial containing 50 microl of N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA). Derivatives were desorbed for 3 min in the GC injector. Influence of several parameters in the efficiency of microextraction (volume of sample, time, pH, type of fiber coating, etc.) and derivatization steps (time, temperature and volume of MTBSTFA) was systematically investigated. In the optimal conditions an excellent linearity over three orders of magnitude and quantification limits at the ng/l level (from 12 to 40 ng/l) were achieved. The proposed method was applied to the determination of acidic compounds in sewage water and results compared to those obtained using solid-phase extraction (SPE) followed by the derivatization of the compounds in the organic extract of the solid-phase extraction cartridge.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2005

Biocompatible in-tube solid-phase microextraction coupled to HPLC for the determination of angiotensin II receptor antagonists in human plasma and urine.

A poly (methacrylic acid-ethylene glycol dimethacrylate, MAA-EGDMA) monolithic capillary was used for the in-tube solid-phase microextraction (in-tube SPME) of several angiotensin II receptor antagonists (ARA-IIs) from human plasma and urine. Under the optimized extraction condition, the protein component of the biological sample was flushed through the monolithic capillary, while the analytes were successfully trapped. Coupled to HPLC with fluorescence detection, this on-line in-tube SPME method was successfully applied for the determination of candesartan, losartan, irbesartan, valsartan, telmisartan, and their detection limits were found to be 0.1-15.3ng/mL and 0.1-15.2ng/mL in human plasma and urine, respectively. The method was linear over the range of 0.5-200ng/mL for telmisartan, 5-2000ng/mL for candesartan and irbesartan, 10-2000ng/mL for valsartan, and 50-5000ng/mL for losartan with correlation coefficients being above 0.9985 in plasma sample and above 0.9994 in urine sample. The method reproducibility was evaluated at three concentration levels, resulting in the R.S.D. <7%. The poly (MAA-EGDMA) monolithic capillary was demonstrated to be robust and biocompatible by using direct injections of biological samples.

Angiotensin Receptor Antagonists↗

PubMed2000

Solid-phase microextraction with on-fibre derivatisation applied to the analysis of volatile carbonyl compounds.

We have used a fast, sensitive and efficient method for the analysis of volatile carbonyl compounds (saturated aliphatic and unsaturated aldehydes) based on solid-phase microextraction with on-fibre derivatisation. Pentafluorophenylhydrazine was absorbed onto a poly(dimethylsiloxane)/divinylbenzene-coated fibre and exposed to the vapours of aldehyde-containing matrices. The hydrazones formed on the fibre were desorbed into the gas chromatograph injection port and quantified by means of electron-capture detection with high sensitivity (10-90 fmol) and good reproducibility (RSD<10%). The method was applied to the headspace-sampling of volatile carbonyl compounds released during the thermally-induced degradation of sunflower oil.

Aldehydes↗

PubMed2002

Bio-compatible in-tube solid-phase microextraction capillary for the direct extraction and high-performance liquid chromatographic determination of drugs in human serum.

A restricted access material (RAM), alkyl-diol-silica (ADS), was used to prepare a highly bio-compatible solid-phase microextraction (SPME) capillary for the automated and direct in-tube extraction of several benzodiazepines from human serum. The bifunctionality of the ADS extraction phase prevented fouling of the capillary by protein adsorption while simultaneously trapping the analytes in the hydrophobic porous interior. This the first report of a restricted access material utilized as an extraction phase for in-tube SPME. The approach simplified the required apparatus in comparison to existing RAM column switching procedures, and more importantly eliminated the excessive use of extraction solvents. The biocompatibility of the ADS material also overcame the existing problems with in-tube SPME that requires an ultrafiltration or other deproteinization step prior to handling biological samples, therefore further minimizing the sample preparation requirements. The calculated oxazepam, temazepam, nordazepam and diazepam detection limits were 26, 29, 22 and 24 ng/ml in serum, respectively. The method was linear over the range of 50-50 000 ng/ml with an average linear coefficient (R2) value of 0.9998. The injection repeatability and intra-assay precision of the method were evaluated with five injections of a 10-microg/ml serum sample (spiked with all compounds), resulting in an average RSD<7%. The ADS extraction column was robust, providing many direct injections of biological fluids for the extraction and subsequent determination of benzodiazepines.

Benzodiazepines↗

PubMed2001

Limitations to the use of solid-phase microextraction for quantitation of mixtures of volatile organic sulfur compounds.

A study of the range of volatile organic sulfur compounds produced by brassica plants has highlighted limitations to the use of Carboxen/PDMS fibers for their analysis by solid-phase microextraction (SPME). These fibers are sometimes advocated for the analysis of sulfur gases, but a quantitative comparison of analytical data derived by SPME and by direct gas sampling of standard mixtures of volatile low molecular weight sulfur compounds at 0.01-10 mg/L has identified potential errors associated with their use. Higher molecular compounds displace lower molecular weight compounds as a consequence of competition for active sites on the fiber, and the relative proportions of the components adsorbed onto the fiber depend on their ratio in the headspace. As their relative concentrations change from sample to sample, the varying interactions result in irregular analytical responses, reflected in erratic calibration curves. Standards containing single components are not valid; only a standard containing all components found in the sample to be analyzed, and at the same relative concentrations, is appropriate. In practice, this may preclude the use of the fibers for quantitative analysis of multicomponent mixtures.

Journal Article↗

PubMedDate not supplied

Simple and rapid determination of amphetamine, methamphetamine, and their methylenedioxy derivatives in urine by automated in-tube solid-phase microextraction coupled with liquid chromatography-electrospray ionization mass spectrometry.

A simple and rapid method for the determination of amphetamine, methamphetamine, and their 3,4-methylenedioxy derivatives in urine samples was developed using automated in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS). In-tube SPME is an extraction technique for organic compounds in aqueous samples in which analytes are extracted from the sample directly into an open tubular capillary by repeated draw/eject cycles of sample solution. LC-MS analyses of stimulants were initially performed by liquid injection onto an LC column to determine spectra. Five stimulants tested in this study gave very simple ESI mass spectra, and strong signals corresponding to [M+H]+ were observed for all stimulants. The stimulants were well separated with a Supelcosil LC-CN column using acetonitrile/50mM ammonium acetate (15:85) as a mobile phase. In order to optimize the extraction of stimulants, several in-tube SPME parameters were examined. The optimum extraction conditions were 15 draw/eject cycles of 35 microL of sample in 50mM Tris-HCI (pH 8.5) at a flow rate of 100 microL/min using an Omegawax 250 capillary column. The stimulants extracted by the capillary were easily desorbed by mobile phase flow, and carryover of stimulants was not observed. Using in-tube SPME-LC-ESI-MS with selected ion monitoring, the calibration curves of stimulants were linear in the range from 2 to 100 ng/mL with correlation coefficients above 0.9985 (n = 18) and detection limits (S/N = 3) of 0.38-0.82 ng/mL. This method was successfully applied to the analysis of human urine samples without interference peaks. The recoveries of stimulants spiked into urine samples were above 81%.

Amphetamines↗

PubMed2005

Quantitative determination of thermally derived off-flavor compounds in milk using solid-phase microextraction and gas chromatography.

Many volatile compounds generated during the thermal processing of milk have been associated with cooked, stale, and sulfurous notes in milk and are considered as off-flavor by most consumers. A headspace solid-phase microextraction (HS-SPME)/gas chromatographic technique for the quantitative analysis of thermally derived off-flavor compounds was developed in this study. The extraction temperature, time, and sample amount were optimized using a randomized 2(3) central composite rotatable design with 2 central replicates and 2 replicates in each factorial point along with response surface methodology. Calibration curves were constructed in milk using the standard addition technique, and then used to quantify 20 off-flavor compounds in raw, pasteurized, and UHT milk samples with various fat contents. The concentrations of these volatiles in raw and pasteurized milk samples were not significantly different. However, dimethyl sulfide, 2-hexanone, 2-heptanone, 2-nonanone, 2-undecanone, 2-methylpropanal, 3-methylbutanal, heptanal, and decanal were found at higher concentrations in UHT milk as compared with raw and pasteurized milk samples. In addition, the concentration of methyl ketones was greater in UHT milk with higher fat content. The calculated odor activity values suggested that 2,3-butanedione, 2-heptanone, 2-nonanone, 2-methylpropanal, 3-methylbutanal, nonanal, decanal, and dimethyl sulfide could be important contributors to the off-flavor of UHT milk. The HS-SPME technique developed in this study is accurate and relatively simple, and can be used for the quantification of thermally derived off-flavor compounds in milk.

Animals↗

PubMed2004

Solid phase microextraction as a tool to predict internal concentrations of soil contaminants in terrestrial organisms after exposure to a laboratory standard soil.

Uptake and accumulation of three chlorobenzenes was studied in both biota (Enchytraeus crypticus) and 30 mum polydimethylsiloxane (PDMS) solid phase microextraction (SPME) fibers after exposure to spiked OECD soil. The OECD soil was spiked with three different concentrations of all contaminants. Uptake of all three chlorobenzenes in E. crypticus was fast and steady state levels were reached within 2-4 days. Also in the PDMS-SPME fibers uptake was very fast for all three compounds, with steady state levels reached after 1 day. Comparison of steady state levels in biota and in the PDMS-SPME fibers showed a relationship which was consistent over the range of concentrations of chlorobenzenes in soil and the difference in logKow. This shows that measuring the concentrations of hydrophobic chemicals in a hydrophobic phase such as PDMS can be used as a simple tool to estimate internal concentrations of these chemicals in biota exposed to complex matrices such as soil.

Animals↗

PubMed2002

Optimization of headspace solid-phase microextraction by means of an experimental design for the determination of methyl tert.-butyl ether in water by gas chromatography-flame ionization detection.

A procedure for determination of methyl tert.-butyl ether (MTBE) in water by headspace solid-phase microextraction (HS-SPME) has been developed. The analysis was carried out by gas chromatography with flame ionization detection. The extraction procedure, using a 65-microm poly(dimethylsiloxane)-divinylbenzene SPME fiber, was optimized following experimental design. A fractional factorial design for screening and a central composite design for optimizing the significant variables were applied. Extraction temperature and sodium chloride concentration were significant variables, and 20 degrees C and 300 g/l were, respectively chosen for the best extraction response. With these conditions, an extraction time of 5 min was sufficient to extract MTBE. The calibration linear range for MTBE was 5-500 microg/l and the detection limit 0.45 microg/l. The relative standard deviation, for seven replicates of 250 microg/l MTBE in water, was 6.3%.

Calibration↗

PubMed2000

Kinetics of solid-phase extraction and solid-phase microextraction in thin adsorbent layer with saturation sorption isotherm.

The effects of sorbent saturation in thin adsorbent layers have been much overlooked in earlier research and should be taken into account in both the theory and practice of solid-phase extraction (SPE) and solid-phase microextraction (SPME). The adsorption kinetics of a single analyte into a thin adsorptive layer was modeled for several cases of agitation conditions in the analyzed volume. The extraction process in the adsorbent layer was modeled using a Langmuir isotherm approximated by the linear isotherm at low concentrations and by a saturation plateau at concentrations exceeding the critical saturation concentration. Laplace transformations were used to estimate the equilibration time and adsorbed analyte concentration profile for no agitation, practical and perfect agitation in the analyzed volume. The equilibration time may be significantly reduced at high degrees of oversaturation and/or agitation in the analyzed volume. The resulting models indicated that the adsorbent layer becomes saturated at some critical value of the oversaturation degree parameter. The critical value of the oversaturation parameter is affected by both the concentration of the analyte in the analyzed volume and the sorbent characteristics. It was also shown that the adsorption process is carried out via the propagation of the saturation adsorption boundary toward the inner boundary of the adsorbent layer. These new adsorption models should serve as "stepping stones" for the development of competitive adsorption kinetic models for both SPE and SPME, particularly in cases where fast sampling is used.

Chromatography, Liquid↗

PubMed2001

New method of derivatization and headspace solid-phase microextraction for gas chromatographic-mass spectrometric analysis of amphetamines in hair.

A simple method for hair analysis of methamphetamine (MAMP) and amphetamine (AMP) by gas chromatography-mass spectrometry (GC-MS) was developed using simultaneous headspace solid-phase microextraction (HS-SPME) with derivatization. After alkaline-digestion of hair, the analytes derivatized with heptafluoro-n-butyryl chloride were adsorbed on a polydimethylsiloxane-coated fiber by HS-SPME and analyzed by GC-MS. Their mass spectra were, respectively, observable at 1 ng per sample. The standard curves in the range of 0.1-100 ng were linear. The intra-day coefficients of variation at each 0.5 ng were 12.5% for AMP and 3.8% for MAMP. The applicability of this method was demonstrated in some case studies.

Amphetamines↗

PubMed2001

Solid-phase microextraction and gas chromatography-mass spectrometry analysis of p,p' -DDE in biological samples.

A simple and rapid extraction method for the analysis of p,p'-DDE from rat whole blood and tissues was developed using headspace solid-phase microextraction (SPME). A vial containing a sample of p,p'-DDE, sodium hydroxide, and benzophenone as internal standard was heated at 120 degrees C. A polydimethylsiloxane-coated SPME fiber was exposed for 15 min in the headspace of the vial. The fiber needle was then injected and desorbed by exposing the fiber in the injection port of a capillary gas chromatography-mass spectrometry system. The calibration curve demonstrated good linearity throughout the concentration range from 0.02 to 50 microg/g for rat whole blood and liver samples. The limit of detection for p,p'-DDE was 0.020 microg/g using 0.5 g rat whole blood and liver samples. Coefficients of variation ranged from 7.0 to 7.9%. This method was used to analyze a rat whole blood sample after administration of p,p'-DDE.

Animals↗

PubMed2002

Headspace solid-phase microextraction--comprehensive two-dimensional gas chromatography of wound induced plant volatile organic compound emissions.

Plant emissions of volatile organic compounds from mechanically wounded Agrostis stolonifera, Pennisetum clandestinum, Eucalyptus leucoxylon and Trifolium repens have been sampled by headspace-solid phase microextraction (HS-SPME) and analysed by using comprehensive two-dimensional gas chromatography (GCxGC) for measurement of the plant emissions. GCxGC produces a fingerprint of the volatile organic compounds in a 2D separation space that may be approximately interpreted as a boiling point-polarity space, and may then be presented as a two-dimensional contour plot. This allows identification of sample-dependent variations in component distributions in the 2D plot, which will contain information about plant differences and should therefore facilitate recognition of different plant materials and displays the gross differences in volatiles between each plant species.

Agrostis↗