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PubMed2001

Comparison between solid-phase extraction methods for the chromatographic determination of organophosphorus pesticides in water.

A solid-phase microextraction (SPME) procedure has been developed to extract eight organophosphorus pesticides (OPs) in water and the method was compared with a conventional solid phase extraction (SPE) technique. The extracted OPs were analyzed by gas chromatography using thermionic specific detection. Both extraction methods presented linear calibration at least over the concentration range investigated (100 to 1000 ng x mL(-1) for SPE and 1 to 100 ng x mL(-1) for SPME). SPME method presented higher sensitivity than SPE. The quantitation limits were between 0.1 to 1.0 ng x mL(-1) for SPME depending upon the analyte, and 100 ng x mL(-1) for SPE. The precision, as measured by the standard deviations (RSD), were in the range 3.6% to 5.8% for SPME and 2.4% to 9.2% for SPE. Along with the feature of being a solvent - free sampling technique, SPME offers additional benefits due to its high sensitivity, simplicity, and small size sample required (typically: SPE - 500 mL, SPME - 5 mL).

Calibration↗

PubMed2006

Evaluating the impacts of some environmentally relevant factors on the availability of bisphenol A with negligible-depletion SPME.

The effect of some environmentally relevant factors including salinity, pH, and humic acids on the availability of bisphenol A (BPA) was evaluated by using the negligible-depletion solid-phase microextraction (nd-SPME) biomimetic method. With the variation of salinity (0-500 mM NaCl) and pH (5.0-8.5) of aqueous solutions, the partition coefficients of BPA between the nd-SPME fiber and the aqueous solution varied in the range of logD=3.55-3.86, which indicates that the salinity and pH can influence the availability of BPA. By using Acros humic acid as model dissolved organic matter (DOM), it was also demonstrated that the environmental factors such as salinity and pH could affect the partitioning of BPA between DOM and aqueous solutions. The determined partition coefficients of BPA between dissolved organic carbon (DOC) and aqueous solutions were in the range of logD(DOC)=4.03-5.60 for Acros humic acid solutions with 1-50 mg l(-1) DOC. The influence of salinity and pH on logD(DOC) was more significant at low concentration (0-5 mg l(-1)) of DOC.

Benzhydryl Compounds↗

PubMed2002

Direct determination of benzodiazepines in biological fluids by restricted-access solid-phase microextraction.

A biocompatible solid-phase microextraction (SPME) fiber was prepared using an alkyl-diol-silica (ADS) restricted-access material as the SPME coating. The ADS-SPME fiber was able to simultaneously fractionate the protein component from a biological sample, while directly extracting several benzodiazepines, overcoming the present disadvantages of direct sampling in biological matrixes by SPME. The fiber was interfaced with an HPLC-UV system, and an isocratic mobile phase was used to desorb, separate, and quantify the extracted compounds. The calculated clonazepam, oxazepam, temazepam, nordazepam, and diazepam detection limits were 600, 750, 333, 100, and 46 ng/mL in urine, respectively. The method was confirmed to be linear over the range of 500-50000 ng/mL with an average linear coefficient (R2) value of 0.9918. The injection repeatability and intraassay precision of the method were evaluated over 10 injections, resulting in a RSD of approximately 6%. The ADS-SPME fiber was robust and simple to use, providing many direct extractions and subsequent determination of benzodiazepines in biological fluids.

Anti-Anxiety Agents↗

PubMed2004

Application of solid-phase microextraction for determining phenylurea herbicides and their homologous anilines from vegetables.

Residues of metobromuron, monolinuron and linuron herbicides and their aniline homologous were analyzed in carrots, onions and potatoes by solid-phase microextraction (SPME) performed with a polyacrylate fiber. A juice was obtained from food samples that were further diluted, and an aliquot was extracted after sodium chloride (14%) addition and pH control. At pH 4 only the phenylureas were extracted. A new extraction at pH 11 allowed the extraction of phenylureas plus homologous aniline metabolites. Determination was carried out by gas chromatography with nitrogen-phosporus detection (NPD) the identity of the determined compounds was studied by gas chromatography-mass spectrometry. Limits of quantification (LOQs) obtained with NPD and MS (selected-ion monitoring) were in the microg/kg order allowing determination of maximum residue levels (MRLs) established in the Spanish regulations. MRLs ranged from 0.02 to 0.1 mg/kg depending on the kind of food and herbicide. Under the proposed conditions matrix effects were low enough to permit calibration with samples proceeding from ecological (non-pesticide treated) crops. Twelve commercial samples of each carrots, onions and potatoes were analyzed and only three samples of potatoes contained residues of linuron at levels below MRLs.

Aniline Compounds↗

PubMed2004

Solid-phase microextraction field sampler.

To facilitate the use of solid-phase microextraction (SPME) for field sampling, a new field sampler was designed and tested. The sampler was versatile and user-friendly. The SPME fiber can be positioned precisely inside the needle for time-weighted average sampling or exposed completely outside the needle for grab sampling. The needle is protected within a shield at all times, hereby eliminating the risk of operator injury and fiber damage. A replaceable Teflon cap is used to seal the needle to preserve sample integrity. Factors that affect the preservation of sample integrity (sorbent efficiency, temperature, sealing materials) were studied. The use of a highly efficient sorbent for the fiber is recommended as the first choice for the preservation of sample integrity. Teflon was a good material for sealing the fiber needle, had little memory effect, and could be used repeatedly. To address adsorption of high boiling point compounds on fiber needles, several kinds of deactivated needles were evaluated. RSC-2 fiber needles were the more effective. A preliminary field sampling investigation demonstrated the validity of the new SPME device for field applications.

Adsorption↗

PubMed2006

Simple approach for the determination of brominated flame retardants in environmental solid samples based on solvent extraction and solid-phase microextraction followed by gas chromatography-tandem mass spectrometry.

A viable approach for the analysis of polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) in sewage sludge samples is presented in this paper. The proposed method combines ultrasound-assisted extraction (UAE) of the solid sample and headspace solid-phase microextraction (HS-SPME) of the obtained extract, followed by gas chromatography coupled to tandem mass spectrometry (GC-MS-MS) analysis. Different parameters affecting the extraction process are evaluated and optimized. The addition of a small amount of Florisil to the sample during UAE provides a significant improvement of the chromatographic background and, at the same time, a much more efficient HS-SPME. Extensive method validation is performed using real sewage sludge samples. The proposed method exhibits good performance in terms of linearity and precision, with recoveries exceeding 92% and limits of detection in the sub ng g(-1) level. Practical applicability is demonstrated through the analysis of real contaminated sewage sludge and sediment samples in which some of the target PBDEs are detected and quantified. This proposed combined methodology represents a large time-saving when compared to other classic multi-step solvent extraction methods and it constitutes a suitable approach for the analysis of the target compounds in environmental complex solid samples.

Bromine↗

PubMed1998

Determination of cannabinoids in water and human saliva by solid-phase microextraction and quadrupole ion trap gas chromatography/mass spectrometry.

Solid-phase microextraction (SPME) is applied to the determination of cannabidiol, delta 8-tetrahydrocannabinol (delta 8-THC), delta 9-tetrahydrocannabinol (delta 9-THC), and cannabinol in pure water and human saliva. The inherent extraction behavior of the cannabinoids in pure water is evaluated along with optimization of the method in human saliva. The commercially available poly(dimethylsiloxane) (PDMS) SPME fibers were found to be the best class for the cannabinoid analysis. Partition coefficients were found to be extremely large for all of the cannabinoids (log K > 4.0). Equilibrium times for the 7- and 30-micron PDMS fibers were 50 and 240 min, respectively. A shorter extraction time of 10 min with the 30-micron PDMS fiber may be used for multiple extractions from the same vial, thus conserving the sample necessary for analysis and speeding up the total analysis time. Recoveries for the cannabinoids in saliva, relative to pure water, were dramatically improved by a method developed in our laboratory involving addition of glacial acetic acid to the sample vial prior to performing SPME. Using this method, recoveries relative to SPME in pure water ranged from 21 to 47% depending on the cannabinoid. The linear range for spiked saliva samples was established at 5-500 ng/mL (r2 > 0.994) with precisions between 11 and 20% RSD. The ultimate level of detection by SPME for the cannabinoids in saliva was 1.0 ng/mL, with signal-to-noise values of > or = 12. A saliva sample collected 30 min after marijuana smoking was subject to SPME and traditional liquid-liquid extraction analysis. Internal standard quantitation results for delta 9-THC by both methods yielded comparable results, indicating that the SPME method of analysis is highly accurate and precise. The level of delta 9-THC by SPME was found to be 9.54 ng/mL for the saliva sample.

Cannabinoids↗

PubMed2004

MTBE oxidation byproducts from the treatment of surface waters by ozonation and UV-ozonation.

In recent years, there has been considerable concern over the release of methyl tert-butyl ether (MTBE), a gasoline additive, into the aquifers used as potable water sources. MTBE readily dissolves in water and has entered the environment via gasoline spills and leaking storage tanks. In this paper, we investigate ozonation and UV-ozonation for treatment of MTBE in contaminated drinking water sources. We report the test protocol and results of using solid-phase microextraction (SPME) to determine the level of MTBE and its oxidation byproducts in samples drawn from laboratory-scale ozone and UV-ozone reactors being evaluated at a US EPA research facility. Analysis of a prepared MTBE standard indicated a detection limit on the order of 0.1 microgl(-1) with a repeatability of +/-0.4%. Results show that the overall rate of removal of MTBE via UV-ozonation in a relatively turbid surface water (15 ntu) is twice that of ozonation alone. In addition, GC-MS analysis of decomposition products showed that tert-butyl formate (TBF), methyl acetate, butene, acetone, and acetaldehyde were produced by both processes. TBF and butene reach similar maximum yields from the two processes, but are more efficiently degraded by UV-ozonation treatment. This indicates that these treatment processes also degrade these byproducts. In contrast, the remaining byproducts (methyl acetate, acetone, and acetaldehyde) are formed at similar levels during treatment, but are not degraded once formed. These byproducts may be resistant to hydrogen abstraction by hydroxyl radical.

Chromatography, High Pressure Liquid↗

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↗

PubMed2006

Multivariate optimization of the factors influencing the solid-phase microextraction of pyrethroid pesticides in water.

A method based on solid-phase microextraction (SPME) and gas chromatography with micro-electron capture detection (GC-microECD) has been optimized for the analysis of pyrethroids in water samples. The influence of parameters such as temperature, fibre coating, salting-out effect and sampling mode on the extraction efficiency has been studied by means of a mix-level factorial design, which allowed the study of main effects as well as two factor interactions. Finally, a method based on direct SPME at 50 degrees C, using polydimethylsiloxane fibre is proposed. The method showed good linearity (R2>0.995) and repeatability (RSD<or=16%) for all compounds, with detection limits ranging from 0.05 pg/mL for transfluthrin to 2.18 pg/mL for permethrin, and in general <or=1 pg/mL for most pyrethroids. Reliability was demonstrated through the evaluation of the recoveries in different water samples, such as tap water, groundwater, river water, runoff water, and wastewater. These studies demonstrated the validity of external standard calibration to quantify the target compounds in real samples, including a simple dilution step for the most complex matrices, which notoriously simplifies quantification by SPME.

Chromatography, Gas↗

PubMed2002

High-speed gas chromatographic analysis of solvents in pharmaceuticals using solid phase microextraction.

A simple, inexpensive and rapid analytical approach for the determination of organic volatile impurities in pharmaceutical drug substances is developed, where sample preparation step was conducted using solid phase microextraction (SPME), followed by a fast GC separation. With an extraction time between 3 and 5 min and separation of 13 solvents in less than 3 min employing fast temperature programming using resistively heated column, organic volatile impurities can be analyzed within a total analysis time of 6-9 min. Various SPME phases were evaluated towards sensitivity and selectivity for the extraction of 13 commonly found solvents in drug substances dissolved in dimethyl sulfoxide and water. A 2-cm Carboxen/polydimethyl siloxane/divinylbenzene (Carboxen/PDMS/DVB) phase and a 65-microm DVB/PDMS phase showed better sensitivity towards these solvents when extracted from organic and aqueous matrix in comparison with the sensitivity obtained with direct injection approach. Extraction parameters such as extraction time, extraction stir rate, etc. are discussed. %RSD of peak area of replicate extraction was between 2 and 10% when 100 microm PDMS was used for extracting solvents from aqueous matrix. When DVB/PDMS fiber was evaluated for precision, %RSD of peak area from replicate extractions of solvents from organic matrix was between 2 and 8%. One-hundred micrometer PDMS showed excellent linearity from 10 to 500 microg/ml for analytes extracted from water solutions. On the other hand, DVB/PDMS phase showed better linearity than Carboxen/PDMS/DVB fiber when it was used to extract analytes in the concentration range of 10-5000 microg/ml from organic matrix.

Acetates↗

PubMed2006

Determination of drug plasma protein binding by solid phase microextraction.

The plasma protein binding of drugs has been shown to have significant effects on the quantitative relationship between clinical pharmacokinetics and pharmacodynamics. In many clinical situations, measurement of the total drug concentration does not provide the needed information concerning the unbound fraction of drug in plasma, which is available for pharmacodynamic action. Therefore, the accurate determination of unbound plasma drug concentrations is important in understanding drug action. Many methodologies exist for determining the extent of plasma protein binding, but different methods produce a rather wide range of results for the same compound at the same concentration level. The solid phase microextraction (SPME) method reported in the present study attempts to eliminate many experimental variables that could lead to the lack of reproducibility, such as the variable content of organic solvent or ionic strength in plasma, pH shifts, and volume shifts. Five well-known drugs were chosen to study plasma protein binding: ibuprofen, warfarin, verapamil, propranolol, and caffeine, with high, intermediate and low binding properties. Dilution of plasma with isotonic PBS or incubation with 10% CO(2) in the atmosphere was found to compensate for changes in pH during incubation. The data obtained using these pH-controlled methods correlate well with the average values of plasma protein binding found in the literature. SPME, which uses an extraction phase that dissolves or adsorbs the drug of interest and rejects proteins, overcomes several limitations of currently available techniques and is a thermodynamically sound method, since the measurements are always performed at equilibrium. Compared to other methods, SPME offers several advantages: small sample size, short analysis time, possibility to automate, and ability to directly study complex samples.

Blood Proteins↗

PubMed2000

Analysis of volatile contaminants in vegetable oils by headspace solid-phase microextraction with carboxen-based fibres.

The headspace solid-phase microextraction (HS-SPME) efficiencies from vegetable oil of the recently available Carboxen-poly(dimethylsiloxane) (PDMS) and divinylbenzene-Carboxen-PDMS fibres were found to be much greater than those of the PDMS fibre for a number of volatile contaminants. Using these Carboxen-based fibres, the commonly used HS-SPME equilibration times for aqueous matrices of 30-45 min at room temperature for a number of halogenated and aromatic analytes with volatilities ranging from 1,1-dichloroethylene to hexachlorobenzene were found to be insufficient for the effective extraction of the less volatile analytes from vegetable oil. HS-SPME at 100 degrees C for 45 min, followed by rapid cooling to 0 degrees C with a 10 min continuing extraction, however, significantly increased the SPME efficiencies for the less volatile analytes. Spiking solutions were prepared in vegetable oil instead of methanol as the latter was found to displace analytes from the Carboxen material. Using either of the Carboxen-based fibres and SPME at 100 degrees C, all the target analytes could be determined at low or sub-microg kg(-1) with repeatability < or =10%, even though an equilibrium SPME of the less volatile analytes was not achieved.

Chromatography, Liquid↗

PubMed2001

SPME-MS-MVA as a rapid technique for assessing oxidation off-flavors in foods.

A new technique using solid-phase microextraction, mass spectrometry, and multivariate analysis (SPME-MS-MVA) was developed for the study of oxidized off-flavors in foods. The analytical column of a GC-MS system was replaced with a 1-m deactivated fused-silica column, which served as a transfer line to deliver volatiles extracted from samples with a Carboxen/PDMS SPME fiber to the mass spectrometer. Mass fragmentation data resulting from the unresolved food volatile components were subjected to MVA. The mass intensities from m/z 50 to m/z 150 were selected to perform MVA. Principal component analysis based on SPME-MS-MVA provided rapid differentiation of the following types of samples: control soybean oil from soybean oil exposed to fluorescent light for various time periods; control nondairy coffee creamer from complaint ("oxidized") nondairy coffee creamer samples; fresh boiled beef from boiled beef with various levels of warmed-over flavor (WOF); and control 2% milk samples from 2% milk samples abused by light or copper exposure. SPME-MS-MVA is rapid and offers significant advantages over commercial electronic nose instruments currently being used as quality assurance tools to differentiate normal tasting food and beverage samples and ingredients from those containing off-flavors and malodors.

Animals↗

PubMed2002

Estimation of the main dill seeds odorant carvone by solid-phase microextraction and gas chromatography.

Solid-phase microextraction (SPME) was examined for its suitability for isolation of volatiles from seeds of dill in comparison with the traditional steam distillation procedure. Two main dill seeds volatiles, carvone and limonene, were taken into consideration. Two Supelco SPME fibers were used for the extraction: polyacrylic (PAc) and polydimethylsiloxane (PDMS). The time required to saturate the fibers was 3 min, while distillation took 3 h. Gas chromatography (GC) separation was reduced to 5 min by use of microcapillary column HP-5 cross-linked 5% Ph Me Siloxane. The standards of limonene and carvone were used to prepare calibration curves. PAc fiber responses were described by quadratic curves while PDMS responded linearly. Six varieties of dill were examined by distillation and SPME with both fibers. The good results were achieved for carvone by SPME-PDMS with significant regression between distillation and SPME. This compound can be measured in dill seeds samples within 10 min. The SPME-PDMS were also tested for its application to chiral resolution of carvone and limonene enantiomers in dill seeds oil. The enantiomeric separation was done with two chiral columns. The enantiomeric ratios measured by SPME were just the same as with distillation.

Anethum graveolens↗

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↗

PubMed2000

Solid-phase microextraction method development for headspace analysis of volatile flavor compounds.

Solid-phase microextraction (SPME) fibers were evaluated for their ability to adsorb volatile flavor compounds under various conditions with coffee and aqueous flavored solutions. Experiments comparing different fibers showed that poly(dimethylsiloxane)/divinylbenzene had the highest overall sensitivity. Carboxen/poly(dimethylsiloxane) was the most sensitive to small molecules and acids. As the concentrations of compounds increased, the quantitative linear range was exceeded as shown by competition effects with 2-isobutyl-3-methoxypyrazine at concentrations above 1 ppm. A method based on a short-time sampling of the headspace (1 min) was shown to better represent the equilibrium headspace concentration. Analysis of coffee brew with a 1-min headspace adsorption time was verified to be within the linear range for most compounds and thus appropriate for relative headspace quantification. Absolute quantification of volatiles, using isotope dilution assays (IDA), is not subject to biases caused by excess compound concentrations or complex matrices. The degradation of coffee aroma volatiles during storage was followed by relative headspace measurements and absolute quantifications. Both methods gave similar values for 3-methylbutanal, 4-ethylguaiacol, and 2,3-pentanedione. Acetic acid, however, gave higher values during storage upon relative headspace measurements due to concurrent pH decreases that were not seen with IDA.

Chromatography, Gas↗

PubMedDate not supplied

Study of ligand-receptor binding using SPME: investigation of receptor, free, and total ligand concentrations.

The theoretical background and practical approaches for studying ligand-receptor (protein) binding by solid phase microextraction (SPME) are investigated, along with methods for simultaneous calculation of receptor, free, and total ligand concentrations. With the introduction of new extraction phases (restricted access materials, molecularly imprinted polymers, and immobilized antibodies), SPME allows better separation of small molecules of ligand from larger molecules of receptor, and improved accuracy. This sample preparation method based on nonexhaustive extraction is well suited as a general method to study and quantify systems involving multiple equilibriums, with significant advantages over currently used methods. SPME was used previously for the determination of protein binding constants, but only with conventional extraction phases and in simple cases, with a 1:1 combination ratio between the ligand and the receptor or when negligible depletion conditions were met. The new theoretical approach presented in this study allows the quantification of any binding equilibrium, regardless of the extent of depletion. Restricted-access particles are used as extraction phase, and if the amount of receptor is limited, selected regions of the binding curve may be obtained using a single sample, with a volume as low as 10 muL. The equations developed here are simple and independent of the analytical method used for the quantification of the amount of ligand. Three different practical approaches are presented: the method of multiple standard solutions, the method of successive extractions from the same sample and the method of successive additions to the same sample. The usefulness of this novel approach is demonstrated by using it to determine the binding parameters of some selected drugs to human serum albumin. These parameters are subsequently used to calculate albumin, free drug, and total drug concentrations from unknown mixtures. The results are in good agreement with previously published data. Quantification of the amount of ligand extracted by SPME is done by liquid chromatography coupled with tandem mass spectrometry.

Cell Extracts↗