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PubMed2004

Ester variability in apple varieties as determined by solid-phase microextraction and gas chromatography-mass spectrometry.

Solid-phase microextraction (SPME) with a polydimethylsiloxane fiber coupled with gas chromatography-mass spectrometry (GC-MS) was applied to the study of variability in volatiles released by 13 apple varieties. The relative amounts of 40 esters and alpha-farnesene were determined. Principal component analyses of these results clustered the apples into three groups according to skin color: red, green, and red-green. Total ester contents were highest with the red cluster apples, and the green cluster apples had the highest alpha-farnesene levels. This technology was also applied to the monitoring of changes in volatiles for apples removed from controlled-atmosphere storage with subsequent storage at 4 degrees C and room temperature. Total ester contents increased 25-fold, with the greater increases coming at room temperature, whereas alpha-farnesene levels increased only 5-fold. For apples stored at room temperature, after 11 days, the amount of increase was inversely proportional to the size of the ester: levels of smallest esters (molecular weight 116) increased 12.5-fold, and the largest esters (molecular weight 228) increased approximately 1.3-fold.

Esters↗

PubMed1999

Solid phase microextraction of pesticide residues from strawberries.

A new solid phase microextraction method for the determination of pesticide residues in strawberries for 16 commonly used compounds was described. The strawberries were crushed and centrifuged. An aliquot of the well agitated aqueous supernatant (4 ml) was extracted with a fibre coated with polydimethylsiloxane (PDMS, 100 microns) for 45 min at room temperature. Identification and quantification were achieved using a gas chromatography-mass spectrometry (GC-MS) system and selective ion monitoring (SIM). The method was tested for the following pesticides: carbofuran, diethofencarb, penconazole, hexaconazole, metalaxyl, folpet, bromopropylate, dichlofluanid, alpha-endosulfan, beta-endosulfan, parathion ethyl, procymidone, iprodione, vinclozolin, myclobutanil and chlorothalonil. Limits of detection, repeatability and linearity for standard calibration in strawberries were obtained. Positive and negative effects of the matrix between the extracting solution of strawberries and water were observed. Stabilities of these compounds in the extracting solution of strawberries were determined. The solvent-free SPME procedure was found to be quicker and more cost effective than the solvent extraction methods commonly used.

Calibration↗

PubMed2006

Analysis of trace amount of bank dye and lachrymators from exploding bank devices by solid-phase microextraction and gas chromatography-mass spectrometry.

Solid-phase microextraction (SPME) is a fast, solvent-free alternative to conventional sample preparation techniques. This technique involves exposing a fused silica fiber that has been coated with a stationary phase to an aqueous solution or its headspace to selectively extract compounds from their matrix. The fiber is then removed, and the analytes are thermally desorbed in the injector of a gas chromatograph. By sampling from the headspace above sample matrices, SPME can be used to extract target analytes from very complex matrices. In this study, SPME in the headspace is used in developing a method for the dye 1-methylaminoanthraquinone (MAAQ) and two lachrymators: orthochlorobenzalmalononitrile (CS) (tear gas) and 2-chloroacetophenone (CN) (tear gas). The focus is to develop a robust method to minimize sample preparation and to reduce matrix interferences encountered by other extraction techniques. In developing the method, several fibers are studied for their affinity for the compounds of interest. Although this method is developed for qualitative analysis, the extraction time and temperature profile are thoroughly investigated to provide the optimal conditions. The use of a salt solution is evaluated to increase the partitioning of MAAQ into the headspace. Using this method, qualitative extraction is achieved for the analysis of CN, CS, and MAAQ from its matrices. CN and CS are extracted in less than 5 min, though MAAQ needed more than 15 min to achieve a reasonable response. If more sensitivity is required, the use of a salt solution increases the response of MAAQ by 90-fold.

Journal Article↗

PubMed2000

Solid-phase microextraction for the analysis of biological samples.

Solid-phase microextraction (SPME) has been introduced for the extraction of organic compounds from environmental samples. This relatively new extraction technique has now also gained a lot of interest in a broad field of analysis including food, biological and pharmaceutical samples. SPME has a number of advantages such as simplicity, low cost, compatibility with analytical systems, automation and the solvent-free extraction. The last few years, SPME has been combined with liquid chromatography and capillary electrophoresis, besides the generally used coupling to gas chromatography, and has been applied to various biological samples such as, e.g., urine, plasma and hair. The objective of the present paper is a survey of the application of SPME for the analysis of biological samples. Papers about the analysis of biologically active compounds are categorised and reviewed. The impact of SPME on various analytical fields (toxicological, forensic, clinical, biochemical, pharmaceutical, and natural products) is illustrated. The main features of SPME and its modes are briefly described and important aspects about its application for the determination of pharmaceuticals, drugs of abuse and compounds of clinical and toxicological interest are discussed. SPME is compared with other sample pretreatment techniques. The potential of SPME and its main advantages are demonstrated. Special attention is paid to new trends in applications of SPME in bioanalysis.

Chromatography, Liquid↗

PubMed2002

Automated headspace solid-phase microextraction and capillary gas chromatography analysis of ethanol in postmortem specimens.

Solid-phase microextraction (SPME) is a relatively new solventless sample preparation technique that allows simultaneous sampling, extraction, pre-concentration, and introduction of analytes from a sample matrix in a single procedure. This methodology has been used for the analysis of several drugs of forensic toxicology interest including volatile compounds. This paper describes a methodology for analysis of ethanol and other volatile compounds using automatic headspace solid-phase microextraction (HS-SPME) and capillary gas chromatography in postmortem specimens. The methodology was initially developed using standard solutions of acetaldehyde, acetone, methanol, and ethanol. Isobutanol was used as internal standard. Postmortem samples of blood, urine, and vitreous humor were obtained during medico-legal autopsies. To date, there are no published paper regarding alcohol analysis in vitreous humor specimens using HS-SPME and limited literature analyzing blood and urine samples. HS-SPME analysis showed that, under optimized conditions, ethanol and isobutanol (internal standard) were well-separated from other volatile compounds such as acetaldehyde, acetone, and methanol considered to be potential interferents in ethanol analysis. The calibration curves for each volatile compound demonstrated good linearity throughout the concentration range from 0.001 to 1.0 g/dl and the detection limit of ethanol in the studied specimens was approximately 0.0001 g/dl.

Adult↗

PubMed2001

Fuel spill identification using solid-phase extraction and solid-phase microextraction. 1. Aviation turbine fuels.

The water-soluble fraction of aviation jet fuels is examined using solid-phase extraction and solid-phase microextraction. Gas chromatographic profiles of solid-phase extracts and solid-phase microextracts of the water-soluble fraction of kerosene- and nonkerosene-based jet fuels reveal that each jet fuel possesses a unique profile. Pattern recognition analysis reveals fingerprint patterns within the data characteristic of fuel type. By using a novel genetic algorithm (GA) that emulates human pattern recognition through machine learning, it is possible to identify features characteristic of the chromatographic profile of each fuel class. The pattern recognition GA identifies a set of features that optimize the separation of the fuel classes in a plot of the two largest principal components of the data. Because principal components maximize variance, the bulk of the information encoded by the selected features is primarily about the differences between the fuel classes.

Journal Article↗

PubMed2002

Optimization of a derivatization-solid-phase microextraction method for the analysis of thirty phenolic pollutants in water samples.

Solid-phase microextraction (SPME) coupled to gas chromatography-mass spectrometry has been applied to the extraction of 30 phenol derivatives from water samples. Analytes were in situ acetylated and headspace solid-phase microextraction was performed. Different parameters affecting extraction efficiency were studied. Optimization of temperature, type of microextraction fiber and volume of sample has been done by means of a mixed-level categorical experimental design, which allows to study main effects and second order interactions. Five different fiber coatings were employed in this study; also, extraction temperature was studied at three levels. Both factors, fiber coating and extraction temperature, were important to achieve high sensitivity. Moreover, these parameters showed a significant interaction, which indicates the different kinetic behavior of the SPME process when different coatings are used. It was found that 75 microm carboxen-polydimethylsiloxane and 100 microm polydimethylsiloxane, yield the highest responses. The first one is specially appropriated for phenol, methylphenols and low chlorinated chlorophenols and the second one for highly chlorinated phenols. The two methods proposed in this study shown good linearity and precision. Practical applicability was demonstrated through the analysis of a real sewage water sample, contaminated with phenols.

Gas Chromatography-Mass Spectrometry↗

PubMed2006

Predicting organic contaminant concentrations in sediment porewater using solid-phase microextraction.

Because of its cost and time saving features, solid-phase microextraction (SPME) is a leading candidate as a biomimic technique in assessing the bioavailable fraction of hydrophobic organic contaminants (HOCs) in sediment porewater. However, no predictive modeling framework in which to systematically address the effect of key parameters on SPME performance for this application exists. In this study, we derived two governing equations to predict (1) the minimum sediment volume (V(s)min) required to achieve non-depletive conditions, and (2) dissolved phase HOC porewater concentrations (C(pw)) as functions of HOC- and sediment specific characteristics in a conceptual three compartment system. The resulting model predicted that V(s)min was independent of HOC concentrations both in sediment and porewater, but did vary with hydrophobicity (characterized by logK(ow)), the fraction of sediment porewater (f(pw)), and the volume (V(f)) of the SPME sorbent phase. Moreover, the effects of these parameters were minimized (i.e., V(s)min reached plateaus) as logK(ow) approached 4-5. Model predictions of C(pw), a surrogate for SPME-based detection limits in porewater, decreased with increasing sediment volume (V(s)) at low V(s) values, but rapidly leveled off as V(s) increased. A third result suggested that the sediment HOC concentration required for SPME is completely independent of K(ow). These results suggest that relatively small sediment volumes participate in exchange equilibria among sediment, porewater and the SPME fiber, and that large sediment HOC reservoirs are not needed to improve the detection sensitivity of SPME-based porewater samplers. The ultimate utility of this modeling framework will be to assist future experimental designs and help predict in situ bioavailability of sediment-associated HOCs.

Algorithms↗

PubMed2006

Simultaneous analysis of polychlorinated biphenyls and organochlorine pesticides in water by headspace solid-phase microextraction with gas chromatography-tandem mass spectrometry.

Headspace solid-phase microextraction combined with gas chromatography-ion trap tandem mass spectrometry (HS-SPME-GC-ITMS-MS) method has been developed and studied for the simultaneous determination of 15 organochlorine pesticides (OCPs) and 20 polychlorinated biphenyls (PCBs) in aqueous samples. To perform the HS-SPME polydimethylsiloxane (PDMS) (7, 30 and 100 microm film thickness) and polydimethylsiloxane-divinylbenzene (PDMS-DVB) fibers were initially compared on the basis of their absorption capacities for the selected compounds, and PDMS 100 microm film thickness was selected to accomplish the rests of essays. The influence of various parameters on OCPs and PCBs extraction efficiency by HS-SPME was thoroughly studied using GC-electron capture detector (ECD). Parameters such as collision induced dissociation (CID) resonant excitation amplitude and RF storage level were optimized to increase specificity and sensibility for ITMS-MS analysis. The performance of proposed HS-SPME-GC-ITMS-MS methodology with respect to linearity, reproducibility and limit of detection (LOD) was evaluated by water spiked with target compounds. The linear range of most compounds was found to be between 0.01 and 1 ng mL(-1) and the limits of detection were between 0.4 and 26 pg mL(-1). The reproducibility of the method (n = 6), expressed as relative standard deviation (RSD), was between 5 and 21%. Finally, developed procedure was applied to determine selected OCPs and PCBs in river water samples in concentration below 0.1 ng mL(-1) can be easily carried out with ultra-selectivity and precision.

Gas Chromatography-Mass Spectrometry↗

PubMed2000

Absorption of hydrophobic compounds into the poly(dimethylsiloxane) coating of solid-phase microextraction fibers: high partition coefficients and fluorescence microscopy images.

The use of solid-phase microextraction with poly(dimethylsiloxane) (PDMS)-coated glass fibers for the extraction and analysis of hydrophobic organic analytes is increasing. The literature on this topic is characterized by large discrepancies in partition coefficients and an uncertainty of whether highly hydrophobic analytes are retained by absorption into the fiber coating or by adsorption to the fiber surface. We applied a new method, which minimizes the impact of experimental artifacts, to determine PDMS water partition coefficients of 17 hydrophobic analytes including chlorinated benzenes, PCBs, PAHs, and p,p'-DDE. These partition coefficients are several orders of magnitude higher than some reported values. Two observations strongly suggest that the retention of hydrophobic organic substances is governed by partitioning into the PDMS coating. (1) The partition coefficients are proportional with octanol/water partition coefficients. (2) The fluorescence of fluoranthene was observed to be homogeneously distributed within the polymer coating when studied by means of fluorescence microscopy. Implications of these findings for the application of solid-phase microextraction with respect to potential detection limits, with respect to biomimetic extraction, and with respect to measurements in multicompartment systems are discussed.

Benzene↗

PubMed2003

Determination of antifouling compounds in marine sediments by solid-phase microextraction coupled to gas chromatography-mass spectrometry.

Solid-phase microextraction (SPME) coupled to gas chromatography-mass spectrometry was applied to determine the antifouling biocides chlorothalonil, dichlofluanid, sea nine 211 and irgarol 1051 in marine sediments. Two experimental approaches were selected before the submission of the aqueous extracts to SPME prior to GC determination. The extraction of the biocides from the sediment samples was conducted using (a) water (containing 5%, v/v, acetone) and (b) acetone which was then diluted with water to give a 5% (v/v) content. The recommended procedures were found to be applicable for quantitative determination of the selected antifouling compounds in sediments with R.S.D.s below 17% and limits of detection ranging from 0.5 to 25 ng/g. The acetone/SPME procedure showed lower detection limits (0.5 to 6 ng/g) and R.S.D. values (< 11%) as well as better recoveries (73 to 92%), proving that it could be successfully performed for the determination of antifouling compounds in sediment analysis, even in samples with high organic matter content. Both optimized water/SPME and acetone/SPME procedures were applied to the analysis of antifouling compounds in marine sediments and compared with the conventional liquid-liquid extraction with subsequent clean up by solid-phase extraction.

Aniline Compounds↗

PubMed2005

Equilibrium in-fibre standardisation technique for solid-phase microextraction.

This note describes a fundamental investigation into solid-phase microextraction (SPME) using a standard loaded into the fibre coating as a means of internal standardisation for the analysis of samples contained in vials. The loading of reproducible amounts of standards into a non-porous SPME fiber was investigated. It was found that spiking low milligram quantities of standards such as benzene, toluene, ethylbenzene, xylenes (BTEX) and/or naphthalene into a few grams of pump oil sealed in a 20 mL vial provided an excellent standard generator. A single solution allowed over a hundred standard loadings with a reproducibility of <4% R.S.D. When a fiber, loaded with the standard(s) was introduced into a sample vial, extraction of analytes into the fiber and desorption of the standard(s) into the sample matrix occur simultaneously. Quantification was then based on the equilibrium distribution of the standards and the analytes between the fibre coating and the sample matrix in the vial. A comparison of equilibration profiles obtained using traditional internal standardisation and the in-fibre approach generally showed the same equilibration behaviour. The developed method was successfully used to correct for matrix effects in the BTEX analysis of a wine sample.

Automation↗

PubMed2005

Vial position in the determination of chlorophenols in water by solid phase microextraction.

The extraction of chlorophenol from water by headspace solid phase microextraction (HS-SPME) in vials located both vertically and horizontally is compared. The results obtained show that kinetic parameters are clearly affected by how the vial is placed in the analysis of semivolatile compounds. Extraction time for reach the equilibrium was three times lower in the horizontal configuration. An on-line extraction unit coupled to a continuous flow system is used to analyse unmodified ground water samples. In order to increase the high throughput, the analysis time is reduced and the sensitivity increased by making the extraction simultaneously with two fibres. The proposed method is applied to the analysis of spiked river water samples. The precision expressed as relative standard deviation ranges from 3.5 to 4.8%, and the recoveries from 94 to 105%.

Chemical Fractionation↗

PubMed2006

Determination of Ochratoxin A in wine at sub ng/mL levels by solid-phase microextraction coupled to liquid chromatography with fluorescence detection.

Solid-phase microextraction (SPME), using a polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber, interfaced with liquid chromatography-fluorescence detection (LC-FD) has been applied to the determination of Ochratoxin A (OTA) in wine samples. Compared to the most widely adopted extraction/clean-up procedure based on immunoaffinity columns (IAC), the solventless extraction is simpler and cost-effective, requiring the simple immersion of the fiber in diluted wine samples. Furthermore, a fast LC separation is achieved under isocratic conditions. The linear range investigated in wine was 0.25-8 ng/mL; at fortification levels of 0.5 and 2 ng/mL, within-day intra-laboratory precision (repeatability) values, expressed as RSD%, were 5.9 and 5.1, respectively, whereas between days (n = 4) precision was 8.5 and 7.1%, respectively. The limit of detection (LOD) at a signal-to-noise (S/N) ratio of 3 was 0.07 ng/mL; the limit of quantification (LOQ) calculated at S/N = 10 was 0.22 ng/mL, well below the European regulatory level of 2 ng/mL. The potential of the method has been demonstrated by the analysis of a number of different wine samples.

Chemical Fractionation↗

PubMed2006

Diffusive sampling of airborne furfural by solid-phase microextraction device with on-fiber derivatization.

The solid-phase microextraction (SPME) device was used as a diffusive sampler for airborne furfural. The polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber was used, and O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was first loaded onto the fiber. The SPME fiber assembly was then inserted into a PTFE tubing as a diffusive sampler. Known concentrations of furfural around the threshold limit values (TLVs)/time-weighted average and specific relative humidities (RHs) were generated by syringe pumps in a dynamic generation system. Validations of the SPME diffusive sampling with the US Occupational Safety and Health Administration (OSHA) organic method 72 were performed side-by-side in an exposure chamber at 25 degrees C. Gas chromatography/mass spectrometry (GC/MS) was used for sample analysis. The experimental sampling constant of the sampler was found to be (1.75 +/- 0.03) x 10(-2) (cm3 min(-1)) at 25 degrees C, whereas face velocity (0-0.25 ms(-1)) as well as RHs (10-80%) were proven to have no effects on the sampler. The correlations between the results from both SPME device and OSHA organic method 72 were found to be linear (r = 0.9849) and consistent (slope = 0.99 +/- 0.03). However, the variations of diffusion coefficients at different temperatures needs to be considered, and the adjustment of sampling constant was a must when sampling at temperatures different from 25 degrees C.

Chromatography, Gas↗

PubMed2005

Development of a simple and sensitive method for the characterization of odorous waste gas emissions by means of solid-phase microextraction (SPME) and GC-MS/olfactometry.

A solid-phase microextraction (SPME) method has been developed for the extraction of odorous compounds from waste gas. The enriched compounds were characterized by gas chromatography-mass spectrometry (GC-MS) and gas chromatography followed by simultaneous flame ionization detection and olfactometry (GC-FID/O). Five different SPME fiber coatings were tested, and the carboxen/polydimethylsiloxane (CAR/PDMS) fiber showed the highest ability to extract odorous compounds from the waste gas. Furthermore, parameters such as exposure time, desorption temperature, and desorption time have been optimized. The SPME method was successfully used to characterize an odorous waste gas from a fat refinery prior to and after waste gas treatment in order to describe the treatment efficiency of the used laboratory scale plant which consisted of a bioscrubber/biofilter combination and an activated carbon adsorber. The developed method is a valuable approach to provide detailed information of waste gas composition and complements existing methods for the determination of odors. However, caution should be exercised if CAR/PDMS fibers are used for the quantification of odorous compounds in multi-component matrices like waste gas emissions since the relative affinity of each analyte was shown to differ according to the total amount of analytes present in the sample.

Chemistry Techniques, Analytical↗

PubMed2000

Solid-phase microextraction in pesticide residue analysis.

The applications of solid-phase microextraction (SPME) for sample preparation in pesticide residue analysis are reviewed in this paper taking into account the different approaches of this technique coupled mainly to gas chromatography but also to high-performance liquid chromatography. A complete revision of the existing literature has been made considering the different applications divided according to the pesticide families (organochlorine, organophosphorus, triazines, thiocarbamates, substituted uracils, urea derivatives and dinitroanilines among others) and the sample matrices analysed which included environmental samples (water and soil), food samples and biological fluids. Details on the analytical characteristics of the procedures described in the reviewed papers are given, and new trends in the applications of SPME in this field are discussed.

Chromatography, Gas↗

PubMed2001

Determination of organochlorine pesticides and their metabolites in soil samples using headspace solid-phase microextraction.

An analytical procedure was developed using headspace solid-phase microextraction (HS-SPME) for the determination of organochlorine pesticides (OCPs) and their metabolites in sandy soil samples. The developed procedures involving fiber selection, temperature effect, absorption time, soil matrix and the addition of solvents of different polarity were optimized. Also, the results were compared to those achieved using Soxhlet extraction standard method. The 100-microm polydimethylsiloxane (PDMS) and 65-microm PDMS-divinylbenzene showed good extraction efficiency for 18 organochlorine pesticides. An increase in the extraction efficiency of organochlorine pesticides and the metabolites was observed when the temperature increased, and an optimum temperature of 70 degrees C for extracting OCPs was obtained. The application of other hydrophilic solvents had different effects on the extraction of organochlorine pesticides and the metabolites. Higher responses of OCPs were obtained when 5 ml of water was added to the soil. Good linearity of OCPs between 0.2 and 4 ng/g soil was observed. The relative standard deviation was found to be lower than 25%. Also the limits of detection were between 0.06 and 0.65 ng/g, which were lower than those obtained using Soxhlet extraction. Moreover, the optimized HS-SPME procedure was applied to the analysis of OCPs in certified reference material (CRM) 804-050 soil and compared with Soxhlet extraction procedure. Results obtained in this study were in good agreement with those obtained using Soxhlet extraction. The mean values obtained using HS-SPME technique were in the range of 16.5 to 1459.6 mg/kg, which corresponds to the recoveries of 68% to 127% of the certified values of CRM soil.

Chromatography, Liquid↗