Use Of Solid-phase Microextraction Research Articles

Theoretical considerations on the use of solid-phase microextraction with complex environmental samples.

The equations governing the use of equilibrium solid-phase microextraction (SPME) for environmental samples with complex heterogeneous matrices were derived in terms of parameters commonly measured or estimated by environmental scientists. Parameterization of the SPME equations allowed for the a priori prediction of SPME performance as a function of analyte and sample properties as well as experimental conditions. A theoretical evaluation of SPME was performed for a broad range of realistic scenarios using calculated equilibrium partitioning parameters and the implications for practical applications were discussed. Potential pitfalls and errors in quantitative measurements were identified, and different approaches to SPME calibration were presented. The concept of an optimum minimum volume for the analysis of heterogeneous environmental samples was presented and fully developed. Data from three previous studies were used to validate the correctness of our theoretical framework; the agreement between the measured relative recoveries of a variety of hydrophobic organic chemicals and theoretical predictions was reasonable. The results of this study highlight the potential for SPME to be a valuable technique for the measurement of hydrophobic organic contaminants in complex environmental samples. The SPME technique appears to be especially well suited for samples with high solids-to-water ratios and/or large sample volumes. Examples of such applications include sediment interstitial water and in situ field measurements, respectively.

Quantitative Measurement of Bromoform in Swimming Pool Water Using SPME with GC-MS. An Undergraduate Instrumental Analysis Experiment

A senior-level undergraduate laboratory experiment that demonstrates the use of solid-phase microextraction (SPME) and capillary gas chromatography-mass spectrometry (GC-MS) was developed for the quantitative determination of bromoform in swimming pool water. Bromoform was extracted by SPME from the headspace of vials containing sodium chloride-saturated swimming pool water. Bromoform concentrations were determined from comparisons of peak areas on a student-generated calibration curve. Students compared results to OSHA water and air exposure limits for bromoform.

Quantitation of 2-chlorovinylarsonous acid in human urine by automated solid-phase microextraction–gas chromatography–mass spectrometry

Lewisite [dichloro(2-chlorovinyl)arsine] is a highly toxic chemical warfare agent with vesicant properties. The accidental exposure to lewisite or its intentional use as a chemical terrorism weapon are a public health threat and warrant investigations for the development of analytical methods to detect biomarkers of exposure to lewisite. Under aqueous conditions, lewisite rapidly hydrolyzes to the non-volatile 2-chlorovinylarsonous acid (CVAA). We have developed a sensitive, simple, and automated method for measuring CVAA in human urine. The assay is based on the use of solid-phase microextraction (SPME) and gas chromatography–mass spectrometry (GC–MS) after derivatization of the CVAA with 1,3-propanedithiol (PDT). The volatile CVAA-PDT is adsorbed onto a SPME fiber and analyzed by GC–MS. The assay was validated on human urine samples spiked with CVAA to determine the accuracy, precision, and limit of detection (LOD). The LOD was 7.4 pg in 1 ml of urine.

Mechanisms effecting analysis of volatile flavour components by solid-phase microextraction and gas chromatography

Quantitative properties of solid-phase microextraction (SPME) have been studied in order to investigate a simple and reliable method for analysing volatile flavour components in strawberries. Monitoring the chemical composition profile of berries will be of interest for the producers in order to optimise growth and storage conditions. By the use of SPME and capillary gas chromatography selected standard components were quantified with accuracy within ±7% and a linear response were found in all concentration ranges studied, covering three orders of magnitude. Equilibrium constants that describe how various components are distributed between the three phases present, sample, headspace and fibre coating were determined. In the system studied, the majority of analytes remained in the sample. This means that repeated analysis can be performed from a single sample without significantly changing the results. The mass transfers of the flavour components, from the sample and into the fibre, were fitted to a transport model assuming that the rate-controlling step is diffusion within the fibre. The experimental results agreed well with the model for most of the components studied. The response for three of the components (geraniol, linalool and trans-2-hexenyl butanoate) did not agree with the model. These components were present in the gas phase in only minute amounts explaining the deviation from the model. Such components will require a long absorption time (longer than 30 min). For quantitative analysis, it is important to use a very precise pre-determined absorption period and well defined sampling conditions. Internal standards can be omitted.

Analysis of free fatty acids in whey products by solid-phase microextraction.

To evaluate the impact of Cheddar cheese starter cultures on the level of free fatty acids in liquid whey, a solid-phase microextraction (SPME) technique was utilized. The determination of response factors relative to an internal standard and the verification of linearity over a wide concentration range allowed for the quantitation of free fatty acids in experimentally produced liquid whey and in a wide range of dry whey ingredients. Results indicated that whey produced with a Lactococcus lactis subsp. lactis starter culture contained the highest level of total free fatty acids with significantly higher levels of lauric, myristic, and palmitic acids. Significant declines in oleic, linoleic, and palmitic acid occurred during storage. Commercial whey ingredients demonstrated a linear increase in free fatty acids with increasing percent protein, except for whey protein isolate, which had the lowest concentration. The use of SPME for the rapid analysis of free fatty acids in whey products should allow for further research to determine the importance of these compounds on the quality and stability of whey products.

A rapid and sensitive method for methyl tert-butyl ether analysis in water samples by use of solid phase microextraction and gas chromatography–mass spectrometry

This work describes a rapid and sensitive solid-phase microextraction (SPME) method for the isolation and analysis of methyl tert-butyl ether in water samples. Methyl tert-butyl ether was extracted from aqueous solutions using SPME fibre coated with Divinylbenzene/Carboxen™/polydimethylsiloxane (30 μm film thickness) and analysed by GC–MS with a Hewlett Packard 6890/5973 system equipped with a capillary column coated with Vocol™ (30 m×0.25 mm,1.5 μm film thickness). Extraction parameters and chromatographic separation conditions were optimised. The developed method showed good analytical performance in terms of precision (RSD between 2% and 8%) and accuracy (mean recovery from 96% to 104%) with a detection limit of 14 ppt. Finally the method was applied to surface, tap and commercial mineral water samples, as well as snow samples collected along a busy road of Bologna town area. The median concentration of methyl tert-butyl ether in all these samples (0.05–0.4 ppb) was well below the maximum aqueous contamination levels in water adopted in the United States (13 ppb).

High levels of monoaromatic compounds limit the use of solid-phase microextraction of methyl tert-butyl ether and tert-butyl alcohol.

Recently, two papers reported the use of solid-phase microextraction (SPME) with poly(dimethylsiloxane)(PDMS)/Carboxen fibers to determine trace levels of methyl tert-butyl ether (MTBE) and tert-butyl alcohol (tBA) in water. Attempts were made to apply this technique to the analysis of water samples containing high levels of benzene, toluene, ethylbenzene, xylenes, and trimethylbenzenes (BTEXsTMBs) as would be expected at leaking underground storage tank sites. It was found that when the sample contained total aromatic compounds above 1 ppm, the response of the internal standards, deuterated MTBE and tBA, dropped by more than 65%. As this decrease in internal standard peak area was unacceptable, a static headspace method was used instead. This headspace method was used successfully to analyze groundwater from 670 monitoring wells at 74 service stations located in the northeast United States. In these monitoring wells, 30% of the samples contained total BTEXsTMBs above 1 ppm. If the SPME method was used to analyze these samples, dilution of more than 200 samples would be required to minimize the adverse matrix effect that high aromatic content had on the internal standard peak area.

Biotransformation of (R)-(+)- and (S)-(−)-limonene by fungi and the use of solid phase microextraction for screening

The biotransformation of (R)-(+)- and (S)-(−)-limonene by fungi was investigated. More than 60 fungal cultures were screened for their ability to bioconvert the substrate, using solid phase microextraction as the monitoring technique. After screening, the best fungal strains were selected for further study and were grown as sporulated surface cultures in conical flasks and as submerged liquid cultures. It was found that (+)- and (−)-limonene were converted by Penicillium digitatum to α-terpineol (main metabolite), cis- and trans-p-menth-2-en-1-ol, neodihydrocarveol and limonene oxide (minor metabolites) using liquid cultures. The bioconversion of (R)-(+)- and (S)-(−)-limonene by Corynespora cassiicola yielded (1S,2S,4R)- and (1R,2R,4S)-limonene-1,2-diol respectively. The bioconversions by liquid cultures were also monitored by solid phase microextraction as a function of time. The optimum conversion of limonene to α-terpineol by Penicillium digitatum was obtained after 8 hours (yield up to 100%). Since an important pH-decrease was noticed in some liquid broths, the stability of limonene under acidic conditions was investigated. No acid catalysed conversion products were recovered after 8 days from control flasks at pH 3.5 containing limonene.

Determination of gaseous toluene diisocyanate by use of solid-phase microextraction with on-fibre derivatisation.

An SPME method was developed for sampling gaseous 2,4-toluene diisocyanate (2,4-TDI) involving derivatisation of the isocyanate by reacting with dibutylamine (DBA). The TDI-DBA derivative thus formed was determined by LC-MS-MS utilising atmospheric pressure chemical ionisation (APCI). As a first step, DBA was loaded onto a poly(dimethylsiloxane)/divinylbenzene (PDMS-DVB) fibre coating by direct vapour-phase extraction of a highly concentrated diethyl ether solution of DBA. The DBA-loaded fibre was then exposed to an artificially generated atmosphere of gaseous 2,4-TDI. The linearity of the method ranged from 52.8 to 3100 microg m(-3) (6.8 to 400 ppbv) with a sampling time of 60 min. The proposed method has been applied to 2,4-TDI determination in an artificially generated dynamic standard atmosphere, yielding an approximate method detection limit (MDL) of 2 microg m(-3) (0.25 ppbv). This concentration is one twentieth of the Occupational Safety and Health Administration (OSHA) 8-hour time-weighted average (TWA) exposure limit. The sampler with the PDMS-DVB-DBA coating was found to be stable and retains the required amount of DBA for at least 10 days, an important feature for sampling systems with potential in-situ applications.

Determination of Methyl tert-Butyl Ether in Surface Water by Use of Solid-Phase Microextraction

Determination of Methyl <i>tert</i>-Butyl Ether in Surface Water by Use of Solid-Phase Microextraction

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.

Evaluation of solid-phase microextraction for the isotopic analysis of volatile compounds produced during fermentation by lactic acid bacteria.

The use of solid-phase microextraction (SPME) coupled with isotope ratio mass spectrometry (IRMS) for the analysis of flavor compounds produced by lactic acid bacteria has been evaluated using both liquid and headspace sampling modes. Initially, it was necessary to optimize the conditions for the SPME extraction of flavors-diacetyl and acetoin-in standard aqueous solutions. The effects of salt, headspace versus liquid sampling, and coating phase were tested. Second, the suitability of the coupling of SPME and gas chromatography-combustion interface-IRMS (GC-C-IRMS) for the determination of delta(13)C values was assessed. It is shown that neither the analyte concentration nor the period of fiber exposure has an effect on the delta(13)C values. Finally, having verified that there are no matrix effects from the fermentation medium, it is reported for the first time that flavor compounds can be extracted directly from culture supernatant by SPME and their delta(13)C values can be obtained by GC-C-IRMS.

Use of Solid-Phase Microextraction for the Quantitative Determination of Herbicides in Soil and Water Samples

An in-depth study of SPME optimization and application has been made, considering not only aqueous (surface water and groundwater samples) but also the more complex soil samples. Seven herbicides widely used in the area of study have been selected including five triazine herbicides (atrazine, simazine, terbumeton, terbuthylazine, terbutryn), molinate, and bromacil. linearity range was between 0.1 and 10 ng/mL and the repeatability below 10% when applying the optimized SPME procedure to water samples. Reproducibility was found to be lower than 20% at the 1 ng/mL level, and the limits of determination in environmental water samples using GC/MS (SIM mode) were well below 0.1 ng/mL (values ranging from 10 to 60 ng/L). Extraction of selected herbicides from soil was carried out by microwave-assisted solvent extraction using methanol in screw-capped vials, leading to recoveries over 80% in spiked soil samples at the 5-200 ng/g level. SPME application over methanolic soil extracts required a 10-fold dilution with distilled water. The recommended procedure was found to be fully applicable for quantitative determination of selected herbicides in soils containing low organic matter content with coefficients of variation below or around 10% and limits of determination ranging from 1 to 10 ng/g. Both procedures were applied to real-world surface water and soil samples where several pesticides were detected including atrazine, simazine, terbuthylazine, and molinate.

The Detection and Analysis of Ignitable Liquid Residues Extracted from Human Skin Using SPME/GC

A simple, fast, inexpensive, and sensitive technique for the detection and identification of flammable or combustible liquid residues on the skin of arson suspects is presented. The use of solid phase microextraction (SPME) for the analysis of ignitable liquid residues has been demonstrated and it is shown in this work that this technique is effective in extracting these liquid residues at extremely low quantities. Microliter quantities of controlled spikes of gasoline, diesel fuel, and charcoal lighter fluid were deposited on the hands of a volunteer and extracted after several time intervals. The SPME technique can recover very small amounts of liquid deposits on skin up to 3.5 h after exposure, depending on the class of the ignitable liquid residue used.

Use of solid-phase microextraction in the investigation of chemical communication in social wasps

Solid-phase microextraction has been used to investigate chemical communication in several social wasp species. Using the technique to analyse exocrine gland secretions, we demonstrate that the results are comparable with those obtained with the more classical methods that use solvents, eliminating, in many cases, the shortcomings of these methods in insect pheromone analysis. As a result of its simplicity this technique is very suitable for research on the chemical ecology of social wasps, and on insect communication in general.

Determination of Methyl tert-Butyl Ether in Surface Water by Use of Solid-Phase Microextraction

A new method based on solid-phase microextraction (SPME) has been developed for the determination of methyl tert-butyl ether (MTBE) in surface water at sub-ppb concentrations. The combination of SP...

The use of solid-phase microextraction in conjunction with a benchtop quadrupole mass spectrometer for the analysis of volatile organic compounds in human blood at the low parts-per-trillion level.

The analysis of volatile organic compounds (VOCs) in whole human blood at the low parts-per-trillion level has until recently required the use of a high-resolution mass spectrometer to obtain the specificity and detection limits required for epidemiological studies of VOC exposure in the general public. Because of the expense and expertise required to operate and maintain a high-resolution instrument, the applicability of this method has been limited. These limitations are overcome in a new method using automated headspace solid-phase microextraction (SPME) in conjunction with a gas chromatograph and a benchtop quadrupole mass spectrometer. A combination of SPME and multiple single-ion monitoring minimizes the interferences and chemical noise associated with whole blood samples. This method permits the analysis of 10 VOCs in human blood while simplifying the sample preparation and reducing the possible exposure of the analyst to blood aerosols. Twelve samples can be run successively in a fully automated mode, thus eliminating the need for operator attention. Detection limits are below 50 ppt (pg/mL) for a majority of the VOCs tested with a 5-mL sample.

The use of Solid Phase MicroExtraction (SPME) devices in analysis for potential mosquito oviposition attractant chemicals from cyanobacterial mats

Females of Anopheles albimanus mosquito are known to prefer floating cyanobacterial mats over open water for oviposition. We used Solid Phase MicroExtraction (SPME) devices on-site to trap substances volatilized from these two environments, followed by analysis by GC-MS (gas chromatograph-mass spectrometer). In enclosed headspace field microcosms, an unidentified C-15 aliphatic alcohol was persistently found over cyanobacterial mats as compared to open water. Based on this finding, we conducted oviposition experiments using a commercially available compound, n-pentadecanol, close in molecular weight and mass spectral pattern to the unknown C-15 aliphatic alcohol. The results indicate a tendency of female mosquito to oviposit more eggs in containers with the tested chemical as compared to water and blank.

Fast field sampling/sample preparation and quantification of volatile organic compounds in indoor air by solid-phase microextraction and portable gas chromatography

Solid-phase microextraction (SPME) was used as a rapid, simple, convenient, and cost-effective technique to sample volatile organic compounds (VOCs) in indoor air. Concentrations of five target VOCs, including benzene, toluene, ethylbenzene, m,p-xylenes, and hexane, were determined on site in several buildings around the city of Waterloo, Canada. Samples were collected with a polydimethylsiloxane/divinylbenzene (PDMS/DVB) porous polymer-coated fiber and 1-min sampling time, followed by 15-min analysis. Fast separation and speciation of common indoor air pollutants was possible with the use of a modified, SRI portable gas-chromatography (GC) instrument, equipped with a photoionization (PID), a flame ionization (FID), and a dry electrolytic conductivity detector (DELCD) in series. The mass calibration for target VOCs was based on the diffusion-controlled extraction onto the adsorptive SPME coating. The method detection limits for the target VOCs in air were between one and nine parts per billion (ppb). Target VOC concentrations measured with SPME/fast GC were comparable to those obtained with the National Institute of Occupational Safety and Health (NIOSH) 1501 method. The use of SPME coupled to a portable GC instrument allowed for at least a tenfold reduction of the total sampling and analysis time. The short SPME sampling time combined with fast, portable GC provided a near-real-time measurement of target VOCs. The results suggest that fast air sampling with adsorptive SPME fibers can be used for analyte speciation based on diffusion coefficients. The combination of SPME and a portable fast GC proved to be a very promising technique for conducting cost-effective indoor air quality surveys and making on-site decisions to control VOC emissions. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 73–84, 2000

Solid-phase micro-extraction in bioanalysis, exemplified by lidocaine determination

Solid-phase micro-extraction (SPME) is a never sample preparation technique that can be used for gaseous, liquid or solid samples in conjunction with GC, HPLC or CE (e.g. [1]). The use of SPME for the analysis of drugs in biofluids is also becoming popular (e.g. [2]). The principle is that a fused silica fibre coated with a polymer such as polydimethylsiloxane (PDMS) is put directly into the sample or placed in the headspace above it (e.g. [3]), analyte desorption is done thermally (for GC) or with liquid. As a model compound to study conditions we have investigated lidocaine in human urine using GC or LC [4] and, with attention to protein binding, in plasma mainly using GC [5].