Steven B. Hawthorne

Quantitative Analysis of Fuel-Related Hydrocarbons in Surface Water and Wastewater Samples by Solid-Phase Microextraction

Solid-phase microextraction (SPME) parameters were examined on water contaminated with hydrocarbons including benzene and alkylbenzenes, n-alkanes, and polycyclic aromatic hydrocarbons (PAHs). Absorption equilibration times ranged from several minutes for low molecular weight compounds such as benzene to 5 h for high molecular weight compounds such as benzo[a]pyrene. Under equilibrium conditions, SPME analysis with GC/FID was linear over 3-6 orders of magnitude, with linear correlation coefficients (r(2)) greater than 0.96. Experimentally determined FID detection limits ranged from ∼30 ppt (w/w hydrocarbon/sample water) for high molecular weight PAHs (e.g., MW > 202) to ∼1 ppb for low molecular weight aromatic hydrocarbons. Experimental distribution constants (K) were different with 100- and 7-μm poly(dimethylsiloxane) fibers, and poor correlations with previously published values suggest that K depends on the fiber coating thickness and the sorbent preparation method. The sensitivity of SPME analysis is not significantly enhanced by larger sample volumes, since increasing the water volume (e.g., from 1 to 100 mL) has little effect on the number of analyte molecules absorbed by the fiber, especially for compounds with K < 500. Water sample storage should utilize silanized glassware, since hydrocarbon losses up to 70% could be attributed to unsilanized glassware walls when samples were stored for 48 h. Hydrocarbon losses at part-per-billion concentrations also occurred with surface waters due to partitioning onto part-per-thousand concentrations of suspended solids. Quantitative determinations of aromatic and aliphatic hydrocarbons (e.g., in gasoline-contaminated water) can be performed using GC/MS with deuterated internal standard or standard addition calibration as long as the target components or standards had unique ions for quantitation or sufficient chromatographic resolution from interferences. SPME analysis gave good quantitative performance with surface waters having high suspended sediment contents, as well as with coal gasification wastewater which contained matrix organics at 10(6)-fold higher concentrations than the target aromatic hydrocarbons. Good agreement was obtained between a 45-min SPME and methylene chloride extraction for the determination of PAH concentrations in creosote-contaminated water, demonstrating that SPME is a useful technique for the rapid determination of hydrocarbons in complex water matrices.

A model for dynamic extraction using a supercritical fluid

Abstract An idealized model is suggested for the analysis of the results of extraction in a flow system by a supercritical fluid from a matrix which contains small quantities of extractable materials, such that the extraction is not limited by solubility. The model is that of diffusion out of a homogeneous spherical particle into a medium in which the extracted species is infinitely dilute. The effect of matrix shape and size variation and also solubility limitations on the model, which occur in real systems, are discussed. Predictions of the model are compared with experimental results for systems which are mostly physically unlike the ideal model. However, important features of the behavior of these systems are found to accord with the predictions of the model. The use of the model gives an insight useful for the design of industrial extraction processes and also provides an extrapolation method for obtaining quantitative analytical extraction results relatively quickly.

Supercritical fluid extraction in environmental analysis

Abstract This review focuses on recent attempts to understand the SFE process and on applications of that understanding to increase SFE recoveries of pollutants from environmental solids. Methods to decrease restrictor plugging and to increase the collection efficiencies of extracted analytes are evaluated. Approaches to obtain quantitative extractions include fluid choice, extraction flow-rate, modifiers, pressure and temperature are presented as is the potential for SFE to extract ionic and metals. Finally, the need for a better definition of “quantitative” extraction and the use of SFE in certification exercises for complex environmental samples is discussed.

Solventless determination of caffeine in beverages using solid-phase microextraction with fused-silica fibers

Caffeine concentrations in beverages were determined using a simple and rapid method based on microextraction of caffeine onto the surface of a fused-silica fiber. The uncoated fiber was dipped into the beverage sample for 5 min after the addition of isotopically labeled (trimethyl 13C)caffeine. The adsorbed caffeine was then thermally desorbed in a conventional split/splitless injection port, and the concentration of caffeine was determined using gas chromatography with mass spectrometric detection. Quantitative reproducibilities were ca. 5% (relative standard deviation) and the entire scheme including sample preparation and gas chromatographic analysis was completed in ca. 15 min per sample. The potential of the microextraction technique for the analysis of flavor and fragrance compounds in non-caffeinated beverages is also demonstrated. Since no solvents or class-fractionation steps are required, the method has good potential for automation.

Directly coupled supercritical fluid extraction—gas chromatographic analysis of polycyclic aromatic hydro-carbons and polychlorinated biphenyls from environmental solids

A method has been developed for the direct coupling of supercritical fluid extractions with gas chromatography (SFE-GC) that yields good chromatographic peak shapes and quantitative recovery of analytes from environmental solids with a total extraction and analysis time of less than one hour. Maximum sensitivity is achieved and analyte degradation or loss is minimized since the extracted species are quantitatively transferred into a fused-silica capillary gas chromatographic column for cryogenic focusing followed by normal GC analysis using flame ionization, electron-capture, or mass spectrometric (MS) detection. Coupled SFE-GC-MS determinations of polycyclic aromatic hydrocarbons from National Bureau of Standards urban dust (SRM 1649) gave excellent agreement with certified values.

Elution of organic solutes from different polarity sorbents using subcritical water

Abstract The intermolecular interactions between organic solutes and sorbent matrices under subcritical water conditions have been investigated at a pressure of 50 bar and temperatures ranging from 50 to 250°C. Both polar and nonpolar organics (chlorophenols, amines, n-alkanes, and polycyclic aromatic hydrocarbons) and five different sorbent matrices (glass beads, alumina, Florisil, silica-bonded C18, and polymeric XAD-4 resins) were used. From the same matrix, the polar solutes always eluted at lower temperatures, while the moderately polar and nonpolar solutes only eluted at higher temperatures. Similar to matrix effects previously observed using supercritical carbon dioxide, the sorbent type greatly influenced the elution efficiency under subcritical water conditions. Lower temperatures are sufficient to elute a particular solute from glass beads, alumina, and Florisil, but higher temperatures (less polar water) are needed to elute the same solute from silica-bonded C18. The highest temperatures were required to elute aromatic organics from XAD-4. These matrix effects demonstrate that, while low temperature water can break inert or dipole interactions between solutes and glass beads, alumina, and Florisil, higher temperature water is required to interrupt the van der Waals attractions between solutes and silica-bonded C18, and even higher temperatures needed to overcome the π-electron interactions between aromatic solutes and XAD-4.

Factors controlling quantitative supercritical fluid extraction of environmental samples

The development of quantitative supercritical fluid extraction (SFE) methods for the recovery of organic pollutants from environmental samples requires three steps: quantitative partitioning of the analytes from the sample into the extraction fluid, quantitative removal from the extraction vessel, and quantitative collection of the extracted analytes. While spike recovery studies are an excellent method to develop the final two steps, they are often not valid for determining extraction efficiencies from complex real-world samples such as soils and sediments, exchaust particulates, and sludges. SFE conditions that yield quantitative recoveries of spiked analytes may recover < 10% of the same analytes from real-world samples, because spiked pollutants are not exposed to the same active sites as the native pollutants. Because of the heterogeneous nature of environmental samples, the partitioning step may be controlled by analyte solubility in the extraction fluid, kinetic limitations, and/or the ability of the extraction fluid to interrupt matrix-analyte interactions. While the interactions that control SFE rates from heterogenous environmental samples are not well understood, a generalized scheme for developing quantitative SFE methods is proposed based on interactive considerations of the collection efficiencies after SFE, fluid flow parameters in the extraction cell, analyte solubility, extraction kinetics, and analyte-matrix-extraction fluid interactions. The proposed development scheme includes increasing SFE extraction rates by the use of more polar fluids than CO2 such as CHClF2, the addition of organic modifiers to CO 2, and the use of high temperature extractions with pure CO2. Validation of quantitative extractions based on multiple extraction methods (SFE followed by liquid solvent extractions) is also described.

Identification of methoxylated phenols as candidate tracers for atmospheric wood smoke pollution

More than 70 organic compounds have been identified in unfractionated methylene chloride extracts of soot from residential wood stoves by a combination of capillary gas chromatography coupled with low-resolution mass spectrometry (GC/MS), GC coupled with high-resolution mass spectrometry, and chemical ionization mass spectrometry with deuteriated methanol as the reagent gas. Thirty of the species are derivatives of guaiacol (2-methoxyphenol) and syringol (2,6-dimethoxyphenol), which result from the pyrolysis of wood lignin. Soots from hardwood and pine show similar proportions of the syingol derivatives, but pine soot has much higher proportions of the guaiacol derivatives. Samples collected onto filters backed up by polyurethane foam (PUF) plus in the cooled smoke plume showed that some of the methoxylated phenols were primarily in the vapor phase, while the majority were associated with the particulates. These species are expected to be unique to wood smoke in urban atmospheres and are therefore suggested as tracers for atmospheric wood smoke pollution.

Solid-phase microextraction of polychlorinated biphenyls

The extraction and analysis of 21 polychlorinated biphenyls (PCBs) ranging from di- to decachlorobiphenyls in ocean, wetland and leachate water samples were achieved using solid-phase microextraction (SPME) with a 100-micron poly(di-methylsiloxane) (PDMS) fiber and gas chromatography-electron-capture detection (GC-ECD). Severe carryover between samples (e.g., 20%) occurs on both stir bars and the SPME fibers demonstrating that it is important to use a new stir bar for each sample, as well as to perform SPME-GC blanks between samples to avoid quantitative errors. The equilibrium partitioning coefficients of individual PCB congeners between PDMS and water were found to be surprisingly different compared to their octanol-water partitioning coefficient (Kow), demonstrating that Kow cannot be used to estimate the partitioning behavior of PCBs in the SPME process. Using a 15-min SPME extraction, SPME analysis with GC-ECD was linear (r2 > or = 0.97) from approximately 5 pg/ml to the solubility limit of each congener. Concentrations in water samples obtained by 15-min SPME extractions compared favorably with those obtained by toluene extractions, demonstrating that SPME combined with GC is a useful technique for the rapid determination of PCBs in water samples.

Selective extraction of oxygenates from savory and peppermint using subcritical water

The yields of oxygenated and non-oxygenated flavour and fragrance compounds from savory (Satureja hortensis) and peppermint (Mentha piperita) were compared using subcritical water extraction, supercritical carbon dioxide extraction (SFE) and hydrodistillation. Extraction rates with subcritical water increased with temperature (100–175 °C), but some desired organics (linalool and γ-terpinene) showed substantial degradation at temperatures >150 °C. However, subcritical water did not expose extracted compounds to atmospheric oxygen (as occurs in hydrodistillation) and thus may avoid the degradation of compounds like thymoquinone. Extraction of savory with subcritical water at 100 °C for 40 min gave ca. 100% recoveries (compared to hydrodistillation) for thymol and carvacrol, and >150% recoveries of borneol and linalool. Recoveries with 60 min of SFE (pure CO2 at 400 bar and 50 °C) were similar to hydrodistillation for borneol and linalool, but only ca. 50% for thymol and carvacrol. For peppermint, 30 min (at 150 °C) or 12 min (at 175 °C) of subcritical water extraction and 1 h of SFE gave good quantitative agreement with 4 h of hydrodistillation for carvone, pulegone, piperitone, eucalyptol, menthone, neomenthol and menthol, but the short subcritical water extractions only recovered ca. 40% of the less polar menthyl acetate. Subcritical water preferentially extracts more polar (oxygenated) flavour compounds, and ca. 80% extraction of oxygenated flavour compounds could be achieved under conditions which only extracted ca. 10–15% of the monoterpenes and <5% of the sesquiterpenes. In contrast, SFE had the lowest degree of selectivity and SFE extracts included plant alkane waxes as well as the same flavour compounds recovered by hydrodistillation. Copyright