Comparison of subcritical water and organic solvents for extracting kava lactones from kava root.

Subcritical water extraction of lactones from a kava (Piper metlhysticum) root was compared to a Soxhlet extraction with water, to boiling in water, and to a sonication in acetone. For ground kava (250-500 microm), 2 h of subcritical water extraction were required for a complete extraction at 100 degrees C, while at 175 degrees C, 20 min were sufficient. For a complete extraction of the unground (shredded) kava, the time of extraction was extended to 40 min at 175 degrees C. Boiling for 2 h and extraction with Soxhlet apparatus for 6 h, both of which employed water at atmospheric pressure, produced yields 40-60% lower than those obtained with subcritical water. With unground kava, 40 min of subcritical water extraction yielded essentially the same recoveries of lactones as 18 h of sonication with acetone, methylene chloride, or methanol.

PAH release during water desorption, supercritical carbon dioxide extraction, and field bioremediation.

Removal rates of polycyclic aromatic hydrocarbons (PAHs) from manufactured gas plant (MGP) soils were determined using water desorption for 120 days and mild supercritical carbon dioxide extraction (SFE) for 200 min. Both techniques were used to compare the changes in desorption rates for individual PAHs from untreated and treated soils that were obtained from a field biotreatment unit after 58, 147, and 343 days. Water desorption profiles (plotted in days) and SFE profiles (plotted in minutes) were very similar regardless of whether a PAH was rapidly or slowly removed. Water and SFE profiles were fit with a simple two-site (fast and slow) model to obtain the fraction of each PAH that was rapidly released (F). There was agreement between the F values obtained from water desorption and SFE for PAHs ranging from naphthalene to benzo[a]pyrene from all soils, with an overall correlation coefficient (r2) of 0.81. F values from water desorption and SFE also agreed with the actual removal of PAHs obtained after 147 and 343 days of field remediation (r2 ca. 0.80). The use of shorter desorption times (2-4 days for water and 20-40 min for SFE) allowed F values to be estimated for all PAHs and showed excellent agreement with the removal of individual PAHs obtained with 147-343 days of field remediation (r2 > 0.9). The comparisons indicate that short-term SFE can provide a reasonable estimate of the fraction of a PAH that is readily released and available for microbial treatment.

Comparisons of soxhlet extraction, pressurized liquid extraction, supercritical fluid extraction and subcritical water extraction for environmental solids: recovery, selectivity and effects on sample matrix.

Extractions of a polycyclic aromatic hydrocarbon (PAH)-contaminated soil from a former manufactured gas plant site were performed with a Soxhlet apparatus (18 h), by pressurized liquid extraction (PLE) (50 min at 100 degrees C), supercritical fluid extraction (SFE) (1 h at 150 degrees C with pure CO2), and subcritical water (1 h at 250 degrees C, or 30 min at 300 degrees C). Although minor differences in recoveries for some PAHs resulted from the different methods, quantitative agreement between all of the methods was generally good. However, the extract quality differed greatly. The organic solvent extracts (Soxhlet and PLE) were much darker, while the extracts from subcritical water (collected in toluene) were orange, and the extracts from SFE (collected in CH2Cl2) were light yellow. The organic solvent extracts also yielded more artifact peaks in the gas chromatography (GC)-mass spectrometry and GC-flame ionization detection chromatograms, especially compared to supercritical CO2. Based on elemental analysis (carbon and nitrogen) of the soil residues after each extraction, subcritical water, PLE, and Soxhlet extraction had poor selectivity for PAHs versus bulk soil organic matter (approximately 1/4 to 1/3 of the bulk soil organic matter was extracted along with the PAHs), while SFE with pure CO2 removed only 8% of the bulk organic matrix. Selectivities for different compound classes also vary with extraction method. Extraction of urban air particulate matter with organic solvents yields very high concentrations of n- and branched alkanes (approximately C18 to C30) from diesel exhaust as well as lower levels of PAHs, and no selectivity between the bulk alkanes and PAHs is obtained during organic solvent extraction. Some moderate selectivity with supercritical CO2 can be achieved by first extracting the bulk alkanes at mild conditions, followed by stronger conditions to extract the remaining PAHs, i.e., the least polar organics are the easiest organics to extract with pure CO2. In direct contrast, subcritical water prefers the more polar analytes, i.e., PAHs were efficiently extracted from urban air particulates at 250 degrees C, with little or no extraction of the alkanes. Finally, recent work has demonstrated that many pollutant molecules become "sequestered" as they age for decades in the environment (i.e., more tightly bound to soil particles and less available to organisms or transport). Therefore, it may be more important for an extraction method to only recover pollutant molecules that are environmentally-relevant, rather than the conventional attempts to extract all pollutant molecules regardless of how tightly bound they are to the soil or sediment matrix. Initial work comparing SFE extraction behavior using mild to strong conditions with bioremediation behavior of PAHs shows great promise to develop extraction methodology to measure environmentally-relevant concentrations of pollutants in addition to their total concentrations.

Static subcritical water extraction with simultaneous solid-phase extraction for determining polycyclic aromatic hydrocarbons on environmental solids.

A rapid and very simple method for extracting polycyclic aromatic hydrocarbons (PAHs) from soils, sediments, and air particulate matter has been developed by coupling static subcritical water extraction with styrene-divinylbenzene (SDB-XC) extraction discs. Soil, water, and the SDB-XC disc are placed in a sealed extraction cell, heated to 250 degrees C for 15 to 60 min, cooled, and the PAHs recovered from the disc with acetone/methylene chloride. If the cells are mixed during heating, all PAHs with molecular weights from 128 to 276 are quantitatively (>90%) extracted and collected on the sorbent disc and are then recovered by shaking with acetone/methylene chloride. After water extraction, the sorbent discs can be stored in autosampler vials without loss of the PAHs, thus providing a convenient method of shipping PAH extracts from field sites to the analytical laboratory. The method gives good quantitative agreement with standard Soxhlet extraction, and with certified reference materials for PAH concentrations on soil, sediment (SRM 1944), and air particulate matter (SRM 1649a).

Introducing selective supercritical fluid extraction as a new tool for determining sorption/desorption behavior and bioavailability of persistent organic pollutants in sediment.

This review article intends to introduce the possibility of utilizing selective supercritical fluid extraction (SFE) as a tool to study sorption/desorption processes and bioavailability of persistent organic pollutants (POP) in sediment. Sorption/desorption behavior and bioavailability studies of POPs is a large research area, but still many unsolved problems exists. Therefore novel approaches to investigate mechanistic behavior of POPs in sediments are needed. Present literature on SFE points to the fact that selective SFE measurements can improve our knowledge, and recent investigations have been performed that demonstrate this. Results obtained with selective SFE can be connected to desorption of POPs in sediments under natural conditions in aquatic ecosytems. The ultimate goal is to use selective SFE as a way to determine the bioavailable fraction present within a matrix. A few preliminary results are presented here which may serve as a starting point for future studies.

Static subcritical water extraction combined with anion exchange disk sorption for determining chlorinated acid herbicides in soil.

Static subcritical water extraction (SbWE) was coupled with collection on a strong anion exchange (SAX) disk for the determination of chlorinated acid herbicides and their esters in soil. With 100-150 degrees C water, esters were hydrolyzed into their acid form, and the herbicide acids extracted by subcritical water were trapped onto/into a SAX disk as the extraction cell was cooled. The trapped solutes were then derivatized for gas chromatographic (GC) analysis by placing the disk into a GC autosampler vial containing 1 mL of N,O-bis(trimethylsilyl)trifluoroacetamide derivatizing reagent. With the static SbWE/SAX disk extraction, nearly quantitative recoveries (typically over 80%) were obtained at 100 degrees C for 30 min in the extraction of herbicide acids and esters spiked on several different soils covering a range of organic content from 0.3 to 12%. Good agreements were reached between this method and EPA method 8151 for aged spiked soils. Detection limits of the static SbWE/SAX disk extraction were from 0.05 to 0.5 ppm and from 0.01 to 0.5 ppm using GC/electron capture detector and GC/mass spectrometry, respectively. The method is fast and simple and uses a small amount of organic solvent.

Comparison of supercritical fluid extraction and Soxhlet extraction for the determination of polychlorinated biphenyls in environmental matrix standard reference materials.

Supercritical fluid extraction (SFE) was compared to traditional Soxhlet extraction for the determination of polychlorinated biphenyl congeners in three standard reference materials: SRM 1941a (Organics in Marine Sediment), SRM 1944 (New York/New Jersey Waterway Sediment) and SRM 2974 [Organics in Mussel Tissue (Mytilus edulis) (Freeze-Dried)]. The concentrations determined using SFE compared well with the certified concentrations for the majority of the polychlorinated biphenyl congeners.

Method for determining the solubilities of hydrophobic organics in subcritical water.

A rapid and simple method has been developed to determine the solubility of organic compounds in water at temperatures from 25 to 250 degrees C and with enough pressure to maintain the liquid state ("subcritical" water). Water is heated and then passed through a cell containing excess test solute. The water, now saturated with solute, is blended with chloroform, cooled, and collected, and the chloroform fraction is analyzed by gas chromatography. Replicate determinations have typical reproducibilities, indicated by the relative standard deviation, of < 5%. Solubilities at 25 degrees C determined by this method are in good agreement with published data. Increasing the temperature of water from 25 degrees C to near the normal melting point of the organic solute results in solubility enhancements ranging from 6-fold for naphthalene (at 65 vs 25 degrees C) to 130,000-fold for chlorothalonil (at 200 vs 25 degrees C).

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.

Solid-phase microextraction with pH adjustment for the determination of aromatic acids and bases in water.

Adjusting the pH of water samples before performing solid-phase microextraction (SPME) analysis can be used to selectively extract organic acids (at pH 2) and bases (at pH 12). Sorption behavior of test organics is predictable based on the acid dissociation constant in water. In general, polyacrylate (PA) and Carbowax-divinylbenzene (CW-DVB) show substantially higher fiber/water sorption coefficients (Kd values) than a polydimethylsiloxane (PDMS) coated fiber. Gas chromatography-flame ionization detection (GC-FID) detection limits with the CW-DVB sorbent are approximately 0.5 to 10 ng/ml in a 2-ml water sample for a variety of aromatic amines, phenols, and chlorinated phenols, and are approximately 1 to 50 ng/ml for the same solutes using the PA sorbent. However, the PA fiber is more selective (depending on the water pH) for the acid or base components than the CW-DVB fiber. With proper pH adjustment, the recovery of spiked aromatic amines and phenols from a surface wetlands water ranged from 73 to 118% of the known values, with a precision (R.S.D.) of approximately 5 to 20%. SPME quantitation of phenols in a coal gasification wastewater using a PA fiber also gave excellent agreement with conventional methylene chloride extraction, although continued use of a single fiber with this wastewater led to poorer precision.

Adsorption versus Absorption of Polychlorinated Biphenyls onto Solid-Phase Microextraction Coatings.

Absorption-based polymeric solid-phase microextraction (SPME) fibers with poly(dimethylsiloxane) (PDMS) coatings were used to determine the partitioning coefficients of polychlorinated biphenyls (PCBs) between the sorptive fiber coatings and water. Previous models showing very good correlations between octanol-water partitioning coefficients (K(ow)) and absorption-based fiber-water partitioning coefficients (K(dv)) for low-molecular-weight analytes failed to predict K(dv) values for PCBs. In fact, K(dv) values for PCBs were 1-7 orders of magnitude lower than those predicted by K(ow) and actually showed a strong negative correlation between K(ow) and K(dv) for higher molecular weight analytes (MW >∼200). K(dv) values obtained using PDMS fibers with 7- and 100-µm coatings also disagree, demonstrating that K(dv) cannot be used to describe the partitioning behavior of PCBs between PDMS and water. However, when PCB partitioning coefficients were calculated on the basis of surface area (K(ds)), the K(ds) values obtained using 7- and 100-µm PDMS fibers agreed reasonably well, demonstrating that surface adsorption is the primary mechanism controlling PCB (and likely other higher molecular weight solutes) partitioning from water to SPME sorbents.

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.

Quantitative determination of sulfonated aliphatic and aromatic surfactants in sewage sludge by ion-pair/supercritical fluid extraction and derivatization gas chromatography/mass spectrometry.

Secondary alkanesulfonate (SAS) and linear alkylbenzene-sulfonate (LAS) surfactants were quantitatively (> 90%) extracted from sewage sludges as their tetrabutylammonium ion pairs using 400 atm of supercritical CO2 for 5 min of static extraction followed by 10 min of dynamic extraction at 80 degrees C. Ion pairs of SAS and LAS quantitatively formed butyl esters in the injection port of the gas chromatograph and were determined by gas chromatography/mass spectrometry without class fractionation of the sewage sludge extracts. Concentrations of SAS and LAS in sludges from five different sewage treatment plants ranged from 0.27 to 0.80 g/kg of dry sewage sluge and from 3.83 to 7.51 g/kg, respectively. Good reproducibility was achieved with RSDs of typically 5% for replicate extractions and analyses. Homologue and isomer distributions of SAS in sewage sludge indicated an enrichment of the more hydrophobic components in sewage sludge during sewage treatment.

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 hydrocarbons 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.

Chromatographic analysis of organic compounds in the atmosphere.

Fused silica capillary columns with thick films of cross-linked coatings have been used to separate many of the organic compounds that are present in the volatile fraction of automobile exhaust and in ambient air. Techniques have been developed that allow reversible collection and pre-concentration of organic compounds in ambient air on polymeric sorbents with minimal artifacts. The exhaust samples, which are directly injected without pre-concentration on sorbents, contain many of the same organic compounds that are found in sorbent-collected samples of urban ambient air. Similar anthropogenic organic compounds are not, in general, detected (less than 0.02 ppbV) in air samples from remote, rural areas in Colorado.