US Environmental Protection Agency Priority Research Articles

Solid-phase extraction of polycyclic aromatic hydrocarbons in surface water: Negative effect of humic acid

The effect of humic acid on solid-phase extraction of polycyclic aromatic hydrocarbons (PAHs) from surface water was studied. The hydrophobic PAHs show significant association with humic acid, and this was confirmed to be the cause of negative effect when conventional reversed-phase solid-phase extraction (RP-SPE) was employed to extract the analytes from aqueous samples. As an alternative, dynamic ion-exchange (DIE) SPE could simultaneously extract both the fraction of the analytes which was associated with humic acid, and that which was freely dissolved. Using the 16 US Environmental Protection Agency priority PAHs as model compounds, the recoveries of the highly hydrophobic components by DIE-SPE were 10–30% higher than those by RP-SPE for a 1000-ml water sample dissolved with Aldrich humic acid (of 4.1 mg/l dissolved organic carbon content). A similar result was also obtained for 500 ml of natural surface water although the difference in recoveries between the two methods for this sample was smaller than that for the simulated sample. For validation of the method, the artifacts in connection with DIE-SPE in extracting the fraction of analytes which was freely dissolved and that which was associated with humic acid were investigated.

On-line flow sample stacking in a flow injection analysis–capillary electrophoresis system: 2000-fold enhancement of detection sensitivity for priority phenol pollutants

A flow injection analysis–capillary electrophoresis system has been used for on-line flow stacking of 11 US Environmental Protection Agency priority phenol pollutants. Samples containing low concentrations of phenols dissolved in deionised water are continuously delivered to the capillary opening by means of a peristaltic pump. The sample components stack at the boundary between the highly conductive separation electrolyte and the introduced sample. By selecting an appropriate electrolyte and stacking conditions the movement of the electrolyte solution inside the capillary can be reduced, thereby improving the stacking efficiency. The electrolyte used here contained 20 m M phosphate, 8% 2-butanol, and 0.001% hexamethonium bromide at pH 11.95, and the stacking was carried out at 2 kV for 240 s. These conditions allowed up to 2000-fold preconcentration of the selected phenols. No matrix removal was necessary.

Characterization and identification of a “mystery” oil spill from Quebec (1999)

This paper describes a case study in which advanced chemical fingerprinting and data interpretation techniques were used to characterize the chemical compositions and determine the source of an unknown spilled oil from Quebec. On 28 February 1999, significant amounts of oil was reported on the river banks of St. Laurence River in front of a company named “Thermex” (in a town – Beauharnois, Quebec, about 50 km northwest of Montreal). The spilled oil was suspected to be released from a nearby factory. In response to this specific site investigation needs, a tiered analytical approach using GC–MS and GC–flame ionization detection was applied. A variety of diagnostic ratios of “source-specific marker” compounds, in particular isomers of biomarkers and alkylated series of polycyclic aromatic hydrocarbons within the same alkylation groups, were determined and analyzed. The hydrocarbon analysis results reveal the following: (1) the spilled oil is very “specific”, and is significantly different from most crude oils in chemical composition; (2) the oil in samples come from the same source, however, the spill sample 2569 was identified to contain a small amount (∼10%) of diesel; (3) the spilled oil was relatively “fresh”, its chemical composition has not undergone significant alteration yet; (4) the spilled oil showed unusually high concentration of the US Environmental Protection Agency priority polycyclic aromatic hydrocarbons (PAHs). The “Pyrogenic Index” values were determined to be as high as 0.11–0.13, significantly higher than crude oils (<0.010) and heavy Bunker type fuels (0.015–0.060). This indicates significant contribution of PAH composition from pyrogenic components; (5) biomarkers were also detected, but their concentrations were unusually low in comparison to most crude oils.

Highly selective and efficient determination of US Environmental Protection Agency priority phenols employing solid-phase extraction and non-aqueous capillary electrophoresis

Non-aqueous capillary electrophoresis has been used in the separation of a complete list of 26 priority phenols included in the 8041 US Environmental Protection Agency method and the 76/464/EEC European Union directive. A highly selective and efficient separation was obtained when the background electrolyte used was 150 m M ammonium acetate dissolved in N-methylformamide–acetonitrile (75:25). Solid-phase extraction was successfully assayed as an enrichment strategy for the analysis of low-concentration samples. A styrene–divinylbenzene functionalized cartridge provided excellent recoveries of phenols from water samples at neutral pH. The limits of quantification obtained permit the application of the proposed method to the determination of priority phenols in wastewater samples.

Comparison of different drying, extraction and detection techniques for the determination of priority polycyclic aromatic hydrocarbons in background contaminated soil samples

Different drying (thermal, freeze-drying, chemical drying), extraction (soxhlet, sonication, KOH-digestion, mechanical shaking, supercritical fluid extraction (SFE), accelerated solvent extraction (ASE)) and detection techniques (high resolution gas chromatography–mass spectrometry (HRGC–MS), liquid chromatography–fluorescence detection (LC–FD)) were applied to real soil samples and their influence studied with respect to the final concentrations of the 16 PAHs included in the US Environmental Protection Agency Priority Pollutants List. Thermal and chemical drying were equally suited whereas applying freeze-drying naphthalene was partly lost. SFE and ASE turned out to be as efficient as classical extraction methods like soxhlet and mechanical shaking. Soxhlet extraction however, showed the smallest variations in the results. Recovery of PAHs after KOH-saponification were generally high as well but differences were rather high especially for the low molecular weight PAHs. Sonication proved to be a less efficient extraction technique. Due to the higher linear range of the MS compared to the fluorescence detector and practical considerations HRGC–MS was superior to LC–FD.

On-line coupling of immunosorbent and liquid chromatographic analysis for the selective extraction and determination of polycyclic aromatic hydrocarbons in water samples at the ng l −1 level

A method employing immunoaffinity chromatography for the selective extraction of polycyclic aromatic hydrocarbons (PAHs) from water was developed. An immunosorbent (IS) based on the immobilization of anti-fluorene antibodies on silica was coupled on-line with LC and applied to the selective extraction of PAHs from water samples. The procedure involves the use of a solubilizer to limit unwanted adsorption on vessels or tubing. Results show that a compromise has to be found between a good solubilization and limitation of the elution from the IS due to the addition of this modifier. The contribution of the selective antigen–antibody interaction to the retention mechanism is demonstrated. The on-line method was optimized for the six more volatile PAHs, and was also applied to the 16 PAHs included in the US Environmental Protection Agency priority list. The sensitivity of the fluorescence detection associated to the selectivity of the extraction sorbent allows one to detect PAHs between 2 and 10 ng l −1 from a sample volume as low as 20 ml. The presence of several PAHs at 20 ng l −1 in surface water was confirmed by spectral identification using diode array detection coupled in series with a fluorescence detector.

Sample stacking using field-amplified sample injection in capillary zone electrophoresis in the analysis of phenolic compounds

This paper discusses a simple on-column concentration with a field-amplified injection technique, using eleven US Environmental Protection Agency (EPA) priority phenols as model compounds. The capillary dimensions (lenght and internal diameter) for enhancing the on-column enrichment for phenolic compounds are studied. Under the proposed operational conditions, the detection limits ( S/ N=3) were in the ppb range, and the relative standard deviations for the compounds were between 1.4 and 8.8%. Field-amplified injections are preferred to off-line preconcentration methods because of their simplicity, rapidity and high enrichment factors.

Cyclodextrin-aided capillary electrophoretic separation and laser-induced fluorescence detection of polynuclear aromatic hydrocarbons (PAHs).

Two neutral cyclodextrins (CDs), hydroxypropyl-beta-CD (HP beta OD) and methyl-beta-CD (M beta CD), and two negatively charged forms, carboxymethyl-beta-CD (CM beta CD) and sulfobutylether-beta-CD (SB beta CD), were used to demonstrate the principle of separation of hydrophobic and non-charged polynuclear aromatic hydrocarbons (PAHs) by capillary electrophoresis (CE) based on differential partitioning of analytes between the CDs. The estimation of the partition coefficient (Ki) confirmed that the PAH components which partitioned most to the negative cyclodextrin (i.e. with the highest Ki) exhibited the longest migration time. The Ki values obtained for the CM beta CD-HP beta CD system are all below 1, indicating that the PAHs prefer to remain in the neutral HP beta CD. The Ki values for the SB beta CD-M beta CD buffer are all greater than 1, and cover a wider range, indicating preference of the PAHs for the anionic derivative. Methods were applied for separation of a PAH mixture containing various important PAHs on the US Environmental Protection Agency priority list. This novel procedure provided much better separation of PAH isomers, including benzo[a]pyrene and benzo[e]pyrene, than has been reported previously using CE. The system was applied to the sensitive determination of nanomolar levels of PAHs in contaminated soil.

Environmental aspects of PAH biodegradation.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants, some of which are on the US Environmental Protection Agency priority pollutant list. Consequently, timely clean-up of contaminated sites is important. The lower-mol-wt PAHs are amenable to bioremediation; however, higher-mol-wt PAHs seem to be recalcitrant to microbial degradation. The rates of biodegradation of PAHs are highly variable and are dependent not only on PAH structure, but also on the physicochemical parameters of the site as well as the number and types of microorganisms present. PAHs sorb to organic matter in soils and sediments, and the rate of their desorption strongly influences the rate at which microorganisms can degrade the pollutants. Much of the current PAH research focuses on techniques to enhance the bioavailability and, therefore, the degradation rates of PAHs at polluted sites. Degradation products of PAHs are, however, not necessarily less toxic than the parent compounds. Therefore, toxicity assays need to be incorporated into the procedures used to monitor the effectiveness of PAH bioremediation. In addition, this article highlights areas of PAH research that require further investigation.

Solid-phase extraction of polycyclic aromatic hydrocarbons from soil samples

A new solid-phase extraction (SPE) method was developed for the analysis of 16 polyaromatic hydrocarbons (PAHs) on the US Environmental Protection Agency priority list, in soil samples. Different types of SPE columns were tested and conditioning and elution steps were optimised. In the final procedure, soil samples are extracted with acetone and, after dilution with HPLC-grade water, loaded on a C 8 SPE column. After washing, all PAHs are eluted with tetrahydrofuran (THF). The final THF extract is analysed on an HPLC system for PAHs. Recoveries of the volatile PAHs, naphthalene, acephthylene and acenaphthalene were 80–90%. All other recoveries are comparable with standard liquid-liquid extraction (LLE) and range from 75 to 90%. The method is compared with the conventional LLE method for different types of real soil samples of a Dutch monitoring programme. Results indicate that SPE is a good method for the sample preparation for the analysis of PAHs in soil samples. Compared with LLE, correlation coefficients are better than 0.9 with relative standard deviations for SPE between 0.8 and 9.1%. LLE standard deviations ranged from 1.1 to 15.1%.