Polycyclic Aromatic Hydrocarbons In Aqueous Samples Research Articles

Development of hollow fiber-membrane microporous liquid–liquid extraction (HF-MMLLE) procedure based on palladium nanoparticles for determination of PAH in leached extracts

In this study, a new analytical methodology was proposed for the simultaneous determination of 16 polycyclic aromatic hydrocarbons (PAH) in leached extracts. This approach consisted of a new configuration based on hollow fiber-microporous membrane liquid–liquid extraction (HF-MMLLE) with palladium nanoparticles (Pd-NPs) impregnated in the pores of the membrane as part of the extraction phase. The analytes were separated and identified by gas chromatography coupled to mass spectrometry (GC–MS). The optimizations of the main extraction and desorption parameters were evaluated using univariate and multivariate strategies. The optimized extraction conditions were achieved with the use of 1-octanol solvent with the Pd-NPs as extraction phase, salt concentration adjusted to 5% (w/v of NaCl), 150 µL of acetonitrile as solvent of desorption, 70 and 30 min of extraction and desorption time, respectively. Satisfactory analytical performance was obtained with correlation coefficients greater than 0.9818, detection and quantification limits of 1.5 and 5.0 ng mL−1, respectively, for all analytes. Relative recoveries varied from 62 to 117%, intra-day precision from 0.3 to 18.3% and inter-day precision from 1.3 to 20.8%. The proposed method was successfully applied to three samples of leached extracts of residues provided by the petrochemical oil industry. The composers phenanthranene (5.6 ng mL−1 ± 8.8%) in leachate extract 1 and anthracene (6.1 ng mL−1 ± 4.8%) in leachate extract 2 were quantified. Leachate extract 3 did not present quantifiable analytes by the proposed method. The results of this approach can provide a simple, easy to prepare and economic strategy (in terms of solvent and sample consumption) for the determination of PAH in aqueous samples.

Selective Discrimination of Toxic Polycyclic Aromatic Hydrocarbons in Water by Targeting π-Stacking Interactions.

The development of highly sensitive and selective devices for rapid screening of polycyclic aromatic hydrocarbons (PAHs) in water is nowadays a crucial challenge owing to their alarming abundance in the environment and adverse health effects. Herein, inspired by the unique π-stacking interactions taking place between identical small aromatic molecules, a novel, generic, and straightforward methodology to electrochemically determine and discriminate such pollutants is described. Such a method is focused on covalently anchoring different PAHs on an indium tin oxide electrode surface by means of self-assembled monolayers. The surface-anchored PAHs act as recognition units to selectivity interact with a specific PAH target of the same nature. By tailoring the recognition platform with four different model PAH molecules (naphthalene, anthracene, pyrene, and fluoranthene) and carrying out an electronic tongue approximation, the selective discrimination and quantification of the selected PAHs in aqueous samples at ultralow concentrations were achieved impedimetrically, which were also validated using a certified reference PAH mixture.

Miniscale Liquid-Liquid Extraction Coupled with Full Evaporation Dynamic Headspace Extraction for the Gas Chromatography/Mass Spectrometric Analysis of Polycyclic Aromatic Hydrocarbons with 4000-to-14 000-fold Enrichment.

A new sample preparation approach of combining a miniscale version of liquid-liquid extraction (LLE), termed miniscale-LLE (msLLE), with automated full evaporation dynamic headspace extraction (FEDHS) was developed. Its applicability was demonstrated in the extraction of several polycyclic aromatic hydrocarbons (PAHs) (acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, and pyrene) from aqueous samples. In the first step, msLLE was conducted with 1.75 mL of n-hexane, and all of the extract was vaporized through a Tenax TA sorbent tube via a nitrogen gas flow, in the FEDHS step. Due to the stronger π-π interaction between the Tenax TA polymer and PAHs, only the latter, and not n-hexane, was adsorbed by the sorbent. This selectivity by the Tenax TA polymer allowed an effective concentration of PAHs while eliminating n-hexane by the FEDHS process. After that, thermal desorption was applied to the PAHs to channel them into a gas chromatography/mass spectrometric (GC/MS) system for analysis. Experimental parameters affecting msLLE (solvent volume and mixing duration) and FEDHS (temperature and duration) were optimized. The obtained results achieved low limits of detection (1.85-3.63 ng/L) with good linearity (r(2) > 0.9989) and high enrichment factors ranging from 4200 to 14 100. The optimized settings were applied to the analysis of canal water sampled from an industrial area and tap water, and this methodology was compared to stir-bar sorptive extraction (SBSE). This innovative combined extraction-concentration approach proved to be fast, effective, and efficient in determining low concentrations of PAHs in aqueous samples.

Condensed Phase Membrane Introduction Mass Spectrometry with Direct Electron Ionization: On-line Measurement of PAHs in Complex Aqueous Samples.

Polycyclic aromatic hydrocarbons (PAHs) are USEPA regulated priority pollutants. Their low aqueous solubility requires very sensitive analytical methods for their detection, typically involving preconcentration steps. Presented is the first demonstrated ‘proof of concept’ use of condensed phase membrane introduction mass spectrometry (CP-MIMS) coupled with direct liquid electron ionization (DEI) for the direct, on-line measurement of PAHs in aqueous samples. DEI is very well suited for the ionization of PAHs and other nonpolar compounds, and is not significantly influenced by the co-elution of matrix components. Linear calibration data for low ppb levels of aqueous naphthalene, anthracene, and pyrene is demonstrated, with measured detection limits of 4 ppb. Analytical response times (t10%–90% signal rise) ranged from 2.8 min for naphthalene to 4.7 min for pyrene. Both intra- and interday reproducibility has been assessed (<3% and 5% RSD, respectively). Direct measurements of ppb level PAHs spiked in a variety of real, complex environmental sample matrices is examined, including natural waters, sea waters, and a hydrocarbon extraction production waste water sample. For these spiked, complex samples, direct PAH measurement by CP-MIMS-DEI yielded minimal signal suppression from sample matrix effects (81%–104%). We demonstrate the use of this analytical approach to directly monitor real-time changes in aqueous PAH concentrations with potential applications for continuous on-line monitoring strategies and binding/adsorption studies in heterogeneous samples.

Monolithic graphene fibers for solid-phase microextraction

Monolithic graphene fibers for solid-phase microextraction (SPME) were fabricated through a dimensionally confined hydrothermal strategy and their extraction performance was evaluated. For the fiber fabrication, a glass pipeline was innovatively used as a hydrothermal reactor instead of a Teflon-lined autoclave. Compared with conventional methods for SPME fibers, the proposed strategy can fabricate a uniform graphene fiber as long as several meters or more at a time. Coupled to capillary gas chromatography (GC), the monolithic graphene fibers in a direct-immersion (DI) mode achieved higher extraction efficiencies for aromatics than those for n-alkanes, especially for polycyclic aromatic hydrocarbons (PAHs), thanks to π–π stacking interaction and hydrophobic effect. Additionally, the fibers exhibited excellent durability and can be repetitively used more than 160 times without significant loss of extraction performance. As a result, an optimum extraction condition of 40°C for 50min with 20% NaCl (w/w) was finally used for SPME of PAHs in aqueous samples. For the determination of PAHs in water samples, the proposed DI-SPME-GC method exhibited linear range of 0.05–200μg/L, limits of detection (LOD) of 4.0–50ng/L, relative standard deviation (RSD) less than 9.4% and 12.1% for one fiber and different fibers, respectively, and recoveries of 78.9–115.9%. The proposed method can be used for analysis of PAHs in environmental water samples.

Sorption of polycyclic aromatic hydrocarbons (PAHs) on glass surfaces

Sorption of polycyclic aromatic hydrocarbons (PAHs) to glass commonly used in laboratories was studied. Sorption coefficients ( K d ) of five selected PAHs to borosilicate glass surfaces were measured using column chromatography. A linear relationship between log K d and the corresponding water solubility of the subcooled liquid (log S w ) of the investigated PAHs was observed. Based on the determined sorption coefficients our data revealed that mass loss caused by sorption on glass walls strongly depends on the ratio of solution volume to contacted surface area ( V/ S). The influence of solution chemistry such as ionic strength, solution pH, presence of cosolvent, and the influence of temperature on the sorption process were investigated. In the presence of ionic strength, sorption coefficients concurrently increased but less than a factor of 2 up to 0.005 M calcium chloride concentration. However, further increasing ionic strength had no influence on K d . The cosolvent reduced sorption at a concentration of methanol in water above 0.5% (v/v); however, for benzo[a]pyrene even with 10% (v/v) methanol the mass loss would be still higher than 10% (with a V/ S ratio less than 0.25). Significant effects of the solution pH and temperature were not observed. These results suggest that van der Waal’s forces dominate the sorption process. In the analysis of highly hydrophobic PAHs in aqueous samples, mass loss due to sorption on glass walls should be accounted for in the final result if untreated glass is used. The presented relationship between log K d and log S w may help to decide if such a correction is necessary. Furthermore, the frequently used silanization of glass surfaces may not be sufficient to suppress sorption for large PAHs.

Nafion membrane-supported ionic liquid–solid phase microextraction for analyzing ultra trace PAHs in water samples

A Nafion membrane-supported ionic liquid (IL)–solid phase microextraction (SPME) coupled to gas chromatography (GC)–mass spectrometry (MS) technique for the simultaneous sampling and determination of ultra trace polycyclic aromatic hydrocarbons (PAHs) in aqueous samples has been developed. The hybrid IL–SPME fiber was precoated with Nafion membrane prior to IL film to enhance the amount and stability of IL film absorbed on the fiber. The analytes were extracted by the head space mode, and then directly desorbed in the injection port of GC–MS. The hybrid IL–SPME fiber was newly coated for each extraction, and the coating and washing out processes accomplished in a few minutes. The extraction efficiency between the IL–SPME fibers coated with and without Nafion-supported membrane for the five tested PAHs was compared. The results show that fibers coated with Nafion could extract two to three times more amount of analytes (based on peak area) than those without it. The extraction efficiency of three ILs (1-methyl-3-octylimidazolium trifluoromethanesulfonate: [C 8mim][TfO], 1-benzyl-3-methylimidazolium trifluoromethanesulfonate: [Bemim][TfO] and 1-methyl-3-phenylpropylimidazolium trifluoromethanesulfonate: [Phpromim][TfO]) was evaluated; [C 8mim][TfO] has the greatest extraction efficiency. The SPME experimental conditions, the extraction temperature, time and the salt effect were studied and optimized. Two natural water samples were used to evaluate this proposed method. Naphthalene, fluorene and anthracene were detected in sample 1 (29.7–70.0 pg mL −1), whereas fluoranthene and pyrene were below the detection limit (5 pg mL −1). For sample 2, all of the five PAHs were below the detection limit (4–5 pg mL −1). However, good spiking recoveries (80–110%) and repeatability (R.S.D. < 12%) were achieved. The results suggest that Nafion-supported IL–SPME has the potential for determining the ultra trace PAHs in aqueous samples.