Chemical analysis of polycyclic aromatic hydrocarbons by surface-enhanced Raman spectroscopy

The use of surface-enhanced Raman spectroscopy (SERS) for trace determination of polycyclic aromatic hydrocarbons (PAHs) is described. This paper focuses on the development of SERS-active substrates that are specific for the characterization and spectroscopic study of PAHs. The SERS-active substrates are based on thin gold films evaporated on a glass surface previously treated with a mercaptoalkylsilane. SERS of PAHs was investigated over uncoated gold island films and over such films coated with a self-assembled monolayer (SAM) of 1-propanethiol. Adsorption of PAHs on a plain SERS-active Au-film led to a surface-induced decomposition of PAHs, due to catalytic properties of nanostructured gold. Thus, the functionalization of the SERS-active substrates by means of SAM was done aiming at a specific chemical interaction toward PAHs. Thus, in addition to preventing decomposition of the PAHs, the coating also concentrates the hydrophobic PAHs close enough to the SERS-active interface. Results show that high sensitivity, SERS-active nanostructured gold substrates that show selectivity towards PAHs were obtained, with the following properties: strong intensification of the Raman signal, reproducibility, and stability over time. The employed methodology enables the observation of excellent Raman spectra of PAHs in aqueous environment at ppm levels.     

Highly sensitive and selective fluorescence optosensor to detect and quantify benzo[a]pyrene in water samples

We describe here a method for detecting and quantifying the highly carcinogenic polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (BaP) in water, based on a flow-trough optical sensor. The technique is fast (response time of 40 s) and simple and at the same time meets the standards of sensitivity and selectivity required by the European Guidelines on Water for Human Consumption. The optosensor is based on the on-line immobilization of BaP on a non-ionic resin (Amberlite XAD-4) solid support in a continuous-flow system. BaP was analyzed in a 15 mM H₂PO₄⁻/HPO₄²⁻ buffer solution with 25% (v/v) 1,4-dioxane at pH 7. Fluorescence intensity was measured at λ_ex/em=392/406 nm. The experimental conditions (reagent phase, pH, type and concentration of buffer solution and organic solvent) and flow-injection values (flow rate and injection volume) were carefully controlled. Under these conditions the optosensor was sensitive to a linear concentration range of between 3.0 and 250.0 ng l⁻¹ with a detection limit of 3.0 ng l⁻¹ and a standard deviation of 1.5% at 150 ng l⁻¹. The optosensor was applied to the quantification of BaP in drinking and waste water samples (95-105% recovery) in presence of the other 15 EPA PAHs at 1000 ng l⁻¹ concentration level. The influence of other fluorescent polycyclic aromatic hydrocarbons and potential interference from ions usually present in water was also evaluated.     

A selective method for the determination of benzo[a]pyrene in soil using porous graphitic carbon liquid chromatography columns

A back-flushing procedure using porous graphitic carbon (PGC) HPLC columns has been used successfully for the cleanup of soil samples for the determination of benzo[a]pyrene in ppb levels by an ODS-fluorescence HPLC column. The procedure was tested on nine random soil samples taken from an industrial area of the Kingdom of Bahrain. The mean percent recovery from the PGC column was 96% and the average coefficient of variation for the whole method was 5.2%.     

Headspace solvent microextraction and gas chromatographic determination of some polycyclic aromatic hydrocarbons in water samples

Headspace solvent microextraction (HSME) was shown to be an efficient preconcentration method for extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample solutions. A microdrop of 1-butanol (as extracting solvent) containing biphenyl (as internal standard) was used in this investigation. Extraction occurred by suspending a 3 μl drop of 1-butanol from the tip of a microsyringe fixed above the surface of solution in a sealed vial. After extraction for a preset time, the microdrop was retracted back into the syringe and injected directly into a GC injection port. The effects of nature of extracting solvent, microdrop and sample temperatures, stirring rate, microdrop and sample volumes, ionic strength and extraction time on HSME efficiency were investigated and optimized. Finally, the enrichment factor, dynamic linear range (DLR), limit of detection (LOD) and precision of the method were evaluated by water samples spiked with PAHs. The optimized procedure was successfully applied to the extraction and determination of PAHs in different water samples.     

The solid-matrix phosphorescence of (±)-anti-dibenzo[a,l]pyrene diol epoxide-DNA adducts and benzo[e]pyrene

New solid-matrix phosphorescence (SMP) methods for (±)-anti-DB[a,l]PDE-DNA adducts and B[e]P were developed. The methods can be used to detect and characterize (±)-anti-DB[a,l]PDE-DNA adducts and B[e]P by employing SMP spectra, intensities, and lifetimes acquired with the heavy-atom salt, TlNO₃, on Whatman 1PS paper. With the SMP data, a number of photophysical parameters were calculated such as biexponential SMP decay curves, pre-exponential factors, and fractional contribution to SMP decay curves. The SMP results were compared with earlier SMP data for (±)-anti-BPDE-DNA adducts and tetrol I-1. The SMP results show that small molecular-weight compounds like B[e]P can be readily detected and characterized by SMP. For example, the limit of detection for B[e]P was 0.60 pmol. Comparison of the SMP properties of the (±)-anti-DB[a,l]PDE-DNA adducts with earlier SMP data for the (±)-anti-BPDE-DNA adducts showed major differences in the SMP spectra, intensities, and lifetimes. The methods developed are important for the comparison of the SMP properties of different diol epoxides of PAH bonded to DNA.     

Fluorescence optosensor using an artificial neural network for screening of polycyclic aromatic hydrocarbons

This paper presents an optosensor for screening of four polycyclic aromatic hydrocarbons: anthracene (ANT), benzo[a]pyrene (BaP), fluoranthene (FLT), and benzo[b]fluoranthene (Bbf) using a photomultiplier device with an artificial neural network as transducer. The optosensor is based on the on-line immobilization on a non-ionic resin (Amberlite XAD-4) solid support in a continuous flow. The determination was performed in 15 mM H₂PO₄⁻/HPO₄²⁻ buffer solution at pH 7 and 25% of 1,4-dioxane. Feed forward neural networks (multiplayer perceptron) have been trained to quantify the considered Polycyclic aromatic hydrocarbons (PAHs) in mixtures under optimal conditions. The optosensor proposed was also applied satisfactorily to the determination of the considered PAHs in water samples in presence of the other 12 EPA–PAHs.     

Preliminary experiments for the analysis of tetrahydrotetrols of benz[a]anthracene and benzo[a]pyrene derived from their hemoglobin adducts using a coupled-column high-performance liquid chromatographic system

Improved technologies for the detection of polycyclic aromatic hydrocarbon adducts are required for human biomonitoring. Therefore, a coupled-column high-performance liquid chromatographic method, with system-integrated sample processing, has been developed and its applicability for determination of tetrahydrotetrols of polycyclic aromatic hydrocarbons in acid hydrolysates of human hemoglobin has been investigated. A novel column-switching technique applying ‘thermotransfer’ is used to separate tetrahydrotetrols of benzo[a]pyrene and benz[a]anthracene more efficiently. Derivatives of polycyclic aromatic hydrocarbons from blood hydrolysates are concentrated on a pre-column and then transferred to the analytical column by applying an electrical current to heat the solvent eluting the pre-column. This method allows for rapid and quantitative transfer of the analytes from the pre-column to the analytical column, after HPLC-integrated sample processing.     

Magnetic N-doped carbon nanotubes: A versatile and efficient material for the determination of polycyclic aromatic hydrocarbons in environmental water samples

This paper describes a new, efficient and versatile method for the sampling and preconcentration of PAH in environmental water matrices using special hybrid magnetic carbon nanotubes. These N-doped amphiphilic CNT can be easily dispersed in any aqueous matrix due to the N containing hydrophilic part and at the same time show high efficiency for the adsorption of different PAH contaminants due to the very hydrophobic surface. After adsorption, the CNT can be easily removed from the medium by a simple magnetic separation. GC/MS analyses showed that the CNT method is more efficient than the use of polydimethylsiloxane (PDMS) with much lower solvent consumption, technical simplicity and time, showing good linearity (range 0.18–80.00 μg L⁻¹) and determination coefficient (R² > 0.9810). The limit of detection ranged from 0.05 to 0.42 μg L⁻¹ with limit of quantification from 0.18 to 1.40 μg L⁻¹. Recovery (n = 9) ranged from 80.50 ± 10 to 105.40 ± 12%. Intraday precision (RSD, n = 9) ranged from 1.91 to 9.01%, whereas inter day precision (RSD, n = 9) ranged from 7.02 to 17.94%. The method was applied to the analyses of PAH in four lake water samples collected in Belo Horizonte City, Brazil.     

Application of sulfur microparticles for solid-phase extraction of polycyclic aromatic hydrocarbons from sea water and wastewater samples

The application of sulfur microparticles as efficient adsorbents for the solid-phase extraction (SPE) and determination of trace amounts of 10 polycyclic aromatic hydrocarbons (PAHs) was investigated in sea water and wastewater samples using high performance liquid chromatography coupled with an ultraviolet detector (HPLC–UV). Parameters influencing the preconcentration of PAHs such as the amount of sulfur, solution flow rate and volume, elution solvent, type and concentration of organic modifier, and salt effect were examined. The results showed that at a flow rate of 10 mL min⁻¹ for the sample solutions (100 mL), the PAHs could be adsorbed on the sulfur microparticles and then eluted by 2.0 mL of acetonitrile. For HPLC–UV analysis of extracted PAHs, the calibration curves were linear in the range of 0.05–80.0 μg L⁻¹; the coefficients of determinations (r²) were between 0.9934 and 0.9995. The relative standard deviations (RSDs) for eight replicates at two concentration levels (0.5 and 4.0 μg L⁻¹) of PAHs were lower than 7.3%, under optimized conditions. The limits of detection (LODs, <!-- no-mfc -->S/N<!-- /no-mfc --> = 3) of the proposed method for the studied PAHs were 0.007–0.048 μg L⁻¹. The recoveries of spiked PAHs (0.5 and 4 μg L⁻¹) in the wastewater and sea water samples ranged from 78% to 108%. The simplicity of experimental procedure, high extraction efficiency, short sample analysis, and using of low cost sorbent demonstrate the potential of this approach for routine trace PAH analysis in water and wastewater samples.     

Characterization of polycyclic aromatic hydrocarbons in environmental samples by selective fluorescence quenching

Selective fluorescence quenching is used to profile polycyclic aromatic hydrocarbons (PAHs) in samples of environmental origin. After separation by high-efficiency capillary liquid chromatography, the PAHs are detected by laser-induced fluorescence spectroscopy. Nitromethane is added to selectively quench the fluorescence of alternant PAHs, whereas diisopropylamine is added to quench nonalternant PAHs. The chromatograms in the absence and presence of fluorescence quenching are evaluated by means of the product moment correlation method to quantify the statistical similarities and differences. This method is demonstrated by application to three samples: a standard mixture of 16 priority pollutants, a coal-derived fluid, and a contaminated soil. The correlation coefficients (r) are typically 0.99 or higher for samples that are identical in origin, 0.90-0.50 for closely related samples, and less than 0.50 for samples that are distinctly unrelated. This method can be used to confirm with high statistical confidence the cause or source of an event with environmental impact, such as an oil leak or spill, contamination or waste by-products from petroleum fuel production and processing, etc.     

Fluorescence optosensors based on different transducers for the determination of polycyclic aromatic hydrocarbons in water

This paper presents the development of two optosensors for the determination of four polycyclic aromatic hydrocarbons (anthracene, benzo[a]pyrene, fluoranthene and benzo[b]fluoranthene) using a photomultiplier device and an intensified coupled charge device (ICCD) as optical transducers, respectively. These optosensors are based on the on-line immobilization of the analytes onto a non-ionic resin solid support (Amberlite XAD-4) in a continuous flow system, followed by the measurement of their native fluorescence. The determinations were performed using 15 mM H₂PO₄^-/HPO₄^2- buffer solution at pH 7 and 25% 1,4-dioxane. Detection limits were 6.4 and 9.3 for ANT, 3.3 and 2.5 for BbF, 1.4 and 13.2 for FLT, and 1.7 and 7.8 for BaP using optosensor 1 or 2, respectively. Relative standard deviations were 7.9 and 6.7 for ANT at 50 ng mL^-1, 3.5 and 7.4 for BbF at 60 ng mL^-1, 3.6 and 8.9 for FLT at 50 ng mL^-1, and 6.7 and 11.6 for BaP at 50 ng mL^-1 using optosensor 1 or 2, respectively. Finally, a critical comparison between the two configurations based on different transducers (photomultiplier and ICCD) for resolving and simultaneously determining mixtures of the polycyclic aromatic hydrocarbons under study in water samples (tap and mineral waters) were carried out.     

Particle-size distribution of polycyclic aromatic hydrocarbons in urban air in southern Spain

The size distribution of polycyclic aromatic hydrocarbons (PAH) was determined for airborne particles from a large city with high vehicular traffic. The analytical method was optimised and validated using NIST standard reference material (SRM 1649a Urban Dust). The 16 priority PAH listed in the US-EPA were Soxhlet-extracted from filtered particulate matter and then fractionated using on-column chromatography. The aromatic fraction was quantified by gas chromatography-mass spectrometry. Real samples of particles collected in Seville (Spain) were analysed using the validated method. Values for the total concentration of PAH in the air, as well as the concentrations of each PAH in six particle-size ranges were obtained. Values of the PAH in TSP, PM₁₀, PM_2.5 and PM₁ were assessed.     

Admicelle-enhanced synchronous fluorescence spectrometry for the selective determination of polycyclic aromatic hydrocarbons in water

A simple and rapid method for the highly sensitive determination of polycyclic aromatic hydrocarbons (PAHs) in water was developed. Benzo[a]pyrene, benzo[k]fluoranthene, perylene, and pyrene in water were concentrated into sodium dodecyl sulfate (SDS)-alumina admicelles. The collection was performed by adding SDS and alumina particles into the sample solution at pH 2. After gentle mixing, the resulting suspension was passed through a membrane filter to collect the SDS admicelles containing highly concentrated PAHs. The filter was placed on a slide glass and then covered admicellar layer with a fused silica glass plate before setting in a fluorescence spectrometer. Benzo[a]pyrene, benzo[k]fluoranthene, perylene, and pyrene were selectively determined by the synchronous fluorescence scan (SFS) analysis with keeping wavelength intervals between excitation and emission to 98, 35, 29, and 45 nm, respectively. Because of the minimum spectral overlapping, 1-40 ng l⁻¹ of benzo[a]pyrene, benzo[k]fluoranthene, and perylene as well as 10-150 ng l⁻¹ of pyrene were selectively determined with eliminating the interferences of other 12 PAHs. The detection limits were 0.3 ng l⁻¹ for benzo[a]pyrene, benzo[k]fluoranthene, and perylene, and 1 ng l⁻¹ for pyrene. They were 2-3 orders of magnitude lower than the detection limits in normal aqueous micellar solutions. The application to water analysis was studied.     

Sensitive determination of polycyclic aromatic hydrocarbons in water samples by HPLC coupled with SPE based on graphene functionalized with triethoxysilane

The graphene functionalized with (3‐aminopropyl) triethoxysilane was synthesized by a simple hydrothermal reaction and applied as SPE sorbents to extract trace polycyclic aromatic hydrocarbons (PAHs) from environmental water samples. These sorbents possess high adsorption capacity and extraction efficiency due to strong adsorption ability of carbon materials and large specific surface area of nanoparticles, and only 10 mg of sorbents are required to extract PAHs from 100 mL water samples. Several condition parameters, such as eluent and its volume, adsorbent amount, sample volume, sample pH, and sample flow rate, were optimized to achieve good sensitivity and precision. Under the optimized extraction conditions, the method showed good linearity in the range of 1–100 μg/L, repeatability of the extraction (the RSDs were between 1.8 and 2.9%, n = 6), and satisfactory detection limits of 0.029–0.1 μg/L. The recoveries of PAHs spiked in environmental water samples ranged from 84.6 to 109.5%. All these results demonstrated that this new SPE technique was a viable alternative to conventional enrichment techniques for the extraction and analysis of PAHs in complex samples.     

在线固相萃取-液相色谱法直接测定水中超痕量多环芳烃

建立了在线固相萃取-液相色谱直接测定水体中16种超痕量多环芳烃（PAHs）的方法。水样经高速离心后，加入适量甲醇，配制成40%（体积分数）甲醇水溶液，直接进样2 mL至在线固相萃取流路，进行萃取富集，再通过阀切换将洗脱的PAHs转移至分析流路进行分离检测。16种PAHs在各自范围内线性关系良好，相关系数均大于0.996；方法的检出限为0.14~12.50 ng/L，其中苯并[a]芘（B（a）P）的检出限为0.38 ng/L。实际水样在10、40和200 ng/L加标水平下的加标回收率为76.1%~134.9%，RSD为0.3%~16.6%。B（a）P在1 ng/L加标水平下的回收率为71.8%~92.7%，RSD为3.9%。结果表明，该方法操作简单，灵敏度高，溶剂消耗量少，可满足水样中PAHs，尤其是B（a）P的超痕量分析要求。     

Sensitive determination of polycyclic aromatic hydrocarbons in water samples using monolithic capillary solid-phase extraction and on-line thermal desorption prior to gas chromatography-mass spectrometry

A methacrylate-based monolithic capillary column has been evaluated for the preconcentration of polycyclic aromatic hydrocarbons (PAHs) from environmental water samples. For this purpose, the monolyte was in situ synthesized in a 6cm×0.32mm id fused-silica capillary. The microextraction unit was fitted to a micro-HPLC pump to pass 10mL of sample. The isolated pollutants were eluted by means of 10μL of methanol, the organic phase being directly collected in a specific interface that can be fitted to the injection port of the gas chromatograph without modification. The interface allows the on-line thermal desorption of the PAHs, avoiding the dilution and providing enough sensitivity to reach the legal limits established for these pollutants in the matrices selected. The limits of detection achieved for 10mL of water ranged between 2.8ng/L (indeno(1,2,3-cd)pyrene) and 11.5ng/L (acenaphthene) with acceptable precision (between 4.5 and 18.2% RSD). The method was applied to the determination of the selected PAHs in tap, river waters and sewage, being fluoranthene and pyrene detected in all of them at concentrations lower than the legal limits established for these compounds in the matrices assayed.     

Determination of trace amounts of polycyclic aromatic hydrocarbons in soil

A method for monitoring the contamination of soil with polycyclic aromatic hydrocarbons (PAHs) is introduced. Drying at elevated temperature is omitted to avoid losses of the more volatile constituents (primarily naphthalene). The soil sample, including its natural water content, is extracted with 2-methoxyethanol and cleaned up using a disposable C₈ cartridge and the PAHs are eluted with pentane, concentrated and measured by capillary gas chromatography with flame ionization detection. Determination limits between 15 and 35μg kg^?1 are obtained and the recovery is 80–90% measured at the 125 μg kg^?1 spike level, except for naphthalene (66%). Special attention is given to the design of the spiking technique, which simulates natural incorporation as far as possible, takes account of evaporation losses and therefore allows “real” recovery rates to be determined.     

Simplified procedures for the analysis of polycyclic aromatic hydrocarbons in water, sediments and mussels

We describe in this paper simple and robust analytical protocols to determine the 16 polycyclic aromatic hydrocarbons (PAHs) of the US Environmental Protection Agency priority list in water, sediment and mussels. For water samples, eight different solid-phase extraction (SPE) sorbents have been compared and among them, C18 provided highest recoveries and limits of detection of 0.3-15 ng/L. For lyophilized sediments, Soxhlet and ultrasonic extraction were compared, and the last one permitted to recover all analytes with highest repetitivity and was validated by analysing a certified reference material. Finally, the analysis of mussels was undertaken using Soxhlet, ultrasonic and pressurized liquid extraction (PLE) and the performance of several clean-up steps are compared. Whereas for the former two, incomplete recovery or losses of some analytes were evidenced, PLE permitted a more efficient extraction and although alkaline digestion was necessary to remove coextracted compounds, the method gave acceptable recoveries and limits of detection of 0.5-7.7 microg/kg dry mass, as for sediments. In all cases, analysis was performed by gas chromatography coupled to mass spectrometry and internal standard quantification was performed using five deuterated PAHs. Each method performance is discussed for the three matrices analysed and the paper reports advantages and disadvantages of each for their routine application in monitoring programs.     

Development of multiwalled carbon nanotubes based micro-solid-phase extraction for the determination of trace levels of sixteen polycyclic aromatic hydrocarbons in environmental water samples

Micro-solid-phase extraction (μ-SPE) was developed for the determination of trace level of 16 United States Environmental Protection Agency priority polycyclic aromatic hydrocarbons (PAHs) in river water samples with gas chromatography-mass spectrometry (GC-MS). In the μ-SPE device, multiwalled carbon nanotubes was employed as sorbent and was packed inside an porous polypropylene membrane "envelope" whose edges were heat-sealed to secure the contents. The μ-SPE device was placed in a stirred sample solution to extract the analytes. The porous polypropylene membrane envelope in μ-SPE device acts as a filter to exclude potential interferences, such as eliminating or reducing the influence of particles that are bigger than the pore size. After extraction, analyte desorption was carried out with a suitable organic solvent under ultrasonication. Important extraction parameters were optimized in detail, including the selection and amount of sorbent materials, the extraction temperature and extraction time, desorption solvent and desorption time, amount of organic modifier, agitation speed and sample ionic strength. Under the developed extraction conditions, the proposed method provided good linearity in the range of 0.1-50 μg/L, low limits of detection (4.2-46.5 ng/L), and good repeatability of the extractions (relative standard deviations, <12%, n=5). The developed μ-SPE method was successfully applied to the extraction of PAHs in river water samples. The μ-SPE method was demonstrated to be a fast and efficient method for the determination of PAHs from environmental water samples.     

Trace level determination of polycyclic aromatic hydrocarbons in river water with automated pretreatment HPLC

A novel on‐line pretreatment pump‐injection HPLC system for polycyclic aromatic hydrocarbons is proposed. We report novel pump‐injection HPLC‐based on‐line SPE with a specially designed pretreatment column for the determination of trace amounts of chemical substances in surface water. Polycyclic aromatic hydrocarbons are well known for strong carcinogenicity and thus a severe concentration control is required for drinking water and/or river water, which is the main resource of tap water. We found it possible to detect ng/L levels of polycyclic aromatic hydrocarbons by using pump‐injection column switching HPLC with fluorescence detection. To avoid the phenomenon, in which polycyclic aromatic hydrocarbons can be often adsorbed on the surface of flow lines of HPLC by their highly hydrophobicity especially resin‐made parts in sample delivery pump, we employed “autodilution” device that provides reliable recovery and repeatability. Additionally, real water samples were collected and then the spiked polycyclic aromatic hydrocarbons were determined at ng/L levels.