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.     

Bioremediation of hydrocarbons contaminated waters and soils: monitoring by luminescent bacteria test

Bioremediation has proven successful in numerous applications to petroleum hydrocarbons or chlorinated aromatic hydrocarbons contaminated soils. There is increasing interest in application of biotoxicity tests for ecological assessment and for supporting management decisions for remediation. Luminescent assays, light-emitting bacteria in particular, can be a suitable tool for environmental analysis, and in vivo luminescence is a rapid and precise indicator of the toxic effects of xenobiotic on micro-organisms. In this study, three different strains of marine bioluminescent bacteria have been employed to follow the changes in biotoxicity occurring during the laboratory scale bioremediation of water and soil samples contaminated by hydrocarbons and collected at an industrial area. The degradation was made by hydrocarbons degrading bacteria, both of commercial sources and isolated from polluted water and soils. The samples were treated for 45 days. The toxicity of the samples, before and after the bioremediation, was determined directly on water samples or on the extracts of soil samples. The yield of extraction by different solvents (acetone, dioxane, ethanol and dichloromethane) was evaluated by the bioluminescent test. The measurements were carried out using a microplate format both for short time of contact (60?minutes, acute toxicity) and for longer time intervals (24 hours, chronic toxicity). The results have been expressed as percentage of inhibition with respect to the blank emission (100% emission). Original and treated samples have been analysed by gas chromatography to assess the hydrocarbons (C?>?12 and Poly Chlorinated Biphenyls, PCB) content. The autochthonous bacteria isolated from polluted samples proved less effective, due to the short time for selection in remediation activity with respect to the commercial ones, but their capacity to degrade long chain hydrocarbons was satisfactory. The presented laboratory study can be applied also in case of on-field conditions.     

Biological-chemical treatment of soils contaminated with exploration and production wastes

Oil-gas exploration and production (E&P) soils contaminated with total petroleum hydrocarbons (TPHs) have been tested for degradation by two different treatments: biological and chemical. Biological treatment includes the use of native microorganisms for transformation of the various hydrocarbons found in E&P soils. Degradation of TPH of 80 and 86%, was achieved for two different soils, respectively in control experiments. The effect of growth stimulants such as glucose, acetic acid, and valeric acid was examined on TPH degradation. Incorporation of inducer (valerate) enhanced the degradation up to 89 and 93%, for the two soils, respectively. A large portion (> 41%) of contaminant in one soil was comprised of compounds in the carbon range of C₁₀-C₁₆ and < 7% constituted carbon range of C₂₄-C_28. The degradation of C₁₀-C₁₆ compounds was higher (> 98%) as compared to C₂₄-C₂₈ compounds (< 75%). Likewise, the degradation rate was also higher (58 mg/kg/d) for lower compounds as compared to higher carbon range compounds (6.7 mg/kg/d). Experiments conducted on chemical treatment included the effect of chelators on stabilization of H₂O₂, comparative studies between buffer and water (used for soil preparation), and the effect of pH on TPH degradation. The rate of oxygen evolution from H₂O₂ was significantly reduced with use of either chelated iron or phosphate buffer using naphthelene as a model compound. Chemical treatment demonstrated a higher degradation of TPH from contaminated soils at pH 4.0 as compared to a pH of 7.0. More degradation was obtained with slurry prepared in phosphate buffer as compared to deionized water.     

Efficiency of Different Methods and Solvents for the Extraction of Polycyclic Aromatic Hydrocarbons from Soils

The efficiencies of supercritical fluid extraction (SFE), accelerated solvent extraction (ASE), Soxhlet, and ultrasonic extraction in the analysis of polycyclic aromatic hydrocarbons (PAHs) in soils were evaluated. Solvents with different polarity were used to extract the PAHs from two soils, one with high and one with low contamination level. ASE showed good results with all solvents almost independent of the solvent polarity and the best results with acetone-toluene (1 : 1). Ultrasonic extraction with acetone-toluene for the uncontaminated soil and acetone-ethanolamine for the highly contaminated also showed good recoveries. The time-consuming Soxhlet extraction with pentane or dichloromethane was less effective. The PAH recovery from SFE was related to the soil matrix or the contamination level. The best extraction conditions (CO 2 /10% pentane) are successful for the soil with a low contamination level and a high humic acid content whereas the extractions of the highly contaminated soil gave poor results irrespective of the solvent used.     

Natural Attenuation and Biosurfactant-Stimulated Bioremediation of Estuarine Sediments Contaminated with Diesel Oil

We evaluated the bioremediation, by natural attenuation (NA) and by natural attenuation stimulated (SNA) using a rhamnolipid biosurfactant, of estuarine sediments contaminated with diesel oil. Sediment samples (30 cm) were put into 35 cm glass columns, and the concentrations of the 16 polycyclic aromatic hydrocarbons (PAHs) prioritized by the US Environmental Protection Agency were monitored for 111 days. Naphthalene percolated through the columns more than the other PAHs, and, in general, the concentrations of the lower molecular weight PAHs, consisting of two and three aromatic rings, changed during the first 45 days of treatment, whereas the concentrations of the higher molecular weight PAHs, consisting of four, five, and six rings, were more stable. The higher molecular weight PAHs became more available after 45 days, in the deeper parts of the columns (20–30 cm). Evidence of degradation was observed only for some compounds, such as pyrene, with a total removal efficiency of 82 and 78 % in the NA and SNA treatments, respectively, but without significant difference. In the case of total PAH removal, the efficiencies were significantly different of 82 and 67 %, respectively.     

Ozonation of pyrene and benzo[a]pyrene in silica and soil –14C-mass balances and chemical analysis of oxidation products as a first step to ecotoxicological evaluation

Ozonation of polycyclic aromatic hydrocarbons (PAHs) in soil is a process that can be used for in-situ soil remediation or in combination with bioremediation techniques. First steps to a comprehensive ecotoxicological evaluation of this method is done by ozonation of radioactively labeled (¹⁴C) pyrene and benzo[a]pyrene in a silty soil (LUFA 2.2) under mass-balancing conditions and GC-MS analysis of aromatic ozonation products. ¹⁴C-Mass-balances for pyrene and benzo[a]pyrene (b[a]p) in soil showed that, apart from ¹⁴CO₂ formation, considerable percentages of both PAHs are oxidized to water soluble substances (20–30%) or to non-extractable or bound residues (10% for pyrene, 30% for b[a]p). TLC and GC-MS analysis of ozonation products extractable from artificially contaminated silica and soil by organic solvents revealed a large number of aromatic substances. PAH-quinones and ten ring fission products with formyl- and carboxy-groups of both pyrene and b[a]p could be identified.     

Comparison of immunoassay and gas chromatography-mass spectrometry for measurement of polycyclic aromatic hydrocarbons in contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are frequently encountered in the environment and may pose health concerns due to their carcinogenicity. A commercial enzyme-linked immunosorbent assay (ELISA), was evaluated as a screening method for monitoring PAHs at contaminated sites. The ELISA was a carcinogenic PAH (C-PAH) RaPID assay testing kit that cross-reacts with several PAHs and utilizes benzo[a]pyrene (BaP) as a calibrator. Soil samples were extracted with 50% acetone in dichloromethane (DCM) for analysis by ELISA and gas chromatography-mass spectrometry (GC-MS). The overall method precision was within ±30% for ELISA and within ±20% for GC-MS. Recovery data for spiked soils ranged from 46 to 140% for BaP as determined by ELISA. Recoveries data of the GC-MS surrogate standards, 2-fluorobiphenyl and chrysene, were greater than 70%. The GC-MS procedure detected a total of 19 priority PAHs (2-6-ring PAHs) including seven probable human carcinogens (4-6-ring B2-PAHs). The ELISA results were compared to GC-MS summation results for the total 19 target PAHs as well as for the subset of the seven B2-PAH compounds. For all soil samples, the PAH concentrations derived from ELISA were greater than the sum of B2-PAH concentrations obtained by GC-MS. ELISA determinations were also frequently greater than the results obtained by GC-MS for the total 19 PAH compounds. This discrepancy can be expected, since the ELISA is a screening assay for the detection of several related PAHs while the GC-MS procedure detects priority PAH compounds. Thus, only a subset of PAHs (e.g. 19 PAHs) in the soil samples were measured by GC-MS while additional PAHs, including alkylated PAHs, and PAH derivatives have been demonstrated to be cross-reactive in the C-PAH ELISA. Results of paired tests show that the PAH data from ELISA and GC-MS methods are significantly different (P<0.001), but highly correlated. The ELISA data had a strong positive relationship with the GC-MS summation data for the B2-PAHs as well as for the 19 PAHs targeted by the GC-MS method. Results indicate that the ELISA may be useful as a broad screen for monitoring PAHs in environmental samples.     

On the semi-quantification of polycyclic aromatic hydrocarbons in contaminated soil by an enzyme-linked immunosorbent assay kit

Polycyclic aromatic hydrocarbons (PAHs) are of environmental concern, for instance when found in contaminated soils at sites where industrial activities have occurred. For efficient screening of such soils, the commercially available enzyme-linked immunosorbent assay (ELISA) kit, the PAH RIS^c® soil test, can be used. However, the site-specific performance may vary due to differences in soil properties and contamination profiles. Hence, in this study we have examined various contributing factors to the total ELISA measurements uncertainties. These factors include contributions from co-extracted (non-target) compounds, the extraction efficiency and differences in cross-reactivity among the target analytes. Reference values were obtained through pressurized liquid extraction (PLE) and gas chromatography coupled to mass spectrometry (GC-MS) analysis. The results showed that the ELISA does not seem to respond to non-target compounds in the soil extracts to any large extent. Furthermore, high molecular weight PAHs were found to be more efficiently extracted with PLE than with methanol agitation, which is used for ELISA. If this, and the cross-reactivity of the individual PAHs, were taken into consideration, the ELISA and GC-MS results were in good agreement.     

Detailed analysis of petroleum hydrocarbon attenuation in biopiles by high-performance liquid chromatography followed by comprehensive two-dimensional gas chromatography

Enhanced bioremediation of petroleum hydrocarbons in two biopiles was quantified by high-performance liquid chromatography (HPLC) followed by comprehensive two-dimensional gas chromatography (GCXGC). The attenuation of 34 defined hydrocarbon classes was calculated by HPLC–GCXGC analysis of representative biopile samples at start-up and after 18 weeks of biopile operation. In general, a-cyclic alkanes were most efficiently removed from the biopiles, followed by monoaromatic hydrocarbons. Cycloalkanes and polycyclic aromatic hydrocarbons (PAHs) were more resistant to degradation. A-cyclic biomarkers farnesane, trimethyl-C13, norpristane, pristane and phytane dropped to only about 10% of their initial concentrations. On the other hand, C29–C31 hopane concentrations remained almost unaltered after 18 weeks of biopile operation, confirming their resistance to biodegradation. They are thus reliable indicators to estimate attenuation potential of petroleum hydrocarbons in biopile processed soils.     

Ozonation of pyrene and benzo[a]pyrene in silica and soil –14C-mass balances and chemical analysis of oxidation products as a first step to ecotoxicological evaluation

Ozonation of polycyclic aromatic hydrocarbons (PAHs) in soil is a process that can be used for in-situ soil remediation or in combination with bioremediation techniques. First steps to a comprehensive ecotoxicological evaluation of this method is done by ozonation of radioactively labeled (¹⁴C) pyrene and benzo[a]pyrene in a silty soil (LUFA 2.2) under mass-balancing conditions and GC-MS analysis of aromatic ozonation products. ¹⁴C-Mass-balances for pyrene and benzo[a]pyrene (b[a]p) in soil showed that, apart from ¹⁴CO₂ formation, considerable percentages of both PAHs are oxidized to water soluble substances (20–30%) or to non-extractable or bound residues (10% for pyrene, 30% for b[a]p). TLC and GC-MS analysis of ozonation products extractable from artificially contaminated silica and soil by organic solvents revealed a large number of aromatic substances. PAH-quinones and ten ring fission products with formyl- and carboxy-groups of both pyrene and b[a]p could be identified. Received: 11 March 1997 / Accepted: 25 April 1997     

The Importance of Long and Short-Term Air-Soil Exchanges of Organic Contaminants

Abstract

Retrospective analysis of archived soil samples collected and stored from long-term agricultural experiments in the UK has shown how soil organic chemical composition has changed over time. High molecular weight polycyclic aromatic hydrocarbons (e.g. benzo[a]pyrene) and polychlorinated dibenzo-p-dioxins and -furans have increased in concentration through this century as a result of cumulative atmospheric depositional inputs. Concentrations of polychlorinated biphenyls and low molecular weight hydrocarbons (e.g. phenanthrene) peaked in the late 1960s/early 1970s, but have declined subsequently. This reflects declining atmospheric inputs of these compounds and losses from surface soils by volatilisation back to the atmosphere and biodegradation. PCBs and low molecular weight PAHs exist predominantly in the vapour phase in air, whilst heavy PAHs and PCDD/Fs are predominantly particulate-bound. Outgassing from soils is probably the most important contemporary source of PCBs to the atmosphere in the UK. Future UK PCB air concentrations will presumably therefore be influenced (controlled) by the rate of desorption and outgassing, as soil and air concentrations move towards a condition of equilibrium partitioning. Archived soils collected and stored before the commercial manufacture of PCBs contain no PCBs indicating that there is no ‘natural production’ of these compounds. However, within a few hours of exposure to contemporary air these samples contain detectable quantities of PCBs. Short-term air-soil exchange, such as during soil drying in the laboratory, can lead to contamination of samples which contain low concentrations of PCBs and loss from samples which contain high concentrations.     

Cyclodextrin-enhanced in situ bioremediation of polyaromatic hydrocarbons-contaminated soils and plant uptake

In situ bioremediation of polycyclic aromatic hydrocarbons (PAH) polluted soils can be improved by the augmentation of degrading microbial populations and by the increase of hydrocarbon bioavailability. β-cyclodextrin (β-CD) significantly accelerate the induction of hydrocarbon biodegradation, but it is not still clear its effectiveness during final, slower stages of degradation. Moreover, it is yet not known if the PAH uptake from plants is influenced by the presence of CD. A field study was carried out by creating two plots (A and B). Diesel fuel was spread on the surface, and on plot B a commercial microbial consortium and β-CD were spread. Soybean was seeded in both plots. Soil samples were withdrawn every 10 cm layers from 0 to 60 cm depth, before fuel spreading, immediately after seeding and after soya harvesting. Chemical and microbial analyses were carried out throughout the process to characterize the soil and to determine residual PAHs. Soybean seeds were analyzed for PAH content. It was observed that β-CD induced a significant increase of PAH degradation rate. The microbial inoculum did not improve the degradation; biodegradation activity was strong in superficial layers, and some PAH leaching was observed, that was reduced by CD. The analysis of PAH in soyabeans revealed that an uptake of hydrocarbons occurred, and that it was more significant in plot B. This suggests that the β-CD-enhanced bioremediation process can further be improved by phytoremediation, that could also allow to simultaneously reach an additional profit from a non-food yield for biofuel production.     

Detailed chemical kinetic modeling of pyrolysis of ethylene,acetylene, and propylene at 1073–1373 K with a plug‐flow reactor model

This study examines the predictive capability of our recently proposed reaction mechanism (Norinaga and Deutschmann, Ind Eng Chem Res 2007, 46, 3547) for hydrocarbon pyrolysis at varying temperature. The conventional flow reactor experiments were conducted at 8 kPa, over the temperature range 1073–1373 K, using ethylene, acetylene, and propylene as reactants to validate the mechanism. More than 40 compounds were identified and quantitatively analyzed by on‐ and off‐line gas chromatography. The chemical reaction schemes consisting of 227 species and 827 reactions were coupled with a plug‐flow reactor model that incorporated the experimentally measured axial temperature profile of the reactor. Comparisons between the computations and the experiments are presented for more than 30 products including hydrogen and hydrocarbons ranging from methane to coronene as a function of temperature. The model can predict the compositions of major products (mole fractions larger than 10^?2) in the pyrolysis of three hydrocarbons with satisfactory accuracies over the whole temperature range considered. Mole fraction profiles of minor compounds including polycyclic aromatic hydrocarbons (PAHs) up to three ring systems, such as phenanthrene, anthracene, and phenylnaphthalene, are also fairly modeled. At temperatures lower than 1273 K, larger PAHs were underpredicted and the deviation became larger with decreasing temperature and increasing molecular mass of PAHs, while better agreements were found at temperatures higher than 1323 K. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 199–208, 2008     

Continuous Pressurized Solvent Extraction of Polycyclic Aromatic Hydrocarbons From Biosolids. Assessment of Their Lability in Soils Amended with Biosolids

An extraction method of polycyclic aromatic hydrocarbons (PAHs) from biosolids, based on continuous pressurized solvent extraction (PSE), was developed and optimized through an experimental design and followed by gas chromatography-mass spectrometry determination. From multivariate analysis, the optimum values for extraction variables were: extraction temperature, 110°C and dynamic extraction time, 42 min, by using a mixture of dichloromethane and acetone (1:1, v/v) as the extraction solvent at a flow rate of 1 ml min^?1. Under optimum extraction conditions, the detection limits for the analytes were between 0.01 and 0.14 mg kg^?1 with recoveries of between 50 and 126%, which were determined by analysis of certified reference material (Sewage Sludge PAH, LGC6182). The method was applied to assess the lability of PAHs in soils amended with biosolids. It was confirmed that a fraction of these compounds undergoes strong retention in the soil, probably due to interaction with humin material. On the other hand, the amount of PAHs extracted was significantly lower after the 30-day incubation process, which is clearly exacerbated in PAHs with molecular weight lower than 228. This effect observed in the four soils under study can be attributed to degradation of these compounds by soil and biosolid microorganisms.     

Biodegradation of Crude Oil from the BP Oil Spill in the Marsh Sediments of Southeast Louisiana, USA

The significant challenges presented by the April 20, 2010 explosion, sinking, and subsequent oil spill of the Deepwater Horizon drilling platform in Canyon Block 252 about 52 miles southeast of Venice, LA, USA greatly impacted Louisiana??s coastal ecosystem including the sea food industry, recreational fishing, and tourism. The short-term and long-term impact of this oil spill are significant, and the Deepwater Horizon spill is potentially both an economic and an ecological disaster. Microbes present in the water column and sediments have the potential to degrade the oil. Oil degradation could be enhanced by biostimulation method. The conventional approach to bioremediation of petroleum hydrocarbon is based on aerobic processes. Anaerobic bioremediation has been tested only in a very few cases and is still considered experimental. The currently practiced conventional in situ biorestoration of petroleum-contaminated soils and ground water relies on the supply of oxygen to the subsurface to enhance natural aerobic processes to remediate the contaminants. However, anaerobic microbial processes can be significant in oxygen-depleted subsurface environments and sediments that are contaminated with petroleum-based compounds such as oil-impacted marshes in Louisiana. The goal of this work was to identify the right conditions for the indigenous anaerobic bacteria present in the contaminated sites to enhance degradation of petroleum hydrocarbons. We evaluated the ability of microorganisms under a variety of electron acceptor conditions to degrade petroleum hydrocarbons. Researched microbial systems include sulfate-, nitrate-reducing bacteria, and fermenting bacteria. The results indicated that anaerobic bacteria are viable candidates for bioremediation. Enhanced biodegradation was attained under mixed electron acceptor conditions, where various electron-accepting anaerobes coexisted and aided in degrading complex petroleum hydrocarbon components of marsh sediments in the coastal Louisiana. Significant degradation of oil also occurred under sulfate-reducing and nitrate-reducing conditions.     

Effects of RAMEB on Bioremediation of Different Soils Contaminated with Hydrocarbons

The limiting factor of soil remediation is often the low accessibility of the pollutants.Laboratory experiments have been carried out to investigate the effect of the randomlymethylated cyclodextrin (RAMEB) on bioremediation of various types of soils spikedwith Diesel and transformer oil and also on actual site soils contaminated with poorlydegradable mazout. The contaminated soil in the aerobic solid phase microcosm-experiments was amended with nutrients and supplemented with different amounts of RAMEB. An integrated chemical-biological-ecotoxicological methodology was applied to follow the bioremediation. The laboratory study proved the bioremediation enhancing effect of RAMEB both on artificially contaminated soils and on actual site mazout contaminated soils. RAMEB activated soil microbes by improving the bioavailability of the contaminants and accelerating biodegradation. Efficacy of RAMEB was influenced both by contaminantand environment related factors, such as the type and concentration of the pollutinghydrocarbons and characteristics of the soil.     

Application of Biosurfactant from Sphingobacterium spiritivorum AS43 in the Biodegradation of Used Lubricating Oil

This study aimed at investigating the application of biosurfactant from Sphingobacterium spiritivorum AS43 using molasses as a substrate and fertilizer to enhance the biodegradation of used lubricating oil (ULO). The cell surface hydrophobicity of bacteria, the emulsification activity, and the biodegradation efficiency of ULO were measured. The bacterial adhesion in the hydrocarbon test was used to denote the cell surface hydrophobicity of the used bacterial species. The results indicate a strong correlation between cell surface hydrophobicity, emulsification activity, and the degree of ULO biodegradation. The maximum degradation of ULO (62 %) was observed when either 1.5 % (w/v) of biosurfactant or fertilizer was added. The results also revealed that biosurfactants alone are capable of promoting biodegradation to a large extent without added fertilizer. The data indicate the potential for biosurfactant production by using low-cost substrate for application in the bioremediation of soils contaminated with petroleum hydrocarbons or oils.     

Rapid assessment of the impact of microwave heating coupled with UV-C radiation on the degradation of PAHs from contaminated soil using FTIR and multivariate analysis

The presence and fate of polyaromatic hydrocarbons (PAHs) in the environment are receiving a great concern. In this study, three oil-contaminated soils (industrial area, Dukhan city, and artificial soils) were utilized to examine the effect of microwave (MW) heating and UV-C irradiation on the PAHs degradation. A rapid assessment of the impact was evaluated using Fourier transform infrared (FTIR) and multivariate analysis. The total organic matter values for the maximum PAHs reduction were evaluated based on the FTIR spectra of the contaminated soils followed with the principal component analysis (PCA). The results showed that the highest total organic carbon reduction was achieved for the industrial soil sample that required a high MW power and long MW exposure time. On the other hand, the Dukhan city soil sample, which has the lowest total organic carbon, required a high MW power and short MW exposure time followed by UV-C treatment for 20 min to reach the maximal FTIR transmittance reduction. The cluster analysis was also used to evaluate the impact of MW heating, and MW heating followed by UV-C irradiation on the degradation of PAHs. The PCA results of the industrial city sample showed that neither MW treatment (100% MW, 15 min exposure time) followed by UV-C treatment for 20 min nor 10 min is significantly different from the MW treatment (100% MW, 15 min exposure time). However, for the Dukhan sample, the UV-C treatment at 10 min after high MW power and long exposure time (100% MW, 15 min exposure time) was the most efficient treatment.     

Effect of drying conditions during sample pre-treatment on the determination of polycyclic aromatic hydrocarbons in soils

In the context of the entire analytical process, pre-treatment of soil samples is often inadequately considered although the reliability of the results is definitely compromised if the sample is not properly prepared. In this paper, the effect of drying conditions in soil sample pre-treatment on the determination of polycyclic aromatic hydrocarbons (PAHs) has been studied. A systematic approach has been adopted by varying soil type, drying temperatures and solvent polarity to highlight the effect on the analyte recovery; the relationship between PAH molecular structure and their evaporation process from soils is discussed. Experimental data demonstrate that, concerning temperature-assisted drying procedures, PAHs are divided in two distinct groups: PAHs lighter than pyrene, which are seriously affected by drying temperature; and heavier PAHs that can be considered as non-volatile compounds. For studies involving the analysis of lighter PAHs in environmental samples, working on as-received samples is necessary.     

Quantitative Measurements of Individual Polycyclic Aromatic Hydrocarbons in a Mixture by Coherent Anti-Stokes Raman Spectrometry

Abstract

Coherent anti-Stokes Raman spectroscopy (CARS) was used to obtain Raman spectra of selected polycyclic aromatic hydrocarbons (PAHs) composed of between three and seven fused rings when the compounds were pumped in the resonance and pre-resonance regions, a simple mixture of three PAHs could be optically separated through the wavelength selectivity of the resonant enhancement process. The spectrum from a component in the mixture and the spectrum of each pure component showed no significant differences when pumped at the same wavelength. Finally, lineshape analysis performed on the CARS spectra facilitated comparisons between classes of compounds and for quantitative purposes.