Microheterogeneity evaluation of polycyclic aromatic hydrocarbons in particulate standard reference materials

With the emergence of highly sensitive analytical techniques, the microanalysis of natural-matrix materials employing smaller sample sizes is increasingly more common, which subsequently warrants a homogeneity assessment for the individual components at the appropriate sampling level. Pressurized liquid extraction (PLE) in combination with gas chromatography/mass spectrometry (GC/MS) has been used to determine the sampling constants and evaluate the relative homogeneity of trace levels of polycyclic aromatic hydrocarbons (PAHs) for two previously certified particulate standard reference materials, SRM 1649a Urban Dust and SRM 1650b Diesel Particulate Matter, in the milligram sampling range. Fluoranthene, pyrene, benz[a]anthracene and benzo[e]pyrene within SRM 1650b Diesel Particulate Matter were deemed to be homogeneous, based on relatively small sampling constants (K _S<100 mg), whereas the larger sampling constants (K _S>100 mg) obtained for all PAHs in SRM 1649a Urban Dust suggest more material heterogeneity. The material heterogeneity of ten individual PAHs (phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, benzo[k]fluoranthene, benzo[e]pyrene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene and benzo[ghi]perylene) was also described via nonlinear relationships (i.e., power law) between subsampling error S _s (%) and sample mass, which are used to predict analyte-specific minimum sample masses that result in a specific level of analytical uncertainty. Electronic supplementary material Supplementary material is available for this article at and is accessible for authorized users.     

Resolution of four k-region arene imines and mutagenicity of the optically pure aziridines

Racemic K-region imines of benz[a]anthracene, 7-methylbenz[a]anthracene, chrysene and benzo[a]pyrene ( 1–4 , respectively) have been resolved by high performance liquid chromatography on a column packed with amylose tris(3,5-dimethylphenylcarbamate) on silica gel. The absolute configuration of the resolved aziridines was assigned by comparison of their circular dichromism spectra to those of the corresponding enantiomerically pure arene oxides. The mutagenicity of the enantiomers of the arene imines was investigated using Salmonella typhimurium strains TA98 and TA100. Although all arene imines investigated were potent mutagens, quantitative and qualitative differences in the mutagenic activity were observed between enantiomers.     

Detection of Benzo[a]pyrene in Fried Food by Ultrasound-Assisted Matrix Solid-Phase Dispersion and Isotope Dilution GC–MS

A simple, sensitive and reliable analytical method was developed for the detection of benzo[a]pyrene in fried food using gas chromatography-mass spectrometry with an isotope-labelled internal standard. Samples were directly extracted and purified by the ultrasound-assisted matrix solid-phase dispersion (MSPD) procedure. The simple pretreatment procedures were tested with different absorbents (C18, NH₂, Oasis, and SiO₂). The optimal ultrasonication-assisted MSPD was achieved by MSPD-SiO₂ and sonication for 10 min in an ultrasonic bath. The samples were quantified using benzo[a]pyrene-d₁₂ as the internal standard. An analysis of the samples spiked with different levels of benzo[a]pyrene showed recoveries ranging from 84.6 to 103.2 %, with an RSD of 3.21–8.32 %, depending on the spiking level. This method was thus shown to be suitable for the detection of benzo[a]pyrene in fried food.

     

Fluorescence study of the solubilization of benzo[a]pyrene: application to its detection in coal washing waters

The solubilization of benzo[a]pyrene by organic solvents (dioxane, toluene and dichloromethane) and a surfactant (Triton X-100) was investigated. These media were successfully used for the determination of benzo[a]pyrene using fluorescence detection, with excellent limits of detection and large linear analytical ranges. Benzo[a]pyrene was detected in coal washing waters using liquid chromatography with fluorescence detection. The stability of this compound in dioxane was also examined.     

Improved efficiency of extraction of polycyclic aromatic hydrocarbons (PAHs) from the National Institute of Standards and Technology (NIST) Standard Reference Material Diesel Particulate Matter (SRM 2975) using accelerated solvent extraction

The efficiency of extraction of polycyclic aromatic hydrocarbons (PAHs) with molecular masses of 252, 276, 278, 300, and 302 Da from standard reference material diesel particulate matter (SRM 2975) has been investigated using accelerated solvent extraction (ASE) with dichloromethane, toluene, methanol, and mixtures of toluene and methanol. Extraction of SRM 2975 using toluene/methanol (9:1, v/v) at maximum instrumental settings (200 °C, 20.7 MPa, and five extraction cycles) with 30-min extraction times resulted in the following elevations of the measured concentration when compared with the certified and reference concentrations reported by the National Institute of Standards and Technology (NIST): benzo[b]fluoranthene, 46%; benzo[k]fluoranthene, 137%; benzo[e]pyrene, 103%; benzo[a]pyrene, 1,570%; perylene, 37%; indeno[1,2,3-cd]pyrene, 41%; benzo[ghi]perylene, 163%; and coronene, 361%. The concentrations of the following PAHs were comparable to the reference values assigned by NIST: indeno[1,2,3-cd]fluoranthene, dibenz[a,h]anthracene, and picene. The measured concentration of dibenzo[a,e]-pyrene was lower than the information value reported by the NIST. The measured concentrations of other highly carcinogenic PAHs (dibenzo[a,l]pyrene, dibenzo[a,i]pyrene, and dibenzo[a,h]pyrene) in SRM 2975 are also reported. Comparison of measurements using the optimized ASE method and using similar conditions to those applied by the NIST for the assignment of PAH concentrations in SRM 2975 indicated that the higher values obtained in the present study were associated with more complete extraction of PAHs from the diesel particulate material. Re-extraction of the particulate samples demonstrated that the deuterated internal standards were more readily recovered than the native PAHs, which may explain the lower values reported by the NIST. The analytical results obtained in the study demonstrated that the efficient extraction of PAHs from SRM 2975 is a critical requirement for the accurate determination of PAHs with high molecular masses in this standard reference material and that the optimization of extraction conditions is essential to avoid underestimation of the PAH concentrations. The requirement is especially relevant to the human carcinogen benzo[a]pyrene, which is commonly used as an indicator of the carcinogenic risk presented by PAH mixtures.     

Sample preparation of sewage sludge and soil samples for the determination of polycyclic aromatic hydrocarbons based on one-pot microwave-assisted saponification and extraction

A microwave-assisted sample preparation (MASP) procedure was developed for the analysis of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge and soil samples. The procedure involved the simultaneous microwave-assisted extraction of PAHs with n-hexane and the hydrolysis of samples with methanolic potassium hydroxide. Because of the complex nature of the samples, the extracts were submitted to further cleaning with silica and Florisil solid-phase extraction cartridges connected in series. Naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[e]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene, benzo[g,h,i]perylene, and indeno[1,2,3-cd]pyrene, were considered in the study. Quantification limits obtained for all of these compounds (between 0.4 and 14.8 μg kg⁻¹ dry mass) were well below of the limits recommended in the USA and EU. Overall recovery values ranged from 60 to 100%, with most losses being due to evaporation in the solvent exchange stages of the procedure, although excellent extraction recoveries were obtained. Validation of the accuracy was carried out with BCR-088 (sewage sludge) and BCR-524 (contaminated industrial soil) reference materials.     

Inhibitory analysis of the effect of polycyclic aromatic hydrocarbons on the activity of chitinase by means of liquid chromatography-mass spectrometry of chitin oligosaccharides

The analytical method of determining enzyme activity by liquid chromatography-mass spectrometry (LC/MS) was developed and applied for investigation of the effect of polycyclic aromatic hydrocarbons (PAHs) on the enzyme activity of chitinase. The measurement of chitinase activity by LC/MS is useful in order to use the nonderivatized substrate, which can show in vivo chitinase activity. Substrate consumption and product formation were monitored in order to determine chitinase activity. It was shown that, for the first time, in vitro addition of PAHs inhibited the activity of chitinase in a noncompetitive manner. The IC₅₀ value of benzo[a]pyrene was 1.4 μM, and PAHs containing four or more aromatic rings showed the same or higher inhibitory effect, whereas PAHs with a lower number of aromatic rings showed lower inhibition of the chitinase activity than benzo[a]pyrene.     

Selective accurate-mass-based analysis of 11 oxy-PAHs on atmospheric particulate matter by pressurized liquid extraction followed by high-performance liquid chromatography and magnetic sector mass spectrometry

An innovative analytical method based on high-performance liquid chromatography and atmospheric pressure chemical ionization magnetic sector mass spectrometry was developed and optimized to determine trace concentrations of 11 compounds belonging to the group of the seldom-analyzed oxy-PAHs (phenanthrene-9,10-dione, chrysene-5,6-dione, benzo[a]pyrene-4,5-dione, benzo[a]pyrene-1,6-dione, benzo[a]pyrene-3,6-dione, benzo[a]pyrene-6,12-dione, 4-oxa-benzo[def]chrysene-5-one, pyrene-1-carboxaldehyde, benzo[de]anthracene-7-one, benzo[a]anthracene-7,12-dione, and napthacene-5,12-dione) on airborne particulate matter (PM₁₀). The mass spectrometer was operated in multiple ion detection mode, allowing for selective accurate mass detection (mass resolution of 12,000 full width at half maximum) of the oxy-PAHs characteristic ions. Optimization of both the vaporizer (450 °C) and capillary temperature (350 °C) resulted into instrumental detection limits in the range between 7 (benzo[a]pyrene-1,6-dione) and 926 pg (benzo[a]anthracene-7,12-dione). The advanced pressurized liquid extraction (PLE) and the more traditionally used ultrasonic extraction (USE) were compared using ethyl acetate as an extraction solvent. For both techniques, high recoveries from spiked quartz fiber filters (PLE, 82–110%; USE, 67–97%) were obtained. Recoveries obtained from real PM₁₀ samples were also high (76–107%), and no significant matrix effects (ME) on the ionization process (enhancement or suppression) were found (ME, 89–123%). Method limits of quantification (S/N = 10) were in the range between 2 and 336 pg/m³. This method was used to analyze real PM samples collected at several urban and rural locations in the Antwerp area. For the first time, concentrations for Belgium are provided. Concentrations of individual oxy-PAHs are in the lower pictograms per cubic meter to 6 ng/m³ range. High concentration differences between individual compounds are found as exemplified by the 75th percentile of the phenanthrene-9,10-dione and benzo[de]anthracene-7-one concentrations being a factor of 4 to 22 higher compared with the other target oxy-PAHs.     

Synthesis and NMR characterization of a dioxa-analog of benzo[a]pyrene: The 1-benzopyrano[6,5,4-mna]-xanthene (1,6-dioxabenzo[a]pyrene)

1,6-Dioxabenzo[a]pyrene, the first dioxa-analog of benzo[a]pyrene, was synthesized from 5-methoxy-1-naphthol in an eight-step reaction involving two peri-heterocyclizations.     

Detection of Benzo[a]pyrene in Fried Food by Ultrasound-Assisted Matrix Solid-Phase Dispersion and Isotope Dilution GC–MS

A simple, sensitive and reliable analytical method was developed for the detection of benzo[a]pyrene in fried food using gas chromatography-mass spectrometry with an isotope-labelled internal standard. Samples were directly extracted and purified by the ultrasound-assisted matrix solid-phase dispersion (MSPD) procedure. The simple pretreatment procedures were tested with different absorbents (C18, NH₂, Oasis, and SiO₂). The optimal ultrasonication-assisted MSPD was achieved by MSPD-SiO₂ and sonication for 10 min in an ultrasonic bath. The samples were quantified using benzo[a]pyrene-d₁₂ as the internal standard. An analysis of the samples spiked with different levels of benzo[a]pyrene showed recoveries ranging from 84.6 to 103.2 %, with an RSD of 3.21–8.32 %, depending on the spiking level. This method was thus shown to be suitable for the detection of benzo[a]pyrene in fried food.     

Development and validation of a differential scanning calorimetry purity determination method for polycyclic aromatic hydrocarbons

Based on a standard test method for purity by differential scanning calorimetry (DSC), ASTM E 928, a purity determination method for highly pure polycyclic aromatic hydrocarbons (PAHs) has been developed and validated. The robustness of the developed method was investigated by determining, under varying measurement conditions, the purity of two PAH certified reference materials (CRMs), benzo[c]phenanthrene and dibenzo[a,h]anthracene. The repeatability and intermediate precision of the developed method was determined by analysing the purity of benzo[c]phenanthrene and dibenzo[a,h]anthracene and PAH candidate CRMs indeno[1,2,3-c,d]pyrene, 6-methylchrysene and benzo[a]pyrene. The trueness of the method was studied using the same (candidate) CRMs and a series of 42 other PAH CRMs. For each of the five (candidate) CRMs, a full measurement uncertainty budget was developed. Also for PAH materials for which the DSC purity determination method has not been explicitly validated, the relative expanded measurement uncertainty was estimated.     

Improvement of an automatic HPLC system for nitropolycyclic aromatic hydrocarbons: removal of an interfering peak and increase in the number of analytes.

An automatic HPLC system for analyzing nitropolycyclic aromatic hydrocarbons (NPAHs, nitroarenes) in airborne particulates was previously described (Anal. Chim. Acta, 2001, 445, 20). Some problems with this system were that it generated a peak originating from an ascorbic acid solution that elutes at a retention time close to that of 1,6-dinitropyrene (DNP), and that it was able to analyze only 1,3-, 1,6-, 1,8-DNPs and 1-nitropyrene (I-NP). Here, we describe an improved system that effectively removes the interfering peak by introducing an ODS column just after the pump for the ascorbic acid solution, and which is capable of analyzing several additional compounds (2-, 4-NPs, 2-nitrofluorene. 6-nitrochrysene, 7-nitrobenz[a]anthracene, 3-nitroperylene and 6-nitrobenzo[a]pyrene etc.). The improved sensitivities were achieved by concentrating the compounds in a benzene-ethanol extract from airborne particulates, by increasing the loading time of the sample solution from 20 to 38 min, and by increasing the flow rate of an ascorbic acid solution from 1.3 to 1.8 mL/min.     

Dibenzopyrenes,other PAHs with molecular weight 302, and selected carcinogenic PAHs seldom determined: identification and one-year quantification in urban air

The unambiguous identification in environmental samples of the potent carcinogen dibenzo[a,l]pyrene (DBalP) and the other DBPs (DBaeP, DBaiP, DBahP), whose evidence of carcinogenicity was recently re-evaluated by the International Agency for Research on Cancer (IARC), is an analytical challenge. This is attributed to their low concentrations in the environment and to the co-presence of several 302?MW isomers. In this study the four DBPs were identified in air, together with further four isomers with MW 302, based on an overall evaluation of five acceptance criteria. Their annual mean concentrations were quantified, for the first time to our knowledge. Thirteen other isomers were tentatively identified by comparison with previously published gas chromatographic profiles. The determinations were performed on PM10 samples collected every sixth day at a site in Rome, solvent extracted and analysed using GC/LRMS. The primary objective was to determine the mean DBP concentrations the population may be exposed to, and their consequent carcinogenic risks relative to benzo[a]pyrene (BaP) taken as a reference polycyclic aromatic hydrocarbon (PAH). The mean concentrations of DBalP, DBaeP, DBaiP and DBahP were, respectively, 0.014, 0.07, 0.02 and 0.01?ng?m^?3 (BaP: 0.65?ng?m^?3). Based on the available toxicity equivalence factors, DBalP contributed the carcinogenic risk of the PAH mixture by a factor of 2 relative to the risk attributable to BaP. DBaeP, DBahP and DBaiP contributed by, respectively, 11%, 1% and 0.3% of BaP. The instrumental conditions used to determine the 302?MW isomers allowed to unambiguously identify and to quantify other PAHs, ‘possibly carcinogenic’ to humans according to IARC, whose atmospheric concentrations reported in literature are scarce or missing: benzo[c]phenanthrene, 5-methylchrysene and benzo[j]fluoranthene (the latter being baseline resolved from isomers b and k). Finally, for completeness of information on PAHs recently upgraded by IARC to ‘possibly carcinogenic’, the concentrations of cyclopenta[cd]pyrene are reported.     

Solubility and partitioning studies with polycyclic aromatic hydrocarbons using an optimized SPME procedure

In order to determine the water solubilitiy (S _W) and octanol/water partition coefficient (K _OW) of polycyclic aromatic hydrocarbons, we have optimized the direct solid-phase microextraction (SPME) of selected compounds (fluoranthene (FLU), phenanthrene (PHE), pyrene (PYR), benz[a]anthracene (BaA), benz[a]pyrene (BaP), and coronene) from the matrices water and octanol-saturated water. By the use of a 100 μm polydimethylsiloxane fibre and magnetic stirring of the sample with glass-coated mini-impellers in combination with gas chromatography we obtained limits of determination (GC-MS) comparable to standard HPLC procedures. Only coronene could not be quantified. The determined S _W of FLU agree with reference data; for B[a]P we have obtained a 2 to 3 times higher value than described in recent literature. The obtained K _OW values are close to reference data for both single components. For a mixture of FLU, PHE, PYR, and B[a]A the measured K _OW values are 0.2–0.3 log units below tabulated values for the single components. Received: 22 July 1998 / Revised: 28 October 1998 / Accepted: 1 November 1998     

Solubility and partitioning studies with polycyclic aromatic hydrocarbons using an optimized SPME procedure

In order to determine the water solubilitiy (S _W) and octanol/water partition coefficient (K _OW) of polycyclic aromatic hydrocarbons, we have optimized the direct solid-phase microextraction (SPME) of selected compounds (fluoranthene (FLU), phenanthrene (PHE), pyrene (PYR), benz[a]anthracene (BaA), benz[a]pyrene (BaP), and coronene) from the matrices water and octanol-saturated water. By the use of a 100 μm polydimethylsiloxane fibre and magnetic stirring of the sample with glass-coated mini-impellers in combination with gas chromatography we obtained limits of determination (GC-MS) comparable to standard HPLC procedures. Only coronene could not be quantified. The determined S _W of FLU agree with reference data; for B[a]P we have obtained a 2 to 3 times higher value than described in recent literature. The obtained K _OW values are close to reference data for both single components. For a mixture of FLU, PHE, PYR, and B[a]A the measured K _OW values are 0.2–0.3 log units below tabulated values for the single components. Received: 22 July 1998 / Revised: 28 October 1998 / Accepted: 1 November 1998     

Evaluation of gas chromatography columns for the analysis of the 15 + 1 EU-priority polycyclic aromatic hydrocarbons (PAHs)

Three different stationary phases were investigated for the analysis of the 15 + 1 EU-priority polycyclic aromatic hydrocarbons (PAHs) by gas chromatography-mass spectrometry. In addition to the most commonly used 5% phenyl methylpolysiloxane, a mid-polar phase (50% phenyl methylpolysiloxane) and a recently commercialised mid-polar to polar phase (Optima® δ-6), were evaluated. Challenging groups of PAHs in terms of separation, such as the pair dibenz[a,h]anthracene-indeno[1,2,3,-cd]pyrene and the two groups benzo[b]fluoranthene-benzo[k]fluoranthene-benzo[j]fluoranthene and cyclopenta[cd]pyrene-benz[a]anthracene-chrysene, were satisfactorily separated by using the mid-polar phase. Moreover, discrimination in terms of peak height for the heaviest PAHs (caused from the strong interaction of these compounds with the stationary phase) was reduced without compromising the resolution of the other target analytes when applying the mid-polar phase in a tailor-made column geometry (20 m?×?0.18 mm internal diameter and 0.14 μm film thickness) in combination with optimised chromatographic conditions. A significant enhancement of the analytical sensitivity for dibenzopyrenes is demonstrated with an almost threefold increase of the signal-to-noise (S/N) ratio for dibenzo[a,h]pyrene, the last eluting PAH. The ability of the selected column to separate potentially interfering PAHs from the target analytes in both solvent solutions and food extracts is demonstrated.     

Development of single-chain variable fragment (scFv) antibodies against hapten benzo[a]pyrene: a binding study

Due to its highly carcinogenic and mutagenic effect on humans, a maximum tolerable limit of 10 ng/L of benzo[a]pyrene (B[a]P) in drinking water was set by the European Commission (Council Directive 98/83/EC). Although several polyclonal and monoclonal antibodies (mAb) for the detection of B[a]P and other polycyclic aromatic hydrocarbons (PAH) have been developed by others, a traditional enzyme-linked immunosorbent assay (ELISA) with a limit of quantification of 10 ng/L for monitoring B[a]P has not been developed. With this in mind, several single-chain variable fragment (scFv) antibodies were created using existing mAbs against the extremely hydrophobic hapten B[a]P, and their heavy and light chains recombined to make unique variable light (V_L) and heavy (V_H) chain combinations. Their binding behaviour was investigated using microtiter plate ELISA and surface plasmon resonance techniques. Specifically, the coding sequences for V_L and V_H chains of 10 murine anti-B[a]P antibody producing hybridoma cell lines were isolated by degenerate oligonucleotide primer sets, cloned in phagemid pIT2 and transferred into Escherichia coli HB2151. To systematically investigate the interaction of the V_L and V_H domains, three high-affinity B[a]P-specific and one nonspecific clone were selected and recombined to build a set of 16 different V_L and V_H combinations. On the basis of our data, it was shown that the V_H plays the major role for specific binding of B[a]P, whilst the V_L can, in some cases, increase the final sensitivity of the assay by one order of magnitude. Furthermore, the sequence analysis of scFvs indicates that the complementarity determining region H3 plays a major role in affinity, whilst cross-reactivity to seven other PAHs demonstrates the importance of the V_L in providing cross-reactivity.     

Analysis of CYP1A1 induction in single cells of urothelial cell populations by flow cytometry

As carcinogenesis is a process starting at the single-cell level it is desirable to study carcinogen-mediated effects in individual cells. A primary step in chemically induced carcinogenesis is the formation of reactive DNA-binding metabolites by cytochromes P450 (CYP). We applied indirect immunofluorescence to stain CYP1A1 in urothelial cells for quantification by flow cytometry. Our studies were carried out with metabolically competent primary porcine urinary bladder epithelial cells (PUBECs) and the human urothelial cell line 5637 for which we have previously demonstrated CYP1A1 mRNA induction by the polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (B[a]P) applying real-time RT-PCR. Flow cytometric analysis revealed that for PUBEC and 5637 cells the fraction of CYP1A1-induced cells increased with B[a]P concentration. Furthermore, in 5637 cells this effect was time-dependent, being more pronounced after 48 h than after 24 h. However, CYP1A1 induction could not be detected in all analyzed PUBEC and 5637 cells after treatment with up to 50 μM B[a]P. The reason for this remains unknown at the moment. Overall, B[a]P-treated cells could be divided into fractions of clearly CYP1A1-induced and clearly uninduced cells. Another fraction of “unclear” CYP1A1-induced cells and one of unclassifiable cells remained, as quantification of CYP1A1 induction by flow cytometry was hampered by B[a]P-related fluorescence. This is ascribed to phenolic B[a]P metabolites formed by CYP1A1 and which are known to fluoresce at wavelengths above 500 nm, whereas B[a]P does not. Overall, the method permits the detection of CYP1A1 protein level in large numbers of individual cells, thereby providing an adequate basis for statistical analyses. Flow cytometric detection of CYP1A1 induction in individual cells allows further insight into the metabolic competence of single cells and therefore could be a valuable tool for toxicological studies. Figure Flow cytometric analysis of immunostained PUBEC cells reveals that CYP1A1 is induced by B[a]P in a concentration-dependent manner Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Separation and analysis of nitroarenes from airborne particulate organic matter by HPLC and capillary GC-MS methods

Normal-phase HPLC has been applied to the separation of nitroarenes from dichloromethane extracts from airborne particulate matter samples collected in urban regions of Upper Silesia. GC-MS and capillary gas chromatography with NP detector analysis of the nitroarene fraction made it possible to identify and determine quantitatively those compounds which dominate in the organic matter emitted to the atmosphere in highly industrialized regions (2-nitrofluorene, isomeric nitroarenes of MW = 247, i.e. nitropyrene/nitrofluoranthene/nitroacephenanthrylene).     

Polycyclic arene sulfides. Preparation of 1a,2,3,11b-tetrahydrobenz-[5,6]anthra[1,2-b]thiirene, 6b,7a,8,9-tetrahydrobenzo[10,11]-chryseno[1,2-b]thiirene,and 7,8,8a,9a-tetrahydrobenzo-[10,11]chryseno[3,4-b]thiirene

The title compounds 5, 7 and 9 which are the first arene sulfides of 7,8-dihydrobenz[a]anthracene, 8,9-and 10,11-dihydrobenzo[a]pyrene, respectively, have been synthesized by treatment of the corresponding arene oxides 4, 6 and 8 with N,N-dimethylthioformamide in the presence of catalytic amounts of trifluoroacetic acid.