Solid-Phase Analysis of Polycyclic Aromatic Hydrocarbonsby Fluorimetric Methods

LUIGI TARPANI, ANNALISA VOCCI, ROBERTA SELVAGGI, ROBERTO PELLEGRINO,FEDERICO RUSPOLINI, LUCA TAGLIERI, and LOREDANA LATTERINI*Dipartimento di Chimica, Universita di Perugia, Via Elce di Sotto, 8-06123 Perugia, Italy (L.T., A.V., R.S., R.P., L.L.); and INAIL–Direzione

Regionale per l’Umbria–Consulenza Tecnica Accertamento Rischi e Prevenzione, via G.B. Pontani, 12 - 06123 Perugia, Italy (F.R., L.T.)

Polycyclic aromatic hydrocarbons (PAHs) adsorbed on the surface of

particulates collected in a working environment have been analyzed using

fluorescence techniques. In particular, fluorescence measurements were

carried out directly on the sampling filters, in solid phase, and for

comparison, on the extract samples in solution. Fluorescence synchronous

acquisitions allowed the detection of signals from different PAH

compounds and, on the basis of the 0–0 transition energy, the assignment

of the emission signals to chemical structures. In particular, the

contribution of benzo-a-pyrene was easily detected and used to evaluate

the sensitivity of the measurements, which is a few nanograms per

milliliter, comparable with other analytical tools. The results of the

fluorimetric investigation were validated through the comparison with the

data obtained by gas chromatography (GC) analysis on the extracted

samples, which allowed identification of the PAHs and the quantification

of their distribution on the filters with different cut sizes. The agreement

between the two series of data led to the conclusion that fluorimetric

analysis directly on the sampling filter could be a new and cost-effective

approach for the analysis of PAHs.

Index Headings: Fluorescence; Laser-induced fluorescence; LIF; Polycyclic

aromatic hydrocarbons; PAHs; Benzo-a-pyrene; Particulates; Environ-

mental monitoring.

INTRODUCTION

Polycyclic aromatic hydrocarbons (PAHs) are semi-volatileorganic compounds generated by incomplete combustionprocesses of organic material, such as coal, gasoline, dieselfuel, and biomasses.1–3

PAHs are ubiquitous in the global environment and are moreconcentrated near urban areas.4,5 The most important sourcesof PAHs are road traffic,6 residential heating systems, andindustrial activities involving combustion. Other possiblesources of PAHs are tire wear debris, asphalt particles,7

crematoria,8 and tobacco smoking.9 PAHs are hazardouscompounds and eight of them are considered possiblecarcinogens,10–12 and in the polluted atmosphere they areassociated with particulate matter.13,14 Several studies of theparticle size distribution in the atmosphere15–19 have shownthat PAHs are adsorbed mainly on fine and ultra-fine particles(aerodynamic diameter , 0.1 lm), which can be taken up bythe bronchioles and alveoli of the lungs20,21 and cause short-and long-term effects for human health.10,22–24

It is particularly important to control PAHs concentrations inworking environments, such as places where digging opera-tions are carried out. The use of machines during diggingoperations is a valid need for workers. Nevertheless, the

exhaust from diesel engines remains airborne in the workplace,leading to an increase of polluted dust due to the adsorption ofPAHs on particulates generated from the diesel engine exhaustand from the milling or crushing of rocks and soil during thedigging activities. In order to lower the incidence and impact ofprofessional diseases, much attention has been paid tomonitoring and controlling the quality of working environmentatmospheres and hence PAHs concentrations.

In the literature, many methods for the determination ofparticle-bound PAHs are described.25 The conventionalmethods require multiple steps, the first of which is theextraction of PAHs from atmosphere particle matter by Soxhletextractors or alternatively by some modern extraction tech-nique, such as microwave-assisted extraction (MAE), sonica-tion, or pressurized liquid extraction (PLE); afterwards, theextracts are analyzed by gas chromatography/mass spectrom-etry (GC/MS) or by high-performance liquid chromatography(HPLC).23,26–28 These analytical methods are expensive andtime consuming. In fact, they require the use of solvents for theextraction of samples, producing large amounts of solventwaste, and preconcentration treatments of the extractionsolutions before analysis.

Generally, PAHs show good fluorescence quantum yields29

and fluorimetric techniques are extremely sensitive30–36 andselective for analyte determinations. Therefore, fluorescence isused as a detection tool for PAHs in high-performance liquidchromatography and in laser-induced fluorescence (LIF) ofvapor-phase PAHs at high temperatures.37,38 LIF allowsquantitative analysis of PAHs absorbed on quartz multi-channel polydimethylsiloxane traps.39 LIF coupled with fiberoptics has also been employed in the determination of PAHs incigarette smoke29 and naphthalene has been determined inair.40 More recently, the fluorescence assay using gasexpansion (FAGE) technique has been developed to monitorchemical pollutants in the atmosphere.41 However, the aboveoptical methods, although extremely sensitive, are based onexpensive and complicated instrumentation, which is difficultto install and maintain in a working environment.

The aim of the present study is to evaluate the feasibility of anovel, rapid, nondestructive, and solventless methodology forparticle-bound PAH determination, based on a steady-statefluorimetric analysis of particulate matter directly on thesampling filter, collected in a polluted working environment.

For this study, outdoor particulate matter (PM) samples werecollected in a road tunnel (Terni, Italy) during diggingoperations using PTFE membrane filters and a personalmedium volume sampler.

Seven PAHs (anthracene, benzo-[a]-pyrene, crysene, fluo-rene, naphthalene, phenanthrene, and pyrene) were identifiedon the basis of comparison with spectra in the literature andsolution measurements using the same experimental condi-

Received 26 April 2011; accepted 8 September 2011.* Author to whom correspondence should be sent. E-mail: loredana@unipg.it.DOI: 10.1366/11-06332

1342 Volume 65, Number 12, 2011 APPLIED SPECTROSCOPY0003-7028/11/6512-1342$2.00/0

� 2011 Society for Applied Spectroscopy

tions. The validation of the results by gas chromatography/mass spectrometry demonstrated the feasibility of in situanalysis, avoiding pre-analysis treatments and giving access tofaster responses.

MATERIALS AND METHODS

Chemicals and Solvents. Dichloromethane and n-hexanefor residue analysis were obtained from Fluka (Milwaukee,WI). The internal standard phenanthrene d10 (2000 lg/L),recovery standards pyrene d10 and fluorene d10, and thecertificate standard mixture included naphthalene, acenaphthy-lene, acenaphthene, fluorene, phenanthrene, anthracene, fluo-ranthene, pyrene, benzo-[a]-anthracene, chrysene, benzo-[b]-fluoranthene, benzo-[k]-fluoranthene, benzo-[a]-pyrene, in-deno-[1,2,3-cd]-pyrene, dibenzo-[a,h]-anthracene, and benzo-[ghi]-perylene (1000 ng/mL), purchased from Sigma-Aldrich.For the fluorimetric test analysis stock solution of eachcomponent in methylene chloride (10 lg/mL) was prepared(Sigma-Aldrich, ACS reagent, �99.5%).

Sampling. Sampling activities were performed during thedigging of a tunnel near Terni in Central Italy. The samplingdevice was designed to separate and collect aerosol by itsdimensional properties, as follows:42,43 a Sioutas CascadeImpactor provided five-step collection corresponding to 50%cut-points of 2.5 lm, 1.0 lm, 0.5 lm, and 0.25 lm on a 25 mmPTFE filter (SKC Cat. No. 225-1708) and a final step to collectthe particles below the ,0.25 lm cut-point on a 37 mm PTFEfilter (SKC Cat. No. 225-1709) equipped with a sample pump(mod. Leland Legacy, SKC Cat. No. 100-3002) capable ofmaintaining a constant flow rate of 9 L/min.

The entire sampling system was calibrated with a digitalcalibrator mod. DryCal DC-Lite. A sampling time of 240 minwas chosen to ensure a volume of about 2 m3 in order to avoidoverload of the impactor plates. At the same time, a samplingprocedure with a coupled system, PTFE filter–glass tubecontaining prewashed XA-D2 resin, was performed accordingto the NIOSH 5800 analytical method (NMAM, 2003). Thesampling site was placed at about 200 m from the tunnelentrance and 25 m from the digging operations, which werecarried out with the help of heavy machines (with dieselengines).

The site conditions were a temperature of 29 8C and relativehumidity of 60%.

Ultraviolet–Visible Absorption and Fluorescence Ana-lytical Procedure. Absorption and steady-state fluorescencespectra were recorded for both the PTFE filter and theparticulate suspension in dichloromethane after sonication for10 to 15 min.

Absorption measurements for the filters were carried outusing a Varian Cary 4000-DRA900 spectrophotometerequipped with an integrating sphere. The absorption spectraof the solutions were recorded with a Perkin Elmer Lambda 10spectrophotometer.

A fluorimeter (Spex Fluorolog) was used to recordfluorescence emission and excitation spectra using right-angleor front-face configuration between the excitation and theemission light for the solutions and the samples deposited onthe filters, respectively.

Fluorescence synchronous scans were carried out scanningthe excitation and the emission monochromator with an off-setof 20 nm and 1 nm band width using a front face configuration.Measurements were used to analyze the PAH mixtures on the

sampling filters and the results compared to the signalsobtained from standard solutions. This comparison allowedthe assignment of the signals to PAH structures.

Gas Chromatography/Mass Spectrometry AnalyticalProcedure. Ultrasound Assisted Extraction. Each filter wastransferred to a 10 mL vial; in each vial 5 mL ofdichloromethane and 10 lL of recovery standard solutions(pyrene d10 and fluorene d10, respectively, 792 ng/mL, 649ng/mL in dichloromethane) were added. The vials were thensealed and extraction was carried out by ultrasonication for 20minutes at room temperature. Afterwards, 2.5 mL ofsupernatant was reduced to about 100 lL using a gentlestream of nitrogen gas and then mixed with 10 lL of theinternal standard phenanthrene d10 (2000 lg/L) and immedi-ately analyzed.

Instrumentation. Quantification was performed on a gaschromatography 6890N coupled to a quadrupolar massselective detector 5975 Agilent Technologies (Santa Clara,CA). The gas chromatograph was equipped with a 30 m length,0.25 mm i.d. fused silica capillary column coated with 0.25 lmof 5% phenyl-methylpolysiloxane (DB5-MS, J&W Scientific,Folsom, CA). Helium (99.9995%, Rivoira, Milan, Italy) at aconstant flow of 0.9 mL/min was used as carrier gas. Thetemperature of the split/splitless injector was set to 290 8C. Thesample was introduced into the GC/MS system with a pressure-pulse injection. The injection port column head pressure washeld to 20 psi for one minute, using splitless injection. Analytewas introduced onto GC by using a 2.0 lL injection volume.

The following temperature program was used: 100 8C (2min) then increased at 158/min to 2008C, followed by anincrease at 58C/min to 3108C (isothermal for 12 min). Thetemperatures of the transfer line and ion source were 280 8Cand 200 8C, respectively.

The quantification of PAHs was performed using selectiveion monitoring (SIM). The GC/MS detector was calibratedwith five diluted standard solutions of sixteen PAH compoundsin the range of 0.1 to 10 ng. The analysis was replicated threetimes. Calibration curves obtained using five standardssolutions containing all the PAHs showed good linearity overthe entire range of concentrations with quadratic correlationcoefficients between 0.9966 and 0.9999. Analysis of dilutedPAH standard solutions showed that the limit of detection forindividual PAH compounds was between 0.02 and 0.08 ng.

The two recovery standards pyrene d10 and fluorene d10showed recovery efficiencies for PAH analysis between 99 and116%.

RESULTS AND DISCUSSION

Spectrophotometric and Fluorimetric Analysis. Thespectrofluorimetric measurements were carried out directly onthe collection filters and show the presence of organic materialat a detectable level in each sample. In particular, thespectrophotometric spectra are characterized by absorptionbands in the 250–450 nm region (Fig. 1). A definitive supportto the presence of PAHs was obtained by fluorescencemeasurements performed directly on the sampling filters. Thespectra recorded in the 300–450 nm range (Fig. 2) displayfluorescence signals upon excitation in the UV (wheregenerally all PAHs absorb) whose intensity and featureschanged with the filter under investigation, likely reflecting thePAHs distribution. In particular, the most intense signals wereobtained from the filters with smaller particle size, suggesting

APPLIED SPECTROSCOPY 1343

that in this sample a higher PAHs concentration is present.However, at this stage the fluorescence data recorded on filtersamples did not allow the assignment of the signals to chemicalstructures and the assessment of their concentrations. In orderto test the sensitivity and selectivity of the fluorimetric methodfor analytical purposes and compare the data with thoseobtained by GC analysis (see below), the spectrofluorimetricmeasurements were also carried out on the particulates inCH2Cl2 solutions once they have been extracted from thesampling filters. In these conditions, interferences from thefilters and scattered light can be excluded. The analysis of therecorded spectra allowed us to confirm the presence of thesame fluorescence emission signal (Fig. 3).

The comparison of the emission spectra of the desorbedmaterial with the fluorescence of common organic compoundsin the literature showed that the signal can be attributed to a

mixture of PAHs (e.g., naphthalene, anthracene, phenanthrene)absorbed on the surface of the particulate matter. The intensityvariation for the series of filters is due to differentconcentrations of PAHs. Despite the ease of detecting a signaleven at low concentrations, steady-state fluorescence measure-ments do not allow the immediate determination of a mixtureof aromatic hydrocarbons and assignment of the bandsunequivocally to a chemical structure.

Synchronous fluorescence scans (SFS) with a fixed wave-length difference (Dk) between excitation and emission arecommonly used to analyze mixtures of fluorophores and gaininformation on their optical properties and hence on theirchemical structure.35,36 The SFS collected from the samplingfilters present a broad band with a few enhanced peaks at 280,330, and 400 nm (Fig. 4).The SFS collected from the extractedsamples present a broad and less intense band in the region

FIG. 1. UV-Vis absorption spectra recorded directly from sampling filters.

FIG. 2. Fluorescence emission spectra recorded directly from sampling filterswith different dimension cuts.

FIG. 3. Fluorescence emission spectra of the extracts (from the PTFE filterswith different dimension cuts) in CH2Cl2 solutions.

FIG. 4. Synchronous fluorescence emission spectra (Dk = 20 nm) recordedfrom (A) the particulate directly on the sampling filter (pores , 0.25 lm); (B)the particulate extracted by a CH2Cl2 solution from the sampling filter (pores ,0.25 lm); and (C) standard solution in CH2Cl2 of fluorene (1), chrysene (2),phenanthrene (3), pyrene (4), anthracene (5), and benzo-[a]-pyrene (6).

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between 300 and 370 nm and another narrow peak centered at400 nm (Fig. 4B). The band at shorter wavelengths can beattributed to a mixture of the more volatile PAHs with a lowernumber of condensed conjugated rings (about 2 to 3). On theother hand, the narrow band at longer wavelengths is probablydue to PAH compounds with 0–0 singlet transition energy inthe range between 390 and 410 nm.

SFS experiments using standard solutions of selected PAHcompounds (on the basis of literature information35) werecarried out to better distinguish the fluorescence contribution ofthe different species absorbed on the particulate surface. Thecomparison of the scan features recorded on the standardssolutions (Fig. 4C) with those obtained from the extractsamples allowed the assignment of the signals at k � 300 nm tonaphthalene and fluorene; the band in the 310–360 nm regionis due to chrysene, phenanthrene, anthracene, and pyrene; and

the intense peak centered at 400 nm is due to benzo-[a]-pyrene.The intensity of the signals in the scans is affected by thefraction of the light absorbed by the single compound andhence by its concentrations, but the fluorescence efficiency hasto be taken into account. These data indicate that fluorescencedetection is suitable for PAH detection, and SFS acquisitionsallow easy separation of the contribution of benzo-[a]-pyrene,which is a marker for the carcinogenic risk of PAHs.44 In orderto evaluate the sensitivity of the fluorescence method in thesolid phase, the benzo-[a]-pyrene SFS signal was monitored asa function of its concentration. In particular, different benzo-[a]-pyrene concentrations were deposited on neat PTFE filtersfrom a standard solution and the SFS signal at 400 nm wasmonitored. The data reproducibility allows the determination ofthe sensitivity of the fluorimetric method, which was about afew nanograms per milliliter, as shown in Fig. 5. This value iscomparable with other analytical tools and allows previouslyreported45 solvent effects on PAH fluorescence signals to beneglected.

Investigations are currently in progress to calibrate thefluorescence procedure in the solid phase and to evaluate theeffects of the nature of the particulates (composition, size,density) normally present in the sampling filters on thesensitivity of the fluorescence measurements.

Chromatographic Analysis. In order to validate the resultsof the fluorimetric measurements, chromatographic analysis,which is a well-established analytical method for PAHs, hasbeen carried out on the extracts. Table I shows theconcentration distribution of PAHs in different size fractionsof the particulate matter, as determined by GC measurements.The concentration values shown in Table I are corrected by therecovery factor. The total PAHs concentration is 22.18 (ng/m3),about 50% of which is adsorbed on the PM , 0.25 fraction.The same distribution is observed for all PAHs analyzed,except for benzo-[k]-fluoranthene and acenaphthylene, whichare detected only in the bigger size fractions, although at verylow concentrations. The most concentrated PAHs are pyrene(5.39 ng/m3) and naphthalene (7.65 ng/m3).

The analysis of gas-phase PAHs, collected with the XAD-2resin, show that the total PAHs concentration is 166.58 ng/m3.The obtained results demonstrate that the most abundant are the

FIG. 5. Synchronous fluorescence emission signal (kobs = 400 nm; Dk = 20nm) recorded in the solid phase upon deposition on neat filters of differentbenzo-[a]-pyrene concentrations.

TABLE I. Concentrations of PAHs (ng/m3) determined by GC analysis in different particle fractions.

PAHs (ng/m3) PM

Particle diameter (lm)

R XAD-2 PTFE R2.5 1 0.5 0.25 , 0.25

Naphthalene 128 1.03 0.96 1.12 0.77 3.77 7.65 80.57 2.33 82.90Acenaphthylene 152 0.05 ,LOQ ,LOQ ,LOQ ,LOQ 0.05 17.97 0.09 18.06Acenaphthene 154 0.08 ,LOQ ,LOQ ,LOQ ,LOQ 0.08 10.73 0.26 11.00Fluorene 166.00 0.10 0.11 0.11 0.10 0.98 1.39 12.95 0.23 13.18Phenanthrene 178.00 0.24 0.26 0.27 0.31 0.87 1.95 23.65 1.28 24.93Anthracene 178.00 0.01 0.02 0.02 0.02 0.18 0.26 4.91 0.09 5.00Fluoranthene 202 0.22 0.23 0.26 0.32 0.78 1.81 2.45 0.83 3.28Pyrene 202 0.76 0.80 0.83 1.01 1.99 5.39 4.69 2.40 7.09Benzo-[a]-anthracene 228 0.02 0.01 0.02 0.02 0.26 0.34 0.92 0.20 1.12Chrysene 228 0.04 0.05 0.04 0.05 0.64 0.81 0.74 0.46 1.20Benzo-[b]-fluoranthene 252 ,LOQ ,LOQ ,LOQ ,LOQ 0.47 0.47 0.81 0.30 1.10Benzo-[k]-fluoranthene 252 0.03 0.01 ,LOQ ,LOQ ,LOQ 0.05 0.81 0.10 0.90Benzo-[a]-pyrene 252 ,LOQ ,LOQ ,LOQ ,LOQ 0.68 0.68 2.02 0.21 2.23Indeno-[1.2.3-cd]-pyrene 276 ,LOQ ,LOQ ,LOQ 0.05 0.24 0.28 0.98 0.28 1.27Dibenzo-[a.h]-anthracene 278 ,LOQ ,LOQ ,LOQ ,LOQ ,LOQ 0.00 1.04 0.11 1.15Benzo-[g.h.i]-perylene 276 0.05 0.06 0.04 0.09 0.73 0.97 1.33 0.57 1.90TOTAL PAHs 2.63 2.52 2.70 2.74 11.59 22.18 166.58 9.73

APPLIED SPECTROSCOPY 1345

lightest PAHs: naphthalene, acenaphthylene, acenaphthene,fluorene, and phenanthrene (Table I); thus, PAH abundance isinversely proportional to molecular weight. This is in agreementwith the fluorescence signals observed in the 300–400 nmregion, although their intensities might be affected by energytransfer processes as previously observed.45 The presence ofbenzo-[a]-pyrene has been confirmed by GC analysis in thesmaller dimension cut-filter with a 0.68 ng/m3 concentrationand gas-phase particulates. The obtained data definitely confirmthe high sensitivity of the fluorescence detection methods andthe possibility to use benzo-[a]-pyrene as a PAH marker due toease of detecting its fluorescence signal, which occurs at a lowenergy region (compared to other PAHs) resulting in its beingless affected by quenching processes.

CONCLUSIONS

In the present work polycyclic aromatic hydrocarbons(PAHs) adsorbed on the surface of particulates collected in aworking environment have been analyzed by gas fluorescencemethods in the solid phase, directly on sampling filters, and theresults were then compared to those obtained by chromatog-raphy (GC) in order to evaluate the feasibility of a fluorimetricanalysis of PAHs directly on the collection filters.

The fluorescence measurements were carried out directly onthe sampling filters and on the extracted samples. Thefluorescence spectra recorded on solid samples (directly fromthe sampling filters) revealed the presence of PAHs withdifferent structures and likely aromaticity and the intensity ofthe signals was strongly dependent on the filter cut, indicatingthat the distribution of the fluorescence compounds iscorrelated with the particulate size. Synchronous fluorescencescans in solid phase and in solution from the extracted samplesallowed distinguishing the signals of different compounds, andtheir assignment to chemical structures. In particular, synchro-nous acquisitions allow easy separation of the contribution ofbenzo-[a]-pyrene, which is a recognized marker for thecarcinogenic risk of PAHs in ambient air. The sensitivity ofthe fluorescence measurements in the solid phase was tested onbenzo-[a]-pyrene signals, obtaining a value (a few ng/mL)comparable with other analytical tools.

To validate the fluorimetric detection method, GC analysis wascarried out on the extract samples according to the standardizedprocedures and it allowed identification of the PAHs andquantification of their distribution on the filters with differentcut sizes, indicating that generally, all the PAHs are mainlyadsorbed on the particulates with smaller size likely due to thehigher surface/volume ratio of the particulate. The results were ingood agreement with the data obtained by fluorescence analysis.

These data indicate that fluorescence analysis on the solidphase directly on the sampling filters has enough sensitivity tobe used in PAH analysis in situ, avoiding the time waste andthe environmental impact of the solvent extraction procedures,although the fluorimetric procedures need to be furthervalidated and standardized in order to carry out quantitativeanalysis of solid samples on filters.

ACKNOWLEDGMENTS

This work was supported by the Universita di Perugia and by the Ministeroper l’Universita e la Ricerca Scientifica e Tecnologica (Rome, Italy).

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