Anal. Chem. 1980, 52, 199-201
vatives and without significant changes in distribution of inorganic arsenic species.
(7) C. Feldman, Oak Ridge National Laboratory, Oak Ridge, Tenn., private communication, 1979.
Dennis E. T a l l m a n * Ali U. Shaikh
LITERATURE CITED (1) R. S. Braman, D. L. Johnson, C. C. Foreback, J. M. Ammons, and J. L. Bricker, Anal. Chem., 49, 621 (1977). (2) M. 0. Andreae, Anal. Chem., 49, 820 (1977). (3) A. U. Shaikh and D. E. Tallman, Anal. Chim. Acta, 98, 251 (1978). (4) A Toxic Substance List, U.S. Department of Health, Education and Welfare, Rockville, Md., 1972. (5) J. A. Cherri, A. U. Shaikh, D. E. Tallman, and R. V. Nicholson, J. Hydro/., in press, 1979. (6) C. Feldman, Anal. Chern., 51, 664 (1979).
199
Department Of Chemistry North Dakota State University North Dakota 58105
RECEIVED for review August 6, 1979. Accepted October 1, 1979. Financial support from the Environmental Protection Agency, R803727-01-1, is gratefully acknowledged.
Recovery of Polycyclic Aromatic Hydrocarbons Sorbed on Fly Ash for Quantitative Determination Sir: T h e characterization of the polycyclic aromatic hydrocarbon (PAH) content of fly ash is important because of the large amounts of fly ash emitted in electric power generation and the potential hazards of PAHs sorbed on finely sized particles. For a PAH analysis to be performed, the PAHs first must be extracted from the sample matrix. In the PAH analysis of a similar matrix, air particles collected by high volume air sampling, the Soxhlet apparatus is widely employed (e.g., 1-8) for extraction with solvents such as benzene, cyclohexane, or methanol. High intensity mechanical or ultrasonic solvent agitation (9-13), and hydrofluoric acid dissolution of air particulate pads (14)also have been reported for P A H extraction. T h e few published (15-18) analyses of fly ash for PAHs used Soxhlet extraction with benzene or cyclohexane, with no apparent consideration for P A H extraction recoveries. One group has mathematically modeled (19) the vapor phase sorption of PAHs by fly ash. Although the literature suggests that air particulate PAHs can be extracted with fairly good recoveries, we are aware of only one report (20) addressing the extraction behavior of fly ash PAHs. This paper describes further studies characterizing in greater detail the absolute extraction behavior of PAHs sorbed on fly ash. The findings should have considerable importance to the development of valid methods for quantifying PAHs on such highly sorptive matrices. EXPERIMENTAL Materials. Fly ash collected from the electrostatic precipitators of two coal-fired electric power generating plants (fly ashes A and B) were obtained from the EPAjORNL Chemical Repository (21), where they were stored at -28 "C in the dark in amber glass bottles until use. Benzene (Fisher Scientific Co., Atlanta, Ga.) was redistilled reagent grade. The 2,2-diphenyloxazole and 1,4-bis(5phenyloxazoly1)benzene (both from Packard Instrument Co., Downers Grove, Ill.), and toluene (Fisher Scientific Co., Atlanta, Ga.) were used as received. Carbon-14 (14C) labeled PAH and paraffin tracers of 9770 or greater purity were obtained from the following sources, with the noted specific activities: l-14Cnaphthalene (5.10 mCi/mmol), 7,10-14C-benzo[a]pyrene(18.3 mCi/mmol) (Amersham/Searle, Arlington Heights, Ill.); 5,6-14Cbenz[a]anthracene (57 mCi/mmol), 16,17-'4C-dotriacontane (52.5 mCi/mmol) (American Radiochemical Corporation, Sanford, Fla.); 9-'4C-phenanthrene (10 mCi/mmol) (ICN Chemical & Radioisotope Division, International Chemical & Nuclear Corp., Irvine, Calif.). The tracers were used as received to prepare tracer solutions in hexane with an activity of approximately 45 000 disintegrations per minute per milliliter of solution (dpm/mL). Extraction and Counting for PAH Ring Size Dependence, A 2-mL volume of a 45000 dpm/mL hexane solution of each I4C-labeled PAH and paraffin tracer was pipetted directly onto separate 3-g aliquots of fly ash A contained in 100-mL glass bottles. The bottles were gently shaken to mix the solutions with the ash, 0003-2700/80/0352-0199$01.00/0
and the solvents were allowed to evaporate at room temperature. Ten mL of redistilled benzene was added and the bottles were sealed with polyethylene-lined screw caps. Each bottle was suspended by a wire hanger approximately half-way into the water bath of a model A-600 Sondgen Automatic Cleaner (Branson Instruments, Inc., Stanford, Conn.) and was sonicated at full power at room temperature for 30 min. The ash was centrifuged to the bottom of the bottles using a Floor Model, size 2 centrifuge (International Equipment Co., Needham Heights, Mass.) with a 16.5-cm radius rotor head spinning at 1500rpm for 5 min. The supernatant liquid was pipetted off. Ten mL of fresh benzene was added, and the bottles were re-sonicated and centrifuged as before. Four to seven such extractions were performed. One mL of the supernatant from each extraction of each tracer was added to a 20-mL glass liquid scintillation vial containing 9 mL of a scintillation solution prepared by dissolving 15 g of 2,2-diphenyloxazole and 190 mg of 1,4-bisl5-phenyloxazolyl)benzene in 1 gallon of reagent grade toluene. Standards were prepared by pipetting 2 mL of each tracer into 8 mL of scintillation solution. Liquid scintillation analysis was performed on a Model C 2425 Packard Tri-Carb liquid scintillation counter (Packard Instrument Co., Downers Grove, Ill.) by counting at room temperature for 10 min, utilizing the automatic external standardization option and the 14C-countingchannel. Recoveries were calculated as a percentage of the tracer applied to the ash by dividing the measured activity of each sample by that of the corresponding standard. Extraction and Counting for the Tracer Activity Balance. Nine 3-g samples of fly ash B (samples a-i) were weighed into 20-mL glass vials. Six samples (a-f) were spiked by the addition of 5 mL of hexane containing 41 000 dpm of 14C-labeledbenzo[alpyrene. The vials were shaken vigorously, and the solvent was allowed to evaporate at room temperature. The dried ash was stirred thoroughly. Three ash samples (a-c) were ultrasonically extracted by adding 10 mL of redistilled benzene and sonicating for 30 s at room temperature with a model 350 sonifier (Branson Instruments, Inc., Stanford, Conn.) at the full power setting using a 0.5-in. 0.d. probe horn. The ash was settled by centrifuging the vials with a model PR-2 centrifuge (International Equipment Co., Needham Heights, Mass.) using a 15-cm radius rotor head spinning a t 1500rpm for 5 min. The supernatant was pipetted off, 10 mL of fresh benzene was added to the ash, and a second extraction was performed. The supernatant extracts were made up to 10 mL and triplicate 1-mL aliquots were analyzed for 14C activity in the presence of 12 mL of the toluene scintillator solution described previously. The activity remaining on the ash was determined by liquid scintillation analyses after burning the ash in a model B306 Sample Oxidizer (Packard Instrument Co., Downers Grove, Ill.). The procedure for burning the ash was to blend 200 mg of ash with an equal weight of powdered cellulose (Whatman, Clifton, N.J.) in a combustion cup followed by the addition of 200 pL of Combustaid (Packard Instrument Company, Downers Grove, Ill.). This sample was then burned for 2 min in the sample oxidizer and the liberated C02was absorbed with 5 mL of Carbosorb (Packard Instrument Company, Downen Grove, C 1979 American Chemical Society
200
ANALYTICAL CHEMISTRY, VOL. 52, NO. 1, JANUARY 1980 {
25 ,
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-
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Table I. W-BaP Activity Balance on Ash Spiking and Extractions
0
DOTR’ACONTANE
0
NAPHTHALENE
I
A
PHEYANTHRENE BENZ(a1ANTHRACENE
I
*
v BENZO(a1PYRENE
study tracer spiking
extraction
3
2
4
6
EXTRACTION NUMBER
Flgure 1. Ultrasonic extraction of PAH and paraffin radiotracers from
fly ash
Ill.). The adsorbed C 0 2 was washed into a scintillation vial along with 12 mL of Permafluor V (Packard Instrument Company, Downers Grove, Ill.) scintillator solution and subsequently was analyzed for 14C activity on the Model C2425 scintillation spectrometer. The control ash (g-i) and the labeled but unextracted ash (d-f) were analyzed for 14C activity in the same manner. Because the fly ash was not completely vaporized in the combustion basket of the oxidizer, the residue from each ash sample was burned a second time for 2 min to generate a second sample for analysis on the liquid scintillation spectrometer. After the second burning, a third sample was prepared by transferring the residue from the combustion basket to a scintillation vial and analyzing in the presence of 12 mL of the toluenebase scintillation solution. The three unextracted, spiked ash samples (d-f) were transferred to fresh vials and were homogenized by adding 10 mL of redistilled benzene, and ultrasonically extracting for 30 s as before. However, the benzene was left on the ash to evaporate at room temperature (now ash d’-f’). Samples of this reequilibrated fly ash (d’-f) were analyzed for ‘T activity using the Sample Oxidizer according t o the procedure described above. The glass vials which originally contained ashes d-f were examined for residual 14C activity by adding 12 mL of the toluene scintillator solution, capping and shaking the vials, and counting as described previously. Counting was repeated after further shaking and also ultrasonication.
RESULTS AND DISCUSSION A determination of the influence of extraction variables such as solvent, temperature, mass ratios of solvent/fly ash or tracer/fly ash were beyond the scope of this study. However, the extraction conditions employed here were chosen to represent the most efficient currently achievable by conventional solvent extraction, and were kept constant across the experiments. T h e cumulative extraction recovery of each radiolabeled PAH tracer in the ring size dependence experiment is plotted in Figure 1. Recovery of I4C-labeledbenzo[a]pyrene (I4C-BaP) was very low even after seven extractions, indicating the highly sorptive nature of fly ash toward PAHs. This result suggests t h a t PAH analyses of fly ash may be seriously in error if no recovery corrections are made. However, the most striking
step tracer solution added t o ash (a-f) tracer found on unextracted ash (d-f) tracer found on sonicated ash (d’-f’) tracer extracted from container walls (of d-f) total recovered tracer found in benzene extracts tracer found on extracted ash (a-c) total recovered
percentage “C-BaP recovery, av. t std. dev. “100”
86.5
i
2.8
98.3 i 3.6 1.3 2 0 . 2 99.6 25.2
t
0.03
73.6
i
3.6
_ _ I _ _
98.8
feature of the results was the obvious decrease in both rate of extraction and overall recovery with an increase in PAH ring system size. Whereas naphthalene and phenanthrene were extracted fairly efficiently, the decreases in recoveries were particularly pronounced above the three-ring PAHs. We have observed this same trend using other samples of fly ash and different extraction methods. A second important observation was that a saturated hydrocarbon of greater molecular weight than BaP or benzanthracene (BaA) was extracted from the ash much more rapidly and completely than either BaA or BaP. These results suggest a binding or strong association of the PAHs with the ash through a mechanism selective for aromatics, which we speculate a t the present as involving a a complex. Considering the enrichment of elements with complexing ability such as antimony, tin, or aluminum in the finer ash particles (22, 23), it seems possible that a strong association or even chemical bonding of the aromatics to the ash surface may occur. The only other study (20) of PAH sorption on ash, of which we are aware, suggested that the carbon content of the fly ash was the decisive factor in PAH extraction. T h a t study also reported the ring-size dependence of PAH extraction recoveries. However, the larger carbon content of their ashes (up to 25.6% vs.
