15,61-9 (1978). (25) Hammond. P. B.. Aronson. A. L.. Ann. N.Y. Acad. Sci.. 111. 595-611 (1963). (26) Staples, E. L. J., N . 2. Vet J., 3,39-46 (1955). (27) Singh, N. P., Thind, I. S.,Vitale, L. F., Pawlow, M., J.Lab. Clin.
Med., 87,273-80 (1976). (28) Odenbro, A.. Kihlstrom. J. E.. Toxicol. A .. n d . Pharmacol.. 39. 359-63 (1977). Received for review July 11,1978. Accepted October 18, 1978.
Analysis of Adsorption Properties and Adsorbed Species on Commercial Polymeric Carbons William L. Fitch and Dennis H. Smith’‘ Department of Genetics, Stanford University, Stanford, Calif. 94305 ~
_ _ _ _ _ _ _ _ ~
Research directed toward the analysis of polymeric carbon and materials adsorbed thereon is described. A new, simple method for measuring the adsorptivity of polymeric carbons, utilizing tritium-labeled benzo[a]pyrene, has been developed and used to compare the adsorptivities of 12 commercial polymeric carbons. Benzene/methanol extraction and analysis by combined gas chromatography/mass spectrometry (GC/ MS) indicate the presence of a series of oxidized polynuclear aromatic hydrocarbons (PAH) as adsorbates on certain commercial carbon black samples. Small amounts or no PAH were detected in extracts of active carbons, graphite, and several other carbon blacks. The implications of this work for the study of environmental polymeric carbons are discussed. Polymeric carbons (also called graphitic or elemental carbons) are defined as those materials which consist structurally of fused polycyclic ring systems composed predominantly of carbon. This definition encompasses a variety of polymers ranging in homogeneity from coal and soot to graphite, but excludes diamond. Polymeric carbons can be of natural origin (coal, graphite, soots from forest fires) or man-made (carbon blacks, fossil fuel derived soots, activated carbons). Polymeric carbons have been detected in all environments where they have been sought, including sediments ( I , 2), the moon ( 3 ) , and atmospheric particulates ( 4 ) . In spite of its widespread occurrence, very little is known about the environmental properties of polymeric carbon ( 5 ) . The physical processes which produce polymeric carbons (6, 7) will also produce the lower homologues, the polynuclear aromatic hydrocarbons (PAHs). These materials have known health effects (8) and are routinely monitored in a variety of environmental compartments. Of the commercial polymeric carbons, the soots such as lampblack and the carbon blacks used in rubber tire manufacture have been shown to contain adsorbed PAHs which are extractable with benzene. However, the finer particle size channel blacks used for pigments and the activated carbons used in water purification have not been shown to contain benzene-extractable PAH in appreciable quantities. The similarities in production methods for these different carbons have led to the suspicion that the small particle size channel blacks and activated carbon will contain adsorbed PAH, but that due to stronger adsorption these PAHs are not extractable by usual methods. This paper will describe our methods for measuring the adsorption of PAH by polymeric carbon samples and the analysis of adsorbed species on commercial samples of carbon. Present address, Department of Chemistry, Stanford University, Stanford, Calif. 94305. 0013-936X/79/0913-0341$01.00/0
@
Experimental Equipment. The gas chromatographs, mass spectrometer, and data analysis equipment routinely used in this laboratory have been described elsewhere (9,IO).Tritium was measured with a Packard Tri-Carb liquid scintillation counter. [3H]Benzo[a]pyrene (158 pCi/hg in benzene) was purchased from the Amersham Corp. Samples of polymeric carbons were obtained from commercial sources as indicated in Table I. Elemental analyses were performed by the Stanford Department of Chemistry Microanalytical Laboratory. Authentic samples of PAH and derivatives were obtained from Aldrich Chemical Co., Eastman Organic Chemicals, and Analabs Inc. All solvents were Baker “Resi-analyzed” grade. Measurement of Benzo[ alpyrene Adsorption. [3H]Benzo[a]pyrene solutions of specific activities 0.00123,0.0510, 1.37, and 158 &i/pg in toluene were prepared from the purchased solution and unlabeled benzo[a]pyrene. These solutions are stable for several months at room temperature if protected from light. Aliquots were added to 10.0 mg of the polymeric carbon sample in a small glass vial along with toluene to a final volume of 2.0 mL. Preliminary experiments indicated that the adsorption was slow, requiring several hours to reach equilibrium. For data collection, the adsorption experiments were left overnight prior to analysis. The solution was filtered through glass wool, and an aliquot of the filtrate was added to a scintillation vial containing Liquifluor scintillation fluid (New England Nuclear, 15 mL) for counting. The channel ratios method was used to correct the counts per minute for quenching. The equilibrium benzo[a]pyrene concentration in solution was then calculated from the specific activity. The concentration of adsorbed benzo[a]pyrene was calculated by subtraction using the known weights of carbon sample and benzo[a]pyrene added. Extraction and Analysis of Carbon Samples. A polymeric carbon sample ( 5 g) was extracted for 20 h in a standard soxhlet apparatus with benzene/methanol (9:l). The residue after removal of the solvent was weighed and dissolved in dichloromethane and the internal standard, 1,2,3,4-tetrachloronaphthalene (200 wg), was added. An aliquot of this solution was injected on a 6 ft X l / ~in. packed column of Dexsil 300 along with a mixture of hydrocarbon standards (C16, (220,C28, and C36, about 1pg each). The column was programmed from 120 to 300 OC a t 4 OC/min. A total of 500 mass spectra were recorded with a mass range of 40-450. For the higher molecular weight PAH present in certain extracts, it was necessary to record 700 spectra to a final temperature of 325 “C. Data Analysis. The raw data from the G C M S experiments were analyzed by the suite of computer programs, CLEANUP, TIMSEK, and SEARCH, which have been described elsewhere ( 9 , I I ) . The CLEANUP program produces “clean” mass spectra of components after subtracting background and resolving overlapping peaks. The TIMSEK program assigns relative re-
1979 American Chemical Society
Volume 13, Number 3, March 1979
341
Table 1. Polymeric Carbons Investigated name
source
channel 19 channel 18 channel 15 channel 13 channel 12 channel 10 channel 4 active 9 active 8 furnace lampblack graphite
b c b b b c b a d b a a
particle size, nm
trade name
Colour Black FW200 Neo Spectra AG Colour Black FW2 Special Black 5 Special Black 4 Neo Spectra Mark 111 Colour Black S160 DarcoG60 Norit A Corax L Lampblack Power Grade 38
13 13 13 20 25 14 20
23 44
