Gas Chromatographic Determination of Polycyclic Aromatic Hydrocarbons Kishan Bhatia Applied Research Laboratory, U.S. Steel Corporation, Monroeuille, Pa. 15146
SEVERAL REPORTS have been published (1-12) describing the use of gas chromatography t o separate and determine various polycyclic aromatic hydrocarbons, including the widely publicized carcinogen, benz(a)pyrene (BaP). None of them, however, describe a complete separation of BaP from its isomer, benz(e)pyrene (BeP). Only two of these reports (3, 12) describe a complete separation of benzpyrenes from benz(k)fluoranthene (BkF) and perylene by using capillary columns with silicone gum rubber SE-52 as the stationary phase. The capillary columns used were 163 feet (245 plates/foot) (3) and 212 feet (115-155 plates/foot) (12) long. In order t o separate these four compounds from each other, columns packed with phenylmethylsilicone (OV greases)coated glass beads or diatomaceous earth were investigated. This note reports the analysis of high-boiling polycyclic aromatic mixtures by using columns packed with OV-7 (20 phenylmethylsi1icone)-coated glass beads which were pretreated with dimethylchlorosilane.
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EXPERIMENTAL
Column Preparation. A typical column preparation procedure follows. Columns were made by packing copper inch in diameter by 20 feet or two tubing inch by 10 feet, joined in tandem) with OV-7-coated glass beads (60/80 mesh o r 100,420 mesh). OV greases and dimethylchlorosilanetreated glass beads were obtained from Supelco, Inc., Bellefonte, Pa., and Corning Glass Works, Corning, N . Y . , respectively. The coated packing material was prepared by adding glass beads (250 grams) to a methylene chloride solution (about 250 ml) of OV-7 (5.17 grams) and evaporating the solvent in a hood. The almost dry beads were left in a n oven at about 130 "C for 30 minutes. The resulting sticky product was vacuum-dried (about 1 Torr) at 250 "C for an hour. These coated beads were still sticky. A part of the OV-7 (about 4 grams) o n the beads was stripped off by immersing the coated beads for 10 minutes in 50 ml of methylene chloride, filtering the liquid through a glasswool plug, and washing the residue with a n additional 50 ml of methylene chloride. The air-dried residue was a free-flowing product containing about 0.4 OV-7, weight/weight (wtjwt). The columns were packed by gentle vertical tapping. The (1) H. J. Dawson, Jr., ANAL.CHEM.,36,1852 (1964). (2) A. Liberti. G. P. Cartoni, and V. Cantuti, J . Chromatogr., 15, 141 (1964). (3) V. Cantuti, G. P. Cartoni, A . Liberti, and A. G. Torri, ibid.. 17,60 (1965). (4) J. R . Wilmshurst, ibid., p 50. ( 5 ) G. C. Guvernator 111, F. L. Gager, Jr., E. W. Robb, and A. Barley, J . Gas Chrornatogr., 3, 363 (1965). (6) 0. T. Chortyk, W. S. Schlotzhauar, and R . L. Stedman, ibid., p 394. (7) E. Sawicki, T. W. Stanley, S. McPherson, and M. Morgan, Tulanta, 13, 619 (1966). (8) L. DeMaio and M. Corn, ANAL.CHEM.,38, 131 (1966). (9) B. B. Chakraborty and R . Long, Enciron. Sci. Techtiol., 1, 828 (1967). (10) J. H. Beeson and R . E. Pecsar, ANAL.CHEhi., 41, 1678 (1969). (11) B. H. Gump,J. Chromatogr. Sci., 7,755 (1969). (12) N. Carugno and S. Rossi, J . Gas Chromatogr., 5, 103 (1967).
packed columns were coiled and preconditioned a t 295 "C with helium flowing through them until a stable base line was attained (about 48 hours). Nearly fifty columns of various sizes ( l / 8 , l / ~ or , 3/8 inch in diameter and 10 t o 30 feet long) were packed with materials obtained by coating OV-1, OV-7, OV-17, Apiezon-L, or poly-m-phenoxylene o n glass beads o r a diatomaceous earth (Gas Chrom P, acid-base washed, 60/80 mesh). The coating weights were usually between 0.1 to 0.5% by weight. A conventional coating method (10) or the modification of it described above was used. Instrumental Conditions. All chromatographic data were collected on a Beckman gas chromatograph, Model GC-4, equipped with a dual-flame ionization detector system and a linear temperature programmer. The columns were run for 4 minutes at 170 "C, followed by a temperature rise of 6 "C/ min to 260 OC, and completed at 260 O C until the end of analysis. Peak areas were integrated by a Perkin-Elmer Model 154 printing integrator. Chemicals. Reference compounds and other chemicals were used as received from various suppliers. Only the major chromatographic peak was utilized, both qualitatively and quantitatively, for each standard. RESULTS AND DISCUSSION
Only columns producing adequate resolution (see below) between peaks due to BkF, BaP, BeP, and perylene are reported here. A chromatogram showing resolution of BkF, BaP, BeP, and perylene from each other, as well as from other polycyclic aromatic hydrocarbons and n-alkanes in a 24-component synthetic mixture, is shown in Figure 1. This chromatogram was obtained with a column (1/8-inch in diameter, 20-foot long) of OV-7 o n 60/80 mesh glass beads. The concentrations of individual components in this synthetic mixture varied from 1.2 to 1 7 S z with concentrations of BkF, BaP, BeP, and perylene being 2.7, 3.6, 2.9, and 3 . 4 z , respectively. Complete separation of benzpyrenes from BkF and perylene was realized o n two columns in tandem (each 1/8-inch in diameter, 10-foot long) of OV-7 o n 100/120 mesh glass beads, but the resolution between the two benzpyrene peaks was not as good as shown in Figure 1. Base-line separation of the two peaks due to the benzpyrenes was not realized, but the resolution obtained, Figure 1 (better than 70 % between the two nearly equal peaks), was considerably better than that previously reported, (3,9-11) and comparable to that reported by Carugno and Rossi (12) on capillary columns. This separation was adequate t o allow determination of each benzpyrene in synthetic mixtures containing as many as 30 components comprising tri-, tetra-, penta-, and hexacyclic aromatic compounds and n-alkanes with carbon numbers of 20, 22, 24, 28, 32, and 36. Relative response factors were determined by using pyrene as a n internal standard. The observed weight percentages were calculated by normalizing corrected peak areas. The observed values for BaP in two synthetic mixtures were 3.77 and 3.93 weight per cent, whereas the actual values were 3.6 and 3.8 weight per cent, respectively. In the analysis of synthetic mixtures, observed concentrations of most polyANALYTICAL CHEMISTRY, VOL. 43, NO. 4, APRIL 1971
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Figure 1. Gas chromatogram of a synthetic mixture of polycyclic aromatic hydrocarbons and n-alkanes Column: 60/80 mesh of glass beads coated with OV-7 Temperature program: 4 min at 170 " C ; 6 "C/minrise to 260 "C; at 260 "Cto end of analysis. (1) phenanthrene, (2) anthracene, (3) carbazole, (4) 2methylphenanthrene, (5) 3-methylphen1-methylanthracene, (7) fluoranthene, (8) pyrene, (9) anthrene, (6) 1-methylphenanthrene chrysofluorene, (10) 2,3-benzfluorene, (11) /?-tetracosane,(12) 1,2-benzanthracene,(13) chrysene, (14) n-octacosane, (15) benz(k)fluoranthene, (16) benz(a)pyrene, (17) benz(e)pyrene, (18) perylene, (19) 3-methylcholanthrene,(20) n-dotriacontane, (21) 1,2,5,6-dibenzanthracene, (22) 1,12benzperylene, (23) iz-hexatriacontane, (24) dibenz(a,i)pyrene. Portion of original chromatogram is shown in the insert to indicate more clearly the resolution between peaks 15,16,17, and 18
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cyclic aromatic hydrocarbons deviated from actual weights percentages by 3 to about 15 % of the amount present. The temperature conditions (170 to 260 "C) for OV-7coated glass bead columns were relatively milder than those reported for other columns found useful in separation of polycyclic aromatic compounds. OV-7-coated glass bead columns deteriorated rapidly when heated at 275 "C over extended periods. When columns were maintained at 160 "C and heated to 260 "C only during analysis, they were found useful for several months. A five-component synthetic mixture containing BkF, BaP, BeP, perylene, and pyrene was analyzed on several columns packed with coated glass beads on a diatomaceous earth. OV-1, OV-7, OV-17, Apiezon-L, and poly-m-phenoxylene were used as liquid phases. A conventional coating method (10) was used to prepare these column packing materials. For reasons not clearly understood, OV-7 columns prepared as described in the experimental section were found relatively more stable and produced better separations of BkF, BaP, BeP, and perylene than did OV-7 columns prepared by the cited conventional method. Columns packed with OV-7 coated glass beads (0.5 %, wtjwt) prepared by the conventional method (10) produced poor separation of individual components of synthetic mixture; peaks tailed and the resolution was considerably poorer than that shown in Figure 1 between peaks due to BkF, benzpyrenes, and perylene. These columns bled heavily when heated beyond 230 "C and they were found useless in 3 to 4 weeks. The resolution between
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the four peaks of interest obtained with columns packed with OV-7 coated Gas Chrom P (2%, wt/wt, conventional method) was somewhat better than that obtained with a similarly prepared column packed with OV-7 coated glass beads, but peaks tailed and, in our judgment, the separation was not good enough to obtain reliable quantitative results. Columns with OV-1, OV-17, Apiezon-L, and poly-m-phenoxylene also performed poorly in the separation of benzpyrenes and perylene. SE-30, which is a pure methylsilicone, affords poorer resolution between the four peaks due to BkF, benzpyrenes, and perylene than SE-52 which is a 5 % phenylmethylsilicone, so phenylation is beneficial (3, 12). As OV-7 has more phenylation (2073, it may be a cause of the observed better resolution. It is certainly not the only cause responsible for the observed resolution since a column prepared with OV-17 which is a 50% phenylmethylsilicone produced poor separation of benzpyrenes and perylene. Our experience indicates that column packing methods, which is an art by itself and methods of preparing column packing materials are significant factors influencing column performance. This method can be adapted to the analysis of airborne particulates and distillates containing polycyclic aromatic hydrocarbons. RECEIVED for review September 4, 1970. Accepted January 4,1971.
