Adsorption isotherms of polycyclic aromatic ... - ACS Publications


behavior of asbestos with different PAHs. The term asbestos is applied to a group of natural mineral fibrous silicates such as chrysotile, crocidolite...
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Anal. Chem. 1984, 56, 1240-1242

(28) Vestal, M. L. Proceedings of the 2nd International Workshop on Ion Formation from Organic Solids, Muster: Benninghoven, A., Ed.: Sprlnger: Berlin, 1983;Springer Series in Chemical Physics, pp 246-263.

RECEIVED for review January 12, 1984. Accepted February

27, 1984. We wish to express our gratitude to the National Institutes Of for their support (Grant GM 28291). Parts of this paper were presented a t the 186th ACS National Meeting, Washington, DC, Aug 1983, papers 5 and 8, Analytical Chemistry Section.

Adsorption Isotherms of Polycyclic Aromatic Hydrocarbons on Asbestos Chrysotile by High-pressure Liquid Chromatography Hugues MBnard,* Luc Noel, Frank M. Kimmerle, Lyne Tousignant, and Maryse Lambert

Department of Chemistry, Universite' de Sherbrooke, Sherbrooke, Qu&bec,Canada J l K 2R1

A new technique to evaluate the adsorptlon of polycyclic aromatic hydrocarbons (PAHs) from solution In toluene on asbestos flber was studied by liquid chromatography. The length of the new column used Is only 3.5 cm and the applied flow Is 1 mL mln-'. The pressure applled on this column at 25 O C is about 18 MPa (2600 psi). The range of PAHs In the samples injected Into the column was from 10 nmol to 1000 nmoi, except for phenanthrene whlch was up to 10 pmol. We estimated Henry's constant at 25 and 40 OC and we noted that benzo[a]pyrene is more adsorbed, comparatively,than the other PAHs. We demonstrated the influence of the HPLC solvent dryness. We estimate an error of less than 5 % in reproduciblllty with another column. By this method It Is possible to produce an adsorption Isotherm more easily and rapidly than by static adsorptlon. The method may be used to test the carclnogenic potential of chemlcaliy treated fibers.

Polycyclic aromatic hydrocarbons (PAHs) constitute an important class of chemical pollutants, many of which are known or suspected carcinogens and mutagens ( 1 , 2 ) . Several industrial sources of these pollutants have been identified and another important source of these pollutants in the air is known t o be tobacco smoke (3). PAHs are among the main identified carcinogenic agents in polluted air and in tobacco smoke. Benzo[a]pyrene (B[a]P) has historically been used as an indicator of the environmental presence of PAHs but it should be stated that it may be subject to atmospheric transformations which severly limit the utility of B[a]P data in risk assessment ( 4 ) . I t is very important for us to ascertain if PAHs can be adsorbed on the surface of dust particulates such as on asbestos. We will not describe the mechanism by which dust particles probably adsorbed PAHs, but we only observe the behavior of asbestos with different PAHs. The term asbestos is applied to a group of natural mineral fibrous silicates such as chrysotile, crocidolite, amosite, etc. (5). These fibers are resistant to corrosion, heat, acids, weathering, etc., and their uses are very widespread. Unfortunately, it is now known that inhalation of asbestos fibers can cause very severe medical problems including asbestosis and mesothelioma (6, 7). Synergetic effects of some organical micropollutants when they are associated with asbestos pollution (8) have been clearly demonstrated. In this paper we will expose PAHs to chrysotile fibers under HPLC conditions. 0003-2700/84/0356-1240$01.50/0

EXPERIMENTAL SECTION Apparatus. The equipment used for this study included a Beckman HPLC, Model 100-A, coupled with a Altex Hitachi UV detector, Model 100-40,with a flow cell volume of 20 wL,a strip chart recorder (Varian Model 9176), and a integrator (HewlettPackard Model 3390 A). We have also used a 10.01 "C thermostated bath (Haake Model FE-2) and a refractive index (RI) detector Altex, Model 156, with an 8-pL cell. To fill the column we used a Haskel air-driven fluid pump. The column tubing, 4.6 mm i.d., is cut to a length of 3.5 cm with an internal diameter of 4.6 mm. Reagents. Benzo[a]pyrene (>98%), anthracene (199.9%), pyrene (299%), chrysene (95%), and fluoranthene (298%) were purchashed from Aldrich Chemical Co., Inc. Purified naphthalene was purchased from Fischer Scientific Co., phenanthrene (295%) from BDH Co., and fluorene from Eastman Kodak Co. (Caution: All of these products are potentially carcinogens (I).) Asbestos chrysotile of 369 pm average length and 12.9 m2 g-' of specific surface was isolated from Paperbestos 3 as described previously (9). Toluene and n-hexane were Accusolv-grade from Anachemia Co. Toluene was dried by molecular sieves (Type 3-A,Grade 564) from Fisher Scientific Co. Procedure. All solvents used for HPLC were treated by bubbling dried nitrogen gas in a 4-L bottle for a period of 15 min and then adding 40 g of molecular sieves. The solvents were vacuum degassed for 15 min. Asbestos chrysotile was heated at 110 "C for 6 h and put in a desiccator. The column and the precolumn were first dry packed with chrysotile fibers and then high pressure (52 MPa) was applied by an Haskel pump filled with n-hexane. The column was then put inside a thermostated casing and connected to the HPLC instrument. Eluent flow rate was 1 cm3 min-l. Different PAH concentrations from stock 5 X lo-' M solutions were prepared, except for phenanthrene which was prepared from a 5 x IO-' M stock solution. A liquid chromatograph was used with a sample loop of 20 pL, and the corresponding amounts injected were 10 nmol to lo00 nmol for the PAHs and 10000 nmol for phenanthrene. Chromatographic Measurements. Chuduk's method (IO) was used for the determination of adsorption isotherms. By this method, the curve of the adsorption isotherm is deduced according to the form of the extended side of the chromatographic peak under equilibrium conditions. Gibbs' adsorption value, ri,can be calculated by eq 1(i indicates the product) 1 ri = A

Cl

o

VR dci

where VR is the column retention volume (cm3per column), A is the surface area of adsorbent in the column (m2),and ci is the concentration of adsorbate in the mobile phase on the considered 0 1984 American Chemical Society

ANALYTICAL CHEMISTRY, VOL. 56, NO. 8, JULY 1984

1241

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8 00

6-

00 7

0.4

0.8

1.2

1.6

20

Figure 1. Chromatograms of different sample slzes of phenanthrene in toluene solution on asbestos flber by HPLC at 25 "C. Vertical arrows

indicate the injection points with a flow rate of the eluent, toluene, is 1 mL min-I. height of chromatogram (mol ~ m - ~ The ) . VR and ci values are expressed in terms of the recorder chromatogram according to

where ni is the amount, in moles, of the injected products in the column. Integral 11,is represented by the area ABCD (see Figure 1). Curve AB is connected to the peak maxima

Zl = J h ( l , - lo) dh

(3)

where, on the recorder chart, h represents the height peak, I , represents the distance between the injection point and the center of the maximum peak, and lo representa the distance of the elution of the dead volume. Integral Z2, eq 4, is the peak area Z2 = S i a hdl

(4)

0.4

0.8

1.2

1.6

2.0

C,(mmol/L)

11

where, on the recorder chart, 1, represents the distance from the injection point to the beginning of the chromatographicpeak and l2 represents the distance from the injection point to the end of the chromatographic peak. The number of moles, ni, in eq 2, is expressed by eq 5 CjWIZ

ni = hr

(5)

where h is the height of chromatographic peak (cm), is the chart speed (cm min-l), and w is the volume flow rate of the eluent (cm3 min-l) . By this method, it is possible to obtain Henry's constant Kr,c,i (cm3 m-2), as described by Chuduk et al. Henry's constant is obtained from the slope of the adsorption isotherm at very low ci values. Furthermore, the adsorption isotherm can be expressed in terms of equilibrium capacity, Q,

where m is the weight of asbestos filling the column. It is possible to transform Q, in ri by m ri = -Q, A Q,(mol g-' of adsorbent)depends on the equilibrium concentration C, (mol L-' of solutions).

RESULTS AND DISCUSSION In Figure 2 different adsorption isotherms of PAHs in toluene are given at 25 and 40 "C. These isotherms were

Figure 2. Different adsorption isotherms of PAHs in toluene at (A) 25 O C and (B) 40 "C: (1) benzo[a]pyrene, (2) fiuoranthene, (3) pyrene, (4) phenanthrene, (5) anthracene, (6) fluorene, (7) naphthalene.

obtained by HPLC and the plots were generated by a computer (Apple 11). We note that the isotherms are very similar at 25 and 40 "C but the adsorption at 25 "C is a little stronger than the one a t 40 "C. On the other hand, the adsorption is stronger with an increasing number of aromatic rings. Compared to the other PAHs, B[a]P is more highly adsorbed a t the surface of the asbestos fibers; furthermore it is the most carcinogenic PAH among those that we have studied. In Figure 3, we show the effect of solvent dryness on the results for phenanthrene at 40 "C. Isotherm 1was obtained with very dry toluene; i.e., 24 h before use, the solvent received 40 g of molecular sieves and we protect the surface of the toluene with a continuous current of dry nitrogen gas to avoid contamination by atmospheric moisture. Curves 2 and 3 show the influence of nitrogen gas flow over the solvent when this flow is not sufficient. Therefore, isotherm 4 has not received this nitrogen treatment; however the solvent is also of HPLC grade. In Figure 4, we used two similar columns. Curves 1 and 2 represent the effects of the first column and curve 3 represents the effects of the second column. With isotherms 1 and 2, we want to describe the influence of the dead volume on the time of elution, to. In curve 1we arbitrarily fix to at 0.40 min compared to the real value, 0.44min in 2. The real

1242 ANALYTICAL CHEMISTRY, VOL. 56, NO. 8, JULY 1984

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/

.2

A

,, L

002

008

006

CE (mrnoI/-)

0 10

Flgure 5. Adsorption isotherm of benzo[a]pyrene (curve 1 and 2) in toluene and curve 3 in benzene ( 1 1 ) .

0.2

Table I. Values of Henry's Constant for Adsorption from Solutions of PAHs in Toluene on Asbestos Chrysotile at 25 and 40 "C

cE (rnrnoi/L) Flgure 3. Effect of solvent dryness on the results for phenanthrene at 40 O C .

/'

t/ / 16

04

08

2.0

1.2

("(m

product benzo[a]pyrene fluoranthene pyrene phenanthrene anthracene fluorene naphthalene

Kr,c,i (25 "C), cm3 m'* 3.30 I 0.50 0.146 i 0.022 0.135 i- 0.020 0.039 i 0.006 0.036 i 0.005

Kr,c,i (40 lc),

cm3 m2.08 i 0.31 0.138 i- 0.021 0.116 i 0.017 0.034 i- 0.005 0.033 r 0.005 0.025 i 0.004 0.021 f 0.003 0.0067 r 0.0001 0.0056 I 0.0008

/3

s

o'2

004

01 / L)

Figure 4. Effect of reproducibility calculated with different t o values. towas precisely estimated on the integrator a t *0.01 min by a mixture of benzene-toluene for curve 2 and evaluated graphicly for curve 3 a t 0.41 f 0.02 min. According to the experimental error on tothe reproducibility between the two columns, shown by curve 2 and 3, thus seems very good. T o verify if time affects the reproducibility for the same column, we obtained the same results 1 month later (curve 2) for the same treatment of eluent. In Figure 5, we give our results on a larger scale for the B[a]P at 25 and 40 "C on curves 1and 2, respectively. Curve 3 describes the results of Pylev and Shabad (11)from B[a]P but in benzene solution. These results are similar to ours although their eluent is less polar and also their chrysotile fiber is not well defined. As the difference of polarity between benzene and toluene is weak, we can say that the results are very similar. In Table I, we have estimated Henry's constant for the PAHs. The values reflect the affinity of adsorption with

asbestos chrysotile. We have accorded a precision of 15% on the results of Kr,c,l,considering the eluent dryness variations. In conclusion, it is expected that this technique will be useful in the adsorption study of the carcinogen products. Investigations on the modified asbestos will be done to improve the affinity of the asbestos fiber for the carcinogen products. Registry No. B[a]P, 50-32-8; chrysotile, 12001-29-5; fluoranthene, 206-44-0; pyrene, 129-00-0; phenanthrene, 85-01-8; anthracene, 120-12-7; fluorene, 86-73-7; naphthalene, 91-20-3.

LITERATURE CITED (1) Woo, Y.-T.; Arcos, J. C. "Carcinogens in Industry and the Envlronrnent"; Marcel Dekker: New York, 1981; Chapter 7. (2) Jerina, D. M.; Lehr, R. E.; Yagi, H.; Hernandez, 0.; Dansette, P.; WlsIocki, P. G.; Wood, A. W.; Chang, R. L.; Levin, W.; Conney, A. H. "In vitro metabolic Activation in Mutagenesis Testing"; Elsevier/North-Hoiland Biomedical Press: Amsterdam, 1976; pp 159-177. (3) Hoffmann, D.; Wynder, F. L. "Chemical Carcinogens ACS Monograph 173"; American Chemical Society: Washington, DC, 1976; pp 324-365. (4) Lindskog, A. EHP, Environ. Health Perspect. 1983, 4 7 , 81-84. (5) Campbell, W. J.; Blake, R. L.; Brown, L. L.; Cather, E. E.; Sjoberg, J. J. Selected Silicate Minerals and Their Asbestiform Varieties"; U S . Bureau of Mines: Washington, DC, 1977; Information Circular 8751. (6) Contour, J. P.; Guerin, I.; Mouorier, G. Atrnos, Pollut ., Proc. Int. Colloq., 73th 1978, 255-259. (7) Craighead, J. E.; Mossman, B. T. Med. Prog. 1982, 306, 1446. (8) Harrington, J. S.; Smith, M. Arch. Environ, Hea/th 1984, 8, 453-458. (9) Noel, L. M.S. Thesis, Universit6 de Sherbrooke, Sherbrooke, Quebec 1982. (10) Chuduck, N. A,; Eltekov, Yu. A,; Kiselev, A. V. J. Colloid Interface Scl. 1981, 8 4 , 149-154. (11) Pyiev, L. N.; Shabad, L. M. "Bloiogical Effects of Asbestos"; IARC (International Agency for Research on Cancer) Scientific Publication: Lyon, 1973; No. 8, pp 99-105.

RECEIVED for review November 14, 1983. Accepted March 2,1984. The authors thank the "Institut de Recherche et de DBveloppement de 1'Amiante (IRDA)" for their financial support.