Anal. Chem. 1999, 71, 3834-3838
A Method To Estimate the Octanol-Air Partition Coefficient of Semivolatile Organic Compounds Xiangmin Zhang,† Karl-Werner Schramm,*,‡ Bernhard Henkelmann,‡ Christian Klimm,‡ Andreas Kaune,§ Antonius Kettrup,‡,§ and Peichang Lu|
GSF-National Research Center for Environment and Health, Institute of Ecological Chemistry, Ingolsta¨dter Landstrasse 1, D-85764 Neuherberg, F. R. Germany, Department of Chemistry, Fudan University, Shanghai 200433, P. R. China, Technische Universita¨t Mu¨nchen, Lehrstuhl fu¨r O ¨ kologische Chemie und Umweltanalytik, D-85350 Freising, F. R. Germany, and Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116011, P. R. China
A multicolumn method for the estimation of the octanolair partition coefficient (KOA) of semivolatile compounds is described. The method is based on the retention time of a compound on gas chromatographic columns of different selectivity and polarity. Log KOA values of polychlorinated biphenyls (PCB) were estimated with the novel multicolumn method. The results were in excellent agreement with previously published data using a generator column method. Therefore, we used our multicolumn method to estimate KOA for more than 100 PCB congeners. Polychlorinated biphenyls (PCB) are ubiquitous toxic contaminants that undergo long-range atmospheric transport and partition between air and other environmental compartments. The most persistent PCB are especially found in cold-temperature regions such as the arctic and high-latitude zones. PCB accumulate in vegetation, wildlife, and man.1-4 The toxic effects of PCB and their impact on the environment have been investigated intensively.5 Analytical methods for congener-specific analysis of PCB and information on their relative retention times are available.6-11 The octanol-air partition coefficient (KOA) was suggested as the best single parameter to describe the partitioning of PCB, pesticides, and other persistent organic compounds * Corresponding author. E-mail:
[email protected]. Fax: +49 89 31 87 33 71.
between air and vegetation, air and biota, and air and aerosols.12,13 KOA can be calculated from the octanol-water and the air-water partition coefficients.14 However, this method can result in large errors due to large discrepancies of reported octanol-water partition coefficients. Alternatively, KOA values were directly measured using a generator column method.12,15 However, this method is time-consuming, especially for investigating semivolatile compounds. For these compounds, a very large volume of air must be sampled to collect an amount of substance that is sufficient for gas chromatography and electron-capture detection. Therefore, the objective of this work is to develop a new method for the estimation of the KOA of semivolatile compounds. PCB congeners are used as examples. Vapor pressures of polycyclic aromatic hydrocarbons, PCB, and other organic compounds and the temperature-dependence of the vapor pressure were determined gas chromatographically.16,17 Nevertheless, this method is not readily applicable to the measurement of partition coefficients because of more complicated intermolecular interactions. The most direct way to determine the octanol-air partition coefficient would be to use octanol as a stationary phase. Unfortunately, this is not possible because octanol has a high vapor pressure compared with PCB and other semivolatile compounds. Therefore, we propose a multicolumn gas chromatographic method that uses several columns with different intermolecular interaction properties to estimate the octanol-air partition coefficient of semivolatile compounds.
†
Fudan University. National Research Center for Environment and Health. § Technische Universita¨t Mu ¨ nchen. | Chinese Academy of Sciences. (1) Gaggi, C.; Bacci, E.; Calamari, D.; Fanelli, R. Chemosphere 1985, 14, 16731686. (2) Simonich, S. L.; Hites, R. A. Nature (London) 1994, 370, 49-51. (3) Dewailly, E.; Nantel, A.; Weber, J. P.; Meyer, F. Bull. Environ. Contam. Toxicol. 1989, 43, 641-646. (4) Duarte-Davidson, R.; Burnett, V.; Waterhouse, K. S.; Jones, K. C. Chemosphere 1991, 23, 119-131. (5) Safe, S. Crit. Rev. Toxicol. 1994, 24, 87-149. (6) Haglund, P.; Wiberg, K. J. High Resolut. Chromatogr. 1996, 19, 373-376. (7) Larsen, B.; Bøwadt, S.; Tilio, R. Int. J. Environ. Anal. Chem. 1992, 47, 4768. (8) Gankin, Y. V.; Gorshteyn, A. E.; Robbat, A., Jr. Anal. Chem. 1995, 67, 25482555. (9) Schulz, D. E.; Petrick, G.; Duinker, J. C. Environ. Sci. Technol. 1989, 23, 852-859. (10) Larsen, B. R. J. High Resolut. Chromatogr. 1995, 18, 141-151. (11) Frame, G. M. Fresenius’ J. Anal. Chem. 1997, 357, 701-713. ‡
3834 Analytical Chemistry, Vol. 71, No. 17, September 1, 1999
EXPERIMENTAL SECTION Chemicals and Reagents. PCB standards were purchased from Ziemer (Mannheim, Germany) (biphenyl and PCB no. 5, 11, 15, 29, 48, 53, 61, 66, 77, 95, 96, 105, 118, 126, 141, 153, 155, 156, 157, 169, 170, 171, 172, 174, 178, 187, 196, 199, 201, 209), AccuStandard (New Haven, CT) (PCB no. 2, 3, 4, 6, 7, 9, 12, 14, 28, 52, 138, 180), and Analabs (PCB no. 18, 28, 31, 44, 47, 49). Eleven 13C12 labeled PCB congeners (no. 28, 52, 77, 101, 105, 126, 138, 153, 169, 180, and 209) and Aroclor 1221, 1016, 1232, 1242, (12) Harner, T.; Mackay, D. Environ. Sci. Technol. 1995, 29, 1599-1606. (13) Mackay, D.; Wania, F. Sci. Total Environ. 1995, 160/161, 25-38. (14) Li, A.; Andren, A. W. Environ. Sci. Technol. 1994, 28, 47-52. (15) Harner, T.; Bidleman, T. F. J. Chem. Eng. Data 1996, 41, 895-899. (16) Falconer, R. L. Atmos. Environ. 1994, 28, 547-554. (17) Foreman, W. T. J. Chromatogr. 1985, 330, 203-216. 10.1021/ac981103r CCC: $18.00
© 1999 American Chemical Society Published on Web 08/03/1999
1248, 1254, 1260, 1262, and 1268 were obtained from Promochem (Wesel, Germany). Aniline; benzyl alcohol; chlorobenzene; 1,3dichlorobenzene; 1,3,5-trichlorobenzene; 1,2,3,4-, 1,2,3,5-, and 1,2,4,5-tetrachlorobenzene; pentachlorobenzene; hexachlorobenzene; 1,4-dibromobenzene; and 1,3,5-tribromobenzene were purchased from Aldrich (Steinheim, Germany). Each chemical was separately dissolved in nonane at a concentration of 1 µg/mL, and 1 µg/mL of pentane was added. One microliter of this solution was injected into the gas chromatograph. The capacity factor (k) was calculated using pentane for the determination of the gas holdup time at temperatures above 150 °C. Safety Considerations. Polychlorinated biphenyls can cause irritation of the nose and throat, acne, and rashes. Polychlorinated biphenyls and hexachlorobenzene are reasonably anticipated to be carcinogens. Aniline is toxic when inhaled, when in contact with skin, and if swallowed. Any contact and inhalation of these substances should be avoided. Therefore, it is recommended to use gloves, a laboratory coat, and safety glasses when preparing and handling standards of the compounds mentioned in this paper. Standards should be prepared in a fume hood. Equipment. A Hewlett-Packard 5890 Series II gas chromatograph was equipped with a Hewlett-Packard autosampler 7673A. A FID (rather than an ECD) detector was used because we also wanted to investigate biphenyl. The detector temperature was 275 °C. In isothermal experiments, the split ratio was 30:1. Helium was used as the carrier gas in all GC experiments at a linear velocity of 20-24 cm/s, depending on the column used. The following fused silica capillary columns were employed: DB-5ms, 60 m × 0.25 mm i.d. × 0.1 µm (J&W Scientific Inc., Folson, CA); DB-Dioxin, 60 m × 0.25 mm i.d. × 0.15 µm (J&W Scientific); Rtx-2330, 60 m × 0.25 mm i.d. × 0.1 µm (Restec Inc.); and 007-FFAP, 60 m × 0.25 mm i.d. × 0.1 µm (Quadrex Inc.). All retention data used for regression analysis and estimation of KOA were obtained by isothermal gas chromatography. Isothermal measurements of solutions containing a single PCB congener and of Aroclors were performed at 200 °C on DB-5ms, at 220 °C on DB-Dioxin, at 190 °C on Rtx-2330, and at 210 °C on 007-FFAP. These temperatures were chosen to obtain good resolution of the least retained PCB congeners. For the investigation of the Aroclors, a Hewlett-Packard 5890 Series II gas chromatograph equipped with a Finnigan MAT A200S autosampler and connected to a Finnigan MAT SSQ 7000 mass spectrometer was used. One microliter of a 1 mg/mL solution of each Aroclor was injected splitlessly. Electron impact ionization was done at 70 eV. In the multiple ion detection mode, the following ions (m/z) were monitored simultaneously: 188 and 190 for monochlorinated biphenyls (CB), 222 and 224 for di-CB, 256 and 258 for tri-CB, 290 and 292 for tetra-CB, 326 and 328 for penta-CB, 360 and 362 for hexa-CB, 394 and 396 for hepta-CB, 428 and 430 for octa-CB, 462 and 464 for nona-CB, 498 and 500 for deca-CB, and m/z values of the 13C12 labeled PCB congeners, which are 12 units higher than those of the native congeners. The following temperature program was used for peak identification and comparison of the elution pattern with literature information: 80 °C for 2 min; 30 °C/min to 150 °C; hold for 4 min; 2.5 °C/min to 280 °C (DB-5ms) or 250 °C (DB-Dioxin, Rtx2330 and 007-FFAP).
Peak Identification. Peaks in the chromatograms of the Aroclor mixtures were identified by the following methods: cochromatography using 11 13C12 labeled PCB congeners; comparison of retention time with that of 48 native PCB congeners; comparison of the elution order and of congener concentrations in Aroclors with those reported in the literature 7,9,18-21 (where the Sil-88 column described in reference 7 is similar to the Rtx2330 column); and 1/2 retention values of PCB congeners as proposed in refs 22 and 23. Decomposition of Retention Values and log KOA Values of PCB into 1/2 Values. The method of 1/2 retention indices and 1/ (log K ) of PCB is useful to estimate retention indices and 2 OA log KOA values that are not available. According to Sissons and Welti,22,23 any PCB congener can be considered to consist of two chloro-substituted phenyl groups each having its own 1/2 retention index. Similarly, a 1/2 (log KOA) can be ascribed to each of the two phenyl rings. All PCB congeners are composed of 20 such basic groups, and the retention index and log KOA value of any PCB congener can be estimated by addition of the 1/2 retention values and 1/2 (log KOA) values, respectively, of the two phenyl groups. Using multiple linear regression analysis, the retention indices measured on the three columns (DB-5ms, DB-Dioxin, and 007FFAP) were decomposed into their 1/2 retention indices. For convenience, biphenyl (bp) and decachlorobiphenyl (DCB) were considered as relative standards by defining the log k of biphenyl (log kbp) to be 0 and the log k of DCB (log kDCB) to be 100:
I1/2 ) 100 ×
log k - log kbp log kDCB - log kbp
(1)
Here, I1/2 is the 1/2 retention index. Experimental log KOA values15 were decomposed into 1/2 (log KOA). RESULTS AND DISCUSSION Theory. The octanol-air partition coefficient (KOA) can be calculated from the gas chromatographic capacity factor measured on a column with octanol as stationary phase (kOA) according to eq 2. Here, β is the column-phase ratio. However, kOA values of
KOA ) kOA β
(2)
semivolatile compounds such as PCB cannot be determined directly (i.e., on an “octanol” column) and have to be related to the retention time measured on commonly available columns. For various classes of organic compounds, we derived an equation (eq 3) that allows the accurate calculation of the retention index on one column from that of another column of different selectivity.24 Here, I and I′ are the retention indices on two different (18) Mullin, M.; Pochini, C.; McCrindle, S.; Romkes, M.; Safe, S.; Safe, L. Environ. Sci. Technol. 1984, 18, 468-476. (19) Bøwadt, S.; Skejø-Andresen, H.; Montanarella, L.; Larsen, B. Int. J. Environ. Anal. Chem. 1994, 56, 87-107. (20) Ballschmiter, K.; Zell, M. Fresenius’ Z. Anal. Chem. 1980, 302, 20-31. (21) Bush, B.; Murphy, M. J.; Connor, S.; Snow, J.; Barnard, E. J. Chromatogr. Sci. 1985, 23, 509-514. (22) Sissons, D.; Welti, D. J. Chromatogr. 1971, 60, 15-32. (23) Albro, P. W.; Harseman, J. K.; Clemmer, T. A.; Corbett, B. J. J. Chromatogr. 1977, 136, 147-153. (24) Zhang, X.; Lu, P. J. Chromatogr., A 1996, 731, 187-199.
Analytical Chemistry, Vol. 71, No. 17, September 1, 1999
3835
I ) AI′ + BN + C
(3)
stationary phases, N is the number of methyl groups, and A, B, and C are constants. The parameter A is related to the ratio of the free energies of the two stationary phases, B is the difference of the free energy of a methyl group between the two phases, and C is the interaction difference of the functional groups on the two phases.24 For PCB, N ) 0, and C ) c1RA + c2 µ2 + c3 χH + c4. Thus, eq 3 reads
I ) AI′ + c1RA + c2µ2 + c3χH + c4
(4)
Here, c1, c2, c3, and c4 are constants; RA is the polarizability; µ is the dipole-moment; and χH is the hydrogen-bonding energy.24,25 Replacing I with log KOA and I′ with log k yields
log KOA ) A′ log k + c′1RA + c′2µ2 + c′3χH + c′4
(5)
It is difficult to calculate log KOA from eq 5 because the PCB interaction parameters (RA, µ2, and χH) are not known. However, according to eq 4, these parameters can be determined from the retention time measured on several GC columns. Similarly, log KOA can be calculated according to eq 6 from capacity factors measured on several GC columns denoted by subscripts 1, 2, 3, ...
log KOA ) A0 + A1 log k1 + A2 log k2 + A3 log k3 + ...
(6)
From the equations given above, we can deduce that for an accurate description of intermolecular interactions at least three columns that show different interaction forces, like dispersion, polarity-induced polarity and hydrogen bonding energy, are required. Column Characterization. The selectivity of a GC column and its intermolecular interactions can be characterized by linear solvation energy relationships according to eq 7.26-29
SP ) SP0 + l log L16 + sπ + aRH + bβH + dδ
(7)
Here, SP is a thermodynamic parameter, such as the logarithm of a partition coefficient between two different phases or the logarithm of the capacity factor in gas chromatography, etc. SP0 is a constant of SP. Log L16, π, RH, βH, and δ are solvation parameters. Log L16 represents dispersive interactions as well as the cavity term of a solute in a solvent. The variable π represents polarity-induced polarity interactions. The variables RH and βH are the hydrogen-bonding acidity and basicity, respectively. For PCB, (25) Lu, P.; Dai, C.; Zhang, X. Theoretical Foundations of Chromatography; Science Press: Beijing, 1996. (26) Kamlet, M. J.; Doherty, R. M.; Abraham, M. H.; Marcus, Y.; Taft, R. W. J. Phys. Chem. 1989, 92, 5244-5255. (27) Abraham, M. H. J. Chromatogr. 1993, 644, 95-139. (28) Li, J.; Carr, P. W. J. Chromatogr., A 1994, 659, 367-380. (29) Li, J.; Zhang, Y.; Carr, P. W. Anal. Chem. 1992, 64, 210-218.
3836 Analytical Chemistry, Vol. 71, No. 17, September 1, 1999
RH ) 0, and the correction term δ equals 2. The coefficients l, s, and a permit a quantitative comparison of the column selectivity.29 For this study, polydimethyl siloxane columns (showing mainly dispersive interaction), cyanopropyl siloxanes, and modified poly(ethylene glycol) phases (having strong polarizability-induced polarizabilities and hydrogen-bonding abilities) were selected. Furthermore, 13 chemicals were used to characterize column interactions: biphenyl; chlorobenzene; 1,3-dichlorobenzene; 1,2,3trichlorobenzene; 1,2,3,4-, 1,2,3,5- and 1,2,4,5-tetrachlorobenzene; pentachlorobenzene; hexachlorobenzene; 1,4-dibromobenzene; 1,3,5-tribromobenzene; aniline; and benzyl alcohol. The latter two were employed to characterize polarity and hydrogen-bonding interactions. Solvation parameters of all 13 compounds are available in the literature.27-29 According to the regression coefficients of eq 7 (Table 1), the DB-5ms column mainly shows dispersive forces. This column was selected because it is widely used in PCB analysis and because many retention data are available. The DB-Dioxin column was designed for separation of polychlorinated dibenzodioxins and dibenzofurans. It exhibits moderate polarity-induced polarity forces (s ) 1.122) as well as hydrogen-bonding basicity. Unfortunately, the phase structure and composition of this column are not known. The Rtx-2330 column that contains 95% cyanopropyl and 5% phenyl polysiloxane has a strong polarity-induced polarity (s ) 2.502) and some hydrogen-bonding acidity. However, this phase does not contain active hydrogen. The proton donor activity is probably due to an inducive effect of the cyano groups on the hydrogen at the β position. Rtx-2330 preferentially interacts with 3,4-, 3,4,5-, and 2,3,4,5-substituted PCB congeners. The 007-FFAP is another typical structure-selective phase. This column possesses polarity and hydrogen-bonding interactions. Its acidity is due to the functional group at the end of the poly(ethylene glycol) chain capped with nitro aromatic acid. Regression of log KOA on log k. KOA values of 19 PCB congeners measured by Harner and Bidleman15 at two temperatures were regressed on their capacity factors determined with the GC columns listed in Table 1. Two separate regression equations were established for the two experimental temperatures. The best regression equation using the capacity factors of only one column (DB-5ms) explained 95% of the variance (r2 ) 0.95) and yielded a standard deviation (SD) of log KOA of 0.20 log unit. The accuracy of the prediction was improved by using the capacity factors of two columns (DB-5ms and 007-FFAP, r2 ) 0.988, SD ) 0.12) and those of three columns (DB-5ms, 007-FFAP, Rtx-2330, r2 ) 0.994, SD ) 0.10). Adding the capacity factors of the fourth column (DB-Dioxin) did not improve the results significantly, so that the three-variable regression equation was selected. Furthermore, capacity factors of PCB congeners measured on the DBDioxin highly correlated with those of the DB-5ms and the 007FFAP (r2 ) 0.996) so that they should not be included in the regression equation to avoid intercorrelation of the independent variables. The retention behavior of PCB congeners on a DB-5ms column is related to their chemical structure. Non-ortho and mono-ortho congeners are coplanar and show weak interactions on DB-5ms compared with an octanol phase and with polar phases. Therefore, the regression of log KOA on the capacity factors determined on the DB-5ms column was improved by addition of a coefficient,
Table 1. Coefficients of Eq 7 for Four Different Columnsa phase
SP0
l
s
a
b
db
SD
r
n
DB-5ms DB-Dioxin Rtx-2330 007-FFAP
-2.911 -3.082 -3.306 -2.672
0.400 0.350 0.142 1.278
0.416 1.122 2.502 1.144
0.011 0.454 0.138 0.588
0.058 0.095 0.575 0.349
0 0 0 0
0.017 0.004 0.005 0.018
1.000 1.000 1.000 0.999
13 13 13 13
a The 13 compounds used for column characterization are listed in the text. The solvation parameters log L16, π, R, and β were taken from the H literature. b The coefficient was neglected because it plays only a minor role in eq 7.
Table 2. Comparison of log KOA Measured by the Method of Harner and Bidleman15 and by the Novel Method log KOA at 20 °C PCB no. 3a 15a 29a 49 53 61a 66a 77a 95 96 101 105a 118a 126a 138 153 155 171 180
Table 3. Logarithm of the Octanol-Air Partition Coefficient of Biphenyl and 103 PCB Congeners at Two Temperatures
log KOA at 0 °C
ref 15
this work (eq 8)
7.01 7.88 8.03 8.57 8.24 8.90 9.22 9.96 9.06 8.77 9.31 10.27 10.08 10.61 10.09 10.04 9.16 10.51 10.75
6.99 7.88 8.05 8.63 8.18 8.93 9.29 9.92 9.06 8.79 9.28 10.20 10.04 10.66 10.20 9.99 9.13 10.51 10.72
log KOAa at
ref 15
this work (eq 9)
B
A
7.88b 8.82b 9.11b 9.64 9.28 9.79b 10.21 10.88 10.20 9.72 10.31 11.43 11.26b 11.81 11.21b 11.17b 12.27b,c 11.71b 11.90b
7.86 8.82 9.16 9.60 9.15 10.12 10.33 10.96 10.08 9.81 10.31 10.33 11.16 11.77 11.33 11.06 10.14 11.70 11.92
3470 3792 3792 3981 3965 3464 3827 3828 3904 3913 3841 4678 4693 4870 4584 4695 3954 4757 4535
-4.82 -5.06 -4.77 -4.96 -5.26 -2.89 -3.82 -3.14 -4.30 -4.60 -3.82 -5.68 -5.92 -5.98 -5.57 -6.02 -2.21 -5.71 -4.70
a Co for coplanar and noncoplanar PCB is 1 and 0, respectively. Calculated according to the equation log KOA ) A + B/T, where T is absolute temperature (K) and the coefficients A and B were taken from the literature and are given in the last two columns. c Value was excluded from the regression analysis (see text).
b
Co, that is 1 for coplanar PCB congeners and 0 for all other congeners (log KOA ) 8.168 log kDB-5ms + 3.004Co, r2 ) 0.987, SD ) 0.13, n ) 19). However, using the capacity factors measured on the DB-Dioxin, Rtx-2330, and 007-FFAP columns, the correlation of log KOA was hardly improved by the addition of Co. Taking coplanar effects into account, an equation (similar to eq 6) to compute log KOA of PCB congeners at 20 °C from log k on three columns (DB-5ms, Rtx-2330, and 007-FFAP) is as follows:
log KOA ) 7.92 + 1.676 log kDB-5ms - 0.856 log kRtx-2330 + 2.149 log k007-FFAP + 0.196 Co (n ) 19, r2 ) 0.997, SD ) 0.07) (8)
Similarly, the equation for obtaining log KOA of PCB congeners at 0 °C was the following:
log KOA ) 8.99 + 2.331 log kDB-5ms - 1.187 log kRtx-2330 + 2.049 log k007-FFAP + 0.291Co (n ) 18, r2 ) 0.994, SD ) 0.10) (9)
log KOA at
PCB no.
0 °C
20 °C
PCB no.
0 °C
20 °C
biphenyl 1 2 3 4 5 6 7 8 9 11 12 14 15 16 17 18 20 22 25 26 28 29 31 32 33 41 44 46 47 48 49 52 53 61 63 64 66 70 71 74 77 83 84 95 96 97 101 105 110 118 126
6.92 7.54 7.90 7.86 7.66 8.55 8.51 8.37 8.58 8.37 8.86 8.71 8.82 8.87 8.87 8.66 8.70 9.51 9.60 9.31 9.30 9.43 9.15 9.43 8.89 9.52 9.79 9.67 9.49 9.55 9.49 9.50 9.46 9.18 10.19 10.15 9.62 10.33 10.29 9.78 10.25 10.92 10.44 10.28 10.07 9.87 10.49 10.25 11.41 10.61 11.13 11.71
6.09 6.65 7.00 6.99 6.86 7.59 7.55 7.39 7.61 7.40 7.90 7.80 7.78 7.88 7.98 7.74 7.79 8.49 8.58 8.28 8.27 8.40 8.05 8.40 7.97 8.52 8.82 8.71 8.56 8.56 8.50 8.63 8.49 8.18 8.93 9.06 8.63 9.29 9.22 8.84 9.14 9.92 9.39 9.28 9.06 8.79 9.44 9.28 10.20 9.58 10.04 10.66
131 132 134 135 136 138 141 144 146 147 149 151 153 155 156 157 158 163 167 169 170 171 172 173 174 175 176 177 178 179 180 183 187 189 190 191 193 194 195 196 197 198 199 200 201 202 203 205 206 207 208 209
10.92 11.16 10.80 10.78 10.59 11.34 11.18 10.73 10.96 10.79 10.83 10.68 11.03 10.19 12.07 12.28 11.25 11.26 11.96 12.51 12.24 11.76 11.84 11.79 11.67 11.35 11.22 11.74 11.28 11.26 11.94 11.44 11.38 12.81 12.09 12.07 11.99 12.83 12.72 12.27 11.74 12.32 12.28 12.05 12.22 11.57 12.36 12.86 13.09 12.60 12.57 13.36
9.83 10.07 9.71 9.69 9.53 10.20 10.07 9.62 9.84 9.67 9.74 9.58 9.99 9.13 10.87 11.07 10.14 10.16 10.77 11.32 11.07 10.51 10.67 10.60 10.51 10.17 10.06 10.58 10.12 10.10 10.72 10.26 10.22 11.54 10.87 10.91 10.82 11.59 11.44 11.03 10.52 11.05 11.05 10.82 10.98 10.38 11.10 11.62 11.79 11.26 11.26 11.96
a The capacity factors of the PCB congeners were determined on three different columns, and log KOA was calculated according to eqs 8 and 9.
Analytical Chemistry, Vol. 71, No. 17, September 1, 1999
3837
Table 4. PCB 1/2 Retention Indices Calculated According to Eq 1 for Three Columns and Two Different Data Sets 007-FFAP (210 °C) substino. tution 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 n r2
data set 1
data set 2
none 0 0 2 19.7 19.9 3 32.7 33.9 4 35.3 34.7 23 56.7 55.7 24 44.8 45.2 25 45.5 46.1 26 39.8 40.8 34 70.1 71.5 35 49.5 50.5 234 85.1 86.0 235 66.6 67.1 236 63.4 64.7 245 68.8 69.4 246 49.3 49.9 345 97.6 98.6 2345 99.2 100.1 2346 76.9 78.1 2356 76.3 76.0 23456 100 100 104a 48b 0.998 0.999
Rtx-2330 (190 °C) data set 1
data set 2
Table 5. Comparison of log KOA Values Computed from Eq 8 with Those Calculated from 1/2 (log KOA) at 20 °C log KOA from
DB-5ms (200 °C) data set 1
data set 2
log KOA (20 °C)
0 0 0 0 3.05 19.0 19.4 15.8 15.8 34.3 35.5 26.7 27.4 3.97 39.1 39.1 28.4 27.6 3.95 58.9 56.5 45.4 45.0 41.1 40.5 40.0 40.6 4.21 43.5 43.7 39.3 39.7 4.28 36.9 38.2 39.3 39.7 3.97 76.7 77.1 31.2 31.2 5.02 47.6 46.8 48.0 49.3 85.9 85.9 70.3 70.9 5.17 65.2 67.7 60.8 61.6 62.2 62.7 55.5 56.5 4.79 68.8 68.9 63.0 63.6 5.01 41.2 40.8 49.4 50.0 4.58 104.4 104.7 79.0 80.2 5.60 104.9 104.1 89.4 90.3 5.86 78.7 78.1 75.2 76.0 5.35 78.6 76.2 73.8 74.5 100 100 100 100 104a 48b 104a 48b 19c 0.996 0.997 0.999 0.998 0.998
a Log k of biphenyl and 103 PCB congeners in Aroclors were used in the multiple linear regression analyses. b 48 native PCB standards. c 19 K OA values from ref 15.
The regression results using eqs 8 and 9 are summarized in Table 2. Log KOA values of some PCB congeners at 0 °C were calculated from the literature value at 20 °C using the equation log KOA ) A + B/T (where T is the absolute temperature in K) and the A and B values given by Harner and Bidleman.15 Log KOA of PCB-155 at 0 °C, calculated by this method, largely deviated from our result. The reason for the large deviation is probably an error in the A and B values. Therefore, this value was not used to establish the final regression equation to predict log KOA at 0 °C. Using eqs 8 and 9, log KOA values of biphenyl and 103 PCB congeners were computed from their experimental retention times (Table 3). PCB congeners for which no values are given in Table 3 could not be clearly identified in the chromatograms. Table 4 presents 1/2 retention indices of the 20 PCB substitution patterns. The retention data determined for 48 PCB standards were compared with the data obtained by using Aroclor mixtures. Both sets of values were in good agreement. Table 4 also gives some 1/2 (log KOA) values calculated from the data in ref 15. Log KOA estimated from this method provides an independent measure of confirmation of our novel method. Table 5 lists some log KOA values estimated using multicolumn chromatography and those calculated from 1/2 (log KOA). For most of the PCB congeners, these two methods compared well.
3838 Analytical Chemistry, Vol. 71, No. 17, September 1, 1999
PCB no.
eq 8
biphenyl 3 7 9 11 12 15 25 26 28 29 31 32 47 49 52 53 61 64 66 70 71 74 77 95 96 101 105
6.09 6.99 7.39 7.40 7.90 7.80 7.88 8.28 8.27 8.40 8.05 8.40 7.97 8.56 8.63 8.49 8.18 8.93 8.63 9.29 9.22 8.84 9.14 9.92 9.06 8.79 9.28 10.20
1/
2
(log KOA) 6.09 6.99 7.25 7.33 7.93 8.06 7.89 8.17 8.24 8.15 8.06 8.23 7.92 8.41 8.48 8.56 8.25 8.90 8.74 9.22 9.29 8.98 8.96 10.03 9.07 8.76 9.29 10.02
log KOA from PCB no.
eq 8
110 118 126 132 136 138 141 144 149 153 155 156 157 158 167 169 170 171 174 176 180 183 189 191 194 196 197
9.58 10.04 10.66 10.07 9.53 10.20 10.07 9.62 9.74 9.99 9.13 10.87 11.07 10.14 10.77 11.32 11.07 10.51 10.51 10.06 10.72 10.26 11.54 10.91 11.59 11.03 10.52
1/ 2
(log KOA) 9.80 10.02 10.61 9.96 9.58 10.18 10.13 9.62 9.80 10.02 9.16 10.87 10.76 10.36 10.60 11.19 11.02 10.50 10.64 10.13 10.86 10.35 11.45 10.93 11.71 11.19 10.68
CONCLUSIONS A novel approach was proposed for the estimation of the octanol-air partition coefficient of semivolatile organic compounds such as PCB. The method is based on the theory of molecular interactions. Four capillary gas chromatographic columns were characterized by linear solvation energy relationships and were used to measure the retention time and capacity factors of PCB congeners. Using the capacity factors of 19 PCB congeners measured on three of the columns and log KOA values given in the literature, a calibration curve was established by multiple linear regression analysis. The regression equation explained 99.4% of the variance and was used to compute log KOA of biphenyl and of 103 PCB congeners from their capacity factors measured on the same three columns. Some of the log KOA values were also compared with those estimated using 1/2 (log KOA) values. The novel method allows for a quick, low-cost, and accurate estimation of log KOA values and of other environmentally important partition coefficients that can be inferred from log KOA such as, e.g., the particle-air and the plant-air partitioning coefficients. Received for review October 6, 1998. Accepted May 21, 1999. AC981103R
