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ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
Characterization of Carbon Black Adsorbates and Artifacts Formed during Extraction William L. Fitch,"' E. Thomas Everhart,' and Dennis H. Smith3 Department of Genetics, Stanford University, Stanford, California 94305
Combined gas chromatographylmass spectrometry and advanced computer techniques are used to characterize the extractable material from a series of carbon black samples. Upon benzene extraction, several highly oxidized channel blacks yielded oxidized polynuclear aromatic derivatives, including ketones, quinones, anhydrides, and nitro compounds. A special extractor was designed to conduct extractions with liquid naphthalene at elevated temperature and reduced pressure. This procedure yielded the same polynuclear aromatic derivatives seen in the benzene extractions as well as several materials believed formed by reaction of naphthalene with surface groups of the carbon. The latter include three binaphthyls, two dinaphthofurans, and two methylbinaphthyls. Similar extractions of a lampblack yielded polynuclear aromatic hydrocarbons, but only traces of the oxidized species and none of the artifacts with naphthalene as extractant.
I t has long been observed t h a t polynuclear aromatic hydrocarbons (PAH) can be extracted from carbon black samples of large particle size (1-4). However t h e corresponding materials of very small particle size (channel and furnace blacks of particle size less t h a n about 20 nm) have not been demonstrated to contain extractable organic material ( I , 5 ) . It has been assumed t h a t P A H are present on these carbon blacks, b u t strong adsorption prevents extraction using conventional methodology (6, 7). T h e lack of a reliable analytical method to demonstrate the absence of carcinogenic P A H on commercial black samples led the FDA in 1976 to suspend t h e uses of these materials as coloring agents in foods a n d cosmetics (8). As part of a project aimed a t examining the environmental health importance of t h e adsorptive a n d catalytic properties of forms of polymeric (graphitic) carbon, we undertook to investigate t h e extraction of PAH from small particle size carbon black samples. One approach which we pursued for t h e extraction of P A H from these materials was based on the assumption t h a t the strongly adsorbed P A H were insufficiently extractable with benzene (the normal solvent for such extractions). A literature report on the solubilization of a large percentage of a coal sample with refluxing phenanthrene (9) led us to consider higher aromatics as being more likely to extract t h e PAH. As a first trial we conducted extractions of several carbon black samples with refluxing naphthalene at reduced pressure. We report here t h e materials identified by extraction of selected carbon blacks with benzene and naphthalene. EXPERIMENTAL Lampblack was obtained from Fisher Scientific Co. Channel blacks were obtained from Pacific Coast Chemicals and are 'Present address, Acurex Corp., 486 Clyde Ave., Mountain View, Calif. 94042. Present address, Department of Civil Engineering, Stanford University, Stanford, Calif. 94306. Present address, Department of Chemistry, Stanford University, Stanford. Calif. 94305. 0003-2700/78/0350-21~2$01.00/0
-
Table I. Characterization of Carbon Blacks Investigated channel lampblack A
channel B
trade name Degussa Fisher Special Lampblack Black 5 particle size, nm PH carbon, % oxygen, % nitrogen, % sulfur, % hydrogen, %
44
7 96.7 0.9 0.0 1.5 0.6
20 3
85.6 13.1 0.3 0.4 0.6
Degussa Colour Black F W 200 13
2 79.2 19.3 0.4 0.4 0.7
manufactured by Degussa Inc. Physical characteristics of these blacks as reported in technical literature and elemental analyses performed at Stanford are listed in Table I, All solvents were Baker "Resi-analyzed" grade. Scintillation grade naphthalene was obtained from Aldrich Chemical Co. Other grades of naphthalene were unsuitable because they contained high molecular weight impurities. The only impurity which we detected in the scintillation grade naphthalene was a 58-ppm contaminant of 2-methylnaphthalene. This impurity could not be detected by gas chromatography but was quantified (combined gas chromatography/mass spectrometry, GC/MS) by selected ion monitoring of the methylnaphthalene molecular ion ( m / e 142) and a major fragment ion ( m / e 115). Acenaphthalene was added to the naphthalene as an internal standard in this experiment. GC and GC/MS experiments were performed on a Finnigan Instruments Corp. model 9500 gas chromatograph, employing 6-ft U-shaped '/8-in. (i.d.1 columns, packed with 3% Dexsil 300 on 100/120 mesh Gas Chrom Q. GC experiments were begun at 150 "C with temperature programming to 350 OC at 4"/min after an initial isothermal period of 2 min. At the end of the isothermal period, the GC effluent was allowed to enter a Finnegan Corp. model 1015 quadrupole mass spectrometer via a jet separator. Mass spectra were repetitively scanned and the data stored on disk in a Digital Equipment Corp. PDP-11/20 minicomputer. Data analysis was conducted with a PDP-11/45 minicomputer. High resolution GC/MS experiments were conducted on a Varian MAT-711 mass spectrometer. E x t r a c t i o n Methods. Benzene extractions were conducted in a standard soxhlet apparatus. The carbon sample ( 5 g) was placed in an pre-extracted Soxhlet thimble and extracted for 20 h. The cooled extract was evaporated to dryness at reduced pressure. The internal standard, 9-phenylanthracene (50 wg), was added and the residue dissolved in dichloromethane for analysis. The naphthalene extractions were conducted in an apparatus designed to maintain the naphthalene in the liquid state. It consisted of a 500-mL round bottom flask, Soxhlet extractor, air condenser, vacuum adapter, and Teflon sleeves to seal all joints. The round bottom flask, containing 250 g of scintillation grade naphthalene was magnetically stirred and heated to 140-155 "C in an oil bath. The Soxhlet cup and siphon tube were kept heated above 80 "C by means of heating tape. The pressure of the system was maintained between 25 and 30 Torr with a well trapped pump and a needle valve. Under these conditions, the naphthalene would reflux up the side arm of the Soxhlet, condense near the C 1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
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Table 11. Comparison of the Relative Concentrations of Benzene and Naphthalene Extractable Materials from Two Aliquots of a Lampblack" benzene naphthalene identification 1 M +C 1 2 RRI~ phenanthrene /anthracene 4-H-cyclopenta [def] phenanthren-4-oned fluoran thene 4 benzo[def] dibenzothiophene 3 pyrene 25 1,8-naphthalenedicarboxylicanhydride cyclopenta[cd] pyrene benzo [ghi] fluoranthene 8 benzo[j or hlfluoranthene 11 11 a naphtho[def] dibenzothiophened 8 perylene/benzo[a] pyrene 83 81 6-H-benzo[cd]pyren-6-oned 33 27 5 41 indeno [ 1,2,3-cd]pyrene 7 29 a sulfur bridged pentacycled 3 19 31 benzo [ghi] perylene/anthanthrene 130 58 37 2 a sulfur bridged hexacycled 12 42 21 coronene 40 163 51 a Concentrations, ppm, for the first and second benzene extracts and the first and second naphthalene extracts. 9Relative retention index. Molecular weight as inferred from Phenylanthracene was used as the quantitation standard. Identifications are tentative. low resolution mass spectral data and high resolution determination of molecular formulas. 1909 2205 2213 2248 2263 2270 2563 2627 2993 3051 3080 3127 3393 3520 3572 3890 3950
178 204 202 208 202 198 226 226 252 258 252 254 276 282 276 306 300
69 12 146 113 523 23 64 26
25
-
36 15 151 90 576 46 68 17
middle of the air condenser, and remain liquid in the Soxhlet apparatus. A pre-extracted (benzene) Soxhlet thimble contained the carbon sample (5 g) held in place with a plug of glass wool. Careful supervision was required; a heat gun was used to prevent the blockage of the Soxhlet siphon tube. At the end of the extraction time (6 h), the apparatus was allowed to cool below 80 "C before air was let into the system. The Soxhlet apparatus was then removed and replaced by a distilling adapter which delivered the distillate to a three-neck 1000-mL round bottom flask cooled in an acetone-dry ice bath. The naphthalene was then removed at about 100 "C and 1 Torr. A heat gun was necessary for removing blockages during this procedure. The residue was transferred to a small flask with dichloromethane, which was removed in vacuo, and the last traces of naphthalene were removed on the vacuum pump. The internal standard. 9-phenylanthracene (50 pg), was then added along with dichloromethane for analysis. A similar apparatus was used for an extraction with 2methylnaphthalene (Aldrich Chemicals 99+ 7 ~ )The . extraction was run for 5 h at an oil bath temperature or 150-155 "C and a pressure of 2-2.5 Torr. The solvent was removed at 175-185 "C and 2 Torr, and the residue treated as above. Synthesis of Materials. Mixed BinaphthjZs. A mixture of binaphthyls was obtained by the thermal decomposition of 2naphthylsulfonyl chloride as described by Badger and Whittle (10). The crude reaction mixture was freed of naphthalene by distillation at 100 OC/l mm and decolorized by adsorption on alumina (neutral, Activity 1) and elution with benzene. GC/MS analysis of this mixture indicated the presence of three binaphthyls in a ratio of 1:266:64 in order of increasing retention on Dexsil 300. The minor component was shown to be the 1.1isomer based on comparison to an authentic sample (Analabs). Two recrystalizations of the crude reaction mixture from ethyl acetate/ methanol yielded pure 2,2'-binaphthyl, m p 182-183 "C (lit. mp 185-186 "C (10))shown by GC/MS to be the third component. The major component of the reaction was assigned the 1,2' structure by default. This product ratio is similar to that described previously (10). Trace quantities of 5 ternaphthyls (M', 380) were also detected in the crude reaction mixture. Mired Methylbirzaphthyls. A mixture of methylated binaphthyls was prepared by a modification of the method of Kovacic and Koch (12). To an oven dried 50-mL flask were added naphthalene (1.62 g, 12.6 mmol), 1-methylnaphthalene (Aldrich, 1.79 g, 12.6 mmol), anhydrous cupric chloride (1.69 g. 12.6 mmol), anhydrous aluminum chloride (0.36 g, 2.7 mmol), and o-dichlorobenzene (15 mL), and the black reaction mixture was stirred at room temperature for 2 h. The reaction mixture was then poured into 6 N HCl(100 mL) in a separatory funnel. The green aqueous layer was extracted once with dichloromethane (50 mL)
and discarded. The combined organic phase was washed several times with 6 N HCI and distilled water, dried (Na2S04),and evaporated to a volume of 40 mL. This solution was analyzed by GC/MS. The major product was a dimethylbinaphthyl (M+, 282; major ions, m / e 265, 252, 141, 133, 132, 126). Two other species of molecular weight 282 were seen along with three species identified as methylbinaphthyls (M+,268; major ions, 253, 252, 134,126). No attempts were made to determine which of the many possible isomers of these materials were present. Dinaphtho[2,1-b:1',2'-d]juran.This dinaphthofuran was prepared by a modification of a procedure of Pring and Stjernstrom (12). 2.2'-Dihydroxy-l,l'-binaphthyl(Eastman Chemicals) (0.60 g, 2.1 mmol) and 10 mL of a 50/50 (v/v) mixture of acetic acid and concentrated HBr were placed in a glass tube. The solution was degassed and sealed under vacuum. It was then heated at 180-190 "C for 20 h in a sand bath. The cooled tube was then opened and the contents poured into ether (50 mL) and water (50 mL). The ether layer was washed with 1 N NaOH several times followed by distilled water. The ether was then dried (MgSO,) and evaporated to a greenish white powder which was recrystallized from benzene/methanol, mp 152-153 "C (lit. mp 156 "C (13)). Analysis by GC/MS indicated a single dinaphthofuran (RRI, 2957; M+, 268; major ions, 239, 119). Data Analysis. The computer programs which are routinely used in the analysis of raw GC/MS data have been described elsewhere (14, 15). Basically, the programs produce clean mass spectra of components after resolving overlapping peaks and subtracting background. Relative retention indices and relative concentrations of each component are then calculated by comparison to hydrocarbon time standards and appropriate internal quantitation standards. Finally, each component with its associated mass spectrum and retention index is compared against a library of previously identified compounds. Compound Identification. A library containing over 100 mass spectra has been assembled from spectra of authentic polynuclear aromatic hydrocarbons and derivatives. Samples were obtained from commercial sources (Analabs, Aldrich, Eastman Organic Chemicals) as well as synthesis (described above). Some entries were mass spectra identified from carbon black extractives by comparison to literature mass spectra (16, 17). Several entries have only been tentatively identified based on mass spectral correlations (18). In several instances, we are not able to distinguish positional isomers based on mass spectral data alone.
RESULTS We first tested our methods on a commercial sample of lampblack. Separate samples were extracted with two portions of benzene or naphthalene. T h e results (Table 11) indicate
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
Table 111. Compounds Obtained by Benzene and Three Consecutive Naphthalene Extractions of Two Aliquots of Channel Black Aa RRI
M-
benzene
1
naphthalene 2
3
identity
173 10.0 1-nitronaphthaleneb 1750 1875 180 8.1 1.0 9-fluorenone 178 7.6 phenanthrenelanthracene 1909 2092 208 3.0 6.9 0.8 anthraquinone 2121 196 xanthone 1.8 2272 198 8.4 25.3 3.6 0.5 1.8-naphthalenedicarboxylic anhydrideb 6.9 2406 208 9,lO-phenanthrenequinone 2432 254 2.8 0.9 0.9 1,l'-binaphthyl 2598 254 2.8 1.5 1,2'-binaphthyl 14.3 2702 268 9.5 1.3 a methylbinaphthyl 6.3 2739 268 10.6 9.5 1.4 a methylbinaphthyl 2780 254 1.5 1.2 2,2'-binaphthyl 2.5 2957 268 3.8 2.4 a dinaphthofuran 4.5 3014 268 29.4 17.3 8.3 a dinaphthofuran These compounds are readily distinguishable from isomeric species which are also present See footnotes to Table 11. in the extracts at lower concentrations. I
Table IV. PAH Derivatives Identified from Benzene, Benzene/Methanol and Naphthalene Extracts of Channel Blacks A and Ba ketones, quinones
nitro derivatives
1,4-naphthoquinone 9-fluorenone anthraquinone ( 2 ) nitrofluorenone ( 3 )
nitronaphthalene ( 2 ) nitrobiphenyl nitrodibenzofuran ( 3 ) dinitronaphthalene ( 3 ) nitrophenanthrene
nitrophenanthrenequinone
xanthone anhydrides phthalic naphthalene dicarboxylic ( 3 ) phenanthrene dicarboxylic ( 2 ) pyrene dicarboxylic
nitronaphthalene dicarboxylic ( 4 ) nitrophthalic ( 2 ) naphthalene tetracarboxylic
methyl esters of phthalic benzene tricarboxylic ( 2 ) benzene tetracarboxylic ( 3 ) benzene pentacarboxylic nitrobenzoic (2) nitrophthalic ( 2 ) nitrobenzene tricarboxylic a
benzene tricarboxylic anhydride benzene tetracarboxylic anhydride benzene pentacarboxylic anhydride naphthalene dicarboxylic fatty acids (decanoic-triacontanoic)
Numbers in parentheses refer to numbers of distinct isomers detected.
that naphthalene is more efficient at extracting high molecular weight P A H from carbon black t h a n is benzene. One 6-h naphthalene extraction results in better yields of hexa- and heptacyclic P A H t h a n two 20-h benzene extractions. T h e lower molecular weight P A H s are partially lost during t h e distillation of naphthalene as indicated by their higher values in the benzene extraction. The identifications in Table I1 were supported by accurate mass measurements and comparison with authentic specimens in many cases. Many isomeric components are not separated by packed column GC (e.g., p h e n a n t h r e n e / a n t h r a c e n e a n d ben zo [ a ] pyre n e be nz o [elpyrene). Capillary techniques ( 2 ) or special GC packings (19) are required for these separations. W i t h these encouraging results on t h e value of our naphthalene extractor, we undertook to study the extractables from a commercial channel black. The results (Table 111)were surprising in that, contrary to expectations from the literature, benzene alone extracted several compounds from channel black A in p p m quantities. Analysis of these materials with high resolution mass spectrometry indicated them to be oxygen-containing. We have identified the species listed in Table I11 by comparison of mass spectra and chromatographic behavior with authentic samples. Several other ketones,
,'
quinones, anhydrides, and nitro derivatives of PAH, present a t lower concentration in this extract have been tentatively identified by their mass spectral fragmentation patterns. These compounds are listed in Table I\'. When benzene/methanol mixtures are used for Soxhlet extraction of these channel blacks, P A H polycarboxylic acid methyl esters are obtained, presumably by acid catalyzed esterification on the highly acidic surface of the black. Table IV lists those methyl esters identified from benzene/methanol extraction of channel blacks A a n d B. A description of the materials extractable from a variety of carbon blacks with benzene/methanol is in preparation (20). When these same carbon samples were extracted with naphthalene, the major extractable materials (Figure 1) were different from those seen in t h e benzene extracts. By comparison with authentic samples, three of these components were shown to be the isomeric binaphthyls. This finding, along with t h e presence of these materials in three consecutive naphthalene extractions (Table 111),led to the suspicion that they were somehow derived from the naphthalene. T h e major compound of molecular weight 268 and molecular formula C20H120displayed a mass spectrum consisting of a strong molecular ion and a doubly charged species ( m j e 134). The
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
2125
I__-
-
~
_____-_______________________ , , ,
,
,
___r
Figure 1. Total ion current trace of the naphthalene extract of channel black A Numbers are relative retention indices I is the internal standard, 9-phenylanthracene
only significant fragment was due to loss of CHO from t h e molecular ion. T h i s behavior is similar to t h a t reported for dibenzofuran (21). A synthetic sample of dinaphtho[2,1b:1’,2’-d]furan displayed a mass spectrum identical to t h e unknown from channel black. T h e two materials were not, however, identical by GC retention behavior. T h e synthetic material does co-chromatograph with a minor isomer present in the crude extract. We believe the major C2&II2Ocomponent to be one of the other five possible dinaphthofuran isomers. A third set of extractable compounds displayed the same molecular weights M’, 268) and the molecular formulas C21Hi6. The fragmentation pattern of the two were identical ( m j e 253. 252, 134, 126) indicating a methylbinaphthyl. Similar fragmentation patterns are observed in methylbiphenyls (22). An alternate possibility, dinaphthylmethane, was discounted on the basis of the unique fragmentation pattern of materials such as diphenylmethane (16). -4mixture of mono- and dimethylbinaphthyls was prepared by a coupling reaction between naphthalene and 1-methylnaphthalene. T h e monomethylbinaphthyls (three isomers were obtained) each showed a fragmentation identical to t h a t observed in t h e channel extractives. We have not determined the substitution patterns of any of these isomers, although it is likely that they are derived from coupling of naphthalene and the impurity 2-methylnaphthalene. These same materials were observed when a second channel black (channel B) was extracted with naphthalene. However, this more highly oxidized black yielded even more of t h e dinaphthofurans. T h e two compounds of RRI’s 2957 and 3014 were isolated in yields representing 21 and 160 ppm based on t h e carbon extracted. T o substantiate t h a t t h e carbon was involved in the formation of t h e binaphthyl compounds, a control experiment was conducted with t h e naphthalene extractor. T h e same apparatus. including a glass wool plug in a n empty Soxhlet thimble, was used for the control, and the extractor was run for 6 h. No products were found in this extract except for traces of a n unknown phthalate impurity. Further support for t h e carbon -naphthalene interaction hypothesis was obtained by conducting a n extraction of channel black A and 2-methylnaphthalene. This extract contained 9-fluorenone, anthraquinone, and l&naphthalene dicarboxylic anhydride at levels comparable to those seen in the naphthalene extracts. However, instead of t h e binaphthyls. dinaphthofurans, and methylbinaphthyls, this extract contained a series of com-
pounds of molecular weight 282, which we tentatively identify as dimethylbinaphthyls. One of these dominated and was measured a t 232 ppm based on t h e carbon extracted. No furans were detected in this extract. This experiment confirms that the binaphthyls and derivatives found in the naphthalene extracts are not adsorbed species on these commercial channel blacks. Previous work has demonstrated that naphthalene can be dimerized under free radical conditions ( I O ) , Friedel-Crafts conditions (11) and by pyrolysis (23). T h e lack of observed binaphthyls in t h e control experiment as well as in t h e lampblack extraction indicates a catalytic role for the oxidized surface of the channel blacks. T h e formation of methylbinaphthyls is likely due to the presence In the scintillation grade naphthalene of the more reactive 2-methylnaphthalene. We d o not a t present have a hypothesis to explain the source of t h e oxygen in the dinaphthofuran products of the channel black-naphthalene interaction.
CONCLUSIONS Carbon blacks in and of themselves are probably not major environmental dangers. Although human exposure to these materials is large (rubber tires, newsprint, etc.), epidemiological investigations in the carbon black industry (24-26) and animal tests (7,27,28)offer no conclusive evidence of dangers in continuous exposure to carbon blacks. Rather it should be emphasized that little is known about the role of polymeric carbons as carriers of dangerous substances in the environment and as catalysts for t h e conversion of adsorbed species into potentially more hazardous compounds. T h e recently described role of atmospheric soot in t h e conversion of sulfur dioxide t o sulfuric acid is one example of this (29). Furthermore, very little is known about the environmental distribution and toxicological properties of oxidized PAH. A series of P A H quinones has been detected in atmospheric particulate samples (30). Based on the work described here, P A H acids, anhydrides, and nitro derivatives are also likely candidates for species adsorbed on carbonaceous atmospheric particulates.
LITERATURE CITED (1) H. L. Falk and P E. Steiner, Cancer Res., 12,30 (1952). (2) M. L. Lee and R. A. Hites, Anal. Chem., 46, 1890 (1976). (3) L. Wallcave, D. L. Naael. J. W. Smith, and R. D. Waniska. Environ. Sci. Techno/., 9, 143 (1975). (4) A. H. Qazi and C. A . Nau, Am. Ind. Hyg, Assoc. J , , 36, 187 (1975). (5) J. Neal, N. Thornton, and C. A. Nau, Arch. Environ. Health, 4, 46 (1962).
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978 (21) B. G. Pring and N. E. Stjernstrom, Acta Chem. Scand., 22, 549 (1968). (22) J. L. Laseter, U. Mende, and G. W. Griffin, Org. Mass. Spectrom., 4, 599 (1970). (23) G. M. Badger, S. D. Jolad, and T. M. Spotswood, Aust. J . Chem., 17, 771 (1964). (24) T. H. Ingalls, Arch. Ind. Hyg. Occup. Med., 1-2, 662 (1950). (25) K. Kay, Clin. Toxicol.. 9, 359 (1976). (26) H. A . Tyroler, D. Andjelkovic, R. Harris, W. Lednar, A. McMichael, and M. Symons, Environ. Health Perspec, 17, 13 (1976). (27) C. A. Nau, J. Neai, and V. Stembridge, AMA Arch. Ind. Health, 17, 21 (1958). (28) C. A. Nau, J. Neal, and V. Stembridge, AMA Arch. Ind. Health, 18, 51 1 (1958). (29) T. Novakov. S. G. Chang, and A. B. Harker, Science, 186, 259 (1974). (30) R. C. Pierce and M. Katz, Enwron. Sci. Techno/., 10, 45 (1976).
(6) H. L. Falk and P. E. Steiner, Cancer Res., 12, 40 (1952). (7) P. E. Steiner, Cancer Res., 14, 103 (1954). (8) Food and Drug Administration, "Color Additives", Fed. Regk., 41, 41852 (Sept. 23, 1976). (9) L. A. Heredy and P. Fugassi. Adv. Chem., 55, 448 (1966). (IO) G. M. Badger and C. P. Whittle, Aust. J . Chem., 16, 440 (1963). (11) P. Kovacic and F. W. Koch. J . Org. Chem., 30, 3176 (1965). (12) B. G. Pring and N. E. Stjernstrom, Acta Chem. Scand., 22, 681 (1968). (13) G. R. Clemo and R. Spence, J . Chem. Soc., 1928. 2811. (14) R. G. Dromey, M. J. Stefik, T. C. Rindfleisch. and A. M. Duffield, Anal. Chem., 48, 1368 (1976). (15) D. H. Smith, M. Achenbach, W. J. Yeager, P. J. Anderson. W. L. Fitch. and T. C. Rindfleisch, Ana/. Chem., 49, 1623 (1977). (16) "Eight Peak Index of Mass Spectra", Mass Spectrometry Data Centre, AWRE, Reading, RG74PR, UK, 1974. (17) A. Gold, Anal. Chem., 47, 1469 (1975). (18) H. Budzikiewicz, C. Djerassi, and D. H. Williams, "Mass Spectrometry of Organic Compounds", Holden-Day, San Francisco, Calif. 1967. ( 19) G. M. Janini, G. M. Muschik, J. A. Schroer, and W. L. Zielinski, Anal. Chem., 48, 1879 (1976). (20) W. L. Fitch and D. H. Smith, submitted to Environ. Sci Techno/.
RECEIVED for review May 22, 1978. Accepted September 11, 1978. This work was supported by a grant from the National Aeronautics and Space Administration (NGR 05-020-004).
Expanded Solubility Parameter Treatment for Classification and Use of Chromatographic Solvents and Adsorbents Barry L. Karger" Institute of Chemical Analysis, Northeastern University, Boston, Massachusetts
02 1 15
Lloyd R. Snyder Technicon Instruments Corporation, Clinical Chemistry Department, Tarrytown, New York
1059 1
Claude Eon Depariment of Chemistry, University of Sherbrooke, Sherbrooke, Canada
and hence to select t h e types and compositions of particular phases for a given separation. Most efforts to d a t e a t classification have involved t h e use of experimental chromatographic data on model systems (e.g., 1-7), since more precision is required than a semitheoretical approach would generally allow. T h e use of essentially empirical classification schemes is of demonstrated value; however, these approaches d o not directly lead to a n understanding of t h e underlying physical and chemical phenomena for a given separation system. Generally they provide only limited insight into t h e fundamental basis of separation and t h e interrelationships among different chromatographic systems (e.g., adsorption vs. partition). An alternative approach to classification of phase systems and prediction of retention and selectivity is through consideration of the fundamental molecular interactions common to all systems, with t h e goal of developing a unified picture of chromatographic retention and selectivity. While such a unified conceptual framework is at hand for band broadening ( 8 ) .it is a t present lacking for chromatographic retention. In previous papers we have outlined a general approach based on interaction forces for t h e classification of solvents and adsorbents @ , I O ) . This treatment accounts for individual interaction forces in terms of specific solubility parameters which are derived mainly from properties of t h e pure compounds themselves. We have already presented methods of derivation and a general justification of the particular values obtained (10). I n t h e present paper we will apply t h e expanded solubility parameter treatment t o a variety of chromatographic systems and indicate both t h e advantages
The application of an expanded solubility parameter treatment in terms of interaction forces to various chromatographic processes is examined. Estimation of selectivity and classification of phase systems is possible with this approach. The general scheme is developed by relating the model to the processes of vaporization, solution, mixing, and adsorption. The scheme is first applied to gas-liquid chromatography. The Rohrschneider empirical approach for classification of stationary liquid phases is derived in terms of the present treatment. The validity of the model is shown with experimental data on a series of moderately polar stationary liquid phases. Gas-solid chromatography is next examined where it is shown that induction forces can be neglected in the adsorption process. These results are then applied in liquid-solid chromatography, where solvent strength with graphitized carbon black as adsorbent is shown to be proportional to the dispersion solubility parameter of the solvent. Solvent strength on polar adsorbents is next correlated with the polar solubility parameters of the solvent. Functional group adsorption strengths are shown to be proportional to the polar solubility parameters of the groups. Finally, the application of the model to liquid-liquid chromatography is briefly discussed, and the limitations in aqueous solutions are noted.
T h e classification of chromatographic phase systems has been of interest for many years. Through such classification schemes, it is possible to estimate retention and selectivity 0003-2700/78/0350-2126601 O O / O
C
1978 American Chemical Society
