2367
Anal. Chem. 1983,55,2367-2374
Separation of Polar Compound Classes in Liquid Fossil Fuels by Liquid Chromatography with Aprotic Dipolar Solvents Jan Chmielowiec Gulf Canada Limited, Research and Development Department, Sheridan Park, Ontario, Canada L5K 1A8
fractions from the oil (1). These fractions were named after the procedure which involved chromatographic separations on anion and cation exchange resins and coordination with ferric chloride, respectively. However, the fractions were found not to be chemically distinct. Some species, which by definition should not occur in the specific fraction types, were identified. For instance, amides and pyrrolic compounds were present in all the fractions (2). In addition, the compositions of the fractions were influenced by the sequence of chromatographic steps performed. Polar compound types were also subjected to class separations (3). Subsequently, more efficient, chromatographic separations were aimed at more discrete characterization by separating the samples into polar concentrates of distinct structural types, High sensitivity for the size and substitution of eluates limited the applicability of reversed-phase systems, but a variety of normal phase systems were utilized. Some normal phase systems were used to separate azaarenes ( 4 , 5 ) and showed that the separations achieved depended on the steric accessibility of the nitrogen electron pair. Sequential elution schemes were reported to yield polar fractions dominated by various functional group types (6-8). Recently developed systems revealed a possibility of controlling separation selectivites by using mobile phases containing additives (9, 10). Amines and carboxylic acids for example were found to promote functional type selectivity on plain silica columns
Aprotlc dlpolar solvents were used as eluent addltlves for moderatlng silica surface. The absolute and relatlve retentlons were controlled by both additlve type and concentration. The selectivities for compound classes were observed. The correspondlng elutlon order was related to the extent of the compiexing afflnltles involving the additlve and functlonal groups of the solutes. The concept of dlscrimlnatlng among compound classes In very complex mixtures was examined wlth model hydrocarbon and polar compounds by using a slllca column and eluents contalnlng dimethyl sulfoxlde and carbon tetrachiorlde. The chromatographic separations of compound classes such as aromatlc hydrocarbons and aza compounds as well as proton-donor classes such as >NH, -CH,OH, -OH, and -COOH compound types were achleved. Separatlons of petroleum, bitumen, and coal ilquld samples are dlscussed.
A wide variety of heteroatom constituents and compounds with attached polar functional groups occur in crude oils. Elemental analyses have revealed increased concentrations of nitrogen- and oxygen-containing species in alternative fossil fuel sources. Higher concentrations of polar compounds, in general, are associated with problems in processing heavier feedstocks and their products. Discrete compositional information on the polar compounds in synthetic oils derived from coal, bitumen, heavy oil, petroleum residue, etc. may contribute to more economic processing of those oils. This study has been launched to characterize the classes of polar compounds present in various nonconventional liquid fossil fuel sources and circumvent drawbacks of multistep chromatographic analyses. Early chromatographic schemes, such as those developed in conjunction with American Petroleum Institute Project 60, allowed the isolation of acidic, basic, and neutral nitrogen
(11).
The role of additives, also called moderators in other applications, has been reviewed by Engelhardt (12). Water or polar organic liquids present in nonpolar eluents were found to influence absolute and relative retentions due to moderating effects on the high polarity and activity of the surfaces of the solid stationary phases. The lower the polarity of the eluent, the greater was the influence of the moderator concentration. Although some selectivities promoted by changes in moderator concentration are potentially useful, poor repeatabilities achieved along with long equilibration times limited the ap-
Table I. Physical Properties of Selected Solvents and Their Parameters Related to Basicity dielec const
solvent N-methylformamide (NMF) propylene carbonate (PC) dimethyl sulfoxide (Me,SO) N,N-dimethylformamide (DMF) acetonitrile (AN) 1-methyl-2-pyrrolidinone (MP ) hexamethylphosphoramide (HMPA) acetone (A) water a Donor numbers listed in ref 16. not in agreement.
D
bP, "C
Dipolar Aprotic Solvents 182.4 3.84 183 64.9 4.94 24 2 46.7 4.3 189 36.7 3.82 152 36.0 3.84 80.1 32.0 4.09 20 2 29.6 5.37 23 5 20.7 2.88 56.2 Amphiprotic Solvent 78.5 1.84 100
Kamlet-Taft parameter values listed in ref 16.
d, g mL-'
0.9988 1.0257 1.1014 0.9445 0.7856 1.027
1.0253 0.792 0.99 7
DN,a kcal mol-' cm-' x
15.1 29.8 30.9 14.1 27.3 38.8 17.0
lo3
0.38 0.76 0.69 0.31
0.75 1.06 0.48
18.0' 0.14 33 ' 0.47' Data from different sources are
0003-2700/83/0355-2367$01.50/00 1983 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983
1
Eluent:
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Hydrocarbons
0
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in CCL4
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k' 0 0 0
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3
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Figure 1. Chart of retentions of model compounds.
plicability of such systems. In contrast to water the organic moderators, such as primary alcohols or other less polar solvents, moderated the silica surface to a lesser extent due to the weaker adsorption and stronger interactions with organic eluents. The studies reviewed by Engelhardt, however, did not deal with highly polar organic additives/moderators, which could interact strongly with the stationary phases. Such solvents, being miscible with nonpolar eluents, might also permit faster equilibration of the chromatographic system. Aprotic dipolar solvents (13), due to their highly polar nature, seemed to meet the requirements of strong surface moderation. They were also expected to be miscible with many relatively nonpolar organic solvents. These solvents of intermediate to high (>20)dielectric constant and of a dipolar nature (dipole moments range from 2.8 to 5.3) give moderately good solvating media. Ketones, nitriles, amides, sulfoxides, and nitro compounds fall into this class. The above solvents do not exhibit any appreciable tendency to participate in the transfer of protons. In contrast to neutral solvents, which can act either as proton donors or as proton acceptors (depending on the properties of the solute), they do not mask or distort the intrinsic acidic and basic properties of solutes. Such solvents usually possess lone pairs of electrons which are able to coordinate with various species. Dimethyl sulfoxide (Me2SO) was reported to form stable association complexes with proton-donating compounds such as -COOH, -OH, >NH, and -CH compound types and dipole-dipole complexes with nitriles and carbonyl compounds (14). The selective interactions of MezSO with a electron and polar compounds were also reported elsewhere (15). Solvent parameters related to basicity (16),such as donor strength for instance, classify some of those solvents with pyridine and quinoline. Since pyridine was used in the sequential elution schemes to elute the most strongly retained polar solutes (6,8),the aprotic dipolar solvents seemed to offer the same potential. The solvents listed in Table I were used as eluent additives to evaluate separating polar compounds with different functional groups. The table compiles the
physical properties and solvent parameters characterizing basicity. Water has been listed for comparison purposes.
EXPERIMENTAL SECTION Equipment. The high-performance liquid chromatograph (HPLC) system (Series 8800) from Du Pont (Wilmington, DE) consisted of a gradient controller, pump, UV spectrometer, and column compartment equipped with injection valve (Rheodyne, Catati, CA). A refractive index detector (Model 401) from the Waters Associates, Inc. (Milford, MA), was used to detect some eluates. Infrared detection was provided by use of a Fourier transform infrared (FTIR) spectrometer Model 60 SX (Nicolet, Madison, WI) equipped with a 7.5-pL flow-through cell. Columns. Retention data on model compounds were obtained on a 300 X 4.6 mm silica (Porasil, 10 pm) column from Waters Associates. A 250 X 4.6 mm silica (Partsil, 10 pm) column from Whalman, Inc. (Clifton, NJ), was used to separate the real satnples. Procedure. Carbon tetrachloride was used as a solvent for preparing solutions of model compounds and real samples. The concentrations of the solutions ranged from 0.1 to 1mg/mL. The 20-pL samples were injected on the column. Mobile phases employed were of carbon tetrachloride containing various concentrations of aprotic dipolar solvents. Flow rates of 2 and 3 mL/min were used in the selectivity and application study, respectively. Reagents. HPLC grade CC1, (Caledon Laboratories, Georgetown, Ontario, or Fisher Scientific, Don Mills, Ontario) was stored over sodium hydroxide and basic alumina filtered before use. The solvent treatment was found to either supress or slow down corrosion/gas evolution effects described elsewhere (17).
Aprotic dipolar solvents from Aldrich Chemical Co. (Montreal, Quebec) and Caledon Laboratories were used as supplied. Model compounds were purchased from Aldrich Chemical Co. and Sigma (St. Louis, MO). The coal liquid samples were obtained from Gulf Oil (Harmarville, PA), while petroleum-type samples were supplied by the operating departments of Gulf Canada.
RESULTS AND DISCUSSION Selectivities. The tendencies of aprotic dipolar solvents
ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983
Yc?Yc?
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983
Table IV. Capacity Factors, k', Observed on the Plain Silica compound class CH type hydrocarbons
aromatic hydrocarbons
> c=o
aza compounds
other
compound triphenylmethane 3-phenylpentane p-isopropyltoluene p-diisopropylbenzene te traisopropylbenzene p-isopropylbiphenyl isobutylbenzene naphthalene anthracene 2-methylanthracene 9-methylanthracene 9,lO-dimethylanthracene p-terphenyl benz [alanthracene chrysene pyrene perylene dibenz [a,hlanthracene benzo[ghi]perylene coronene decacyclane 9-anthraldehyde 9-acetylanthracene anthrone benzan throne 9,10-dihydrobenzo[a]pyren-7(8 H )-one phenan threnequinone benz [alanthracene- 7,12-dione pyridine 2,6-diphenylpyridine quinoline 5,6-benzoquinoline 7,8-benzoquinoline acridine p he nant hridine 10-methylbenz[g]acridine dibenz [a, i] acridine 2,2'-biquinoline phenazine benzo[ clcinnoline 1,7-~henanthroline 6,12-diazaanthrathrene terpyridyl 1,2,4-benzotriazine 1,4,5-triazanaphthalene thianthrene 0-thionaph tho1 1,2-benzobiphen ylene sulfide xanthene 9-anthracenecarbonitrile 1-nitronaphthalene diphenylamine N-phenyl-1-naphthylamine
pyrrolic
N-methylformanilide 1,2,5-trimethylpyrrole N-ethylcarbazole vanadium(1V) rneso-tetraphenylpoirphine mesoporphyrin IX dimethyl ester protoprophyri'n IX dimethyl ester pyrrole carbazole 2-methylcarbazole benzo[u]carbazole 1-azacarbazole 13H-dibenzo[a,ilcarbazole 2-methylindole 7-methylindole 4,5-diphenyl-4-oxazoline2-thione phenothiazine 2,4,5-triphenylimidazole
-CH,OH
benzyl alcohol phenethyl alcohol
eluent:
eluent:
0.05% Me,SO
1%Me,SO
in CCl, 0.5 0.3 0.4 0.4 0.4 0.4 0.3 0.5 0.6 0.6 0.6 0.7 0.4 0.8
0.9 0.9 0.9 1.0 0.9 1.1 0.8
1.6 1.6 1.6 2.3 2.4 1.2 1.2 4.9 1.2 3.5 4.7 1.4 2.3 4.0 4.0 3.2 1.3 1.3 3.8 6.0 4.9 1.4 2.9 s.r. 0.6 3.9 0.9 0.4 1.6 1.7 4.0 2.7 5.9 0.6 0.8 2.2 4.4 5.6 22.4
in CC1, 0.2 0.2 0.2 0.2 0.2 0.3 0.2 0.2 0.2 0.2
0.3 0.3 0.3 0.3 0.4 0.4 0.4 0.4 0.4 0.5 0.6 0.6 0.5 0.5 0.7 0.4 0.5 0.5 0.6 0.4 0.7 0.7 0.4 0.4 0.6 0.5
-
0.4 0.3 0.7 0.6 0.5 0.6 0.6 1.8 0.3 0.3 0.3 0.3 0.6 0.7 1.4 1.3 0.7 0.4 0.4 0.9
0.7 0.8
3.2 3.6 3.1 3.8 3.6 3.4 3.0 3.3 3.0 3.3 3.5 3.2 3.0
ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983
2371
~
Table IV (Continued) compound
compound class
compound
compound class
phenol 3-ethyl-5-methylphenol
PhOH
4-c yclohexylphenol
1-naphtho1 2-naphthol 2-hydroxy fluorene
,
9-phenanthrol isocarbostyril benzylamine aniline 1-aminoanthracene 2-aminoanthracene 1-aminopyrene
2(-CH,OH) 2(>NH) >NH and -CH,COOH >NH and -OH -CH,OH and -OH >NH and -COOH 2(-OH)
2(-",)
in CCl,
eluent: 1%Me,SO in CCl, 5.4 4.3 4.6 7.0 7.6 7.5 8.4 7.5 3.6 3.8 4.8 5.8 8.2
compound
eluent: 10% Me,SO in CCl,
benzoic acid 1-naphthoic acid 2-naphthoic acid 9-anthracenecarboxylic acid 2-thiophenecarboxylic acid 1,2-benzenedimethanola 1,3-ben~enedimethanol~ benzoyleneurea phthalhydrazide tryptophol indole-3-acetic acida 2-hydroxycarbazole 5-hydroxyindole 5-hydroxyoxoindole 2-hydroxybenzyl alcohol 3-hydroxybenzyl alcohol indole-!&carboxylicacid indole-5-carboxylic acid p,p'-biphenol 1,5-dihydroxynaphthalene 1,3-dihydroxynaphthalenea 2,7-dihydroxynaphthalene 4,4'-thiodiphenol 2,3-diaminonaph thalene l15-diaminonaphthalene
0.8 1.0 1.2 2.3 1.5 1.5 1.9 2.4 2.8 2.6 2.4 3.2 3.5 3.5 2.4 3.2 3.4 3.6 3.7 3.6 3.9 4.0 3.8 3.9 4.5
compound class PhCOOH
eluent: 1%Me,SO
3.1 3.2 3.9 3.8 3.6 4.0 5.3 4.4 4.0 3.8
benzylbenzyl alcohol 2-biphenylme thanol 1-naphthalenemethanol 1-naphthalenee thanol 2-naphthaleneethanol 9-anthraceneme thanol phenylacetic acid 2-phenylbutyric acid 3-phenylbutyric acid 4-phenylbutyric acid
Ph-alkyl-COOH
Ph-alkyl-" PhNH,
eluent: 0.05% Me,SO in CC1,
a Monitored with RI detector. -
toward selective complexation with various functional groups were investigated by moderating the silica surface with the solvents of this class. Evaluation of the moderators was based on their ability to discriminate among chemically distinct compound classes, Le., to form "envelopes" of solutes with specific functional groups. Carbon tetrachloride was used as a major eluent component in all the chromatographies performed. Although relatively nonpolar, this solvent is miscible with most of aprotic dipolar solvents and dissolves petroleum samples. The eluents con-
tained 1% of aprotic dipolar solvent. Due to poor miscibility with CC14,the concentration of N-methylformamide (NMF) in CC1, was 0.4%. These highly polar components of the eluent decreased the absolute retentions of model compounds selected to represent hydrocarbons and various polar compound classes. The corresponding retention data are shown in Table 11. Additive concentrations as low as 0.03% moderated the silica surface. The moderators also influenced the relative retentions of the standards. The selectivities sufficient to resolve aromatic hydrocarbons, >NH, -OH, and -COOH
2372
ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983
In
1% D M S O i n C C L 4
DMSOiCCL4
7
* I
10% D M S O i n CCL4
F--
b
L
0
10
T I M E (rnin)
Chromatograms of hydrocarbon-free polar subfractions collected from a clay column using dlethyl ether-methanol (80:20) as a mobile phase: (A) standards, (1) acridine, (2) carbazole, (3) 13Hdibenzo[a ,i] carbazole, (4) 2-naphtho1, (5)9-anthracenecarboxylic acid; (B) Rainbow Oil polars; (C) Gulf Alberta Oil polars. Samples were 20 pg. Eluent was CCI,/Me,SO: (99:l) 0-10 min, (9O:lO) 10-20 min. Figure 3.
YO 03 99 97)
( 1 89)
n
/
n
$"
TIME
(mi")
Chromatograms of bltumen and petroleum samples: (A) blank: (B) standards, (1) coronene, (2) phenazine, (3) 1,7phenanthrollne, (4) 1,4,54riazanaphthalene, (5) 2-methylindole, (6) carbazole, (7) 2-naphthol, (8) 9-anthracenecarboxylic acid; (C) Athabasca bitumen; (D) Athabasca bitumen residuum (>504 OC); (E) Basrah 011 fractlon (>360 "C); (F) Petrosar oil fraction (>360 "C). Samples were 5 pg. Eluent composition was CCI,/Me,SO: (99.97:0.03)0 min, (99:l) 0-8 min, gradient-exponent 5 (99:l to 5050)8-16 min, (5050) 16-20 min. Figure 2.
compounds were obtained. Some aza compounds stayed on the column when the eluents containing acetone, acetonitrile, or propylene carbonate were used. Lower base strengths might have been responsible for the strong retentions of these Nheterocyclics. Hexamethylphosphoramide-spikedeluent was found to resolve the aza and >NH compounds to a lesser extent than l-methyl-2-pyrrolidinone, dimethylformamide, Me2S0, and NMF containing mobile phases. The latter moderators promoted similar selectivity types, which agree with those that might be anticipated from Snyder's classification of solvent group selectivity (18). The repeatability of the selectivities observed was examined in relation to the equilibration and reequilibration of the column. A system consisting of a silica column and carbon tetrachloride containing Me2S0 has been found to offer excellent repeatability. However, the time necessary for equilibrating the silica column depended on the MezSO concentration range (see Table 111). The aprotic dipolar additives were easily and completely removed from the silica surface. 2-Propanol and water were routinely used when switching from one type of additive to another. Thus, the interactions of aprotic dipolar solvents with the silica surface might be reversible in spite of their highly polar nature. The equilibration of the silica column with water followed by 2-propanol and eluent containing Me2S0 did not affect the repeatabilities of retentions observed. Unlike systems moderated by water, this system offered good repeatability and equilibrated considerably more quickly because of (1)greater miscibility of the moderators with C C 4 and (2) weaker interactions with the silica surface than water. With the above background information, the chromatographic system employing MezSO was selected to examine systematically the chromatographic discrimination of polar compound classes. Discrimination of Compound Classes. The formation of compound class envelopes was investigated by injecting
model compounds on the silica column. The solutes were eluted with mobile phases containing Me2S0. The capacity factor values of hydrocarbons and polar compounds as well as corresponding values, In k ', are presented in Table IV and Figure 1,respectively. The chart illustrates the class formation tendencies, system resolving nature, and overlaps between compound envelopes. The aromatic hydrocarbons, including H!H type structures, constituted the first envelope, which was followed by >C=O and aza compounds forming overlapping envelopes. Other weakly retained compounds, which might be considered in the first envelope, included those with sulfur, oxygen, or nitrogen atoms built into a hydrocarbon backbone. The retentions of injected secondary amines, porphyrins, thiol, nitrile, and amide indicated that compounds of such classes would be eluted together with aza compounds. Neither alkyl substitution of the aromatic rings nor their increasing number was found to affect significantly the spread of envelopes. Higher concentrations of Me2S0 in the mobile phases were necessary to elute acids, primary amines, alcohols, hydroxyl, and pyrrolic compounds. Alcohols and pyrrolic structures formed an envelope followed by a second one containing primary amines and hydroxyl compounds. The aryl-alkylCOOH type acids were retained in the intermediate region. The aryl-COOH type acids were eluted as a class tailed by various bifunctional compounds. The tendency to form and resolve compound classes was apparently not impaired by the number of aromatic rings of the solutes studied. An approximate retention order of compound classes for this system appears to be as follows: aromatic hydrocarbons € =C=O, ma compounds < =NH, -CH20H < Ph-alkyl-COOH, -OH < PhCOOH. The envelopes of bifunctional proton donors such as alcohols and pyrrolic and hydroxyl compounds were completely resolved. However, the retentions of aromatic acids and diamino compounds overlapped those of dialcohols and dihydroxyl compounds, respectively. The retentions of standards with two different proton-donating groups placed those compounds between or within the dipyrrolic and dihydroxyl envelopes. The discrimination of bifunctional compounds reflected the additivity principle operative for proton-donating groups. However, to extend the elution order for polyfunctional compounds, more data on the retention of model compounds are necessary.
ANALYTICAL CHEMISTRY, VOL. 55, .0501
NO. 14, DECEMBER
1983
2373
1620-1590 crn-l
C
'O"t--iZ,000
2990-2920 cm-l A
3100-3300
ern-'
,025
,000
6 TIME (min)
4
2
0
.0251 1
6
2
0
-
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,000
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2990-2920 cm-'
,000
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,050- 3500-3400 cm-l
0
2
U
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m 4
.050]
3300-3100 cm-'
.025
,000-
-
!
0
2
4
6
TIME ( m i d
0
3
6
TIME (min)
Figure 4. (Top) Chromatograms of coalderived naphtha fraction using UV or FTIR detection: (A) standards, (a) toluene, (b) phenol; (B) and (C) naphtha fraction. Samples were 20 pg. Eluent was CCI,/Me,SO (98.5: 1.5). (Bottom) Chromatograms of coal-derived middle distillate fraction using UV or FTIR detection: (A) standards in order as follows, naphthalene, indole, 1-naphthol: (B) and (C) middle distillate fractions. Samples were 20 pg. Eluent was CCI,/Me,SO (98.5:1.5).
The strong influence of the concentration of MezSO on the retentions was observed over a wide range of concentrations. The retentions of aza arenes decreased drastically after approximately 1h when reaching complete column equilibration
with the eluent containing 0.05%of Me2S0. It was apparent that the equilibration might have led to an immobilized moderator layer on the silica surface. The presence of the polar phase bonded to the surface water (silanob) is very likely
2374
ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983
since thermodynamic, dielectric, and spectroscopic data provide extensive evidence of the strong preferential association between water and Me2S0 (14). Consequently, the bonded moderator permitted only weak interactions between the aza compounds and stationary phase, while proton-donating solutes stayed on the column. They were eluted with the eluents that contained higher concentrations of Me2S0. The corresponding elution order was related to the extent of hydrogen bonding interaction involving MezSO and the "bound" hydrogen of the functional group. The class formation tendencies and elution order observed in the system provide various analytical options. Compounds, which form a well-resolved envelope during chromatography, can be isolated from interfering components. The classes formed, but resolved to a limited extent, can be analyzed by use of specific spectrometric techniques. Due to the capability of discriminating proton-donating compounds, the system appears to be particularly applicable for analyzing species of this type in multicomponent mixtures. Consequently, various on- and off-line spectrometric techniques can be applied to quantitate or characterize various polar compound classes. Separations of Petroleum and Bitumen Samples. The concept of resolving/separating polar compound classes was examined by using samples expected to contain naturally occurring polar species. Two or three peak chromatograms were recorded (Figure 2). Hydrocarbons and other relatively nonpolar constituents probably constituted the first peaks. Lack of peaks in those retention ranges, where monofunctional polar compounds may be expected, indicates predominantly polyfunctional polar species. However, such interpretation of the regions between peaks could change when using another type of detection. Polyfunctional species capable of moderately strong interaction with MezSO probably formed the second peaks. 1,4,5-Triazanaphthalene is a good example of compounds, which are strongly retained and rapidly eluted when using eluents containing 0.03% and 1% of Me2S0, respectively. The third peaks may be assigned to protondonating species such as acids or those polyfunctional compounds, which exhibit very strong affinities to Me2S0. Although the above interpretation of the chromatograms is based on the extent of interaction between Me2S0 and model compounds, it is also consistent with the character of the samples injected on the column. Differences in peak intensity of Athabasca bitumens and its residual fraction appear to reflect compositional changes perhaps caused by distillation. The higher intensity of the second peak may be ascribed to the increased concentration of polyfunctional species generated in the process of residuum formation. The lower intensity of the third peak may be explained by a decomposition of acids during bitumen distillation. In turn, differences in peak intensity of the bunker samples correspond to different contents of aromatic and polar components. Our experience has shown that the Basrah oil fraction is a bunker of heavier type, i.e., more abundant in aromatic and polar type components than that of Petrosar oil. The polar fractions of conventional oils (Figure 3) yielded chromatograms consisting of a sharp peak overlapped by a wide band and weak diffuse peak. These hydrocarbon-free fractions were collected from a sequential elution scheme by using a clay column and diethyl ether-methanol (80:20) as mobile phase. They were characterized by high-resolution mass spectrometry as predominantly nitrogen compounds. Since ether-alcohol based eluents were reported to elute basic nitrogen compounds tailed by polyfunctional molecules (6), the first peak and band are assumed to contain mostly aza
and secondary amine type compounds, respectively. Separations of Coal-Derived Samples. The discrimination of compound classes in real samples was also tested on the samples abundant in proton-donating constituents. The chromatograms of coal-derived liquids containing -OH species are shown in Figure 4. Two distinct envelopes were formed. The envelope "a" was dominated by hydrocarbons followed by the envelope "b" dominated by hydroxyl-containing components. The chromatograms obtained with a FTIR spectrometer as detector indicated that the -OH species were eluted as a class permitting its on-line quantitation. The -OH species were monitored at the 3100-3300-~m-~ window, because the presence of Me2S0 in CC4 was found to shift the absorption of model hydroxyl compounds to that frequency range. The FTIR detection at the 3400-3500 cm-' window indicated the presence of species in the region between the envelopes. On the basis of the retention data these absorbances may be assigned to pyrrolic-type compounds.
CONCLUSIONS The proposed chromatographic system is capable of giving improved and quicker class separations than those employing sequential elution or involving transfer of sample from one column to another one. Due to low costs of the unmodified silica and used solvents, the system also offers a scale-up potential for the separations. The results of the present studies demonstrate the potential for improving the isolation and characterization of the polar nonvolatile components of samples from a variety of processes currently being developed to produce fuel from noncoventional sources.
ACKNOWLEDGMENT The author thanks Nicolet Instruments, Madison, WI, for providing research facilities during the course of the HPLC/FTIR experiments. The laboratory assistance of J. Gschwend and discussions with D. W. Vidrine are appreciated. Registry No. Me2S0, 67-68-5; C C 4 , 56-23-5.
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RECEIVED for review May 16, 1983. Accepted September 2, 1983.
