Anal. Chem. 1986, 58,3011-3016
3011
Separation and Characterization of Hydroxyl Aromatics in Complex Fractions from Nondistillable Coal-Derived Liquids Howard A. Cooper and Robert J. Hurtubise* Chemistry Department, The University of Wyoming, Laramie, Wyoming 82071 Howard F. Silver
Chemical Engineering Department, The University of Wyoming, Laramie, Wyoming 82071 Complex hydroxyl aromatlc fractions isolated from nondlstlllable coal-derlved llqulds were separated by a comblnatlon of normal-phase and reversed-phase llquld chromatography. The normal-phase chromatographlc step effected the separation of hydroxyl aromatics Into mono- and dlhydroxyl fractlons. The mono- and dlhydroxylfractlons from the coal-llquld sample were characterized with infrared and field-ionization mass spectrometry (FIMS). A monohydroxyl fraction of oils from a Kentucky coal-liquid sample was separated with an optimized reversed-phase chromatographlc system. The monohydroxyl fraction was completely eluted by uslng a comblnatlon of lsocratlc and gradient elution condltlons. The comblnatlon of reversed-phase liquid chromatography and FIMS provided a unique method for the characterization of the monohydroxyl fractlon of 011s from the Kentucky coal-liquid sample.
The development and optimization of coal liquefaction processes for converting coal to environmentally acceptable liquids necessitate a fundamental understanding of coal liquefaction chemistry. This requires the development of new analytical separation methods and characterization procedures. However, no single method may suffice since sample composition and required compositional information will vary with the specific fuel and its intended use. Thus, if a coal-derived liquid is to be used as an energy source, compound-class separations may provide sufficient analytical information. On the other hand, if the coal-derived liquid is to be used as a petrochemical feed stock, separation and characterization of specific compounds may be required. Furthermore, the identification and elimination of toxic and carcinogenic compounds is necessary to reduce environmental and occupational health hazards. The extreme complexity of coal-derived liquids requires compound-class or functional-group-type separations prior to detailed characterization. Of particular interest are hydroxyl aromatics which are important in coal liquefaction processes and are abundant in coal-derived liquids. In addition, hydroxyl aromatics are important in many chemical processes and a number of exhibit carcinogenic and mutagenic activity ( I ) . Poirier and George (2),Trusell (3), and Yonko (4) have reviewed methods for separating coal-derived liquids according t o compound types and the analytical methods used to characterize these fractions. In particular, Gorbaty et al. (5) have discussed the need for analytical methods for the separation and characterization of various oxygen functional groups in coal-derived liquids. Several methods have been developed for isolating and in some cases characterizing hydroxyl aromatic fractions from coal-derived liquid samples (2-4). However, very little work has been done in the subsequent separation and characterization of hydroxyl aromatic coal-liquid fractions. In general, both normal- and reversed-phase high-performance liquid chromatography (HPLC) have been used to
separate hydroxyl aromatics (6-20, and several of these HPLC systems have been applied to distillable hydroxyl aromatic coal-liquid fractions (15-21). Recently we briefly discussed HPLC systems for the isolation of hydroxyl aromatic fractions form nondistillable coal-liquid samples (22). However, no HPLC method has been previously discussed in detail for the separation and characterization of nondistillable hydroxyl aromatic coal-liquid fractions. The purpose of this work was to develop and apply normaland reversed-phase HPLC separation methods to extremely complex nondistillable hydroxyl aromatic coal-derived fractions. Results are discussed for the separation of mono- and dihydroxyl aromatics and the characterization of mono- and dihydroxyl aromatic fractions of oils and asphaltenes from two nondistillable coal-derived liquids. In addition, the limitations of the methods are considered, and the general characterization of the hydroxyl aromatic fractions by fieldionization mass spectrometry, infrared spectrometry, and elemental analysis is discussed.
EXPERIMENTAL SECTION Material Studied. Samples of two nondistillable (>427 "C) coal-denied liquids produced by the direct liquefaction of Wyodak and Kentucky coals in an SRC-I process were investigated. The Wyodak nondistillable coal-derived liquids were produced from a subbituminous coal obtained from the Canyon-Anderson seams in the Amax Coal Co. Belle Ayr Mine in Wyoming. These samples were supplied by Catalytic, Inc., from the Southern Company Services, Inc., SRC pilot plant located in Wilsonville, AL. The Kentucky nondistillable coal-derived liquids were produced from a bituminous Kentucky 9/ 14 coal. These samples were supplied by the Pittsburg and Midway Coal Mining Co. SRC pilot plant located near Tacoma, WA. All samples were stored in the dark in small tightly sealed containers and were analyzed as received. Hydroxyl aromatic fractions were isolated from the Wyodak and Kentucky samples using previously described procedures (23,25, 26). A more detailed description of the samples is given in ref 27.
Apparatus and Chemicals. The liquid chromatograph used was a Water Model ALC/GPC 244 equipped with a Model 6000A pump and Model M-45 pump, both controlled by a Model 680 automated gradient controller for operation in the isocratic or gradient modes. The unit also consisted of a Waters Model U6K injector, a dual-channel Model 440 UV absorbance detector set at 254 and 280 nm, a Bascom-Turner Model 8120 electronic recorder, and a Hewlett-Packard Model 3390A integrator. The chromatographic systems used in the separation were a 10-pm particle size pBondapak NH2 column (Waters Associates) with n-heptane/2-propano1(90:10and 50:50) for the mono- and dihydroxyl fractions of oils (hexane solubles), respectively, from the Wyodak and Kentucky samples, and chloroform/2-propano1 (955 and 75:25) for the mono- and dihydroxyl fractions of asphaltenes (hexane insolubles, toluene solubles),respectively, from the Wyodak and Kentucky samples, all at 4.0 mL/min. A 10-pm particle size Resolvex C8 column (Fisher) with acetonitrile/tetrahydrofuran/water (15.2:27.8:57.0) was used for the monohydroxyl fraction of oils from the Wyodak and Kentucky samples, at 1.0 mL/min. Other mobile phases used with the Resolvex C , column were acetonitrile/tetrahydrofuran/water (19.2:24.7:56.1), methanol/tetrahydrofuran/water (30.0:21.5:48.5), and tetra-
0003-2700/86/0358-3011$01.50/00 1386 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 14, DECEMBER 1986
hydrofuran/water (40:60) for the monohydroxyl fraction of oils from the U'yodak sample, all a t 1.0 mL/min. HPLC grade 2-propanol and chloroform were obtained from Baker Chemical Co., Phillipsburg, NJ. HPLC grade n-heptane was obtained from MCB Manufacturing Chemists, Inc., Cincinnati, OH. HPLC grade methanol, acetonitrile, and tetrahydrofuran were obtained from Fisher Scientific Co., Fair Lawn. N J . These solvents were all filtered with a Millipore (Bedford, MA) type FH 0.5-gm filter prior to use. Distilled water was prefiltered through a Millipore Milli-Q water purification system obtained from Millipore, Bedford, MA. Sample Separation. The procedure used in this work for obtaining hydroxyl aromatic rich oils and asphaltenes fractions from coal-derived liquids has been previously described (23, 25, 26). The original procedure (25,26) used Fluoropak 80, 20-40 mesh as the inert chromatographic support material; however, due tu the unavailability of Fluoropak, Chromosorb-T 30-60 mesh was used in this work (23). The results of the separation of coal-liquid samples into solvent-derived and compound-class fractions utilizing Fluoropak were described elsewhere (25,26), and similar results have been reported using Chromosorb-T (23, 24).
The hydroxyl aromatic fractions isolated from oils and asphaltenes from the Wyodak and Kentucky samples using the Chromosorb-T/basic alumina procedure mentioned above were subjected to a normal-phase HPLC separation on a gBondapak NH2 column (see Figure 1). This step separated the complex hydroxyl aromatic mixtures into mono- and dihydroxyl fractions. This step of the separation was developed by using standard hydroxyl compounds, which were completely separated into monoand dihydroxyl fractions with n-heptane/2-propano1(9010)(24). From previous work ( 1 4 , 2 4 ) ,it was shown that monohydroxyl and dihydroxyl compounds were almost completely separated by using a mobile phase of n-heptane/2-propanol (60:40). Compositions weaker than this gave complete separation, and a n-heptane /2-propanol(9010) mobile phase gave a separation greater than 24 min between the longest retaining monohydroxyl standard compound and the shortest retaining dihydroxyl compounds ( 2 4 ) . The NH2 separation step was originally designed for an analytical size column, but was scaled up to a semipreparative column, which allowed for the recovery of milligram quantities of the mono- and dihydroxy fractions. The respective hydroxyl aromatic fractions of oils and asphaltenes from the Wyodak and Kentucky samples were dissolved in chloroform/methanol (4:l) of sufficient volume to allow the injection of 10-15 mg of the samples onto a semipreparative gBondapak NH2 column with a 50-gL injection. The hydroxyl aromatic fractions of oils from the Wyodak and Kentucky samples were separated into monohydroxyl fractions by eluting with n-heptane/2-propanol (9010) a t 4.0 mL/min and collecting 100 mL of the respective eluents. Dihydroxyl fractions were obtained by switching the mobile phase to n-heptane/2propanol (5050) and collecting the next 200 mL of the respective eluents. The fractions were evaporated to dryness and weighed, and corresponding wt % values were calculated. The hydroxyl aromatic fractions of asphaltenes from the Wyodak and Kentucky samples were separated with the gBondapak NH2column and characterized in a similar manner to the discussion above. However, the monohydroxyl fractions were eluted with chloroform/2-propanol(95:5), whereas the dihydroxyl fractions were eluted with chloroform/2-propanol(75:25). The change from n-heptane to chloroform was necessitated due to the insolubility of the hydroxyl fractions of asphaltenes in the n-heptane/2-propanol mobile phases used for the hydroxyl fractions of oils. The compositions of the chloroform/2-propanol mobile phases were established by using standard compounds to give a similar separation for the mono- and dihydroxyl standards as that achieved with the n-heptane/2-propanol compositions discussed previously. In the final step of the separation scheme for complex hydroxyl aromatic mixtures, the monohydroxyl fractions of oils from the Wyodak and Kentucky samples were subjected to a reversed-phase HPLC separation on a Resolvex C, column. The samples were dissolved in THF prior to injection on the reversed-phase system. The mobile phases investigated were an optimum composition and several nonoptimum compositions described previously for the systematic optimization of monohydroxyl aroma2c standards
COAL
LIQUID
SAMPLE
I
1 CHROMOSORE-T/BASIC ALUMINA SEPARATION
YYOROXYL RICH F R A C T I O N
FRACTION 1
I
MONGHYOROXYL COMPOUNDS
FRACTION 2
I
D I H Y O R O X Y L COMPOUNOS
Fbure 1. Separation scheme for complex hydroxyl aromatic mixtures. (See ref 23, 25, and 26 for discussions related to the ChromosorbT/basic alumina step.)
on gBondapak C18 and Resolvex C8 (12). A comparable reversed-phase separation was developed on gBondapak CI8for the dihydroxyl fractions of oils from the Wyodak and Kentucky samples. However, these fractions comprised less than 5% of the total hydroxyl fractions of oils, respectively, and thus were not investigated in detail. Field-Ionization Mass Spectra. Field-ionization mass spectrometry (FIMS) was applied to the characterization of the mono- and dihydroxyl fractions of oils and asphaltenes from the Wyodak and Kentucky samples obtained from the gBondapak NH2 separation step. In addition, FI mass spectra were obtained from the monohydroxyl fraction of oils from the Kentucky sample further separated by reversed-phase HPLC using the Resolvex CBstep. The FI mass spectra were obtained from SRI International, Menlo Park, CA, using procedures previously described (28). Details of the mass spectrometer and procedure for acquiring FI mass spectra have been discussed elsewhere (28-31). FIMS produces unfragmented molecular ions and their isotopic signals. An HP-87 computer equipped with a Model 82908A 64K expansion memory module, a Model 8290B printer, and a Model 7470A graphics plotter was used to evaluate the FI data in this work. Basic computer programs were developed to correct peak intensities for the natural abundance of carbon-13 and to plot the FI data. General Characterization of the Hydroxyl Aromatic Fractions. Infrared Spectrometry. Infrared spectra were obtained from the mono- and dihydroxyl fractions of oils and asphaltenes from the Wyodak and Kentucky samples using a Perkin-Elmer Model 621 grating infrared spectrophotometer. The spectra of the mono- and dihydroxyl fractions were recorded from 4000 to 400 cm-' in methylene chloride at concentrations between 10 and 40 mg/mL using matched 0.5-mm NaCl cells. At a concentration of 40 mg/mL there was no problem with the solubility of the samples if they were used shortly after preparation. With asphaltene samples a t 40 mg/mL, the samples had to be used immediately after preparation because of the solubility of the samples. Elemental Analysis. Determinations of carbon, hydrogen, nitrogen, and oxygen were obtained from Huffman Laboratories, Inc., Wheatridge, CO. Average results of duplicate determinations are reported. Oxygen determinations were made by using the Unterzaucher pyrolysis method.
RESULTS AND DISCUSSION Separation of Hydroxyl Aromatics and Weight Percent of Fractions. Figure 1 shows the separation scheme for the mono- and dihydroxyl aromatic fractions of oils and asphaltenes from the Wyodak and Kentucky coal-derived liquids. Hydroxyl aromatics =e the predominant components in both Wyodak and Kentucky asphaltenes accounting for
ANALYTICAL CHEMISTRY, VOL. 58, NO. 14, DECEMBER 1986
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Table I. Approximate Weight Percent Values of Mono- and Dihydroxyl Aromatic Fractions of Oils and Asphaltenes from Wyodak and Kentucky Coal-Liquid Samples wt % "
fraction
monohydroxyl
dihydroxyl
4.3 3.8
0.2
17.0 17.8
7.4 5.2
oils Wyodak
Kentucky asphaltenes Wyodak Kentucky
1.0
" Averaee of three determinations. Table 11. Elemental Analysis Data for Mono- and Dihydroxyl Aromatic Fractions from the Wyodak and Kentucky Samples wt %"
fraction
C
H
O
N
Wyodak monohydroxyl Kentucky monohydroxyl asphaltenes Wyodak monohydroxyl Wyodak dihydroxyl
81.1 80.6
7.3
9.1
7.5
9.5
0.73 0.47
84.3 80.1
6.3 6.2
8.5 11.3
1.0 0.90
oils
"Average of duplicate determinations. Data provided by Huffman Laboratories, Inc. approximately 65 wt % of these respective fractions (24,27). Hydroxyl aromatics in oils of the Wyodak and Kentucky samples account for approximately 32 w t % of their respective fractions (24,27). In addition, the Wyodak sample contains more hydroxyl aromatic oils and asphaltenes than the Kentucky sample (24, 27). Table I shows the approximate weight percentages of the mono- and dihydroxyl fractions of oils and asphaltenes in the Wyodak and Kentucky samples obtained from the KBondapak NH2 separation in Figure 1. Data given in Table I1 and Figures 2,3, and 4 strongly support the presence of hydroxyl aromatics. The results in Table I show that monohydroxyl aromatics are the major components of oils and asphaltenes in the Wyodak and Kentucky samples. In addition, oils and asphaltenes of the Kentucky sample contain less dihydroxyl aromatic material than the oils and asphaltenes of the Wyodak sample. Furthermore, oils of the Kentucky sample contain slightly less monohydroxyl aromatics compared to oils of the Wyodak sample, whereas the converse is true for asphaltenes. The results in Table I were reproducible with greater than 98% recovery of the individual fractions. Elemental Analysis Data. Elemental analysis data obtained for the monohydroxyl aromatic fractions of oils from the Wyodak and Kentucky samples and the mono- and dihydroxyl fractions of asphaltenes from the Wyodak sample are given in Table 11. Elemental analysis data for the hydroxyl fractions isolated from the Wyodak sample with the fluorocarbon/alumina step were reported earlier (27). The data in Table I1 clearly show that the fractions contain large amounts of oxygen. In addition, a relatively small amount of nitrogen is present in the fractions. Therefore, complete separation of compounds with only nitrogen and only hydroxyl functionality was not obtained with the Chromosorb-T/basic alumina procedure. Nevertheless, the data in Table I1 suggest a good separation between these two compound classes based on the small amounts of nitrogen present in the fractions. Furthermore, the data in Table I1 show that the dihydroxyl fraction of asphaltenes from the Wyodak sample contains a much larger amount of oxygen than the monohydroxyl fraction of asphaltenes from the same sample. This important result
4000
3500
3000
2500
WAVENUMBER (cm-1) Figure 2. Infrared spectra for a monohydroxyl fraction of oils (A) and
a dihydroxyl fraction of oils (B) from the Kentucky sample. coupled with model compound retention data and infrared data gave strong support that the KBondapak NH2 separation step separated the oils and asphaltenes into mono- and dihydroxyl aromatic fractions. Because nitrogen was found in the mono- and dihydroxyl aromatic fractions, structures containing both nitrogen and hydroxyl functionality or only nitrogen functionality are also most likely present. Infrared Spectral Results. Infrared spectra of the monoand dihydroxyl fractions of oils and asphaltenes from the Wyodak and Kentucky samples all showed a very strong absorption band centered at 3590-3602 cm-' that is characteristic of free hydroxyl groups of alcohols and phenols. In addition, spectra of these fractions showed a weak to moderate band around 3300 cm-' indicative of intermolecular hydrogen bonding and a weak band centered at 3460 cm-l that is characteristic of pyrrolic -NH groups. The infrared spectra also showed strong absorption bands centered a t 1600 cm-l and 2900 cm-l indicative of aromatic C-C skeletal vibrations and aliphatic C-H stretch, respectively. Typical infrared spectra for a monohydroxyl and dihydroxyl aromatic fraction of oils from a Kentucky sample are shown in Figure 2. The infrared spectral results gave strong support that hydroxyl aromatics were present in the fractions. Also, the results suggested that alkyl-substituted hydroxyl aromatics and therefore possibly hydroaromatic hydroxyl types were present in these fractions. In addition, it was apparent that these fractions were also comprised of nitrogen-containing compounds. Field-Ionization Mass Spectral Results. Field-ionization mass spectral data were obtained for the eight mono- and dihydroxyl aromatic fractons of oils and asphaltenes from the Wyodak and Kentucky samples isolated with the NH2 chromatographic system (Figure 1). Field-ionization mass spectrometry is unique in its ability to produce virtually only molecular ions and their isotopic signals and essentially no fragmentation ions (32). Therefore, FIMS yields simpler spectra compared to conventional mass spectrometry. This
130
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.-z0
2:. ,
,
~
,
:,
, . ~ .
0
Figure 3. F I mass spectrum of monohydroxyl fraction of oils from the Kentucky sample: oddleven mass ratio = 0.33.
10
20
30
40
50
60
70
TIME ( m i d
Flgure 5. Chromatogram of reversed-phase soluble monohydroxyl fraction of oils from the Wyodak sample on Resolvex C, with aceto. nitrileltetrahydrofuranlwater(15.227.657.0) at 1.0 mllmin. UV detection was at 254 nm.
h
w
Y
L 4 m
cc
0
Ln
m < n "
100
, ,
21:l
v ,: I,,
,,I",
,
,410
,>
Flgure 4. F I mass spectrum of monohydroxy1fraction of asphaiienes from the Kentucky sample: oddleven mass ratio = 0.73. is an important consideration when complex samples such as coal-derived liquids are involved. Some examples of the usefulness of FIMS in the characterization of distillable and nondistillahle coal-derived liquids have been reported in the literature (27, 29, 30). Figure 3 and 4 show typical FI mass spectra, corrected for 'SC.abundance, obtained for the monohydroxyl fractions of oils and asphaltenes from the Kentucky sample. These figures exemplify the extreme complexity of the fractions investigated. The FI mass spectrum of the fraction shown in Figure 3 had a number of average molecular weight of 430 and was 88% volatile, while the fraction in Figure 4 had a number average molecular weight of 527 and was 85% volatile. However, it should he emphasized that in all cases the number of average molecular weights for the fractions were significantly larger than t h e largest standard compound (294 for 13hydroxypicene) used in this work. The dark areas in these spectra are attributable to even and odd m m material, whereas the light area is due to even mass material. Even mass peaks in this work are characteristic of hydroxyl compounds. Odd mass peaks are indicative of uitrogen-containing compounds comprised of an odd number of nitrogen atoms in the molecule. Percent of total in these f w e s refers to the percent of total ionized material for a given mass relative to the total ionized material for the mass range investigated. A more detailed interpretation of the FI mass spectral data obtained for the mono- and dihydroxyl fractions of oils and asphaltenes from the Wyodak and Kentucky samples was not possible without considerable speculation. Additional chro-
0
10
20
30
40
50
-
60
70
TIME ( m i d
Flgure 6. Chromatogram of reversed-phase soluble monohydroxyl fraction of 011s from the Kentucky sample on Resolvex C, with acetonitrileltetrahydrofuranlwater (15.227.657.0) at 1.O mllmin. UV detection was at 254 nm. matographic separation of these fractons would be required for a detailed interpretation of these fractions. The HPLC/FIMS method developed by Boduszynski e t al. (29, 30),which effected the separation and characterization of hydrocarbons according to the number of double bonds in the ring system, could not he implemented in this work. Previous work showed that the hydroxyl aromatic standard compounds were not separated according to the number of double bonds in the ring system on pBondapak NH, with n-heptane/2propanol mobile phases (14.24). However, in this work the combination of reversed-phase liquid chromatography (RPLC) and FIMS was used to separate and characterize in some detail the monohydroxyl fraction of oils from the Kentucky sample as discussed below. Separation w i t h t h e Optimum Reversed-Phase Chromatographic System. The monohydroxyl fractions of oils from the Wyodak and Kentucky samples were chromatographed on the optimum reversed-phase system, Resolvex C,, with a mobile phase of acetonitrile/tetrahydrofuran/water (15.227.857.0). The experimental details of this system were reported previously (12). Figure 5 and 6 show the chromatograms obtained for the monohydroxyl aromatic fractions of oils from the Wyodak and Kentucky samples, respectively,
ANALYTICAL CHEMISTRY, VOL. 58, NO. 14, DECEMBER 1986
3015
n ti. U
Z 4
m [L
0 Lo
m 4
c
L p p A 23
1 4s TillE
6C
, 9:
1D[
(nir:
Figure 7. Chromatogram of monohydroxyl fraction of oils from the Wyodak sample on Resolvex CBwith acetonitrile/tetrahydrofuran/water (15.2:27.8:57.0) mobile phase (0-60 min) and a gradient step to 100% tetrahydrofuran (60-100 min) at 1.0 mL/min. UV detection was at 254 nm.
with the optimum reversed-phase system. The chromatogram in Figure 5 shows that better resolution was obtained for the monohydroxyl aromatic fraction of oils from the Wyodak sample than for the monohydroxyl aromatic fraction of oils from the Kentucky sample shown in Figure 6. However, the chromatograms in Figures 5 and 6 do not show the chromatographic profile of the entire monohydroxyl fractions of oils from the samples. Recovery studies showed that approximately 22% of the monohydroxyl fractions of oils from the Wyodak and Kentucky samples could be eluted from the Resolvex C8 column in 66 min with the optimum reversed-phase mobile phase a t 1.0 mL/min. These fractions were designated the reversed-phase soluble monohydroxyl fractions of oils. No measurable amount of the monohydroxyl fractions of oils from both samples were eluted after approximately 66 min with the above chromatographic system. These fractions were eluted, however, by switching to a nonaqueous mobile phase of CHC13/2-propanol (955) or tetrahydrofuran (100%).These fractions were designated the reversed-phase insoluble monohydroxyl fractions of oils from the coal-liquid samples and represent approximately 78% of the fractions. Figure 7 shows the reversed-phase chromatographic profile obtained for the monohydroxyl fraction of oils from the Wyodak sample by eluting the fraction first with the optimum mobile phase followed by a linear gradient to 100% THF. This technique allowed the complete recovery of the monohydroxyl fractions of oils from both coal-liquid samples from the Resolvex C8 column. Presumably, this method would be useful for recovering dihydroxyl fractions of oils; however, this was not investigated. Figure 7 shows that a highly resolved chromatographic profile was obtained initially corresponding to the reversed-phase soluble fraction followed by two major chromatographic bands corresponding to the reversed-phase insoluble fraction with the application of the reversed-phase gradient step. Additional work is needed to ascertain if the reversed-phase insoluble monohydroxyl fractions of oils from the coal-liquid samples can be better separated by modifying the chromatographic system. This was not investigated further. The main point to be made is that the entire complex fractions were eluted from the reversed-phase system. In general, the monohydroxyl fractions of oils from the coal-liquid samples are not very soluble in aqueous solvent compositions. Moreover, mono- and dihydroxyl fractions of asphaltenes are essentially insoluble in aqueous solutions of
0
IO
20
30
40
50
60
70
T I M E (rnin)
Flgure 8. Chromatogram of reversed-phase soluble monohydroxyl fraction of oils from the Wyodak sample on Resolvex CB with the nonoptimum mobile phase tetrahydrofuranlwater (40:60)at 1.O mL/ min. UV detection was at 254 nm. acetonitrile, methanol, and tetrahydrofuran. In order to compare the chromatographic profiles obtained for the monohydroxyl fractions of oils using the optimum reversed-phase mobile phase (see Figures 5 and 6), several additional nonoptimum mobile phases were used to obtain chromatographic profiles of the fractions. Figure 8 shows a typical chromatographic profile obtained with a nonoptimum reversed-phase composition (12) for the monohydroxyl aromatic fraction of oils from the Wyodak sample. Comparison of the chromatogram in Figure 8 with the chromatogram in Figure 5 shows that the optimum mobile-phase composition apparently gave the best overall resolution and selectivity for this fraction. Similar results were obtained for the monohydroxyl fraction of oils from the Kentucky sample. A possible reason for this result is that a large number of the standard monohydroxyl compounds exist in these fractions. Therefore, optimization of the standard compounds along with unknown compounds is being observed. Indeed, the comparison of the optimum chromatogram obtained earlier for the monohydroxyl (12) standards with the ones in Figures 5 and 6 showed that all of the model monohydroxyl compounds could conceivably exist in the monohydroxyl fractions of oils from the coal-liquid samples based on retention. To explore this possibility, FIMS was used to characterize the reversed-phase soluble and insoluble monohydroxyl aromatic fractions of oils from the Kentucky sample as discussed below. FI Mass Spectrum of Reversed-Phase Soluble and Insoluble Fractions. Figure 9 shows the FI spectrum (corrected for 13C abundance) for the reversed-phase soluble monohydroxyl fraction of oils from the Kentucky sample (Figure 6). The FI mass spectrum of the reversed-phase soluble fraction (Figure 9) is significantly simplified compared to the FI mass spectra shown in Figures 3 and 4. This fraction had a number average molecular weight of 276 and was 85% volatile. On the other hand, the FI mass spectrum of the reversed-phase insoluble fraction had a number of average molecular weight of 425 and was 85% volatile. The FI mass spectrum of the insoluble fraction was much more complex than the one shown in Figure 9. In addition, the FI mass spectrum for the insoluble material closely resembled the FI mass spectrum shown in Figure 3 for the monohydroxyl fraction of oils from the Kentucky sample. The detailed interpretation of the FI mass spectral data obtained from Figure 9 is beyond the scope of this paper. This information will be the subject of a future paper. However, it should be noted here that all of the model monohydroxyl
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ANALYTICAL CHEMISTRY. VOL. 58, NO. 14, DECEMBER 1986
associated with complex mixtures. The combined use of HPLC and FIMS represents one important avenue toward the solution of these prohlems.
LITERATURE CITED 111 . . Poivcvclk Hvdmcartmns andCBncer: Gelboin. H. V.. Ts'o. P. 0.. Ed%: Academic &s: New YOR, 1981: Val. 1 and 2. 1983: Val. 3: (2) Poirier. M. A.: George, A. E. Energy Sources 1981. 5 . 339. (3) Tru~sIl,F. C. AMI. Chem. 1983. 55, 248R. (4) Yonka, T. AM!. Chem. 1985. 5 7 . 192R. (5) Gorbaty. M. L.: Wright. F. J.: Lyon. R. K.: Long. R. 8.: Schiosberg. R. H.: Baset. 2.:Liotta. R.; Silbernagel. E. 0.; Neskora. D. R. Scisnce Iwashimton. D.C.I 1979. 206. 1029.
(9) Hussaln. A,: HURUbiSe. R. J.: Silver. H. F. J. Chromalogr. 1982. 252. 21.
Flgure 9. F I mass spectwm 01 reversed-phase soluble monchydroxyl haction of dk hom the Kentucky sample: oddleven mass ratio = 0.22.
aromatic compounds investigated (12) rould he assigned to masses in the various even nominal-mass Z series present in the reversed-phase soluhle monohydroxyl frartion of oils from the Kentucky sample. In addition, previous reversed.phase retention data for the monohydroxyl standards (12)roincided with several of the peaks in the chromatogram shown in Figure
6. The general approach developed rould be used for the separation and characterization of hydroxyl aromatirs in other complex samples. Additional separation and characterization of the hydroxyl aromatic frartions discussed in this work would be needed to comment on the existenre of specific hydroxyl aromatics in the fractions. However, the combination of HPI.C, FIMS strongly supports the presence of the model compounds in the mmnhydroxyl frartion of oils from the Kenturky sample. Furthermore, additional model compounds are desperately needed t o facilitate a more vigorous interpretation of the FI mass spectra for this and other fractions. In addition, the optimum reversed.phase system used in this work is highly dependent on the number of monohydroxy1 standards used to determine optimal conditions. It is clear the results of this researrh demonstrate the necessity for a high degree of sample separation prior to detailed characterization with FIMS to provide accurate compositional information for the sample. In general, the separation and characterization of hydroxyl aromntics ohtained from nondistillable coal-derived liquids discussed in this work are typical of the analytical prohlems
J. J. Uvomamgr. 1983. 281, 35. (11) Shaikh, 8.: Tomaszewski. J. E. Chromalographla 1983. 17, 675. (12) Cooper, H. A.: Hurtubise. R. J. J. Chromatogr. 1985. 324. 1. (13) Cooper, H. A.: Hurtubise. R. J. J. Chromtogr. 1986. 360. 313. (14) Cooper. H. A.: Hunubise, R. J. J. Chrmmtogr. 1986. 360. 327. (15) Schabron. J. F.: Hurtubise. R. J.; Silver. H. F. Anal. Chem. 1978. 50.
(IO) Vespalec. R.; Ne=.
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