Anal. Chem. 1981,53,2356-2358
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A
6
Flgure 4. Partlal trees resultlng from several stages of the Improved heuristic: (A) partial tree after repositioning point 6, (B) partial tree after positioning point 10, (C) partial tree after positioning point 8.
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1
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Flgure 1. The two-dimensional,ten-point, test data set, from ref 2.
E
1 2
3 4
5 6
7 8
9 10
Figure 2. Tree resulting from formal Clustering algorlthm, and the
improved heuristic.
spectrum is checked once, in the order that they happen to be sequentially stored in the tree array. With more involved data sets, changes in tree connections for one spectrum might effect the most appropriate connection for other spectra. In this situation, a slightly more elaborate checking scheme might be used in which a detected change in the tree would trigger the checking of other related spectra in that subtree. The efficiency of these approaches can be compared using the number of distances as an efficiency metric. For this ten-point test data set, constructing the tree using the formal clustering algorithm required 165 distance calculations. The Zupan heuristic used only 39 distances to form the tree in Figure 3. The improved heuristic used an additional 159 distances to modify the Zupan tree into the formal tree. The efficiency of the approach becomes improved as N increases. For a 20 data point test set, the formal algorithm required 1110 distances while the Zupan heuristic used only 114 distances and the improved heuristic used an additional 495 distances. We are presently employing this approach to construct trees of vapor-phase infrared spectra (4) for library searching and related studies.
LITERATURE CITED
10
Figure 3. Tree resulting from the Zupan heurlstlc.
propriate way. When point 6 is repositioned it assumes its correct place connected to the pair 4 , 5 (Figure 4A). Then point 5 is checked with no change, followed by point 10 which is changed to be correctly paired with point 9 (Figure 4B). Point 8 is then repositioned to be paired with point 7 (Figure 4C). Then points 9, 7, and 4 are checked with no change. Finally, points 1, 3, and 2 are checked with only a trivial change since points 1and 3 are equidistant from point 2. The tree is now identical with the formal clustering tree (Figure 2). In the present version of the program, the order in which spectra are selected for checking is not specified. Each
(1) Penca, M.; Zupan, J.; Hadzi, D. Anal. Chim. Acta 1977, 95, 3. (2) Zupan, J . Anal. Chin?.Acta 1980, 122, 337. (3) Warren, F. V.; Delaney, M. F., submitted for publication In Appl. Spec-
.
trosc (4) Delaney, M. F.; Warren, F . V . Anal. Chem. 1881, 53, 1460.
Michael F. Delaney Department of Chemistry Boston University Boston, Massachusetts 02215 RECEIVED for review July 10,1981. Accepted August 28,1981. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for the support of this research.
Liquid Chromatography of Coal Oil Fractions Sir: During the last years, interest in coal liquefaction products has rapidly increased. These products contain many more heterocyclic compounds such as phenols and pyridines than petroleum fractions in the same boiling range. Therefore it was necessary to develop an analytical procedure for characterizing these compounds as well as the aromatics and naphthenes. We assume that high-performance liquid chromatography (HPLC) is especially suitable for high boiling fractions. Although thousands of HPLC applications have been published, only a few papers deal with liquid coal products (1-10). The literature cited results partly from a computer search. It may not be complete, but it reflects the
present level of research in this field. The primary aim of our work was not to separate and determine compounds but to get well-resolved chromatograms as fingerprints of each fraction. For this reason it was necessary to test many stationary and mobile phases in order to determine the optimum conditions for each fraction.
EXPERIMENTAL SECTION Apparatus. The liquid chromatograph used in the experiments was a modular system manufactured by Laboratory Data Control, Division of Milton Roy (LDC). The columns were of
0003-2700/81/0353-2356$01.25/00 1981 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 53, NO. 14, DECEMBER 1981
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Table I. Description of the Stationary Phases Used abbreviation NO,
Diol Pol yarnid
CN . TNF SB SA Kat An Downloaded by UNIV OF NEBRASKA-LINCOLN on September 8, 2015 | http://pubs.acs.org Publication Date: December 1, 1981 | doi: 10.1021/ac00237a055
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commercial name
manufacturer
Nucleosil 10 NO, LiChrosorb Diol HPLC-Sorb Polyamid-6/0520 Nucleosil 10 NH, Nucleosil 10 N(CH,), Nucleosil 10 C, Nucleosil 10 C,, LiChrosorb A 6 X T Nucleosil 50-5 Zorbax BP-CN Tetranitrofluorenonsilica Nucleosil 1 0 SB Nucleosil 10 SA Kationenaustauscher HPLC Anionenaustauscher HPLC
Macherey -Nagel Merck Macherey-Nagel Macherey -Nagel Macherey -Nagel Macherey -Nagel Macherey-Nagel Merck Macherey -Nagel Du Pont see reference 14 Macherey -Nagel Macherey -Nagel Riedel de Haen Riedel de Haen
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Table 11. Solubility Values of Different Fractions in the Used Solvents solubility, % fraction a b acids bases nonbasic heterocompounds morioaromat ics diaromatics polyaromatics
27.9 14.5 92.3 100 100 100
a 80% n-hexane, 20% dichloromethane. methanol, 10% water.
60 63.1 52.6 81.9 90.5 65.0 90%
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b4-a
Fb
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nominal particle size, pm 10 10
5-20 10 10 10 10 10
5 10 10 10 10
15 20-32
particle shape spherical irregular irregular spherical spherical spherical spherical irregular spherical irregular spherical spherical spherical spherical
The performance of all columns was tested by chromatography of reference compounds. A description of the stationary phases used is given in Table I. Samples. The coal liquefaction product chosen for the chromatographic experiments was prepared in a laboratory-scaled plant using subbituminous coal. The so-called shift reaction a t 350 "C and 600 bar was used to produce liquid products (12). The average molecular weight of the product was 474 and the C/H ratio 77.9/7.5. Group type separation (13)yielded the following weight percentage: acids 43.1, bases 26.1, nonbasic heterocompounds 3.2, saturates 3.1, monoaromatics 2.6, diaromatics 3.6, polyaromatics 17.6. To prepare the samples 100-150 mg of each fraction was weighed into a vial and mixed with the solvent (see Table 11). After treating the mixture in an ultrasonic bath for 30 min the resulting suspension was transferred quantitatively into a specially designed microfiltration unit (Figure 1). This consists of a glass cylinder with a plane collar at its lower end (part a) pressed against a plane glass plate with a porous frit in its center (part b). Filter paper was placed between parts a and b. After the filtration process was performed by means of a vacuum pump, the sediment was washed with the solvent until the filtrate was clear. If necessary the amount of solvent evaporated during the filtration process is compensated by adding fresh solvent. The solubility values are given in Table 11. Screening. Each fraction yielded from the group type separation process was chromatographed on all stationary phases described in Table I. Solutions of the b type were chosen, when the mobile phase was aqueous, whereas solutions of the a type were injected, when it was nonaqueous. The results of screening experiments are given in Table 111. The evaluation of the separation was made visually; therefore other workers may obtain slightly different results.
RESULTS AND DISCUSSION
Figure 1. Microfiltration unit (all dimensions in cm); for explanations see text. stainless steel with dimensions of 4.1 X 250 mm. The column ends were made of modified Swagelok parts. A balanced density procedure was used to fill the columns ( I I ) , except for the two organic ion exchange resins (Riedel de Haen), for which the slurry was prepared with water. The Alox-T-column was packed by a viscosity method; i.e., a slurry of the gel in B paraffin oil (Merclr, Art. 71 60) was pumped upward from a reservoir into the column. Usually the following parameters were w e d flow rate 2 cm3/min, sample concentration about 0.5 mg/cm3, injection volume 20 fiL; RI detector for saturated fractions, UV detector operating at 270 nm for all other fractions.
Table I11 shows that good or fair separations can be obtained for each fraction, but it is necessary to use a set of different stationary and mobile phases. However, two kinds of stationary phases dominate in the liquid chromatographic analysis of the coal liquefaction product investigated. Octadecylsilica (ODs). An advantage of ODs, which is most commonly used in HPLC, is its resolution power and its capability to separate saturated compounds by nonaqueous reversed-phase chromatography. The main advantage is the necessity of applying aqueous solutions for separating all other fractions in order to obtain a good resolution. Tetranitrofluorenonsilica (TNF). TNF has a remarkable separation power, too. Unlike ODs, the TNF column can be used with nonaqueous solvents like n-hexane, halogenated hydrocarbons, tetrahydrofuran, and mixtures of these. With these solvents, the investigated liquid coal fractions codd be nearly completely dissolved, an important condition for
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ANALYTICAL CHEMISTRY, VOL. 53, NO. 14, DECEMBER 1981
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the application of liquid chromatography to the analysis of liquid coal fractions. Studies with model compounds showed that separation is not simply dependent on the number of aromatic rings. The degree of alkylation and the structure of the molecules also influence the elution order. The separation mechanism seems rather complex, a main factor is certainly the formation of electron donor-acceptor complexes. A detailed discussion of these problems is given in ref 14. Nevertheless, the T N F column is useful for characterizing coal liquids by their fingerprint chromatograms.
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OTHER STATIONARY PHASES
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As expected, Nucleosil C8 shows characteristics similar to ODS. Retention times are shorter; therefore it may be used to separate acidic fractions for which a high water content of the mobile phase is necessary for good resolution. It should be mentioned that the not chemically modified supports, silica and alumina, were not found suitable in HPLC-separations of coal oil fractions under the conditions used. They can be used, however, in group type separation schemes which do not require high resolution. Only the neutral heterocompounds were well resolved on silica. Because of their different selectivities NO2-,Diol-, and N(CH&modified silicas may have some analytical advances over ODS and T N F in separating the heterofractions. We found that Polyamide, NH2,CN, Kat, and An gels were not suitable for Characterizing the coal liquid fractions. In most cases there was none or just only a slight resolution of individual compounds. Finally, surprising results for inorganic ion exchangers (Nucleosil SB and SA) were reported. These columns originally developed for ionic compounds also show fair performance in separating the aromatic fractions. It can be certainly excluded that an ion exchange mechanism is responsible for the separation.
LITERATURE CITED
N
(1) Jolley, R. L.; Pitt, W. W.; Thompson, J. E. 23rd Annual Technical Meetino of the Institute of Envlronmental Science. Los Anaeles. CA 23-27%prll 1977. (2) Jolley, R. L.; Pitt, W. W.; Scott, C. D.; Jones, G.; Thompson, J. E. Trace Subst. Environ. Health 1975, 9, 247-253. (3) Holy, Norman L.; Lln, T. Y. J . Liq. Chromatogr. 1979, 2, 687-695. (4) Schabron, J. F.; Hurtubise, R. J.; Sllver, H. F. Anal. Chem. 1977, 49, 2253-2260. (5) Dark, William A.; McFadden, William H.;Bradford, Donald L. J . Chromatogr. Sci. 1977, 15,454-4130, (6) Prather, John. W.; Tarrer, Arthur R.; Guin, James A.; Johnson, Donald R.; Neely, W. C. Prepr. Pap.-Am. Chem. SOC., Div. Fuel Chem. 1976, 21, 144-153. (7) Schabron, J. F.; Hurtubise, R. J.; Silver, H. F. Anal. Chem. 1979, 57, 1426-1 433. (8) Dark, W. A.; McFadden, W. H. J . Chromatogr. Sci. 1978, 76, 289-293. (9) Holstein, W.; Severin, D. Erdol Kohle 1981, 34, 77-80. (10) Suatonl, J. C.; Swab, R. E. J . Chromatogr. Sci. 1975, 13, 361-366. (11) Cassidy, R. M.; Legay, D. S.;Frei, R. L. Anal. Chem. 1974, 46, 340-342. (12) Seikmann, R. W. Dissertatlon TU Clausthal 1979, Institut for Chemical Technology, Erzstr. 18, D-3392 Clausthal. (13) Oelert, H. H.; Neumann, H. J. Deutsche Gesellschaft fur Mineralolwissenschafland Kohlechemie e.V., Forschungsbericht 4508, Hamburg, 1974. (14) Hemetsberger, H.; KIar, H.; Ricken, H. Chromatographia 1960, 73, 277-286.
Wolfgang Holstein Dieter Severin* Institut fur Erdolforschung Am Kleinen Felde 30 D-3000 Hannover, Federal Republic of Germany RECEIVED for review January 26, 1981. Accepted August 17, 1981.
