Anal. Chem. 1980, 52, 406-411
406
While identification of the remaining constituents of SRC will primarily need acquisition of additional standards, this work demonstrates feasibility of the described analytical approach. Adequate glass capillary column technology is now available for studying basic components within the described volatility range. However, high-efficiency separations of heavier aza-arenes need further attention.
ACKNOWLEDGMENT We are grateful to the following individuals for their generous gifts of standard compounds: C. Kaslow (Indiana University, Bloomington, Ind.), A. G. Osborne (The City University, London, Great Britain), J. J. Eisch (State University of New York a t Binghamton, N.Y.), C. M. Leir (Riker Laboratories, 3M Company, St. Paul, Minn.), L. H. Klemm (University of Oregon, Eugene, Ore.), F. H. Case (Temple University, Philadelphia, Pa.), D. B. MacLean (McMaster University, Ontario, Canada), R. M. Acheson (University of Oxford, Great Britain), and Dietrich Hoffman (Naylor Dana Institute for Disease Prevention, Valhalla, N.Y.).
Symposium on Analysis, Chemistry, and Biology), P. W. Jones and R. 1. Freudenthal, Eds., Raven Press, New York, 1978, p 21. M. Dong, I. Schmeitz, E. LaVoie, and D. Hoffman, Ref. 2, p 97. M. Novotny, M. L. Lee, and K. D. Bartle, J. Chromatogr. Sci.. 12, 606 (1974). M. L.Lee, M. Novotny, and K. D. Bartle, Anal. Chem., 48, 405 (1976). M. L. Lee, M. Novotny, and K. D. Bartle, Anal. Chem., 48, 1566 (1976). M. L. Lee, D. L. Vassihros. C. M. White, and M. Novotny, Anal. Chem., 51, 798 (1979). M. L. Lee, D. L. Vassihros, W. S. Pipkin, and W. L. Sorenson, in "Trace Organic Analysis: a New Frontier in Analytical Chemistry", H. S. Hertz and S. N. Cheder, Eds., Natl. Bur. Stand. (U.S.) Spec. Pub/., 519, 731 (1979). P. M. Draper and D. 8.MacLean, Can. J. Chem., 48, 1487 (1968). P. M. Draper and D. 5. MacLean, Can. J. Chem., 48, 738 (1970). H. W. Sternberg, R. Raymond, and F. Schweighart, Science, 188, 49 (1975). K . D. Bartle, Rev. Appl. Chem., 22, 79 (1972). M. Novotny and K. Tesarlk, Chromafographia, 1, 332 (1968). J. J. Franken and M. M. F. Trijbels, J . Chromatogr., 91, 425 (1974). M. Novotny and R. Farlow, J. Chromafogr., 103, 1 (1975). R. V. Schuitz, J. W. Jorgenson, M. P. Maskarinec, M. Novotny, and L. J. Todd. Fuel, 58, 783 (1979). L. Biomberg. J. Chromatogr., 115, 365 (1975). M. L. Lee, D. L. Vassilaros, L. V. Phillips, D. M. Hercules, H. Azumaya, J. W. Jorgenson. M. P. Maskarinec, and M. Novotny, Anal. Led., 12(A2), 191 (1979).
LITERATURE CITED (1) A. Lacassagne, N. P. Buu-Hoi, R. Daudel, and F. Zajdela, CancerRes., 4, 316 (1956). (2) M. R. Guerin, J. L. Epier, W. H. Griest, B. R . Clark, and T. K . Rao, in "Polynuclear Aromatic Hydrocarbons" (Proceedings of 2nd International
RECEIVED for review August 20, 1979. Accepted November 26, 1979. This research was supported by the Department of Energy, under contract EY-76-S-02-2856.
Preparative Hydrocarbon Group Type Determination by Automated Medium Pressure Liquid Chromatography Matthias Radke," Helmut Wilisch, and Dletrich H. Welte Kernforschungsanlage Julich GmbH, Institut fur Chemie 5: Erdol und Organische Geochemie, Postfach 19 13, D-5 170 Julich, West Germany
An automated method for preparatlvely separating hydrocarbon groups has been established using medlum pressure liquid chromatography. The procedure, which includes automatic sampling, has been adapted to rapid sample throughput by comblnatlon of a dual column operation, backfiushing technique, and flow programming. Up to 20 samples in the 1- to 500-mg range may be run in one series wlth an analysis time of 20 min per 100 mg sample. Under routine conditlons, the percent relative standard deviation was shown to be less than 5 % for samples greater than 10 mg. This method can be applied to geochemical analysis of crude 011s and soluble organic matter removed from rock samples.
In recent years, the impact of organic geochemistry on oil and gas exploration has continually increased ( I ) . As a consequence, analytical laboratories engaged in petroleum geochemistry are now more frequently faced with the necessity to process large sample series coming in from exploratory drilling. Conventional techniques of liquid chromatography, which have been extensively used in this field, have often been found either lacking in reliability or being too time-consuming. Soluble organic matter, taken from core or cutting samples, and crude oils obtained from tests, are generally separated into hydrocarbon groups on a preparative scale for quantification purposes and for further study by GC and other techniques. Previously, liquid chromatography was carried
out on single adsorbents or adsorbent combinations using low boiling alkanes as the mobile phase. In this way, saturated hydrocarbons have been separated from other constituents of heavy petroleum fractions and similar samples (2, 3 ) . However, recovery has been found insufficient in some cases; for example, polycyclic naphthenes and long-chain alkanes tend to remain on alumina ( 4 ) . These hydrocarbons, referred to as geochemical fossils or biological markers, are generally present only in trace amounts. Nevertheless, they are of great importance in petroleum geochemistry ( I ) . Using alumina overlying silica gel, recovery of saturated hydrocarbons has been demonstrated to be dependent on adsorbent ratio (5). Recovery from silica gel has proved to be excellent for high molecular weight hydrocarbons (6-8). Losses of saturated hydrocarbons during chromatographic separation have a t least partly been attributed to their interaction with asphaltenes (9, 10). There exists some ambiguity concerning this point (11),for example, L. R. Snyder and Roth reported on contradictory results (3). However, on-column alteration of asphaltenes may cause problems which can be avoided by using deasphalted samples as was suggested by Kleinschmidt (12). Attempts have been made to separate aromatic hydrocarbons from polar N, S, and 0 compounds by stepwise increasing the solvent strength (13-16). Very long analysis times with poor separations were the main drawbacks of this approach. A variety of methods have been designed to fulfill special requirements of the petroleum industry, for example,
0003-2700/60/0352-0406$01.00/06 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 3, MARCH 1980
407
Stream Splitter
Dual Channel Sample LOOPS ( 2 0 max.)
UV- Photometer
Fraction -Collector
Filter
-m
Chromatographic Column Dlrection of solvent flow Pump
Reversed f l o w during backflush
Solvent Reservoir
Figure 1. Schematic representation of automated MPLC system
acceptance of only specific distillation cuts (17, 18). When applied to geochemical samples, they often fail to give clean separations. Application of the more sophisticated techniques such as SARA resulted in clear-cut separations of saturates and aromatics for a wide variety of samples ( 1 S Z I ) ;however, separation of higher polycyclic aromatics from polar N, S, and 0 compounds was generally not achieved (22). Repacking of chromatographic columns is required after each run, which makes the method laborious to perform. This drawback was claimed to have been overcome by using an HPLC technique, the column being regenerated between runs (22,23). Accuracy of aromatics determination seems to be improved, though some very weak polar N, S, and 0 compounds may get into the aromatics fraction. T h e method suffers only from insufficient recovery of polar N, s, and 0 compounds from samples, which contain large amounts of this group. Polar N, S, and 0 compounds, which stay behind on the column, will make its reuse somewhat hazardous in respect to crosscontamination. These problems axe overcome by the novel medium pressure liquid chromatographic (MPLC) technique described in this paper. In contrast to existing methods, some series of 20 samples may be run automatically on one single column without cross-contamination. Polar N, S, and 0 compounds are removed from each sample by a separate precolumn. Since elution is done in the isocratic mode, there is no need of reconditioning the column between runs. Short analysis times are achieved using a backflush technique and flow programming. Polar N, s, and 0 compounds are generally calculated by difference. They are readily recovered, however, by washing the precolumns with polar solvent. Silica gel was preferred to alumina for precolumn application as it is known to give preferential elution of polycyclic aromatic hydrocarbons and analogous furan and thiophene derivatives from heterocompounds (24). Different types of silica gel were selected for use with each column type. According to Schwartz and Brasseaux (2), wide-pore silica gel is best suited to remove asphaltic and resinous materials and, therefore, was used with the precolumns. Thermal deactivation of silica gel was carried out before use according to R. P. W. Scott and Kucera (25) to reduce retention times of polycyclic aromatic hydrocarbons. The narrow- to mediumpore silica gel types were found to give better separations of hydrocarbon types when used with the main column. Column
chromatography on wide-pore silica gel overlying a narrowpore type of the same adsorbent has been used in the analysis of soluble organic matter removed from rock samples by Ferguson (26). Capacity of a given adsorbent quantity was greater by a factor of 20 with the dual adsorbent compared with the narrow-pore silica gel. However, heat deactivated adsorbents are not known to have been used previously in the area of petroleum geochemistry.
EXPERIMENTAL Apparatus. The liquid chromatograph used in this study, the basic unit is shown schematically in Figure 1,was built up mainly from Cheminert parts (Laboratory Data Control, Riviera Beach, Fla.), as specified in Figure 2. Model CAV 4060 4-way (backflush) valves and Model CAV 3060 3-way valves are air-actuated by several pairs of Model P A 875 pneumatic actuators in connection with Model SOL-3-24VDC solenoid 3-way valves. Motor driven dual 20-way rotary valves, Model ROV-2-20,were equipped with an electronic control module. Valves and columns were connected with Teflon tubing using Cheminert and Swagelok fittings. A Knauer (Berlin,West Germany) Labtimer, Model FR-10, was used to control flow rate, valve action, fraction collector indexing, and integration runs. Further instrumentation was as follows: Spectra-Physics pump, Model 740B, equipped with a pressure monitor module; Laboratory Data Control Model 1103 Refractomonitor differential refractometer used in connection with a 1O:l stream splitter; Knauer, Model 7100, fixed wavelength (254 nm) UV absorption detector equipped with preparative cell (1.5-mm optical path length); Spectra-Physics Autolab System I computing integrator; Philips, Model 8222, dual channel recorder; and Gerstel (Mulheim/Ruhr, West Germany), Model 25-400, Multi Meander fraction collector. Materials. Spectrograde n-hexane, analytical reagent grade solvents, silica gel Type 100, LiChrosorb Si 60, and pre-packed Lobar size A and B columns were obtained from E. Merck (Darmstadt, West Germany). Silica gel Type 100 was thermally modified before use at the following conditions: 200 "C for 1 h and 600 "C for 2 h. Alumina, Woelm B-Super I, Type W 200, was purchased from Woelm Pharma (Eschwege,West Germany). Silica gel, Davison Grade 12, was obtained from W. R. Grace (Baltimore, Md.), 30-60 mesh Attapulgus clay, which was obtained from Engelhard (Attapulgus, Ga.), exhibited an azobenzene activity (27) of 26. Standard compounds obtained from Aldrich, Serva, Fluka, and E. Merck were recrystallized before use, if specified purity was less than 99%. Column Preparation. The chromatographic columns M (microcolumn),A, and B were used in connection with appropriate precolumns referred to as PM, PA, and PB throughout this paper.
408
ANALYTICAL CHEMISTRY, VOL. 52, NO. 3, MARCH 1980
Table I. Experimental Conditions for MPLC Hydrocarbon Group Type Determination Precolumn-Column Combinations PM-M column dimensions, mm length (packing) 0.d. i.d. packing silica gel type particle size, p m sample size, mg elution sequence initial period flow rate, mL/min pressure, bar saturates fraction, mL backflush period flow rate, mL/min pressure, bar aromatics fraction, mL a
Pre-packed column.
PA- A”
100
340
6
7
4
4
Si 60 30
lOOb
63-200 1-10
3.4 4 17 4.2 6 30
100 12 9
PB-B”
13
100 28
270 28
10
25
25
200
Si 60 40-63 10-100
lOOb Si 60 63-200 40-63 100-500
1OOb
63-200
8
l b
4
10
40
270
10 G
19
70
430
11
Thermally modified.
Flgure 2. Photograph of chromatographic unit, equipped with control modules: (1) septum injector valve, (2) sample loops, (3) precolumns, (4) column bypass valve, (5) column inlet selector valve, (6) backflush valves, (7) column outlet selector valve, (8) chromatographic columns, (9) fraction collector bypass valve, (A) solenoid valves, pressurized air lines, (B) timer, (C) control module for dual 20-way valves, (D) pump control module
The main features of the columns are given in Table I. Precolumns P B were made from empty columns B that were reduced in length. Both end fittings of column M included 10-pm stainless steel frits, while precolumns were equipped with stainless steel frits or ceramic frits only a t their outlet ends. Column M and precolumns PM, PA, and PB were dry-packed using the “tap-fill”
procedure. Columns M, A, and B were initially purged with dry nitrogen in an oven at 120 “C and washed in place with n-hexane until nitrogen was completely removed from the packings. Precolumns were mounted on dual 20-way valve, shown in Figure 2, and air was completely removed from the packings by washing with n-hexane; columns M, A, and B being bypassed. Column activity was checked in advance of each sample series run by injecting a standard solution of n-triacontane and noctylbenzene in hexane. Only columns giving base-line separation of standard compounds were used in subsequent runs. No loss of activity was observed throughout continuous operation, as columns were protected from moisture by an alumina guard column (stainless steel, 500 mm X 15 mm id.), situated upstream from the injection port. Precolumns were repacked after each run. Columns M, A, and B were replaced as soon as decoloration of silica gel became obvious, which generally occurred after approximately 50 runs. Sample Preparation. Soluble organic matter was removed from finely ground rock samples using the “flow-blending” method (28) with methylene chloride as solvent. After removing the solvent at room temperature under reduced pressure (250 mbar), 1-2 mL n-hexane were added and the sample vial was immersed in an ultrasonic bath to hasten solution of the sample. Insolubles were allowed to settle and an aliquot of the clear solution was injected. Volatiles were removed from crude oils a t room temperature under reduced pressure (250 mbar) and the residue was dissolved in a minimum amount of benzene. Precipitation of asphaltenes was carried out using n-hexane. Asphaltenes were collected on a preweighed filter and washed with n-hexane. The filtrate was concentrated on a rotary evaporator and an aliquot of the solution injected. Automated Procedure. Once samples are loaded to the sample loops, all further processing of a whole sample series will be fully automatic. During the initial period (Table I), the first sample is applied to the first precolumn; saturates are separated from the sample and collected. Total aromatics will have entered the chromatographic column, while elution of the monoaromatics will not yet have begun. Flow through the chromatographic column is then reversed by action of a backflush valve and flow rate increased. Precolumn valve indexing is performed at the same time, allowing solvent path through the second precolumn. Polar N, S, and 0 compounds from the first sample will remain on the first precolumn which is disconnected from the solvent line. Thus, pure aromatics will be collected during the backflushing period (Table I). The initial conditions are restored after this period, i.e., the backflush valve is switched back and flow rate is reduced according to the initial settings. Sample loop valve indexing is then performed to apply the second sample. Since rotor motion is rather slow, dual 20-way valves have to be bypassed during
ANALYTICAL CHEMISTRY, VOL. 52, NO. 3, MARCH 1980
409
Table 11. Model Compound Study retention volume ( m L ) for columna compound
compound type
PA 1
A,
PA,,A , b
PA,, A,'
5.60 5.60 5.60 5.67 5.95 6.11 6.04 6.41 8.17
12.78 13.50 14.01 14.25 14.19 18.17 18.63 24.05 37.97
18.38 19.10 19.61 19.92 20.14 24.28 24.67 30.46 46.14
20.64 21.50 22.08 22.45 22.37 26.40 26.95 31.71 44.17
triolefin S-aromatic aromatic aromatic aromatic aromatic aromatic S-aromatic aromatic S-aromatic 0-aromatic aromatic aromatic aromatic aromatic aromatic
8.05 7.69 8.21 7.17 8.68 18.37 9.85 9.45 12.61 11.22 12.63 13.17 13.54 22.02 20.13 21.92
53.20 57.98 65.38 70.98 79.76 86.68 108.12 112.95 138.65 163.36 210.85 225.56 237.75 425.88 526.14 565.73
61.25 65.67 73.59 78.75 88.44 105.05 117.97 122.40 151.26 174.58 223.48 238.73 251.29 447.90 546.87 587.65
70.20 71.00 70.41 70.82 64.87 61.62 64.29 62.04 63.88 61.76 59.44 61.76 61.90 60.05 59.21 57.63
N-aromatic N-aromatic N-aromatic
n.e.d n.e. n.e.
n.e. n.e. n.e.
n.e. n.e. n.e.
n.e. n.e. n.e.
saturates fraction dotriacontane pristane n-heptane cyclohexane cholestane a-pinene decene-1 cyclohexene 3.5-cholestadiene
saturate saturate saturate saturate saturate olefin olefin olefin diolefin
aromatics fraction 1.3.5-cycloheptatriene thiophene n-de cy 1benzene benzene 0 , rn, p-xylene dodecahydrotriphenylene naphthalene benzothiophene durene di benzothiophene di benzofuran anthracene phenanthrene coronene chr yse ne perylene polar N-compounds car baz ole pyridine quinoline
Amount of silica gel present in column P A , : 2.40 g; A , : 8.74 g ; PA : 2.50 g ; A , : 8.56 g. Flow rates P A , : 5 mL/ min, A , : 14 m l i m i n , P A , , A:: 7 mL/min and 8 mL/min (backflush). Obtained by addition of retention volumes from P A , and A , . Taken from real run on dual column assembly with flow reversal after 45 mL. n.e. = non eluted. indexing to prevent buildup of excessive pressure. After separation of hydrocarbons has been accomplished for a given sample series, polar N, S, and 0 compounds may be recovered by washing the precolumns with ethanol, guard column, chromatographic column, and detectors being bypassed. Ethanol is delivered by a separate pump, which is exclusively used with this solvent. To reduce on-column alteration of polar N, S, and 0 compounds, precolumns should be protected from light. Solvent Removal. Solvents were removed from collected fractions using a standardized evaporation procedure. Solutions were concentrated to near dryness at 30 "C on a rotary evaporator equipped with a pressure monitor. Evaporation was stopped as soon as pressure drop below 250 mbar was indicated. Residues were transferred to preweighed 1- to 5-mL vials by washing the flasks with small amounts of solvent. Solvent was then removed a t room temperature under reduced pressure. A t the given pressure (250 mbar), no bumping was observed. RESULTS AND DISCUSSION C o l u m n Evaluation. Efficiency of precolumns depends mainly on adsorbent activity, which must be high enough to prevent the breakthrough of any polar N, S, and 0 compounds. On the other hand, strong retention of polycyclic aromatic compounds is undesirable. Therefore, silica gel could not be used for this purpose unless it was deactivated t o a certain degree. Deactivation by addition of water was infeasible since precolumns were used in connection with chromatographic columns which had to be kept a t a high activity level. Otherwise no clean-cut separation of saturates from aromatic hydrocarbons could be obtained. Commercially available silanized silica gel Type 60, which was tried first, was found lacking in that activity was too low. However, partly
silanized silica gel, which was tried next, exhibited the desired properties and for this reason has been in use with precolumns for nearly two years. Nevertheless, work with this material has been discontinued since inter-batch variation of activity was too high. Furthermore, accidental breakthrough of polar N, S, and 0 compounds was observed. The thermal treatment of silica gel, which is described in the Experimental section, was found superior to silanization in that the specific degree of deactivation was achieved in a n easier and more reliable way. No breakthrough of polar N, S, and 0 compounds was observed with thermally treated silica gel Type 100 having been used for over a several-month period. A series of standards representing different compound types was run in order to evaluate retention behavior on columns PA and A. Runs were carried out on each column separately and on the dual column system using rz-hexane as the mobile phase. As is evident from Table 11, larger retention volumes were observed for diolefins on column A compared with retention volumes of polycyclic aromatic compounds on precolumn PA. For running a mixture on the dual column system this means that passage of any polycyclic aromatic hydrocarbon from precolumn PA to column A must be accomplished before solvent flow is reversed after elution of diolefins. Polar N, S, and 0 compounds will stay behind on precolumns unless solvent strength of the mobile phase is increased. Contamination. Since fractions obtained by the MPLC method, had t o meet the requirements of more advanced geochemical studies, including GC/MS analysis, care had t o be taken t o keep the whole procedure contamination free. Thus, only glass, Teflon, and stainless steel were used for parts
410
ANALYTICAL CHEMISTRY, VOL. 52,
NO. 3,
MARCH 1980
-~
____
Table 111. ComDarison of MPLC Method with ASTM D 2607 polar N, s, 0 satuarocom- insolu crude oil rates, matics, pounds, Ibles,“ wt % method w t 7c wt% wt% no.
EL’,TiCh
TIVE , n i #
MPLC MPLC D 2007 D 2007 D 2007 D 2007
47.1 47.3 51.2’ 51.3’ 47.7c 47.9c
31.0 29.3 36.0 34.7 39.5 38.1
21.6 23.1 12.6 13.8 12.6 13.8
2
MPLC MPLC D 2007 D 2007 D 2007 D 2007
34.8 36.0 36.Bb 35.4’ 33.4c 32.6c
26.6 25.7 45.3 44.2 48.7 47.0
36.4 37.1 14.5 17.2 14.5 17.2
MPLC MPLC D 2007 D 2007 D 2007 D 2007
40.9 41 3 46.0’ 46.4’ 41.lC 41.gC
26.1 26.4 32.3 29.7 37.2
30.6 29.9 17,6 19.9 17.6 19.9
MPLC MPLC D 2007 D 2007 D 2007 D 2007
28.0 26.7 37.8’ 37.0’ 25,SC 24,3c
22.8
21.6 35.1 35,7 47.1 48.4
MPLC MPLC D 2007 D 2007 D 2007 D 2007
32.3 32.6 31.1’ 29,l’ 25 8 C
21.7 22.1 36.3 40.8 41.6
24.3c
4.5.6
2 2 2
~~
2
Flgure 3. Chromatogram of the sequential analysis of four crude oil samples; sample size 100 mg. (-) RI detector trace: attenuation X16. (---) UV detector trace: 2 AUFS. I = Injection. B = Backflush. (1)
2 8 3 3
Saturates. (2)Aromatics of the apparatus coming in contact with sample or solvent. Pre-packed columns were checked to ensure no contaminant release after having been washed with n-hexane. Silica gel used with the precolumns was found to be free from contaminants after heat treatment. No detectable amounts of contaminants were present in the high purity n-hexane used as the mobile phase. Contaminants could not have been introduced in this way, since n-hexane was passed over activated alumina before entering the sample loop. Procedure blanks and standard mixtures which were run routinely did not indicate any contamination. Cross-contamination of samples having been run in series was not a problem with the present method, as proved by frequent checks including GC analysis. This is also evident from Figure 3, which shows that exhawtive elution of saturates and aromatics was achieved in each run. Accuracy and Precision. An example of a chromatogram showing four successive runs of similar crude oil samples is given in Figure 3. For column combination PAi-A (i = 1-4) along with high sample loads, clean-cut separation of saturates from aromatic hydrocarbons is evident from recorder traces, Aromatics did not get into the saturates fraction which may happen with the ASTM D 2007 method (23), Superior accuracy of the MPLC method has been proved by determination of hydrocarbon group types in stripped crude oil samples (Table 111). Saturates determinations using the ASTM D 2007 method gave a better match with MPLC data when having been corrected for monoaromatics contents by means of UV and MS analyses (29). Owing to higher selectivity and efficiency of the chromatographic system, far better separations of aromatics from polar N, S, and 0 compounds have been achieved by MPLC, which has been proved by HPLC and glass capillary-GC/MS. Soluble organic matter obtained from sedimentary rock samples may contain elemental sulfur (Sa) that w d d be eluted along with the saturates, thus interfering with the gravimetric determination. For this reason, sulfur has to be removed completely from either the extraction mixture or the saturates fraction by activated copper treatment. Olefinic hydrocarbons with a maximum of two double bonds would get into the saturates fraction, but generally only negligible amounts of these compounds will be found in crude oils OT rock extracts. The precision of the MPLC technique is illustrated in Table IV. Replicate separations have been carried out on soiubie organic matter removed from a shale sample, No significant loss of precision was observed unless sample size w w reduced to less than 10 mg. Precision loss in the analysis of very s a d 1 samples can be attributed mainly to weighing error being as
1 1 1 1 i i
3 3 3
4 4 4 4
4 4 5 2
5 3
5 .j
34.2
0.3 0.3 0.2
0.2 0.2 0.2 2.2
2.2 3.4 3.2 3.4 3.2 2.4 2.4 4.1 4.0 4.1 4.0
40.6 43.1 14.7 16.2
8.6 8.6 12.4
14,7
16.2
12.4 11.1
31.7
14.3
11.1
31.0
14.3
16.1 16.4
16.5
16.1 16,4
13.7 16,5 13,7
Insolubles by MPLC are hexane insolubles, D 2007 are pentane insolubles These fractions contained monoarnrnatic hydrocarbons. e These fractions were corrected for content of monoaromatics cr
’
high as i O . 1 mg with the analytical balance used in the present study. The relative amount of saturated hydrocarbons decreased continuously as the initial sample size of 700 mg was reduced to PO mg, which did not happen with the aromatics. GC analysis of the saturate fractions showed that the observed shift was due to evaporation losses While n-pentadecane content remained nearly unaffected throughout the whole series, loss of compounds in the CI2 to CI4 molecuiar range increased with sample size reduction. Compounds in the C1; to CIAmolecular range were found predominating in the 3atuate fraction of the 100-mg sample. Though this was also true for the aromatics. exhibiting a high content of dimethyl naphthalenes, they were only slightly affected by evaporatioa loss as volatility fer these compounds was ~ Q W ~ T . Attempt5 have been made in the present stud57 to cd9cdat.e fraction weights from RI peak meaB to avoid any B’PTCP inevitably encountered with gravimetric determinations. This approach has been applied to hydrocarbon grcup type analysis by SuatQni and Swab (23). Individual calibration factora had to 0%astablished for each s a n p i e type which was difficult with the wide variety of sample types analyzed. However, c o r d a t i c n between peak areas azd weights \+as fmmd to be significant and high enough for the saturate !:-actions t o be checked for outliers.
CONCLUSIONS The %pid medium prcssuzr liquid chromatographic techpaper has been shown suitable for a wd5 Fanety ~ >S fR K Y ~ tips5 ~ ~ E The
ANALYTICAL CHEMISTRY, VOL. Table
ics, pounds, wt %
sats"
wt%
arom.
pol. Fc.
25.4 25.7
41.7 41.3
a 33.0
>?5.5 41.5
49.6 1.6 3.3 47.7
29.1 29.6 28.6 26.8
21.5 22.7 21.7 21.5
49.4 47.7 49.7 51.7
a 28.5 b 1.2 c 4.3
21.9 0.6 2.6
49.9 49.9 49.9 50.3
30.1 30.5 28.5 2S.6
22.8 23.0 23.0 22.9
47.1 46.5 48.5
a 29.4
22.9
b 1.0 c 3.5
0.1
1.0
0.4
2.1
19.1 19.1 19.1 19.1
26.7 28.8 26.3 26.2
22.0 22.0 23.6 24.1
51.3 49.2 48.1 49.7
a 27.5
22.9
b 1.2
1.1 4.8
49.6 1.3 2.7
10.8 10.8 10.8 10.8
25.9 25.6 25.9 24.1
24.1 23.1 24.1 22.2
50.0 51.9 50.0 53.7
a 25.2 b 0.9 c 3.4
23.4
51.4
0.9
1.8
3.9
3.5
5.0 5.0 5.0 5.0
34.3 28.3 34.3 30.3
28.3 30.3 30.3 28.3
37.4 41.4 35.4 41.4
a 31.8 h 3.0 c 9.4
29.3 1.2 3.9
38.9 3.0 7.7
1.8 1.8
44.4 33.3 33.3 44.4
38.9 33.3 38.9 38.9
16.7 33.4 27.8 16.7
a 38.9 b 6.4 c 16.5
37.5 2.8 7.5
23.7 8.3 35.3
0.9 0.9 0.9 0.9
33.3 22.2 22.2 33.3
55.6 44.4 33.3 33.3
11.1 33.4 44.5 33.4
a 27.8 b 6.4 c 23.1
41.6 10.7 25.6
30.6 14.0 45.8
48.5
a = mean, wt %, b = std dev ___ - - __ - - - - __ -
The authors are indebted to W. L a m e r and H. G. Sittardt for their technical assistance and W. Ludtke for valuable help with the electronics. We thank M. J. Kania for reading the manuscript.
LITERATURE CITED
99.0 99.0 95.8 99.5
1.8
411
ACKNOWLEDGMENT
polar N, S, 0 mat- comUO-
1.8
MARCH 1980
series on a routine basis at minimum cost.
1V. P r e c i s i o n D a t a of MPLC Method
sample satuweight, rates, wt 9% mg 741.0 32.9 741.0 33.0
52, NO. 3,
c
, %,-c
4.5
= re1 std
__-
-
dev , % -
technique is rapid not only in short separation times but samples can be processed in series w t h no delay between runs. The procedure has been automated without using advanced electronics or other expensive equipment. Results show that this technique can be successfully used to run large sample
(1) Tissot, 8. P.; Weite, D. H. "Petroleum Formation and Occurrence": Springer: Berlin-Heidelberg-New York, 1978. (2) Schwartz, R. D.; Brasseaux, D. J. Anal Chem. 1958. 30, 1999. (3) Snyder, L. R.; Roth, W. F Anal. Chem. 1964, 3 6 , 128. (4) Evans, E. D.; Kenny, G. S . ; Meinschein, W. G.; Bray, E. E. Anal. Chem. 1957,29, 1858. ( 5 ) Gearing, J. N.; Gearing, P J ; Lytle, T. F ; Lytle, J. S. Anal. Chem. 1978, 50 1833. (6) Seifert. W. K. I n "Advances in Organic Geochemistry 1975", Campos, R., Goni. J., Eds.; Enadimsa: Madrid, 1977, p 21. (7) Leythaeuser, D.:Hollerbach, A.; Hagemann, H. W. Ref. 6, p 3. (8) Hollerbach, A.; WeRe, D. H. Eralil, Kohle, Erdgas, Pefrochem. 1977, 30, 565. (9) Nagy, 6.:Hamway, P.; Gagnon, G. C.; Cefob. M. Geochim. Cosmochim. Acta 1960,27. 151 (10) Hamway, P.; Cefola, M.; Nagy, B. Anal. Chem. 1962, 34. 43. ( 1 1 ) Middleton, W. R. Anal Chem. 1967,39, 1839. (12) Kieinschmidt, L. R. J. Res. NaN. Bur. Stand. ( U . S . ) 1955, 54, 163. (13) Lipkin, M. R.; Hoffecker, W. A.; Martin, C. C.; Ledley, R. E. Anal. Chem. 1948,20, 130. (14) Furby, N. W. Anal. Chem. 1950, 22. 876. (15) Karr, C.; Weatherford. W. D.; Capell, R. G. Anal. Chem. 1954,26, 252. (16) Mair, B. J.; Marcubitis, W. J.; Rossini, F. D. Anal. Chem. 1957,29. 92. (17) Snyder, L. R. Anal. Chem 1965,3 7 , 713. (18) Hirsch, D. E.; Hopkins, R. L.; Coleman, H. J.: Cotton, F. 0.; Thompson, C. J. Anal. Chem. 1972, 4 4 , 915. (19) Jewell, D. M.; Ruberto, R. G.; Davis, 8. E. Anal. Chem. 1972,44, 2318. (20) Jeweli, D. M.; Albaugh, E. W.; Davis, 8. E.; Ruberto, R. G. Am. Chem. SOC.,Div. Pet. Chem. Prepr. 1912, 77(4), F 81. (21) Jeweii, D. M.; Aibaugh. E. W.: Davis, 8.E.: Ruberto, R. G. Ind. Eng. Chem. Fundam. 1974, 73,278. (22) Suatoni, J. C. I n "Chromatography in Petroleum Analysis", Aitgelt, K. H.. Gouw, T. H., Eds., Marcel Dekker: New York-Basel. 1979; p 121. (23) Suatoni, J. C.; Swab, R. E. J. Chromatogr. Sci. 1976, 7 4 , 535. (24) Snyder, L. R.; Buell, B. E. Anal. Chem. 1968,4 0 , 1295. (25) Scott, R. P. W.; Kucera, P. J . Chromatogr. Sci. 1975, 13, 337. (26) Ferguson. W.S. Bull. Am. Assoc. Pet. Geol. 1962, 46, 1613. (27) "1975 Annual Book of ASTM Standards", Part 24; American Society for Testing and Materials: Philadelphia, Pa.; p 158; Method D 2007-75. (28) Radke. M.; Sinardt. H. G.; Welte, D. H. Anal. Chem. 1978, 50, 663. (29) Snyder, L. R. Anal. Chem. 1964,36, 774. l..
RECEIVED for review June 25,1979. Accepted November 12, 1979. Financial support by the German Federal Ministry for Research and Technology (B.M.F.T.) Grant No. ET 3070 B is gratefully acknowledged.
