nature and geochemistry of high molecular weight ...€¦ · the occurrence of extended series of...

Org. Geochem. Vol. 18, No. 4, pp. 541-553, 1992 0146-6380/92 $5.00 + 0.00 Printed in Great Britain. All rights reserved Copyright © 1992 Pergamon Press Ltd

Nature and geochemistry of high molecular weight hydrocarbons (above C4o) in oils and solid bitumens

J. C. DEL RIO,* R. P. PHILP and J. ALLEN School of Geology and Geophysics, The University of Oklahoma, Norman, OK 73919, U.S.A.

(Received 8 May 1991; accepted 1 April 1992)

Al~traet--Series of hydrocarbons ranging up to C75 have been detected by high temperature gas chromatography (HTGC) in a number of geochemical samples, including oils and waxes precipitated in drill stem pipes. A saturated hydrocarbon fraction isolated from a fossil bitumen, ozocerite, and enriched in branched/cyclic compounds, was analysed by direct insertion probe mass spectrometry (DIP/MS) and showed the presence of cyclic structures in the high molecular weight region (>C40). The asphaltene fractions isolated from the various samples were analysed by flash pyrolysis-high temperature gas chromatography (Py-HTGC). Similar distributions of high molecular weight hydrocarbons were produced from the asphaltenes of both the oils and waxes. In vitro simulation experiments of the asphaltene fractions produced a similar distribution of high molecular weight hydrocarbons as observed from Py-HTGC, suggesting that thermal breakdown of asphaltenes may be responsible for the production, or release, of some naturally occurring high molecular weight hydrocarbons.

Key words--oils, waxes, asphaltenes, high molecular weight hydrocarbons (C40 + ), high temperature gas chromatography (HTGC), flash pyrolysis-HTGC

INTRODUCTION

Traditionally, organic geochemistry has been con- cerned with the characterization of organic compounds ranging from C] to C40 present in the geosphere since such compounds are widely distributed and easily detected by conventional gas chromatography-mass spectrometry (C~-MS) techniques. However, the presence of lipids up to C]00 and higher (mainly polyisoprenyl alcohols) have been widely reported in living organisms (Sasak and Chojnacki, 1973; Hemming, 1983; Lehle and Tanner, 1983; Chojnacki and Vogtman, 1984; Chojnacki et aL, 1987; Swiezewska and Chojnacki, 1988, 1989; Suga et al., 1989; Liaeen-Jensen, 1990), and it can be anticipated that these compounds, or their diagenetic products, should be present in the sedimentary record. A few papers have presented data describing the occurrence of extended series of acyclic isoprenoids and trieyclic terpanes beyond C40, and suggested polyprenols as the biological precursors for these compounds (Albaiges, 1980; Moldowan et al., 1983).

The study of high molecular weight hydrocarbons has been overlooked in the past for two main reasons. The first being the lack of appropriate analytical techniques. The second, particularly in the case of oils, being that the higher molecular weight components are often absent from oils collected at the well-head. Rather these components precipitate out

*Permanent address: Instituto de Recursos Naturales y Agrobiologia, C.S.I.C., P.O. Box 1052, 41080-Sevilla, Spain.

in the drill stem pipe or remain in the reservoir rocks due to their low mobility.

Recently, with the development of columns suitable for high temperature gas chromatography (HTGC) (Lipsky and Duffy, 1986a, b), and the introduction of supercritical fluid chromatography (SFC), (Hawthorne and Miller, 1987, 1989; Smith et al., 1987), it has been possible to extend the carbon number range of the compounds analysed and identified. These HTGC columns have also been success- fully coupled with mass spectrometers (Smith et al., 1987; Hawthorne and Miller, 1987; Blum et al., 1990; Olesik, 1991). Kohnen et al. (1990), reported the analysis of a novel series of alkylthiophenes ranging up to C~ using high temperature gas chromatography. Van Aarssen and de Leeuw (1989) described the identification of C4s hydrocarbons, thought to be trimeric cadinanes, in crude oils and sediments from South East Asia, using fused silica capillary columns.

In this paper a number of samples, including a microcrystalline wax, Fischer-Tropsch wax, and a solid ozocerite bitumen from the Uinta Basin, have been analysed using aluminum coated high temperature capillary columns. Some waxes and their associ- ated asphaltenes that frequently occur in the drill stem pipes of oil wells have also been analysed and their hydrocarbon distributions compared with their co-occurring oils collected at the well-head. The asphaltenes isolated from the oils were analysed by flash pyrolysis-HTC~ and selected samples have been analysed by direct insertion probe mass spectrometry in both the electron impact (EI) and chemical ionization (CI) modes of ionization.

541

542 J.C. DEL RIo et at.

E X P E R I M E N T A L

A bitumen sample, ozocerite, from the Uinta basin, Utah, a microcrystalline wax (Micro 195) and a synthetic wax obtained by Fischer-Tropsch synthesis (FT H-l) were selected for the initial part of this study. (Samples of the Micro wax-195 and FT wax H-l were provided by Dr Hawthorne). Two wax deposits (wax SB and wax H) collected from different drill stem pipes along with the oils produced from the corresponding wells (oil SB and oil H), an asphaltene-type deposit (FRL 9170) collected from another pipeline, along with its respective oil (FRL 9169) were also analysed. The saturate frac-

tions of the oils were isolated by alumina column chromatography and elution with cyclohexane. The branched/cyclic fractions were isolated by removal of n-alkanes under reflux with 5/~ molecular sieve in i s o - o c t a n e for 15 h. The asphaltenes were isolated from the oils by precipitation with excess n-pentane and subsequent centrifugation followed by re-precipitation with n-pentane to purify the asphaltenes.

High temperature gas chromatography analyses were performed using a Carlo Erba gas chromato- graph equipped either with a short (3 m) or long (25m) aluminum clad capillary column coated with the HT-5 liquid film. The conditions were:

C4 o

/L

C3o

C5o

i

C6o

C 70

M ic ro w a x 195

C4o

C5o I =

We x F T H-1

C6o

vvA

4

I I -- I ----T ~ I ...... ~ .... I r . . . . 7 - - - I

9 13 18 22 27 32 36 4.! 45 .50

Minutes

Fig. I. Capillary HTGC (3 m) of(a) a microcrystalline wax (wax 195) and (b) a Fischer-Tropsch synthetic wax (wax FT H-I). GC oven temperature: I00-440°C at 8°C/min and 50 min isothermal.

Analysis of C4o + hydrocarbons in oils and solid bitumens 543

split/splitless injector and flame ionization detector at 400°C and the column was heated from 60 to 440°C at a rate of 8°C/min with 50 min final hold time. The samples were dissolved in warm p-xylene before injection.

The mass spectra were obtained in both the EI and CI mode by direct insertion probe (DIP) using a Finnigan TSQ 70 triple stage quadrupole mass spec- trometer. Chemical ionization was performed using either methane or ammonia as reagent gas at a pressure of 0.7 tort.

Flash pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) of the asphaltenes was performed with a Finnigan GCMS system equipped with

a high temperature aluminum dad capillary column coated with HT-5 liquid film. The asphaltenes were pyrolysed at 800°C using a platinum ribbon CDS pyroprobe and the oven was programmed from 60 to 400°C at 8°C/rain. Helium was used as the carrier gas and the GCMS transfer line was set at the maximum temperature of 350°C.

The artificial simulation, or maturation, experiments with the asphaltenes were carried out by heating them in glass tubes, sealed under N2, at 350°C overnight. After cooling, the tubes were opened, the products extracted, and the saturate fractions isolated and analysed by HTGC using the conditions described above.

Oil H

%0

c o/l Wax H

1

I I I I I I I I I I I

6 t 2 1 9 2 5 3 2 3 8 4 4 5 1 5 7 6 4 7 0

M i n u t e s

Fig. 2. Capillary HTGC (25 m) of the oil (oil H) and the wax deposit (wax H) collected from drill stem pipe of the same well. GC oven temperature: 50-440°C at 4°C/min and 50 min isothermal.

544 J.C. DEL Rio et al.

RESULTS AND DISCUSSION

Microcrys ta l l ine w a x - 195 and w ax F T H - 1

Microcrystalline waxes are products derived from the crystalline residues left after distillation of petroleum waxes which, when purified, yield a wax dominated by n-alkanes. Fischer-Tropsch waxes are produced from coal via the Fischer-Tropsch synthesis of n-alkanes. Samples of both the microcrystalline wax Micro-195 and the synthetic wax FT H-I had been previously analysed by supercritical fluid chromatography-mass spectrometry (SFC-MS). In the present study, both samples were analysed by high temperature gas chromatography using the short

aluminum coated capillary column and the chromatograms obtained are shown in the Fig. I. The Micro-195 wax showed a distribution of n-alkanes up to C70, with maximum around C40 and a marked even over odd carbon number predominance. The wax FT H-1 showed an n-alkane distribution from C20 to C75 without any pronounced even/odd predominance as may be expected from a synthetic product of Fischer-Tropsch synthesis. Previous studies on these samples by supercritical fluid chromatography (SFC) have shown a similar distribution of hydrocarbons, although the FT H-1 showed hydrocarbons extending up to CI00 (Hawthorne and Miller, 1987).

i

Czo

I

Oil SB

C4o

C~o Wax SB

7- i i i i 6 112 '9 2'5 3 I;~ ~8 44 ;1 = - - 57 64 70

Minu tes

Fig. 3. Capillary HTGC (25 m) of the oil (oil SB) and the wax deposit (wax SB) collected from drill stem pipe of the same well. (Temperature conditions as for Fig. 2.)

545

100

Wax precipitates

The saturate fractions of the waxes (wax H and wax SB) taken from the oil well drill stem pipes and their corresponding oils (oil H and oil SB) were analysed by HTGC using the long (25 m) aluminum coated capillary column (Figs 2 and 3). While the oils produced a fairly typical n-alkane distribution ranging up to C3s, the waxes showed a bimodal distribution of n-alkanes ranging up to C~0 with maxima at C17 and around C4o--C42. No significant odd/even n-alkan¢ predominance could be observed for the n-alkane distributions in either the low- or high molecular weight region for the wax deposits apart from the C30-C40 region of wax SB. Despite the major differences in the n-alkane distributions, the saturate fractions of the waxes possessed the same biomarker

fingerprint as the oils (for example see the ra/z 191 distributions for oil H and wax H in Fig. 4). The presence of high concentrations of these high molecular weight hydrocarbons in the wax deposits collected from the drill stem pipes is not altogether surprising, but the results demonstrate that high molecular weight hydrocarbons are absent, or present in very low concentrations, from oils collected at the well- head. These components precipitate out in the drill stem pipes or remain in the reservoir rocks due to their low mobility. Several branched/cyclic hydrocarbons can be observed in the chromatograms in the region above C40. Further attempts to concentrate the high molecular weight branched/cyclic fraction by molecular sieving failed, probably due to the fact that the structure of these compounds is mainly comprised of long linear aliphatic chains, with few branching

80

6O

4 0

20.

100

80 C~

6O

40

20

m/z 191 Hopones Cao

Czs

Tricyclic triterpanes

m/z 191

Oil H

C3t

~ 3 2

C 3 o

Csl

C27

Wax H

i 32 Cas

Analysis of C40 + hydrocarbons in oils and solid bitumens

. . . . , . . . . t • • , i . . . . i - • , . . . . ! . . . . i . . . . t . . . . i . . . . I . . . . i . . . . 1 . . . . w

Time

Fig. 4. A comparison of the mass chromatograms (m/z 191) for the saturated fractions of oil H and wax H. GC oven temperature: 40-320°C at 2°C/min and 30 min isothermal.

546 J.C. DEL RIO et al.

points or ring structures. Direct analyses of the total saturate fractions of the waxes by HTGC-MS were not very satisfactory due to problems experienced with heating the GC-MS interface to a suitable temperature.

Analysis of the asphaltenes isolated.from the oils

The asphaltenes isolated from the oils H and SB were characterized initially by flash pyrolysis-gas chromatography using a fused silica capillary column. (Note: It is important to emphasize here that the asphaltene fractions were prepared in the classical sense by precipitation with pentane and purification by reprecipitation with additional n-pentane. It is

entirely possible that during this isolation process, higher molecular weight hydrocarbons also precipitate due to lack of solubility in pentane. Despite not being chemically bound within the asphaltene structure these hydrocarbons are by definition still a part of the so-called asphaltene fraction). The pyrograms (not shown here) consisted of series of n-alkanes and n-alk-l-enes, dominated by n-aikanes extending beyond C40, with a predominance of the higher molecular weight hydrocarbons. Prist-l-ene, a common constituent of many asphaltene pyrolysates, was not observed in any of the pyrograms. The flash pyrolysis-GC experiments were repeated using high temperature gas chromatography and the aluminium

C2o

C40

1 I

' 011 H

I

i Oil SB

C J C~ °

I I I I I I [ I F I I

10 16 22 28 3 4 4 0 4 6 52 58 6 4 7 0

M i n u t e s

Fig. 5. Flash pyrolysis-HTGC of the asphaltenes isolated from the oils H and SB. Pyrolysis temperature 800°C. Oven temperature: 60-400°C at 8°C/rain and 50 rain isothermal. Interface at 350°C and detector

at 400°C.


coated columns and programming the oven temperature to 400°C. The results of these analyses showed that the pyrolysis products were dominated by n- alkanes extending to C60, with a predominance of the higher molecular weight hydrocarbons (Fig. 5). In vitro maturation of asphaltenes isolated from oils SB and H were performed in glass tubes, sealed under N 2, at 350°C overnight. Analysis of their thermal degradation products by HTGC showed a hydrocarbon distribution ranging up to C70 (Fig. 6), similar to that observed from the flash pyrolysis analyses.

On the basis of the results described above, it is proposed that the waxes precipitate as a result of the decreasing temperature and pressure experienced by the oil as it is brought to the surface. The production

of high molecular weight hydrocarbons during the pyrolysis of the asphaltenes isolated from the oils leads us to suggest that the asphaltenes may also undergo thermal breakdown at the high temperatures and pressures existing in reservoirs to produce high molecular weight hydrocarbons which are soluble in the oil under reservoir conditions.

Asphaltene deposit

The so-called "asphaltene" pipeline deposit, FRL 9170, collected from an oil production pipeline was extracted and the resulting saturate fraction had a hydrocarbon distribution similar to that of the oil collected from the well-head of the same pipeline (not shown here), with no indication of any high

C2o

Oil H

C~

/ O i l S B

~o

I' I I I i I I I I I I

2 7 12 17 2 2 2 8 3 3 3 8 4 3 4 8 53

M i n u t e s

Fig. 6. HTGC analyses for the hydrocarbons produced after in vitro artificial maturation of the asphaltenes isolated from the oils H and SB. (Chromatographic conditions as for Fig. 2.)

548 J.C. DEL RIO et al.

molecular weight hydrocarbons. However, py-HTGC of the asphaltene fractions isolated from both oil FRL 9169 and the pipeline deposit, FRL 9170, showed a very different hydrocarbon distribution. Whereas the pipeline deposit, FRL 9170, showed a distribution of n-alkanes ranging only up to C40, the asphaltenes isolated from the oil FRL 9169 showed the presence of high molecular weight hydrocarbons

ranging up to at least C60 (Fig. 7). In vitro artificial maturation experiments of the asphaltenes isolated from the oil FRL 9169 and subsequent analysis of the products by HTGC produced a hydrocarbon distribution ranging up to at least C70 (Fig. 8). A possible explanation for this difference in the pyrolysis products of the asphaltenes may be that the oil did not reach high enough pressures and/or temperatures in

FRL 9169

C2o

J C2o

FRL 9170

f I ! ! ! I I I I

7 12 17 22 28 33 38 43 48

Minutes

Fig. 7. Flash pyrolysis-HTGC of t~¢ asphaltcn¢ fraction isolated from (a) the oil FRL 9169 and (b) the asphaltene pipeline deposit FRL 9170. (Pyrolysis and chromatographic conditions as for Fig. 4).

I 53

Analysis of C40 + hydrocarbons in oils and solid bitumens 549

C2o

Moturotion products from ospholtenes

of oil FRL 9169

C 3 o

Cao

C6O /

C 7 0

I I I I I I [ I I I I

10 16 22 2B 34 40 46 52 58 64 70

Minutes

Fig. 8. HTGC Analyses of the hydrocarbons produced by in vitro artificial maturation of the asphaltenes isolated from the oil FRL 9169. (Chromatographic conditions as for Fig. 2.)

the reservoir for breakdown of the asphaltenes to occur and produce high molecular weight hydrocarbons. Instead, only partial fragmentation occurred leading to the formation of the pipeline deposit having very different solubility and mobility be- haviour with respect to the original material, and which subsequently precipitated in the production pipeline and not the drill stem pipe.

Ozocer i te

The analysis of the total saturate fraction from the fossil bitumen, ozocerite, by high temperature gas chromatography showed a distribution of n-alkanes ranging up to C75 with maxima at C32 and another

around C42 and no even/odd predominance (Fig. 9). The saturate fraction was comprised mainly of n-alkanes and relatively small amounts of branched/cyclic hydrocarbons, which after molecular sieving were found to be concentrated in the C50-C~5 n-alkane region.

An EI mass spectrum for the total saturate and branched/cyclic fractions from the ozoeerite was obtained using the direct insertion probe. Molecular ions of hydrocarbons ranging up to C80 were observed in the spectrum (not shown here) of the total saturate hydrocarbons. The mass spectrum (DIP-EIMS) of the high molecular weight branched/cyclic fraction isolated from the ozocerite is shown in Fig. 10.

5 5 0 J . C . DEL R I O et al.

C4o

tl

2 6 11

O z o c e r i t e

S a t u r a t e f r a c t i o n

ro

I . . . . . . . . 7 . . . . . . . . ~ - - T ~ . . . . ~ - - ~ . . . . . . . . 7 - - - - 1

15 19 24 28 32 36 41 45

M i n u t e s

Fig. 9. Capillary HTGC (3 m) analysis of the saturate fraction isolated from the ozocerite bitumen. (Chromatographic conditions as for Fig. I.)

Although the mass spectrum is from the mixture and not individual compounds, some significant information can be obtained from it. The mass spectrum of the branched/cyclic fraction showed a base peak at m/z 97 and a series of peaks at m/z 97 + 14n, reveal- ing the presence of aikyl side-chain structures. The m/z 97 fragment ion is probably due to the C7H~3 methylcyclohexyl ion after the bond between the methylcyclohexane ring and the alkyl side chain has been cleaved. (n-Alkylthiophenes also give a major fragment ion at m/z 97 but examination of this sample by GC-FPD did not reveal the presence of any sulphur compounds.) The El-MS spectrum also

showed a series of even-numbered fragments at m/z Cn H2,-2, typical of long chain dialkylcyciohexanes. This fragment is due to a hydrogen transfer from the ring (or the another side chain) to the side chain group which is cleaved to produce a neutral n-alkane moiety. Dialkylcyclopentanes cannot be totally excluded as a possible structure-type. Therefore, cycloalkyl systems appear to be an important com- ponent of the branched/cyclic fraction and comprise mainly single units rather than fused polycyclic systems. Another series of even mass fragments corresponding to C, H2~ fragments were also detected, at lower intensities, but are characteristic of branched


0

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~.~ • D

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• '~ "~ :~.~. • ~ ' ~

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552 J.C. DEL RIo et al.

alkanes and result from fragmentation of the mol- ecule adjacent to the branching point. Under El-MS conditions, no further information on these structures could be obtained due to significant molecular fragmentations. The mass spectrum obtained in the CI(CH4) mode from the branched/cyclic fraction (not included here) showed a high degree of fragmentation and was very similar to that obtained in the EI mode. Several fragments could be identified corresponding to carbon numbers up to C60, and indicating acyclic and cyclic compounds with one, two and maybe even three degrees of unsaturation.

Origin of the high molecular weight hydrocarbons

In discussing the origin of these high molecular weight compounds, the presence of natural precursors must be included since polyisoprenyl alcohols up to Cl00 have been reported in several organisms (Hemming, 1983; Lehle and Tanner, 1983; Chojnacki and Vogtman, 1984; Chojnacki et al., 1987; Swiezewska and Chojnacki, 1988, 1989) and bacterial carotenoid skeletons containing up to C50 are well known (Liaeen-Jensen, 1990). Although detailed structures have not yet been determined, it is possible that the high molecular weight compounds in the oils could be formed by intramolecular cyclisation of high molecular weight polyisoprenoid alcohols. Moldowan et al. (1983) proposed that cyclisation of solanesol (a C45 polyprenol) could lead to the extended series of tricyclic terpenoids up to C45 and Albaiges (1980) also proposed polyprenols as precursors of isoprenoids extending up to C45. These alcohols may be converted into high molecular weight isoprenoid alkanes just as the low molecular weight analogues (i.e. phytol) are converted into hydrocarbons by attack at the alcohol moeity, followed by reduction and thermal cracking.

Another possibility is that these high molecular weight hydrocarbons are di- and trimerization products of lower molecular weight precursors (del Rio and Philp, 1992). Previous papers strongly support this hypothesis. For instance, de Leeuw et al. (1980) obtained di- and trimerization products of phytol after heating it in presence of clay minerals. Rubin- stein and Strausz (1979) reported the formation of dimerization products of fatty acids when heating them in the presence of clay minerals. More recently, Van Aarssen and de Leeuw (1989) discovered some C45 hydrocarbons, thought to be trimeric cadinanes, in crude oils and sediments from South East Asia, suggesting that sesquiterpenes may dimerize or oligomerize under appropriate conditions by an abiotic process.

CONCLUSIONS

High molecular weight hydrocarbons have been found to be concentrated in the wax deposits that frequently occur in drill stem pipes of producing oil wells. Pyrolysis of the asphaltenes isolated from

the oils suggest that thermal breakdown under reservoir conditions may lead to the formation of high molecular weight hydrocarbons. The presence of high molecular weight hydrocarbons has been observed in the saturated fraction of ozocerite, a fossil bitumen. Cyclic structures ranging up to C80 could be observed in the ozocerite although no detailed structures were confirmed for these compounds.

It is suggested that the study of high molecular weight hydrocarbons has been overlooked in the past for two main reasons. The first being the lack of appropriate analytical techniques. The second reason is that, particularly in the case of produced oils, the higher molecular weight components are often absent in the oil collected at the well-head. Rather these components precipitate out in the drill stem pipes or remain in the reservoir rocks due to their low mobility. In view of the results presented herein it is proposed that continued study of these high molecular weight fractions will provide additional insights into the origin and types of organic source materials responsible for various types of oils. Major advances can be expected in this area over the next few years largely because of improvements in the analytical techniques that will make it easier to identify the high molecular weight compounds on a molecular level.

Traditional gas chromatographic methods are limited to species with sufficient volatility. High temperature gas chromatography and supercritical fluid chromatography coupled with mass spectrometry offer the potential to provide high resolution separ- ation of very high molecular weight compounds with selective mass spectrometric analysis and could be the appropriate techniques to analyse these new high molecular weight compounds, possibly potential bio- markers, although instrumentation and interfaces are still being developed. The potential of HTGC-MS and SFC-MS will continue to grow as HTGC and SFC techniques are extended by the introduction of new mobile and stationary phases, new approaches for the interfaces are developed and as improved mass spectrometric detectors continue to become available.

REFERENCES

Albaiges J. (1980) Identification and geochemical signifi- cance of long chain acyclic isoprenoid hydrocarbons in crude oils. In Advances in Organic Geochemistry 1979 (Edited by Douglas A. G. and Maxwell J. R.), pp. 19-28. Pergamon Press, Oxford.

Blum W., Ramstein P. and Eglinton G. (1990) Coupling of high temperature glass capillary columns to a mass spec- trometer. GC/MS analysis of metalloporphyrins from Julia Creek oil shale samples. J. High Res. Chromatogr. 13, 85-94.

Chojnacki T. and Vogtman T. (1984) The occurrence and seasonal distribution of C504260 polyprenols and of Ci00- and similar long chain polyprenols in leaves of plants. Acta Biochem. Polonica 31, 115-126.

Analysis of C40 + hydrocarbons in oils and solid bitumens 553

Chojnacki T., Swiezewska E. and Vogtman T. (1987) Polyprenols from plants-structural analogues of mam- malian dolichols. Chem. Scripta 27, 209-214.

del Rio H. and Philp R. P. (1992) High molecular weight hydrocarbons: a new frontier in organic geochemistry. Trends in Analytical Chemistry. In press.

Hawthorne S. B. and Miller D. J. (1987) Analysis of commercial waxes using capillary supercritical fluid chromatography-mass spectrometry. J. Chromatogr. 388, 397-409.

Hawthorne S. B. and Miller D. J. (1989) Supercritical fluid chromatography-mass spectrometry of polycyclic aro- matic hydrocarbons with a simple capillary direct interface. J. Chromatogr. 468, 115-125.

Hemming F. W. (1983) The biosynthesis of polyisoprenoid chains. Biochem. Soc. Trans. 11, 497-504.

Kohnen M. E. L., Peakman T. L., Sinninghe Damste J. S. and de Leeuw J. W. (1990) Identification and occurrence of novel C36-C~, 3,4-dialkylthiophenes with an unusual carbon skeleton in immature sediments. Org. Geochem. 16, 1103-1113.

Lehle L. and Tanner W. (1983) Polyprenoid-linked sugars and glycoprotein synthesis in plants. Biochem. Soc. Trans. 11, 568-574.

de Leeuw J. W., Simoneit B. R. T., Boon J. J., Rijpstra I. C., de Lange F., de Leeden J. C. W., Correia V. A., Burlingame A. L. and Shenck P. A. (1980) Phytol derived compounds in the geosphere. In Advances in Organic Geochemistry 1979 (Edited by Douglas A. G. and Maxwell J. R.), pp. 61-79. Pergamon Press, Oxford.

Liaeen-Jensen S. (1990) Marine carotenoids-selected topics. New J. Chem. 14, 747-759.

Lipsky S. R. and Duffy M. L. (1986a) High temperature gas chromatography: the development of new aluminum clad flexible fused silica glass capillary columns coated with thermostable nonpolar phases. Part 1. J. High Resol. Chromatogr. Chromatogr. Commun. 9, 376-382.

Lipsky S. R. and Duffy M. L. (1986b) High temperature gas chromatography: the development of new aluminum clad flexible fused silica glass capillary columns coated with thermostable nonpolar phases. Part 2. J. High Resol. Chromatogr. Chromatogr. Commun. 9, 725-730.

Moldowan J. M., Seifert W. K. and Gallegos E. J. (1983) Identification of extended series of tricyclic terpanes in petroleum. Geochim. Cosmochim. Acta 47, 1531-1534.

Olesik S. V. (1991) Recent advances in supercritical fluid chromatography/mass spectrometry. J. High Resol. Chro- matogr. 14, 5-9.

Rubinstein I. and Strausz O. P. (1979) Geochemistry of the thiourea adduct fraction from an Alberta petroleum. Geochim. Cosmochim. Acta 43, 1387-1392.

Sasak W. and Chojnacki T. (1973) Long chain polyprenols of tropical and subtropical plants. Acta Biochim. Polonica 20, 343-350.

Smith R. D., Kalinoski H. T. and Udseth H. R. (1987) Fundamentals and properties of supercritical fluid chromatography-mass spectrometry. In Mass Spectrometry Reviews 1987 6, 445-496.

Suga T., Ohta S., Nakai A. and Munesada K. (1989) Glycinoprenols: novel polyprenols possessing a phytyl residue from the leaves of soybean. J. Org. Chem. 54, 3390-3393.

Swiezewska E. and Chojnacki T. (1988) Long chain polyprenols in gymnosperm plants. Acta 8iochim. Polonica 35, 131-147.

Swiezewska E. and Chojnacki T. (1989) The occurrence of unique, long-chain polyprenols in the leaves of Potentilla species. Acta Biochem. Polonica 36, 143-158.

Van Aarssen and de Leeuw J. W. (1989) On the identification and occurrence of oligomerized sesquiterpenoids compounds in oils and sediments of Southeast Asia, 14th International Meeting on Organic Geochemistry-Abstracts, Paris, France, 18-22 September 1989.

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