Nature and geochemistry oI".high molecular weight hydrocarbons (above CojO) in oils and solid bitumens

J. e. DEL RIO,· R. P. PmLP and J. ALLEN School of Geology and Geophysics, The University of Ol::lahoma. Norman, OK 73919, U.S.A.

A......,.-Series of hydrocarbons rangins up lo c" ha"" been detccted by high temperature gas chromatosraphy (HTGC) in a number of ...,.,hemical samples, incIuding oil. aOO waxes precipitated in driII stem pipes. A saturated hydrocarbon f .... ction isolated from a fossil bitumen, ozocerite, and enriched in lxanchedfcyclic compounds, was anaIyoed by direct insertioa probe mass spectrometry (DIPfMS) and showed Ihe presence of cyclic structures in !he high molccular weight region (> C .. ). The asphaltene fractions isolated from Ihe various samples were analyoed by Hash pyrolysis-high temperature gas chromatography (Py-HTGC). Similar distributions ofhigh molecular weight hydroearbons were produced frona !he asphaltencs of bo!h !he oil. and waxcs. In vilro simulation experiments of!he asphaltene fraelions produced a similar distribution of high molecular wcighl hydrocarbons as obscrved from Py-HTGC, sugpting thal !hennal breal::down of asphallencs may be responsible for Ihe production, or release, of sorne naturaUy occurring high molecular weight hydrocarbons.

Key words---oiJs, waxcs, asphaltenes, high molecular weight hydrocarbons (C.tO + ). high temperature gas chromatography (HTGC), Hash pyrolysis-HTGC

lNTRODUcnON

Traditionally, organic geochemistry has been con­cerned with the characteñzation of organic com­pounds ranging from el to e.. present in the geosphere since such compounds are widely distñbuted and easily detected by conventional gas chromatography-mass spectrometry (GC-MS) tech­niques. However, the presence of Iipids up to e lOO 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; ehojnacki et al., 1987; Swiezewska and ehojnacki, 1988. 1989; Suga el al., 1989; Liaeen-Jensen, 1990), and it can be anticipated that these compounds, or their diagenetic products, should be present in the sedimerÍt8.ry record. A few papers have presented data descñbing the occurrence of extended señes of acyclic iso­prenoids and tricyclic terpanes beyond e .. , and suggested polyprenols as the biological precursors for these compounds (Albaiges, 1980; Moldowan et al., 1983).

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

in the dñll 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 (SFe), (Hawthome and Miller, 1987, 1989; Smith et al., 1987), it has been possible to extend the carbon number range of the compounds analysed and ident­ified. Tbese HTGC columns have a1so been success­fully coupled with mass spectrometers (Smith et al., 1987; Hawthome 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 e .. using bigh temperature gas chromatog­raphy. Van Aarssen and de Leeuw (1989) descñbed the identification of e., hydrocarbons, thought to be tñmeñc cadinanes, in crude oils and sediments from South East Asia, using fused silica capillary columns.

In thls paper a number of samples, including a microcrystalline wax, Fischer-Tropsch wax, and a solid ozoceñte bitumen from. the Uinta Basin, have been analysed using aluminum coated high tempera­ture capillary columns. Some Waxes and their associ­ated asphaltenes tbat frequently occur in the dñll stem pipes of oil wells have also been analysed and their hydrocarbon distñbutions compared with their co-occurñng oils collected at the weIl-head. The aspbaltenes isolated from the oils were analysed by flash pyrolysis-HTGC and selected samples have been analysed by direct insertion probe mass spec­trometry in both the electron impact (El) and chemi­cal ionization (el) modes of ionization.

EXPERIMENTAL

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-I) were selected for the initial part of this study. (Samples of the Micro wax-195 and FT wax H-I 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 ojl H). an asphaltene-type deposit (FRL 9170) collected from anolher pipeline. along with its respective oil (FRL 9169) were also analysed. Tbe saturate frac-

4 9 13 18

e...,

22 27

Minutes

tions of the oils were isolated by alumina column chromatography and elutíon with cyclohexane. Tbe branched/cyclic fractions were ísolated by removal of n-alkanes under reftux with 5 Á molecular sieve in iso-octane 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 peñormed using a Carlo Erba gas chromato­graph equipped either with a short (3 m) or long (25 m) aluminum cIad capillary colurnn coated with the HT-5 liquid film. The conditions were:

Micro WQX 195

Wox FT H-1

32 36 41 50

Fil. 1. Capillar}' HTGC (3 m) of (a) a microcrystalline wax (wax 195) and (b) a FISCher-Tropsch synthetic wax (wax FT H-I). OC oven temperature: lOO-44O°C al 8°Cjmin and SOmin isothermal.

splitfsplitless ínjector and ftame ionization detector at 400°C and the cotumn was heated from 60 to 440°C at arate of 8°C/min with 50 min final hold time. The samples were dissolved in warm p-xylefl$: before injection.

The mass spectra were obtained in both the El and CI mode by direct insertion peobe (DIP) using a Finnigan TSQ 70 triple stage quadrupole mass spec­trometer. Chemical ionization was performcd using eitber methane 01" ammonia as Iagent gas at a pressure of 0.7 tOrf.

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

Czo

I

eX!

a high temperature aluminum ciad 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 lo 400"C at gOC/min. Helium was used as the carrier gas and the GCMS transfer Jine 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, seaJed underN2 • at 350°C overnight. Mter cooling. the tubes were opened, the products extractcc1. and the saturate fractions isolated and analysed by HTGC using the conditions de­scribed aboye.

Oil H

I

~~~~ll,~,~.u~~~.~.~~~.l~l.l~I_~. ______________ _

<;o I

.IJ J t I1 ti I 1 J 1~ J I J j l. L •

6 f2 19 25 32 38

Minutes

44

C40 \

I 5t

¡so IÁ1A .

57

WoxH

Ceo

, 64 70

Fig. 2. Capillary HTOC (25 m) of tite oiI (00 H) ud the wax deposit (wax H) oollected from drill stem pipe of the same weU. OC oven temperature: SO--44O°C at 4°C/min and SO min isothermal.

RESVL 1'8 AND DISCVSSION

Microcrystalline wax-195 and wax FT H-I

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

I 6

, 12

j

•• I

2S j

32 I

;,e

aluminum coated capillary column and the chro­matograros obtained are shown in the Fig. l. Tbe Micro-l95 wax showed a distribution of n...aJkanes up to ~. with maximum around C40 and a marked even over odd carbon number predominance. The wax FT H-l showed an n-alkane distribution from ~ to C n without any pronounced even/odd predom­inance as may be expected from a synthetic product oC Fischer-Tropsch synthesis. Prevíous studies on these samples by supercriticaJ fluid chromatography (SFC) have shown a similar distribution of hydro­carbons, although the FT H-l showed hydro­carbons extending up to CIOO (Hawthorne and Miller, 1987).

I «

C40

\

I 51

Oí' S8

Wox S8

I 57

I 64 10

Minutes

F"¡g. 3. Capillary HTGC (25m) oftbe 00 (00 S8) and tbe wax deposit (wax S8) col1eeted Crom driD stem pipe oC tbe same -n. (femperature conditions as for F"¡g. 2.)

Wax precipitates

Tbe saturate fractions of tbe waxes (wax H and wax S8) taken from the oil well drill sterq pipes and their corresponding oils (oil H and oil .S8) were analysed by HTGC using the long (25 m) aluminum coated capillary column (Figs 2 and 3). Whilc tbe oils produced a fairly typical ,.-alkane distribution cang­ina up to C 3S • the waxes showed a bimoda1 distri­bution of n-allcanes canpag up to e. witb maxima al C 17 and around C..-c41- No signifialnt odd/even n-alkane predominance could be obscrved Cor the n-alkane distributions in cither the low- or high molecular weight regioll fOl' the wax deposits apart Crom the C~40 regíon of wax SB. Despite tbe major di~rences in tbe n-alkane distributions. the saturate Cractions of the waxes posscssed tbe same biomarker

100 mIz 191

80

60

;e !..

Tricyclic triter pones

40

fingerprint as tbe oils (for example see the mIz 191 distributions Cor oil H and wax H in Fig. 4). Tbe presence of high concentrations oC tbese high molecu­lar weight bydrocarbons in the wax deposits collected from the drill stem pipes is not altogethec surprising. but the results demonstrate that high molecular weigbt bydrocarbons are absent, or plescnt in very low concentrations. Crom oíls collectcd. at the well­head. Tbese components precipitate out in the drill stem pipes or rcmain in the RSCrVoir rocks duc to their low mobility. Scvcral bnmched/cydic bydrocar­bons can be obscrved in thc chromatopams in the regían above C 40 • Furthcr attempts to ooacentrate the high molecular weight branched/CYclic fraction by molecular sieving Cailed. probably due to thc Cact tbat the structure oC these compounds is maiIlIy comprised oC long linear aliphatic chains. witb few branching

Hopones

OilH

Cs.

C3a Cn \ \

20 .JlJU

;e !..

100 mIz 191 C3<)

Ca Wax H 80

60 Cs.

\3a Css

en 40 \ \ eS.

\ 20

Time

Fig. 4. A comparisoa oC the mass chromatograms (miz 191) Coc the saturated fractiODS oC oil H and wax H. GC oven temperature: 4O-320°C at 2°C/min and 30 min isothermal.

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

Analysis of lhe asphaltenes iso/ated 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 ernphasize here that the asphaltene fraetions were prepared in the classical sense by precipitation with pentane and purifieation by reprecipitation with additional n-pentane. It is

10 16 22 28 34 40

entirely possible that during this isolation process, higher molecular weight hydrocarbons aIso precipi­tate due to laek of solubility in pentane. Despite not being ehemically bound within the asphaltene struc­ture these hydrocarbons are by definition still a part of the so-called asphaltene fraetion). The pyrograms (not shown here) consisted of series of n-aIkanes and n-alk-I-enes, dominated by n-alkanes extending be­yond C40 , with a predominance of the higher molecu· lar weight hydrocarbons. Prist-I-ene, a commor constituent of many asphaltene pyrolysates, was no observed in any of the pyrograms. The flash pyrol ysis-GC experiments were repeated using high tern perature gas chromatography and the aluminim

c.., \

46 58

Oí! H

O¡I S8

64 70

Minutes

Fig. 5. Flash pyrolysis-HTGC of the aspbaltenes isolated from the oils H and SB. Pyrolysis temperatu 800°C. Oven temperature: 60-400"C at 8°C¡min and 50 min isotbermal. Interface at 350°C and detect.

al 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 n­alkanes extending to C6(J, witb a predomi~ce 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 z, at 350°C ovemight. Analysis of tbeir thermal dcgradation products by HTGC showed a hydro­carbon distribution ranging up to c,. (Fig. 6). similar to that observed from the flash pyrolysis analyses.

On the basis of tbe results described above, ít is proposed tbat !be waxes precipi1ate as a result of tbe decreasing temperature and pressure experienced by the oil as it is brought to the surface. The productíon

c..,

of high molecular weight hydrocarbons during the pyrolysis of the asphaltenes isolated from the oils leads us lo suggest that the asphaltenes may also undergo thermal breakdown at the high temperatures and pressures existing in reservoirs 10 produce higb molecular weight hydrocarbons which are soluble in the oíl under reservoir conditions.

Asphaltene deposit

The so-called "asphaltene" pipeline deposit. FRL 9170, collected from an oíl productíon pipeline was extracted aOO tbe resulting saturate fraction had a bydrocarbon distributíon similar to that of tite oi) collected from the well-head of the same pipeline (not shown bere), with no indication of any higb

ClO \

1

c""

OilH

Oil 56

2 7 12 22 28 I

33 38 43 I

48 53

Minutes

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

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 oíl FRL 9169 showed the presence of bigh molecular weigbt hydrocarbons

FRL 9169

2 7 12 I 17

I 22

ranging up to at least C 60 (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 C ro (Fig. 8). A possible explanation for tbis difference in the pyrolysis prod­ucts of the asphaltenes may be that the oil did not reach high enough pressures and/or temperatures in

I 28

Minutes

FRL 9170

I 33

I 38

CO(J

I

i 43

I 48

I 53

Fig. 1. Flash pyrolysis-HTGC oC the aspbaltcne Craction isolatcd Crom (a) the oil FRL 9169 ~ (b) the asphaltcn

e pipeline deposit FRL 9110. (Pyrolysis and chromatographic conditions as Cor Flg. 4).

10 16 22

Moturation pro.ducts fro.m aspholtenes

0.1 o.il FRL 9169

28 34 52 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 weíght hydro­carbons. Instead, only partial fragmentation occurred leading to the formation of the pipeline deposit having very different solubility and mobility be­haviour with respect to the original material. and which subscquently precipitated in the productíon pipetine and not the drill stem pipe.

OztICeTite

The analysis of the total saturate fraetíon from the fosal bitumen, ozocerite, by high temperature gas chromatography showed a distributíon of n -alkanes ranging up to Cn with maxima at C 32 and another

around C42 and no even/odd predominance (Fig. 9). The saturate fmetíon 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 C SO--C7S

n -alkane region. An El mass spectrum for the total saturate and

branehed/cyelic fractions from the ozocerite was ob­tained using the direct insertion probe. Molecular ions of hydrocarbons ranging up to c.. were observed in the spectrum (not shown here) ofthe total saturate hydrocarbons. The mass spectrum (DIP-EIMS) of the high molecular weight branehed/eyclíe fraetíon isolated from the ozocerite is shown in Fig. 10.

2 I 6

I 11

I 15

I 19 24

Ozocerite

Soturote froctíon

eso I

28 36 41 I

45

Minutes

Fig. 9. Capillary HTGC (3 m) analysis of tbe saturate fmetion isolated from tbe ozocerite bitumen. (Chromatographie conditions as for Fig. 1.)

A1thougb the mass spectrum is from the mixture and not individual compouncls. some significant infor­mation can be obtaíned from it. The mass spectrum oC the branched/cyclic fraction showed a base peak at mIz 97 and a series oC peales at mIz 97 + 14n. reveal­ing the presence of alkyl side-chain structures. The miz 97 fragment ion is probably due to the C 7 H¡'; methylcyclohexyl ion after the bond between the methylcyclohexane ring and the alkyl side chain has been cleaved. (n-Alkylthiophenes also give a major Cragment ion at miz 97 but examination of this sample by GC-FPD did not reveal the presence oC any sulphur compounds.) The EI-MS spectrum also

showed a series of even-numbered fragments at mIz C"H2It _ 2 • typical of long chain dialkylcyclohexanes. This fragment is due lo a hydrogen transfer rrom 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 exc1uded as a possible structure-type. Therefore. cycloalkyl systems appear to be an important com­ponent of the branched/cyclic fraction and comprise mainly single units rather than fused polycyclic sys­tems. Another series oC even mass Cragments corre­sponding to C"H,.. fragments were also detected. at lower intensities. but are characteristic oC branched

r-100

97.2 100., 4~.s *11'011 *E +05

Fig. 10. DIP-(EI)MS of the enriched branchedjcyc1ic fraction from the ozocerite bitumen. (Note that the expanded insert was obtained from a second DIP analysis of the same sample. Hence there is a slight variation in the position of the maxima in the m jz 480-530 region of the spectrum.)

alkanes and result Crom Cragmentation oC the mol­ecule adjacent to the branching point. Under EI-MS conditions. no Curther inCormation on these struc­tures could be obtained due to significant molecular Cragmentations. The mass spectrum obtained in the CI(CH4 ) mode Crom the branched/cyclic Craction (not included bere) showed a high degree oCCragmentation and was very similar to that obtained in the El mode. Several Cragments could be identified corresponding lo carbon numbers up to C 60 , and indicatíng acydic and cyclic compounds with one, two and maybe even three degrees oC unsaturation.

Origin of the high molecular weight hydrocarbons

In discussing the origin oC these high molecular weight compounds, the presence oC natural precur­sors must be included since polyisoprenyl alcohols up to e 100 have been reported in several organisms (Hemming, 1983; Lehle and Tanner, 1983; Chojnacki and Vogtman, 1984; Chojnacki el al., 1987; Swíezewska and ehojnacki, 1988, 1989) and bacterial carotenoid skeletons containing up to eso are well known (Liaeen-Jensen. 1990). Although detailed structures have not yet been determined, it is possible that the higb molecular weight compounds in the oils could be Corroed by intramolecular cyclisation oC high molecular weigbt polyisoprenoid aIcohols. Moldowan et al. (1983) proposed that cyclisation oC solanesol (a e", polyprenol) could lead to the extended series oC tricydic terpenoids up to e", and Albaiges (1980) also proposed polyprenoIs as precur­SOIS oC isoprenoids extending up to e",. These aleo­hols may be converted into high molecular weigbt isoprenoid alkanes just as the low molecular weigbt analogues (i.e. phytol) are converted into hydrocar­bons by attack at the alcohol moeity, Collowed by reduction and thermal cracking.

Another possibility is that these high molecular weight hydrocarbons are di- and trimerization prod­ucts oC 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 oC phytol alter heating it in presence oC clay minerals. Rubin­steiD and Strausz (1979) reported the Cormation oC diJDerization products of fatty acids when heating tbem in the presence oC day minerals. More recently, Van Aarssen and de Leeuw (1989) discovered sorne C'" hydrocarbons. thougbt to be trimeric cadinanes. in erude oils and sediments Crom South East Asia. suggesting that sesquilerpenes may dimerize or oligomerize under appropriate conditions by an abiotic process.

CONCLUSIONS

High molecular weigbt hydrocarbons have been found to be concentrated in the wax deposits that frequent1y occur in drill stem pipes oC producing oíl wells. Pyrolysis oC the asphaltenes isolated Crom

the oils suggest that thermal breakdown under reservoir conditions may lead to the formation of high molecular weight hydrocarbons. The presence of higb molecular weight hydrocarbons has been observed in the saturated fraction of ozocerile. a fossil bitumen. Cyclic structures ranging up 10 e8() could be observed in the ozocerite although no detailed structures were confirmed for these com­pounds.

It is suggested that the study of high molecular weigbt hydrocarbons has been overlooked in the past for two main rcasons. The first being the Iack of appropriate analytical techniques. The second reason is that. particu1arly in the case oC produced oíls. the higher molecular weigbt components are often absent in the oil collected al 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 oC these high molecu­lar weight fractions will provide additional insigbts into the origiD and types oC organic source materials responsible for various types oC oils. Major advances can be expected in this arca over the next few years largely because oC improvements in the analytical techniques that will make it easier to identiCy the high molecular weigbt compounds on a molecular leve!.

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 separ­ation oC very high molecular weight compounds with selective mass spectrometric analysis and could be the appropriate techniques to analyse these new jiigh molecular weigbt compounds. possibly potential bío­markers, although instrumentation and interfaces are still being developed. The potential of HTGC-MS and SFC-MS will continue to grow as HTGC and SFe techniques are extended by the introduction 01 new mobile and stationary phases, new approache~ for the interfaces are developed and as improvec mass spectrometric detectors continue to becom( availab1e.

REFERENCES

A1baips J. (1980) Identification and geochemical signifi canee of long cbain acyclic isoprenoid hydrocarbons i crude oiJs. In Adua1tces in Organic G~tT)' 197 (Edited by Douglas A. G. and MaxweU J. R.). pp. 19-21 Pergamon Presa, Oxford. •

Blum W .• Ramstein P. and Eglinton G. (1990) Coupling ( bisb tempetature gIass capillary columns to a mass spo trometc:F. GC/MS analysis of metalloporphyrins fro: Julia Creek oil shale samples. J. High Res. Chromatog 13, 85-94.

Chojnackí T. and Vogtman T. (1984) The oa::urrence al

seasonal distribution of C,.,-C. polyprenols and of C tr and similar long cbain polyprenols in aves of plan Acto Biochem. P%nicQ 31, 115-126.

Chojnaeki T., Swiezewska E. and Vogtman T. (1981) Pelyprenols from plants-structural analegues of mam­malian doliehols. C~m. Scripta n, 209-214.

del Rio H. and Philp R. P. (1992) High mol~lar weight hydrocarbons: a new frontier in organic ge9(:hemislry. Trends in Analytical Chemistry. In press.

Hawthome S. B. and Miller D. J. (1981) Analysis of commercial waxes using capillary supercritical fluid ebro­matography-mass spcctrometry. J. Clrromatogr. 388, 397--409.

Hawthome S. B. and MilIer D. J. (1989) Supercritical fluid chromatography-mass spectrometry of polycyclic aro­matic bydrocarbons with a simple capiUary direct inter­face. J. CM_top'. 468. 115-125.

Heaaming F. W. (1983) The biosyntbesis oC polyísoprenoid chains. Biochem. &le. Trans. 11,497-504.

Kobnen M. E. L., Peabnan T. L., Sinninshe Damste J. S. and de Leeuw J. W. (1990) IdentificatiOll and occurrence oC novel ~-CS4' 3,4-dialkylthiophenes witb an unusual

'cacbon skeleton in immature sediments. Org. Geochem. 16, 1103-1113.

Leble L. and Tanner W. (1983) Polyprenoid-linked sugars and glycoprotein synthesis in plants. Biodu!m. Soc. Trans. n.568-514.

de Leeuw J. W., Simoneit B. R. T., Boon J. J., Rijpstra 1. c., de Lange F., de Leeden J. C. W., Correia V. A., Burlingame A. L. and Shenek P. A. (1980) Phytol derived compounds in the geosphere. In Advonces in Organic Geochemistry 1919 (Edited by Douglas A. G. and Maxwell J. R.), pp.61-19. Pergamon Press, Oxford.

yacen-Jensen S. (1990) Marine carotenoids-selected topies. . New J. Chem. 14, 747-159. Lipsky S. R. and Dutry M. L. (1986a) High temperature gas

chromatography: the development of new aluminum ciad flexible fused silica pass capillary columns eoated with thennostable nonpolar phases. Part L J. High Resol. CM_Iogr. Chromlltogr. Commun. 9,316-382.

Lipsky S. R. and Duffy M. L. (l986b) High temperature gas chromatography: the development of new alu­minum ciad ftexible fused silica glass capillary columns coated with thermostable nonpolar phases. Part 2. J. High Resol. CMomatogr. Chromatogr. Commun. 9. 125-730.

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

Olesi1c: S. V. (1991) Recent advances in supercritical fluid cbromatographY/mass spectrometry. J. High Resol. Chro­matogr. 14, 5-9.

Rubinstein l. and Strausz O. P. (1979) Geochemistry ofthe thioun:a adduct fraction from an Alberta petroleum. Geochim. Co~. Acta 43, 1387-1392.

Sasak W. and Olojnacki T. (1913) Long chain polyprenols of tropical and subtropical plants. Acta Biochim. Polonica lO, 343-350.

Smith R. D., Kalinoski H. T. and Udseth H. R. (1987) Fundamentals and properties of supercritical ftuid eme­matography-mass spectrometry. In Mass Spectrometry Reviews 19876, 445-496.

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

Swiezewska E. and Chojnacki T. (1988) Long ehain polyprenols in gymnospenn plants. Acta Biochim. Po/onica 35. \31-147.

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

Van Aarssen and de Leeuw J. W. (1989) On tbe identifi­cation and occurrence of oligomerized sesquiterpenoids compounds in om and sediments of Southeast Asia, 14th Internationa! Meeting on Organic Geochemistry-Abstracts, París, France, 18-22 September 1989.