Analysis of series of aromatic isomers by high resolution spectrofluorimetry and capillary gas chromatrography in HPLC fractions of crude petroleums and sedimentary rock extracts

Org. Geochem. Vol. 6, pp, 829-837, 1984 Printed in Great Britain. All rights reserved

0146-6380/84 $113.01)+l).01) Copyright© 1984 Pergamon Press Lid

Analysis of series of aromatic isomers by high resolution spectrofluorimetry and capillary gas chromatography in HPLC fractions of crude petroleums and sedimentary rock extracts P. GARRIGUES1, R. DE VAZELHES-DE SURY1, M. L. ANGELINI, M. EWALD 1, J. L. OUDIN 2 and J. CONNAN3 'Groupe d'Oc6anographie Physico-Chimique du LA 348, Laboratoire de Chimie Physique A, Universit6 Bordeaux I, 33405 Talence Cedex, France TOTAL-CFP. Laboratoires Exploration, Service de G6ochimie Organique, 33600 Pessac, France S.N.E.A.(P) Exploration~ Service de G6ochimie Organique, Drag-Gesed-Centre Micoulau, 64018, Pau. France

Abstract--High performance liquid chromatography (HPLC) on normal phase has been performed on sedimentary rocks and crude petroleums to obtain fingerprints on polycyclic aromatic hydrocarbons (PAH) separated by degree of aromaticity. Chromatographic fractions containing methylphenanthrenes (MP) and methylchrysenes (MC) have been collected to obtain the relative distribution of these isomers by capillary gas chromatography (GC) and/or high resolution spectrofluorimetry (HRS). Trends in the distribution are tentatively correlated with the maturity of the studied samples.

Key words: methyl-PAH, Shpol'skii-luminescence, maturity-index

INTRODUCTION Studies on the aromatic fraction of hydrocarbons from sedimentary rock extracts or crude oils have increased in interest since correlation was recently carried out with thermal evolution and maturity of sedimentary matter (Seifert and Moldowan, 1978; Radke et al., 1982). This is also due to the capability of new and modern analytical techniques, i.e. high performance liquid chromatography (HPLC), capillary gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), which allow the resolution of natural complex mixtures and lead to the molecular identification of the aromatic compounds. Among the polycyclic aromatic hydrocarbons (PAH) the distribution of alkylated phenanthrenes has shown changes with increasing degree of thermal alteration (Radke et al., 1982; Radke and Welte, 1983). However, only these selected alkylated aromatics (tricyclics) are partially attainable by GC: in fact lower aromatics (cycles number < 3) may be lost during extraction and concentration of samples and higher alkylated aromatics cannot be unambiguously identified due to the great number of isomers. An alternative analytical approach is the use of high resolution spectrofluorimetry (HRS) which can be observed when aromatic compounds are dissolved in a suitable n-alkane matrix at low temperature (so-called Shpol'skii effect). This technique has proved to be very good for a clear identification of methylated derivatives of P A H (Ewald et al., 1983; Garrigues and Ewald, 1983b) and also for their quantification (Garrigues and Ewald, 1983a). OG

6 :I/4-AA

829

In this paper, we report the complementary use of HPLC, GC and HRS in studying the distribution patterns of methylated PAH. On the one hand, fingerprints for the degree of aromaticity can be obtained by the use of normal phase HPLC. On the other hand, the collected fractions are further analysed by GC and by HRS. This last technique leads to the distribution pattern of monoalkylated homologs of phenanthrene and chrysene both in rock extracts and crude oils. The relative distribution of the isomers observed in these two series is related to the increasing maturity of the studied samples.

EXPERIMENTAL

Preparation of samples (a) Sedimentary rocks. The powdered rock samples w e r e e x t r a c t e d with d i c h l o r o m e t h a n e . Elemental sulfur was removed by open column liquid chromatography on Cu-Zn. Asphaltenes were eliminated by precipitation in n-pentane. Then open column liquid chromatography was performed on microcolumns of florisil (Sep-pak, Waters) to retain polar NSO compounds. (b) Crude oils. They were only submitted to liquid chromatography on a microcolumn of florisil eluted with pentane to retain asphaltenes and polar compounds. Alkanes and aliphatics are eluted first, then the PAH.

830

P. GARRIGUESet al.

High performance liquid chromatography (HPLC) (a) Normal phase chromatography. Extracts of rocks and petroleums were fractionated by normal phase HPLC analysis on a Spherisorb aminosilane (NH2) stationary phase eluted with heptane or pentane with 0.2% of CH2C12. Aromatic fractions were separated according to number of aromatic rings (Wise et al., 1977). The fractions suspected (by calibration of the retention times with those of standards) to contain phenanthrene and chrysene compounds were collected, reduced to a small volume by blowing N2 and then submitted to analysis by GC and/or reverse phase liquid chromatography. (b) Reverse phase chromatography. This allows the separation or aromatic compounds according to the degree of alkylation. The fractions containing the. parent compound and alkylated derivatives were collected for further HRS analysis.

Capillary gas chromatography (GC) The fractions containing triaromatic compounds were analysed using a Carlo-Erba (model 4160) gas chromatograph equipped with a splitless injector and flame ionization detector (FID). Conditions: glass capillary columns, 50 m x 0.3 mm i.d., SE-52 or CP-Sil 8 CB silicone gum phase; temperature programmed: 75°C (2 min), 25°C rain -1 to 160°C, then 2°C min -1 to 260°C; carrier gas helium: 6 ml min -l. Quantitative calculations were obtained by the use of a data processor (Shimadzu, model ICR 1B).

High resolution spectrofluorimetry (HRS) Fluorescence spectra at 15 K were obtained using an analytical procedure previously described (Garrigues et al., 1981; Garrigues and Ewald, 1983b).

Chemicals and reagents Four methylphenanthrenes (1-MP, 3-MP, 4-MP and 9-MP), 4,5-methylenephenanthrene (4,5-MP) and 1-methylanthracene (1-MA) were synthesized in the laboratory by Lapouyade et al. (1982). The 2-methylphenanthrene (2-MP), was provided by "K and K" p h a r m a c e u t i c a l s . A n t h r a c e n e , 2methylanthracene (2-MA) and 9-methylanthracene (9-MA) were provided by Fluka AG (Buchs, Switzerland). The six methylchrysenes (MC) were purchased at the Community Bureau of Reference (Commission of the European Communities, Brussels, Belgium). The used solvents (n-pentane, n-hexane, n-octane and methanol) from Fluka (purissimum grade, Buchs, Switzerland) or SDS (chromasol grade, Peypin, France) were dried and kept on molecular sieves (5 and 10/~). Fluorescence transparency was checked using an MPF-44 Perkin-Elmer spectrofluorimeter. Sedimentary rocks came from the Handil field (TOTAL-C.F.P.) located in the Mahakam delta area (Indonesia). The reflectance value, indicating their maturation stage is 0.40, 0.52 and 0.64%, respective-

ly for rocks 1-3. Crude oils were provided by SNEA(P) and came from wells in China. They correspond to a set of crudes with various degrees of maturity determined by C29 sterane isomer ratios according to Mackenzie et al. (1980) (cf. Table 2); the following maturity scale has been established: crude oil 1 < crude oil 2 < crude oil 3. RESULTS AND DISCUSSION

H P L C fingerprints on tx-silica-NH2 Chromatograms obtained on tx-silica-NH2 for the aromatic fractions have been shown to exhibit useful fingerprints on sedimentary rocks and crude oils (Angelin et al., 1983) as presented in Fig. 2. By comparison with the artificial mixture and results obtained in previous works (Wise et al., 1977; Berthou and Friocourt, 1982), the numbered peaks are assigned as follows: (1) Monoaromatics. (2) Diaromatic compounds. (3)f 3a--Fluorene derivatives and substituted dibenzothiophenes. 3b---Tricyclic compounds and also pyrene components in the tail of the chromatographic peaks. (4) Tetra-aromatic compounds (without pyrene homologs). The striped peaks correspond to the chromatographic fractions which were collected. A relative increase of a peak, from rock samples 1-3, is observed, corresponding to diaromatics (peak 2). On chromatograms obtained for the crude oils, a relative decrease in the heights of the peaks corresponding to the fluorene compounds (peak 3) from crude oils 1-3 samples was noted. Another point is the more resolved chromatogram obtained for the crude oil 3.

l

GC analysis (a) Triaromatic compounds. In the best resolved cases, four chromatographic peaks are observed for the five isomers of monomethylphenanthrenes (MP); indeed, the 4-MP and 9-MP have almost the same retention time on SE-52 (Bellocq et al., 1981), on SE-54 (Radke et aL, 1982) and also on the new silicone gum column CP-Sil 8 CB (De Vazelhes-De Sury, 1983). However, other triaromatic compounds often interfere on SE-52, on SE-54, and on CP-Sil 8 CB with the monomethylphenanthrenes: the 4,5methylenephenanthrene (4,5-MP) and the 9methylantracene (9-MA) co-elute with 9-MP and the 4-MP (Fig. 3). Consequently, the quantitative distribution of the MP determined by GC analysis can be biased by the presence of these compounds. Therefore, a true identification of each MP isomer cannot be made using apolar columns alone (Ewald et al., 1983). As shown below, HRS can easily resolve this problem.

831

HPLC on crude petroleums and sedimentary rocks Table 1. Phenanthrene and chrysene ratios, vitrinite reflectance (Ro), depth and MPI values of the sedimentary rocks from Handil

Rock 1 Rock 2 Rock 3

Z MP/P

E MC/C

Ro (%)

depth (m)

MPI

0.95 1.95 2.60

0.90 2.70 2.35

0.40 0.50 0.65

1290 2480 2798

0.30 0.6(I 0.75

E MP/P (E MC/C) = ratio of the sum of concentrations of monomethylated phenanthrenes (chrysene) over the concentration of phenanthrene (chrysene). Table 2. Phenanthrene, chrysene and sterane ratios (see text) and MPI values of the crude oils from China

Crude oil 1 Crude oil 2 Crude oil 3

E MP/P

E MC/C

2.40 4.20 2.85

2.30 2.55 3.95

29auS

29~S

29eeR

29ear

0.5 0.7 0.9

0.3 0.4 1.3

MPI

0.65 0.80 11.85

29aaS = (20 S) - 5cx(H) 14a(H) 17~(H) C29 sterane. 29c~aR = (20 R) - 5a(H) 14a(H) 17c~(H) C2~ sterane. 29[?,[3S = (20 S) - 5cx(H) 1413(H) 1713(H) C~9 sterane.

3

2 1

Rock

9

1

!

Rock 3

Depth: 1290m

Depth: 318Om

2 9 PhenGnthrene

D

R Anthracene >,

1

6

4.5 Methylene-

Chrysene

phenonth rene

0

5

Fig. 1. Selected aromatic molecules analysed in this study. Numbers on aromatic rings refer to the monomethylated derivatives.

H R S measurements H R S m e a s u r e m e n t s were m a d e on c h r o m a t o g raphic fractions o b t a i n e d using a two-step H P L C procedure described elsewhere (Garrigues and

5

Time ( rain )

Crude oil I

3

(b) Chrysene compounds. Chromatograms of t e t r a - a r o m a t i c fractions are c o m p l i c a t e d by the large n u m b e r of possible isomers a n d co-elution problems: c h r y s e n e a n d t r i p h e n y l e n e elute in the same c h r o m a t o g r a p h i c peak. T h e part of the c h r o m a t o g r a m (Fig. 4) c o r r e s p o n d i n g to the methyltetracyclics is not sufficiently well resolved to lead to an u n a m b i g u o u s identification of individual m e t h y l c h r y s e n e s (Wise et al., 1981).

0

Time ( min )

~

-o

Crude oll 3

D

c

2

2

~

~

u 0

5

0

5

Time ( rain ) Time ( rain ) Fig. 2. Sedimentary rocks from Indonesia and crude oils from China. Chromatograms obtained by HPLC on txsilica-NH2. Detection at 254 nm. Each numbered peak (1-4) refers to mono-, di-, tri- and tetra-aromatics. The striped areas indicate the collected fractions which were further analysed by GC and/or by HRS (see text).

P. GARaIGt;ESet al.

832

The selectivity of the low temperature spectrofluorimetry allows us to observe the researched aromatic compounds in all the studied samples, and is particularly useful in the detection of methylchrysenes (MC) (Fig. 7), despite the possible presence of isomers, particularly derivatives of triphenylene, benzanthracene, benzo(c)phenanthrene or tetracene (De Vazelhes-De Sury, 1983). (b ) Quantitative analysis. Quantitative analysis of MP and MC has been performed both by GC and by HRS. HRS and GC, in conjunction with mass spectrometry, have shown to be in good agreement in previous works (Garrigues et al., 1982). For GC measurements, using FID detection, phenanthrene and its monoalkylated derivatives have quite the same response factor. For HRS measurements, the relative quantification of each isomer is obtained by intercalibrating with the equimolar synthetic mixture and by measuring the emission peak height.

Rock 2 Depth:

2480m

monoMe

- t rlaromcllics

c o

5mn

3MP

.

2MP

---It

.

.

1MP

.

I i

....

9MP,461P,

45MP,gMA

M,~

Fig. 3. Gas capillary chromatogram of the triaromatic fraction of the sedimentary rock 2 on SE-52. Chromatographic conditions are detailed in the experimental section. Phe = phenanthrene; An = anthracene; MP = methylphenanthrene; MA = methylanthracene.

Phenanthrene compounds For the crude oils, quantitative measurements have been obtained only by GC. The 4,5-MP and the 9-MA are in fact completely absent from the three samples analysed by HRS. The very small peak of 4-MP observed in the crude oil 2 sample in Fig. 5 indicates a very low contribution ( < 1%) of this compound to the phenanthrene distribution pattern. For the sedimentary rocks, 4-MP and 9-MA, present in small amounts, co-elute with the 9-MP on the GC columns used (SE-52 or CP-Sil 8 CB). The quantification of MP, thus, has been performed by HRS where the forementioned interference problem does not occur (Figs 5 and 6).

Ewald, 1983b). The fractions containing tricyclic and tetracyclic aromatics were dissolved respectively in n-hexane and n-octane which are suitable Shpol'skii solvents for these molecules (Garrigues and Ewald, 1983b). (a) Qualitative analysis. The specific identification of the parent compounds and of each methylated isomer can easily be done either by fluorescence or by for phosphorescence (Figs 5-7). The only exception is for 2-MA which does not exhibit a sufficiently resolved emission spectra at low temperature in n-hexane matrix.

Rock 3 Depth

Me - tet roaromat

: 3180

m

ItS

r

diMe -tetrooromatics r

~

<

g tri Me-tetronromotics

.m J I

t4;

)

5mn

Fig. 4. Gas capillary chromatogram of the tetracyclic fraction of the sedimentary rock 3 on CP Sil 8 CB column. BaA = benz(a)anthracene: Ch = chrysene: Tr = triphenylene.

HPLC on crude petroleums and sedimentary rocks

833

Rock 2

3 i

Crude oil I

I

g i

I i

W

4,5 MP r

9MP

i t I

2MP

3MP

i I I

I I I i

I

1 MP

,, I I

I

I

9MP

Ph

5ynthet/c mixture T i i i

-~ ~ I 345

"~" ~ ~ I 350

i 460

! 465

Wavelength ( n m )

Fig. 5. Emissionspectra of an HPLC fraction frozen at T = 15K in n-hexane, containingphenanthrene (Ph) and MP isomers. Excitation wavelengths at 299.5 and at 297 nm, respectively for fluorescence (F) and phosphorescence (P) spectra. Note the small amount of 4-MP in the sedimentary rock 2 (see also Fig. 9) and the absence of 4,5-MP. For the synthetic equimolar mixture, each compound at c = 2 × 10 7 M.

Chrvsene compounds The relative distribution of these compounds is only obtainable by HRS measurements both in the sedimentary rocks and the crude oils because of the complex mixture of isomers present as shown by GC (Fig. 4). A small amount of 4-MC is observed only in sedimentary rocks 1 and 2. The 5-MC is absent in all the studied samples.

Geochemical implications The comparison of the results obtained on the MP and MC series (Fig. 8) leads to some interesting observations. In the two families, isomers bearing

methyl substituents on the 4 and 5 positions (4,5-MP, 4-MP, 4-MC, 5-MC) are much less abundant that the other compounds. Their formation appears to be unfavorable since they are sterically hindered. Nevertheless, we can note that both the 4-MP and the 4-MC are present in the sedimentary rock 2, while being absent in all the other samples. The origin of such aromatics in the sedimentary matter is still unknown since such high strained compounds have been demonstrated as being produced during high temperature pyrolysis (Adams et al., 1982). Another general trend is the decrease in concentration of the parent compounds (phenanthrene, chrysene) relative to their respective alkylated derivatives and with the increasing maturity of the

834

P. GARRIGUESet al.

Crude

oH l

E~

tn E

o E

o I

o

i

LL

Synthetic mixture

I I

An

1MA

I 380

9MA

I 385 Wavelength ( nm )

Fig. 6. Emission spectra of anthracene (An) and MA isomers in HPLC fraction frozen in n-hexane at T = 15K. Excitationwavelengthsat 257 nm. Note the presence of 9-MA in rock 2. The 2-MA, not observed, does not exhibit quasilinear spectra but is also present in the synthetic mixture (each compound at c = 10 ~'M).

already been noted in previous works (Ishiwatari and Fukushima, 1979; Radke et al., 1982) and supports the idea of the formation of methylated homologs through alkylation of unsubstituted parent compound. The same tendency has also been observed in the anthracene series (De Vazheles-De Sury, 1983) and demonstrates to some extent that this alkylation phenomenon seems to occur in all aromatic series that we have studied. We have calculated for the phenanthrene series the methyl phenanthrene index MPI as defined by Radke et al. (1982) on the basis of the two following

observations: relative decrease of P, 1-MP, 9-MP as a function of thermal maturation and relative increase of 2-MP and 3-MP. MPI = 1.5 (2-MP + 3-MP) P + 1-MP + 9-MP In this ratio the very small contributor of the 4-MP has not been introduced so that a direct comparison can be done on the MPI values obtained in this study and those obtained by Radke etal. (1982), and Radke and Welte, (1983). These calculated values for the crude oils and the

HPLC on crude petroleums and sedimentary rocks

®

®

Rock2 ,

835

'If~'

,

I I

Crudo

v

oi! !

t

I I

, i

I I

.

UJ

1MC

I

I

I

I

362

367

495

500

Wavelength ( n m )

Fig. 7. Emission spectra of HPLC fraction frozen at T = I5K in n-octane containing chrysene (Ch) and MC isomers. Excitation wavelengthsat 327 and 271 nm, respectivelyfor fluorescence (F) and phosphorescence (P) spectra. Note the small amount of 4-MC in the sedimentary rock 2 (see also Fig. 9). For the synthetic mixture. each compound at c = 10 ~' M.

sedimentary rocks have been obtained in Table 1 and 2. The MPI exhibits increasing values related to the increasing maturity of the studied samples defined either by vitrinite reflectance maturity of the studied samples defined either by vitrinite reflectance (R0) or sterane ratios. The MPI values obtained on the rocks 2 and 3 are in the same range as those obtained by Radke et al. (1983) on samples located in the oil window. We can also note that the MPI values calculated for the crude oils are greater than those obtained for the rocks. All these observations demonstrate that the methylphenanthrene index is in good agreement with

the other parameters of maturity. Further investigations are underway in our laboratory to determine other molecular indices in methylated aromatic series (methylchrysenes, methylanthracenes) and to substantiate the trends revealed in this study.

Acknowledgements--We thank J. Joussot-Dubien for his

continuous support, interest and valuable discussions, J. Bellocq who performed HPLC extractions and R. Lapouyade who kindly provided several standards of methylated PAH. We also thank TOTAL-C.F.P. and SNEA(P) for providing the samples and for having authorized this publication.

836

P. GARRIGUESet al.

Methyl- phenanthrenes distribution

Methyl- chrysenes distribuhon

50%-~] Rock I

50%-~-]

30%-[ [

30%-II

1°%-I I

10%-I I

Rock I

30%-

30%--~

Rock

Rock 2

2

10%--

10%-

m

20%-~-~ 10%- [ I P 1MP 2MP 3MP 4MP 9MP 10%-~--]

Rock 3

Rock 3 I

C

o/I I

I-1

30"/.-~] 10%-I

Crude

~

1MC 2MC 3MC 4MC 5MC 6MC

lO%-[--~

Crude o/I I

10%-~

Crude off 2

20%--ll

10%-[--]

Crude Of7 2

10%-F-~

Crude oii 3

20% --I I

P 1MP 2MP 5MP 4MP 9MP

C 1MC 2MC 3MC 4MC 5MC 6MC

Fig. 8. Distribution pattern of MP and MC in the sedimentary rocks and the crude oils.

REFERENCES

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(Edited by Albaiges J.), pp. 221-230. Pergamon Press, Oxford. De Vazelhes-De Sury R. (1983) Unpublished results. Laboratoire de Chimie Physique A, Universit~ Bordeaux I.

HPLC on crude petroleums and sedimentary rocks Ewald M., Lamotte M., Garrigues P., Rima J., Veyres A., Lapouyade R. and Bourgeois G. (1983) Determination of isomers of monomethylphenanthrene extracted from petroleum by capillary gas chromatography coupled to mass spectrometry and by high resolution spectrofluorimetry in n-alkane crystals at a temperature of 15 K. In Advances in Organic Geochemistry 1981 (Edited by Bjorcy M. et al.), pp. 705-709. John Wiley, Chichester. Garrigues P. and Ewald M. (1983a) Natural occurrence of the 4-methyl phenanthrene in petroleums and marine recent sediments. Org. Geochem. 5, 53-56. Garrigues P. and Ewald M. (1983b) Distribution of monomethylated polycyclic aromatic hydrocarbons isolated from crude oils by high performance liquid chromatography and detected by high resolution spectrofluorimetry (Shpol'skii effect). Analyt. Chem. 55, 2155-2159. Garrigues P., Ewald M., Lamotte M., Rima J., Veyres A., Lapouyade R. and Joussot-Dubien J. (1982) Low temperature spectrofluorimetry of complex mixtures of PAH. Application to the analysis of isomeric PAH extracted from environmental samples (Petroleum, Marine sediments). Int. J. Environ. Anal. Chem. 11, 305-312. Garrigues P., Lamotte M., Ewald M. and Joussot-Dubien J. (1981) Utilisation d'un cryog6n6rateur h cycle ferm6 pour l'analyse fluorim6trique des hydrocarbures aromatiques polynucl6aires en matrice Shpol'skii h 15 K. C.R. Acad. Sci. Paris 293, 567-571. lshiwatari R. and Fukushima K. (1979) Generation of unsaturated and aromatic hydrocarbons by thermal alteration of young kerogen. Geochim. Cosmochim. Acta 43, 1343-1349. Lapouyade R., Veyres A., Hanafi N., Couture A., Lablache-Combier A. (1982) Photocyclisation of 1,2-

OG 6 : I / / ~ - A A ~

837

diarylethylenes in primary amines: a convenient method for the synthesis of dihydroaromatic compounds and a means of reducing the loss of methyl groups during the cyclisation of orthomethyl stilbenes. J. org. Chem. 47, 1361-1364. Mackenzie A. S., Patience R. L., Maxwell J. R., Vandenbroucke M. and Durand B. (1980) Molecular parameters of maturation in the Toarcian shales, Paris Basin, France--l. Changes in the configuration of acyclic isoprenoid alkanes, steranes and triterpanes. Geochim. Cosmochim. Acta 44, 1709-1721. Radke M. and Welte D. M. (1983) The methylphenanthrene index: maturity parameter based on Aromatic Hydrocarbons. Advances in Organic Geochemistry 1981 (Edited by Bjoroy M. et al.), pp. 504--512. John Wiley, Chichester. Radke M., Welte D. M. and Willsch M. (1982) Geochemical study on a well in the western Canada Basin: relation of the aromatic distribution pattern to maturity of organic matter. Geochim. Cosmochim. Acta 46, 1-10. Seifert W. K. and Moldowan J. M. (1978) Applications of steranes, terpanes and monoaromatics to the maturation, migration and source of crude oils. Geochim. Cosmochim. Acta 42, 77-95. Wise S. A., Bonnett W. J., Guenther F. R. and May W. E. (1981) A relationship between reversed-phase C18 liquid chromatographic retention and the shape of Polycyclic Aromatic Hydrocarbons. J. chromatogr. Sci. 19, 457465. Wise S. A., Chesler S. N., Hertz H. S., Hilpert L. R. and May W. E. (1977) Chemically-bound aminosilane stationary phase for the high performance liquid chromatographic separation of polynuclear aromatic compounds. Analyt. Chem. 49, 2306-2310.