Directory UMM :Data Elmu:jurnal:O:Organic Geochemistry:Vol31.Issue7-8.2000:

Organic Geochemistry 31 (2000) 635±643
www.elsevier.nl/locate/orggeochem

The in situ analytical pyrolysis of two di€erent organic
components of a synthetic environmental matrix doped
with [4,9-13C] pyrene
Paul F. Greenwood a,*, Elizabeth A. Guthrie b,1, Patrick G. Hatcher b
a

CSIRO, Division of Petroleum Resources, PO Box 136, North Ryde, NSW 1670, Australia
b
Department of Chemistry, Ohio State University, Columbus, OH 43210, USA

Abstract
Laser micropyrolysis GC±MS was used for in situ analysis of the coal and lignin components of a synthetic mixture.
Designed to mimic environmental matrices such as soils and sediments, the mix comprised several possible soil precursors and was also amended with [4,9-13C]pyrene as part of concurrent research on the interaction of PAH pollutants
and sedimentary organic matter. The labeled spike was consistently detected as the major pyrolysate in the in situ
analyses of both lignin and coal components of the synthetic mix, indicating its e€ective sorption by these moieties of
the mix. The remaining hydrocarbon distribution detected from the lignin was dominated by guiaicyl (i.e. methoxyphenol) compounds, whereas high abundances of aromatic (e.g. benzene, naphthalene, phenol and alkyl derivatives
thereof) and aliphatic (e.g. n-alkene/alkane, prist-1-ene, hopanes) products were detected in the coal. Apart from the
high concentrations of the 13C-spike, these data were very similar to molecular data obtained from the respective

pyroprobe pyrolysis GC±MS analysis of pure lignin and coal samples. The untainted (i.e. apart from the 13C-spike)
molecular signatures detected from the in situ analysis of the coal and lignin constituents indicates minimal organic
contamination from the other constituents of the synthetic mix, successfully demonstrating the capability of the laser
micropyrolysis GC±MS technique to selectively analyse the discrete organic entities within complex and heterogeneous
mixtures. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Laser pyrolysis; GC±MS; Soil; Polycyclic aromatic hydrocarbon; Sorption;

1. Introduction
Soils and sediments, by their very nature of formation, represent a highly complex mixture of organic and
mineral matter. The major organic precursors are
degraded plant matter that may comprise a wide array of
autochthonous compounds due to variable plant type and
composition and allochthonous components transported
by aquatic or aeolian processes. Analytical pyrolysis has
* Corresponding author. Present address: Isotope and
Organic Geochemistry Laboratory, Australian Geological Survey Organisation, PO Box 378, Canberra, ACT 2601, Australia. Fax: +61-6249-9961.
1
Present address: Department of Biological and Environmental Sciences, The University of Tennessee, Chattanooga,
TN 37403, USA.

13

C-labeling

provided useful molecular information from soils (Saiz
Jimenez and de Leeuw, 1984, 1986; Saiz Jimenez, 1992,
1994). Traditionally, these analyses have been applied to
bulk samples or chemically derived fractions of the bulk
soil. This approach can not account for the heterogeneous morphology of the organic matter that exists
prior to chemical manipulation and disturbance.
Distinct organic entities within heterogeneous materials
such as soils may now be analyzed with the recently
developed technique of laser micropyrolysis gas chromatography mass spectrometry (GC±MS) (Stout, 1993;
Greenwood et al., 1993, 1996, 1998). This technique has
emerged from the need to analyze micro-sample quantities of organic matter in organic geochemistry
research. Recently, laser microprobes have been used in
combination with various traditional analytical methods
to analyse microscale portions of soils and soil fractions.

0146-6380/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.

PII: S0146-6380(00)00048-6

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P.F. Greenwood et al. / Organic Geochemistry 31 (2000) 635±643

For example, the use of a laser microprobe with mass
spectrometric detection revealed the heterogeneous
binding pattern of PAHs to geosorbents at a lateral
resolution of 40 mm (Gillette et al., 1999).
To test whether the laser micropyrolysis technique
can be used to identify and characterize organic constituent microparticles, it is used here to analyze two
morphologically distinct components of a synthetically
prepared mixture. Puri®ed lignin, coal, cuticle, peat,
humin, and humic acids were mixed together to produce
an environmental matrix typical of the complex mixture
of chemical compounds found in soils and other organic
sediments. Lignin, coal, and cuticle are representative of
composite phases often recognisable in soils and sediments. Sapropelic material from an algal-dominated
sediment (its humin fraction) and humic acids are

representative of the types of biopolymeric organic
matrices present in sediments. The in situ analysis
focused on the lignin and coal components because
these components are easily recognised by microscopic
observation and by their molecular composition. The
lignin was from a sample of brown-rot infected wood
collected from Mount Rainier, Washington state
(Hatcher et al., 1988) and the coal was collected from an
outcrop of the Wilcox Formation near San Antonio,
Texas. Lignin, is a resistant component of wood cell
walls that is preferentially preserved during biological
degradation. For this reason, it is an important terrestrial marker in soils and sediments (Hedges et al., 1985;
Shevchenko and Bailey, 1995). Coals usually represent a
more modi®ed version of the plant remains found in
soils and sediments (Wilson, 1987; Schmidt et al., 1996,
1999).
Conventional pyrolysis data obtained from the pyroprobe pyrolysis GC±MS of pure lignin and coal samples
was used to assess the purity of the laser pyrolysis data.
A 13C-labeled, four ring polycyclic aromatic hydrocarbon, [4,9-13C]pyrene, was added to the synthetic mix
so that the capabilities of this technique for detecting

PAH contaminants in analogous environmental settings
could also be assessed. The use of 13C labeled organic
contaminants in conjunction with pyrolysis GC±MS
detection to measure the extent of [4,9-13C]pyrene
sequestration by the refractory humin fraction of a
sediment was recently demonstrated (Guthrie et al.,
1999). Complementary data concerning the molecular
fate of the 13C label following the interaction of 13Clabeled compounds with sedimentary organic matter has
also been previously obtained by other analytical methods
including chemolysis (Richnow et al., 1997, 1998), thermochemolysis GC±MS (Knicker and Hatcher, 1997), 13C
NMR (Hatcher et al., 1993; Bortiatynski et al., 1994,
1997; Castro et al., 1995; Guthrie et al., 1999) and Cisotopic analysis (Richnow et al., 1998).
Here, we assess the sorptive capacity of a 13C-probe
to di€erent matrix constituents (i.e. lignin and coal) by

laser micropyrolysis GC±MS. Sorptive interactions
between di€erent soil biomacromolecules and organic
pollutants may di€er dramatically (Luthy et al., 1997).
However, it should be stressed that monitoring the 13Cprobe by laser micropyrolysis GC±MS alone, will only
provide a qualitative analysis. Additional factors (e.g.,

relative lability/bonding strengths) may also in¯uence
the detection of such pollutants. The consideration of
GC±MS data in association with complementary data
from analytical techniques such as 13C NMR and/or 13C
isotopic analysis may provide a more de®nitive quantitation of the degree of sorption. However, analysis of
the lignin and coal entities of the synthetic mix by these
techniques was beyond the scope of the present paper.

2. Experimental
2.1. Sample composition and preparation
The composition of the synthetic mix is shown in
Table 1. The di€erent components were simply mixed
together in a glass beaker and stirred with a steel spatula.
None of the components were ground before or during
the mixing process to maintain the morphology of the
coal, lignin and cuticle constituents. 2 mg of
[4,9-13C]pyrene (synthesized as reported by Guthrie et
al., 1999) was added to 2.22 g of the synthetic mix via 50
ml of methanol carrier. The mixture was air-dried for
four hours to allow for the evaporation of the methanol.

An even distribution of the 13C-probe throughout the
mixture cannot be assumed since it consists of granules
of irregular size and shape. The synthetic mix did not
appear to be physically altered by the spiking process. A
photomicrograph of the synthetic mix in which the lignin and the coal components are readily identi®able is
shown in Fig. 1. (NB: This photo was taken with an
Olympus PM-10ADS photomicrographic camera system
interfaced to a Zeiss Universal microscope equipped
with Epiplan HD objectives, in epi-dark®eld mode using
Kodak Elite II ED135-36 transparency ®lm.)

Table 1
Composition of the synthetic mixture
Component

Source

Mass
(mg)

Humin
Coal and resin
Peat
Lignin

Warwick pond, Bermuda
Wilcox lignite, TX, USA
Everglades peat, FL, USA
Brown-rotted wood from Mt Rainier,
WA, USA
Everglades peat, FL, USA
Tomato cuticle (provided by
Dr. Erik Tegelaar)

1000
430
330
250

Humic acid

cuticle

170
40

P.F. Greenwood et al. / Organic Geochemistry 31 (2000) 635±643

2.2. Laser micropyrolysis GC±MS
Details of the hardware and experimental protocol
associated with the laser technique have been outlined

637

previously (Greenwood et al., 1996, 1998) and only a
brief description will be included here. The laser
microprobe comprises a Laser Applications continuous
wave Nd:YAG laser and an Olympus re¯ected light/

Fig. 1. A photomicrograph of the synthetic mixture. L = lignin and C = coal components. Scale bar = 1 mm.

Fig. 2. TIC from the in situ laser micropyrolysis GC±MS analysis of a lignin component of the synthetic mixture. Peak assignments
correspond to products listed in Table 2.

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P.F. Greenwood et al. / Organic Geochemistry 31 (2000) 635±643

¯uorescence microscope. A small portion of the synthetic sample was dispersed on a 5.9 mm DeckglaserTM
glass cover-slip and located in the sample pyrolysis
chamber. The pyrolysis chamber is interfaced to the GC
via an intricate gas inlet system designed for ecient
product transfer. A window at the top of the pyrolysis
chamber provides the laser microprobe with access to
the sample inside.
The samples were typically pyrolysed with a laser
energy of 19 watts/s for a period of 10 s. Individual
lignin and coal grains were of sucient size (0.1±1 mm)
to accommodate the relatively large (200 mm diameter)
laser craters obtained with these parameters when focusing
the laser beam through the10 microscope objective.

Where possible, large craters are preferred as they give
rise to higher pyrolysate concentrations. The pyrolysis
chamber was manually positioned under the microscope
objective such that the particular granule (or part
thereof) to be analysed was located in the target area of
the laser.
GC±MS detection of the laser pyrolysates was performed with a HP 5890/Series II gas chromatograph
interfaced to a Micromass-Autospec UltimaQ mass
spectrometer. Chromatography was carried out on a 25
m DB-5 capillary column (5% phenyl polysiloxane, 0.32
mm i.d., 0.52 mm ®lm thickness). The GC was typically
temperature-programmed for an initial 40 C, held for 2
min, then increased at 4 C/min to a ®nal temperature of
300 C, held for 25 min. Full scan mass spectra (m/z 50±
550) were obtained using standard detection parameters
(electron energy = 70 eV; ®lament current = 200 mA;
source temperature = 250 C; electron multiplier = 200
V; mass resolution = 1000).
2.3. Pyroprobe pyrolysis GC±MS
Conventional analytical pyrolysis was performed
with a Chemical Data Systems 160 pyroprobe interfaced to a HP 6890/5973 GC±MS. A small powdered
portion (1±2 mg) of the pure lignin, pure coal and bulk
synthetic mix were separately pyrolysed at a temperature of 650 C which was applied for 10 s. The pyrolysates were swept from the pyroprobe interface onto
the GC-column with a helium carrier (1.3 ml/min).
Chromatography was carried out on a 30 m, AT-5
capillary column (5% phenylmethyl silicone, 0.25 mm
i.d., 0.25 mm ®lm thickness). The pyrolysates were cryogenically focussed onto the GC column by immersing
a short section of the column in a liquid nitrogen
bath for 1 min. A GC temperature program of an
initial 40 C (2 mins hold) increased at 2 C/min to 300 C
(25 min hold) was started on removal of the column
from the cold trap. A HP 5973 mass spectrometer was
used for product detection with relatively standard
MS parameters (70 eV; m/z 50±550; 250 C source
temperature).

3. Results and discussion
3.1. Analysis of the Mt Rainier lignin moiety of the
synthetic mixture
The total ion chromatogram (TIC) from the in situ
laser micropyrolysis GC±MS analysis of a lignin component of the synthetic mix is shown in Fig. 2. Product
assignments are listed in Table 2 and were based on
both mass spectral and GC retention time data. The
major peak eluting at a retention time of 42 min can
be assigned as [4,9-13C]pyrene, indicating e€ective sorption
of the 13C-labeled probe onto the lignin component of
the synthetic mix. It was consistently the most abundant
product detected from several repeat analyses of lignin
constituents of the synthetic mix.
Table 2
Pyrolysates detected from either the synthetic mixture and/or
the lignin and coal components of the mixture
Peak label

Product

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36

Benzene
Toluene
C2-Benzene
Ethynylbenzene
Styrene
C3-Benzene
Methylstyrene
Phenol
Indane
Indene
o-Cresol
m-Cresol + p-cresol
Guiaicol
Methylindene
2,4-Dimethylphenol
Naphthalene
4-Methylguaiacol
Ethylguaiacol
2-Methylnaphthalene
1-Methylnaphthalene
Vinylguaiacol
Eugenol
cis-Isoeugenol
Vanillin
Biphenyl
Methylsyringol
C2-Naphthalene
Acenaphthylene
trans-Isoeugenol
C3-Naphthalene
Acetoguaiacone
Guaiacol acetic acid
trans-Coniferylaldehyde
Fluorene
Trimethoxystyrene
Phenanthrene

P.F. Greenwood et al. / Organic Geochemistry 31 (2000) 635±643

639

Fig. 3. TIC from the in situ laser micropyrolysis GC±MS analysis of a coal component of the synthetic mixture. The chromatogram
abundance has been 3 to enhance coal pyrolysates otherwise overwhelmed by the large [4,9 13C]pyrene peak. Peak assignments
correspond to products listed in Table 2. !=n-alkene; *=n-alkane; Pr=prist-1-ene; H=hopanoid.

The remaining product distribution is dominated by
guaiacyl units re¯ecting the gymnosperm origins of the
Mt Rainier lignin (Hatcher et al., 1988). The major peaks
are phenol (8), guaiacol (13), 4-methylguaiacol (17), vinylguaiacol (21), eugenols (22,23,29) and coniferylaldehyde
(33). Subordinate peaks were assigned as alkylphenols
(11,12,15), other side-chain oxidized products (e.g.
31,32) and polycyclic hydrocarbons (e.g. 10,16,28). The
phenolic products are indicative of a biodegraded wood
(Sigleo, 1978; Obst, 1983), whereas the signi®cant PAH
abundances are probably a consequence of the pyrolysis
mechanism.
In a recent study in which we compared the laser
micropyrolysis and pyroprobe pyrolysis GC±MS analyses of (pure) Mt Ranier lignin (unpublished data), the
applicability of laser energy as a source of pyrolysis for
the study of lignin was established. Except for the major
[4,9-13C]pyrene peak, the hydrocarbon distribution from
the in situ analyses of lignin components of the synthetic
mix (e.g. Fig. 2) was almost identical to the guiaicyl
dominated pyrolysis distribution from the laser pyrolysis GC±MS of pure Mt Ranier lignin observed in our
recent study. The laser result was also in good agreement
with previous data obtained from Mt Rainier lignin
(Hatcher et al., 1988). The consistency between the laser
pyrolysis GC±MS data from the in situ analysis of a
lignin component in the heterogeneous matrix and corresponding molecular data obtained from pure Mt
Rainier lignin indicates minimal contamination from the
other precursors of the synthetic matrix. Thus, the laser

microprobe has been successfully used to selectively
pyrolyse the lignin moiety of a complex environmental
matrix without prior chemical or physical isolation.
3.2. Analysis of the Wilcox coal moiety of the synthetic
mixture
The total ion chromatogram (TIC) from the in situ laser
micropyrolysis GC±MS analysis of a coal component of
the synthetic mixture is shown in Fig. 3. Product
assignments are listed in Table 2. [4,9-13C]pyrene was
again the major pyrolysate consistently detected from
the in situ analysis of several coal components, indicating
that this moiety of the synthetic mixture has also eciently
sorbed the 13C-probe. The TIC was deliberately set o€
scale (3) in Fig. 3 so that the complete pyrolysate distribution can be more readily observed. A high abundance
of aromatic pyrolysates including alkylaromatic, alkylphenol and polycyclic aromatic hydrocarbons was detected.
A signi®cant distribution of aliphatic pyrolysates consisting of prist-1-ene in high abundance, a wide MW
distribution of n-alkene/alkanes and a number of high
MW hopane/hopenes was also detected.
Apart from the large peak due to the 13C-probe, the
pyrolysate distribution detected from the in situ analysis
of the coal component of the synthetic mix is generally
consistent with molecular data obtained previously from
py-GC±MS analysis of low-rank coals (Larter and
Hors®eld, 1993). The Wilcox coal was additionally analysed here by pyroprobe pyrolysis GC±MS to provide a

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P.F. Greenwood et al. / Organic Geochemistry 31 (2000) 635±643

Fig. 4. (a) m/z 57 and (c) the m/z 191 mass chromatograms from the in situ laser micropyrolysis GC±MS analysis of a coal component
of the synthetic mixture; (b) m/z 57 and (d) the m/z 191 mass chromatograms from the pyroprobe pyrolysis of Wilcox coal. Pr=prist-1-ene;
Ts=C27 18a(H),22,29,30-trisnorneohopane; Tm=C27 17a(H),22,29,30-trisnorhopane; ba=17b(H)21a(H) hopanes; ~=hopenes.

P.F. Greenwood et al. / Organic Geochemistry 31 (2000) 635±643

comparative data set. The respective m/z 57 and m/z 191
mass chromatograms obtained from the in situ analysis
of a coal component of the synthetic mixture by laser
micropyrolysis GC±MS and the analysis of pure Wilcox
coal by pyroprobe pyrolysis GC±MS are shown in Fig. 4.
The aliphatic products consist of a bimodal distribution
of n-alkene/alkanes from C10 out to C31, with maxima
at C11 and C27, and a very prominent prist-1-ene. The
hopanoid distributions consist of C27, C29 and C30
hopanes and hopenes. The respective acyclic aliphatic
and hopanoid data sets re¯ect little qualitative di€erence.
The small variance observed in the relative abundance
of some products may be due to the di€erent heating
regimes of the pyrolyis methods (laser>>pyroprobe)
or simply may re¯ect the reproducibility limitations of
these methods. A slight intermolecular chemical heterogeneity within the coal macromolecule (averaged out by
the bulk pyroprobe analysis) might also be evident.
3.3. Pyroprobe pyrolysis of the synthetic mixture
Consistent with the multi-precursor composition of
the synthetic mixture, the pyrolysate distribution detected
from the bulk mix is considerably more complex than

641

the corresponding data from its coal and lignin moieties.
The total ion chromatogram (TIC) and m/z 57 chromatogram from the pyroprobe pyrolysis of the synthetic
mixture is shown in Fig. 5. The bulk pyrolysates essentially constitute a mean of the molecular composition of
each of the precursors of the synthetic mixture. Several
molecular features due to the lignin and coal precursors
can be recognised. Vinylguiaicol (21) and trans-isoeugenol
(29), two of the major pyrolysates detected from the
lignin moiety of the mix (Fig. 2), are also detected in
high abundance in the synthetic mixture (Fig. 5a).
In contrast to the direct guiaicyl product/lignin precursor link, aliphatic hydrocarbons are not so source
speci®c. Nevertheless, the bimodal n-alkene/alkane distribution and prominent prist-1-ene observed from the
m/z 57 chromatogram detected from the synthetic mixture
(Fig. 5b) is largely consistent with the aliphatic distribution
measured from the Wilcox coal (Figs 4a and b). The Wilcox
coal is probably the major source of aliphatic hydrocarbons in the synthetic mixture, inundating the aliphatic contribution of the other precursors.
Many other products detected from the bulk pyrolysis
of the synthetic mix cannot be attributed to either the coal
or lignin precursors. Products which may have derived from

Fig. 5. (a) TIC (1.5 - [4,9 13C]pyrene peak o€ scale); and (b) m/z 57 chromatogram from the 650 C pyroprobe pyrolysis of the bulk
synthetic mixture. Peak assignments correspond to aromatic products listed in Table 2. !=n-alkane; Pr=prist-1-ene; H=hopanoid.

642

P.F. Greenwood et al. / Organic Geochemistry 31 (2000) 635±643

other precursors of the synthetic mixture include alkylated
pyrolles, pyridines and several other low MW nitrogen
containing compounds (NB: pyroprobe pyrolysates
detected from the Everglades humic acid) and low MW
branched aliphatic products (NB: pyroprobe pyrolsates
detected from the tomato cuticle). The complexity of the
pyrolysate distribution detected from the synthetic mixture
is typical of the complex chemical material which accumulates in soils and sediments.

Acknowledgements
We thank the Oce of Naval Research through
Grants N-00149510209 and N-00149910073 for ®nancial
assistance. We also thank Dr. Erik Tegelaar for providing
a sample of tomato cuticle. The reviews by Drs. Claude
Largeau and Pim van Bergen were appreciated and their
comments signi®cantly improved the manuscript.

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