OIL SPILL SCIENCE chapter 5 – introduction to oil chemical analysis

Chapter 5

Introduction to Oil Chemical
Analysis
Merv Fingas

Chapter Outline
5.1. Introduction
87
5.2. Sampling and Laboratory 87
Analysis
5.3. Chromatography
89

5.4. Identification and Forensic 96
Analysis
5.5. Field Analysis
107

5.1. INTRODUCTION
An important part of the field of oil spill control is the analysis of oil in various
media. Oil analytical techniques are a necessary part of the scientific, environmental, and engineering aspects of oil spills.1-4 Analytical techniques are used
extensively in environmental assessments of fate and effects. Laboratory analysis
can provide information to help identify an oil if its source is unknown or what its
sources might be. With a sample of the source oil, the degree of weathering and the
amount of evaporation or biodegradation can be determined for the spilled oil.
Through laboratory analysis, the more toxic compounds in the oil can be
measured, and the relative composition of the oil at various stages of the spill can
be determined. This is valuable information to have as the spill progresses.
In nonspill situations, analytical techniques are used extensively to measure
the oil content of soil and water for environmental quality purposes. Many

jurisdictions have standards on the petroleum content of waters and soils for
various uses. In addition, many laws exist for the maximum oil content in soils.
Soils must often be removed for treatment before lands can be transferred from
one owner to another.

5.2. SAMPLING AND LABORATORY ANALYSIS
Taking a sample of oil and then transporting it to a laboratory for subsequent
analysis is common practice. While there are many procedures for taking oil
Oil Spill Science and Technology. DOI: 10.1016/B978-1-85617-943-0.10005-X
Copyright Ó 2011 Elsevier Inc. All rights reserved.

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samples, it is always important to ensure that the oil is not tainted from contact
with other materials and that the sample bottles are precleaned with solvents,
such as hexane, that are suitable for the oil.5
The simplest and most common form of analysis is to measure how much
oil is in a water, soil, or sediment sample.6 Such analysis results in a value
known as total petroleum hydrocarbons (TPH). The TPH measurement can be
obtained in many ways, including extracting the soil, or evaporating a solvent
such as hexane and measuring the weight of the residue that is presumed to
be oil.
There now exist certified laboratories that use certified petroleum hydrocarbon measurement techniques.6 These should be used for all studies. One of

the most serious difficulties in older studies occurred when inexperienced staff
tried to conduct chemical procedures. Analytical methods are complex and
cannot be conducted correctly without chemists familiar with the exact
procedures. Furthermore, field instrumentation requires calibration using
standard procedures and field samples during the actual test. These samples
must be taken and handled by standard procedures. Certified standards must be
used throughout to ensure good Quality Assurance/Quality Control (QA/QC)
procedures. In this era, it is simply unacceptable not to use certified methods,
laboratories, and chemists.

5.2.1. Incorrect and Obsolete Methods
Several attempts to perform oil analysis have been made using methods that are
not scientifically valid. One of these is the use of colorimetry. This method has
never been scientifically valid for oil measurement as oil does not have what is
known as a color center, that is, a molecular absorption center for a specific
band of light.7-9 As oil is a mixture of hundreds of compounds, there is obviously not a single light-absorbing centre. This method results in oil measurements that are typically 100% incorrect.
Another series of methods involved extracting oil from soil or water using
fluorinated or chlorinated hydrocarbons. Since these extractants were ozonedepleting, they were removed from the market over 20 years ago. The
extracted hydrocarbons were then “measured” using infrared light, as hydrocarbons in such solvents do absorb at specific wavelengths. The method was
the standard oil in soil technique in several countries and yielded repeatable
results.
The ozone-depleting substances were replaced with hexane. Hexane is not
a good extractant of oil from soil, and thus these methods are not as popular
as the older methods were. The use of hexane also led to renaming the results
of these methods from Total Petroleum Hydrocarbons (TPH) to hexaneextractables.10
There are several “meters” sold on the market that offer oil readings;
however, none of these are reliable or accurate.8


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Introduction to Oil Chemical Analysis

89

Fluorometry is a technique sometimes used for measuring or estimating
concentrations of oil in water. A fluorometer uses UV or near UV to activate
aromatic species in the oil.11 The UV activation energy is more sensitive to the
naphthalenes and phenanthrenes, whereas the near UV is more sensitive to
large species such as fluorenes. The composition of the oil changes with respect
to aromatic content as it weathers and is dispersed in water, with the concentration of aromatics increasing. Thus, the apparent fluorescent quantity
increases in this process. It must be noted that fluorometers cannot truly be
calibrated for the oil as there are many variables, as explained above. The errors
encountered all increase the apparent value of the oil concentration in the water
column. Incorrect calibration procedures can distort concentration values up to
10 times their actual value, or even more. Correct analytical methods involve
performing accurate gas chromatograph (GC) measurements both in the
laboratory and in the field.

5.3. CHROMATOGRAPHY
The primary method for oil analysis, as well as for many chemicals in the
environment, is gas chromatography; this method will be described in the
subsequent section. One should note that other chromatography methods and
other analytical methods are sometimes used for oils. These include liquid
chromatography, sometimes used for PAH analysis and inductively coupled
plasma (ICP) instruments for measuring metals in oils. These and many other
techniques are not described in this section.

5.3.1. Introduction to Gas Chromatography
The standard method for oil analysis is to use a GC.2,3,12,13,14 A small sample of

the oil extract (typically measured in microliters, mL), often in hexane, and
a carrier gas, usually helium or hydrogen, are passed through a capillary
column. The sample is injected into a heated chamber from where its vapors
pass into the silica column. The silica column is coated with absorbing materials, and, because the various components of the oil have varying rates of
adhesion, the oil separates because these components are absorbed at different
rates onto the column walls. The gases then pass through a sensitive detector.
The injector, column, and detector are often maintained at constant temperatures to ensure repeatability. The system is calibrated by passing known
amounts of standard materials through the unit. The amount of many individual
components in the oil is thereby measured. The components that pass through
the detector can also be totaled, and a TPH value determined. It is important to
note that only the vapors pass into the column initially. Heavier contaminants
can foul the injector and first part of the column. It is therefore important that the
sample be subjected to a cleanup procedure before it is injected into the column.
Cleanup procedures can be complex and involve several steps.


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While a GC measurement is highly accurate, this measurement does not
include resins, asphaltenes, and some other components of the oil with higher
molecular weight that do not vaporize and pass through the column. These
heavier components can be determined separately using open column chromatography or precipitation techniques.
The detectors used in chromatography are important. An important
detector for petroleum hydrocarbons is the flame ionization detector (FID).2,3
The principle behind this instrument is simple as most compounds show
variable ion conductivity burned in a hydrogen flame. This detector is simple

and has the advantage of yielding relatively similar signals for different
hydrocarbons, thus making calibration and quantification simple. Another
detector commonly used for oils is the mass spectrometric detector. The
analytes from the GC column are introduced into a vacuum chamber and
ionized, and then these ions are separated according to mass and passed to
a detector. The detected signals are then analyzed by a computer and output to
the user as peaks of given mass or even possible compound identification. The
mass spectrometer provides information about the structure of the substance so
that each peak in the chromatogram can be more positively identified. The
methods are abbreviated as GC-FID, if a gas chromatograph and flame ionization detector are used or GC-MS, if a gas chromatograph and a mass
spectrometer detector are used.
A typical GC-FID chromatogram of a light crude oil with some of the
more prominent components of the oil identified is shown in Figure 5.1.2,3
This chromatogram shows some of the many features of oil that are identified by this analytical technique. The bulk of crude oils, especially light
ones, have a large proportion of n-alkanes, as can be seen by the large peaks
that constitute a large portion of this chromatogram. This is a light crude oil
that can be evidenced by the fact that the highest peak is C15. A more
weathered crude might have its highest peak at C18 or more. The top of the
chromatogram is typically shaped as a curve, peaking to C15, as it is here.
Under the peaks is a hump, often called the unresolved complex mixture, or
UCM. This is an aggregate of largely unresolved peaks of alkane origin. At
C16, for example, there are already thousands of isomers that cannot be
resolved by typical GC methods. Between the n-alkane peaks are smaller
peaks, most of which are aromatic compounds. Two standard biomarkers
(here, isoprenoids and branched alkanes) are usually evident in such a
chromatogram, Pristane (near nC17) and Phytane (near nC18). These have
been used to assess state of weathering; however, other compounds are now
typically used.
Figure 5.2 shows the GC-FID chromatograms of 10 oils. Figure 5.2A to C
shows the chromatograms of three lighter crude oils: Arabian medium crude

oil, Hedrun crude oil, and Gullfaks,2,3 Figure 5.2D shows a chromatogram
of Orimulsion, a bitumen. In this chromatogram one notes that almost all
n-alkanes are not present, and the chromatogram largely consists of the


91

C28

C26

C24

C22

C20

Introduction to Oil Chemical Analysis

C21

Chapter | 5

Chromatographic retention time
FIGURE 5.1 GC-FID of a light crude oil. This chromatogram illustrates many features of
the chromatograms of crude oils. The bulk of crude oils, especially light ones, have a large
proportion of n-alkanes, as can be seen by the large peaks that constitute a large portion of this
chromatogram.

unresolved complex mixtures, or UCM. Figure 5.2E shows the chromatogram

of IFO-30, Intermediate fuel oil, which is a mixture of a diesel fraction and
Bunker C. Figure 5.2F shows the chromatogram of Bunker C, and Figures
5.2G-J show jet fuel, diesel fuel, lubrication oil, and number 6 fuel oil,
respectively.
The mass spectrometer provides information about the structure of the
substance so that each peak in the chromatogram can be positively identified.
An important technique is that of SIM (selective ion monitoring), where one
can monitor the ion most typically associated with the target compound. This
technique enables the detection and quantification of many compounds in oil
that otherwise would not be separately resolved.2,3 Figure 5.3 shows three
chromatograms first by GC-FID and then by GC-MS using SIM. Figures 5.3A
and B are chromatograms of a light Alberta crude oil; Figures 5.3C and D are
chromatograms of California heavy crude oil, and Figures 5.3E and 5.3F are
chromatograms of Orimulsion Bitumen. The two chromatograms (e.g., FID/
SIM) are quite different. The SIM chromatograms are no longer recognized as
the types of oils as shown by FID. However, one can see that the peaks are more
clearly defined and that the SIM can provide different and important information. The disadvantage of the SIM is that each peak must be quantified
separately using an internal standard.
Most fuels and oils show a typical distribution pattern in GC-FID.
The idealized patterns can be seen in Figure 5.4, a figure that shows the
alkane distribution. All graphs are n-alkanes except for the lube oils where
the alkanes are highly branched. These bar graphs were created from


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FIGURE 5.2 GC-FIDs of several oils. Figure 5.2A shows the chromatogram of Arabian medium
crude oil. Figure 5.2B is a chromatogram of Hedrun crude oil, a light oil. Figure 5.2C is a chromatogram of Gullfaks, another light oil. Figure 5.2D shows a chromatogram of Orimulsion,
a bitumen. In this chromatogram one notes that almost all n-alkanes are not present, and the
chromatogram largely consists of the unresolved complex mixtures or UCM. Figure 5.2E shows
the chromatogram of IFO-39, Intermediate fuel oil, which is a mixture of a diesel fraction and
Bunker C. One can see the peaks of diesel fuel, peaking at about C14 and that of Bunker C,
peaking at about C28. In Figure 5.2F the chromatogram of Bunker C is shown. Figures 5.2G, 2H,
2I, and 2J show jet fuel B, diesel fuel, lubrication oil, and number 6 fuel oil, respectively.


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93

FIGURE 5.2 Continued

quantitative analysis and approximate the alkane chromatograms of the
same oils.

5.3.2. Methodology
Modern chromatographic methods require that the injected sample contents
be of certain types and that they do not foul the injector or column. Thus,
several cleanup methods have developed over the years.1,6 The basic methods
involve extracting the oil using dichloromethane (DCM), sometimes in
combination with other solvents such as hexane. This procedure will leave the
DCM insoluble material, such as soil and wood, and remove the DCM
soluble material, which is largely petroleum oil. Surrogate chemicals are
often added at this stage; these substances are compounds, typically deuterated hydrocarbons, that are not present in oil and will serve to identify peaks

in subsequent analyses. The DCM extract is often filtered and treated to


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FIGURE 5.3 The GC-FID and GC-MS with SIM at ion 85m/e. The left-hand columns are the
GC-FID chromatograms, and the right-hand side are the GC-MS and SIM chromatograms. Figures
A and B are chromatograms of a light Alberta crude oil; Figures C and D are chromatograms of
California heavy crude oil, and Figures E and F are chromatograms of Orimulsion Bitumen. One
notes that the two chromatograms (e.g., FID/SIM) are quite different. The SIM chromatograms no
longer have the recognizability of the types of oils as shown by FID. However, one can see that the
peaks are more clearly defined and that the SIM can provide separate information. The disadvantage of the SIM is that each peak must be quantified separately using a standard.


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Introduction to Oil Chemical Analysis

Lube Oil

Gasoline

4 6

8 10 12 14
Carbon Number

15

20

25

30

35

40

Carbon Number

Jet Fuel

Typical Crude

6 8 10 12 14 16 18
Carbon Number
0

5

10
15
Carbon Number

20

25

30

35

40

35

40

Diesel Fuel
Bunker C
6 8 10 12 14 16 18 20 22 24
Carbon Number

10

15

20

25
30
Carbon Number

FIGURE 5.4 The bar graph distribution of alkanes for typical oils and fuels. These graphs
were generated from the quantitative analysis of several oils. It should be noted that the
alkanes are typically n-alkanes for all oils except for lube oils, where they are highly branched
alkanes.

remove water before injection into the GC. At each point in this cleanup, the
sample is quantified to allow measurement of those groups of materials
removed. These measurements then form the basis for various forms of TPH
measurement. One such method as developed by Dr. Zhendi Wang of
Environment Canada is shown in Figure 5.5.2,3
In the method illustrated in Figure 5.5, the sample is separated into
aliphatic, aromatic, and polar fractions using an open silica column. Several
tests of this have been carried out to ensure that separation is complete. Having
these fractions separated ensures that subsequent chromatographic analysis is
not affected by interferences between the three fractions.
The peaks that are typically quantified for analysis and possibly for identification are listed in Table 5.1.2,3 As described later, many of the these peaks
are useful when combined in ratios. Often these ratios are unique and can be
used for positive identification of an oil.
There are many published methods and standards for oil analysis; several of
these are listed in Table 5.2.


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Weigh Sample
add surrogates

serially extract sample with
dichloromethane/hexane

filter and
concentrate
extract

gravimetrically
determine TPH

silica column fractionation
fraction 1
aliphatics

fraction 2

fraction 3

aromatics

mixed

50% DCM/Hexane
hexane
gravimetric
saturates
aromatics
determinations
5-- -Androstane d14-Terphenyl

internal
standards Hopane

GC/MS
SIM

GC/MS (SIM)

GC/FID
PAHs
n-alkane
hopanes
n-alkane
quantification distribution & steranes

half F1&F2
TPH
5- -Androstane

fraction 4
polars
Methanol
polars
polars

GC/FID

Benzenes
PAH alkylated
homologues

TPH

FIGURE 5.5 Illustration of the Dr. Wang analysis method developed for Environment Canada.
After cleanup procedures, the sample is separated into aliphatic, aromatic, and polar fractions. This
enables very clear chromatographic analysis without interference between these fractions. This
method yields many analytical parameters.

5.4. IDENTIFICATION AND FORENSIC ANALYSIS
The foregoing information can then be used to predict how long the oil has
been in the environment and what percentage of it has evaporated or biodegraded.15-23 This is possible because some of the components in oils,
particularly crude oils, are very resistant to biodegradation, whereas others are
resistant to evaporation. This difference in the distribution of components then
allows the degree of weathering of the oil to be measured. The same technique
can be used to “fingerprint” an oil and positively identify its source. Certain
compounds are consistently distributed in oil, regardless of weathering, and
these are used to identify the specific type of oil.
The effect of weathering is particularly important as it may negate the use of
standard GC-FID to positively identify an oil.23, 28-31 Figure 5.6 shows the
effect of weathering on the GC-FID chromatogram of a light crude oil. As
the oil weathers, more and more of the lower n-alkanes are lost to evaporation,
the most important component of weathering. Figure 5.6A shows the


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Introduction to Oil Chemical Analysis

TABLE 5.1 Target Analytes/Compounds for Oil Spill Studies
Analyte

Analyte

Target Ion

Aliphatic Hydrocarbons

BTEX and C3 Benzenes

n-C8

Benzene

78

n-C9

Toluene

91

n-C10

Ethylbenzene

105

n-C11

Xylenes

105

n-C12

C2 - benzenes

105

n-C13

C3 - benzenes

105

n-C14

PAHs

n-C15

Naphthalene

128

n-C16

C1 - naphthalene

142

n-C17

C2 - naphthalene

156

Pristane

C3 - naphthalene

170

n-C18

C4 - naphthalene

184

Phytane

Phenanthrene

178

n-C19

C1 - phenanthrene

192

n-C20

C2 - phenanthrene

206

n-C21

C3 - phenanthrene

220

n-C22

C4 - phenanthrene

234

n-C23

Fluorene

166

n-C24

C1 - fluorene

180

n-C25

C2 - fluorene

194

n-C26

C3 - fluorene

208

n-C27

Chrysene

228

n-C28

C1 - chrysene

242

n-C29

C2 - chrysene

256

n-C30

C3 - chrysene

270

n-C31

Biphenyl

154

(Continued )


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TABLE 5.1 Target Analytes/Compounds for Oil Spill Studiesdcont’d
Analyte

Analyte

Target Ion

n-C32

Benzo[e]pyrene

252

n-C33

Benzo[a]pyrene

252

n-C34

Perylene

252

n-C35

Dibenzothiophene

184

n-C36

C1 - Dibenzothiophene

198

n-C37

C2 - Dibenzothiophene

212

n-C38

C3 - Dibenzothiophene

226

n-C39
n-C40
EPA Priority
PAH pollutants
Naphthalene

128

Phenanthrene

178

Fluorene

166

Chrysene

228

Acenaphthylene

152

Acenaphthene

153

Anthracene

178

Fluoranthene

202

Pyrene

202

Benz[a]anthracene

228

Benz[b]fluoranthene

252

Benzo[k]fluoranthene

252

Benzo(g,h,i)perylene

276

Biomarkers
Triterpanes
Tricyclic terpanes

191


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Introduction to Oil Chemical Analysis

TABLE 5.1 Target Analytes/Compounds for Oil Spill Studiesdcont’d
Analyte

Analyte

Target Ion

Tetracyclic terpanes

191

Pentacyclic terpanes

191

C23H42

191

C24H44

191

C27H46 (Ts) & (Tm)

191

C29H50&C30H52 ab-hopane

191

C30-35H52-62 22S/22R

191

Steranes
C27 20 R/S-cholestanes

217,218

C28 20 R/S-ergostanes

217,218

C29 20 R/S-stigmastanes

217,218

unweathered oils with the Cn Benzenes and naphthalenes very obvious. After
about a 30% loss of oil through evaporation, the Cn Benzenes are lost, and
many of the lower alkanes are shown in Figure 5.6B. After 44.5% of the mass is
evaporated, as shown in Figure 5.6C, even the naphthalenes are not clearly
present. It would be very difficult to simply compare weathered and
unweathered oils simply by comparing the chromatograms. Although there are
some ways to partially compensate for this, modern technology uses other
components of the oil to forensically identify oils.

5.4.1. Biomarkers
Biological markers or biomarkers are an important hydrocarbon group in
petroleum analysis.32-34 Biomarkers are complex molecules derived from
formerly living organisms. Biomarkers found in crude oils, rocks, and sediments show little change in structures from their parent organic molecules, or
so-called biogenic precursors (for example, hopanoids, and steroids), in living
organisms. Biomarker concentrations are relatively low in oil, often in the
range of several hundred ppm. Biomarkers are useful because they retain all
or most of the original carbon skeleton of the original natural product;
this structural similarity reveals more information about oil origins than
other compounds. Petroleum geochemists have historically used biomarker

100

TABLE 5.2 List of Standards Applicable to Oil Measurement
Standards
Organization

Method
Number

ASTM

Analyte

Description

Reference

D5739-06

Standard Practice for Oil Spill
Source Identification by Gas
Chromatography and Positive
Ion Electron Impact Low
Resolution Mass Spectrometry

GC-EI

GC pattern

Fingerprinting for
oil identification

24

ASTM

D3328-06

Standard Test Methods for
Comparison of Waterborne
Petroleum Oils by Gas
Chromatography

GC-EI

GC pattern

Fingerprinting for
oil identification

24

ASTM

D3415-98

Standard Practice for
Identification of
Waterborne Oils

GC-FID

oil ID

Identification of
oils on water

24

ASTM

D3326-07

Standard Practice for
Preparation of Samples for
Identification of
Waterborne Oils

GC-FID

oil ID

Identification of
oils on water

24

ASTM

D5739-00

Standard Practice for Oil Spill
Source Identification by Gas
Chromatography and Positive
Ion Electron Impact Low
Resolution Mass Spectrometry

GC-EI

GC pattern

Fingerprinting for
oil identification

24

Oil Analysis and Remote Sensing

Technique

PART | III

Title


TABLE 5.2 List of Standards Applicable to Oil Measurementdcont’d
Method
Number

ASTM

Technique

Analyte

Description

Reference

F2059-06

Standard Test Method for
Laboratory Oil Spill Dispersant
Effectiveness Using the
Swirling Flask

GC-FID

TPH

TPH for water,
chemical dispersion
quantification

24

ASTM

D5412-93

Standard Test Method for
Quantification of Complex
Polycyclic Aromatic
Hydrocarbon Mixtures or
Petroleum Oils in Water

GC-EI

PAHs

Quantification of
PAHS

24

ASTM

D6352-04

Standard Test Method for
Boiling Range Distribution of
Petroleum Distillates in Boiling
Range from 174 to 700 C by
Gas Chromatography

SIM-DIS

Boiling
Distribution

Method to carry out
a simulated
distillation on oil e
extended range

24

ASTM

D2887-08

Standard Test Method for
Boiling Range Distribution of
Petroleum Fractions by Gas
Chromatography

SIM-DIS

Boiling
Distribution

Method to carry
out a simulated
distillation on oil

24

ASTM

D5307-97

Standard Test Method for
Determination of Boiling Range
Distribution of Crude Petroleum
by Gas Chromatography

SIM-DIS

Boiling
Distribution

Method to carry
out a simulated
distillation on
crude oil

24

ASTM

D7169-05

Standard Test Method for
Boiling Point Distribution of
Samples with Residues Such as
Crude Oils and Atmospheric

SIM-DIS

Boiling
Distribution

Method to carry out
a simulated distillation

24

101

(Continued )

Introduction to Oil Chemical Analysis

Title

Chapter | 5

Standards
Organization


102

TABLE 5.2 List of Standards Applicable to Oil Measurementdcont’d
Standards
Organization

Method
Number

Title

Technique

Analyte

Reference

Method to preserve
oil samples

24

and Vacuum Residues by
High Temperature Gas
Chromatography
D3325-90

Standard Practice for
Preservation of Waterborne
Oil Samples

Sample
Preservation

API

PHC

Determination of
Petroleum Hydrocarbons

GC-FID

PHC

Petroleum Hydrocarbons

25

API

GRO

Determination of
Petroleum Hydrocarbons

GC-FID

GRO

Gasoline range organic
compounds

25

API

DRO

Determination of
Petroleum Hydrocarbons

GC-FID

DRO

Diesel range organic
compounds

25

EPA

846

Gas Chromatographic
(GC) Methods

GC-FID/EI

organics

General GC method

26

Oil Analysis and Remote Sensing

ASTM

PART | III

Description


TABLE 5.2 List of Standards Applicable to Oil Measurementdcont’d
Method
Number

EPA

Technique

Analyte

Description

Reference

610

Determination of priority
PAHS in municipal and
industrial wastes

GC-EI

PAHs

PAHs in wastes

26

EPA

1664

N-hexane Extractable Material
(HEM; Oil and Grease) and
Silica Gel Treated N-Hexane
Extractable Material (SGT-HEM:
Non-polar Material) by
Extraction and Gravimetry

gravimetry

TPH

N-hexane extractables
in various substrates

26

CCME

1397

Canada-Wide Standard for

Petroleum Hydrcarbons
(PHC) in Soil

GC-FID/EI

TPH

Suite of analysis
techniques for
hydrocarbons in soil

27

CCME

1399

Canada-Wide Standard for
Petroleum Hydrcarbons
(PHC) in Soil: Scientific
Rationale

GC-FID/EI

TPH

Background to suite of
analysis techniques for
hydrocarbons in soil

27

Reference Method for CanadaWide Standard for Petroleum
Hydrcarbons (PHC) in Soil- Tier
1 Method

GC-FID/EI

TPH

Reference method to
above for hydrocarbons
in soil

27

CCME

Introduction to Oil Chemical Analysis

Title

Chapter | 5

Standards
Organization

103

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Oil Analysis and Remote Sensing

FIGURE 5.6 Illustration of the effect of oil weathering on the chromatograms. As the oil
weathers, more and more of the lower n-alkanes are lost to evaporation, the most important
component of weathering. Figure A shows the unweathered oils with the Cn Benzenes and
naphthalenes marked. After about 30% loss of oil through evaporation, the Cn Benzenes are lost
and also many of the lower alkanes as shown in Figure B. After 44.5% of the mass is evaporated as
shown in Figure C, even the naphthalenes are not clearly present. It would be very difficult to
compare weathered and unweathered oils simply by comparing the chromatograms.

fingerprinting in characterizing oils in terms of (1) the type(s) of precursor
organic matter in the source rock (such as bacteria, algae, or higher plants); (2)
correlation of oils with their source rocks; (3) determination of depositional


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105

environmental conditions (such as marine, terrestrial, deltaic, or hypersaline
environments); (4) assessment of thermal maturity and thermal history of oil
and the degree of oil biodegradation; and (5) providing information on the
age of the source rock for petroleum. For example, oleanane (C30H52) is
a biomarker characteristic of angiosperms (flowering plants) found only in

Tertiary and Cretaceous (<130 million years) oils.35
The conversion of precursor biochemical compounds from living organisms
into biomarkers creates a vast suite of compounds in crude oils that have
distinct structures. Due to the wide variety of geological conditions under
which oil has formed, every crude oil exhibits a unique biomarker fingerprint.
Biomarkers can be detected in very low quantities (ppm and below) in the
presence of many other types of petroleum hydrocarbon by using GC-MS.
Relative to other hydrocarbon groups such as alkanes and many aromatic
compounds, biomarkers are highly stable and degradation-resistant. Therefore,
the usefulness of analyzing biomarkers is that they generate information useful
in determining the source of spilled oil, monitoring the degradation process,
and weathering the state of oils. They have proven useful in identifying
petroleum-derived contaminants in the marine environment.22,36-38 In the past
decades, the use of biomarker fingerprinting techniques to study spilled oils has
rapidly increased, and biomarker parameters have been playing a prominent
role in almost all oil-spill forensic investigations.
Table 5.1 lists some typical biomarkers used in forensic analysis. The
concentration of the biomarkers is important, while the ratio of various
biomarkers in an oil is extremely useful in making the comparisons. The ratios
of the biomarker contents in most oils are constant throughout processes such
as weathering and biodegradation, and thus serve as an identity tag for an oil.

5.4.2. Sesquiterpanes and Diamondoids
The commonly used biomarkers that occur within crudes and heavier refined
products include pentacyclic triterpanes (e.g., hopanes), regular and rearranged
steranes, and mono- and tri-aromatic steranes.2,39,40 However, the high boiling
point pentacyclic triterpanes and steranes are generally absent or in very low
abundances in lighter petroleum products such as jet fuels and midrange
diesels. For lighter petroleum products, refining processes have removed most
high-molecular-weight biomarkers from the crude oil feed stocks, while the

smaller compounds of bicyclic sesquiterpanes are greatly concentrated in these
petroleum products. Figure 5.7 shows some of the typical biomarkers used for
oil identification.
Sesquiterpanes are ubiquitous components of crude oils and ancient sediments. Bicyclic sesquiterpanes are also widely found in intermediate petroleum
distillates and finished petroleum products. The abundance of the three major
compounds in the m/z 123 chromatograms has been employed to differentiate
the organic matter input from various sedimentary environments. Early studies


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Terpanes
(hopanes)

hopane - general

Steranes

general sterane
structure

Sesquiterpanes

8 (H) - drimane

Diamondoid

Adamantane

Oil Analysis and Remote Sensing

FIGURE 5.7 Illustration of some typical biomarkers used for oil identification.

focused mainly on geological application of sesquiterpane compounds. The
naturally occurring bicyclic sesquiterpanes are stable in biodegradation, and
therefore in recent years, they found potential applications in oil-source
correlation and differentiation.
Recently, environmental scientists have also considered fingerprinting the
diamondoid hydrocarbons as a promising forensic technique for oil spill
studies.41-47 These naturally occurring compounds are thermodynamically
stable, and therefore, they may have potential applications both in oil-source
correlation and differentiation for those cases where the traditional biomarker
terpanes and steranes are absent due to removal in the refining processes. There
is increased awareness of possible application of diamondoid compounds
for source identification. Diamondoids have the general molecular formula
C4nþ6H4nþ12 and are a class of saturated hydrocarbons that consist of threedimensional fused cyclohexane rings, which results in a diamond-like structure.
The simplest compound of these polycyclic diamondoids is adamantane
(C10H16), followed by its homologues diamantane (C14H20), tri-, tetra-, penta-,
and hexamantane. Adamantine and diamantane and their various substituted
equivalents are widely found in crude oils, intermediate petroleum distillates,
and other petroleum products. Diamondoid compounds (adamantanes and
diamantanes) in petroleum are believed to be the result of carbonium ion
rearrangements of suitable cyclic precursors on clay substances in the source
rock. The higher homologues of diamondoids are considered to be formed from


Chapter | 5

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107

the smaller diamondoid compounds under extreme temperature and pressure
conditions.

5.5. FIELD ANALYSIS
Analysis performed in the field is faster and more economical than analysis
done in a laboratory.8 As analytical techniques are constantly improving and
lighter and more portable equipment is being developed, more analytical work
can be carried out directly in the field. Test kits have also been developed that
can measure total petroleum hydrocarbons directly in the field. Some new
methods use enzymes that are selectively affected by oil components. While
these test kits are less accurate than laboratory methods, they are a rapid
screening tool that minimize laboratory analysis and may provide adequate
data for making response decisions. It is important to stress, however, that these
field kits may have limitations and that results should be verified by laboratory
analysis.

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