Chemical Oxigen Demand

WATER ANALYSIS / Chemical Oxygen Demand 325
Chemical Oxygen Demand
Z Hu, Cornell University, Ithaca, NY, USA
D Grasso, Smith College, Northampton, MA, USA
& 2005, Elsevier Ltd. All Rights Reserved.
Introduction
In addition to biochemical oxygen demand (BOD),
chemical oxygen demand (COD) is widely used as a
surrogate measure for carbon bioavailability. Compared to the BOD test, which requires days, the COD
test is designed to yield results in a much shorter time
(within hours). The COD test uses strong oxidants to
oxidize organic matter that microorganisms may oxidize only partially or not at all. The sample COD is
finally calculated by comparing with standards that
are typically used, e.g., phthalate, oxalate, and
glucose. In this article, standard reflux methods with
dichromate digestion are reported, although determination of COD based on permanganate index is
still in practice for natural waters. Due to some limitations and disadvantages of the standard methods,
other modified methods are also presented. These
include: the replacement of hexavalent chromium,
mercury, and silver metals; microwave digestion; automation and online COD measurement; and electrochemical oxidation to measure the sample COD.
Determination of the colloidal COD fraction is also
discussed and applications of COD tests are presented
in light of water and wastewater analysis.
Background
COD is defined as the amount of oxygen equivalents
consumed in the chemical oxidation of organic matter by strong oxidant (e.g., potassium dichromate).
The COD test consists of refluxing a sample for 2 h
in the presence of a known amount of oxidant. The
concentration of organic matter in terms of oxygen
equivalents can be determined from the difference of
initial and remaining oxidant concentrations in the
sample.
Most organic matter can be oxidized by strong
oxidants, although straight chain carboxylic acids
may not be oxidized in the absence of a silver sulfate
catalyst. Silver sulfate is, therefore, added during
COD tests to facilitate the complete oxidation.
However, the chloride ion, a common aqueous constituent, reacts with silver ions to precipitate silver
chloride, and thus eliminates the catalytic activity of
silver yielding a negative interference. Alternatively,
chloride, bromide, or iodide can react with dichromate
to produce the elemental form of the halogen, yielding an overestimate of COD. Hence, mercury sulfate
is added to minimize reaction interference.
Both organic and inorganic components are oxidized during COD tests. If only the COD associated
with the organic component is desired, provisions
need to be made to eliminate contributions from oxidation of inorganic components. For instance, chloride interference is removed by Hg2 þ complexing of
Cl . Corrections for chloride interference vary as
elemental chlorine may react with ammonia and its
derivatives in the sample even though ammonia and
its derivatives are not oxidized. Nitrite (NO2 ) has a
COD of 1.1 mg O2 mg 1 NO2 -N. To eliminate its
interference, nitrite is converted by sulfamic acid
with the addition of 10 mg sulfamic acid for each
milligram NO2 -N present in the sample. Finally,
separate determinations of other reduced inorganic
species (e.g., ferrous iron and sulfide) are needed if
the samples contain significant levels of these ions.
Stoichiometric oxidation of the known reduced
inorganic species can be assumed and corresponding
corrections are made.
Sampling
Samples are commonly stored in glass bottles, although it is still possible for a trace of organic matter
to sorb to the glassware. A standard sample preparation practice to avoid trace organic contamination
may, therefore, apply by baking out glass bottles at
4001C for at least 1 h. If a sample contains significant
amount of particulates, it should be blended first in
order to obtain a representative aliquot. All samples
should be analyzed as soon as possible. If delay is
unavoidable, samples may be stored by acidification
to pH p2 with concentrated sulfuric acid.
If only the soluble COD is desired, the sample
should be coagulated with lanthanum chloride (LaCl3)
and filtered through a 0.45 mm membrane to eliminate colloidal and particulate fractions. The filtrate
can then be subjected to standard COD analyses.
Standard Methods
Most types of organic matter (electron donor) are
oxidized to carbon dioxide and water by boiling a
mixture of dichromate and sulfuric acid. Samples are
refluxed in a strong acid with a known excess of
potassium dichromate (K2Cr2O7). Dichromate (Cr6 þ ,
orange color) is reduced to chromate (Cr3 þ , green
326 WATER ANALYSIS / Chemical Oxygen Demand
color) via the following reaction:
3þ
þ
Cr2 O2
þ 7H2 O
7 þ 6e þ 14H -2Cr
½1
By using a titrimetric method, the remaining dichromate is back-titrated with ammonium iron(II)
sulfate (ferrous ammonium sulfate (FAS)) to determine the amount of Cr2O27 consumed:
2þ
Cr2 O2
þ 14Hþ -2Cr3þ þ 6Fe3þ þ 7H2 O
7 þ 6Fe
½2
The amount of oxidized organic matter is calculated
in terms of oxygen equivalents (1 equivalent weight
electron equals 8 g of oxygen) with the following
equation:
COD as mg O2 l1 ¼ ðA BÞ M 8000=V
½3
where A ¼ FAS used for blank (ml), B ¼ FAS used for
sample (ml), M ¼ molarity of FAS, and V ¼ sample
volume (ml).
By using a colorimetric method, the formation of
Cr3 þ (green color) is quantified as the oxidation
proceeds and the absorbance is read at 600 nm.
Alternatively, the disappearance of the orange Cr6 þ
can be determined at 420 nm. The sample COD is
determined colorimetrically at 600 and 420 nm, respectively, based on standard COD calibration
curves.
Most organic compounds are oxidized with the
dichromate reflux method under standard procedure,
but ammonia and organic nitrogen are not oxidized
by dichromate in the absence of significant concentration of elemental chlorine. Hence, the dichromate
reflux method is preferred over procedures using
other oxidants because of its superior oxidation ability. There are, however, several potential sources of
limitation in the test including the following:
*
*
*
Pyridine and related aromatic compounds resist
oxidation.
Straight chain aliphatic compounds are not oxidized in the absence of AgSO4 and may not be
completely destroyed even in the presence of
AgSO4.
Volatile organic compounds may escape and are
oxidized only to the extent that they remain in
contact with the oxidant.
milliliter concentrated H2SO4) while gently mixing
to dissolve use HgSO4 and avoid possible loss
of volatile organic components. Add 25.00 ml of
0.0417 mol l 1 K2Cr2O7 and mix. Attach the flask to
a condenser and turn on cooling water. While continuously stirring, add the remaining 70 ml sulfuric
acid–silver sulfate mixture through the open end of
the condenser. Heat the sample for 2 h in the flask
under reflux conditions. Wash down the condenser
with de-ionized (DI) water into the flask and cool to
room temperature. Titrate excess K2Cr2O7 with
standard 0.25 mol l 1 FAS using two to three drops
ferroin indicator to determine the volume of FAS
utilized. Acquire a blank sample (50 ml DI water)
through the same procedure to determine the value
of A. For quality assurance and quality control purpose, conduct a test on a standard potassium hydrogenphthalate (KHP) solution (500 mg O2 l 1).
The above procedure is suitable for a sample with
a COD in the range of 0–900 mg O2 l 1. For high
COD (41000 mg O2 l 1) samples, dilution may be
necessary. Selection of a dilution ratio can be determined from the color after mixing the sample with
dichromate and sulfuric acid. If the sample solution
becomes bluish green or green within a few minutes,
a 10-fold dilution is suggested. Solutions showing
predominantly orange color with little change within
minutes should not require dilution.
For low COD (o50 mg O2 l 1) samples, the
standard procedure is still valid by using dichromate
and FAS at 1/10 the concentration given above (i.e.,
0.00417 mol l 1 K2Cr2O7 and 0.025 mol l 1 FAS).
Great care must be taken with this procedure because
even slight contamination of organic compounds on
glassware can lead to significant error. If a further
increase of sensitivity is required, a large volume of
sample may be concentrated to 150 ml (equivalent to
the total volume in the standard procedure) after the
addition of all reagents by boiling in the refluxing
flask open to the atmosphere without the condenser
attached. Before refluxing, the amount of chloride
must be determined in order to add sufficient
HgSO4 on the basis of a weight ratio of 10:1
for HgSO4:Cl . A blank should be carried out
through the same procedure. Compared to ordinary
evaporative concentration methods, this technique
has the advantage of reducing losses of easily digested volatile organic compounds.
Open Reflux Method
For an open reflux method, the standard procedure
follows: pipette 50 ml sample (for samples with COD
higher than 900 mg O2 l 1, use a small sample portion diluted to 50 ml) in a 500 ml refluxing flask. Add
1 g HgSO4, and glass beads. Slowly add 5 ml sulfuric
acid–silver sulfate mixture (10–15 g Ag2SO4 per
Closed Reflux Methods
Compared to the open reflux method, volatile
organic compounds are more easily oxidized with
closed reflux methods, because those compounds remain in contact with the oxidant in closed vessels.
WATER ANALYSIS / Chemical Oxygen Demand 327
(o90 mg O2 l 1) values can be determined by measuring the decrease of absorbance at 420 nm, which
directly correlates with Cr6 þ concentration.
A calibration curve must be prepared before COD
can be determined with this colorimetric method. At
least 5 standards of KHP solution should be prepared
to cover a range of sample COD values. Aliquots of
standard KHP stock are diluted with DI water to the
same volume for samples. A reference solution
(blank) contains DI water only. The same reagent
volumes, tube, and digestion procedure as for samples are followed (Table 1). Digestion vessels containing a blank, standards, and samples are placed on
a block heater preheated to 1501C for 2 h. Samples
are cooled to room temperature and their absorbances are measured against the blank. A linear calibration curve is created by measuring the difference
between absorbencies of digested standards and the
digested blank. COD values are determined based on
calibration curves.
Furthermore, closed reflux methods are preferred
because fewer reagents are used, and therefore less
hazardous wastes are generated. The methods are
equivalent to ISO 15705–Determination of the chemical oxygen demand index (ST-COD) – Small-scale
sealed-tube method.
Closed reflux: titrimetric method The procedure is
a scaled-down adaptation from the one described
above with the same chemistry, and is applicable to
samples with COD between 40 and 400 mg O2 l 1.
Samples with higher COD values (4400 mg O2 l 1)
must be diluted while those with lower COD values
(o40 mg O2 l 1) may be determined by using more
dilute dichromate and FAS solutions. Since small
sample volumes are used, diluted dichromate
(0.0167 mol l 1) and FAS (0.10 mol l 1) are prepared, and it is critical to obtain accurate volumes for
samples and digestion solutions. Digestion vessels
with premixed reagents and other accessories are
commercially available. Otherwise, sample volumes
and reagent quantities for various digestion vessels
are suggested below. The digestion vessels are placed
on a block heater preheated to 1501C for 2 h. The
remaining K2Cr2O7 is determined by titrating with
standard 0.10 mol l 1 FAS. A blank containing the
water reagents and DI is examined the same way for
samples and the COD is calculated using eqn [3].
Comparison of Chemical and
Theoretical Oxygen Demand
Ideally, COD values obtained from the standard reflux methods should equal the solution’s theoretical
oxygen demand (ThOD), which is the amount of
oxygen required to stoichiometrically oxidize compounds to end products, including CO2, NH3, and
H2O. Examination of a database of 565 organic
compounds has recently showed, however, that an
average 85% of the ThOD value is obtained from
COD tests due to the incomplete oxidation of some
organic compounds by dichromate. Some halogenated
aromatic and aliphatic hydrocarbons have especially
low COD/ThOD ratios (as low as 0.03). The low
COD/ThOD ratios also apply to many aliphatic alkane compounds with the lowest value down to 0.01.
If a water or wastewater sample contains a large
fraction of such refractory organic compounds, standard COD tests may be an inappropriate surrogate to
Closed reflux: colorimetric method The colorimetric method is another standard method to quantify
COD values based on the change of chromate and
dichromate concentrations. The chromate ion absorbs strongly in the 600 nm region while the dichromate ion has almost zero absorption. Therefore,
samples with high COD (100–900 mg O2 l 1) values
convert sufficient amount of Cr6 þ to Cr3 þ , which
can be determined in the 600 nm region. On the other
hand, the dichromate ion absorbs strongly in the
420 nm region while the chromate ion absorbs weakly
at this wavelength. Hence, samples with low COD
Table 1 Suggested digestion vessels and sample and reagent volumes in COD tests
Digestion vessel
Sample volume
(ml)
H2SO4 volume
(ml)
K2Cr2O7 volume
(ml)
HgSO4
(g)
500- or 250-ml
Erlenmeyer flasks
16 100 mm capped
tube
20 150 mm capped
tube
25 150 mm capped
tube
50
75
25
1
2.5
3.5
1.5
0.05
5.0
7.0
3.0
0.1
6.0
0.2
10.0
14
328 WATER ANALYSIS / Chemical Oxygen Demand
represent the degree of contamination. Alternatively,
total organic carbon analyses may be performed to
measure the total organic contents in the samples.
Modifications of Standard Procedures
In addition to the incomplete oxidation of some
chemicals with the reflux methods, laboratory wastes
generated from the standard COD tests contain
hexavalent chromium, mercury, and silver metals, all
of which are classified as hazardous wastes by the US
Environmental Protection Agency and their disposal
is regulated under Resource Conservation and
Recovery Act. Consequently, various modifications
of the standard procedures or alternative methods
have been reported for the COD test. These include:
the replacement of hexavalent chromium, mercury,
and silver metals; microwave digestion; automation
and online COD measurement; and electrochemical
oxidation to measure the sample COD.
Elimination of Mercury and Chromate
Mercury is used in a standard COD test to suppress
the chloride interference. Mercury sulfate can be
used up for samples with chloride values as high as
2000 mg l 1. For samples containing more than
2000 mg l 1, however, various chloride removal
methods may be considered. These include precipitation as silver chloride, ion exchange, addition of
Cr3 þ as a complexing agent, and oxidation of Cl to chlorine by pentavalent bismuth (Bi5 þ ). Of these
methods, the removal of chloride by Bi5 þ proposed
by Miller et al. is novel and promising. In this method, solid sodium bismuthate containing pentavalent
bismuth oxidizes the chloride rapidly without affecting
sample organics according to the following reaction:
2Cl þ Bi5þ -Bi3þ þCl2
½4
A special chloride removal cartridge containing a
glass-fiber filter (upper cartridge, for removal of particulates) and a column packed with a mixture of solid
sodium bismuthate and an inert, free-flow agent (lower
cartridge) is used. The acidified sample is drawn
through the chloride removal cartridge under carefully controlled conditions of contact time, flow rate,
and acid strength to allow chloride and bismuthate to
react effectively without destroying sample organics.
Solid sodium bismuthate is not soluble in the acidified
solution and remains in the cartridge. The by-product,
trivalent bismuth (Bi3 þ ), dissolves in the acidified
sample solution but has no effect on COD results. The
glass-fiber filter containing particulates is removed
from the top of the cartridge and combined with the
treated liquid component in a COD reagent vial for
total COD measurement. Alternatively, soluble and
particulate COD can be determined separately by
digesting only the sample component of interest.
Permanganate (Mn7 þ ) and trivalent manganese
(Mn3 þ ) have been proposed to replace hexavalent
chromium as strong oxidants in COD analysis. In fact,
the permanganate method is widely used in Japan to
monitor organic pollution. Oxidation potentials of
Mn3 þ –Mn2 þ and Mn7 þ –Mn2 þ half-reactions are
1.54 and 1.51 E1 (V), respectively, both of which are
greater than that of Cr6 þ –Cr3 þ half-reaction (1.35E1
(V)). Trivalent manganese (Mn3 þ ) is a strong, noncarcinogenic chemical oxidant that changes quantitatively from purple to faint pink when it reacts with
organic matter. Sample COD values are determined
colorimetrically, and the color intensity is inversely
proportional to the amount of COD in the sample.
Unfortunately, the permanganate and trivalent
manganese methods have relatively low oxidation
power and poor reproducibility. Manganese (Mn3 þ )
in sulfuric acid can oxidize B80% of synthetic and
naturally occurring organic compounds.
Microwave Digestion
The standard reflux methods require a long time (2 h)
for the digestion step in the COD analysis. A rapid
COD determination technique using microwave
digestion has been developed. One of the advantages
of using microwave digestion over the standard reflux method is that compounds such as pyridine and
aromatic organic compounds are oxidized better. A
special microwave with six individual magnetrons is
designed to focus the microwave radiation on each
sample in a 250 ml glass digestion tube. Each digestion tube is connected to a condenser circulating with
cooling water to avoid any loss of volatile organic
compounds in the sample.
An aliquot (20 ml) of a sample is added in the glass
digestion tube, followed by the addition of 0.5 g of
mercuric sulfate, 10 ml of dichromate solution, and
5 ml of sulfuric acid. The tube is placed into the
microwave and connected to a condenser. An additional volume (25 ml) of sulfuric acid is added to the
top of the condenser. The mixture is digested in the
microwave at 1501C for 8 min. Excess dichromate in
the digestion tube is determined with the standard
titrimetric or colorimetric procedure. COD determination of real water and wastewater samples indicates that the results obtained from both microwave
digestion and closed reflux digestion are consistent.
Automation and Online COD Measurement
Standard reflux methods require 2 h of digestion, a
length of time that would eliminate the benefits of
WATER ANALYSIS / Chemical Oxygen Demand 329
online COD measurement. With the development of
microwave digestion and innovative thermal oxidation
techniques, attempts to automate COD analysis in continuous flow systems (also called flow-injection analysis, FIA) have shortened the analysis period to 15 min.
One flow-injection method based on microwave
digestion techniques is as follows. A sample is taken
with an autosampler and mixed with reagents from a
fast loop arrangement into a microwave heated
chamber, where it is digested in an acid solution
containing mercuric sulfate, dichromate solution,
and sulfuric acid for 5–15 min. The process and system design ensures the constant sample volume and
the reduced chromate (Cr3 þ ) with green color is determined colorimetrically to give accurate COD values.
Other FIA methods have been developed by using
innovative thermal oxidation techniques. The addition of a strong oxidizing agent, cerium(IV) sulfate,
results in a high degree of sample oxidation. Potassium permanganate may also be used as both an oxidant and a colorimetric reagent during a segmented
FIA to determine COD in aqueous environmental
samples. But, it may not apply for analysis of samples
containing abundant recalcitrant organic matter due
to its limited oxidation power.
COD Measurement with Electrochemical Oxidation
COD may also be determined with electrochemical
methods. An electrochemical cell with the capacity for
electrochemical oxidation of organic matter into water and carbon dioxide might enable a fast method to
measure the sample COD based on coulometry (the
number of electrons consumed in the degradation).
The system includes a copper electrode, a potentiostat,
and a personal computer. Copper in alkaline media
can act as an electrocatalyst to oxidize organic matter.
The potentiostat is used to maintain constant potentials during electrolysis. The data are recorded with a
data acquisition system. The net charge, corresponding to the number of electrons consumed in the electrochemical oxidation, is correlated to the COD
determined by standard reflux methods. The time required for a single sample COD measurement is
B30 min, which is much less than the 2–4 h required
by the standard methods. However, electrochemical
methods may not provide sufficient oxidation power
to completely electrolyze all the organic matter. Furthermore, the electrodes may be easily contaminated
with significant fouling, especially in a sample containing high concentrations of humic acid.
Applications
COD is often used as a measurement of pollutants in
water, wastewater, and aqueous hazardous wastes.
One application of the COD test is to measure soluble COD in wastewater, since characterization of
total COD in wastewater is critical for accurate
modeling of biotransformation in wastewater treatment processes.
Another application is to rapidly infer biodegradability of samples from the COD tests. This is commonly accomplished by establishing a correlation
between COD and BOD. This method has been
found successful when the proportions and types of
materials in a wastewater remain relatively constant.
For example, BOD in domestic wastewater samples
from 5-day BOD tests can be approximated as
BOD5 ¼ 0.476 COD.
See also: Sample Dissolution for Elemental Analysis:
Microwave Digestion. Sampling: Theory. Water Analysis: Overview; Seawater – Dissolved Organic Carbon; Industrial Effluents; Sewage; Biochemical Oxygen Demand.
Further Reading
APHA, AWWA, WEF (1998) Standard Methods for the
Examination of Water and Wastewater. Washington, DC.
American Society for Testing and Materials (1995) Standard Methods for Chemical Oxygen Demand (Dichromate Oxygen Demand) of Water. Philadelphia, PA.
Baker JR, Milke MW, and Mihelcic JR (1999) Relationship
between chemical and theoretical oxygen demand for
specific classes of organic chemicals. Water Research 33:
327–334.
Balconi ML, Borgarello M, Ferraroli R, and Realini F
(1992) Chemical oxygen demand determination in well
and river waters by flow-injection analysis using a microwave oven during the oxidation step. Analytica Chimica
Acta 261: 295–299.
Baumann FI (1974) Dichromate reflux chemical oxygen demand: A proposed method for chloride correction in
highly saline waters. Analytical Chemistry 46: 1336–1338.
Chen S, Tzeng J, Tien Y, and Wu L (2001) Rapid determination of chemical oxygen demand (COD) using
focused microwave digestion followed by a titrimetric
method. Analytical Sciences (Japan) 17: 551–553.
Hu Z, Chandran K, Smets BF, and Grasso D (2002)
Evaluation of a rapid physical-chemical method for the
determination of extant soluble COD. Water Research
36: 617–624.
ISO 6060 (1989) Water Quality – Determination of the
Chemical Oxygen Demand.
ISO 8467 (1993) Water Quality – Determination of Permanganate Index.
ISO 15705 (2002) Water Quality – Determination of the
Chemical Oxygen Demand Index (ST-COD) – Smallscale Sealed-tube Method.
Korenga T, Zhou X, Okada K, Moriwake T, and Shinoda S
(1993) Determination of chemical oxygen demand by
a flow injection method using cerium(IV) sulfate as
oxidizing agent. Analytica Chimica Acta 272: 237–244.
330 WATER ANALYSIS / Oil Pollution
Lee K-H, Ishikawa T, McNiven SJ, et al. (1999) Evaluation of chemical oxygen demand (COD) based
on coulometric determination of electrochemical
oxygen demand (EOD) using a surface oxidized c
opper electrode. Analytica Chimica Acta 398:
161–171.
Messenger AL (1981) Comparison of sealed chamber and
standard method COD tests. Journal of the Water Pollution Control Federation 53: 232–236.
Miller DG, Brayton SV, and Boyles WT (2001) Chemical
oxygen demand analysis of wastewater using trivalent
manganese oxidant with chloride removal by sodium
bismuthate pretreatment. Water Environment Research
73: 63–71.
Westbroek P and Temmerman E (2001) In line measurement of chemical oxygen demand by means of multipulse
amperometry at a rotating Pt ring–Pt/PbO2 disc electrode. Analytica Chimica Acta 437: 95–105.
Oil Pollution
E Smith, University of Plymouth, Plymouth, UK
& 2005, Elsevier Ltd. All Rights Reserved.
Introduction
Oils are very complex mixtures of hydrocarbons in
which the boiling points of components can vary
from a few to several hundred degrees. Crude oils
vary in their physical and chemical composition
depending on their geochemical derivation, but all
crude oils consist of a complex mixture of compounds comprised mainly of hydrocarbons. The
hydrocarbon components of crude oil consist of
straight and branched chain alkanes, cycloalkanes,
and aromatics, and the relative content of these
groups of compounds varies from oil to oil. Compounds containing oxygen, nitrogen, and sulfur, and
various metals (Ni, V, Fe, Zn, Cu, U) are also present
in crude oil.
The pollution of water and other matrices caused
by the accidental leakage or chronic release of crude
oil and refined products into the environment occurs
each year. As the use and transportation of crude oil
occurs on a large scale throughout the world,
contamination of the environment with oil is an
issue of concern. The amount of total hydrocarbons
entering the oceans from all sources has been
estimated at 2.35 million tons per year. Oil spills
and hydrocarbons from land-based sources are
usually limited to the coastal zone, but can be found
even in the open oceans.
The characterization of a spilled oil in a contaminated environmental sample can be important for the
assessment of environmental damage, and also in the
selection of appropriate response and cleanup
measures. The identification of an oil spill source is
also extremely important for settling any dispute
relating to liability and compensation. Petroleum
hydrocarbon analysis may also be required to
determine the gradient of concentration around a
point source, e.g., an oil platform, or provide
baseline/benchmark and distribution concentrations.
Oil or petroleum products spilled on water undergo a series of biotic and abiotic processes that in
combination are termed weathering, and cause
changes in the physical and chemical properties of
the oil. Weathering processes occur at very different
rates but begin immediately after oil is released into
the environment. These processes include evaporation, dissolution, dispersion, photochemical oxidation,
water–oil emulsification, microbial degradation, and
adsorption onto suspended particles. The changes in
chemical composition of spilled oil can affect the
toxicity of the oil and its biological impact over time,
and also further complicate the identification of residual oil in the impacted environment. These factors
make it difficult to select the most appropriate
analytical methods for evaluating environmental
samples.
A wide variety of instrumental and noninstrumental techniques are currently used in the analysis of oil
hydrocarbons. These include gas chromatography
(GC), gas chromatography coupled with mass
spectrometry (GC–MS), infrared (IR) spectrometry,
ultraviolet fluorescence spectroscopy (UVF) and
gravimetry. Accurate and reliable analytical measurements are extremely important in order to unambiguously characterize spilled oil, to understand its
fate and behavior, and to predict its long-term impact
in environment. Despite advances in recent years in
analytical technology, and in our understanding of
the environmental fate of spilled oil, the complexity
of oil means that there is no one method that can ‘do
it all’ for the whole spectrum of oils and petroleum
products that may be polluting an ecosystem. Each
analytical technique measures only a subset of the
complex mixture spilled or subsequently formed.
This article gives a brief survey of several
analytical techniques currently used for the analysis