OIL SPILL SCIENCE chapter 5 – introduction to oil chemical analysis

OIL SPILL SCIENCE chapter 5 – introduction to oil chemical analysis OIL SPILL SCIENCE chapter 5 – introduction to oil chemical analysis OIL SPILL SCIENCE chapter 5 – introduction to oil chemical analysis OIL SPILL SCIENCE chapter 5 – introduction to oil chemical analysis OIL SPILL SCIENCE chapter 5 – introduction to oil chemical analysis

Introduction to Oil Chemical Analysis

be determined This is valuable information to have as the spill progresses

In nonspill situations, analytical techniques are used extensively to measurethe oil content of soil and water for environmental quality purposes Manyjurisdictions have standards on the petroleum content of waters and soils forvarious 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 fromone owner to another

5.2 SAMPLING AND LABORATORY ANALYSIS

Taking a sample of oil and then transporting it to a laboratory for subsequentanalysis 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

samples, it is always important to ensure that the oil is not tainted from contactwith 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 muchoil is in a water, soil, or sediment sample.6 Such analysis results in a valueknown as total petroleum hydrocarbons (TPH) The TPH measurement can beobtained in many ways, including extracting the soil, or evaporating a solventsuch as hexane and measuring the weight of the residue that is presumed to

be oil

There now exist certified laboratories that use certified petroleum carbon measurement techniques.6These should be used for all studies One ofthe most serious difficulties in older studies occurred when inexperienced stafftried to conduct chemical procedures Analytical methods are complex andcannot be conducted correctly without chemists familiar with the exactprocedures Furthermore, field instrumentation requires calibration usingstandard procedures and field samples during the actual test These samplesmust be taken and handled by standard procedures Certified standards must beused 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

hydro-5.2.1 Incorrect and Obsolete Methods

Several attempts to perform oil analysis have been made using methods that arenot scientifically valid One of these is the use of colorimetry This method hasnever been scientifically valid for oil measurement as oil does not have what isknown as a color center, that is, a molecular absorption center for a specificband of light.7-9As oil is a mixture of hundreds of compounds, there is obvi-ously not a single light-absorbing centre This method results in oil measure-ments that are typically 100% incorrect

Another series of methods involved extracting oil from soil or water usingfluorinated or chlorinated hydrocarbons Since these extractants were ozone-depleting, they were removed from the market over 20 years ago Theextracted hydrocarbons were then “measured” using infrared light, as hydro-carbons in such solvents do absorb at specific wavelengths The method wasthe standard oil in soil technique in several countries and yielded repeatableresults

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 extractables.10

hexane-There are several “meters” sold on the market that offer oil readings;however, none of these are reliable or accurate.8

Fluorometry is a technique sometimes used for measuring or estimatingconcentrations of oil in water A fluorometer uses UV or near UV to activatearomatic species in the oil.11The UV activation energy is more sensitive to thenaphthalenes and phenanthrenes, whereas the near UV is more sensitive tolarge 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 tration of aromatics increasing Thus, the apparent fluorescent quantityincreases in this process It must be noted that fluorometers cannot truly becalibrated for the oil as there are many variables, as explained above The errorsencountered all increase the apparent value of the oil concentration in the watercolumn Incorrect calibration procedures can distort concentration values up to

concen-10 times their actual value, or even more Correct analytical methods involveperforming accurate gas chromatograph (GC) measurements both in thelaboratory and in the field

5.3 CHROMATOGRAPHY

The primary method for oil analysis, as well as for many chemicals in theenvironment, is gas chromatography; this method will be described in thesubsequent section One should note that other chromatography methods andother analytical methods are sometimes used for oils These include liquidchromatography, sometimes used for PAH analysis and inductively coupledplasma (ICP) instruments for measuring metals in oils These and many othertechniques are not described in this section

5.3.1 Introduction to Gas Chromatography

The standard method for oil analysis is to use a GC.2,3,12,13,14A small sample ofthe oil extract (typically measured in microliters, mL), often in hexane, and

a carrier gas, usually helium or hydrogen, are passed through a capillarycolumn The sample is injected into a heated chamber from where its vaporspass into the silica column The silica column is coated with absorbing mate-rials, and, because the various components of the oil have varying rates ofadhesion, the oil separates because these components are absorbed at differentrates onto the column walls The gases then pass through a sensitive detector.The injector, column, and detector are often maintained at constant tempera-tures to ensure repeatability The system is calibrated by passing knownamounts of standard materials through the unit The amount of many individualcomponents in the oil is thereby measured The components that pass throughthe detector can also be totaled, and a TPH value determined It is important tonote that only the vapors pass into the column initially Heavier contaminantscan foul the injector and first part of the column It is therefore important that thesample be subjected to a cleanup procedure before it is injected into the column.Cleanup procedures can be complex and involve several steps

While a GC measurement is highly accurate, this measurement does notinclude resins, asphaltenes, and some other components of the oil with highermolecular weight that do not vaporize and pass through the column Theseheavier components can be determined separately using open column chro-matography or precipitation techniques.

The detectors used in chromatography are important An importantdetector for petroleum hydrocarbons is the flame ionization detector (FID).2,3The principle behind this instrument is simple as most compounds showvariable ion conductivity burned in a hydrogen flame This detector is simpleand has the advantage of yielding relatively similar signals for differenthydrocarbons, thus making calibration and quantification simple Anotherdetector commonly used for oils is the mass spectrometric detector Theanalytes from the GC column are introduced into a vacuum chamber andionized, 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 tothe user as peaks of given mass or even possible compound identification Themass spectrometer provides information about the structure of the substance sothat each peak in the chromatogram can be more positively identified Themethods are abbreviated as GC-FID, if a gas chromatograph and flame ioni-zation detector are used or GC-MS, if a gas chromatograph and a massspectrometer detector are used

A typical GC-FID chromatogram of a light crude oil with some of themore prominent components of the oil identified is shown in Figure 5.1.2,3This chromatogram shows some of the many features of oil that are iden-tified by this analytical technique The bulk of crude oils, especially lightones, have a large proportion of n-alkanes, as can be seen by the large peaksthat constitute a large portion of this chromatogram This is a light crude oilthat can be evidenced by the fact that the highest peak is C15 A moreweathered crude might have its highest peak at C18 or more The top of thechromatogram 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, orUCM This is an aggregate of largely unresolved peaks of alkane origin AtC16, for example, there are already thousands of isomers that cannot beresolved by typical GC methods Between the n-alkane peaks are smallerpeaks, most of which are aromatic compounds Two standard biomarkers(here, isoprenoids and branched alkanes) are usually evident in such achromatogram, Pristane (near nC17) and Phytane (near nC18) These havebeen used to assess state of weathering; however, other compounds are nowtypically used

Figure 5.2shows the GC-FID chromatograms of 10 oils.Figure 5.2A to Cshows the chromatograms of three lighter crude oils: Arabian medium crudeoil, Hedrun crude oil, and Gullfaks,2,3 Figure 5.2D shows a chromatogram

of Orimulsion, a bitumen In this chromatogram one notes that almost alln-alkanes are not present, and the chromatogram largely consists of the

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 andBunker C Figure 5.2F shows the chromatogram of Bunker C, and Figures5.2G-J show jet fuel, diesel fuel, lubrication oil, and number 6 fuel oil,respectively

The mass spectrometer provides information about the structure of thesubstance so that each peak in the chromatogram can be positively identified

An important technique is that of SIM (selective ion monitoring), where onecan monitor the ion most typically associated with the target compound Thistechnique enables the detection and quantification of many compounds in oilthat otherwise would not be separately resolved.2,3 Figure 5.3 shows threechromatograms first by GC-FID and then by GC-MS using SIM.Figures 5.3Aand B are chromatograms of a light Alberta crude oil;Figures 5.3C and D arechromatograms of California heavy crude oil, andFigures 5.3E and 5.3F arechromatograms of Orimulsion Bitumen The two chromatograms (e.g., FID/SIM) are quite different The SIM chromatograms are no longer recognized asthe types of oils as shown by FID However, one can see that the peaks are moreclearly defined and that the SIM can provide different and important infor-mation The disadvantage of the SIM is that each peak must be quantifiedseparately 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 thealkane distribution All graphs are n-alkanes except for the lube oils wherethe alkanes are highly branched These bar graphs were created from

FIGURE 5.2 GC-FIDs of several oils Figure 5.2 A shows the chromatogram of Arabian medium crude oil Figure 5.2 B is a chromatogram of Hedrun crude oil, a light oil Figure 5.2 C is a chro- matogram of Gullfaks, another light oil Figure 5.2 D 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 5.2 E 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 5.2 F the chromatogram of Bunker C is shown Figures 5 2 G, 2H,

2 I, and 2J show jet fuel B, diesel fuel, lubrication oil, and number 6 fuel oil, respectively.

quantitative analysis and approximate the alkane chromatograms of thesame 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.1,6The basic methodsinvolve extracting the oil using dichloromethane (DCM), sometimes incombination with other solvents such as hexane This procedure will leave theDCM insoluble material, such as soil and wood, and remove the DCMsoluble material, which is largely petroleum oil Surrogate chemicals areoften added at this stage; these substances are compounds, typically deuter-ated 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

FIGURE 5.2 Continued

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 disad- vantage of the SIM is that each peak must be quantified separately using a standard.

remove water before injection into the GC At each point in this cleanup, thesample is quantified to allow measurement of those groups of materialsremoved These measurements then form the basis for various forms of TPHmeasurement One such method as developed by Dr Zhendi Wang ofEnvironment Canada is shown inFigure 5.5.2,3

In the method illustrated in Figure 5.5, the sample is separated intoaliphatic, aromatic, and polar fractions using an open silica column Severaltests of this have been carried out to ensure that separation is complete Havingthese fractions separated ensures that subsequent chromatographic analysis isnot affected by interferences between the three fractions

The peaks that are typically quantified for analysis and possibly for tification are listed inTable 5.1.2,3As described later, many of the these peaksare useful when combined in ratios Often these ratios are unique and can beused for positive identification of an oil

iden-There are many published methods and standards for oil analysis; several ofthese are listed inTable 5.2

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.

5.4 IDENTIFICATION AND FORENSIC ANALYSIS

The foregoing information can then be used to predict how long the oil hasbeen in the environment and what percentage of it has evaporated or bio-degraded.15-23 This is possible because some of the components in oils,particularly crude oils, are very resistant to biodegradation, whereas others areresistant to evaporation This difference in the distribution of components thenallows the degree of weathering of the oil to be measured The same techniquecan be used to “fingerprint” an oil and positively identify its source Certaincompounds are consistently distributed in oil, regardless of weathering, andthese are used to identify the specific type of oil

The effect of weathering is particularly important as it may negate the use ofstandard GC-FID to positively identify an oil.23, 28-31 Figure 5.6 shows theeffect of weathering on the GC-FID chromatogram of a light crude oil Asthe 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

aliphatics aromatics mixed polarshexane 50% DCM/Hexane half F1&F2 Methanol gravimetric

determinations saturates aromatics TPH polars

polars internal

PAHs Benzenes

PAH alkylated homologues GC/FID

GC/MS SIM n-alkane

quantificationn-alkanedistribution

hopanes

& steranes 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.

TABLE 5.1 Target Analytes/Compounds for Oil Spill Studies

Aliphatic Hydrocarbons BTEX and C3Benzenes