Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Method for the differentiation of alternative sources of naphthenic acids
The present invention relates to a method for the differentiation of
alternative sources
of naphthenic acids, particularly but not exclusively the differentiation of
naphthenic
acids from natural oil sands and oil sands process water.
Oil sands are large natural deposits containing bitumen, a viscous form of
petroleum.
The process used for the extraction of bitumen from these sands generally uses
substantial amounts of water resulting in a corresponding amount of process
water
being produced which is stored in large lagoons called tailing ponds. Concerns
have
been raised about the impact of potentially toxic, acid extractable organic
matter known
as naphthenic acids (NA) that are present in these tailing ponds. Such matter
has
been found to be toxic to fish, trees, birds and plankton. It is desirable to
be able to
monitor the potential leaching of NA from these tailing ponds into surface
waters and to
be able to differentiate between leakage from natural oil sands and leakage
from tailing
ponds.
It is known that toxic action is often structure-specific. However, prior to
recent
research by the present inventors, no individual naphthenic acid had been
identified in
oil sands process water (OSPW), despite decades of research.
It would be desirable to be able to differentiate between NAs emanating from
OSPW as
well as from other sources, such as natural oil sands, offshore oil production
platforms
and other waste sources, such as wear of automobile tyres in which naphthenate
salts
are used to bond steel to rubber and the disposal and weathering of certain
naphthenic
acids-based biocides and fungicides.
It is an aim of the present invention to provide a method for the
differentiation of
alternative sources of NAs, particularly but not exclusively, the
differentiation of NAs
from natural oil sands and OSPW.
Accordingly, the present invention provides a method for differentiating
between
alternative sources of naphthenic acids, the method comprising the steps of:
(a) analysing the naphthenic acid content from a sample obtained from an
unknown source to identify any diamondoid acids selected from the group
consisting of
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a tricyclic (I) or pentacylic (II) carboxylic acid having at least one of the
general
formulae given below:
R3 RICOOH
R2
(I)
where each of R1, R2 and R3 are either absent or present, R1 comprises an
alkylene
group having 1 to 5 carbon atoms and R2 and R3 each comprise an alkyl group
having
I to 5 carbon atoms, being the same or different;
and
R R40OOH
R65
(II)
where each of R4, R5 and R6 are either absent or present, R4 comprises an
alkylene
group having 1 to 5 carbon atoms and R5 and R6 each comprise an alkyl group
having
1 to 5 carbon atoms, being the same or different;
(b) measuring the concentration of any diamondoid acids identified in step
(a);
(c) plotting the ratios of the concentrations of said acids to provide a
distinctive
profile of diamondoid acids for the sample: and
(d) comparing the profile with profiles for a selection of known sources to
determine
the source of the naphthenic acids.
Preferably, R, and R3 are either a methylene or methyl group respectively or
absent.
Preferably, R2 is either a methyl or ethyl group or absent.
Preferably, R4, R5 and R6 are either absent or a methylene or methyl group.
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It has surprisingly been found that OSPW contains at least one of the
carboxylic acids
falling within either the general formula (I) or (II) described above.
Furthermore, due to
the unique distribution of these acids in different sources as a result of,
for example,
different biodegradation processes that can occur at a particular source, the
distribution
of these acids may be used to compare and contrast naphthenic acids mixtures
emanating from different sources, including but not limited to commercial NAs
preparations, offshore oil production platforms, oil sands process waters and
other
waste, wear of automobile tyres and the disposal and weathering of certain NA-
based
biocides and fingicides.
The concentration of at least two specific naphthenic acids of the general
formulas (I)
or (II) above found in a sample are measured and the ratios of these
concentrations
plotted to provide a distinctive profile for a given naphthenic acid source.
Preferably, the diamondoid acids are identified using two-dimensional
comprehensive
gas chromatography coupled with time of flight-mass spectrometry (GCxGC/ToF-
MS).
Preferably, the acids of a sample are first extracted into an organic solvent
by any
conventional means. It is preferable for the acids to be derivatised prior to
carrying out
the GCxGC/ToF-MS, for example by refluxing with BF3-methanol or BF3-
trideuterated
methanol. Alternatively, the distribution of these acids and their derivatives
may be
monitored by techniques such as liquid chromatography-mass spectrometry of
amides
(Smith and Rowland, "A derivatisation and liquid chromatography /electrospray
ionisation multistage mass spectrometry method for the characterisation of
NAs". Rapid
Commun. Mass Spectrom. 2008, 22, 3909-3927) or other means based on
chromatography and mass spectrometry, such as those reviewed by Headley et al
("Mass spectrometric characterization of NAs in environmental samples: a
review".
Mass Spec. Rev. 2009, 28, 121-134).
In a preferred embodiment of the present invention, the concentrations of
adamantane
-1-carboxylic acid, adamantane-2-carboxylic acid, adamantane-1-ethanoic acid
and 3-
methyladamantane-1 -ethanoic acid are measured and the ratios of their
concentrations
plotted to provide a distinctive profile of a given NA source.
In a further embodiment, the concentrations of other diamondoid acids may be
used,
such as the pentacyclic acids and di-acids, in particular diamantane, methyl
and
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dimethyldiamantane, diamantane ethanoic acid, methyl and dimethyldiamantane
ethanoic and higher alkylated diamantane acids.
More preferably, the method employs the use of a co-chromatographed known
concentration of a tri-deuterated methyl esters of adamantane-1-carboxylic
acid and 3-
methyladamantane-1-ethanoic acid, compared to which the responses of the
diamondoid acid in a particular source can be measured.
It is to be appreciated that the profiles may be compared with commercially
available
synthetic mixtures of NAs and individual diamondoid acids, such as adamantane-
1-
carboxylic, adamantane-l-ethanoic, 3-methyladamantane-1-ethanoic and 3-ethyl-
adamantane-1-carboxylic acids for calibration and confirmation purposes. These
can
be purchased from commercial suppliers such as Sigma (Poole, U.K.).
The present invention will now be further illustrated, by way of example only,
to the
following Examples in which Example 1 investigates the identification of
tricyclic
diamondoid acids in OSPW; Example 2 investigates the identification of tetra-
and
pentacyclic NAs in OSPW; and Example 3 describes the plotting of a distinctive
profile
for the concentration of particular diamondoid acids from alternative
naphthenic acid
sources in accordance with the method of the present invention, and with
reference to
the accompanying figures in which:
Figures IA to 1 H are the structures of diamondoid acids identified in oil
sands process
water;
Figures 2A to 2C are examples of mass spectra of methyl esters of tricyclic
acids
identified in OSPW compared with the mass spectra of purchased reference acids
(methyl esters);
Figure 3 is a total ion current chromatogram of OSPW naphthenic acids (methyl
esters)
examined by GCxGC/ToF-MS illustrating high chromatographic resolution by GCxGC
compared with GC/MS (white line on black background);
Figures 4A to 4F are examples of mass spectra of methyl esters of pentacyclic
acids
positively identified in OSPW NA by comparison of the spectra and GCxGC
retention
times with those of reference acids (methyl esters); and
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Figure 5 is a plot of ratios of chromatographic volumes for selected compounds
within
commercial NA preparations A and B to illustrate how the distinctive profiles
differentiate between different sources using the method of the present
invention.
5 Examples 1 and 2 below describe how the methods set out in our recent
publications
may be used for the identification of specific tricyclic and pentacylic
diamondoid acids
in OSPW (Rowland, S.J., Scarlett, A.G., Jones, D., West, C.E. and Frank, R.A.
(2011)
Diamonds in the rough: Identification of individual naphthenic acids in oil
sands process
water. Environmental Science & Technology 45, 3154-3159 and Rowland et al.,
(2011)
Identification of individual tetra- and pentacyclic naphthenic acids in oil
sands process
water by comprehensive two-dimensional gas chromatography-mass spectrometry.
Rapid Communications in Mass Spectrometry 25, 1198-1204). As demonstrated
below, the identifications are far from simple and, as far as we aware, have
only been
achieved by the inventors to date. Once identification has taken place, the
ratio of the
concentrations of the diamondoid acids in the sample can be measured and used
to
differentiate between different sources of NAs according to the method of the
present
invention (see Example 3).
Example 1: Identification of Tricyclic Diamondoid Acids in Oil Sands Process
Water
Adamantane-l-carboxylic and 3-ethyl-adamantane-1-carboxylic acid were
purchased
from Sigma (UK) and the OSPW NA was obtained from a previous study of the
inventors. Acids were derivatized by refluxing with BF3-methanol.
Two-dimensional comprehensive gas chromatography-time-of-flight-mass
spectrometry
(GCxGC-ToF-MS) analyses were conducted using an Agilent 7890A gas
chromatograph (Agilent Technologies, Wilmington, DE) fitted with a Zoex ZX2
GCxGC
cryogenic modulator (Houston, TX, USA) interfaced with an Almsco Bench TOFdx
time-of-flight-mass spectrometer (Almsco International, Llantrisant, Wales,
UK)
operated in positive ion electron ionization mode and calibrated with
perfluorotributylamine. The scan speed was 50Hz. The resolution of the mass
spectrometer was 1000 at mass 1000. The first-dimension column was a 100%
dimethyl polysiloxane 50 m x 0.25mm x 0.40 pm VFI-MS (Varian, Palo Alto, USA)
with
an efficiency of 211700 theoretical plates (n-tridecane) and the second-
dimension
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column was a 50% phenyl polysilphenylene siloxane 1.5m x 0.1 mm x 0.1 mm x
0.11i m
BPX50 (SGE, Melbourne, Australia) with an efficiency of 5121 theoretical
plates per
meter (biphenyl). Thus the product efficiency of the GCxGC system was
calculated as
approximately 1.6 billion theoretical plates. Helium was used as carrier gas,
and the
flow was kept constant at 0.7 mL min. Samples (1 NL) were injected at 280 C
splitless. The oven was programmed from 40 C (held for 1 min) and then heated
to
300 at 2 C min and then at 10 C min to 320 C (held for 10 min). The
modulation
period was 5 s. The mass spectrometer transfer line temperature was 280 C and
ion
source temperature 300 C. Data processing was conducted using GC Image v2.1
(Zoex, Houston, TX, USA).
A sample of the methyl ester derivatives of OSPW NA were examined by GCxGC-ToF-
MS. The OSPW was collected en route to storage in an in-pit settling basin. By
conventional GC-MS the OSPW NA were almost completely unresolved. In contrast
GCxGC resolution under the optimized conditions was very high allowing
electron
ionisation mass spectra containing molecular and fragment ions of many
individual
acids to be obtained. Figure 1 of the accompanying drawings illustrates the
structure of
some of the acids identified. The normal background of ions which is caused by
the
thermal desorption of the GC stationary phases (so-called "bleed" ions) was
also well
separated by GCxGC from ions produced by ionization of the acid methyl esters,
which
further improved the quality of the mass spectra of the unknown esters. Thus,
due to
these factors and the over 1.6 billion theoretical plates calculated for the
combined
GCxGC columns, the mass spectra obtained for many of the OSPW acids (methyl
esters) were essentially those of individual compounds, as was also shown by
the
close similarities with the spectra of some relevant authentic acids (methyl
esters).
The mass spectra contained clear molecular ions which showed that the OSPW NA
comprised mainly C11-19 bi-to pentacyclic acids, fitting the formula
CnH2n+zO2.
Although numerous other compounds have been suggested to be present in OSPW
NA (Grewer et al., "Naphthenic acids and other acid-extractables in water
samples
from Alberta: What is being measured?" Sci. Total Environ. 2010. 408, 5997-
6010), we
detected overwhelmingly NA (methyl esters) fitting the above formula, with
only a few
minor hydrocarbons and other constituents. Unrefined oil sands bitumen has
been
reported previously to contain 90% tricyclic acids, and electrospray mass
spectra of
OSPW NA have routinely shown that tricyclic and bicyclic acids are the major
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components (Frank et at, "Toxicity Assessment of collected fractions from an
extracted
NA mixture." Chemosphere 2008 72, 1309-1314 and Headley et al., "Mass
spectrometric characterization of NAs in environmental samples: a review."
Mass.
Spec. Rev. 2009, 43, 266-271); therefore, this study concentrated on
identifying the
tricyclic compounds.
The mass spectra of the tricyclic OSPW acids did not match those in mass
spectral
libraries or in any published literature available. However, the inventors
were able to
identify several of them by interpreting the spectra from first principles,
then obtaining
as many reference acids as were available, esterifying these, and obtaining
the spectra
of the methyl esters by GCxGC-ToF-MS for comparison with the spectra of the
GCxGC
retention times of the unknowns.
The results thus far show that the OSPW comprises an extensive series of
diamondoid
tricyclic acids (as shown in Figure 1). Thus adamantane-1-carboxylic acid
(Fig. 1A)
was identified by comparison to the mass spectrum and GCxGC retention times
with
that of a reference sample. The spectrum contained a minor molecular ion (m/z
194)
and was dominated by a base peak ion m/z 135 due, we suggest, to fragmentation
and
loss of the methylated carboxyl group. The corresponding adamantane-2-
carboxylic
acid (Fig. I B) was also identified. This isomer is known to have a later
retention time
on the first apolar GC column than the 1-isomer, and the mass spectrum of the
unknown and of a synthetic acid (Figure 2A) was also characterized by a
molecular ion
(M+ 194) and major fragment ions due to loss of methanol (m/z 162), typical of
methyl
esters and again, loss of the methylated carboxy group (mlz 135). However, a
noteworthy difference to the spectrum of the 1-isomer in which the carboxy
group is
substituted at a quaternary center (C-1), was the base peak ion at m/z 134 in
the
putative 2-isomer. Formation of this ion was interpreted as being due to loss
of the
methylated carboxy group followed by H-transfer at the tertiary center to form
an even
mass alkenyl ion (mlz 134). This dominance of an even mass base peak ion might
prove to be a useful feature for distinguishing isomers of diamondoid acids
substituted
at tertiary centers (e.g., C-1) compared with those substituted at quaternary
centers
(e.g., C-2). This was confirmed by the synthesis of a sample of the methyl
ester of
adamantane-2-carboxylic acid (Fig. 2A).
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Also identified was the methyl ester of 3-ethyladamantane-1-carboxylic acid
(Fig. 1F)
by comparison of the spectrum with that of a reference sample. The mass
spectrum,
like that of a reference sample (Fig. 2B) contained a molecular ion m/z 222
and ions
due to loss of the ethyl group (m/z 193) and the methylated carboxy group (m/z
163).
In addition, also identified were numerous methyl, dimethyl and
ethyladamantane
carboxylic acids and adamantane ethanoic acid isomers by interpretation of the
mass
spectra from first principles and in some cases by the purchase of additional
reference
acids. The spectra of the methyl esters of the methyl adamantane carboxylic
acids
were characterized by molecular ions (m/z 208) and were dominated by a base
peak
ion m/z 149 due to fragmentation and loss of the methylated carboxy group;
those of
the esters of the dimethyladamantane carboxylic acids (numerous isomers were
present, separated by GCxGC) by a molecular ion (m/z 222), dominated by a base
peak ion m/z 163; those of the esters of the trimethyladamantane carboxylic
acids
(numerous isomers were present, separated by GCxGC) by a molecular ion (m/z
222),
dominated by a base peak ion m/z 163, one identical to a spectrum of 3,5,7-
trimethyl-
adamantane-1-carboxylic acid (methyl ester; Figure 2C) purchased from
Maybridge
Chemicals, Tintagel, Cornwall. (Common components such as phthalate esters,
which
also have dominant m/z 149 ions in their mass spectra, were well separated
from such
NA by GCxGC as they are esters of aromatic acids, the aromaticity resulting in
good
separation from the methyl esters of the NA on the second, more polar, GC
phase.
Thus the NA were easily differentiated from common laboratory contaminants,
such as
phthalates).
Other isomers of ethyl adamantane carboxylic acids were identified by the
presence of
the latter ions in different relative abundances. Adamantane ethanoic acids
were also
present; for example, the spectrum of a methyladamantane ethanoic acid
contained in
a molecular ion (m/z 222) consistent with the methyl ester of a C13 tricyclic
acid, but the
base peak ion was m/z 149, indicative of a methyl substituted (C11) tricyclic
core, rather
than the m/z 163 characteristic of the dimemthyl C12 adamantane core. This
formation
of ethanoic acids is consistent with an origin from biodegradation of
adamantane
hydrocarbons (Smith and Rowland, supra).
The distributions of multiple series of adamantane carboxylic acids (methyl
esters) may
be displayed by selected ion mass chromatography of key ions in the spectra.
Thus
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GCxGC-ToF-MS allows the distributions of multiple individual acids in
different OSPWs
or OSPW and environmental samples to be compared routinely.
It is proposed that most, if not all, of the diamondoid acids are
biotransformation
products of methyl, dimethyl, ethyl, and ethyl-methyladamantane hydrocarbons.
Although an origin from oxidation during oil sands processing may also be
feasible
since the hydrocarbons are widely reported in crude oils including in Western
Canada
oils, laboratory and field studies have shown that both adamantane and the
methyl
adamantane hydrocarbons are indeed slightly biotransformed by some bacteria.
However, the acidic products have never been identified previously.
The discovery of adamantane diamondoid acids in OSPW NA allows identification
not
only of the first specific structural class of NA in oil sands, but also of
some of the first
individual isomers of oil sands NA to be made, including members of the
abundant
tricyclic constituents.
Example 2: Identification of individual tetra- and pentacyclic naphthenic
acids
in oil sands process water
Synthetic diamantane-1-, diamantane 3- and diamantane-4-carboxylic acids and
diamantane- 1,4-, 1,6- and 4,9-diacids were obtained from a third party. The
OSPW NA
was obtained from a previous study of the inventors. The acids were
derivatised by
refluxing with BF3-methanol.
Comprehensive two-dimensional gas chromatography/time-of-flight mass
spectrometry
(GCxGC/ToF-MS) analyses were conducted as described in Example 1.
Examination, by GCxGC/ToF-MS, of a sample of the methyl ester derivatives of
OSPW
NA resulted in a highly resolved chromatogram (Fig. 3) allowing electron
ionisation (EI)
mass spectra containing molecular and fragment ions of many individual tetra-
and
pentacyclic acids to be obtained.
The mass spectra of the acids did not match those available in mass spectral
libraries,
or in any published literature of which the inventors were aware. However,
many were
identified by interpretation of the spectra from first principles, and in two
cases by
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obtaining reference diamantane acids, esterifying these and obtaining the mass
spectra and GCxGC retention times of the methyl esters. Some isomers were also
ruled out by examination of further reference acids.
5 Previous reports have suggested that whilst adamantane and some lower
alkyladamantanes are slightly susceptible to biodegradation, the corresponding
pentacydic diamantane nanodiamonds are resistant to biodegradation (K. Grice
et al.,
"Diamondoid hydrocarbon ratios as indicators of biodegradation in Australian
crude
oils." Org. Geochem. 2000, 31, 67 and Z. Wang et al., "Forensic fingerprinting
of
10 daimondoids for correlation and differentiation of spilled oil and
petroleum products.
Environ. Sci. Technol. 2006, 40, 5636). However, the present results suggest
that the
extent of the biodegradation of some of the organic matter from which the OSPW
NA
originate exceeds some conventional biodegradation scales since, in addition
to the
tricyclic acids, pentacyclic diamondoid acids have now been identified.
The methyl ester of diamantane-l-carboxylic acid (I, Fig. 4A) was identified
by
interpretation of the mass spectrum and by comparing this with the mass
spectra and
GCxGC retention times of reference samples of each of the three possible (1-
,,3- and
4-) isomers (Figs. 4(B), 4(C) and 4(E)). The suspected molecular ion M. m/z
246)
was observed in the spectrum of unknown I (Fig. 4(A)), along with a major
fragment ion
(mlz 187, base peak) assigned to loss of the methylated carboxy substituent
from a
quaternary centre. Many of the same ions were present in the spectrum of
synthetic
diamantane-1 -carboxylic acid (methyl ester; Fig. 4 (B)), although the
molecular ion was
more abundant in the latter and some other ions in the spectra of the unknown
and the
reference acid were different. This difference could be due to some residual
co-elution
of other compounds with the OSPW acid (I) although the retention times
(GCxGG/MS)
of the unknown were the same as those of the reference acid (within 0.01 mm in
first-
dimension GC). The mass spectrum of the unknown was also very similar to that
of
diamantane-4-carboxylic acid (methyl ester, Fig. 4 (C)) but the GC retention
time of the
latter in the second dimension was very slightly less than that of the
unknown. Thus,
acid I was identified as diamantane-1 carboxylic acid (methyl ester), although
both the
1- and the 4-isomers could be present.
The spectrum of the methyl ester of a component assigned as a further isomeric
diamantane carboxylic acid (II) was also obtained in the OSPW acids (Fig. 4
(D)). The
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latter was characterised by a molecular ion (m/z 246), an ion assigned to loss
of
methanol (mlz 214), and a base peak of m/z 186 rather than m/z 187. This
change in
the base peak was attributed to the differences between the ease of formation
and
subsequent stability of the secondary and tertiary carbocations at the medial
and apical
positions, respectively, with the secondary carbocation formed at C-3 leading
to an
alkenyl ion (m/z 186). This was further confirmed when the mass spectrum and
GCxGC retention times of a reference sample of diamantane-3-carboxylic acid
(methyl
ester, Fig. 4 (E)) was examined. Thus, this compound was identified as
diamantane-3-
carboxylic acid (methyl ester).
The reference sample of diamantane-1-carboxylic acid also contained a small
amount
of an unknown component (Fig. 4F). Thus, the molecular ion (m/z 246) and an
ion
assigned to the loss of methanol (m/z 214) were present, in addition to the
m/z 187
base peak (Fig 4(F)). No similar component was present in the OSPW acids. As
far
as the inventors are aware, no mass spectra of the methyl esters of the
diamantane
carboxylic acids have been published previously.
Spectra consistent with some higher diamantane acid homologues were also
obtained.
For example, the methyldiamantane carboxylic acids (methyl esters, numerous
isomers) were tentatively assigned from spectra containing the molecular ion
(m/z 260)
and base peak (mlz 201) due to loss of the methylated carboxy substituents. In
one
isomer, tentatively assigned as 3-methyldiamantane-4-carboxylic acid, a loss
of 101Da
from the molecular ion (to form m/z 159) suggested the presence of a 3-methyl
branched ester. A minor amount of diamantane ethanoic acid with a non-alkyl-
substituted diamantyl core was tentatively assigned from the molecular ion
(m/z 260)
and base peak (mlz 187) formed by loss of the substituent. A
dimethyldiamantane
carboxylic acid was tentatively assigned from the molecular ion (m/z 274) and
abundant ion at m/z 215 due to loss of the methylated carboxy substituents
(56%); the
base peak was at m/z 199, representing a loss of 75Da from the molecular ion.
This
may be due to loss of the so-called McLafferty+1 fragment and it is suggested
that this
abundant ion may be indicative of disubstitution of one of the methyl groups
and the
methylated carboxy substituent, necessarily on one of the secondary positions.
A
methyldiamantane ethanoic acid was also identified from the molecular ion (m/z
274)
and base peak m/z 201 formed by loss of the methylated carboxy substituent. A
further methyldiamantane ethanoic acid was tentatively identified with the
methylated
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carboxy substituent on a secondary carbon atom (i.e. C-3) due to the formation
of an
even-mass base peak (B+ 200) in place of the odd-mass ion (B+ 201) for the
reasons
discussed above. By similar arguments, the dimethyldiamantane ethanoic acids
substituted in apical and secondary carbons, respectively, were also
tentatively
assigned (M+ 288, B+ m/z215; IX, M+ 288, B+ m/z 214).
The foregoing acids can be rationalised as partial biotransformation products
of methyl,
dimethyl-, ethyl-, trmethyl-, ethylmethyl- and dimethylethyldiamantanes,
although they
may result from other oxidative processes. Methyl-, dimethyl- and
ethyldiamantanes
are known hydrocarbons in crude oils and condensates but trimethyl-,
ethymethyl- and
dimethylethyldiamantanes have not been reported, to our knowledge. Our data
suggests that they may be found in the future. Also tentatively identified
were other
diamantane acids for which no known hydrocarbon precursors have been reported.
A
mass spectrum consistent with a diamantane butanoic acid was obtained. The ion
(m/z 288) was accompanied by a base peak of m/z 187 consistent with a non-
alkylated
diamantane nuclear. However, it is suggested that the butanoic acid
substituent
originates from biotransformation of ter-butyl substituent; n-iso- and sec-
butyl
substituents are more easily oxidised by microbes and might be more easily
further
degraded. Also tentatively identified was a dimethyl-substituted analogue of
the above
diamantane butanoic acid (M+ 316, B+ 215), suggesting that higher alkylated
diamantane homologues are present in the oils from which the OSPW NA were
originally produced. Other branched alkanoate substituents were present in
some
diamantane acids. Thus, methyl- and dimethyipropanoic acids, derived, we
suggest,
from methyl-i-propyl- and dimethyl-i-propyldiamantanes, were tentatively
identified from
the molecular ions (M+ m/z 288 and 302) and the base peaks (B+, m/z 201 and
215).
Methyl branched alkanoate-substituted cyclohexyl acids were shown previously
to be
resistant to microbial transformation, and we therefore considered the
presence of such
acids as further evidence of the extensive degradation of some of the organic
matter
from which the OSPW was derived.
Thus, numerous diamantane, methyl and dimethyl diamantane, diamantane
ethanoic,
methyl and dimethyl-diamantane ethanoic and higher alkylated diamantane acids
were
observed in OSPW NA, it is believed for the first time. The distributions of
isomeric
diamantane acids could be readily displayed by mass chromatography of selected
ions.
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Since such pentacydic compounds have never previously been considered as
components of OSPW, their toxicities are also unstudied. Synthetic methods
exist for
numerous of these compounds, so these should be re-synthesised, used to
confirm the
tentative assignments above and assayed for possible toxicological effects. No
evidence was found for the biodegradation of triamantanes or tetramantanes,
but
traces of compounds tentatively identified as unaltered methyletetramantane
hydrocarbons M+, M+-CH3) were present. Pre-processing of the waste removes
most
hydrocarbons, however, so it is to be expected that the hydrocarbons will be
minor
constituents. Likewise, diamantane dicarboxylic acids were not detected, using
the
spectra of the dimethyl esters of diamantane-1, 6, -1-4 and -4-9, - diacid
reference
compounds as guides, all spectra were indistinguishable from one another),
suggesting
that further degradation of the mono-acids does not proceed by this route.
However,
the mass spectra of some of the tetracydic acids in the OSPW were tentatively
interpreted as being due the methyl esters of ring-opened diamantane and
methyl-
diamantanes (viz alkyltetracyclo [7.3.1.02.7 06.11] tridecane-4-carboxylic
acids).
The distributions of individual diamantane carboxylic acids (methyl esters)
could be
displayed by selected ion mass chromatography of key ions in the spectra.
Thus,
GCxGC/ToF-MS allows the distributions of multiple individual acids in
different OSPW,
or OSPW and environmental samples, to be compared routinely. Once suitable
GCxGC/MS response calibrations have been constructed with reference acids, the
quantities of these acids in OSPW NA can also be estimated and profiles
plotted to
provide an identification profile for a particular source of NAs, such as OSPW
or
otherwise.
Example 3: The plotting of a distinctive profile for the concentration of
particular diamondoid acids from two commercial preparations of
naphthenic acids (A and B).
A sample of naphthenic acids was derivatised by refluxing with BF3-methanol
(30
minutes). A solution of the derivatised mixture in hexane was injected into a
two-
dimensional comprehensive gas chromatography-time of flight-mass spectrometer
as
described above in relation to Example 1.
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CA 02743156 2011-06-14
w,a/, r nc-r.n, i lao
14
Mass chromatograms of ions at masses m/z 194+135 and m/z 194+134 were plotted,
the results of which are shown in Tables 1 and 2 below, showing elution times
and
chromatographic volumes for three adamantane acids present in the two
commercially
prepared NAs respectively.
Table 1 - Commercial Preparation A
Diamondoid acid Is elution 2"elution Integrated volume
time/min timelsec (no units)
Adamantane-1-carboxylic 35.25 2.67 132505
acid
Adamantane-2-carboxylic 35.92 2.89 251006
acid
3-methyladamantane-1- 37.67 2.54 424525
ethanoic acid.
Table 2 - Commercial Preparation B
Diamondoid acid Is elution 2" elution Integrated volume
time/min time/sec (no units)
Adamantane-1 -carboxylic Np
acid
Adamantane-2-carboxylic 35.92 2.87 355516
acid
3-methyladamantane-1- Np
ethanoic acid.
The areas due to chromatographic peaks with the retention times of authentic
methyl
esters of adamantane-l-carboxylic acid and adamantane-2-carboxylic acid were
integrated and a ratio of the areas plotted (Figure 5). As only adamantane-2-
carboxylic
acid is present in preparation B, all ratios = 0 and thus the profile is
entirely distinct to
that of preparation A.
31164679-1-klees
CA 02743156 2011-06-14
mai, r r rc+.rra Sao
It is to be appreciated that the distinctive profiles of tricyclic and
pentacydic diamondoid
acids contained within samples from other sources can be mapped and used to
identify
samples originating from that same source.
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