Mass spectrometry characterization of peroxycarboxylic acids as proxies for reactive oxygen species and highly oxygenated molecules in atmospheric aerosols

Article abstract of DOI:10.1021/acs.analchem.6b04127

A significant fraction of atmospheric aerosol particles is composed of organic material with a highly complex but poorly characterized composition. For a better understanding of aerosol effects and processes in the atmosphere, a more detailed knowledge of aerosol components at a molecular level is needed. Peroxy acids might play a significant role in particle toxicity, due to their oxidizing properties, and they were recently found to be involved in particle formation. Because of the lack of appropriate standards, the identification and quantification of peroxy acids is often highly uncertain. Mass spectrometry (MS) is a powerful tool to characterize unidentified compounds in complex mixtures. However, so far there is only little information regarding the ionization and fragmentation behavior of peroxy acids in mass spectrometers. To study their fragmentation patterns, we synthesized 12 peroxy acids with C₈ to C₁₀ carbon backbones and mono- or diperoxy acid functionality. The peroxy acids were separated using liquid chromatography, detected via negative mode electrospray ionization high-resolution MS, and their fragmentation patterns (MS/MS spectra) were identified. The MS/MS spectra of the peroxy acids showed fragmentation patterns clearly different from the corresponding acid, with a strong similarity between compounds of different chain length but analogous functional groups. Neutral loss of CH₂O₂ was observed for all investigated linear peroxy acids but not for carboxylic acids and could therefore serve as a diagnostic ion for peroxy acids. The obtained results are a large step toward unambiguous characterization of peroxy acids in the atmosphere. (Graph Presented).

Full text of DOI:10.1021/acs.analchem.6b04127

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Article
Mass spectrometry characterization of peroxycarboxylic
acids as proxies for reactive oxygen species (ROS) and
highly oxygenated molecules (HOMs) in atmospheric aerosols
Sarah Sulamith Steimer, Ivan Kourtchev, and Markus Kalberer
Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b04127 • Publication Date (Web): 25 Jan 2017
Downloaded from http://pubs.acs.org on January 26, 2017
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Mass spectrometry characterization of peroxycarboxylic acids
as proxies for reactive oxygen species (ROS) and highly
oxygenated molecules (HOMs) in atmospheric aerosols
§
Sarah S. Steimer, Ivan Kourtchev , Markus Kalberer*
Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, United Kingdom
A significant fraction of atmospheric aerosol particles is composed of organic material with a highly complex but poorly
characterized composition. For a better understanding of aerosol effects and processes in the atmosphere a more detailed
knowledge of aerosol components at a molecular level is needed. Peroxy acids might play a significant role in particle
toxicity, due to their oxidizing properties, and they were recently found to be involved in particle formation. Due to the
lack of appropriate standards the identification and quantification of peroxy acids is often highly uncertain. Mass
spectrometry (MS) is a powerful tool to characterize unidentified compounds in complex mixtures. However, so far there
is only little information regarding the ionization and fragmentation behavior of peroxy acids in mass spectrometers. To
study their fragmentation patterns, we synthesized 12 peroxy acids with C to C10 carbon backbones and monoꢀ or
8
diperoxy acid functionality. The peroxy acids were separated using liquid chromatography, detected via negative mode
electrospray ionization high resolution MS and their fragmentation patterns (MS/MS spectra) were identified. The MS/MS
spectra of the peroxy acids showed fragmentation patterns clearly different from the corresponding acid, with a strong
similarity between compounds of different chain length but analogous functional groups. Neutral loss of CH O was
2
2
observed for all investigated linear peroxy acids, but not for carboxylic acids and could therefore serve as a diagnostic ion
for peroxy acids. The obtained results are a large step towards unambiguous characterization of peroxy acids in the
atmosphere.
11
e.g. in BaeyerꢀVilliger oxidations, and find wide
INTRODUCTION
A large number of epidemiological studies show that
ambient aerosols are correlated with a wide range of
industrial application as disinfectants and bleaching
12–16
agents.
Given the multitude of industrial
applications of peroxy acids, a wide range of methods
have been developed for their analysis, including
1
–3
respiratory and cardioꢀvascular diseases.
It is not
17
18
known which particle components cause these negative
health effects, but reactive oxygen species (ROS), a
term summarizing various oxidizing compounds, are
hypothesized to be a main contributor to the toxicity of
particles in ambient air. An example of this is the
strong oxidative potential of isopreneꢀderived
iodometry,
spectrophotometry
and
different
chromatographic methods such as gas chromatography
19
with flame ionization detection or high performance
liquid chromatography (HPLC) with postcolumn
4
,5
20
derivatization followed by UV/VIS detection. When
unspecific detectors such as UV/VIS detectors are used,
authentic standards are needed to get an unambiguous
identification of the analyte. This presents a problem for
the analysis of atmospheric aerosols, which can contain
thousands of different organic compounds for which
standards are rarely commercially available.
6
hydroxyhydroperoxide. Peroxy acids are a subtype of
ROS suggested to be present in secondary organic
7,8
aerosol (SOA) and therefore potentially relevant for
particle toxicity. It was recently shown that compounds
with multiple hydroperoxy and peroxy acid groups (also
termed ‘highly oxygenated molecules’, HOMs), formed
via autoxidation in the gas phase, are strongly involved
in the initial stages of SOA formation . Because there
are no standards available for HOMs, their
characterization and quantification remains challenging.
Mass spectrometry and especially MS/MS analyses in
principle provide powerful tools to characterize peroxy
acids in organic aerosol without the need of an authentic
standard. While there are several papers describing the
use of MS to detect the presence of peroxyacetic acid in
9
,10
21–23
Apart from their relevance for atmospheric science,
peroxy acids are used as reagents in synthetic chemistry,
the gas phase,
there are only few MS measurements
of any other peroxy acids, and usually MS/MS is not
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utilized.
A few other studies describe the mass
acid, C H O ) was adapted from Parker et al. The
10 20 3
spectrometry detection of peroxy acids in particulate
matter based on elemental composition and observed
fragmentation; however, without confirmation from
authentic standards. To the best of our knowledge,
there is only one systematic study of peroxy acid
MS/MS fragmentation , which focusses on aromatic
peroxy acids, which are of limited relevance considering
the type of peroxy acids thought to be present in SOA.
synthesis
(monoperoxyoctanedioic
of
monoperoxysuberic
acid,
acid
C H O ),
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diperoxysuberic acid (diperoxyoctanedioic acid,
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,8
C H O ),
monoperoxyazelaic
acid
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(monoperoxynonanedioic acid,
C H O ),
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diperoxyazelaic acid (diperoxynonanedioic acid,
C H O ),
monoperoxysebacic
acid
and
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(monoperoxydecanedioic acid, C H O )
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diperoxysebacic acid (diperoxydecanedioic acid,
C H O ) was based on the procedure by Parker et al.
The same procedure was employed for the synthesis of
monoperoxycamphoric acid (C H O ). The chemical
structures of the different peroxy acids are shown in
Figure Sꢀ1.
Our study aims to fill this gap and provide insight into
general and characteristic fragmentation patterns of
atmospherically relevant organic peroxy acids to
provide a method of identifying unknown peroxy acids
in highly complex organic mixtures. We have
synthesized 12 aliphatic compounds with peroxy acid
functionalities: the peroxy acid analogues of the
straightꢀchain saturated C ꢀC monocarboxylic acids,
the monoꢀ and diperoxy acid derivatives of the
corresponding dicarboxylic acids and two cyclic
monoperoxy dicarboxylic acids. The compounds were
separated by HPLC and their fragmentation patterns
were studied using ESIꢀMS/MS in negative mode with
collision induced fragmentation (CID).
2
8
10 18
6
10 16
5
To synthesize the peroxy acids, the corresponding
carboxylic acid was dissolved under stirring in
concentrated sulfuric acid (95ꢀ98%) in an open beaker.
The resulting solution was cooled in an ice water bath to
10ꢀ15°C. Under constant stirring, 50% H O was slowly
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10
2
2
added dropwise over ~5 min (see Table Sꢀ1). A white
precipitate forms in all cases.
For the monocarboxylic acid derived peroxy acids,
the reaction mixture was continuously stirred for a total
of 60 min reaction time with the vessel slowly warming
to room temperature. Thereafter, 3 ml of 4°C water were
added to the reaction vessel and the same volume of
liquid removed again using a pipette to wash the
solution. This step was repeated twice. The remaining
precipitate and solution were then dissolved in 10 ml
20/80 water/acetonitrile.
EXPERIMENTAL SECTION
Safety considerations
The syntheses described in this paper are strongly
exothermic. Additionally, peroxymonosulfuric acid
Caro's acid), which is explosive and an extremely
(
strong oxidizer, is generated as a byꢀproduct. Pure
peroxy acids and their concentrated solutions
themselves may cause severe explosions. They are also
strong oxidizers and need to be kept away from easily
oxidizable materials. Appropriate safety precautions
need to be taken when working with peroxy acids and
the quantity of material handled should be kept to a
minimum.
For the dicarboxylic acid derivatives, the reaction was
continued for a total of 180 min with the vessel slowly
warming to room temperature. The addition of 4 ml
halfꢀsaturated ammonium sulfate solution (4°C) to the
reaction mixture for washing resulted in a finely
dispersed precipitate in the liquid phase which did not
readily settle and which made repeated washing steps
impossible. Therefore, 10 ml 20/80 water/acetonitrile
were directly added to the solution to dissolve the
precipitate. Two phases form, of which the upper one
Chemicals
Sulfuric acid (H SO , 95ꢀ98%), caprylic acid
(octanoic acid, C H O , ≥ 99%), pelargonic acid
(nonanoic acid, C H O , ≥ 97%), capric acid (decanoic
2
4
8
16
2
9
18
2
(
acetonitrile phase) is used for analysis. The syntheses
result in product solutions containing both monoꢀ and
diperoxydicarboxylic acids.
acid, C H O , ≥ 98%), suberic acid (octanedioic acid,
1
0
20
2
C H O , ≥ 98%), azelaic acid (nonanedioic acid,
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C H O , 98%), sebacic acid (decanedioic acid,
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4
The exact quantities of chemicals used in the
syntheses are shown in Table Sꢀ1. The product solutions
were stored in a freezer at ꢀ22°C.
C H O , 99%) and hydrogen peroxide (H O , 50%,
10 18
4
2
2
stabilized) were purchased from SigmaꢀAldrich. D(+)ꢀ
Camphoric acid ((1R,3S)ꢀ1,2,2ꢀtrimethylꢀ1,3ꢀ
cyclopentanedicarboxylic acid, C H O , 99%) was
purchased from Acros Organics. All carboxylic acids
were used without further purification. Acetonitrile,
formic acid and water, all in OPTIMA® LC/MS grade,
were purchased from Fisher Scientific.
1
0
16
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Analysis
Direct injection ESIꢀMS/MS was performed to
optimize instrument conditions. For this, each product
solution was diluted by a factor 100 with 50/50
water/acetonitrile and measured separately. For
peroxycapric acid, two additional solutions in different
solvents (100% acetonitrile and 50/50 0.1% formic
acid/acetonitrile) were prepared to test the influence of
solvent on the ionization of the mononcaboxylic acid
Synthesis
The synthesis of peroxycaprylic acid (peroxyoctanoic
acid, C H O ), peroxypelargonic acid (peroxynonanoic
8
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3
acid, C H O ) and peroxycapric acid (peroxydecanoic
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derived peroxyacids. Two different analyte solutions
negative ionization mode. For direct injection, the
source settings were: spray voltage −3.1 to ꢀ3.7 kV,
source heater temperature 150°C, capillary temperature
275°C, sheath gas flow 12 arbitrary units, auxiliary gas
flow 5ꢀ7 arbitrary units, no sweep gas flow and Sꢀlens
RF level 60%. The sample flow rate was 9ꢀ18 ꢁL/min.
The following source parameters were used for HPLC:
spray voltage −3.2 kV, source heater temperature
250°C, capillary temperature 275°C, sheath gas flow 40
arbitrary units, auxiliary gas flow 10 arbitrary units, no
sweep gas flow and Sꢀlens RF level 55%. Mass spectra
for the HPLCꢀMS measurements were collected in full
scan mode over a mass range of m/z 100−650, using the
lock mass of the deprotonated dimer of formic acid at
m/z 91.0037 and a resolution of 100 000 at m/z 400.
Parallel MS/MS scans were performed using a global
mass list, with a resolution of 60 000, a mass range of
m/z 50−300 and three different isolation widths (1.0, 1.5
and 2.0) for comparison. CID was used for ion
fragmentation; the energies used for the different
precursor ions are given in Table 1 and Table 2. Direct
infusion measurements were used to optimize this CID
method.
were prepared for HPLCꢀMS analysis. The first solution
was a mixture of the products from the monocarboxylic
acid based syntheses, diluted by factor 100 with 50/50
water/acetonitrile. The second solution contained the
products of the four dicarboxylic acid based syntheses,
diluted by a factor 100 in 80/20 water/acetonitrile. The
mixtures were analyzed using HPLCꢀESIꢀMS. The
HPLC was an Accela system (Thermo Scientific, San
Jose, USA) equipped with a T3 Atlantis C18 column (3
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ꢁ
m; 3.0 × 150 mm; Waters, Milford, USA). A highꢀ
resolution LTQ Orbitrap Velos mass spectrometer
Thermo Scientific, Bremen, Germany), equipped with a
(
heated electrospray ionization (HESI) source, was used
as the detector.
HPLC separation
The monocarboxylic acids and their peroxy acid
derivatives were separated using gradient elution with a
flow rate of 200 ꢁL/min. The mobile phase was
composed of a mixture of three solvents: 0.1% formic
acid in water (solvent A), acetonitrile (solvent B) and
water (solvent C). The initial mobile phase composition
of 90% A and 10% B was maintained for 5 min. Solvent
A was then linearly decreased to 0% over 3 min, while
B and C increased to 50% each. After this, B was
increased further to 90% over 11 min, accompanied by a
decrease in C to 10%. This composition was kept for
1 min. During the subsequent 3 min, solvent A was
increased to 63%, while B was reduced to 37% and C to
0%. A was then further increased to 90% and B
decreased to 10% over 3 min. This composition was
maintained for the last 5 min. Formic or acetic acid are
often used as additives in HPLC to improve the
retention and peak shape of acidic species. It was found
that addition of formic or acetic acid led to strong
suppression of the signals from deprotonated peroxy
acid molecules in both direct injection and HPLCꢀMS
even at low concentrations (0.01%ꢀ0.1%). The
chromatographic method was therefore developed to
minimize presence of formic acid during the elution
time of the peroxy acids. This improved the signal
intensity by about 1.5 orders of magnitude.
Data evaluation
The Thermo Xcalibur 2.2 software was used for data
evaluation. The assignment of elemental composition
had a mass tolerance of 6 ppm. For the investigation of
MS/MS fragmentation, the mass list contains all m/z
smaller than the precursor ion which have a relative
abundance above the chosen threshold, usually >1%.
The same procedure was then repeated with
a
background subtracted version of the spectrum. The
final list of product ions is based on the background
subtracted mass list, but additionally excludes m/z which
did not have an assigned elemental composition, which
could be dismissed as product ions based on the
assigned elemental composition or whose extracted ion
chromatogram showed a poor overlap with the base
peak chromatogram of the MS/MS measurement. While
the selection of product ions and their relative
abundance was based on the background subtracted
mass list, the masses were taken from the raw data,
which shows higher mass accuracy.
To separate the dicarboxylic acids and their peroxy
acid derivatives, gradient elution was carried out at a
flow rate of 200 ꢁL/min with a mobile phase composed
of only solvent A and B in varying composition. The
starting concentration of 15% B was held constant for
two minutes and then raised to 32.4% over 20 min.
After an increase of B to 90% during the following
11 min segment, it was reduced back to 15% within
5 min and held at this concentration for an additional
RESULTS AND DISCUSSION
Liquid chromatography separation of carboxylic
acids and peroxy acids
The three monocarboxylic acids and their three
peroxy acid derivatives were clearly separated using the
HPLC method described above (Figure 1). The three
monocarboxylic acids elute about 1ꢀ1.5 minutes before
their corresponding peroxy acids due to their higher
polarity. Peaks were assigned based on presence of the
1
0 min.
MS
ꢀ
®
deprotonated analyte molecule ([MꢀH] ).
The instrument was calibrated using Pierce ESI
Negative Ion Calibration Solution (Thermo Scientific,
Rockford, USA. measurements were carried out in
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Figure 2. Base peak chromatogram showing the separation
of four dicarboxylic acids and their corresponding peroxy
acid analogues: suberic acid (1), monoperoxysuberic acid
(2), diperoxysuberic acid (3), camphoric acid (4),
monoperoxycamphoric acid (5, 6), azelaic acid (7),
monoperoxyazelaic acid (8), diperoxyazelaic acid (9),
sebacic acid (10), monoperoxysebacic acid (11) and
diperoxysebacic acid (12).
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Mass spectrometry analyses
Extracted ion chromatograms show that all acids and
the synthesized peroxy acids are detected in form of
ꢀ
their [MꢀH] ions. The chromatographic peaks of both
monoꢀ and diperoxycarboxylic acids additionally show
the presence of the corresponding carboxylic acid [Mꢀ
ꢀ
ꢀ
H] . In case of the diperoxycarboxylic acids, the [MꢀH]
Figure 1. Base peak chromatogram showing the separation
of three monocarboxylic acids and their corresponding
peroxy acid analogues: caprylic acid (1), peroxycaprylic
acid (2), pelargonic acid (3), peroxypelargonic acid (4),
capric acid (5) and peroxycapric acid (6).
of the corresponding monoperoxy acid is observed as
well. An example of the apparent coꢀelution of acid and
peroxy acid can be seen in Figure
3 for the
monocarboxylic acids and their corresponding peroxy
acids. The extracted ion chromatograms for the
dicarboxylic acids and their peroxy acid derivatives are
shown in Figure Sꢀ3. The ratio of monoperoxy acid to
The base peak chromatogram of the separation of
dicarboxylic acids and their derivatives shows 12 peaks
in the region of interest (Figure 2). The peaks are well
separated with the exception of diperoxysuberic acid
and camphoric acid, which show a slight overlap (peaks
ꢀ
carboxylic acid [MꢀH] signal within the monoperoxy
acid chromatographic peak ranges from 0.42 to 0.98 for
the monocarboxylic acids and 13.30 to 20.09 for the
dicarboxylic acids. The ratio of diperoxy acid to
carboxylic acid signal in the diperoxy acid peak ranges
from 0.13 to 0.15, while the range of diperoxy acid to
3
and 4). The only peroxy acid that could not be
synthesized with the method described here was
diperoxycamphoric acid. The extracted ion
2
6
monoperoxy acid signal is 1.90 to 2.33. Harman et al.
chromatogram of the monoperoxycamphoric acid mass
(Figure Sꢀ2) shows two peaks: a large peak equivalent to
peak 6 in Figure 2 and a smaller peak at an earlier
retention time equivalent to the small peak 5 in Figure 2.
This peak’s area is about 16 times smaller than that of
the larger peak 6. It shows the same major product ions
made similar observations for peroxybenzoic acid. It is
well known that electrochemical processes occurring in
ESI can significantly influence the observed mass
3
1–33
spectra.
active
Peroxy acids 35are electrochemically
and Awad et al. concluded that the
2
4,34
electroreduction of peroxyacetic acid proceeds as a twoꢀ
step electron transfer mechanism which results in
formation of the acetate ion. Therefore, electroreduction
as
peak
6,
unambiguously
identified
as
monoperoxycamphoric acid, and is therefore likely the
other monoperoxycamphoric acid isomer. For the more
commonly applied synthesis of monoperoxycamphoric
seems to be a likely cause for the observed presence of
ꢀ
[
MꢀH] ions from reduced compounds in the peroxy acid
acid
from
camphoric
acid
a2n9hydride,
3ꢀ
peaks in our samples.
peroxycamphoric acid is dominant.
Rinaldi found a 15:1 mixture of the two isomers,
supporting our findings.
Pirkle and
30
ꢀ
Figure 3. Extracted ion chromatograms for the [MꢀH] ions
of caprylic acid (blue dashed line), peroxycaprylic acid
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38
(
cyan solid line), pelargonic acid (purple dashed line),
acid. Contrary to the linear dicarboxylic acids, the
peroxypelargonic acid (magenta solid line), capric acid
(dark green dashed line) and peroxycapric acid (bright
green solid line).
camphoric acid MS/MS spectrum shows only one
product ion, [MꢀHꢀCO ] (Table 2). This is consistent
with the observation of CO2 loss as the main
fragmentation pathway for similar dicarboxylic acids
such as pinic acid.
ꢀ
2
MS/MS of monocarboxylic acids and their
derivatives
38,39
Consistent with their dicarboxylic acid analogues, the
three linear monoperoxydicarboxylic acids show a
combined loss of (CO +H O) as their dominant
fragmentation process (Table 2). They do however have
a larger range of additional product ions than the
corresponding dicarboxylic acids. Three types of these
less intense product ions were observed for all three of
the linear monoperoxydicarboxylic acids. One of them,
MꢀHꢀH O] , is nonspecific, while [MꢀHꢀCH O ] (16ꢀ
2%) and [MꢀHꢀCH O ] (3ꢀ12%) were not observed for
any of the carboxylic acids. Only monoperoxysuberic
acid shows the presence of [MꢀHꢀCO ] , while [MꢀHꢀ
The MS/MS spectra of the three monocarboxylic acids
show loss of water as the only fragmentation pathway
(
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2
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Table 1). The signal intensity of the detected [MꢀHꢀ
ꢀ
H O] product ions is low compared to the abundance of
2
the respective precursor ion both in the mass spectra,
and the MS/MS spectra at 0 eV collision energy. This is
in good agreement with the results from a study e.g. by
Šťávová et al., who found [Mꢀ19] to be the only
observed product ion for monocarboxylic acid MS/MS
and reported difficulties in obtaining an efficient
fragmentation. These results suggest that the main
fragmentation pathway of the monocarboxylic acid [Mꢀ
3
6
ꢀ
ꢀ
ꢀ
[
2
2
2
2
ꢀ
4 4
ꢀ
2
ꢀ
ꢀ
2H
2
O] was only observed for monoperoxysebacic acid.
H] leads to formation of small product ions below the
m/z range of our mass spectrometer, which therefore are
not detected.
As with camphoric acid compared to the linear
dicarboxylic acids, the product ion spectrum for
monoperoxycamphoric acid differs from the linear
monoperoxydicarboxylic acids. While the dominant
fragmentation pathway is again the combined loss of
ꢀ
Fragmentation of all three peroxyacid [MꢀH]
precursor ions shows the same two neutral losses:
CH O (or CO+H O) and H O (Table 1). The product
ion spectra are dominated by [MꢀHꢀCH O ] ions, while
2
2
2
2
ꢀ
(CO +H O), there is no overlap in any of the less intense
2 2
2
2
ꢀ
product ion types (see Table 2).
[
MꢀHꢀH O] only gives rise to a minor signal of a few
2
A combined loss of (CO +H O) dominates the
percent relative intensity. The only saturate2d6
peroxycarboxylic acid investigated by Harman et al.,
peroxycyclohexylcarboxylic acid, shows loss of nominal
mass 46 as the main fragmentation pathway. This
neutral loss is interpreted as a likely stepwise or
2
2
fragmentation of all three linear diperoxydicarboxylic
acids, just as for their dicarboxylic acid and
monoperoxydicarboxylic acid analogues (Table 2).
Equally to the linear monoperoxydicarboxylic acids, the
ꢀ
ꢀ
product ions [MꢀHꢀH O] , [MꢀHꢀCH O ] and [MꢀHꢀ
concerted loss of CO and H O, which agrees well with
our observations. It was absent from the product ion
2
2
2
2
ꢀ
CH O ] are again present for all three molecules.
4
4
ꢀ
ꢀ
2
6
Additionally, [MꢀHꢀOH] , [MꢀHꢀC H O ] and [MꢀHꢀ
spectrum of the aromatic analogue . Compared to the
aliphatic peroxymonocarboxylic acids measured in our
study, peroxycyclohexylcarboxylic acid shows a much
wider spectrum of additional product ions , a difference
which could be explained by its cyclic structure.
2
4
5
ꢀ
H O ] are also present for all three linear
2
2
diperoxydicarboxylic acids. It should be noted that all
three diperoxydicarboxylic acids show relatively low
product ion signal intensities (10 ꢀ10 ) considering the
intensity of the precursor ion signal in the mass
spectrum.
2
6
3
5
MS/MS of dicarboxylic acids and their derivatives
For the three linear dicarboxylic acids, a combined
loss of (CO +H O or CH O ) was the dominant
fragmentation process (Table 2). This is in agreement
with the observations made e.g. by Grossert et al. in
their detailed study of dicarboxylic acid fragmentation.
Consistent as well is the fact that the only other neutral
losses observed were CO or H O. The combined loss of
Since a loss of CH O was observed for all of the linear
peroxy acids, this fragmentation could be seen as
indicating the general presence of a peroxy acid
functionality, while [MꢀHꢀCH O ] is specific for all
linear dicarboxylic acid derived peroxyacids and the
2
2
2
2
2
3
37
ꢀ
4
4
ꢀ
ꢀ
presence of [MꢀHꢀOH] , [MꢀHꢀC H O ] and [MꢀHꢀ
2
4
5
2
2
ꢀ
H O ] were only observed for diperoxy acids.
2
2
(
CO +H O) was also found to be an important process
2 2
Representative MS/MS spectra of the C10 linear
peroxyacids are shown in Figure Sꢀ4.
in the fragmentation of atmospherically relevant linear
terpenoic acids, such as 3ꢀmethylꢀ1,2,3ꢀ
butanetricarboxylic acid (MBTCA) and homoterpenylic
-
1
Table 1. MS/MS fragmentations of [M-H] ions from monocarboxylic acids and their peroxyacid analogues.
Compound
Deprotonated
m/z
Collision
Product ion m/z
Neutral loss(es)
1
The data shown were averaged from four spectra measured with an isolation width of 1.0.
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ꢀ
2
molecule [MꢀH]
(ꢂ ppm)
energy
%)
(rel. abund.)
(
ꢀ
Caprylic acid
[C H O ]
143.10768 (ꢀ0.493)
157.12327 (ꢀ0.847)
171.13860 (ꢀ2.633)
159.10267 (0.015)
28
30
32
26
125.09719 (100)
139.11283 (100)
153.12844 (100)
113.09722 (100)
H O
8
15
2
2
ꢀ
Pelargonic acid
Capric acid
[C H O ]
H O
2
9
17
2
ꢀ
[C H O ]
H O
2
1
0
19
2
ꢀ
Peroxycaprylic acid
[C H O ]
CH O2
8
15
3
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
41.09218 (3)
H O
2
ꢀ
Peroxypelargonic acid
Peroxycapric acid
[C H O ]
173.11827 (ꢀ0.276)
187.13388 (ꢀ0.469)
27
28
127.11284 (100)
155.10776 (2)
CH O2
9
17
3
2
H O
2
ꢀ
[C H O ]
141.12850 (100)
CH O2
1
0
19
3
2
1
69.12337 (2)
H O
2
-
3
Table 2. MS/MS fragmentations of [M-H] ions from dicarboxylic acids and their peroxyacid analogues.
Compound
Deprotonated
molecule [MꢀH]
m/z
ꢂ ppm)
Collision
energy
Product ion m/z
Neutral loss(es)
ꢀ
4
(
(rel. abund.)
(%)
ꢀ
Suberic acid
[C H O ]
173.08164 (ꢀ1.688)
24
111.08150 (100)
CH O3
8
13
4
2
1
29.09208 (3)
CO2
ꢀ
Azelaic acid
Sebacic acid
[C H O ]
187.09719 (ꢀ2.097)
201.11277 (ꢀ2.299)
25
24
125.09713 (100)
139.11286 (100)
CH O3
9
15
4
2
ꢀ
ꢀ
[C H O ]
CH O3
1
0
17
4
2
1
83.10270 (34)
H O
2
Camphoric acid
[C H O ]
199.09721 (ꢀ1.870)
189.07655 (ꢀ1.570)
22
25
155.10767 (100)
CO2
1
0
15
4
ꢀ
Monoperoxysuberic
acid
[C H O ]
127.07639 (100)
143.07133 (22)
171.06613 (8)
CH O3
8
13
5
2
CH O2
2
H O
2
1
1
09.06588 (3)
45.08694 (3)
CH O4
4
CO2
ꢀ
Monoperoxyazelaic
acid
[C H O ]
203.09207 (ꢀ2.102)
217.10757 (ꢀ2.657)
25
25
141.09205 (100)
57.08688 (19)
CH O3
9
15
5
2
1
CH O2
2
185.08181 (16)
123.08150 (5)
H O
2
CH O4
4
ꢀ
Monoperoxysebacic
acid
[C H O ]
155.10761 (100)
CH O3
1
0
17
5
2
1
1
1
99.09746 (30)
71.10251 (16)
37.09716 (12)
H O
2
CH O2
2
4
CH O4
181.08687 (4)
2 H O
2
ꢀ
Monoperoxycamphoric [C H O ]
215.09211 (ꢀ1.799)
22
153.09199 (100)
CH O3
1
0
15
5
2
acid
1
1
1
54.09974 (9)
11.08152 (7)
25.09715 (4)
CHO3
C H O
3
4
4
C H O
2
2
4
2
Only product ions with an abundance ≥ 1.0 % relative to the main product ion are listed.
The data shown were averaged from two spectra measured with an isolation width of 1.5.
Only product ions with an abundance ≥ 1.0 % relative to the main product ion are listed.
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27.11280 (3)
38.06862 (2)
2CO2
C H O
2
5
3
ꢀ
Diperoxysuberic acid
[C H O ]
205.07146 (ꢀ1.470)
23
143.07130 (100)
87.06103 (38)
CH O3
8
13
6
2
1
H O
2
97.06585 (15)
188.06884 (14)
C H O
2
4
5
OH
10
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1
1
1
59.06618 (4)
25.06072 (3)
71.06613 (1)
CH O2
2
CH O4
4
H O
2
2
ꢀ
Diperoxyazelaic acid
[C H O ]
219.08704 (ꢀ1.695)
27
157.08691 (100)
202.08454 (64)
111.08153 (43)
CH O3
9
15
6
2
OH
C H O
5
2
4
2
1
1
1
1
01.07679 (35)
85.08184 (14)
73.08182 (9)
39.07646 (7)
83.06618 (1)
H O
2
H O
2
2
CH O2
2
CH O4
4
2H O
2
155.07136 (1)
CH O3
4
ꢀ
Diperoxysebacic acid
[C H O ]
233.10270 (ꢀ1.551)
27
171.10251 (100)
CH O3
1
0
17
6
2
2
2
1
1
16.10017 (31)
15.09241 (21)
25.09715 (16)
99.09749 (13)
OH
H O
2
C H O
5
2
4
H O
2
2
153.09203 (6)
197.08186 (3)
CH O4
4
2H O
2
1
87.09748 (3)
CH O2
2
organic mixtures containing unknown peroxy acids,
such as atmospheric aerosols, but also other
environmental samples or in industrial applications.
CONCLUSIONS
We have synthesized and characterized 12 peroxy
acids, as proxies for a key compound class present in
atmospheric aerosol particles, which could play a
significant role in the formation processes of organic
aerosol particles (e.g. soꢀcalled highly oxidized
molecules, HOMs) and in their health effects (soꢀcalled
reactive oxygen species, ROS). In recent years ROS and
HOMs have gained significant attention in atmospheric
science but due to the lack of available commercial
standards the unambiguous identification of the
involved compounds remains often uncertain and
speculative.
In addition, a neutral loss of CH O was observed for
2
2
all ten linear peroxy acids and could therefore serve as a
general indicator for peroxy acid functional groups in
these types of compounds. However, the only measured
cyclic
monoperoxydicarboxylic
acid
showed
fragmentation behavior different from the linear
compounds. This indicates the need for further studies
of cyclic peroxy acids to establish their characteristic
fragmentation patterns, as cyclic peroxy acids are
expected to form in the atmosphere, for example
7,40
through oxidation of terpenes.
We have shown here that the 12 synthesized peroxy
acids can be distinguished from the corresponding
carboxylic acids via their MS/MS fragmentation
behavior. This is the first time that the fragmentation
patterns of aliphatic peroxy acids were investigated
systematically. We found characteristic fragmentation
patterns for linear peroxymonocarboxylic acids,
ASSOCIATED CONTENT
Supporting Information
Supporting Information Available:
Figures Sꢀ1 to Sꢀ4 and Table Sꢀ1 (PDF)
monoperoxydicarboxylic
acids
and
This material is available free of charge via the Internet at
http://pubs.acs.org.
diperoxydicarboxylic acids. They could be used to
distinguish between these three different types of peroxy
acids in a prognostic way when characterizing complex
AUTHOR INFORMATION
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Spenceley, H. Lett. Appl. Microbiol. 1990, 11, 255–259.
Kitis, M. Environ. Int. 2004, 30, 47–55.
Corresponding Author
Eꢀmail: markus.kalberer@atm.ch.cam.ac.uk
(13)
*
(
(
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15)
Milne, N. J. J. Surfactants Deterg. 1998, 1, 253–261.
Ramirez, J. A. In Disinfection and decontamination:
Principles, applications and related issues; Manivannan,
G., Ed.; CRC press: Boca Raton, 2008; pp 73–86.
Reinhardt, G.; Borchers, G. In Handbook of detergents,
part E: applications; Zoller, U., Ed.; CRC Press: Boca
Raton, 2009; Vol. 141, pp 375–418.
Greenspan, F. P.; MacKellar, D. G. Anal. Chem. 1948,
20, 1061–1063.
Davies, D. M.; Deary, M. E. Analyst 1988, 113, 1477–
Present Addresses
§Now at: Department of Chemistry and Environmental
Research Institute, University College Cork, Cork, Ireland
(16)
Author Contributions
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(17)
(18)
(19)
SS and MK planned the experiments. SS performed the
experiments with the help of IK. SS wrote the manuscript
with contributions of IK and MK. All authors have given
approval to the final version of the manuscript.
Notes
1
479.
Cairns, G. T.; Diaz, R. R.; Selby, K.; Waddington, D. J.
J. Chromatogr. A 1975, 103, 381–384.
Effkemann, S.; Pinkernell, U.; Neumüller, R.; Schwan,
F.; Engelhardt, H.; Karst, U. Anal. Chem. 1998, 70,
The authors declare no competing financial interest.
(20)
3
857–3862.
ACKNOWLEDGEMENTS
(21)
Crounse, J. D.; McKinney, K. A.; Kwan, A. J.;
Wennberg, P. O. Anal. Chem. 2006, 78, 6726–6732.
Pacenti, M.; Dugheri, S.; Boccalon, P.; Arcangeli, G.;
Dolara, P.; Cupelli, V. Ind. Health 2010, 48, 217–221.
Phillips, G. J.; Pouvesle, N.; Thieser, J.; Schuster, G.;
Axinte, R.; Fischer, H.; Williams, J.; Lelieveld, J.;
Crowley, J. N. Atmos. Chem. Phys. 2013, 13, 1129–
This work was supported by ERC grant no. 279405. S.S.S.
acknowledges support from the Swiss National Science
Foundation (project no. 162258). The authors would like to
thank David R. Spring and Jamie E. Stokes for helpful
discussions regarding the peroxy acid syntheses and for
provision of safety equipment.
(22)
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1
139.
(24)
Ferdousi, B. N.; Islam, M. M.; Okajima, T.; Ohsaka, T.
Talanta 2008, 74, 1355–1362.
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