Identification of Compounds in Water above a Pollutant Plume by High
 

Resolution Mass Spectrometry
 

Andrew H. Grange and G. Wayne Sovocool
 

U.S. EPA, ORD, NERL, Environmental Sciences Division, PO Box 93478, Las Vegas, NV
 

89193-3478
 

e-mail addresses: grange.andrew@epa.gov, sovocool.wayne@epa.gov,
 

phones: (702) 798-2137 (ahg), (702) 798-2212 (gws)
 

fax: (702) 798-2142 (ahg & gws)
 

Running head title: Compound ID by Ion Composition Elucidation 

Keywords: exact mass, elemental formula, compound identification, ion composition elucidation 

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Abstract 

Identification of compounds in contaminated media is essential for determining sources 

of pollution and for assessing risks posed by the chemicals to ecosystems or human 

health. Eighty-five compounds were identified or tentatively identified in a 1-L extract of 

water sampled above a pollutant plume containing wastes from a chemical plant. Gas 

chromatography/high resolution mass spectrometry determined exact masses of apparent 

molecular ions and the exact masses and relative isotopic abundances of their +1 and +2 

isotopic mass peaks, which provided their elemental compositions. Ion compositions, 

mass spectral libraries, the presence of related compounds, and knowledge of organic 

chemistry provided tentative identifications, half of which were confirmed by comparison 

of analyte retention times and mass spectra with those of standards. 

Introduction 

A chemical manufacturer for the rubber and plastics industries used over 100 chemicals 

for syntheses. For at least 30 years, some fractions of these chemicals, synthesis products, and 

their byproducts were transferred to a waste pond. After exposure to air, rain, solar radiation, and 

soil particles, fractions of these compounds, reaction byproducts, and transformation products 

had migrated into an underground plume 3/4 of a mile long and up to 1/3 of a mile wide. During 

droughts, water above the plume might be used as part of a nearby town’s drinking water supply. 

It was therefore essential to identify as many of the compounds present in this water as possible 

in order to assess toxicological risk to humans and to provide a list of target compounds for 

evaluating the efficacy of drinking water treatments. 

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For the past decade, the Environmental Chemistry Branch (ECB) has characterized and 

identified compounds in complex environmental extracts using Ion Composition Elucidation 

(ICE) (Grange et al. 1998, 2001, 2003; Grange and Sovocool, 2003; Snyder et al., 2001), a high 

resolution mass spectrometric technique that measures both exact masses of ions and the relative 

abundances of the mass peaks heavier by 1 and 2 Da than the mass peak of the monoisotopic ion. 

The heavier mass peaks result from the presence of ions containing one or two atoms of heavier 

isotopes such as 13C, 2

H, 15N, 17O, 18O, 33S, 34S, 37Cl, or 81Br. A Profile Generation Model (PGM) 

calculates the possible compositions corresponding to the measured exact masses for the three 

mass peaks and the relative isotopic abundances of the +1 and +2 mass peaks based on the error 

limits of the measurements (Grange and Brumley 1997). This strategy fully exploits two 

independent physical properties of atoms, their masses and their isotopic abundances, to provide 

complementary discrimination among elemental compositions of ions. 

While ICE was recently adapted for use with accurate mass triple quadrupole and 

orthogonal acceleration, time-of-flight mass spectrometers interfaced with HPLCs (Grange et al., 

2005; Grange, Zumwalt, and Sovocool, 2006), this paper deals only with GC/HRMS application 

of ICE. Eighty-five compounds having a wide range of concentrations in the most complex 

extract of eighteen 1 L water samples were identified or tentatively identified. 

Experimental 

Field Samples. A total of 18 1-L water samples were collected from six locations at three 

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depths to survey the chemicals present. Six samples came from the water just above the plume. 

At each sampling site and depth, "ambient pH," "base extracted," and "acid extracted" samples 

were prepared by measuring the pH, adjusting the pH to 12-13 by addition of 6 N sodium 

hydroxide, or adjusting the pH to 2-3 by addition of 6 N sulfuric acid. 

Extraction. Extraction of the analytes into methylene chloride and volume reduction to 

about 1 mL was performed as described in EPA Methods 625 (EPA Methods) and 1625 (EPA 

Methods). The extracts were then shipped on ice to the EPA's Environmental Sciences Division 

in Las Vegas. 

Standards. Standards available from Aldrich (Milwaukee, WI) were purchased to 

confirm or refute tentative identifications of analytes based on comparisons of mass spectra and 

retention times. 

Gas Chromatography/Mass Spectrometry (GC/MS). An HP 5890 GC (Wilmington, 

DE) containing a 30-m, 0.25-mm i.d., 0.25-μm film, Rtx-5 GC column (Restek, Bellfonte, PA), 

was interfaced to the mass spectrometer. The temperature program was 40 o

C for 1 min, 7 

Co/min to 300 oC, and hold for 2 min. 

A VG 70SE-250J double focusing mass spectrometer (VG, Danvers, MA, USA) acquired 

full scan data over a mass range of 50-600 Da at 1 s/scan using a resolving power of 1000 (10% 

valley definition). Selected Ion Recording (SIR) data were acquired with 25 ms dwell times for 

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each m/z ratio at resolving powers of 3,000 or 10,000. Ion source conditions were 70 eV electron 

ionization, a 500-FA filament current, an ion source temperature of 250 oC, a transfer line 

temperature of 280 oC, and a photomultiplier voltage of 350 V. The photomultiplier voltage was 

increased to 400 V and to 450 V to increase sensitivity when resolutions of 3,000 and 10,000 

were used, respectively. 

Mass spectral data acquired by a double focusing mass spectrometer at a resolving power 

of 10,000 provide exact masses accurate to within a few ppm. Unfortunately, at this resolving 

power full scans over wide mass ranges cannot be acquired rapidly enough to delineate GC 

peaks. However, SIR provides ion abundances for up to 25 pre-selected m/z ratios within 1 s 

when a VG 70SE mass spectrometer with B2.2 data system software is used. The m/z ratios 

usually chosen when using EPA analytical methods [e.g. Methods 8270 (EPA Methods), 8290 

(EPA Methods), and 1613 (EPA Methods)] correspond to the maxima in mass peak profiles of 

ions arising from analytes and internal standards. Instead, to measure exact masses and relative 

isotopic abundances (RIAs), the SIR mode is used to monitor multiple m/z ratios across 

individual mass peak profiles. The areas under the chromatographic peaks for each m/z ratio are 

then plotted to provide the mass peak profiles in Figures 1b-d. The exact mass of each profile 

was obtained as the weighted average of several points across the top of the profile. Other groups 

have also employed the technique of monitoring multiple m/z ratios across individual mass peak 

profiles to obtain accurate exact masses (Vetter et al. 1999, Wu et al. 2002, Jörundsdóttir et al. 

2006). 

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Relative to full scanning, SIR provides: (1) the speed necessary to make measurements of 

exact masses and relative isotopic abundances practical as chromatographic peaks elute; (2) 

about 100-fold greater sensitivity; (3) greater selectivity, since a higher resolving power can be 

used for low-level analytes; and (4) calibration stability, since a lock mass profile is scanned at 

the start of each SIR cycle for recalibration. 

Ancillary Software. Disadvantages of using SIR to plot mass peak profiles are that only 

very narrow mass ranges can be monitored, which must be pre-selected based on an estimate of 

an analyte profile's exact mass, and that custom software on an ancillary computer is required. To 

compensate for narrow mass ranges, the multi-step approach illustrated in Figure 1 was 

employed. 

First, a full scan was acquired using a resolving power of 1000 to provide the full mass 

spectrum of each analyte. The highest-mass monoisotopic ion (m/z 139 in Figure 1a) was 

selected for further study. Three SIR data acquisitions were made after using ASCII files of 

commands prepared by a Lotus 123 version 2.2 (Lotus Development Corp., Cambridge, MA) 

spreadsheet to automatically enter exact masses, resolving power, data file name, and other 

parameters into SIR menus. 

The first SIR menu of m/z ratios covered the widest mass range using a 100-ppm mass 

increment, and data was acquired using a resolving power of 3000. The full mass peak profile 

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delineated by three points in Figure 1b provided an estimate of the exact mass of the m/z 139 ion 

and indicated only one m/z 139 ion was present. Other peaks in Figure 1b could result from 

calibrant or column bleed ions, but their ion chromatograms would reveal a constant or slowly 

increasing ion abundance, rather than a chromatographic peak (Grange et al. 2001). 

The exact mass estimate from Figure 1b was used as the center mass to prepare the SIR 

menu to acquire the data displayed in Figure 1c, which were acquired using a 10-ppm mass 

increment and 10,000 resolving power. A full mass peak profile well delineated by about 10 

points resulted, and the exact mass measured as the weighted average of the top several points 

was accurate to within 6 ppm. Using this mass error and assuming only atoms of C, H, N, O, and 

S were present in the ion, the measured exact mass of 139.02612 from Figure 1c yielded only one 

possible composition, C6H5NO3

+

. When P was also considered, two compositions were possible, 

and when P and F were considered, four possible compositions were found. When dealing with 

complex environmental extracts from a site for which a complete history is not available, 

numerous elements must be considered. 

Because multiple compositions remained viable, the user picked a hypothetical 

composition from which center masses were calculated for the SIR menu that monitored the 

partial profiles displayed in Figure 1d for a monoisotopic ion and its associated +1 and +2 mass 

peaks. Because too few m/z ratios are available to delineate full profiles for these three ions and 

a calibration ion, only six m/z ratios each are used to delineate the top portions of the three 

analyte profiles and four m/z ratios capture the top portion of the calibrant ion. The relative 

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isotopic abundances of the +1 and +2 partial profiles were determined as the sum of the areas 

under the ion chromatograms for each m/z ratio used to plot the +1 or +2 partial profile divided 

by the sum of the areas used to plot the monoisotopic partial profile. Often, when ion abundances 

are low and the +2 profile relative abundance is less than 2%, the shape of the +2 profile is badly 

distorted due to insufficient ion abundance or the presence of mass interferences. In our 

experience, the possible composition with the fewest heteroatoms and lacking F atoms is usually 

correct. Hence, to acquire the data for Figure 1d, the last of the possible compositions for m/z 

139.02916 (CH4N4O3F+

, C2H8N2O3P+, C4H7NSF2

+

, and C6H5NO3

+

) was chosen. The three exact 

masses and two RIAs provided by Figure 1d were entered into the PGM to determine which of 

the four possible compositions remained viable based on five comparisons between the measured 

values and values calculated for each composition. 

Profile Generation Model. The PGM calculates the exact masses and RIAs for each 

composition that is possible based on the measured exact mass from the monoisotopic partial 

profile assuming an error limit of 6 ppm when the resolving power is 10,000. The error limit 

estimate was based on 15 data acquisitions for each of four standards using a resolving power of 

20,000 (Grange et al. 1996; Grange and Brumley 1997). The largest observed mass error was 2.5 

ppm. This value was rounded to 3 ppm and doubled when a resolving power of only 10,000 was 

used. This conservative estimate of the mass error ensured that compositions were not rejected 

that should be considered when low ion abundances or minor mass interferences were 

encountered. For the exact masses listed below, only three of 171 exact masses were measured 

with errors larger than 6 ppm. 

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For each composition, the five pairs of measured and calculated values are compared. An 

"X" is placed next to a calculated value when it is inconsistent with the measured value. Table 1 

is the output from the PGM for the measured exact masses and RIAs obtained from Figure 1d. 

Only for the last composition, C6H5NO3

+

, were all five pairs of measured and calculated values 

in agreement. 

The RIA error ranges result from several errors associated with partial profiles: 

consideration of (i) instrumental precision, (ii) isotopic abundance variation for each 

composition, (iii) offset error in monitoring the profiles if the wrong hypothetical composition is 

chosen to calculate the center masses of the profiles to be monitored, (iv) up to one mass 

increment of offset error by the data system, and (v) up to 10% error in the resolution. These 

errors are discussed in more detail elsewhere (Grange and Brumley 1997). 

Results and Discussion 

Total Ion Chromatograms. Figure 2 is the total ion chromatogram for the sample 

extract that provided the largest number of chromatographic peaks. The peaks are labeled with 

the apparent molecular ion compositions or largest fragment ion compositions determined from 

exact masses and RIAs using the PGM and with the names of identified or tentatively identified 

compounds. The wide linear dynamic range of the double focusing mass spectrometer allowed 

compositions to be determined for compounds that provided large, moderate, and small 

chromatographic peak areas. Aromatic and halogenated aromatic compounds commonly provide 

predominant molecular ions with distinctive isotopic patterns for compounds containing Cl or Br, 

which resulted in their compositions being determined for very small chromatographic peaks. 

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Compounds for which only a fragment ion composition was determined were characterized to the 

extent that the elemental composition of a large portion of the molecule was obtained. 

Compositional information was obtained for most of the discernable chromatographic peaks 

during this study. 

Determining Ion Compositions. When fewer than three exact masses and two RIAs 

were measured reliably and multiple compositions remained viable, preference was given to 

compositions lacking F or P atoms, the composition with the fewest hetero atoms, compositions 

for which related compounds had been found, and to odd electron ions when four or more rings 

and double bonds were present, which suggested the presence of an aromatic ring and a stable 

molecular ion (except for phthalates). In addition, it was often assumed that at least 1/3 of each 

ion's mass was from C atoms. This eliminated carbonless compositions and those having very 

few carbon atoms relative to heteroatoms. Finally, if the +2 isotopic peak in the full scan mass 

spectrum was less than about 10%, Cl and Br atoms were not considered. In three instances, no 

compositions or no plausible compositions were found using the 6-ppm mass error limit; in these 

cases the error limit was increased to 12 ppm. In some cases, although a criterion was not met, 

the value measured still provided a basis for preferring a particular composition. For example, 

the %1 RIA was 7.02% for benzothiazole, which was outside of the acceptable range of 7.16­

9.68% for C7H5NS+

. However, the maximum acceptable value for all other possible 

compositions was 5.51%. After a tentative identification has been confirmed, the assumptions 

made to choose that compound become irrelevant. The quality assurance is provided by the 

similar mass spectra and retention times for the analyte and standard. 

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Identified Compounds. The identifications of compounds in Table 2 were confirmed 

against standards based on similar mass spectra and retention times usually consistent within 2 s 

and always within 4 s. Numerous injections were made over several weeks and GC column 

degradation could shift retention times slightly. For a few aromatic compounds, two or more 

isomers remain possible due to a lack of available standards. In addition, a number of specific 

isomers were shown to be absent from the sample. Compounds not found in the sample were: 

2,6-di-tert-butylphenol; 3,5-di-tert-butylphenol; 4-bromo-2-chlorophenol; 2-bromo-4­

methylphenol; 3-bromotoluene; 3-bromo-o-xylene; 4-bromo-o-xylene; 2-chlorophenol; 3-methyl2-nitrophenol; 3-methyl-4-nitrophenol; 5-methyl-2-nitrophenol; 2,3,4-trichlorophenol; 2,3­

dichlorophenol; 6,7-dihydro-4(5H)-benzofuranone; and 4-bromo-3-methylpyrazole. 

Tentatively Identified Compounds. The tentative identifications of compounds in Table 

3 were not confirmed against standards. They were identified by considering the following 

factors: (1) the composition of the apparent molecular ions, (2) comparisons of the low resolution 

mass spectra to those in the NIST (NIST/EPA/NIH 2002) and Wiley (Wiley 2002) mass spectral 

libraries, (3) the presence of related compounds in the extract, (4) a list of chemicals of concern 

associated with the site provided by EPA Region 1, and (5) knowledge of organic chemistry. 

Examples. Halogenated Benzenes, Alkyl Benzenes , Phenols, and Cresols. Chlorinated, 

brominated, and bromochlorinated compounds were found deriving from benzene, toluene, 

xylene, and other alkyl benzenes. Phenol and the cresols were found as were halogenated 

compounds deriving from them. Benzene, alkyl benzenes, phenol, and "alkylated phenol" were 

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used by the plant, but the halogenated derivatives were not and were apparently formed as 

transformation products. The halogenated phenols included singly or multiply chlorinated, 

brominated, chlorobrominated, iodinated, and bromoiodinated phenols. Multiple isomers 

differing in the position of attachment of the halogens to the benzene rings of many of the 

halogenated phenol compositions were found. The halogenated phenols were probably formed by 

electrophilic addition of Cl, Br, and/or I in water to the aromatic ring. Addition to the 2-, 4-, or 2­

and 4- positions would be expected. Chlorination and oxidation by chlorine, chlorate, and 

hypochlorite likely also contributed. 

Figure 3 provides nine background-subtracted mass spectra. Figures 3a-c are mass spectra 

for three halogenated phenols, 2-iodophenol, a bromoiodophenol, and a dibromoiodophenol. A 

standard was available only for the 2-iodophenol, but its confirmation provides support for the 

tentative identifications of the brominated iodophenols. Although iodine was not normally 

included as an element when using the PGM, the very small %1 RIA and %2 RIA indicated one 

or more elements lacking significant abundances of +1 and +2 isotopes was present. The 

dominant apparent molecular ion suggested aromaticity. Six C atoms would account for the 

observed %1 RIA, but only 72 of the 220 Da of the ion's mass. The presence of Cl and Br 

containing molecules in the extract made iodine a likely candidate. C6I accounted for all but 21 

Da of the molecular ion’s mass. 

For the bromoiodophenol isomer, a second composition also passed four of five criteria 

(CHNO10SBr+). Based on the presence of numerous other halogenated phenols, the composition 

C6H4OIBr+ was chosen as far more likely. In addition,C6H4OIBr+ is an odd electron ion and the 

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prominence of this probable molecular ion in the mass spectrum suggested the compound 

contained an aromatic ring, which would account for the 4.0 rings and double bonds (RDB) for 

this composition. Finally, 2-iodophenol was identified, and dibromoiodophenol was tentatively 

identified in the extract. 

Hydrazine-carbonyl condensates. The mass spectra in figures 3d and 3e provide evidence 

for the presence of two hydrazine-carbonyl condensates. Two other compounds containing 2 N 

atoms with 3 rings and double bonds (C6H10N2O+ and C5H7N2OCl+

) were also found. These 

compounds were not found in the NIST or Wiley libraries, but were suggested based on the use 

of hydrazine for chemical syntheses at the plant responsible for the pollutant plume. 

Composite mass spectra. Mass spectra in Figures 3d and 3f were among those revealed to 

be composite mass spectra from coeluting analytes based on the ion compositions determined for 

apparent molecular ions and apparent fragment ions. In Figure 3d, the loss of 16 Da from the 

apparent molecular ion could correspond to a neutral loss of CH4, O, or NH2. However the ion 

compositions indicated that the m/z 240 and 224 ions were unrelated, even though the similar 

isotopic patterns suggested that both ions might contain the same set of halogen atoms. The 

possibility that the common loss of 43 Da accounted for the mass difference between the m/z 240 

and 197 ions was also eliminated after the ion composition of the m/z 197 ion was determined. 

Clearly, determining ion compositions of multiple ions in a mass spectrum provided clarification 

of the origin of the ions. The isotopic patterns in Figure 3f for the m/z 250 and 186 ions indicated 

2 and 1 Br atoms were present, respectively. The mass difference of 64 Da indicated these ions 

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arose from two different compounds, since the loss of a Br atom corresponds to 79 Da. In this 

example, one is well aware that two apparent molecular ions are present before determining their 

ion compositions. 

Dichlorocarboxylic acid. Figure 3g provided a good NIST library match with a 

dichlorocarboxylic acid. This compound could be formed by hydrolysis of dichlobenil, which is a 

pesticide that might have been used for lawn care at the chemical plant. However, the purchased 

standard was not observed to elute when injected weeks after this mass spectrum was obtained. It 

is likely that as the column aged, the carboxylic acid retention time increased and its peak 

became extremely broad, or it did not elute at all. 

Pseudo-isotopic pattern. The mass spectrum in Figure 3h appears to have an isotopic 

pattern for m/z 112, 114, and 116 characteristic of a compound containing 2 Cl atoms. However, 

determining the ion compositions of the m/z 112 and 114 ions refuted this supposition. 

Mysteries remain. Figure 3i provides a simple mass spectrum for a prevalent compound 

not found in the NIST or Wiley libraries having five rings and double bonds. This compound has 

only been partially characterized. Some, but not all of its structural features have been deduced. 

A number of compositions for compounds and fragments of compounds were found that have not 

been assigned specific chemical structures. Numerous isomers are possible for most elemental 

compositions and if good library matches are not found, no tentative identification is possible. 

Similarly, the atoms in compound fragments can be assembled in multiple ways. In addition, 

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numerous background-subtracted mass spectra were essentially chemical noise. They arose from 

multiple compounds present at levels too low to investigate further. Finally, only a fraction of all 

compounds elute from a GC, and mass spectra from numerous other compounds might not have 

been obtained. It is unlikely that one could identify all of the compounds in such a complex 

mixture, but the ion composition elucidation strategy demonstrated herein greatly increased the 

number of compounds that were identified and tentatively identified relative to library matching 

of low resolution mass spectra alone. 

Possible Sources of Other Compounds Found. Several additional phenolic compounds 

were also found: 2-hydroxyacetophenone, bromomethylisopropylphenol, tert-butylphenol, and 2­

phenoxyphenol. In addition, benzoquinone, a known oxidation product of phenol, was found. 

O-cresol was an often used reagent in the chemical plant and was found in the extract. 

Several oxidative coupling products of the cresols were found, which were consistent with the 

oxidative conditions at the plant. In Figure 4a are overlaid ion chromatograms for two m/z ratios 

used to plot points on the mass peak profiles for the m/z 214 ion seen in Figure 4b. The resolving 

power of 10,000 provided strong evidence that three isomers were present. The NIST library 

match for the most abundant isomer was for Pummerer's ketone [4a,9b-dihydro-8,9b-dimethyl3(4H)-dibenzofuranone], 

Alkanes, Alkenes, Alkyl Oxygenated Compounds and their Halogenated Analogs. Many 

hydrocarbon fragment ions and oxygenated hydrocarbon fragment ions were observed. Their 

elemental compositions indicated most were alkyl hydrocarbons or had one or two double bonds 

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and/or rings. Many of the fragments likely originated from branched-chain alkanes, alkenes, 

cycloalkanes and related alcohols, ethers, and carbonyl compounds that do not provide intact 

molecular ions in electron ionization mass spectrometry. This often prevented specific compound 

identification. Some may have originated from alkenes, alcohols, ethers, and "petroleum 

distillates" used at the nearby chemical manufacturing plant. Another likely origin would be from 

oils and other natural products, such as terpenes. Many of these compounds were likely oxidized 

and halogenated to produce many of the compounds listed in the tables. These compounds would 

be expected to be formed from disinfectant chlorination in the presence of endogenous bromide 

and iodide salts or from the use of bromide salts at the site. They would be expected to form in 

the presence of an oxidizing agent, like chlorine, used in water treatment. Historically, liquid 

chlorine was used at the site to produce hydrazine from excess urea for chemical production. An 

alternative possibility for the source might be from oxidation of bromide and iodide ions by 

chlorate or hypochlorite used at the site. Sodium bromide, chlorate and hypochlorite were also 

used. 

Nitrophenol, Nitrocresol, and Bromonitrophenol. Nitration products of phenols were 

found, namely isomers of nitrophenol, nitrocresol, and bromonitrophenol. Nitrophenols were not 

used by the plant. Most likely, the different nitrophenols derived from the chemical reaction of 

phenol with the nitrates and nitrites present in the acidic waters. The plant used sodium nitrite 

and acid (nitrous acid) for chemical production. Nitrosophenols initially formed could have 

been oxidized to nitrophenols by oxygen or previously mentioned oxidizing agents. 

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Miscellaneous Compounds. Several cyclic silicone congeners probably consistent with an 

anti-foaming agent used at the site were observed. Bromoform, trimethylpentenes, 

bromodiphenyl ether and bis(2-ethylhexyl)phthalate, and diphenyl ether were also found. 

Additionally, Dibutyl phthalate, butylbenzylphthalate, di-2-ethylhexyladipate, and 

triphenyl phosphate were found. These compounds are plasticizers that were also found in the 

control water and are so ubiquitous as to be found almost everywhere. 

Benzothiazole, a common rubber-related compound, was found and was probably 

consistent with industrial activities in the area. Several polycyclic aromatic hydrocarbons were 

found: biphenyl, naphthalene, anthracene/phenanthrene, and pyrene/fluoranthene. These may be 

components of oil or among combustion products, and are also practically ubiquitous. 

Ongoing and Future work. Newer double focusing mass spectrometers no longer 

provide a macro language and a command line. Consequently, one cannot enter the name of an 

ASCII file containing macro language commands to prepare SIR menus and another ASCII file 

of instructions to display ion chromatograms over narrow windows, to integrate the areas under 

chromatographic peaks, and to save m/z ratios and areas in an ASCII output file. Hence, other 

types of mass spectrometers were investigated for determining ion compositions. 

The mass error limits provided by both an accurate mass triple quadrupole mass 

spectrometer (AM3QMS) (Grange et al. 2005) and orthogonal acceleration, time-of-flight mass 

spectrometers (oa-TOFMSs) (Grange, Zumwalt, and Sovocool, 2006; Grange, et al., 2006) are 

greater than those for mass measurements made using the double focusing mass spectrometer. To 

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compensate, an Ion Correlation Program (ICP) was written to correlate precursor and product 

ions and thereby increase the mass of ions for which unique compositions could be determined 

based on larger mass errors. 

A second advantage of using the ICP to correlate ions became apparent. Figure 3d 

illustrated that for composite mass spectra, determining the composition of the highest-mass, 

monoisotopic ion is often insufficient to reveal the source of the remaining ions through logical 

neutral losses from this ion. The ICP can help to characterize or tentatively identify multiple 

analytes providing a composite mass spectrum by determining the composition of all prominent 

ions in the mass spectrum and by correlating the related ions for each analyte (Grange, Zumwalt, 

and Sovocool, et al. 2006; Grange, et al., 2006). 

The oa-TOFMS provided a major advantage by acquiring the necessary exact masses and 

RIAs for precursor and product ions from full scan data acquisitions. Hence, only two generic 

data acquisitions were required, one each at a low or high collisionally induced dissociation 

voltage, rather than the four data acquisitions including three that were analyte-specific depicted 

in Figure 1. Three data acquisitions, two of which were analyte-specific, were required when 

using the AM3QMS. 

Both the AM3QMS and oa-TOFMS were interfaced to an HPLC. The double focusing 

MS will continue to be used for determining ion compositions for analytes introduced by GC. 

However, it may be possible to use the ICP to determine ion compositions from full scan data. 

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But acquiring full scan data at higher than 1000 resolving power will necessitate slower scan 

speeds that will not resolve chromatographic peaks, but rather yield composite mass spectra. In 

addition, the mass error will probably be larger. Correlating apparent molecular ions with 

fragment ions and deconvoluting mass spectra might provide numerous ion compositions and 

tentative identifications for analytes present at a high level and perhaps at moderate levels. ICE 

may still be necessary to determine compositions of ions present at low levels. If application of 

the ICP to full scan data is successful, the time to characterize or tentatively identify 100 analytes 

could be reduced substantially. 

Conclusion 

A methylene chloride extract of 1 L of water sampled above a pollutant plume contained 

hundreds of compounds. Many of the compounds yielded molecular ions for which the elemental 

compositions could be determined by measuring the exact masses of the monoisotopic ion and its 

+1 and +2 mass peaks and the relative isotopic abundances of the +1 and +2 mass peaks. 

Comparing the five pairs of measured and calculated values using a Profile Generation Model 

provided the correct composition. Often, for molecules not containing Cl or Br, the +2 isotopic 

peak abundance was very small or mass interferences were present, and only three comparisons 

could be made. This was also true for the +1 isotopic peak when Cl or Br atoms were present. 

Then multiple compositions were sometimes possible. In these cases, the composition with the 

fewest heteroatoms was usually correct. No apparent molecular ions or fragment ions were found 

to contain F atoms, and compositions containing F atoms were discarded. Compositions related 

to those of other compounds already found were also preferred. Knowledge of organic chemistry 

19
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

was also considered when culling multiple possible ion compositions. 

Forty-two identifications were confirmed based on comparisons of retention times and 

mass spectra with those of purchased standards. Forty-three tentative identifications remained. 

Many of these compounds were closely related to identifed compounds. Compounds that did not 

provide molecular ions could only be characterized by determining the composition of the largest 

observed fragment ion. 

Longer lists of identified and tentatively identified compounds were compiled using ICE 

than could be compiled from data acquired with low resolving power. These lists could enable a 

more thorough assessment of the risk posed to humans by the water overlying the pollutant 

plume and would provide a more detailed inventory of compounds and transformation products 

for establishing one or more pollutant sources. 

Notice: The U.S. Environmental Protection Agency (EPA), through its Office of Research and 

Development (ORD), funded and performed the research described. This manuscript has been 

subjected to the EPA=s peer and administrative review and has been approved for publication. 

References 

Final drafts of Grange et al. articles through 2003 are available at 

http://www.epa.gov/nerlesd1/chemistry/ice/default.htm. 

20
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Grange, A. H., J. R. Donnelly, W. C. Brumley, and G. W. Sovocool. 1996. Determination of 

Elemental Compositions from Mass Peak Profiles of the Molecular (M), M+1, and M+2 Ions 

Anal. Chem. 68: 553-560. 

Grange, A. H., and W. C. Brumley. 1997. A Mass Peak Profile Generation Model to Facilitate 

Determination of Elemental Compositions of Ions Based on Exact Masses and Isotopic 

Abundances. J. Amer. Soc. Mass Spectrom. 8: 170-182. 

Grange, A. H., G. W. Sovocool, J. R. Donnelly, F. A. Genicola, and D. F. Gurka. 1998. 

Identification of Pollutants in a Municipal Well Using High Resolution Mass Spectrometry. 

Rapid Commun. Mass Spectrom. 12: 1161-1169. 

Grange, A. H., L. Osemwengie, G Brilis, and G. W. Sovocool. 2001. Ion Composition 

Elucidation (ICE): An Investigative Tool for Characterization and Identification of Compounds 

of Regulatory Importance. International J. Environmental Forensics 2: 61-74. 

Grange, A. H. and G. W. Sovocool, 2003. Identifying Compounds Despite Chromatographic 

Limitations: Organophosphates in Treated Sewage. LC-GC 21: 1072-1076. 

Grange, A. H., P. M.Thomas, M. Solomon and G. W. Sovocool, 2003. Identification of 

Compounds in South African Stream Samples Using Ion Composition Elucidation (ICE). 

Poster: 51st ASMS Conf. on Mass Spectrom. & Allied Topics, Montreal, Ontario, 

21
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6/2-6/6. Available at: http://www.epa.gov/nerlesd1/chemistry/ice/sa.htm
 

Grange, A. H., W. Winnik, P. L. Ferguson, and G. W. Sovocool. 2005. Using a Triple
 

Quadrupole Mass Spectrometer in Accurate Mass Mode and an Ion Correlation Program to
 

Identify Compounds. Rapid Commun. Mass Spectrom. 19: 2699-2715.
 

Grange, A.H., M. C. Zumwalt, and G. W. Sovocool. 2006. Determination of Ion and Neutral
 

Loss Compositions and Deconvolution of Product Ion Mass Spectra Using an Orthogonal
 

Acceleration, Time-of-Flight Mass Spectrometer and an Ion Correlation Program.
 

Rapid Commun. Mass Spectrom. 20: 89-102.
 

Grange, A. H., R. B. Cody, Jr. and G. W. Sovocool, 2006. An Ion Correlation Program for
 

Deconvoluting Composite Mass Spectra Acquired using a Direct Surface Ionization Source
 

Interfaced to a Time-of Flight Mass Spectrometer. Poster: Pittsburgh Conference, Orlando, FL,
 

3/12-3/16. Available from author.
 

Jörundsdóttir, H., K. Norström, M. Olsson, H. Pham-Tuan, H. Hühnerfuss, A. Bignert, and C.
 

Bergman. 2006. Temporal Trend of Bis(4-chlorophenyl) Sulfone, Methylsulfonyl-DDE and ­

PCBs in Baltic Guillemot (Uria aalge) Egg 1971)2001 ) A Comparison to 4,4'-DDE and PCB
 

Trends. Environ. Pollut. 141: 226-237.
 

NIST/EPA/NIH Mass Spectral Library, Version 2.0, Standard Reference Data Program, National
 

Institute of Standards and Technology, U.S. Dept. of Commerce, NIST Mass Spectrometry Data
 

22
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Center, Gaithersburg, MD 20899, 2002.
 

Snyder, S.A., K. L. Kelly, A. H. Grange, G. W. Sovocool, E. M. Snyder, and J. P. Giesy. 2001.
 

Pharmaceuticals and Personal Care Products in the Waters of Lake Mead, Nevada, in
 

Pharmaceuticals and Personal Care Products in the Environment: Scientific and
 

Regulatory Issues; Daughton, C.G. & Jones-Lepp, T., Eds.; Symposium Series 791, Amer.
 

Chem. Soc.: Washington, DC, 116-141.
 

Vetter, W., L. Alder, and R. Palavinskas, 1999. Mass Spectrometric Characterization of Q1, a 

C9H3Cl7N2 Contaminant in Environmental Samples. Rapid Commun. Mass Spectrom. 13: 

2118-2124. 

Wiley Registry of Mass Spectra, 6th ed. Palisade Corp., Newfield, NY. 

Wu, J., W. Vetter, G. W. Gribble, J. S. Schneekloth Jr., D. H. Blank, and H. Görls. 2002. 

Structure and Synthesis of the Natural Heptachloro-1'-methyl-1,2'-bipyrrole (Q1) Angew. Chem. 

Int. Ed 41 10: 1740-1743. 

EPA Methods 

Appendix A to Part 136, Methods for Organic Chemical Analysis of Municipal and Industrial 

Wastewater, Method 625 -- Base/Neutrals and Acids at 

http://www.epa.gov/waterscience/methods/guide/625.pdf 

Appendix A to Part 136, Method 1625 Revision B -- Semivolatile Organic Compounds by 

Isotope Dilution GC/MS at http://www.epa.gov/waterscience/methods/guide/1625.pdf 

23
 
 

 

 

 

 

 

Method 8270C, Semivolatile Organic Compounds by Gas Chromatography/Mass Spectrometry 

(GC/MS) at http://www.epa.gov/epaoswer/hazwaste/test/pdfs/8270c.pdf 

Method 8290, Polychlorodibenzodioxins (PCDDs) and Polychlorodibenzofurans (PCDFs) by 

High-Resolution Gas Chromatography/High-Resolution Mass Spectrometry (HRGC/HRMS) at 

http://www.epa.gov/epaoswer/hazwaste/test/pdfs/8290.pdf 

Method 1613, Revision B, Tetra- through Octa-Chlorinated Dioxins and Furans by Isotope 

Dilution HRGC/HRMS at http://www.epa.gov/waterscience/methods/1613.pdf 

24
 
 

 

 

 

 

 

 

 

 

 

 

 

Tables 

Table 1. Output from the Profile Generation Model based on the exact masses and relative 

isotopic abundances from the partial profiles in Figure 3d 

Table 2. Compounds confirmed with standards by retention times and mass spectra 

Table 3. Tentatively Identified Compounds 

Figure Captions 

Figure 1. (a) A low resolution mass spectrum and three outputs provided by a Lotus 123 

spreadsheet using SIR data: (b) full profile, 100-ppm mass increment, and 3,000 resolving 

power; (c) full profile, 10-ppm increments, and 10,000 resolving power; and (d) partial profiles, 

10-ppm increment, and 10,000 resolving power. The lock mass (m/z 142.99199) is a calibration 

ion from perfluorokerosene. 

Figure 2. The total ion chromatogram for the extract containing the largest number of 

chromatographic peaks 

Figure 3. Nine background-subtracted mass spectra for chromatographic peaks observed in the 

25
 
 

 

 

 

total ion chromatogram in Figure 2. 

Figure 4. (a) ion chromatograms for two m/z ratios of the mass peak profile, (b) a background 

subtracted mass spectrum for the most abundant isomer, and (c) the NIST library match for 

Pummerer's ketone. 

26
 
Table 1. Output from the PGM based on the exact masses and RIAs from the partial profiles in Figure 1d* 

m/z = 139.0269 ± 6 ppm Resolving Power: 10,000 

# RDB Range Composition Monoistopic Ion Exact Mass (M+1) Profile Exact Mass (M+2) Profile Exact Mass %1 RIA Allowed Range (%) %2 RIA Allowed Range (%) 

1 1.5 2.5 CH4N4O3F 139.02674 140.02645 X 141.03098 X 1.66 (1.17-2.29) X 0.61 (0.47-0.75) 

2 0.5 1.5 

C2H8N2O3P 139.02725 140.03003 141.03148 X 2.64 (2.18-3.18) X 0.63 (0.49-0.76) 

3 1.0 

C4H7NF2S 139.02673 140.02952 141.02252 X 5.06 (4.14-5.05) X 0.38 (0.03-1.11) 

4 5.0 6.0 

C6H5NO3 139.02694 140.03028 141.03168 6.89 (5.88-7.93) 0.78 (0.65-0.92) 

Experimental Values: 139.02690 140.03027 141.03238 6.70 0.66 

*The mass of the electron was not subtracted from ion masses. The calibrant ion closest in mass to each analyte ion was automatically chosby the software and differed by no more than 7 Da from the analyte ion mass. Hence, this oversight had no significant effect on determinincompositions. For example, 0.00055 Da, the mass of an electron, is 3.0 ppm of 180.98882 Da, the mass of a perfluorokerosene ion, and 2.of 187.97772 Da, a mass about 7 Da greater. These two errors nearly cancel out. 

27
 
Table 2. Compounds Confirmed with Standards by Retention Times and Mass Spectra
 

(M+1) 

Apparent Monoisotopic Ion (M+1) Profile (M+2) Profile Profile 

Note Identified Compound Molecular Ion or Exact Mass Exact Mass Exact Mass Relative 

Fragment Ion (F) (ppm Mass Error) (ppm Mass Error) (ppm Mass Error) Isotopic 

Abundance 

§ dibromochloromethane CHBr2Cl+ 205.81372 (+4.5) 

‡ Fragment CHBrCl+ (F) 126.89563 (+4.9) 127.89837 (

S 0.2) 128.89341 (+5.1) 1.16 

§‡ Bromoform CHBr3 + 249.76279 (

S0.2) 251.76073 (

S0.2) 

§ p-benzoquinone 

C6H4O2 + 108.02103 (+4.2) 

§‡ Phenol 

C6H6O+ 94.04147 (

S4.1) 95.04491 (

S3.6) 96.04691 (

S4.5) 5.83 

§‡ Benzonitrile 

C7H5N+ 103.04231 (+1.1) 104.04557 (+0.4) 7.26 

§‡ octamethylcyclotetrasiloxane 

C7H21

O4Si4 + (F) 281.05181 (+2.3) 28.06 

§‡ 1,3-dichlorobenzene 

C6H4Cl2 + 145.96897 (

S0.3) 147.96528 (

S5.3) 

§ 1,4-dichlorobenzene 

C6H4Cl2 + † † 

§ 1,2-dichlorobenzene 

C6H4Cl2 + † † 

§‡ 2-bromotoluene 

C7H7Br+ 169.97383 (+4.2) 170.97730 (+4.7) 171.97191 (+4.8) 7.80 

§ 4-bromotoluene 

C7H7Br+ † † 

§‡ 2-bromophenol 

C6H5OBr+ 171.95246 (+0.5) 172.95582 (+0.3) 173.95035 (0) 6.24 

§ 2-cresol 

C7H8O+ 108.05750 (

S0.1) 109.06053 (

S3.5) 

§ 4-cresol &/or 3-cresol 

C7H8O+ † † 

§‡! ┌ 2-bromo-m-xylene 

C8H9Br+ 183.98824 (

S2.8) 184.99152 (

S3.5) 185.98610 (

S3.4) 

| 2-bromo-p-xylene | 4-bromo-m-xylene 

└ 5-bromo-m-xylene 

§‡ 2,4-dichlorophenol 

C6H4OCl2 + 161.96397 (+0.3) 162.96732 (+0.1) 163.96168 (+4.1) 

§‡ 2-iodophenol 

C6H5OI+ 219.93957 (+4.8) 220.94311 (+5.5) 6.58 

§‡ 4- &/or 3-iodophenol 

C6H5OI+ † † † 

§‡* 4- &/or 3-chlorophenol 

C6H5OCl+ 128.00303 (+1.1) 129.00638 (+0.8) 130.00012 (+1.0) 6.21 

§‡ Benzothiazole 

C7H5NS+ 135.01366 (

S4.5) 136.01735 (+0.1) 137.00957 (

S4.3) 

28 
+ § 4-methyl-2-nitrophenol C7H7NO3 153.04207 (S3.4) 154.04531 (S3.3) 155.04760 (+0.7)
 

+
 § 3-methyl-2-nitrophenol C7H7NO3 153.04188 (S4.6) 7.82 

§ 2-bromo-4-chlorophenol C6H4OClBr+ 205.91256 (S4.1) 206.91597 (S4.0) 207.91038 (S3.7) 

§ 4-bromo-2-chlorophenol C6H4OClBr+ † † † 

§‡ 2-bromomesitylene C9H11Br+ 198.00450 (+0.5) 200.00221 (S0.9) 

§‡* 4- &/or 3-bromophenol C6H5OBr+ 171.95246 (+0.5) 172.95582 (+0.3) 173.95035 (0) 6.25 

§‡ 4-tert-butylphenol C10H14O+ 150.10520 (+4.9) 151.10786 (-0.1) 

+ §‡ 2,4-dibromophenol C6H4OBr2 249.86401 (+4.5) 250.86743 (+4.6) 251.86197 (+4.4) 6.84 + §‡ 2,6-dibromophenol C6H4OBr2 † †	 † † 

§ 4-bromo-3-methylphenol C7H7OBr+ 185.96720 (S4.4) 187.96518 (S4.5) 8.20 

+ §‡ Biphenyl	 C12H10 154.07765 (S3.9) 155.08101 (S4.0) 156.08467 (S2.2) 11.92 

§‡ diphenyl ether C12H10O+ 170.07320 (+0.2) 171.07666 (+0.6) 172.08038 (+5.3) 12.36
 

+
 § dimethyl phthalate C9H7O3 (F) 163.03898 (S3.3) 164.04287 (S0.2) 165.04411 (S4.5)
 

§# 2,4-di-tert-butylphenol C14H22O+ 206.16627 (S3.9) 207.16999 (S2.4) 13.83
 

§ DEET C12H17NO+ 191.13046 (S2.7) 192.13354 (S3.5)
 

+ §# diethyl phthalate C10H9O3	 (F) 177.05459 (S3.3)
 

+
 § 2,4,6-tribromophenol C6H3OBr3 327.77222 (S3.6)	 329.77027 (S3.3) 

§‡ 4-bromodiphenylether C12H9OBr+ 247.98304 (S2.6) 248.9873 (+1.0) 249.9813 (S1.6) 12.40 

+ §‡# anthracene/phenanthrene C14H10 178.07764 (S3.4) 179.08240 (+4.3) 15.69 

§ Pyrene C16H10 + 202.07741 (S4.2) 203.08099 (S3.2) 204.08511 (+0.5) 

§ Fluoranthene C16H10 + † † † 

§# Triphenylphosphate C18H15O4P+ 326.07066 (S0.4) 327.07433 (+0.4) 328.07664 (S0.6) 20.37 

§ The tentative identification was confirmed using a purchased standard. ‡ Only one composition was possible. No assumptions regarding the presence of P or F atoms were necessary. † The exact masses and RIAs were measured for a different isomer. ! These four isomers co-elute and cannot be distinguished from each other. * The RTs for both standards were indistinguishable. The para isomer is more likely based on electrophilic reaction chemistry. # Also found in the blank. 

29
 
Table 3. Tentatively Identified Compounds 

(M

Apparent Monoisotopic Ion (M+1) Profile (M+2) Profile Pr

Note Tentatively Identified Compound Molecular Ion or Exact Mass Exact Mass Exact Mass Re

Fragment Ion (F) (ppm Mass Error) (ppm Mass Error) (ppm Mass Error) Iso

Abu

‡ Dichloroethylene C2H2Cl2 + 95.95331 (S0.5) 96.95627 (S4.8) 97.95046 (+0.5) 

‡ Dibromomethane CH2Br2 + 171.85159 (S4.1) 173.84953 (S4.3) 1

‡! Toluene C7H8 + 92.06199 (S6.6) 93.06551 (S5.3) 94.06928 (S1.3) 7

‡ 2-methyl-1-butanal C5H10O+ 86.07284 (S3.7) 87.07625 (S3.8) 

‡ Xylene C8H10 + 106.07780 (S 4.2) 107.08132 (S 3.0) 108.08472 (S3.1) 8

‡ Xylene C8H10 + 106.07842 (+1.6) 107.08192 (+2.6) 8

Xylene C8H10 + † † † 

‡ 3-decanol C8H17O+ (F) 129.12769 (S1.9) 9

‡ Chlorotoluene C7H7Cl+ 126.02363 (0) 127.02759 (+4.5) 128.02068 (S0.2) 

Chlorotoluene C7H7Cl+ † † † 

1,3-dibromo-3-methylbutane C5H10Br+ (F) 148.99652 (S0.5) 150.99438 (S1.1) 

‡ 3,6-dimethyl-3-heptanol C8H17O+ (F) 129.12769 (S1.9) 

‡ alpha-methylbenzyl alcohol C8H10O+ 122.07286 (S2.5) 123.07641 (S1.2) 9

‡ acetyl hydroxy methylcyclohexane C7H13O+ (F) 113.09662 (S0.2) 114.09973 (S2.9) 8

‡ Nitrophenol C6H5NO3 + 139.02690 (S0.3) 140.03027 (S0.1) 141.03238 (+5.0) 

‡ Nitrophenol C6H5NO3 + 139.02641 (S3.8) 140.02965 (S4.5) 141.03102 (S4.7) 6

◊ decamethylcyclopentasiloxane C9H27O5Si5 + (F) 355.06904 (S4.1) 356.06952 (S4.7) 357.06716 (S4.3) 1

2-hydroxy acetophenone C8H8O2 + 136.05256 (+1.0) 137.05638 (+4.1) 138.05737 (S3.6) 

‡ 1-bromo-2-butanone C4H7OBr+ 149.96873 (+4.7) 151.96672 (+4.8) 

‡! dibromochlorobenzene C6H3Br2Cl+ 267.82676 (S8.4) 268.82974 (S9.8) 269.82563 (S4.4) 

‡ 2,4,6-trichlorophenol C6H3OCl3 + 195.92505 (+0.5) 196.92833 (0) 197.92219 (+0.9) 

‡ bromomethylphenol C7H7OBr+ 185.96720 (S4.5) 187.96518 (S4.4) 8

5-bromo-4-hydroxy-m-cymene C10H13OBr+ 228.01517 (+0.8) 229.01827 (S0.5) 230.01301 (+0.2) 

‡# surfynol 104 C10H15O+ (F) 151.11218 (S0.7) 152.11571 (+0.1) 153.11858 (+0.7) 1

‡ bromonitrophenol C6H4NO3Br+ 216.93831 (+3.9) 218.93542 (S0.2) 

30 
‡ bromonitrophenol C6H4NO3Br+ 216.93806 (+2.8)	 218.93480 (S3.1) 

‡	 bromodichlorophenol C6H3OCl2Br+ 239.87462 (+0.8) 241.87240 (+1.5) 

+ ‡	 dibromomethylphenol C7H6OBr2 263.87734 (S4.5) 265.86197 (S4.8)
 +
 dibromomethylphenol C7H6OBr2 † †
 

bromoiodophenol C6H4OBrI+ 297.84953 (+1.7) 298.85234 (S0.2) 299.84837 (+4.6) 

bromoiodophenol C6H4OBrI+ † † † 

bromoiodophenol C6H4OBrI+ † † † 

+ chlorodibromophenol C6H3OClBr2 283.82286 (S3.7) 285.82089 (S3.0) + chlorodibromophenol C6H3OClBr2 † † 

+ 2-phenoxyphenol C12H10O2 186.06715 (S5.0) 1

+ ‡ 4-methoxy-nitrobenzene C7H7NO3 153.04207 (S3.4) 154.04531 (S3.3) 155.04760 (+0.7) 

‡	 Benzophenone C13H10O+ 182.07322 (+0.3) 183.07661 (+0.3) 184.07867 (S4.6) 1

+
 2-acetyl-6-methoxynaphthalene C13H12O2 200.08288 (S4.2) 201.08640 (S3.6) 202.08886 (S4.7)
 

+
 ‡#! 2,2'-diethylbiphenyl C16H18 210.13884 (S9.6) 211.14315 (S5.2)	 1

dibromoiodophenol C6H3OBr2I+ 375.76124 (+4.6) 377.75767 (+0.5) 

*# butylbenzylphthalate C12H14O3+ (F) 206.09385 (S2.1) 208.10120 (+5.6) 1

‡*# di-2-ethylhexyl adipate C14H27O4+ (F) 259.18978 (S4.4) 260.19459 (+0.8) 261.19765 (+3.4) 1

*# bis(2-ethylhexyl)phthalate C16H23O4+ (F) 279.15863 (S3.6) 280.16325 (+0.7) 

‡ Only one composition was possible. No assumptions regarding the presence of P or F atoms were necessary. ! 12-ppm mass error limits used. † The exact masses and RIAs were measured for a different isomer. # Also found in the blank. * Fragment ion 

31
 
Figure 1. 

32
 
33
 
34
 
Figure 2. 

35 
Figure 3 

36
 
Figure 4. 

37