Dean’s Analytical Chemistry Handbook 2nd Edition by Pradyot Patnaik 2

Source: DEAN’S ANALYTICAL CHEMISTRY HANDBOOK

SECTION 10

MASS SPECTROMETRY
10.1 INSTRUMENT DESIGN
Figure 10.1 Components of a Mass Spectrometer
10.1.1 Inlet Sample Systems
10.2 IONIZATION METHODS IN MASS SPECTROMETRY
10.2.1 Electron Ionization
10.2.2 Chemical Ionization
10.2.3 Other Ionization Methods
10.3 MASS ANALYZERS
10.3.1 Magnetic-Deflection Mass Analyzer
10.3.2 Double-Focusing Sector Spectrometers
10.3.3 Quadrupole Mass Analyzer
10.3.4 Time-of-Flight Spectrometer
Figure 10.2 Quardrupole Mass Analyzer
10.3.5 Ion-Trap Mass Spectrometer
10.3.6 Additional Mass Analyzers
10.3.7 Resolving Power
10.4 DETECTORS
10.4.1 Electron Multiplier
10.4.2 Faraday Cup Collector
10.5 CORRELATION OF MASS SPECTRA WITH MOLECULAR STRUCTURE
10.5.1 Molecular Identification
10.5.2 Natural Isotopic Abundances
Table 10.1 Isotopic Abundances and Masses of Selected Elements
10.5.3 Exact Mass Differences
10.5.4 Number of Rings and Double Bonds
10.5.5 General Rules

10.5.6 Metastable Peaks
10.6 MASS SPECTRA AND STRUCTURE
10.6.1 Initial Steps in Elucidation of a Mass Spectrum
10.6.2 General Rules for Fragmentation Patterns
10.6.3 Characteristic Low-Mass Fragment Ions
10.6.4 Characteristic Low-Mass Neutral Fragments from the Molecular Ion
Table 10.2 Mass Spectra of Some Selected Compounds
10.7 SECONDARY-ION MASS SPECTROMETRY
10.8 ISOTOPE-DILUTION MASS SPECTROMETERY (IDMS)
10.9 QUANTITATIVE ANALYSIS OF MIXTURES
Table 10.3 Mass Spectral Data (Relative Intensities) for the C1 to C3 Alcohols
10.10 HYPHENATED GC-MS AND LC-MS TECHNIQUES
10.10.1 GC-MS
10.10.2 LC-MS
Bibliography

10.2
10.2
10.2
10.3
10.3
10.3
10.4
10.4
10.5
10.5
10.5
10.5
10.6
10.6

10.7
10.7
10.7
10.7
10.8
10.8
10.8
10.8
10.8
10.9
10.10
10.10
10.10
10.11
10.11
10.11
10.12
10.12
10.13
10.23
10.24
10.24
10.25
10.26
10.26
10.27
10.28

10.1
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MASS SPECTROMETRY

10.2

SECTION TEN

Mass spectrometry is the analytical technique that provides the most structural information for the least
amount of analyte material. It provides qualitative and quantitative information about the atomic and
molecular composition of inorganic and organic materials and their chemical structures. As an analytical technique it possesses distinct advantages:
1. Increased sensitivity over most other analytical techniques because the analyzer, as a mass-charge
filter, reduces background interference.
2. Excellent specificity from characteristic fragmentation patterns to identify unknowns or confirm
the presence of suspected compounds.
3. Information about molecular weight.
4. Information about the isotopic abundance of elements.
Mass spectrometry often fails to distinguish between optical and geometrical isomers and the
positions of substituent in o-, m- and p- positions in an aromatic ring. Also, its scope is limited in
identifying hydrocarbons that produce similar fragmented ions.
Sec. 20 and in the environmental analysis of trace organic pollutants is highlighted in Sec. 21.

10.1 INSTRUMENT DESIGN
Functionally, all mass spectrometers have these components (Fig. 10.1): (1) inlet sample system,
(2) ion source, (3) ion acceleration system, (4) mass (ion) analyzer, (5) ion-collection system, usually an electron multiplier detector, (6) data-handling system, and (7) vacuum system connected to
components (1) through (5). To provide a collision-free path for ions once they are formed, the pressure in the spectrometer must be less than 10–6 torr.
10.1.1 Inlet Sample Systems
Gas samples are transferred from a vessel of known volume (3 mL), where the pressure is measured,

into a reservoir (3 to 5 L). Volatile liquids are drawn through a sintered disk into the low-pressure
reservoir in which they are vaporized instantly. Oftentimes a nonvolatile compound can be converted
into a derivative that has sufficient vapor pressure.
The gaseous sample enters the source through a pinhole in a piece of gold foil. For analytical
work, molecular flow (where the mean free path of gas molecules is greater than the tube diameter)
is usually preferred. However, in isotope-ratio studies viscous flow (where the mean free path is

FIGURE 10.1 Components of a mass spectrometer. (From Shugar and Dean, The Chemist’s Ready
Reference Handbook, McGraw-Hill, New York, 1990.)

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MASS SPECTROMETRY

MASS SPECTROMETRY

10.3

smaller than the tube diameter) is employed to avoid any tendency for various components to flow
differently from the others.

10.2 IONIZATION METHODS IN MASS SPECTROMETRY
Ionization methods in mass spectrometry are divided into gas-phase ionization techniques and methods that form ions from the condensed phase inside the ion source. All ion sources are required to
produce ions without mass discrimination from the sample and to accelerate them into the mass analyzer. The usual source design has an ion withdrawal and focusing system. The ions formed are
removed electrostatically from the chamber. Located behind the ions is the repeller, which has the
same charge as the ions to be withdrawn. A strong electrostatic field between the first and second
accelerating slits of 400 to 4000 V, which is opposite in charge to the ions, accelerates the ions to

their final velocities.

10.2.1 Electron Ionization
The electron ionization source is a commonly used ionization method. The ionizing electrons from
the cathode of an electron gun located perpendicular to the incoming gas stream collide with the sample molecules to produce a molecular ion. A source operating at 70 V, the conventional operating
potential, also has sufficient energy to cause the characteristic fragmentation of sample molecules.
Some compounds do not produce a molecular ion in an electron ionization source. This is a disadvantage of this source.
A mass spectrometer is calibrated in the electron ionization mode. Perfluoroalkanes are often
used as markers because they provide a peak at intervals of masses corresponding to CF2 groups.

10.2.2 Chemical Ionization1
Chemical ionization results from ion–molecule chemical interactions that involve a small amount of
sample with an exceedingly large amount of a reagent gas. The source must be tightly enclosed with
an inside pressure of 0.5 to 4.0 torr. The pressure outside the source is kept about 4 orders of magnitude less than the inside by a differential pumping system.
Often the primary reason for using this technique is to determine the molecular weight of a compound. For this purpose a low-energy reactant, such as tert-C4H9+ (from isobutane) is frequently used.
In the first step the reagent gas is ionized by electron ionization in the source. Subsequent reactions
between the primary ion and additional reagent gas produce a stabilized reagent gas plasma. When
a reagent ion encounters a sample molecule (MH), several products may be formed:
MH2+ by proton transfer
M+ by hydride abstraction
MH+ by charge transfer
Practically all the spectral information will be clustered around the molecular ion, or one mass unit
larger or smaller, with little or no fragmentation. This type of ionization is desirable when an analysis of a mixture of compounds is needed and the list of possible components is limited. The general
absence of carbon–carbon cleavage reactions for the chemical ionization spectra means that they
provide little skeletal information.

1

B. Munson, “Chemical Ionization Mass Spectrometry,” Anal. Chem. 49:772A (1977).

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MASS SPECTROMETRY

10.4

SECTION TEN

Negative chemical ionization2 can be conducted with hydroxide and halide ions. For these studies the charges on the repeller and accelerating slits in the ion source are reversed with the repeller
having a negative charge.

10.2.3 Other Ionization Methods
The less frequently used ionization methods receive only brief mention here. For more details consult the references cited.
Field ionization3 and field desorption4 are techniques used for studying surface phenomena, such
as adsorbed species and trapped samples, and the results of chemical reactions on surfaces; they are
also suitable for handling large lipophilic polar molecules.
Fast atom bombardment5 and plasma (californium-252) desorption6 techniques deal rather effectively with polar substances (usually of higher molecular weight) and salts. Samples may be bulk
solids, liquid solutions, thin films, or monolayers.
In thermal ionization the sample is put on a filament substrate (a metal ribbon), which is heated in
the mass spectrometer source until the sample evaporates (ca. 2000°C). Filament-loading procedures
tend to be element-specific. Both positive and negative ions are produced, and thermal ionization usually results in the formation of long-lived, stable ion beams. Thermal ionization is appropriate for
inorganic compounds that have ionization potentials in the range from 3 to 6 eV. On the other hand,
the technique is inefficient for organic compounds because their ionization potentials usually range
from 7 to 16 eV.
Laser desorption methods7–9 produce a microplasma that consists of neutral fragments together
with elementary molecular and fragment ions. Suitable mass spectrometers are limited to time-offlight and Fourier-transform spectrometers.
The recent development of electrospray ionization10 has extended the range of masses amenable

to study by mass spectrometery to above several hundred kilodaltons, and commercial instruments
are available.

10.3 MASS ANALYZERS
The function of the mass analyzer is to separate the ions produced in the ion source according to their
different mass–charge ratios. The analyzer section is continuously pumped to a very low vacuum so
that ions may be passed through it without colliding with the gas molecules. The energies and velocities v of the ions moving into the mass analyzer are determined by the accelerating voltage V from
the ion source slits and the charge z on the ions of mass m:
1
1
1
m1v12 = m2 v22 = m3 v32 = L = zV
2
2
2

2

(10.1)

R. C. Dougherty, “Negative Chemical Ionization Mass Spectrometry,” Anal. Chem. 53:625A (1981).
M. Anbar and W. H. Aberth, “Field Ionization Mass Spectrometry,” Anal. Chem. 46:59A (1974).
4 W. D. Reynold, “Field Desorption Mass Spectrometry,” Anal. Chem. 51:283A (1979).
5 M. Barber et al., “Fast Atom Bombardment Mass Spectrometry,” Anal. Chem. 54:645A (1982).
6 R. D. MacFarlane, “Californium-252 Plasma Desorption Mass Spectrometry,” Anal. Chem. 55:1247A (1983).
7 R. J. Cotter, “Lasers and Mass Spectrometry,” Anal. Chem. 56:485A (1984).
8 E. R. Denoyer et al., “Laser Microprobe Mass Spectrometry: Basic Principles and Performance Characteristics,” Anal.
Chem. 54:26A (1982).
9 D. M. Hercules et al., “Laser Microprobe Mass Spectrometry: Applications to Structural Analysis,” Anal. Chem. 54:280A
(1980).

10 C. M. Whitehouse et al., Anal. Chem. 57:675 (1985).
3

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MASS SPECTROMETRY

MASS SPECTROMETRY

10.5

10.3.1 Magnetic-Deflection Mass Analyzer
In a single-focusing magnetic-sector mass analyzer, the ion source, the collector slit, and the apex of
the sector shape (usually 60°) are colinear. Upon entering the magnetic field, the ions are classified
and segregated into beams, each with a different m/z ratio.
m H 2r2
=
2V
z

(10.2)

where H is the strength of the magnetic field and r is the radius of the circular path followed by the
ions. Since the radius and the magnetic field strength are fixed for the particular sector instrument,
only ions with the proper m/z ratio will pass through the analyzer tube without striking the walls,
where they are neutralized and pumped out of the system as neutral gas molecules. Focusing is
accomplished by changing either the electrostatic accelerating voltage or the magnetic field strength;

often the former is allowed to diminish while the spectrum is scanned. Each m/z ion from light to
heavy is successively swept past the detector slit at a known rate. The detector current is amplified
and displayed on a strip-chart recorder. Since the ion paths are separated from one another, the
recorder signal will fall to the baseline and then rise as each mass strikes the detector. The height of
the peaks on the chart will be proportional to the number of ions of the corresponding mass–
charge ratio.
A magnetic-sector mass analyzer has a mass range of 2500 Da at 4-kV ion accelerating voltage.
Mass resolution is continuously variable up to 25 000 (10% valley definition). Metastable peaks that
aid in structural elucidation are also recorded.

10.3.2 Double-Focusing Sector Spectrometers
Because single-focusing mass analyzers are not velocity focusing for ions of a given mass, their
resolving power is limited. In double-focusing mass spectrometers an electrostatic deflection field is
incorporated between the ion source and the magnetic analyzer. Resolving power lies in the range of
100 000. Additional focusing is achieved with quadrupole lenses placed before the electrostatic field
and between the electrostatic and magnetic fields.

10.3.3 Quadrupole Mass Analyzer
In the quadrupole mass analyzer, ions from the ion source are injected into the quadrupole array,
shown in Fig. 10.2. Opposite pairs of electrodes are electrically connected; one pair at +Udc volts and
the other pair at −Udc volts. An rf oscillator supplies a signal to each pair of rods, but the signal to the
second pair is retarded by 180°. When the ratio Udc/Vrf is controlled, the quadrupole field can be set
to pass ions of only one m/z ratio down the entire length of the quadrupole array. When the dc and rf
amplitudes are changed simultaneously, ions of various mass–charge ratios will pass successively
through the array to the detector and an entire mass spectrum can be produced.
Registration of negative ions, as from a chemical ionization source, is possible with two electron
multipliers, one for positive and one for negative ions.
Scan rates can reach 780 Da ⋅ s–1 before resolution is significantly affected. The quadrupole mass
analyzer is ideal for coupling with a gas chromatograph. Practical m/z limits are 4000 Da.

10.3.4 Time-of-Flight Spectrometer
In the time-of-flight (TOF) mass spectrometer, the ions leave the source as discrete ion packets by
pulsing the voltage on the accelerating slits at the exit of the ion source. Upon leaving the accelerating slits, the ions enter into the field-free region (drift path) of the flight tube, 30 to 100 cm long,

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MASS SPECTROMETRY

10.6

SECTION TEN

FIGURE 10.2 Quadrupole mass analyzer. (From Shugar and Dean, 1990.)

with whatever velocity they have acquired [Eq. (15.1)]. Because their velocities are inversely proportional to the square roots of their masses, the lighter ions travel down the flight tube faster than
the heavier ions. The original ion packet becomes separated into “wafers” of ions according to their
mass–charge ratio. The wafers are collected sequentially at the detector.
A spectrum can be recorded every 10 s. This makes the TOF mass spectrometer suitable for
kinetic studies and for coupling with a gas chromatograph to examine effluent peaks.

10.3.5 Ion-Trap Mass Spectrometer
A quadrupole ion-trap consists of three electrodes; two end-cap electrodes normally are held at ground
potential and between them a ring electrode to which an rf potential, often in the megahertz range, is
applied to generate a quadrupole electric field. These components can be held in the palm of the hand.
Ionization in ion traps is commonly achieved by electron ionization, which occurs within the trap.
Chemical ionization uses the variable time scale of the ion trap first to generate reagent ions via electron impact and then allows these reagent ions to react with the vaporized analyte molecules. Both
ionization methods are limited to gaseous samples.

Desorption ionization methods enable mass spectrometry application to fragile nonvolatile compounds, which can be implemented by forming ions in an external source by fast ion bombardment
or secondary ion mass spectrometry, and then injecting them into the trap. Although trapped ions can
be mass-analyzed by several methods, a mass-selective instability scan is used most commonly. In
this procedure, a change in operating voltages is used to cause trapped ions of a particular m/z ratio
to adopt unstable trajectories. By scanning the amplitude of the rf voltage applied to the ring electrode, ions of successively increasing m/z are made to adopt unstable trajectories and to exit the ion
trap, where they can be detected by using an externally mounted electron multiplier. Other methods
for mass analysis have been described.11

11 R.

G. Cooks et al., Chem. Eng. News 1991(March 25):26.

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MASS SPECTROMETRY

MASS SPECTROMETRY

10.7

10.3.6 Additional Mass Analyzers
Space precludes more than mention of the more sophisticated mass analyzers, such as the Fouriertransform (ion-trap) mass spectrometer,12,13 tandem mass spectrometers,14 triple quadrupole mass
spectrometer,15 and inductively coupled plasma–mass spectrometer.16 Triple quadrupole instruments
are now routinely used in protein structure determinations, pesticide residue analysis, and drug
metabolism studies.
10.3.7 Resolving Power
The most important parameter of a mass analyzer is its resolving power. Using the 10% valley definition, two adjacent peaks (whose mass differences are ∆m) are said to be separated when the valley between them is 10% or less of the peak height (and the peak heights are approximately equal).

For this condition, ∆m/m equals the peak width at a height that is 5% of the individual peak height.
A resolution of 1 part in 800 adequately distinguishes between m/z values 800 and 801 so long
as the peak intensity ratio is not greater than 10 to 1. However, if one wanted to distinguish between
the parent peaks of 2,2-naphthylbenzothiophene (260.0922) and 1,2-dimethyl-4-benzoylnaphthalene
(260.1201), the required resolving power is
m
260
=
= 9319
∆ m 260.1201 − 260.0922

(10.3)

10.4 DETECTORS
After leaving a mass analyzer, the resolved ion beams sequentially strike some type of detector. The
electron multiplier, either single or multichannel, is most commonly used.

10.4.1 Electron Multiplier
In the electron multiplier the ion beam strikes a conversion dynode, which converts the ion beam to
an electron beam. A discrete dynode multiplier has 15 to 18 individual dynodes arranged in a venetian blind configuration and coated with a material that has high secondary-electron-emission properties. A magnetic field forces the secondary electrons to follow circular paths, causing them to strike
successive dynodes.
A microchannel plate is a solid-state electron multiplier composed of a hexagonal closepacked array of millions of independent, continuous, single-channel electron multipliers all fused
together in a rigid parallel array. With channel densities on the order of 106 per cm2, these devices
are one of the highest pixel density sensors known. Pore diameters range from 10 to 25 mm. The
inside of each pore, or channel, is coated with a secondary-electron-emissive material; thus each
channel constitutes an independent electron multiplier. The onset of ion feedback within the
channel can be staved off by curving each channel in the plate but at the cost of considerable
spatial distortion.
12 M. V. Buchanan and R. L. Hettich, “Fourier Transform Mass Spectrometry of High-Mass Biomolecules,” Anal. Chem.
65:245A (1993).

13 A. G. Marshall and L. Schweikhard, Int. J. Mass Spectrom. Ion Proc. 118/119:37 (1992).
14 J. V. Johnson and R. A. Yost, “Tandem Mass Spectrometry for Trace Analysis,” Anal. Chem. 57:758A (1985).
15 R. A. Yost and C. G. Enke, “Triple Quadrupole Mass Spectrometry for Direct Mixture Analysis and Structure Elucidation,”
Anal. Chem. 51:1251A (1979).
16 R. S. Houk, “Mass Spectrometry of Inductively Coupled Plasma,” Anal. Chem. 58:97A (1986).

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MASS SPECTROMETRY

10.8

SECTION TEN

10.4.2 Faraday Cup Collector
The Faraday cup collector consists of a cup with suitable suppressor electrodes, to suppress
secondary-ion emission, and guard electrodes. It is placed in the focal plane of the mass spectrometer.

10.5 CORRELATION OF MASS SPECTRA
WITH MOLECULAR STRUCTURE
10.5.1 Molecular Identification
In the identification of a compound, the most important information is the molecular weight. The
mass spectrometer is able to provide this information, often to four decimal places. One assumes that
no ions heavier than the molecular ion form when using electron-impact ionization. The chemical
ionization spectrum will often show a cluster around the nominal molecular weight.
Several relationships aid in deducing the empirical formula of the parent ion (and also molecular
fragments). From the empirical formula hypothetical molecular structures can be proposed using the

entries in the formula indices of Beilstein (Beilsteins Handbuch der Organischen Chemie) and
Chemical Abstracts.

10.5.2 Natural Isotopic Abundances
The relative abundances of natural isotopes produce peaks one or more mass units larger than the
parent ion (Table 10.1a). For a compound CwHxNyOz, there is a formula that allows one to
calculate the percentage of the heavy isotope contributions from a monoisotopic peak PM to
the PM +1 peak:
100

PM +1
PM

= 0.015 x + 1.11w + 0.37 y + 0.037z

(10.4)

TABLE 10.1 Isotopic Abundances and Masses of Selected Elements
(a) Abundances of some polyisotopic elements, %
Element
1H
2H
12C
13C
14N
15N

Abundance
99.985
0.015

98.892
1.108
99.63
0.37

Element

Abundance

Element

Abundance

16O

99.76
0.037
0.204
92.18
4.71
3.12

33S

0.76
4.22
75.53
24.47
50.52
49.48

17O
18O
28Si
29Si
30Si

34S
35Cl
37Cl
79Br
81Br

(b) Selected isotope masses
Element

Mass

Element

Mass

1H

1.0078
12.0000
14.0031
15.9949
18.9984
27.9769

31P

30.9738
31.9721
34.9689
55.9349
78.9184
126.9047

12C
14N
16O
19F
28Si

32S
35Cl
56Fe
79Br
127I

Source: J. A. Dean, ed., Lange’s Handbook of Chemistry, 14th ed., McGraw-Hill, New York, 1992.

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MASS SPECTROMETRY

10.9

Tables of abundance factors have been calculated for all combinations of C, H, N, and O up to mass
500.17
Compounds that contain chlorine, bromine, sulfur, or silicon are usually apparent from prominent
peaks at masses 2, 4, 6, and so on, units larger the nominal mass of the parent or fragment ion. For
example, when one chlorine atom is present, the P + 2 mass peak will be about one-third the intensity of the parent peak. When one bromine atom is present, the P + 2 mass peak will be about the
same intensity as the parent peak. The abundance of heavy isotopes is treated in terms of the binomial expansion (a + b)m, where a is the relative abundance of the light isotope, b is the relative abundance of the heavy isotope, and m is the number of atoms of the particular element present in the
molecule. If two bromine atoms are present, the binomial expansion is
( a + b) 2 = a 2 + 2 ab + b 2

(10.5)

Now substituting the percent abundance of each isotope (79Br and 81Br) into the expansion:
(0.505) 2 + 2(0.505)(0.495) + (0.495) 2
gives
0.255 + 0.500 + 0.250
which are the proportions of P:(P + 2):(P + 4), a triplet that is slightly distorted from a 1:2:1 pattern. When two elements with heavy isotopes are present, the binomial expansion
( a + b ) m (c + d ) n
is used.
Sulfur-34 enhances the P + 2 peak by 4.22%; silicon-29 enhances the P + 1 peak by 4.71% and
the P + 2 peak by 3.12%.

10.5.3 Exact Mass Differences
If the exact mass of the parent or fragment ions is ascertained with a high-resolution mass spectrometer, this relationship is often useful for combinations of C, H, N, and O (Table 10.1b):
Exact mass difference from nearest
integral mass + 0.0051z − 0.0031y

= number of hydrogens
0.0078

(10.6)

One substitutes integral numbers (guesses) for z (oxygen) and y (nitrogen) until the divisor becomes
an integral multiple of the numerator within 0.0002 mass unit.
For example, if the exact mass is 177.0426 for a compound containing only C, H, O, and N (note
the odd mass which indicates an odd number of nitrogen atoms), thus
0.0426 + 0.0051z − 0.0031y
= 7 hydrogen atoms
0.0078

17

J. H. Beynon and A. E. Williams, Mass and Abundance Tables for Use in Mass Spectrometry, Elsevier, Amsterdam, 1963.

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MASS SPECTROMETRY

10.10

SECTION TEN

when z = 3 and y = 1. The empirical formula is C9H7NO3 since
177 − 7(1) − 1(14) − 3(16)

= 9 carbon atoms
12
10.5.4 Number of Rings and Double Bonds
The total number of rings and double bonds can be determined from the empirical formula
(CwHxIzNy) by the relationship
1
2( 2 w − x + y + 2 )
when covalent bonds comprise the molecular structure. Remember the total number for a benzene
ring is 4 (one ring and three double bonds); for a triple bond it is 2.
10.5.5 General Rules
1. If the nominal molecular weight of a compound containing only C, H, O, and N is even, so is the
number of hydrogen atoms it contains.
2. If the nominal molecular weight is divisible by 4, the number of hydrogen atoms is also divisible
by 4.
3. When the nominal molecular weight of a compound containing only C, H, O, and N is odd, the
number of nitrogen atoms must be odd.

10.5.6 Metastable Peaks
A further means of ion characterization is achieved by monitoring specific fragmentations of a chosen parent ion. This approach involves monitoring of metastable peaks that correspond to fragmentation that occurs in the first field-free region of a double-focusing mass spectrometer (also of a 60°
sector instrument). The field-free region is between the exit of the ion source and the entrance to the
mass analyzer. Signal detection is dictated by the mass-to-charge ratios of both parent and daughter
ions. Metastable peaks m* appear as a weak, diffuse (often humped-shaped) peak, usually at a nonintegral mass. The one-step decomposition process takes the general form
Original ion → daughter ion + neutral fragment

(10.7)

The relationship between the original ion and daughter ion is given by
m* =

( mass of daugher ion) 2

mass of original ion

(10.8)

For example, a metastable peak appeared at 147.9 mass units in a mass spectrum with prominent
peaks at 65, 91, 92, 107, 108, 155, 172, and 200 mass units. After trying all possible combinations
in the above expression, the fit is given by
147.9 =

(172) 2
200

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MASS SPECTROMETRY

MASS SPECTROMETRY

10.11

which provides this information:
200+ → 172+ + 28
The probable neutral fragment lost is either CH2 = CH2 or CO.

10.6 MASS SPECTRA AND STRUCTURE
The mass spectrum is a fingerprint for each compound because no two molecules are fragmented and
ionized in exactly the same manner on electron-impact ionization. When mass spectra are reported,

the data are normalized by assigning the most intense peak (denoted as base peak) a value of 100.
Other peaks are reported as percentages of the base peak.
A very good general survey for interpreting mass spectral data is given by Silverstein et al.18

10.6.1 Initial Steps in Elucidation of a Mass Spectrum
1. Tabulate the prominent ion peaks, starting with the highest mass.
2. usually only one bond is cleaved. In succeeding fragmentations a new bond is formed for each
additional bond that is broken.
3. When fragmentation is accompanied by the formation of a new bond as well as by the breaking
of an existing bond, a rearrangement process is involved. These will be even mass peaks when
only C, H, and O are involved. The migrating atom is almost exclusively hydrogen; six-membered
cyclic transition states are most important.
4. Tabulate the probable groups that (a) give rise to the prominent charged ion peaks and (b) list the
neutral fragments.

10.6.2 General Rules for Fragmentation Patterns
1. Bond cleavage is more probable at branched carbon atoms: tertiary > secondary > primary. The
positive charge tends to remain with the branched carbon.
2. Double bonds favor cleavage in a beta position to the carbon (but see rule 6).
3. A strong parent peak often indicates a ring.
4. Saturated ring systems lose side chains at the alpha position carbon. Upon fragmentation, two ring
atoms are usually lost.
5. A heteroatom induces cleavage at the bond in the beta position to it.
6. Compounds that contain a carbonyl group tend to break at this group; the positive charge remains
with the carbonyl portion.
7. For linear alkanes, the initial fragment lost is an ethyl group (never a methyl group), followed by
propyl, butyl, and so on. An intense peak at mass 43 suggests a chain longer than butane.
8. The presence of Cl, Br, S, and Si, can be deduced from the unusual isotopic abundance patterns of these elements. These elements can be traced through the positively charged

18 R. M. Silverstein, G. C. Bassler, and T. C. Morrill, Spectrophotometric Identification of Organic Compounds, 5th ed.,

Wiley, New York, 1991.

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MASS SPECTROMETRY

10.12

SECTION TEN

fragments until the pattern disappears or changes due to the loss of one of these atoms to a
neutral fragment.
9. When unusual mass differences occur between some fragment ions, the presence of F (mass difference 19), I (mass difference 127), or P (mass difference 31) should be suspected.

10.6.3 Characteristic Low-Mass Fragment Ions
Mass 30 = Primary amines
Masses 31, 45, 59 = Alcohol or ether
Masses 19 and 31 = Alcohol
Mass 66 = Monobasic carboxylic acid
Masses 77 and 91 = Benzene ring

10.6.4 Characteristic Low-Mass Neutral Fragments from the Molecular Ion
Mass 18 (H 2 O) = From alcohols, aldehydes, ketones
Mass 19 (F) and 20 (HF) = Fluorides
Mass 27 (HCN) = Aromatic nitriles or nitrogen heterocycles
Mass 29 = Indicates either CHO or C2 H 5
Mass 30 = Indicates either CH 2 O or NO

Mass 33 (HS) and 34 (H 2 S) = Thiols
Mass 42 = CH 2 CO via rearrangement from a methyl ketone or an aromatic
acetate or an aryl -NHCOCH 3 group
Mass 43 = C 3 H 7 or CH 3 CO
Mass 45 = COOH or OC 2 H 5
Table 10.2 is condensed, with permission, from the Catalog of Mass Spectral Data of the
American Petroleum Institute Research Project 44. These, and other tables, should be consulted for
further and more detailed information.
Included in the table are all compounds for which information was available through the C7 compounds. The mass number for the five most important peaks for each compound are listed, followed
in each case by the relative intensity in parentheses. The intensities in all cases are normalized to the
n-butane 43 peak taken as 100. Another method for expressing relative intensities is to assign the
base peak a value of 100 and express the relative intensities of the other peaks as a ratio to the base
peak. Taking ethyl nitrate as an example, the tabulated values would be
Ethyl nitrate 91(0.01)(P) 46(100) 29(44.2) 30(30.5) 76(24.2)
The compounds are arranged in the table according to their molecular formulas. Each formula is
arranged alphabetically, except that C is first if carbon occurs in the molecules, followed by H if it
occurs. The formulas as then arranged alphabetically and according to increasing number of atoms
of each kind, all C4 compounds being listed before any C5 compounds, and so on.

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MASS SPECTROMETRY

MASS SPECTROMETRY

10.13

TABLE 10.2 Mass Spectra of Some Selected Compounds
Mass numbers (and intensities) of:
Molecular
formula
B2H6
B3H6N3
B5H9
CBrClF2
CBr2F2
CCl2F2
CCl3F
CCl4
CF3I
CF4
CHBrClF
CHBrF2
CHCl3
CHF3
CHN
CH2ClF
CH2Cl2
CH2F2
CH2O
CH2O2
CH3Cl
CH3F
CH3I
CH3NO2
CH4
CH4O

CH4S
CH5N
CO
COS
CO2
CS2
C2F4
C2F6
C2F6Hg
C2H2
C2H2ClN
C2H2Cl2
C2H2Cl2
C2H2Cl4
C2H2F2
C2H3Cl3
C2H3Cl3
C2H3F3
C2H3N
C2H4
C2H4BrCl
C2H4Br2
C2H4Cl2
C2H4Cl2
C2H4N2

Name
Diborane
Triborine triamine
Pentaborane

Difluorochlorobromomethane
Difluorodibromomethane
Difluorodichloromethane
Fluorotrichloromethane
Tetrachloromethane
Trifluoroiodomethane
Tetrafluoromethane
Fluorochlorobromomethane
Difluorobromomethane
Trichloromethane
Trifluoromethane
Hydrogen cyanide
Fluorochloromethane
Dichloromethane
Difluoromethane
Methanal (formaldehyde)
Methanoic acid (formic)
Chloromethane
Monofluoromethane
Iodomethane
Nitromethane
Methane
Methanol
Methanethiol
Aminomethane (methylamine)
Carbon monoxide
Carbonyl sulfide
Carbon dioxide
Carbon disulfide
Tetrafluoroethene

Hexafluoroethane
Hexafluorodimethylmercury
Ethyne
Chloroethanenitrile
cis-1,2-Dichloroethene
trans-1,2,Dichloroethene
1,1,2,2-Tetrachloroethane
1,1-Difluoroethene
1,1,1-Trichloroethane
1,1,2-Trichloroethane
1,1,1-Trifluoroethane
Ethanenitrile
Ethene (ethylene)
1-Chloro-2-bromoethane
1,2-Dibromoethane
1,1-Dichloroethane
1,2-Dichloroethane
Diazoethane

Parent
peak
28(0.13)
81(21)
64(15)
164(0.23)
208(1.7)
120(0.07)
136(0.04)
152(0.0)
196(51)

88(0.0)
148(5.5)
130(13)
118(1.3)
70(0.25)
27(92)
68(48)
84(41)
52(2.7)
30(19)
46(72)
50(66)
34(29)
142(78)
61(35)
16(67)
32(26)
48(49)
31(30)
28(78)
60(83)
44(76)
76(184)
100(20)
138(0.14)
340(0.83)
26(102)
75(51)
96(53)
96(49)

166(5.9)
64(32)
132(0.0)
132(3.9)
84(0.94)
41(89)
28(66)
142(7.9)
186(1.6)
98(5.7)
98(1.7)
56(16)

Base
peak
26(54)
80(58)
59(30)
85(86)
129(70)
85(33)
101(54)
117(39)
196(51)
69(57)
67(120)
51(83)
83(69)
69(20)
27(92)

68(48)
49(71)
33(26)
29(21)
29(118)
50(66)
15(31)
142(78)
30(65)
16(67)
31(38)
47(65)
30(53)
28(78)
60(83)
44(76)
76(184)
31(47)
69(95)
69(111)
26(102)
75(51)
61(72)
61(73)
83(95)
64(32)
97(37)
97(43)
69(81)
41(89)

28(66)
63(93)
27(93)
63(89)
62(12)
28(27)

Three next most intense peaks
27(52)
79(37)
60(30)
87(27)
131(68)
87(11)
103(35)
119(37)
127(49)
50(6.8)
69(38)
31(18)
85(44)
51(18)
26(15)
33(25)
86(26)
51(25)
28(6.6)
45(56)
15(54)
33(28)

127(29)
15(34)
15(58)
29(25)
45(40)
28(47)
12(3.7)
32(48)
28(5.0)
32(40)
81(34)
119(39)
202(26)
25(20)
48(46)
98(34)
98(32)
85(60)
45(21)
99(24)
83(41)
65(31)
40(46)
27(43)
27(82)
107(72)
27(64)
27(11)
27(25)

24(48)
53(29)
62(24)
129(17)
79(18)
50(3.9)
66(7.0)
35(16)
69(40)
19(3.9)
31(13)
132(13)
47(24)
31(9.9)
12(3.8)
70(15)
51(21)
31(7.3)
14(0.94)
28(20)
52(21)
14(5.3)
141(11)
46(23)
14(11)
28(2.4)
46(9.5)
29(8.7)
16(1.3)
28(6.9)

16(4.7)
44(33)
50(14)
31(17)
271(22)
24(5.7)
40(23)
63(23)
26(25)
95(11)
31(16)
61(19)
99(27)
15(13)
39(17)
26(41)
65(30)
109(67)
65(28)
49(4.9)
26(21)

25(30)
52(22)
61(21)
131(16)
31(18)
101(2.8)
35(5.8)
47(16)

177(16)
31(2.8)
111(11)
79(13)
35(13)
50(2.9)
28(1.6)
49(11)
47(13)
32(2.9)
13(0.92)
17(20)
49(6.6)
31(3.2)
15(10)
29(5.3)
13(5.5)
18(0.7)
15(8.9)
27(8.6)
29(0.9)
12(5.0)
12(1.9)
78(16)
12(3.6)
50(9.6)
200(21)
13(5.7)
77(16)
26(22)

63(23)
87(9.7)
33(13)
117(7.1)
85(26)
45(10)
38(10)
25(7.8)
26(24)
26(23)
26(21)
64(3.9)
41(5.2)
(Continued)

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MASS SPECTROMETRY

10.14

SECTION TEN

TABLE 10.2 Mass Spectra of Some Selected Compounds (Continued)
Mass numbers (and intensities) of:
Molecular
formula

C2H4O
C2H4O
C2H4O2
C2H4O2
C2H5Br
C2H5Cl
C2H5F
C2H5N
C2H5NO2
C2H5NO3
C2H6
C2H6O
C2H6O
C2H6O2
C2H6S
C2H6S
C2H6S2
C2H6S3
C2H7N
C2H7N
C2H8N2
C3F6
C3F8
C3H3N
C3H4
C3H4
C3H4ClN
C3H4O
C3H5Cl
C3H5ClO

C3H5ClO2
C3H5Cl3
C3H5N
C3H6
C3H6
C3H6Cl2
C3H6Cl2
C3H6O
C3H6O
C3H6O
C3H6O
C3H6O2
C3H6O2
C3H6O2
C3H6O2
C3H6O3
C3H7Br
C3H7Br
C3H7Cl
C3H7Cl
C3H7F

Name

Parent
peak

Base
peak

Ethanal (acetaldehyde)
Ethylene oxide
Ethanoic acid (acetic)
Methyl formate
Bromoethane
Chloroethane
Fluoroethane
Ethylenimine
Nitroethane
Ethyl nitrate
Ethane
Ethanol
Dimethyl ether
Dimethyl peroxide
2-Thiapropane
Ethanethiol
2,3-Dithiabutane
2,3,4-Trithiapentane
Aminoethane (ethylamine)
N-Methylaminomethane
1,2-Diaminoethane
Hexafluoropropene
Octafluoropropane
Propenenitrile
Propadiene
Propyne (methylacetylene)
3-Chloropropanenitrile
Propenal (acrolein)
1-Chloro-1-propene
3-Chloro-1,2-epoxypropane

Methyl chloroacetate
1,2,3-Trichloropropane
Propanenitrile
Cyclopropane
Propene
1,1-Dichloropropane
1,2-Dichloropropane
1-Propen-3-ol (allyl alc.)
Propanal
Propanone (acetone)
1,2-Epoxypropane
1,3-Dioxolane
Propanoic acid
Ethyl formate
Methyl acetate
Methyl carbonate
1-Bromopropane
2-Bromopropane
1-Chloropropane
2-Chloropropane
2-Fluoropropane

44(30)
44(30)
60(19)
60(27)
108(35)
64(36)
48(2.4)
43(31)

75(0.0)
91(0.01)
30(26)
46(9.7)
46(32)
62(28)
62(56)
62(44)
94(95)
126(54)
45(18)
45(36)
60(2.7)
150(16)
188(0.0)
53(55)
40(72)
40(79)
89(12)
56(16)
76(30)
92(0.19)
109(0.23)
146(0.71)
55(8.3)
42(64)
42(39)
112(0.0)
112(2.6)
58(12)

58(25)
58(24)
58(19)
74(3.1)
74(27)
74(5.8)
74(22)
90(3.3)
122(14)
122(11)
78(3.6)
78(14)
62(1.0)

29(66)
29(46)
43(37)
31(96)
29(54)
64(36)
47(24)
42(56)
29(85)
46(95)
28(99)
31(63)
45(71)
29(47)
47(69)
62(44)

94(95)
126(54)
30(96)
44(71)
30(111)
31(56)
69(171)
26(55)
40(72)
40(79)
49(68)
27(25)
41(70)
57(55)
59(56)
75(61)
28(83)
42(64)
41(58)
63(27)
63(51)
57(43)
29(66)
43(85)
28(44)
73(52)
28(34)
31(82)
43(148)
15(93)

43(94)
43(100)
42(60)
43(58)
47(84)

Three next most intense peaks
43(18)
15(30)
45(33)
29(60)
27(48)
28(32)
27(8.9)
28(44)
27(74)
29(42)
27(33)
45(22)
29(56)
31(45)
45(42)
29(43)
45(59)
45(32)
28(28)
28(48)
18(14)
69(44)
31(49)

52(41)
39(69)
39(73)
54(54)
26(15)
39(43)
27(53)
49(44)
110(22)
54(51)
41(58)
39(41)
41(25)
62(36)
29(34)
28(46)
15(26)
29(30)
43(36)
29(28)
28(60)
29(16)
45(54)
27(55)
27(50)
29(27)
27(20)
46(24)

42(6.1)

14(12)
15(21)
32(33)
110(33)
29(30)
33(8.2)
15(20)
30(19)
30(29)
26(23)
29(14)
15(41)
15(16)
46(29)
47(36)
79(56)
79(27)
44(19)
15(14)
42(6.9)
131(41)
169(42)
51(18)
38(29)
38(29)
51(29)
28(13)
40(10)
29(40)
15(43)

77(19)
26(17)
39(44)
27(22)
77(22)
27(29)
31(26)
27(38)
27(5.9)
27(28)
44(30)
27(21)
29(54)
42(15)
29(43)
41(47)
41(47)
27(22)
63(15)
61(12)

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26(6.1)
43(7.1)
14(8.0)
28(6.8)
26(16)

27(27)
26(3.0)
41(11)
26(11)
76(23)
29(21)
27(14)
14(8.9)
30(12)
35(24)
27(35)
46(34)
47(19)
27(13)
42(13)
43(5.9)
100(20)
50(16)
27(10)
37(23)
37(22)
26(20)
55(11)
78(9.6)
31(21)
29(37)
61(18)
27(15)
27(23)
40(17)

62(19)
41(25)
27(19)
26(14)
42(5.9)
26(18)
29(30)
45(19)
27(36)
59(8.4)
31(34)
39(22)
39(24)
41(14)
41(13)
27(7.6)


MASS SPECTROMETRY

MASS SPECTROMETRY

10.15

TABLE 10.2 Mass Spectra of Some Selected Compounds (Continued)
Mass numbers (and intensities) of:
Molecular
formula

Name

Parent
peak

C3H7N
C3H7N
C3H7NO
C3H7NO2
C3H7NO2
C3H8
C3H8O
C3H8O
C3H8O
C3H8O2
C3H8O2
C3H8S
C3H8S
C3H8S
C3H9N
C3H9N
C3H12B3N3
C4F6
C4F6
C4F6
C4F8
C4F8
C4F8
C4F10
C4HF7O2
C4H2

C4H4
C4H4O
C4H4S
C4H4S2
C4H5N
C4H5N
C4H6
C4H6
C4H6
C4H6
C4H6Cl2O2
C4H6O2
C4H6O2
C4H7BrO2
C4H7Cl
C4H7ClO2
C4H7ClO2
C4H7N
C4H7N
C4H8
C4H8
C4H8
C4H8
C4H8
C4H8Cl2

2-Methylethylenimine
N-Methylethylenimine
N,N-Dimethylformamide
1-Nitropropane

2-Nitropropane
Propane
1-Propanol
2-Propanol
Methyl ethyl ether
Dimethoxymethane
2-Methoxy-1-ethanol
2-Thiabutane
1-Propanethiol
2-Propanethiol
1-Aminopropane
Trimethylamine
B,B′,B′′-Trimethylborazole
Hexafluorocyclobutene
Hexafluoro-1,3-butadiene
Hexafluoro-2-butyne
Octafluorocyclobutane
Octafluoromethylpropene
Octafluoro-1-butene
Decafluorobutane
Heptafluorobutanoic acid
1,3-Butadiyne
1-Buten-3-yne
Furan
Thiophene
2-Thiophenethiol
3-Butenenitrile
Pyrrole
1,2-Butadiene
1,3-Butadiene

1-Butyne
2-Butyne
Ethyl dichloroacetate
2,3-Butanedione
Methyl 2-propenoate
2-Bromoethyl acetate
2-Chloro-2-butene
2-Chloroethyl acetate
Ethyl chloroacetate
2-Methylpropanenitrile
n-Butanenitrile
Cyclobutane
2-Methylpropene
1-Butene
cis-2-Butene
trans-2-Butene
1,2-Dichlorobutane

57(22)
57(31)
73(54)
89(0.0)
89(0.0)
44(25)
60(7.2)
60(0.45)
60(24)
76(1.6)
76(7.3)
76(47)

76(30)
76(41)
59(1.5)
59(37)
123(30)
162(21)
162(27)
162(18)
200(0.12)
200(14)
200(11)
238(0.0)
214(0.0)
50(133)
52(55)
68(36)
84(93)
116(68)
67(27)
67(67)
54(65)
54(46)
54(64)
54(93)
156(0.12)
86(13)
86(2.0)
166(0.03)
90(27)
122(0.0)

122(0.96)
69(1.7)
69(0.15)
56(41)
56(36)
56(32)
56(36)
56(37)
126(0.30)

Base
peak
28(76)
42(94)
44(63)
43(68)
43(75)
29(85)
31(115)
45(112)
45(94)
45(117)
45(122)
61(73)
47(43)
43(65)
30(20)
58(95)
108(102)
93(80)

93(90)
93(47)
100(97)
69(74)
131(122)
69(178)
45(26)
50(133)
52(55)
39(58)
84(93)
116(68)
41(80)
67(67)
54(65)
39(53)
54(64)
54(93)
29(192)
43(118)
55(98)
43(158)
55(68)
43(162)
29(130)
42(79)
41(112)
28(65)
41(85)
41(87)

41(76)
41(80)
41(39)

Three next most intense peaks
56(34)
15(46)
42(29)
27(67)
41(55)
28(50)
27(18)
43(19)
29(46)
29(51)
29(44)
48(40)
43(34)
41(44)
28(2.5)
42(44)
107(77)
31(51)
31(45)
143(38)
131(84)
181(54)
31(86)
119(33)
69(24)

49(57)
51(28)
38(9.7)
58(56)
71(64)
39(36)
39(46)
27(35)
27(36)
39(49)
27(42)
27(58)
15(40)
27(66)
27(35)
27(21)
73(43)
27(41)
68(38)
29(70)
41(58)
39(37)
39(30)
39(27)
27(27)
77(35)

30(24)
28(25)
28(25)

41(58)
27(53)
27(33)
29(17)
27(18)
15(23)
75(51)
15(38)
47(30)
27(34)
27(41)
27(1.3)
15(32)
67(38)
143(15)
74(10)
31(25)
31(53)
31(44)
69(44)
31(22)
119(17)
48(14)
50(23)
29(9.3)
45(49)
45(31)
27(30)
41(42)
53(29)

53(31)
53(27)
53(41)
83(23)
14(12)
15(27)
106(31)
39(21)
15(36)
77(37)
28(26)
27(38)
27(27)
28(18)
27(26)
27(25)
39(26)
27(20)

29(19)
27(17)
15(24)
39(24)
39(23)
43(19)
59(10)
29(11)
27(19)
15(48)
31(32)

27(27)
41(32)
61(26)
41(1.0)
30(17)
66(34)
74(6.9)
112(10)
69(20)
69(24)
93(22)
93(16)
100(15)
100(14)
25(12)
49(7.2)
40(6.7)
39(24)
39(11)
40(20)
40(36)
39(28)
28(24)
27(26)
39(24)
28(19)
42(8.6)
26(22)
108(30)
29(18)

27(29)
49(29)
54(19)
28(11)
26(15)
27(17)
28(26)
28(24)
28(26)
76(16)
(Continued)

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MASS SPECTROMETRY

10.16

SECTION TEN

TABLE 10.2 Mass Spectra of Some Selected Compounds (Continued)
Mass numbers (and intensities) of:
Molecular
formula

Name

C4H8Cl2
C4H8Cl2
C4H8Cl2
C4H8N2
C4H8O
C4H8O
C4H8O
C4H8O
C4H8O
C4H8O
C4H8O2
C4H8O2
C4H8O2
C4H8O2
C4H8O2
C4H8O2
C4H8O2
C4H8S
C4H8S
C4H9Br
C4H9Br
C4H9N
C4H9NO2
C4H10
C4H10
C4H10Hg
C4H10O
C4H10O
C4H10O
C4H10O

C4H10O
C4H10O
C4H10O2
C4H10O2
C4H10O2
C4H10O2
C4H10S
C4H10S
C4H10S
C4H10S
C4H10S
C4H10S
C4H10S
C4H10S2
C4H10S2
C4H10SO3
C4H11N
C4H11N
C4H11N
C4H11N
C4H11N

1,4-Dichlorobutane
dl-2,3-Dichlorobutane
meso-2,3-Dichlorobutane
Acetaldazine
Butanal
2-Butanone
Ethyl ethenyl ether
cis-2,3-Epoxybutane

trans-2,3-Epoxybutane
Tetrahydrofuran
2-Methyl-1,3-dioxacyclopentane
1,4-Dioxane
2-Methylpropanoic acid
n-Butanoic acid
n-Propyl formate
Ethyl acetate
Methyl propanoate
3-Methylthiacyclobutane
Thiacyclopentane
1-Bromobutane
2-Bromobutane
Pyrrolidine
n-Butyl nitrite
2-Methylpropane
n-Butane
Diethylmercury
2-Methyl-1-propanol
2-Methyl-2-propanol
1-Butanol
2-Butanol
Diethyl ether
Methyl isopropyl ether
1,1-Dimethoxyethane
1,2-Dimethoxyethane
2-Ethoxyethanol
Diethyl peroxide
3-Methyl-2-thiabutane
2-Thiapentane

3-Thiapentane
2-Methyl-1-propanethiol
2-Methyl-2-propanethiol
1-Butanethiol
2-Butanethiol
2,3-Dithiahexane
3,4-Dithiahexane
Ethyl sulfite
N-Ethylaminoethane
1-Amino-2-methylpropane
2-Amino-2-methylpropane
1-Aminobutane
2-Aminobutane

Parent
peak

Base
peak

126(0.03)
126(0.95)
126(0.95)
84(23)
72(19)
72(17)
72(27)
72(3.6)
72(3.5)
72(22)

88(0.33)
88(42)
88(8.1)
88(1.0)
88(0.41)
88(7.1)
88(23)
88(42)
88(44)
136(7.0)
136(0.72)
71(24)
103(0.0)
58(3.2)
58(12)
260(12)
74(7.5)
74(0.0)
74(0.37)
74(0.30)
74(22)
74(8.3)
90(0.06)
90(12)
90(0.49)
90(20)
90(41)
90(58)
90(41)
90(35)

90(34)
90(40)
90(34)
122(37)
122(73)
138(3.3)
73(17)
73(1.0)
73(0.25)
73(12)
73(1.2)

55(87)
63(63)
63(64)
42(92)
27(41)
43(97)
44(64)
43(67)
43(69)
42(76)
73(67)
28(138)
43(77)
60(40)
31(123)
43(181)
29(110)
46(101)

60(82)
57(86)
57(108)
43(102)
27(55)
43(117)
43(100)
29(188)
43(84)
59(92)
31(52)
45(116)
31(73)
59(126)
59(93)
45(177)
31(112)
29(116)
41(49)
61(126)
75(59)
41(60)
41(68)
56(74)
41(56)
80(53)
29(82)
29(131)
58(83)
30(22)

58(127)
30(200)
44(170)

Three next most intense peaks
41(29)
62(58)
27(57)
15(47)
29(38)
29(24)
43(56)
44(39)
44(35)
41(39)
43(48)
29(51)
41(33)
73(12)
42(89)
29(46)
57(83)
45(31)
45(29)
41(63)
41(65)
28(38)
43(54)
41(45)
29(44)

27(54)
31(56)
31(31)
56(44)
31(23)
59(34)
29(42)
29(52)
29(53)
29(57)
15(42)
75(47)
48(50)
47(51)
43(46)
57(61)
41(65)
57(50)
43(36)
66(81)
31(59)
30(81)
28(2.0)
41(26)
28(23)
18(25)

27(24)
27(57)
62(54)

28(46)
44(34)
27(15)
29(49)
27(35)
29(32)
27(25)
45(44)
58(33)
27(26)
27(9.6)
29(38)
45(24)
27(40)
39(24)
46(29)
29(50)
29(61)
70(33)
41(50)
42(39)
27(37)
28(21)
42(48)
41(19)
41(31)
59(22)
29(29)
43(37)
15(37)

15(50)
59(56)
45(34)
43(41)
41(43)
27(39)
56(34)
29(44)
27(42)
61(46)
41(27)
27(57)
45(42)
28(30)
41(1.2)
42(20)
27(16)
41(18)

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90(23)
55(29)
55(31)
69(38)
43(32)
57(6.0)
27(43)

29(33)
27(31)
71(20)
29(34)
31(24)
73(19)
41(9.1)
27(36)
27(24)
59(27)
47(21)
47(22)
27(46)
27(36)
42(20)
30(47)
27(33)
28(33)
231(15)
41(47)
43(14)
43(30)
27(20)
45(28)
15(32)
31(37)
60(16)
27(31)
62(30)
48(38)

27(43)
61(33)
47(29)
39(21)
47(31)
29(46)
27(25)
94(53)
27(39)
27(24)
27(1.1)
15(18)
18(12)
58(18)


MASS SPECTROMETRY

MASS SPECTROMETRY

10.17

TABLE 10.2 Mass Spectra of Some Selected Compounds (Continued)
Mass numbers (and intensities) of:
Molecular
formula

Name

C4H12Pb

C5F10
C5F12
C5F12
C5HF9
C5H5N
C5H6
C5H6
C5H6N2
C5H6O2
C5H6S
C5H6S
C5H8
C5H8
C5H8
C5H8
C5H8
C5H8
C5H8
C5H8
C5H8
C5H8
C5H8
C5H8
C5H8
C5H8N2
C5H8O2
C5H8O2
C5H8O2
C5H9ClO2
C5H10

C5H10
C5H10
C5H10
C5H10
C5H10
C5H10
C5H10
C5H10
C5H10
C5H10O
C5H10O
C5H10O
C5H10O
C5H10O
C5H10O
C5H10O2
C5H10O2
C5H10O2
C5H10O2
C5H10O2

Tetramethyllead
Decafluorocyclopentane
Dodecafluoro-2-methylbutane
Dodecafluoropentane
Nonafluorocyclopentane
Pyridine
Cyclopentadiene
trans-2-Penten-4-yne
2-Methylpyrazine

Furfuryl alcohol
2-Methylthiophene
3-Methylthiophene
Methylenecyclobutane
Spiropentane
Cyclopentene
3-Methyl-1,2-butadiene
2-Methyl-1,3-butadiene
1,2-Pentadiene
cis-1,3-Pentadiene
trans-1,3-Pentadiene
1,4-Pentadiene
2,3-Pentadiene
3-Methyl-1-butyne
1-Pentyne
2-Pentyne
3,5-Dimethylpyrazole
2,4-Pentanedione
2-Propenyl acetate
Methyl methacrylate
Ethyl 3-chloropropanoate
cis-1,2-Dimethylcyclopropane
trans-1,2-Dimethylcyclopropane
Ethylcyclopropane
Cyclopentane
2-Methyl-1-butene
3-Methyl-1-butene
2-Methyl-2-butene
1-Pentene
cis-2-Pentene

trans-2-Pentene
3-Methyl-1-butanal
2-Pentanone
3-Pentanone
Ethyl-2-propenyl ether
Ethenyl isopropyl ether
2-Methyltetrahydrofuran
Tetrahydrofurfuryl alcohol
2-Methoxyethyl ethenyl ether
2,2-Dimethylpropanoic acid
2-Methylbutanoic acid
n-Butyl formate

Parent
peak
268(0.14)
250(0.62)
288(0.0)
288(0.08)
232(0.07)
79(135)
66(95)
66(77)
94(81)
98(3.4)
98(68)
98(74)
68(38)
68(8.9)
68(41)

68(53)
68(40)
68(39)
68(40)
68(41)
68(40)
68(62)
68(8.5)
68(8.7)
68(67)
96(47)
100(22)
100(0.16)
100(26)
136(0.70)
70(39)
70(42)
70(26)
70(44)
70(30)
70(26)
70(31)
70(27)
70(30)
70(31)
86(3.0)
86(16)
86(15)
86(6.2)
86(21)

86(8.9)
102(0.02)
102(3.0)
102(2.0)
102(0.32)
102(0.27)

Base
peak
253(69)
131(173)
69(277)
69(259)
131(61)
79(135)
66(95)
66(77)
94(81)
98(3.4)
97(125)
97(138)
40(67)
67(58)
67(99)
68(53)
67(48)
68(39)
67(53)
67(52)
39(47)

68(62)
53(74)
67(50)
68(67)
96(47)
43(120)
43(177)
41(78)
27(65)
55(77)
55(79)
42(93)
42(148)
55(97)
55(102)
55(88)
42(89)
55(89)
55(93)
41(30)
43(106)
57(87)
41(52)
43(87)
71(57)
71(8.9)
29(69)
57(83)
74(54)
56(80)

Three next most intense peaks
223(59)
100(41)
119(45)
119(76)
113(49)
52(95)
65(40)
39(54)
67(48)
41(3.3)
45(26)
45(35)
67(48)
40(56)
39(36)
53(40)
53(41)
53(38)
39(43)
39(43)
67(35)
53(42)
67(45)
40(44)
53(61)
95(37)
85(33)
41(30)

69(52)
29(62)
42(35)
42(34)
55(47)
55(43)
42(36)
27(31)
41(31)
55(53)
42(41)
42(41)
43(26)
29(23)
29(87)
29(48)
44(69)
43(55)
43(6.8)
45(58)
41(38)
57(34)
41(48)

208(46)
31(40)
131(23)
169(25)
69(34)
51(48)

39(35)
65(38)
26(33)
39(3.3)
39(17)
39(14)
39(47)
39(52)
53(23)
39(28)
39(34)
39(37)
53(38)
53(39)
53(33)
39(36)
27(35)
39(42)
39(32)
39(16)
15(23)
39(29)
39(31)
91(42)
39(32)
41(33)
41(39)
41(43)
39(34)
42(28)

39(28)
41(39)
39(30)
39(30)
58(20)
27(23)
27(32)
58(44)
41(46)
41(40)
41(4.8)
15(48)
29(27)
29(33)
31(47)

251(36)
69(28)
31(18)
31(24)
31(19)
50(35)
40(30)
40(35)
39(30)
42(2.6)
53(11)
27(11)
53(21)
53(23)

41(19)
41(26)
27(23)
27(31)
41(25)
41(26)
41(30)
41(31)
39(21)
27(34)
27(27)
54(12)
27(11)
15(28)
15(16)
63(37)
41(32)
39(30)
39(35)
39(31)
41(28)
29(27)
42(27)
39(31)
29(26)
41(28)
29(20)
57(20)
28(9.4)
57(42)

27(45)
27(27)
27(3.8)
58(45)
39(12)
41(28)
29(42)
(Continued)

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MASS SPECTROMETRY

10.18

SECTION TEN

TABLE 10.2 Mass Spectra of Some Selected Compounds (Continued)
Mass numbers (and intensities) of:
Molecular
formula
C5H10O2
C5H10O2
C5H10O2
C5H10O2
C5H10O2
C5H10O2

C5H10O2
C5H10O3
C5H10S
C5H10S
C5H10S
C5H10S
C5H11N
C5H11NO
C5H11NO2
C5H12
C5H12
C5H12
C5H12O
C5H12O
C5H12O
C5H12O
C5H12O
C5H12O
C5H12O
C5H12O
C5H12O
C5H12O2
C5H12O2
C5H12S
C5H12S
C5H12S
C5H12S
C5H12S
C5H12S
C5H12S

C5H12S
C5H12S
C5H12S
C5H12S
C5H12S
C5H12S2
C5H12S2
C5H14Pb
C6F6
C6F12
C6F14
C6F14
C6H5Br
C6H5Cl
C6H5NO2

Name

Parent
peak

Base
peak

Isobutyl formate
sec-Butyl formate
n-Propyl acetate
Isopropyl acetate
Ethyl propanoate
Methyl 2-methylpropanoate

Methyl butanoate
Ethyl carbonate
2-Methylthiacyclopentane
3-Methylthiacyclopentane
Thiacyclohexane
Cyclopentanethiol
Piperidine
N-Methylmorpholine
3-Methylbutyl nitrite
2,2-Dimethylpropane
2-Methylbutane
n-Pentane
2-Methyl-1-butanol
3-Methyl-1-butanol
2-Methyl-2-butanol
1-Pentanol
Methyl n-butyl ether
Methyl isobutyl ether
Methyl sec-butyl ether
Methyl tert-butyl ether
Ethyl isopropyl ether
Diethoxymethane
1,1-Dimethoxypropane
3,3-Dimethyl-2-thiabutane
4-Methyl-2-thiapentane
2-Methyl-3-thiapentane
2-Thiahexane
3-Thiahexane
2,2-Dimethyl-1-propanethiol
2-Methyl-1-butanethiol

2-Methyl-2-butanethiol
3-Methyl-2-butanethiol
1-Pentanethiol
2-Pentanethiol
3-Pentanethiol
4,4-Dimethyl-2,3-dithiapentane
2-Methyl-3,4-dithiahexane
Trimethylethyllead
Hexafluorobenzene
Dodecafluorocyclohexane
Tetradecafluoro-2-methylpentane
Tetradecafluorohexane
Bromobenzene
Chlorobenzene
Nitrobenzene

102(0.27)
102(0.17)
102(0.07)
102(0.17)
102(10)
102(8.9)
102(1.0)
118(0.30)
102(37)
102(40)
102(43)
102(19)
85(22)
101(4.4)

117(0.0)
72(0.01)
72(4.7)
72(10)
88(0.18)
88(0.02)
88(0.0)
88(0.0)
88(3.1)
88(12)
88(2.0)
88(0.02)
88(2.6)
104(2.1)
104(0.05)
104(30)
104(37)
104(82)
104(38)
104(30)
104(31)
104(28)
104(18)
104(23)
104(35)
104(28)
104(23)
136(12)
136(20)
282(0.64)

186(95)
300(0.96)
338(0.0)
338(0.13)
156(75)
112(102)
123(39)

43(58)
45(99)
43(176)
43(155)
29(151)
43(69)
43(53)
29(114)
87(88)
60(45)
87(44)
41(48)
84(43)
43(18)
29(75)
57(126)
43(74)
43(114)
57(57)
55(47)
59(43)
42(41)

45(211)
45(186)
59(142)
73(119)
45(143)
31(104)
75(84)
57(83)
41(46)
89(119)
61(77)
75(72)
57(100)
41(65)
43(88)
61(73)
42(91)
43(72)
43(56)
57(74)
94(49)
223(61)
186(95)
131(138)
69(317)
69(268)
77(98)
112(102)
77(93)

Three next most intense peaks
56(48)
29(49)
61(34)
45(50)
57(97)
71(23)
74(37)
45(80)
41(30)
41(31)
68(33)
69(47)
57(22)
42(8.6)
41(68)
41(52)
42(64)
42(66)
29(55)
42(42)
55(37)
55(30)
56(36)
41(30)
29(50)
41(33)
43(46)
59(99)
73(62)

41(62)
56(38)
62(79)
56(50)
27(53)
41(55)
29(44)
71(54)
43(55)
55(44)
61(52)
41(48)
41(38)
27(46)
253(52)
117(59)
69(97)
131(41)
119(74)
158(74)
77(49)
51(55)

41(46)
27(32)
31(31)
27(22)
27(52)
41(19)
71(29)

31(60)
45(29)
45(25)
61(32)
39(26)
56(22)
15(3.4)
57(43)
29(49)
41(49)
41(45)
41(53)
43(39)
45(25)
41(25)
29(36)
29(30)
27(27)
43(32)
73(40)
29(62)
29(43)
29(42)
27(29)
43(63)
41(39)
47(50)
55(48)
57(40)
41(46)

27(33)
41(39)
27(39)
75(29)
29(36)
43(39)
208(51)
31(58)
100(40)
119(36)
169(51)
51(41)
114(33)
50(23)

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31(38)
41(31)
27(26)
61(18)
28(24)
59(17)
27(23)
27(46)
59(18)
74(23)
41(28)

67(18)
44(17)
71(2.9)
30(42)
27(20)
57(40)
27(39)
56(50)
41(38)
73(22)
70(23)
27(28)
15(27)
41(25)
57(32)
27(24)
103(39)
45(37)
39(16)
39(23)
61(58)
27(33)
62(33)
29(42)
70(40)
55(34)
55(28)
70(39)
55(38)
47(23)

80(13)
66(37)
221(33)
93(23)
31(30)
169(29)
131(37)
50(36)
51(17)
30(15)


MASS SPECTROMETRY

MASS SPECTROMETRY

10.19

TABLE 10.2 Mass Spectra of Some Selected Compounds (Continued)
Mass numbers (and intensities) of:
Molecular
formula
C6H6
C6H6
C6H6
C6H6S
C6H7N
C6H7N
C6H7NO
C6H8

C6H8
C6H8O
C6H8S
C6H8S
C6H8S
C6H8S
C6H8S
C6H9N
C6H10
C6H10
C6H10
C6H10
C6H10
C6H10
C6H10
C6H10
C6H10
C6H10
C6H10
C6H10O
C6H10O
C6H10O2
C6H10O3
C6H10O3
C6H11N
C6H11N
C6H12
C6H12
C6H12
C6H12

C6H12
C6H12
C6H12
C6H12
C6H12
C6H12
C6H12
C6H12
C6H12
C6H12
C6H12
C6H12
C6H12

Name
Benzene
1,5-Hexadiyne
2,4-Hexadiyne
Benzenethiol
Aminobenzene (aniline)
2-Methylpyridine
1-Methyl-2-pyridone
Methylcyclopentadiene
1,3-Cyclohexadiene
2,5-Dimethylfuran
2,3-Dimethylthiophene
2,4-Dimethylthiophene
2,5-Dimethylthiophene
2-Ethylthiophene
3-Ethylthiophene

2,5-Dimethylpyrrole
Isopropenylcyclopropane
1-Methylcyclopentene
Cyclohexene
2,3-Dimethyl-1,3-butadiene
2-Methyl-1,3-pentadiene
1,5-Hexadiene
3,3-Dimethyl-1-butyne
4-Methyl-1-pentyne
1-Hexyne
2-Hexyne
3-Hexyne
Cyclohexanone
4-Methyl-3-penten-2-one
2,5-Hexanedione
Propanoic anhydride
Ethyl acetoacetate
4-Methylpentanenitrile
Hexanenitrile
1,1,2-Trimethylcyclopropane
1-Methyl-1-ethylcyclopropane
Isopropylcyclopropane
Ethylcyclobutane
Methylcyclopentane
Cyclohexane
2,3-Dimethyl-1-butene
3,3-Dimethyl-1-butene
2-Ethyl-1-butene
2,3-Dimethyl-2-butene
2-Methyl-1-pentene

3-Methyl-1-pentene
4-Methyl-1-pentene
2-Methyl-2-pentene
3-Methyl-cis-2-pentene
3-Methyl-trans-2-pentene
4-Methyl-cis-2-pentene

Parent
peak

Base
peak

78(113)
78(58)
78(108)
110(68)
93(19)
93(86)
109(71)
80(53)
80(53)
96(57)
112(44)
112(27)
112(67)
112(27)
112(54)
95(73)
82(20)

82(26)
82(33)
82(41)
82(23)
82(1.3)
82(0.57)
82(2.3)
82(1.0)
82(56)
82(55)
98(32)
98(40)
114(4.0)
130(0.0)
130(8.3)
97(0.13)
97(0.54)
84(38)
84(25)
84(2.0)
84(3.8)
84(18)
84(58)
84(27)
84(23)
84(30)
84(32)
84(29)
84(25)
84(12)

84(36)
84(37)
84(38)
84(35)

78(113)
39(65)
78(108)
110(68)
93(19)
93(86)
109(71)
79(87)
79(92)
43(65)
97(53)
111(36)
111(95)
97(68)
97(147)
94(127)
67(92)
67(98)
67(83)
67(60)
67(48)
41(98)
67(101)
67(82)
67(131)

67(58)
67(59)
55(102)
55(82)
43(148)
57(190)
43(150)
55(98)
41(73)
41(132)
41(78)
56(114)
56(138)
56(116)
56(75)
41(117)
41(112)
41(74)
41(108)
56(91)
55(85)
43(110)
41(120)
41(104)
41(102)
41(122)

Three next most intense peaks
52(22)
52(38)

51(55)
66(26)
66(6.5)
66(36)
81(49)
77(29)
77(35)
95(48)
111(44)
97(18)
97(59)
45(16)
45(38)
26(52)
41(47)
39(21)
54(64)
39(55)
39(30)
67(80)
41(57)
41(74)
41(88)
53(50)
41(55)
42(86)
83(82)
15(25)
29(119)
29(52)

41(51)
54(49)
69(81)
55(58)
41(84)
41(89)
41(74)
41(44)
69(96)
69(107)
69(66)
69(88)
41(73)
41(67)
41(80)
69(111)
69(82)
69(81)
69(114)

77(20)
51(32)
52(38)
109(17)
65(3.6)
39(28)
39(34)
39(19)
39(21)
53(37)

45(16)
45(9.4)
59(23)
39(8.9)
39(20)
80(22)
39(46)
81(16)
41(31)
41(44)
41(26)
39(60)
39(31)
43(64)
27(85)
27(39)
39(37)
41(35)
43(64)
99(22)
27(62)
27(32)
43(45)
27(43)
39(34)
69(53)
39(30)
27(35)
69(37)
55(25)

39(36)
39(28)
55(56)
39(35)
55(39)
69(60)
56(47)
39(35)
55(46)
55(47)
39(35)

51(18)
50(26)
50(31)
51(15)
39(3.5)
51(16)
80(29)
51(11)
27(18)
81(24)
27(9.4)
39(7.0)
45(19)
27(5.4)
27(12)
42(19)
27(22)
41(16)

39(30)
54(22)
27(13)
54(52)
27(11)
39(55)
43(67)
41(36)
53(20)
27(34)
29(38)
14(14)
28(26)
15(27)
27(39)
55(40)
27(24)
27(33)
43(28)
55(34)
42(33)
42(21)
27(24)
27(26)
27(38)
27(20)
39(36)
27(43)
27(37)
27(28)

27(36)
27(35)
27(26)
(Continued)

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MASS SPECTROMETRY

10.20

SECTION TEN

TABLE 10.2 Mass Spectra of Some Selected Compounds (Continued)
Mass numbers (and intensities) of:
Molecular
formula
C6H12
C6H12
C6H12
C6H12
C6H12
C6H12
C6H12N2
C6H12O
C6H12O
C6H12O

C6H12O
C6H12O2
C6H12O2
C6H12O2
C6H12O2
C6H12O2
C6H12O2
C6H12O3
C6H12S
C6H12S
C6H12S
C6H12S
C6H12S
C6H12S
C6H12S
C6H12S
C6H12S
C6H12S
C6H12S
C6H13N
C6H13N
C6H13NO
C6H14
C6H14
C6H14
C6H14
C6H14
C6H14N2
C6H14O
C6H14O

C6H14O
C6H14O
C6H14O
C6H14O
C6H14O
C6H14O
C6H14O
C6H14O2
C6H14O2
C6H14O3

Name
4-Methyl-trans-2-pentene
1-Hexene
cis-2-Hexene
trans-2-Hexene
cis-3-Hexene
trans-3-Hexene
Acetone azine (ketazine)
Cyclopentylmethanol
4-Methyl-2-pentanone
Ethenyl n-butyl ether
Ethenyl isobutyl ether
4-Hydroxy-4-methyl-2-pentanone
n-Butyl acetate
n-Propyl propanoate
Isopropyl propanoate
Methyl 2,2-dimethylpropanoate
Ethyl butanoate
2,4,6-Trimethyl-1,3,5trioxacyclo-hexane

1-Cyclopentyl-1-thiaethane
cis-2,5-Dimethylthiacyclopentane
trans-2,5-Dimethylthiacyclopentane
2-Methylthiacyclohexane
3-Methylthiacyclohexane
4-Methylthiacyclohexane
Thiacycloheptane
1-Methylcyclopentanethiol
cis-2-Methylcyclopentanethiol
trans-2-Methylcyclopentanethiol
Cyclohexanethiol
Cyclohexylamine
3-Methylpiperidine
N-Ethylmorpholine
2,2-Dimethylbutane
2,3-Dimethylbutane
2-Methylpentane
3-Methylpentane
n-Hexane
cis-2,5-Dimethylpiperazine
2-Ethyl-1-butanol
2-Methyl-1-pentanol
3-Methyl-1-pentanol
4-Methyl-2-pentanol
1-Hexanol
Ethyl n-butyl ether
Ethyl sec-butyl ether
Ethyl isobutyl ether
Diisopropyl ether
1,1-Diethoxyethane

1,2-Diethoxyethane
bis-(2-Methoxyethyl) ether

Parent
peak

Base
peak

84(34)
84(20)
84(27)
84(32)
84(28)
84(32)
112(31)
100(0.02)
100(12)
100(5.7)
100(5.8)
116(0.0)
116(0.03)
116(0.03)
116(0.26)
116(3.2)
116(2.2)
132(0.12)

41(123)
41(70)

55(91)
55(112)
55(81)
55(89)
56(99)
41(35)
43(115)
29(80)
29(73)
43(149)
43(172)
57(147)
57(116)
57(85)
43(50)
45(196)

69(112)
56(60)
42(51)
42(54)
41(62)
41(72)
15(31)
68(32)
58(37)
41(59)
41(65)
15(45)
56(58)

29(84)
43(88)
41(32)
71(45)
43(107)

39(34)
42(52)
41(45)
41(46)
42(54)
42(62)
97(31)
69(31)
41(22)
56(45)
57(58)
58(32)
41(30)
27(57)
29(54)
29(24)
29(43)
29(35)

27(26)
27(48)
27(45)
27(41)
27(32)

27(35)
39(26)
67(24)
57(22)
57(35)
56(40)
27(14)
27(27)
75(47)
27(46)
56(21)
27(31)
89(23)

116(31)
116(32)
116(32)
116(42)
116(41)
116(46)
116(60)
116(20)
116(32)
116(28)
116(21)
99(8.9)
99(23)
115(2.0)
86(0.04)
86(5.3)

86(4.4)
86(3.2)
86(12)
114(0.38)
102(0.0)
102(0.0)
102(0.0)
102(0.08)
102(0.0)
102(3.8)
102(1.5)
102(8.7)
102(1.4)
118(0.0)
118(1.2)
134(0.0)

68(72)
101(85)
101(85)
101(81)
101(55)
116(46)
87(75)
83(76)
55(55)
67(48)
55(56)
56(92)
44(49)

42(9.8)
43(85)
43(157)
43(147)
57(105)
57(87)
58(10)
43(114)
43(110)
56(26)
45(111)
56(63)
59(108)
45(150)
59(124)
45(125)
45(132)
31(124)
59(140)

41(64)
59(34)
59(34)
41(37)
41(47)
101(44)
41(66)
55(58)
83(54)
55(46)

41(45)
43(25)
30(34)
57(7.0)
57(82)
42(136)
42(78)
56(80)
43(71)
28(7.7)
70(40)
41(40)
41(20)
43(34)
43(52)
31(87)
73(76)
31(95)
43(66)
73(69)
59(88)
29(74)

39(37)
41(26)
74(25)
27(32)
39(33)
41(40)
67(48)

41(39)
60(48)
41(42)
67(35)
28(13)
28(27)
100(5.2)
71(61)
41(49)
41(47)
41(67)
41(64)
30(4.7)
29(39)
29(34)
29(19)
41(17)
41(37)
29(61)
29(51)
29(53)
87(23)
29(36)
29(72)
58(57)

67(37)
74(24)
41(25)
67(30)

45(28)
27(39)
47(46)
67(33)
41(47)
83(40)
83(32)
30(13)
57(26)
28(4.3)
41(51)
27(40)
27(40)
29(64)
29(55)
44(4.2)
27(38)
27(33)
55(18)
27(14)
55(36)
27(42)
27(39)
27(38)
27(19)
27(27)
45(53)
15(56)

Three next most intense peaks

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MASS SPECTROMETRY

MASS SPECTROMETRY

10.21

TABLE 10.2 Mass Spectra of Some Selected Compounds (Continued)
Mass numbers (and intensities) of:
Molecular
formula
C6H14S
C6H14S
C6H14S
C6H14S
C6H14S
C6H14S
C6H14S
C6H14S
C6H14S
C6H14S
C6H14S
C6H14S
C6H14S2
C6H14S2

C6H14S2
C6H14S2
C6H15N
C6H15N
C6H15N
C6H16Pb
C7F14
C7F16
C7H5N
C7H7Br
C7H7Br
C7H7Cl
C7H7Cl
C7H7Cl
C7H7F
C7H7F
C7H8
C7H8S
C7H9N
C7H10S
C7H12
C7H12
C7H12
C7H12
C7H12
C7H12
C7H12
C7H12
C7H12
C7H14

C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14

Name

Parent
peak

Base
peak

2,2-Dimethyl-3-thiapentane
2,4-Dimethyl-3-thiapentane
2-Methyl-3-thiahexane
4-Methyl-3-thiahexane
5-Methyl-3-thiahexane
3-Thiaheptane
4-Thiaheptane
2-Methyl-1-pentanethiol
4-Methyl-1-pentanethiol
4-Methyl-2-pentanethiol
2-Methyl-3-pentanethiol
1-Hexanethiol
2,5-Dimethyl-3,4-dithiahexane
5-Methyl-3,4-dithiaheptane

6-Methyl-3,4-dithiaheptane
4,5-Dithiaoctane
Triethylamine
Di-n-propylamine
Diisopropylamine
Dimethyldiethyllead
Tetradecafluoromethylcyclohexane
Hexadecafluoroheptane
Benzonitrile
1-Methyl-2-bromobenzene
1-Methyl-4-bromobenzene
1-Methyl-2-chlorobenzene
1-Methyl-3-chlorobenzene
1-Methyl-4-chlorobenzene
1-Methyl-3-fluorobenzene
1-Methyl-4-fluorobenzene
Methylbenzene (toluene)
1-Phenyl-1-thiaethane
2,4-Dimethylpyridine
2,3,4-Trimethylthiophene
Ethenylcyclopentane
Ethylidenecyclopentane
Bicyclo[2.2.1]heptane
3-Ethylcyclopentene
1-Methylcyclohexene
4-Methylcyclohexene
4-Methyl-2-hexyne
5-Methyl-2-hexyne
1-Heptyne
1,1,2,2-Tetramethylcyclopropane

cis-1,2-Dimethylcyclopentane
trans-1,2-Dimethylcyclopentane
cis-1,3-Dimethylcyclopentane
trans-1,3-Dimethylcyclopentane
1,1-Dimethylcyclopentane
Ethylcyclopentane
Methylcyclohexane

118(33)
118(33)
118(206)
118(195)
118(171)
118(35)
118(47)
118(19)
118(30)
118(6.3)
118(20)
118(16)
150(31)
150(14)
150(4.9)
150(44)
101(21)
101(7.1)
101(5.0)
296(0.98)
350(0.0)
388(0.0)

103(246)
170(48)
170(46)
126(44)
126(51)
126(44)
110(79)
110(73)
92(82)
124(76)
107(76)
126(50)
96(13)
96(40)
96(12)
96(29)
96(32)
96(28)
96(13)
96(42)
96(0.44)
98(21)
98(19)
98(25)
98(12)
98(13)
98(6.7)
98(14)
98(41)

57(147)
43(94)
43(540)
89(585)
75(520)
75(55)
43(86)
43(96)
56(142)
43(68)
41(64)
56(66)
43(152)
29(86)
29(42)
43(167)
86(134)
30(89)
44(171)
267(89)
69(244)
69(330)
103(246)
91(97)
91(97)
91(121)
91(120)
91(120)
109(129)
109(122)

91(108)
124(76)
107(76)
111(81)
67(118)
67(180)
67(64)
67(193)
81(83)
81(84)
81(71)
43(49)
41(75)
55(92)
56(85)
56(93)
56(81)
56(81)
56(81)
69(83)
83(94)

Three next most intense peaks
41(70)
61(85)
41(317)
29(343)
41(230)
29(33)
89(74)

41(51)
41(57)
69(61)
43(63)
41(41)
108(41)
94(66)
66(40)
27(65)
30(46)
72(70)
86(52)
223(83)
131(107)
119(89)
76(80)
172(46)
172(45)
63(20)
63(19)
125(19)
83(17)
83(16)
39(20)
109(34)
106(29)
125(47)
39(44)
39(44)
68(50)

39(36)
68(38)
54(50)
67(52)
81(43)
81(70)
83(90)
70(77)
41(63)
70(78)
70(68)
55(63)
41(78)
55(78)

29(54)
41(48)
42(301)
27(296)
47(224)
27(33)
41(57)
56(32)
43(57)
41(56)
75(50)
27(40)
41(36)
66(57)
122(30)

41(64)
27(36)
44(36)
58(24)
208(79)
181(48)
169(68)
50(42)
39(21)
39(20)
39(19)
39(18)
63(18)
57(12)
57(12)
65(14)
78(25)
79(16)
45(22)
68(38)
41(30)
81(44)
41(35)
67(37)
39(44)
41(48)
27(39)
29(65)
41(69)
41(65)

55(61)
41(64)
41(63)
69(56)
68(60)
41(55)

27(40)
103(44)
27(287)
41(279)
56(217)
62(28)
27(55)
27(31)
27(32)
84(42)
27(28)
43(38)
27(30)
27(41)
94(29)
108(35)
58(35)
43(28)
42(22)
221(44)
100(38)
131(44)
51(24)

63(20)
65(19)
89(18)
128(16)
39(17)
39(12)
39(9.3)
51(10)
91(19)
92(13)
39(18)
54(35)
27(30)
54(30)
27(26)
39(33)
55(34)
39(35)
39(38)
27(47)
39(41)
55(65)
70(54)
55(59)
55(58)
41(55)
55(46)
42(34)
(Continued)

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MASS SPECTROMETRY

10.22

SECTION TEN

TABLE 10.2 Mass Spectra of Some Selected Compounds (Continued)
Mass numbers (and intensities) of:
Molecular
formula
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14

C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14
C7H14O
C7H14O2
C7H14O2
C7H14O2
C7H14O3
C7H14S
C7H15N
C7H16
C7H16
C7H16
C7H16
C7H16
C7H16
C7H16
C7H16

C7H16
C7H16O
C7H16O
C7H16O
C7H16O
C7H16O2

Name
Cycloheptane
2,3,3-Trimethyl-1-butene
3-Methyl-2-ethyl-1-butene
2,3-Dimethyl-1-pentene
2,4-Dimethyl-1-pentene
3,3-Dimethyl-1-pentene
3,4-Dimethyl-1-pentene
4,4-Dimethyl-1-pentene
3-Ethyl-1-pentene
2,3-Dimethyl-2-pentene
2,4-Dimethyl-2-pentene
3,4-Dimethyl-cis-2-pentene
3,4-Dimethyl-trans-2-pentene
4,4-Dimethyl-cis-2-pentene
4,4-Dimethyl-trans-2-pentene
3-Ethyl-2-pentene
2-Methyl-1-hexene
3-Methyl-1-hexene
4-Methyl-1-hexene
5-Methyl-1-hexene
2-Methyl-2-hexene
3-Methyl-cis-2-hexene

4-Methyl-trans-2-hexene
5-Methyl-2-hexene
2-Methyl-trans-3-hexene
3-Methyl-cis-3-hexene
3-Methyl-trans-3-hexene
1-Heptene
trans-2-Heptene
trans-3-Heptene
2,4-Dimethyl-3-pentanone
n-Butyl propanoate
Isobutyl propanoate
n-Propyl n-butanoate
n-Propyl carbonate
cis-2-Methylcyclohexanethiol
2,6-Dimethylpiperidine
2,2,3-Trimethylbutane
2,2-Dimethylpentane
2,3-Dimethylpentane
2,4-Dimethylpentane
3,3-Dimethylpentane
3-Ethylpentane
2-Methylhexane
3-Methylhexane
n-Heptane
2-Heptanol
3-Heptanol
4-Heptanol
n-Propyl n-butyl ether
Di-n-propoxymethane

Parent
peak

Base
peak

98(37)
98(20)
98(22)
98(13)
98(9.1)
98(9.4)
98(0.61)
98(2.6)
98(19)
98(31)
98(26)
98(30)
98(31)
98(27)
98(28)
98(33)
98(4.6)
98(7.7)
98(4.9)
98(1.6)
98(28)
98(30)
98(23)
98(13)

98(24)
98(28)
98(28)
98(15)
98(27)
98(27)
114(13)
130(0.03)
130(0.07)
130(0.05)
146(0.02)
130(28)
113(5.3)
100(0.03)
100(0.06)
100(2.1)
100(1.6)
100(0.03)
100(3.1)
100(5.9)
100(4.0)
100(17)
116(0.01)
116(0.01)
116(0.02)
116(3.7)
132(0.58)

41(57)
83(101)

41(71)
41(92)
56(117)
69(104)
56(75)
57(161)
41(116)
83(80)
83(97)
83(87)
83(89)
83(96)
83(105)
41(86)
56(105)
55(76)
41(98)
56(91)
69(113)
41(95)
69(118)
56(90)
69(86)
69(98)
69(97)
41(91)
55(64)
41(98)
43(226)
57(152)

57(187)
43(96)
43(171)
55(138)
98(73)
57(110)
57(130)
43(94)
43(139)
43(166)
43(175)
43(154)
43(110)
43(126)
45(131)
59(61)
55(102)
43(120)
43(194)

Three next most intense peaks
55(54)
55(83)
69(71)
69(86)
43(68)
41(85)
55(62)
41(86)
69(91)

55(75)
55(71)
55(82)
55(83)
55(92)
55(89)
69(80)
41(54)
41(60)
57(94)
41(75)
41(99)
69(90)
41(106)
55(74)
41(74)
41(82)
41(86)
56(79)
56(59)
56(65)
71(62)
29(98)
29(87)
71(90)
27(61)
97(70)
44(43)
43(84)
43(95)

56(93)
57(93)
71(103)
70(77)
42(59)
57(52)
41(65)
43(29)
69(41)
73(72)
57(102)
73(114)

56(50)
41(61)
55(62)
55(40)
41(61)
55(42)
43(55)
29(52)
27(43)
41(63)
41(52)
41(52)
41(52)
41(62)
41(58)
55(74)
27(30)

69(57)
56(80)
55(47)
27(36)
55(42)
55(40)
43(71)
55(62)
39(33)
55(63)
29(64)
41(50)
69(55)
27(49)
56(54)
56(52)
27(54)
63(55)
81(44)
42(34)
56(67)
41(59)
57(67)
41(59)
27(38)
71(77)
41(57)
71(52)
57(60)
27(25)

41(29)
43(45)
41(51)
27(45)

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42(49)
39(33)
27(38)
39(35)
39(39)
27(36)
41(54)
55(49)
39(37)
39(34)
39(34)
27(32)
27(34)
39(35)
39(31)
27(33)
39(27)
56(48)
29(70)
27(42)
39(33)

27(36)
39(35)
41(57)
56(37)
27(33)
39(35)
55(54)
27(35)
55(47)
41(42)
27(52)
27(47)
89(48)
41(49)
41(44)
28(26)
41(64)
56(52)
41(64)
56(50)
41(36)
29(45)
85(49)
41(50)
29(58)
29(23)
31(25)
27(32)
29(49)
41(34)

MASS SPECTROMETRY

MASS SPECTROMETRY

10.23

TABLE 10.2 Mass Spectra of Some Selected Compounds (Continued)
Mass numbers (and intensities) of:
Molecular
formula
C7H16O2
C7H16O2
C7H16S
C7H16S
C7H16S
C7H16S
C7H18Pb
C7H18Pb
C7H18Pb
C7H18Pb
C8H10
C8H10
C8H10
C8H10
F3N
HCl
H2S
H3N

H3P
H4N2
NO
NO2
N2
N2O
O2
O2S

Name
Diisopropoxymethane
1,1-Diethoxypropane
2,2,4-Trimethyl-3-thiapentane
2,4-Dimethyl-3-thiahexane
2-Thiaoctane
1-Heptanethiol
Methyltriethyllead
n-Butyltrimethyllead
sec-Butyltrimethyllead
tert-Butyltrimethyllead
1,2-Dimethylbenzene
1,3-Dimethylbenzene
1,4-Dimethylbenzene
Ethylbenzene
Nitrogen trifluoride
Hydrogen chloride
Hydrogen sulfide
Ammonia
Phosphine
Hydrazine

Nitric oxide
Nitrogen dioxide
Nitrogen
Nitrous oxide
Oxygen
Sulfur dioxide

Parent
peak
132(0.16)
132(0.0)
132(30)
132(30)
132(34)
132(14)
310(0.84)
310(0.14)
310(1.8)
310(0.09)
106(52)
106(58)
106(52)
106(45)
71(10)
36(54)
34(75)
17(32)
34(59)
32(48)
30(76)

46(6.6)
28(65)
44(60)
32(54)
64(47)

Base
peak
43(133)
59(138)
57(149)
61(94)
61(73)
41(48)
281(86)
253(76)
253(94)
252(95)
91(91)
91(93)
91(85)
91(146)
52(33)
36(54)
34(75)
17(32)
34(59)
32(48)
30(76)
30(18)

28(65)
44(60)
32(54)
64(47)

Three next most intense peaks
45(84)
47(88)
41(74)
103(60)
56(53)
27(40)
208(76)
223(75)
223(85)
223(82)
105(22)
105(26)
105(25)
51(19)
33(13)
38(17)
32(33)
16(26)
33(20)
31(23)
14(5.7)
16(4.0)
14(3.3)
30(19)

16(2.7)
48(23)

73(71)
87(84)
29(35)
41(51)
27(46)
56(39)
223(66)
208(68)
208(74)
208(65)
39(15)
39(17)
51(13)
39(14)
14(3.0)
35(9.2)
33(32)
15(2.4)
31(19)
29(19)
15(1.8)
14(1.7)
29(0.47)
14(7.8)
28(1.7)
32(4.9)

27(28)
29(74)
43(32)
43(46)
41(44)
70(38)
237(60)
295(52)
251(45)
250(46)
51(14)
51(14)
39(13)
65(12)
19(2.7)
37(2.9)
1(4.1)
14(0.7)
32(7.5)
30(15)
16(1.1)
47(0.02)
…
28(6.5)
34(0.22)
16(2.4)

Source: L. Meites, ed., Handbook of Analytical Chemistry, McGraw-Hill, New York, 1963.

Nearly all these spectra have been recorded using 70-V electrons to bombard the sample

molecules.

10.7 SECONDARY-ION MASS SPECTROMETRY 19,20
Secondary-ion mass spectrometry (SIMS) is used for the analysis of surface layers and their composition to a depth of 1 to 3 nm. A focused ion beam strikes the sample surface and releases secondary ions, which are detected by a mass spectrometer. Typical instrumentation might involve a
plasma-discharge source coupled with a quadrupole mass analyzer. The plasma discharge also serves
as a sputtering device to remove successive layers of sample for profiling the material.
The SIMS technique affords qualitative identification of all surface elements and permits identification of isotopes and the structural elucidation of molecular compounds present on a surface.
Detection sensitivity is in parts per million. SIMS is also useful for analyzing nonvolatile and thermally labile molecules, including polymers and large biomolecules.
19 K. F. J. Heinrich and D. E. Newbury, eds., Secondary Ion Mass Spectrometry, NBS Spec. Publ. No. 427, U.S. Government
Printing Office, Washington, D.C., 1975.
20 R. J. Day, S. E. Unger, and R. G. Cooks, “Molecular Secondary Ion Mass Spectrometry,” Anal. Chem. 52:557A (1980).

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MASS SPECTROMETRY

10.24

SECTION TEN

10.8 ISOTOPE-DILUTION MASS SPECTROMETRY (IDMS)
Stable isotopes can be used to “tag” compounds and thus serve as tracers to determine the ultimate
fate of the compound in chemical or biological systems and also as an analytical method. A number
of stable isotopes in sufficiently concentrated form are available for studying organic and inorganic
systems: H, B, C, N, O, S, and Cl. In principle, IDMS is applicable to all 60 elements that have more
than one available stable isotope.21 These isotopes complement the relatively larger number of
radioactive isotopes. The isotope-dilution method (Sec. 11.2.3) can be employed equally well with

stable isotopes.22 IDMS is based on the addition of a known amount of enriched isotope (called the
spike) to a sample. After equilibration of the spike isotope with the natural element in the sample,
MS is used to measure the altered isotopic ratio(s). It is only necessary to know the ratio of isotopes
present in the added sample of the substance, the ratio present in the final sample isolated from the
mixture, and the weight of the added sample.
The measured ratio (Rm) of isotope A to isotope B can be calculated as follows:
Rm =

Ax C x Wx + As Cs Ws
Bx C x Wx + Bs Cs Ws

(10.9)

where Ax and Bx are the atom fractions of isotopes A and B in the sample, As and Bs are the atom
fractions of isotopes A and B in the spike, Cx and Cs are the concentrations of the element in the sample and spike, respectively, and Wx and Ws are the weights of the sample and spike, respectively. The
concentration of the element in the sample can then be calculated:
C W   A −R B 
m s
Cx =  s s   s

 Wx   Rm Bx − Ax 

(10.10)

Because IDMS requires equilibration of the spike isotope and the natural isotope(s), the sample
must be dissolved. If the sample does not completely dissolve, if the spike or sample isotopes are selectively lost before equilibration, or if contamination occurs in the dissolution process, the measured isotopic ratios will not reflect the accurate ratio of added spike atoms to sample atoms for that element.
Thermal ionization is the ionization method of choice for precise and accurate IDMS. Precision and
accuracy are typically 0.1% or better. Other useful types of mass spectrometry include electron ionization with thermal probes, spark source, secondary ions, resonance ionization, and field desorption.
The isotope-ratio mass spectrometer, a less expensive adaptation of the usual mass spectrometer,
is available for work in this field. In the modified instrument the ion currents from two ion beams—

for example, the ion beams from 32SO2 and 34SO2, are collected simultaneously by means of a double exit slit and are amplified simultaneously by two separate amplifiers. The larger of the two
amplified currents is then attenuated by the operator until it exactly balances the smaller signal from
the other amplifier. The ratio of the two signals is determined from the attenuation required. This is
a null method and practically eliminates the effect of other variables in the system.

10.9 QUANTITATIVE ANALYSIS OF MIXTURES
Sensitivity and specificity are the major advantages of mass spectrometry as a quantitative analytical
technique. An ion incorporating the intact molecule (molecular ion peak) is most characteristic.
Production of molecular ions (or at least high-mass fragment ions) is favored by the use of low-energy
electron-impact ionization or by the use of chemical ionization. By judicious choice of reagent gases,
21 “Relative Abundance of Naturally Occurring Isotopes,” in J. A. Dean, ed., Lange’s Handbook of Chemistry, 14th ed.,
McGraw-Hill, New York, 1992, pp. 4.53 to 4.56.
22 J. D. Fassett and P. J. Paulsen, “Isotope Dilution Mass Spectrometry for Accurate Elemental Analysis,” Anal. Chem.
61:643A (1989).

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MASS SPECTROMETRY

MASS SPECTROMETRY

10.25

the latter ionization method provides the opportunity for selective ionization of certain components
of complex mixtures. Detection of analytes with high electron affinities through negative chemical
ionization provides another useful technique.
The flow of each kind of molecule through the leak in the inlet system is molecular; that is, the

rate of flow is proportional to the partial pressure of the species behind the leak and independent of
the presence of other kinds of molecules. Consequently, the intensities of the various ion beams from
the source are also proportional to the partial pressures of the substance behind the leak. If two or
more species yield ion beams having the same m/z ratio, the beam intensities, which are usually measured in arbitrary units and conventionally called peak heights, are additive. Thus, for a mixture of x
number of substances at a total pressure of P0 in the reservoir behind the leak, x peaks are selected
for measurement. Spectra are recorded on pure samples of each component. From inspection of the
individual mass spectra, analysis peaks are selected on the basis of both intensity and freedom from
interference. It possible, monocomponent peaks (perhaps molecular-ion peaks) are selected.
Computation is simplified if the components of the mixture give at least one peak whose intensity is
entirely due to the presence of one component.
From the mass spectrum of each pure compound, the sensitivity is obtained by dividing the peak
height of each significant peak by the pressure of the pure compound in the sample reservoir of the
mass spectrometer. From the simplified case in mixtures when the intensity of one peak is entirely
due to the presence of one component, the height of the monocomponent peak is measured and
divided by the appropriate sensitivity factor to give its partial pressure. Then division by the total
pressure in the sample reservoir at the time of analysis yields the mole fraction of the particular
component.
If the mixture has no monocomponent peaks, simultaneous linear equations are then set up from
the coefficients (percent of base peak) at each analysis peak. For example, the significant portion of
the mass spectral data is given in Table 10.3 for individual C1 to C3 alcohols. Using mass peaks at
32, 39, 46, and 59, four equations are written:
68.03x1 + 1.14x2 + 2.25x3 = M32

(10.11)

4.00x3 + 5.52x4 = M39

(10.12)

16.23x2 = M46

(10.13)

9.61x3 + 3.58x4 = M59

(10.14)

TABLE 10.3 Mass Spectral Data (Relative Intensities) for the C1 to C3 Alcohols
Percent of base peak (italic)
m/z
15
27
29
31
32
39
43
45
46
59
60
Sensitivity, divisions
per 10–3 torr

Methyl

Ethyl

n-Propyl

Isopropyl

35.48
—
58.80
100
68.03(P)
—

9.44
21.62
21.24
100
1.14
—
7.45
37.33
16.23(P)

3.77
15.20
14.14
100
2.25
4.00
3.18
4.39
—
9.61
6.36(P)

10.70
15.50
9.49
5.75
—
5.52
16.76
100
—
3.58
0.44(P)

8.76

17.98

26.51

23.47

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Unknown

600
3000

1100
2300