Forensic Mass Spectrometry

1
Forensic Mass Spectrometry Distinguished Prof.
Eric Block CHM 450B, W 2006
2
NYSP Laboratory Report
cocaine mw 303
cocaine, cocaethylene, methadone Identified in
urine
cocaethylene mw 317
methadone mw 309
3
82
182
303
272
Mass Spectrum of Cocaine
4
Mini Gas Chromatograph/Mass Spectrometer (on
right full sized GC-MS on left) The Mini GC/MS
is a robust, reliable, and field-deployable
instrument. With an ability to analyze samples at
sensitivities of parts per billion within 15 to
40 minutes, the portable GC/MS can be used during
homeland-defense activities, incident response,
and law-enforcement investigations. For example,
the instrument can precisely identify compounds
that indicate the production of chemical-warfare
agents and illicit drugs.
5
Electron-Impact Mass Spectrometry

• Mass spectrometry is a technique used for
  measuring the molecular weight and determining
  the molecular formula of an organic compound.
• In an electron-impact mass spectrometer (EI-MS),
  a molecule is vaporized and ionized by
  bombardment with a beam of high-energy electrons.
• The energy of the electrons is 1600 kcal (or 70
  eV).
• Since it takes 100 kcal of energy to cleave a
  typical s bond, 1600 kcal is an enormous amount
  of energy to come into contact with a molecule.
  Usually only a portion of this energy is
  transferred to the molecule.
• The electron beam ionizes the molecule by causing
  it to eject an electron.

6
Chemical Ionization Mass Spectrometry
Chemical ionization mass spectrometry (CI-MS)
begins with ionization of methane, ammonia or
another gas, creating a radical cation (e.g.
CH4 or NH3). This in turn will impact the
sample molecule M to produce MH molecular ions.
Some of MH fragments into smaller daughter ions
and neutral fragments. Both positive and negative
ions are formed but only positively charged
species will be detected. Less fragmentation
occurs with CI than with EI, hence CI yields less
information about the detailed structure of a
molecule, but does yield the molecular ion
sometimes the molecular ion cannot be detected by
the EI method, hence the two methods are
complementary.
7
Mass Spectrometry
Introduction
8
For descriptive purposes, an analogy can be drawn
between a mass spectrometer and an optical
spectrophotometer. In the latter, light is
separated into its various wavelength components
by a prism and then detected with an optical
receptor (such as the eye).
Analogy between mass analysis and the analysis of
light
9
Analogously, a mass spectrometer contains an ion
source that generates ions, a mass analyzer that
separates the ions according to their
mass-to-charge ratio, and an ion detector.
Components of a Mass Spectrometer
10
Ion Sources and Sample Introduction

• Sample Introduction
• The sample inlet is the interface between the
  sample and the mass spectrometer. A sample at
  atmospheric pressure must be introduced into the
  instrument such that the vacuum within remains
  unchanged.

Introduction and Ionization Components in a Mass
Spectrometer
11

• Sample Introduction (continued)
• A sample can be introduced in several ways, the
  most common being with a direct insertion probe
  or by infusion through a capillary column.

Samples are often introduced using a direct
insertion probe or a capillary column. The probe
and capillary carry the sample into the vacuum of
the mass spectrometer. Once inside the mass
spectrometer, the sample is exposed to the
ionization source
12
Mass Analyzers

• Mass analyzers scan or select ions over a
  particular m/z range. The key feature of all mass
  analyzers is their measurement of m/z, not mass.
  The mass analyzers contribute to the accuracy,
  range and sensitivity of an instrument. Six
  common types of mass analyzers are quadrupole,
  magnetic sector, time-of-flight, time-of-flight
  reflection, quadrupole ion traps and Fourier
  transform-ion cyclotron resonance (FT-ICR).

13
Quadrupole Analyzer
Mass Analyzers (continued)

• Quadrupoles are four precisely parallel rods with
  a direct current (DC) voltage and a superimposed
  radio-frequency (RF) potential. The field on the
  quadrupoles determines which ions are allowed to
  reach the detector. Quadrupoles thus function as
  a mass filter.

the B
14
Mass Analyzers (continued)
Quadrupole Analyzer (continued)

• Quadrupole mass analyzers have been used in
  conjunction with electron ionization since the
  1950s. EI coupled with quadrupole mass analyzers
  are employed in the most common mass
  spectrometers today.
• Quad mass analyzers have found new utility in
  their capacity to interface with electrospray
  ionization. This interface has three primary
  advantages
• 1. Quads are tolerant of relatively high
  pressures (5 x 10-5 Torr), which is well
  suited to electrospray ionization since the
  ions are produced under atmospheric pressure
  conditions.
• 2. Quads are now capable of routinely analyzing
  up to an m/z of 3000, which is useful because
  electrospray ionization of proteins and other
  biomolecules commonly produces a charge
  distribution below m/z 3000.
• 3. The relatively low cost of quadrupole mass
  specs makes them attractive as electrospray
  analyzers. Thus, it is not surprising that
  most of the successful commercial electrospray
  instruments thus far have been coupled with
  quadrupole mass analyzers.

15
Tandem Mass Spectrometry
The new ionization techniques are relatively
simple and do not produce a significant amount of
fragment ions, in contrast to EI which produces a
lot of fragment ions. Tandem mass spectrometry
(MS/MS) was developed to induce fragmentation. In
tandem MS (abbreviated MSn where n refers to the
number of generations of fragment ions being
analyzed) collisionally induced fragment ions are
mass analyzed.
16
Tandem Mass Spectrometry (continued)
Fragmentation is achieved by inducing
ion-molecule collisions via collision-induced
dissociation (CID) or collision activated
dissociation. CID is accomplished by selecting an
ion of interest with a mass filter/analyzer and
introducing that ion into the collision cell. A
collision gas (typically Ar) is introduced into
the collision cell, where the selected ion
collides with the argon atoms, resulting in
fragmentation. The fragments are then analyzed to
obtain a daughter ion spectrum. The term MSn is
applied to processes which analyze beyond
daughter ions (MS2) to grandaughter (MS3), and to
great-granddaughter ions (MS4). Tandem mass
analysis is primarily used to obtain structural
information.
17
Interpretation of EIMass Spectra
18
Important Terminology

• Amuatomic mass unit/dalton
• M?, molecular ionthe ionized molecule the
  molecular ion peak is the peak representing the
  ionized molecule that contains only the isotopes
  of natural abundance
• Base Peakthe peak in the spectrum that
  represents the most abundant ion
• Daughter Ionthe product produced by some sort of
  fragmentation of a larger ion
• Isotopic Peaka peak in the spectrum that
  corresponds to the presence of one or more
  heavier isotopes of an ion
• A Elementan element that is monoisotopic
• A 1 Elementan element with an isotope that
  is 1 amu above that of the most abundant isotope,
  but which is not an A 2 element
• A 2 Elementan element with an isotope that
  is 2 amu above that of the most abundant isotope

19
Things to keep in mind

• Interpretation is based on the chemistry of
  gaseous ions.
• Ion abundances of ltlt0.1 can be measured
  reproducibly. The error of non-high resolution
  spectra is 10 relative or 0.2 absolute,
  whichever is greater.
• General spectra are shown with unit mass
  resolution (x-axis).
• Generally, measured spectra contain additional
  peaks due to background in the instrument. This
  arises from compounds that are desorbing from the
  walls of the instrument or leaking from various
  sources. Thus, a background spectrum is usually
  run before the actual sample is introduced to the
  instrument, and subtracted from the sample
  spectrum.
• Small peaks with masses above that correspond to
  the molecular weight are due to the presence of
  less abun-dant isotopes.

20
Mass Spectrometry
Introduction

• When the electron beam ionizes the molecule, the
  species that is formed is called a radical
  cation, and symbolized as M.
• The radical cation M is called the molecular
  ion or parent ion.
• The mass of M represents the molecular weight
  of M.
• Because M is unstable, it decomposes to form
  fragments of radicals and cations that have a
  lower molecular weight than M.
• The mass spectrometer analyzes the masses of
  cations.
• A mass spectrum is a plot of the amount of each
  cation (its relative abundance) versus its mass
  to charge ratio (m/z, where m is mass, and z is
  charge).
• Since z is almost always 1, m/z actually
  measures the mass (m) of the individual ions.

21
Basic Mechanisms of Fragmentation

• Mass spectral reactions are unimolecular the
  sample pressure in the EI source is kept
  sufficiently low so that bimolecular
  (ion-molecule) or other collisions are usually
  negligible. If sufficiently excited, the M
  ions can decompose by a variety of energy
  dependent mechanisms each of which results in the
  formation of an ion and a neutral species
  (radical). This primary product may have
  sufficient energy to decompose further.
• In the MS of ABCD, the abundance of BCD will
  depend on the average rates of its formation and
  decomposition, whereas BC will depend upon the
  relative rates of several competitive reactions.
  There are several types of unimolecular
  reactions that can take place

e
ABCD
ABCD
A BCD
A BCD
D BC
A BC
D ABC
AD BC
22
Unknown 1

• m/z Int
• 1 lt0.1
• 16 1.0
• 17 21.0
• 18 100
• 20 0.2

18
relative abundance
17
16
Mass (mass-to-charge ratio)
23

• m/z Int
• 12 1.0
• 13 8.1
• 14 16.
• 15 85.
• 16 100.
• 17 1.1

16
15
relative abundance
14
13
17
12
Mass (mass-to-charge ratio
24
Mass Spectrometry
Introduction
Consider the mass spectrum of CH4 below

• The tallest peak in the mass spectrum is called
  the base peak.
• The base peak is also the M peak, although this
  may not always be the case.
• Though most C atoms have an atomic mass of 12,
  1.1 have a mass of 13. Thus, 13CH4 is
  responsible for the peak at m/z 17. This is
  called the M 1 peak.

25
Mass Spectrum of Neon Showing Major and Minor
Natural Isotopes
20Ne 90.48
rel. int
22Ne 9.25
21Ne 0.27
m/z
26
Mass Spectrometry
Introduction

• The mass spectrum of CH4 consists of more peaks
  than just the M peak.
• Since the molecular ion is unstable, it fragments
  into other cations and radical cations containing
  one, two, three, or four fewer hydrogen atoms
  than methane itself.
• Thus, the peaks at m/z 15, 14, 13 and 12 are due
  to these lower molecular weight fragments.

27
CH3OH

• m/z Int
• 12 0.3
• 13 1.7
• 14 2.4
• 15 13.
• 15.5 0.2
• 16 0.2
• 17 1.0
• 28 6.3
• 29 64.
• 30 3.8
• 31 100.
• 32 66.
• 33 1.0
• 34 0.1

31
32
29
relative abundance
15
28
Mass Spectrometry
Introduction
29
Mass Spectrometry
Alkyl Halides and the M 2 Peak

• Most elements have one major isotope.
• Chlorine has two common isotopes, 35Cl and 37Cl,
  which occur naturally in a 31 ratio.
• Thus, there are two peaks in a 31 ratio for the
  molecular ion of an alkyl chloride.
• The larger peak, the M peak, corresponds to the
  compound containing the 35Cl. The smaller peak,
  the M 2 peak, corresponds to the compound
  containing 37Cl.
• Thus, when the molecular ion consists of two
  peaks (M and M 2) in a 31 ratio, a Cl atom is
  present.
• Br has two isotopes79Br and 81Br, in a ratio of
  11. Thus, when the molecular ion consists of
  two peaks (M and M 2) in a 11 ratio, a Br atom
  is present.

30
Mass Spectrometry
Alkyl Halides and the M 2 Peak
(CH3)2CH
31
Mass Spectrometry
Alkyl Halides and the M 2 Peak
(CH3)2CH
32
Elemental Composition

• With high resolution mass spectrometers, exact
  mass measurements provide the number of each
  constituent element
• Even with unit mass spectrometers, the presence
  of natural abundance isotopes makes possible the
  deduction of the elemental composition of many
  ions
• A chemically pure compound will give a mixture of
  mass spectra because the elements that compose it
  are not isotopically pure
• Of the common elements encountered in organic
  compounds, many have more than one isotope in
  appreciable abundance. Thus, characteristic
  isotopic ratios can result in easy identification
  of elements in a structure

33
A elements those with only one natural
isotope in appreciable abundance A 1
elements those that have two isotopes, the
second of which is one mass unit heavier A
2 elements are the easiest to recognize and
are two mass units higher
A A 1
A 2 Element Element Mass
Mass Mass type H 1
100 2 0.015 A C 12 100
13 1.1 A 1 N 14 100
15 0.37 A 1 O 16 100
17 0.04 18 0.20 A 2 F 19
100 A Si 28 100
29 5.1 30 3.4 A 2 P 31 100
A S 32 100
33 0.79 34 4.4 A 2 Cl 35 100
37 32.0 A 2 Br 79 100
81 97.3 A 2
34
A 2 Elements oxygen, silicon, sulfur,
chlorine and bromine

• A second isotope makes an especially prominent
  appearance in the spectrum if it is more than one
  mass unit higher than the most abundant isotopic
  species. Bromine and chlorine and to a lesser
  extent silicon and sulfur are striking common
  examples
• The presence of these elements in an ion is
  usually easily recognized from the isotopic
  clusters produced in the spectrum
• Because of Linear Superposition of Isotopic
  Ions, the isotopic patterns are even more
  striking when more than one A 2 isotope is
  present in an ion. For HBr the isotopic molecular
  ions at m/z 80 and 82 (H79Br and H81Br) are in
  relative proportions of 11. The MS of Br2 shows
  prominent molecular ions at 158, 160 and 162,
  representing 79Br-79Br, 79Br-81Br, 81Br-79Br and
  81Br-81Br.

1

2

1
35
How many peaks will a molecule containing 3
bromine atoms exhibit?
4 peaks at intervals of 2 mass units in the
ratio of 1331.
What species are responsible for the four
peaks?
CHBr3
79Br79Br79Br 237 79Br79Br81Br
239 79Br81Br79Br 239 81Br79Br79Br
239 81Br81Br79Br 241 81Br79Br81Br
241 79Br81Br81Br 241 81Br81Br81Br 243
36
The MS of SO2 contains no A 1 element, shows
m/z 65/m/z 64 of 0.9, which is close to that
expected for one carbon (but is actually due to
33S16O2 and 32S16O17O). This is another reason
to check the M 2 peak first!
SO2

• m/z Int
• 64 100.
• 65 0.9
• 66 5.0

rel. int.
m/z
37
Are A 2 peaks present?
No!
What does the fact that the base peak M.
imply?
stability
How many carbons are implied by the M 1 peak?
6.8/100- 6 carbons (and 6 hydrogens)
What is the molecules identity?
Benzene
What does the A 2 peak at m/z 80 arise from?
13C212C4H6

• m/z Int
• 37 3.8
• 39 13.
• 50 16.
• 51 19.
• 52 20.
• 63 2.9
• 74 3.9
• 75 2.2
• 76 7.0
• 77 15.
• 78 100.
• 79 6.8
• 80 0.2

78
51
39
63
38
The Molecular Ion

• M Provides the most valuable information in
  the spectrum.
• Its mass and elemental composition show molecular
  boundaries into which the structural fragments
  indicated must be fitted.
• Unfortunately, for some compounds, the molecular
  ion is not sufficiently stable to be found in
  appreciable abundance in an EI spectrum
• By convention, mass spectrometrists calculate the
  molecular weight (m/z of molecular ion peak) in
  terms of the mass of the most abundant isotope of
  each of the elements present. Eg The molecular
  weight of benzene, which has substantial peaks
  from m/z 78 and m/z 80 has a molecular weight of
  m/z 78 Br2 has peaks at m/z 158 and m/z 160, but
  has a molecular weight of 158. Within these
  constraints in an EI spectrum of a pure compound,
  the molecular ion, if present, must be found at
  the highest value of m/z in the spectrum

39
The Molecular Ion (continued)
Requirements of the Molecular Ion

• The following are necessary but not sufficient
  requirements for the molecular ion in the mass
  spectrum of a pure sample free from extraneous
  peaks such as those from background and
  ion-molecule interactions
• It must be the ion of highest mass in the
  spectrum.
• It must be an odd electron ion.
• It must be capable of yielding the important ions
  in the high mass region of the spectrum by loss
  of logical neutral ions
• If the ion in question fails any of these tests,
  it cannot be the molecular ion if it passes all
  these tests, it may or may not be the molecular
  ion!

40
The Molecular Ion (continued)
Odd Electron Ions

• The species formed when a sample molecule becomes
  ionized by losing an electron, leaving one
  electron unpaired is called an odd electron ion.
  It is designated by the symbol .. It should be
  noted that ions in which the outer-shell
  electrons are paired are called even-electron
  ions. These are designated by the symbol .
• The ease of ionization of outer-shell electrons
  is ngt?gt?. Usually, several canonical resonance
  forms can be drawn to approximate the electron
  distribution of the ion.

41
The Molecular Ion (continued)
Odd Electron Ions

• Note that indicates only an ion with an
  unpaired electron, not an electron in addition to
  those the formula represents i.e. adding an
  electron to CH4 would give CH4- .
• In general, ions containing only paired electrons
  (EE) are more stable, and thus more often the
  abundant fragment ions in an EI spectrum. Eg
  cleavage of a C-H bond in CH4. forms the stable
  EE ions CH3 and H.
• Soft ionization techniques such as FAB, ESI and
  MALDI tend to give EE molecular species such as
  MH.
• OE ions have special mechanistic significance
  and should be identified on the spectrum early in
  the interpretation procedure.
• The importance of a peak after one has corrected
  for abundance for contributions of ions
  containing less common isotopes, generally
  increases with
• Increasing intensity
• Increasing mass in spectrum
• Increasing mass in peak group, particularly the
  most or second most number of hydrogen atoms for
  an OE peak.

42
Mass Spectrometry
High Resolution Mass Spectrometers

• Low resolution mass spectrometers report m/z
  values to the nearest whole number. Thus, the
  mass of a given molecular ion can correspond to
  many different masses.
• High resolution mass spectrometers measure m/z
  ratios to four (or more) decimal places.

• This is valuable because except for 12C whose
  mass is defined as 12.0000, the masses of all
  other nuclei are very closebut not exactlywhole
  numbers.
• Table 14.1 lists the exact mass values for a few
  common nuclei. Using these values it is possible
  to determine the single molecular formula that
  gives rise to a molecular ion.

43
Mass Spectrometry
High Resolution Mass Spectrometers

• Consider a compound having a molecular ion at m/z
  60 using a low resolution mass spectrometer.
  The molecule could have any one of the following
  molecular formulas.

44
Hydrocarbons
Saturated Hydrocarbons For straight chain
compounds, M is always present but with
generally low intensity. Fragmentation is
characterized by clusters of peaks, with
the corresponding peaks of each cluster being
14 (CH2) mass units apart. The largest peak
in each cluster represents a CnH2n1
fragment. Fragment abundances decrease in a
smooth curve down to M-C2H5. The M-CH3
peak is characteristically very weak or
missing. Compounds containing more than 8
carbon atoms show fairly similar spectra.
Thus, identification depends on the
molecular ion peak.
45
n-decane
- 14
- 14
142
46
n-tridecane
184
47
n-pentadecane
212
48
n-eicosane
282
49
Mass Spectrometry
Gas Chromatography-Mass Spectrometry (GC-MS)
interface
Sample introduced into GC inlet vaporized at 250
C , swept onto the column by He carrier gas
separated on column. Sample components emerge
from column, flowing into the capillary column
interface connecting the GC col-umn and the MS
(He removed).
The computer drives the MS, records the data, and
converts the electrical impulses into visual
displays and hard copy displays.  Identification
of a compound based on it's mass spectrum relies
on the fact that every compound has a unique
fragmentation pattern  A large library of known
mass spectra is stored on the computer and may be
searched using computer algorithms to assist the
analyst in identifying the unknown.
50
Mass Spectrometry
Gas Chromatography-Mass Spectrometry (GC-MS)

• To analyze a urine sample for tetrahydrocannabinol
  , (THC) the principle psychoactive component of
  marijuana, the organic compounds are extracted
  from urine, purified, concentrated and injected
  into the GC-MS.
• THC appears as a GC peak, and gives a molecular
  ion at 314, its molecular weight.

To improve GC separa-tions, compounds are often
derivatized, e.g. as their trimethylsilyl (TMS)
ethers or trifluor-oacetate (TFA) esters.
THC TMS ether (l) TFA ester (r)
51
Liquid Chromatography-Mass Spectrometry
(LC-MS) Similar to gas chromatography MS (GC-MS),
liquid chromatography mass spectrometry (LC/MS or
LC-MS) separates compounds chromatographically
before they are introduced to the ion source and
mass spectrometer. It differs from GC-MS in that
the mobile phase is liquid, usually a combination
of water and organic solvents, instead of gas.
Most commonly, an electrospray ionization (ESI)
source is used in LC-MS.
52
Electrospray Ionization (ESI) ESI is a
method used to generate gaseous ionized molecules
from a liquid solution. This is done by creating
a fine spray of highly charged droplets in the
presence of a strong electric field. The sample
solution is sprayed from a region of a strong
electric field at the tip of a metal nozzle
maintained at approximately 4000 V. The highly
charged droplets are then electrostatically
attracted to the mass spectrometer inlet.
Either dry gas, heat or both are applied to the
droplets before they enter the vacuum of the mass
spectrometer, thus causing the solvent to
evaporate from the surface. As the droplet
decreases in size, the electric field density on
its surface increases. The mutual repulsion
between like charges on this surface becomes so
great that it exceeds the forces of surface
tension, and ions begin to leave the droplet
through what is known as a Taylor cone. The
ions are directed into an orifice through
electrostatic lenses leading to the mass analyzer.
53
Advantages and Disadvantages of ESI-MS

• Advantages
• Practical mass range of up to 70,000 Da.
• Femtomole to low picomole sensitivity
• Softest ionization technique
• Easily interfaced with LC
• No matrix interference
• Easily adaptable to triple quadrupole analysis,
  conducive to structural analysis
• Multiple charging, allowing for analysis of
  high-mass ions with relatively low m/z range
  instrument
• Multiple charging giving better mass accuracy
  through averaging

• Disadvantages
• Low salt tolerance
• Difficulty in cleaning overly contaminated
  instrument due to high sensitivity for certain
  compounds
• Low tolerance for mixtures. Simultaneous mixture
  analysis can be poor. The purity of the sample is
  important
• Multiple charging, which can be confusing,
  especially with mixture analysis

54
Forensic Mass Spectrometry

• Analysis of Body Fluids for Drugs of Abuse
• Analysis of Hair in Drug Testing
• Sports Testing
• Analysis of Accelerants in Fire Debris
• Analysis of Explosives
• Use of Isotope Ratios

J. Yinon, Ed., Forensic Applications of Mass
Spectrometry, CRC Press, 1995
55
Forensic Mass Spectrometry

• Analysis of Hair in Drug Testing

An important feature of hair analysis is its
long-term information on an individuals drug use
in contrast to the short-tern information
provided by urinalysis. Head hair grows at ca.
1.3 cm/month. Consequently by sampling the
segment of hair corresponding to a particular
time frame, hair analysis can uncover drug use
from a week to years prior to collection of the
specimen. Hair analysis by GC-MS methods has been
used to establish the presence of Cannabinoids
(marijuana) Cocaine Amphetamines Opiates
(heroin) Barbiturates Phencyclidine (PCP).
J. Yinon, Ed., Forensic Applications of Mass
Spectrometry, CRC Press, 1995
56
Forensic Mass Spectrometry

• Analysis of Accelerants in Fire Debris

When a fire is extinguished fire debris samples
must be quickly obtained and placed in airtight
unlined and unused metal cans for GC-MS analysis.
Forensic chemist need to explain in court GC/MS
principles methods used to identify accelerant.
Accelerant recovery techniques involve direct
headspace methods with or without adsorbent
although such techniques discriminate against
high boiling accelerants. Other methods include
distillation, solvent extraction, thermal
desorption. Accelerants include gasoline, light
petroleum distillates, turpentine diesel fuel.
Matrices from which volatiles are recovered
include carpet, wood, sheet rock, soil, concrete,
roofing. Identification involves pattern
matching between a GC profile and a series of
standard accelerants correcting for solid matrix
contributions.
J. Yinon, Ed., Forensic Applications of Mass
Spectrometry, CRC Press, 1995
57
Forensic Mass Spectrometry

• Analysis of Explosives

Screening of evidentiary material for explosives
(postblast) residue as well as detection of
hidden explosives in aviation security present
many challenges. There are three classes of
explosives high explosives, propellants (low
explosives) and primary explosives. High
explosives are subdivided into three groups TNT
(trinitrotoluene) and related aromatic nitro
compounds RDX (cyclotrimethylene trinitramine)
and related nitramines with NNO2 groups
nitroglycerin, pentaerythritol tetranitrate
(PETN) and related nitrated esters with CONO2
groups. Explosives are most often mixtures of the
above, e.g. PETN and RDX are associated with
SEMTEX, a Czechoslovakian explosive. Richard
Reid, the shoe bomber was found to have
triacetone peroxide, TATP, which was to be used
to set off the more powerful plastic explosive
PETN. Difficult to analyze some high explosives
because of thermal instability and weak molecular
ions due to easy fragmentation. LC-MS may be
preferable to GC-MS. Negative chemical ionization
(CI) MS better than positive ion CI due to high
electronegativity.
J. Yinon, Ed., Forensic Applications of Mass
Spectrometry, CRC Press, 1995
58
Forensic Mass Spectrometry

• Use of Isotope Ratios

Starting from raw materials with various isotopic
compositions and undergoing various isotope
effects all along the synthetic or biosyn-thetic
pathways, molecules progressively acquire a
characteristic isotopic composition that
constitutes their own isotopic signature.
Measurement of isotopic ratios of each of its
constituent elements can act as the specific
isotopic signature. This isotopic signature can
be self-generated during synthetic processes
without an intentional modification. This
signature can also be intentionally produced by
adding precursors artifically enriched with
stable isotopes in the reaction medium where the
synthesis or biosynthesis takes place. Therefore,
this intentionally modified isotope composition
can be considered as an isotope signature of the
commercial property of the compound. Isotope
ratios can be accurately measured using isotope
ratio mass spectrometers, IRMS. IRMS has been
used to distinguish natural vanillin (2500/kg
from Tahiti) from synthetic vanillin made from
clove oil (10/kg) and natural honey from honey
adultrated with cheaper high fructose corn syrup.
J. Yinon, Ed., Forensic Applications of Mass
Spectrometry, CRC Press, 1995
59
Natural Isotopes and Trace Elements in Forensics
Most criminal activities result in the generation
of some kind of debris, either at the scene of
the crime and/or on the individual perpetrators.
Subsequently this material becomes available to
investigators as physical evidence of the crime.
However, traditionally the generation of
analytical and forensic chemical data is often
compro-mised by a number of factors Sample
mass may be extremely small, this being
especially true as criminals become more
sophisticated, The generation of data is often
time consuming and costly and increasingly the
budget of police forces is being diminished,
The range of analytes accessible for analysis is
often compromised by a requirement to retain
a significant portion of the sample for
corroborative studies. New developments in
instrumentation, especially the combination of
Laser Ablation with either Quadrupole, Time of
Flight, Sector or Multi-Collector ICP-MS
(Inductively Coupled Plasma-Mass Spectrometry),
have created exciting possibilities for the
routine "nondestructive" isotope and
trace-element analysis of small and valuable
specimens. Laser Ablation-Inductively Coupled
Plasma-Mass Spectrometry (LA-ICP-MS) offers the
potential of producing fast, definitive, cost
effective elemental and isotopic ratio data for a
wide variety of forensic chemical evidence for
use in identifying and comparing physical
evidence and thereby unambiguously relating a
suspect to a crime scene. Forensic investigations
significantly benefit from the study of unique
natural isotopic and trace-elemental fingerprints
in most materials involved.
60
Inductively Coupled Plasma Mass Spectrometry
Mass Spectrometry of Ionized Atoms
ICP-MS (Inductively Coupled Plasma Mass
Spectrometry) is a highly sensitive mass
spectrometer capable of analysis of metals and
non-metals at below one part in 1012. It is based
on coupling an inductively coupled plasma (ICP),
which produces atomic ions (as opposed to
molecular ions), with a mass spectrometer as a
method of identifying and detecting the ions.
ICP - a high temperature argon plasma sustained
with a radiofrequency electric current produces
ions. The electric current is transferred to the
plasma by an induction coil, wrapped around
concentric quartz tubes (the plasma torch).
Operating frequencies are 27.12 and 40.68 MHz
operating power is 800 to 1500 W. The plasma is
sustained within a constant, high flow of argon
gas and reaches temperatures of 10,000 C. Total
gas consumption is 14 - 18 L/min. MS - the ions
from the plasma are extracted through a series of
cones into a quadrupole mass spectrometer and are
separated according to their m/z ratio. A
detector receives an ion signal proportional to
the concentration. Sample concentration is
determined through calibration with elemental
standards. Quantitative determination using
ICP-MS requires isotope dilution, a single point
method based on an isotopically enriched
standard. Laser ablation (LA) ICP-MS uses lasers
to generate samples for ICP-MS analysis.
61
J. Agric. Food Chem., 53 (10), 4041-4045,
2005. Determination of the Country of Origin of
Garlic (Allium sativum) Using Trace Metal
Profiling Ralph G. Smith U.S. Customs and Border
Protection Laboratory, 214 Bourne Boulevard,
Savannah, Georgia 31408 Abstract A method for
determining the country of origin of garlic by
comparing the trace metal profile of the sample
to an authentic garlic database is presented.
Protocols for sample preparation, high-resolution
inductively coupled plasma mass spectrometry, and
multivariate statistics are provided. The
criteria used for making a country of origin
prediction are also presented. Indications are
that the method presented here may be used to
determine the geographic origin of other
agricultural products.
Introduction U.S. Customs and Border Protection
(CBP) Laboratories have been working on
laboratory methods to facilitate scientific
identification of the country of origin of
various agricultural products. One such method
presented here includes the determination of the
trace metal profile of the agricultural product
for comparison with an established database of
trace metal profiles of the product from various
countries. The uptake of trace metals by
agricultural products from the soil in which they
are grown provides a mechanism for identification
of their geographic origin. There are a number of
factors such as rainfall, sunshine, temperature,
soil characteristics, and plant species that may
play an important role in the uptake of trace
metals. It is the combination of these factors
that influence the uptake of trace metals
creating a rough snapshot or historical record of
the plant's growth. In most cases, the trace
metal profiles of agricultural products from
various countries display enough statistical
uniqueness to make a definitive country of origin
prediction. The use of trace metal profiling for
determining the geographic origin of agricultural
products uses high-resolution ICP-MS with lowered
detection limits and elimination of many of the
isobaric interferences prevalent with quadrupole
ICP-MS instruments. Garlic samples were analyzed
for 18 elements by high-resolution ICPMS
including Li, B, Na, Mg, P, S, Ca, Ti, Mn, Fe,
Cu, Ni, Zn, Rb, Sr, Mo, Cd, and Ba.
62
Forensic Mass Spectrometry

• Analysis of Body Fluids for Drugs of Abuse

1) Hydrolyze drug metabolites (acid, base,
enzymatic) 2) extract from biological matrices
(liquid-liquid or SPE) 3) derivatize to improve
volatility, separation and analysis 4)
chromatographically separate, typically by GC
using a narrow-bore (0.20 to 0.32 mm i.d.)
fused-silica methyl-silicone or
phenylmethylsilicone capillary GC column 5)
deuterated internal standards to confirm
extraction process, GC RT fragmentation
patterns 6) analysis by EI- or CI-MS (e.g. using
NH3 CI is more sensitive giving only parent ion
7) mass analysis using full scan data acquisition
or selected ion monitoring (SIMs can provide
signal intensities 100-fold better and is less
subject to interferences but can miss significant
unsuspected drugs). Cannabinoids (marijuana)
Cocaine Amphetamines Opiates (heroin)
Barbiturates Phencyclidine (PCP) Lysergic acid
diethylamide (LSD) Benzodiazepines Fentanyl.
J. Yinon, Ed., Forensic Applications of Mass
Spectrometry, CRC Press, 1995
63
Forensic Mass Spectrometry

• Analysis of Accelerants in Fire Debris

GC methods used include GC-MS, GC-IR and GC-AE.
GC analysis of hydrocarbons is most useful when
fragmentation pattern is unique and particularly
if several ions can be found that are
characteristic for a substance class, usually
alkanes and alkyl-benzenes. Typical fragment
ions 43, 57, 71 alkanes, 91, 106, 120
alkylbenzenes, 128, 142, 156 naphthalenes
alcohols 31, 45, ketones 43, 58, esters 43,
73, terpenes 93, 136. Critical to discriminate
against artifacts (e.g. from matrices, extraction
sol-vents, pyrolysis products from the effect of
the fire). GC patterns may show evenly spaced
peaks corresponding to n-alkane homo-logs (medium
and high boiling range distillates and kerosene)
but this is not the case for gasoline. Note also
that 90 evaporated gasoline appears quite
different from the original gasoline. Gaso-line
consists of more than 250 components above the 10
ppm level and is one of the most complex
accelerants.
J. Yinon, Ed., Forensic Applications of Mass
Spectrometry, CRC Press, 1995