Page 170 - Advances in Forensic Applications of Mass Spectrometry - Jehuda Yinon

1522_C04.fm Page 153 Thursday, November 13, 2003 9:54 AM

by analyzing the isotopic composition of trimethoxycocaine and truxilline
extracted from coca leaves sampled at different geographic locations in South
17
America. This work confirmed that the stable isotope make-up of a sub-
stance is a function of its origin. In other words, two substances that are
chemically the same may have different stable isotope compositions if either
their origin and/or (bio)chemical history differ. This finding will remove the
defense of substances that are chemically the same not necessarily originating
from identical sources and will thus be a significant advance in forensic
science, intelligence gathering, and crime detection and reduction.
Stable isotope finger-printing or “chemical DNA,” in conjunction with
other spectroscopic data, will significantly increase the probative power of
analytical results for drugs, flammable liquids, explosives, fibers, textiles,
paints, varnishes, papers, inks, plastics, adhesives, and organic materials in
general æ indeed any nonbiological physical evidence. Multidimensional
isotope analysis (or multiisotope analysis) of a given material can provide a
combined specificity on a scale hitherto known only for DNA analysis. If one
assumes that two given organic compounds (e.g., truxilline and trimethox-
ycocaine) made up of C, N, H, and O would occur naturally in only 14
significantly different isotopic variations (in fact, this number would be much
2
higher), the combined specificity of a 4-dimensional isotope analysis ( H,
18
15
2 4
13 C, N, and O) would thus be 1/{(14 ) } or 1/14( ), i.e., 1 in 1.47 billion.
2*4
4.2 Instrumentation
4.2.1 Introduction
Mass spectrometry is best known among chemists as one of the most impor-
tant analytical techniques for the characterization of molecular structure and
amount, elemental composition, and spatial arrangement. In contrast, nat-
18
ural or life scientists such as biomedical, biological, food, and geochemical
scientists regard MS as a tool that reveals origin and genesis, or the state of
complex systems through high precision measurements of isotopic abun-
dances. The latter type of MS is more aptly named IRMS to denote differences
in instrumental design between IRMS and scanning MS systems, as well as
the fact that IRMS determines isotope abundances by measuring isotope
ratios to reveal this other dimension of information locked into matter, which
is usually not available from structural or quantitative studies.
In contrast to single collector MS that yield structural information by
scanning a mass range over several hundred Dalton for characteristic frag-
ment ions, IRMS instruments achieve highly accurate and precise measure-
ment of isotopic abundance at the expense of the flexibility of scanning MS.
However, scanning mass spectrometers universally employ single detector

© 2004 by CRC Press LLC