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158 Mass Spectrometry

number of possible empirical formulas that can sum to the we now follow the same process with MS/MS data. At
accurately measured ion mass is greatly reduced. The ap- the same time, new instrumental capabilities (specifically
proach is general to any particular isotopic incorporation. with ion traps and Fourier transform mass spectrometers)
It is not a development in instrumental capability; it is a mean that multiple-stage MS/MS can be completed, and
development in which instrumental capability is synergis- the sequential induced dissociations of a mass-selected
tically coupled with reasoned use of other information. parent ion into product ions can be measured. It is easy to
The same coupling is evident in the ability of FTMS to record and easy to store multidimensional MS/MS data.
provide accurate mass measurements for ions generated What does this data mean? It is most certainly a series of
in multistep dissociations in MS/MS. It is not necessary insights into the structure and reactivity of the ions. But in
that the value of exact mass measurement differentiate a larger sense, it is also a collection of a pattern of informa-
between all possible ion empirical formulas, but only be- tion that can reach a complexity sufficient that the pattern
tween possible empirical formulas for product ions that itself becomes a specific identifier for a particular molec-
can be formed from the mass-selected parent ion for which ular structure and identity. This concept is not unfamiliar
the empirical formula is already known. As a simple ex- to users of nuclear magnetic resonance (NMR) data. Tar-
ample, if the parent ion contains no sulfur atoms, then the geted sifting of a complex database of multidimensional
product ion cannot either. Further, “weak” points within a MS/MS has not yet impacted the analytical community,
molecular structure, and therefore probable sites of cleav- and the clear advantages for unambiguous sample identi-
age, are usually apparent to experienced analysts. With fication have not yet been reaped. It is merely a matter of
the number of possibilities thus even further reduced, the time, and closer to five years than fifty.
value of the exact mass measurement is amplified further.
Thepossibilitiesnarrowasthenumberofstagesofinduced
dissociation increases, relaxing the need for accurate mass SEE ALSO THE FOLLOWING ARTICLES
measurement as the ion signal grows smaller.
ANALYTICAL CHEMISTRY • DATABASES • GAS CHRO-
B. Multidimensional MS/MS MATOGRAPHY • ION KINETICS AND ENERGETICS • LIQUID
CHROMATOGRAPHY • MASS SPECTROMETRY IN FOREN-
The central analytical role of mass spectrometry continues
SIC SCIENCE
to be twofold: what is the sample and how much of it
is there? Certainly there are extraordinary new insights
into chemical behavior between complex species in BIBLIOGRAPHY
solution and in the gas phase that will be part of the
next fifty years of mass spectrometry, made possible
Aston, K. W. (1942). “Mass Spectra and Isotopes,” Arnold, London.
by advances in ESI and MALDI. Forecasting in the Busch, K. L. (2000a). Spectroscopy 15(11), 30–39.
new realms of biological mass spectrometry is difficult. Busch, K. L. (2000b). Spectroscopy 15(9), 22–25.
But in looking exclusively to these new and exciting Cooks, R. G., and Busch, K. L. (1983). Int. J. Mass Spectrom. Ion Phys.
areas, the implications of modern mass spectrometry 53, 323.
Mamyrin, B. A. (1994). Int. J. Mass Spectrom. Ion Phys. 131, 1–19.
for the “tried and true” are often overlooked. In the
Manura, J. J., and Manura, D. J. (2000). American Laboratory 33(3),
introduction, it was stated that a billion mass spectra are 40–53.
recorded daily around the world. Most certainly, the vast McFadden, W. (1973). “Techniques of Combined Gas Chromatography/
majority of these are never examined by human hand and Mass Spectroscopy: Applications in Organic Analysis,” John Wiley
mind, neither assessed nor interpreted. Some decision Interscience, New York.
Rodgers, R. P., Blumer, E. N., Hendrickson, C. L., and Marshall, A. G.
of some value is reached, perhaps automatically, and
(2000). J. Amer. Soc. Mass Spectrom. 11, 835–840.
the mass spectra are then archived. With tremendous Zenobi, R., and Knochenmuss, R. (1999). Mass Spectrom. Rev. 17(5),
advancements in computing and data storage capabilities, 337–366.