Mass spectrometry across the sciences

ass is a fundamental yet easily understood characteristic of a chemical species.For many analytical problems, mass is also highly specific.J. J. Thomson's 1912 mass spectrum of neon showed isotopes of masses 20 and 22 in a 10:1 ratio, explaining its apparently anomalous atomic weight of 20.2 (1).Mass spectrometry (MS) then became important for such fundamental data of elements and for isotopic analysis, such as 235 U/ 238 U in the nuclear weapons program.Also critical in World War II, MS replaced laborious analytical distillations of light hydrocarbon gases, such as butadiene feedstocks for the synthetic rubber program.Gaseous ions are required for mass separation; ionization of a molecule such as butane, C 4 H 10 , causes bond dissociation into many fragments (CH 3 , C 2 H 5 , C 3 H 7 , etc.), so that their masses and relative abundances provide multiple characteristics for both specificity and quantitation (2).Furthermore, ion detectors give unusual sensitivity and recording speed.Complex mixture analysis became routine by coupling MS online to gas and liquid chromatography, with computer automation providing far more information far faster.Additional molecular specificity became possible with ''MS/MS,'' in which additional mass spectra are obtained from the molecule's fragment ions or from the individual molecular ions of a mixture mass spectrum (3).In the last two decades, these molecular MS capabilities have been dramatically extended by the development of methods such as laser desorption (4) and electrospray ionization (ESI) (5) to ionize and introduce nonvolatile molecules into the mass spectrometer.It became possible to obtain mass spectra of proteins, DNA/RNA, carbohydrates, lipids, polymers, etc., with their increased data complexity offset by dramatic instrument improvements in resolving power and mass accuracy.This has led to diverse MS methodology for research and analysis, with unique capabilities of specificity, sensitivity, speed, sampling, and automated computer data acquisition/ reduction.This special issue attempts to illustrate the breadth and uniqueness of applications of molecular MS to a variety of scientific fields with current examples.The specificity of MS is shown dramatically by the characterization of petroleum, a notoriously complex mixture (6).