Courtesy: Human Genome Program, U.S. Department of Energy, Genomics and Its Impact on Science and Society: A 2008 Primer, 2008. (Original version 1992, revised 2001 and 2008.) http://genomicscience.energy.gov.
Today, the disciplinary distinctions between biology, chemistry, and mass spectrometry are often blurred. These disciplines and their many subfields have been interwoven for the past 50 years. Frank Field, who himself moved from the petrochemical industry and mass spectrometry to biomedical research noted in 2009, “The real excitement in science is in biology, and mass spectrometry has made significant contributions to biology” (50).While biological applications of mass spectrometry are a current focus and strength of the field, the roots of this research trace back to some of the earliest adopters of mass spectrometry in the 1940s.
The Early Adopters
In the late 1940s mass spectrometry’s main applications were in the petroleum industry and in physics; however, a minority of interested scientists was ready to explore the connection between biology and mass spectrometry. While mass spectrometry remained a relatively unknown tool at the time for most scientists, the biology community was predisposed to the collaborative, problem-solving type of energy that propelled early mass-spectrometry research.
And it was really quite remarkable the difference in problem solving. If you take the techniques of biologists and sit with them and have coffee with them, and be part of them, people come and talk to you, bring you things to do. If you’re half a mile away in chemistry, you’re willing to do exactly the same thing, but nobody ever talks to you because you’re half a mile away. (Keith Jennings, 53)
Early research, of course, relied on the few knowledgeable experts—the physics community—to provide mass-spectrometry expertise. Mildred Cohn was one of the few scientists working at the convergence of mass spectrometry, biology, and chemistry. Having earned her Ph.D. in 1938 under Harold Urey, she became well-versed in an early version of mass spectrometer during her Ph.D. studies at Columbia University. After working with Urey she continued using mass spectrometry with Nobel laureate Vincent du Vigneaud at George Washington University, where she used the instrument to study metabolic pathways.
Mildred Cohn at the University of Pennsylvania. CHF Collections.
In her 1988 oral history Cohn noted that her research at George Washington University in the 1950s with Nobel laureates Carl and Gerty Cori was her “chance to apply this [research] to biochemical reactions” (59). But in the early 1950s mass spectrometers were still fairly unknown instruments, and making them work required an extensive amount of manual effort and problem solving. At that time the mass-spectrometry community was small—adoption of the instruments was quite limited—and finding an expert to troubleshoot problems was difficult, if not impossible, for most early adopters of mass spectrometry, especially if they were outside the scope of the biggest group of early mass-spectrometry adopters, those in the petroleum industry. Cohn discussed the challenges of early work with mass spectrometers:
Hear Mildred Cohn: I thought it would be very interesting to compare the enzymatic with the non-enzymatic cleavage. I knew by that time that enzymes were highly specific, so I figured there would be only one pathway with an enzyme. I told [Carl] Cori about this, and he was sufficiently interested to finance the construction of a mass spectrometer. That was the only way I could do this problem. I not only had the problem of assembling a mass spectrometer, but of devising a method of converting the oxygen of phosphate to CO2 so that its isotopic composition could be determined by mass spectrometry. (59–60)
Research like that of Cohn was rare, as most labs were unfamiliar with mass spectrometry or its capabilities.
Although the body of mass-spectrometry adopters was small and scattered, companies like Consolidated Engineering Corporation (CEC) began producing commercial mass spectrometers after World War II, hoping to capitalize on the new and growing interest in the instrumentation. In the late 1940s CEC introduced the Consolidated–Nier Isotope Ratio Mass Spectrometer Model 21-201 for the exclusive investigation of isotope ratios of hydrogen, carbon, nitrogen, and oxygen. Mass spectrometry provided unequivocal information about the molecular weight of compounds under study. Analyzing fragmentation patterns in the mass spectrum could elucidate unknown and often complex molecular structures. Klaus Biemann and others found this work challenging owing to the limitations of the early instruments, but they persevered with their research. According to Biemann, highly polar compounds, large molecules, or polymers were not in the scope of the instrumentation of the 1960s: because these compounds were not volatile below 100 degrees Celsius, they could not be ionized as easily as many other compounds. Biemann astutely perceived that mass spectrometry could perform better qualitative analysis of molecules like the peptides that Biemann studied—even if those applications were not yet the current “acceptable” applications of the technology. While the early instruments possessed limitations in terms of their application to broad biological problems, such as their inability to analyze nonvolatile samples, dedicated researchers, like Biemann, felt that the information provided by mass spectrometry justified its application to more challenging biological problems.
Because the peptides are not volatile, I had to devise a method of chemical conversion of the peptide to something that is more volatile—which I did by converting it to a polyamino alcohol, which is a linear molecule exactly like the peptide, but it was much more volatile. And of course you weren’t supposed to put things like that into a mass spectrometer because the reason why the mass spectrometer existed at that time—the commercial types—was that the petroleum industry during World War II had to produce more and better fuels, in part, for the Air Force. The analysis of the product from crude oil to gasoline to jet fuel was very important. (Biemann, 14)
As Biemann alludes, the technique of mass spectrometry had certain conditions a scientist had to follow in order to successfully use it. For example, the ion source had to be very clean if a researcher sought to perform accurate analyses of samples like hydrocarbon mixtures. And the technique had limitations, but lipids and small steroids were within the scope of the instrumentation Biemann used. His pioneering work in sequencing peptides laid the foundation for much more complex analysis. However, the instrumentation would need to improve if molecules like proteins and polymers were to be analyzed via mass spectrometry.