The instrumental revolution

 The instrumental revolution

As far as the daily practice of chemical research is concerned, probably the most dramatic change during the 20th century was the revolution in methods of analysis. In 1930 chemists still used “wet-chemical,” or test-tube, methods that had changed little in the previous hundred years: reagent tests, titrations, determination of boiling and melting points, elemental combustion analysis, synthetic and analytic structural arguments, and so on. Starting with commercial labs that provided an out-source for routine analyses and with pH meters that displaced chemical indicators, chemists increasingly began to rely on physical instrumentation and specialists rather than personally administered wet-chemical methods. Physical instrumentation provides the sharp “eyes” that can see to the atomic-molecular level.

In the 1910s J.J. Thomson and his assistant Francis Aston had developed the mass spectrograph to measure atomic and molecular weights with high accuracy. It was gradually improved, so that by the 1940s the mass spectrograph had been transformed into the mass spectrometer—no longer a machine for atomic weight research but rather an analytical instrument for the routine identification of complex unknown compounds (see mass spectrometry). Similarly, colorimetry had a long history, dating back well into the previous century. In the 1940s colorimetric principles were applied to sophisticated instrumentation to create a range of usable spectrophotometers, including visible, infrared, ultraviolet, and Raman spectroscopy. The later addition of laser and computer technology to analytical spectrometers provided further sophistication and also offered important tools for studies of the kinetics and mechanisms of reactions.

Chromatography, used for generations to separate mixtures and identify the presence of a target substance, was ever more impressively automated, and gas chromatography (GC) in particular experienced vigorous development. Nuclear magnetic resonance (NMR), which uses radio waves interacting with a magnetic field to reveal the chemical environments of hydrogen atoms in a compound, was also developed after World War II. Early NMR machines were available in the 1950s; by the 1960s they were workhorses of organic chemical analysis. Also by this time, GC-NMR combinations were introduced, providing chemists unexcelled ability to separate and analyze minute amounts of sample. In the 1980s NMR became well known to the general public, when the technique was applied to medicine—though the name of the application was altered to magnetic resonance imaging (MRI) to avoid the loaded word nuclear.

Many other instrumental methods have seen vigorous development, such as electron paramagnetic resonance and X-ray diffraction. In sum, between 1930 and 1970 the analytical revolution in chemistry utterly transformed the practice of the science and enormously accelerated its progress. Nor did the pace of innovation in analytical chemistry diminish during the final third of the century.