Milestones of Spectroscopy
This article is intended to provide an overview of developments in spectroscopy within the last 60 years. Since a common time line for all spectroscopy methods would be very difficult to follow, I decided to present one method at a time over the period of the last 60 years.
Although the timeframe of this review begins very far before the fifties of the last century, the mention of Friedrich Wilhelm Herschel's discovery of IR radiation in 1800 is nevertheless important. However, it was not until 1880 that exact wavelength measurement was achieved with the development of the bolometer. Furthermore, suitable window materials, grids and detectors had to be developed. Only 105 years after the discovery of infrared light, the first absorption spectra of various substances were recorded by William W. Coblentz using the IR technique. Infrared spectroscopy did not gain importance though, until fully automatic spectrometers were available. The first device of this type was developed by E. Lehrer in 1937.
The Michelson interferometer (1891), which was actually supposed to show that luminiferous ether is the medium in which light spreads, provided interferograms. Lord Rayleigh (early 20th century) discovered that a spectrum can be calculated from an interferogram using Fourier transformation. The first Fourier transformation was carried out by Rubens and Wood in 1911 and a spectrum obtained. Due to the high computational effort, however, this method was rejected.
In 1953, once again more interferograms were recorded, the reason for this being the so-called multiplex advantage: the sample is simultaneously irradiated with all frequencies of the radiation source, thus improving the signal-to-noise ratio.
In 1956, the first spectrum measured by a Michelson interferometer was published by Gebbie and Vanesse. After that, only a few years passed until the first commercial FTIR spectrometers were built by Grubb Parsons (1962) and Research and Industrial Instruments Company (1964).
With the development of the Fast Fourier Transform algorithm by Cooley and Tuckey in 1965, the computational effort could also be reduced decisively.
By the development of ever more powerful computers that began simultaneously, FTIR spectroscopy finally achieved a breakthrough.
In the 1970s, the FTIR devices began to dominate the market, so that FTIR devices are predominantly found in today's laboratories.
In 1946, Bloch observed the alternating voltage which is induced by the precessing dipole moment of the nuclei in a coil, when this is no longer parallel to the direction of the static field in case of resonance. For this discovery, Bloch and Purcell received the Nobel Prize in Physics in 1952. Only one year after the discovery, Bloch and Varian filed the first patent for a functioning NMR device. The company Varian Associates introduced the first commercial NMR spectrometer in 1952, and in 1956, also JEOL launched its first NMR spectrometer.
The early NMR spectrometers had the disadvantage that either the irradiated frequency was changed under a constant magnetic field or the magnetic field was changed under a constant frequency. These methods known as CW (Continuous Wave) are characterized by a poor signal-to-noise ratio and require a very long time for the recording of the spectrum. Therefore, no real improvement in the signal quality can be achieved in a sufficiently short time even by averaging the spectra.
In the 1960s, Richard R. Ernst developed a pulsed Fourier transform NMR spectrometer which was to enable a faster recording of the spectra. It was the company Bruker that built the first commercial pulse spectrometer that derived transmitter frequencies and gate pulses from a single quartz so that a very accurate control of the radio frequency phase was achieved - something that is indispensable in modern applications of the NMR method.
With the development of the fast-Fourier transform algorithm already mentioned in the paragraph on IR spectroscopy, here also the path had already been paved to carry out the conversion of the signals from the time domain to the frequency domain with the still limited computational capacities at the time.
Early in the 1970s, multi-pulse experiments were performed in which the waiting time between two pulses was systematically varied so that a two-dimensional spectrum could be obtained from the subsequent Fourier transformation. At the same time, Mansfield and Lauterbur began to develop NMR spectroscopy into an imaging process, now known as nuclear magnetic resonance imaging. This technique has been further improved so that biochemically interesting molecules such as proteins can be structurally examined. In 2002, Wüthrich was awarded the Nobel Prize for Chemistry for this work.*
UV / Vis Spectroscopy
In the 1930s, the American government conducted research to exactly determine the vitamin concentrations in the food for soldiers. It was discovered that some vitamins, in particular vitamin A, absorb in the UV range. The first spectrophotometers were then commercially available around 1940. In the 1950s the spectrophotometers became increasingly inexpensive due to mass production. The first double-beam device, in which the speed of measurement was significantly improved by the fact that solvent and sample are measured simultaneously, was presented in 1954.
This trend to increase the measurement throughput continued in 1969 with the first UV-Vis detector for HPLC. It was developed for variable long waves so that the user could measure the desired wavelength without changing filters or lamps on a single detector. As a further development, the first diode array spectrophotometer was introduced in 1979, which allowed the measurement of the entire spectrum in a single pass within seconds.
The microprocessor was introduced with the double-beam UV / Vis spectrophotometer in 1980, and the first UV-Vis instrument with a graphical user interface, which could be operated with a mouse, followed in 1987.
In the 1990s, control and analysis of spectra at the PC with external software continued to spread. The devices became smaller and thanks to the use of glass fiber optics measurements can now also be performed outside the measuring chamber.
The miniaturization of the instruments progressed in the 2000s. Meanwhile, great advances have been made in the measuring of small sample volumes (less than 1 μL). UV / Vis was also applied in new fields such as photovoltaic research.
In 2004, Shimadzu introduced the first combined UV / Vis-NIR spectrophotometer. In 2005, a UV-Vis spectrometer was presented in which the sample is directly dripped onto the measuring surface (a glass fiber) and measured directly.
It is common to all the historical processes in the development of spectroscopy presented here that the spectrometers go through a process: from a first, very complexly produced device, that requires a large amount of expert knowledge on the part of the user and often an equally large-sized equipment, up to a small, ideally mobile device, that carries out routine measurements on site virtually "at the push of a button" and provides the results in processable formats. The combination of different methods and the further development of the existing technologies draws the devices ever closer into the everyday life of humans, especially in spectroscopy. In the quality control of, for example, foodstuffs or in environmental analysis, such devices are already used in the direct vicinity of people. The leap into our mobile phones will not take long.