(b. Hoddlesten, England, 19 December 1916;
d. Melbourne, Australia, 3 August 1998), physics, chemical analysis, atomic absorption spectroscopy.
Walsh originated and developed the atomic absorption method that revolutionized chemical analysis in the 1960s. Atomic absorption spectroscopy provided for the first time a rapid, easy, accurate, and highly sensitive method of determining the concentrations of nearly all the elements in the periodic table. In the early twenty-first century the method is used worldwide in many fields, including medicine, agriculture, mineral exploration, metallurgy, food analysis, and environmental control.
Early Years. Alan Walsh grew up in Hoddlesden, a small moorland village in Lancashire, England. He was the eldest son of Thomas Haworth Walsh, who managed a small cotton mill, and Betsy Alice Walsh. He attended the local grammar school in the nearby town of Darwen, and in 1935 he entered the honors school of physics at the University of Manchester. He went on to do postgraduate research in x-ray crystallography in the Physics Department at the Manchester College of Technology—later to become the University of Manchester Institute of Science and Technology (UMIST)—where he was awarded an MSc (Tech).
Walsh’s postgraduate research was interrupted by the outbreak of World War II. In September 1939 he started work with the British Non-Ferrous Metals Research Association (BNF) in London to determine the composition of alloys being used in enemy bombers that had been shot down. The procedure he used was to make the alloy sample an electrode of an electric arc or spark discharge and to analyze the wavelengths of the emitted atomic spectral lines in a spectrograph. During his time at the BNF he devised and built a prototype of the General Purpose Source Unit (Walsh, 1946), which was a versatile but simple electrical source unit that could generate arc-like and spark-like discharges for use in spectrographic emission analysis. The source unit was subsequently manufactured by Hilger and Watts Ltd., London, as the BNF Spectrographic Source Unit FS 130.
CSIR/CSIRO Years. After World War II, Walsh accepted a position as research officer in the Division of Industrial Chemistry at the Council for Scientific and Industrial Research (CSIR)—now the Commonwealth Scientific and Industrial Research Organization (CSIRO)—in Melbourne, Australia. Shortly after arriving in Melbourne he met an English-born nurse, Audrey Dale Hutchinson, whom he married on 25 June 1949. They had two sons, Thomas Haworth and David Alan.
At CSIR Walsh established the first infrared spectrometer in Australia—a Perkin-Elmer Model 12B— which was used for research in infrared molecular spectroscopy and was also available for use by various chemists around Australia. Walsh soon realized, however, that the resolution of the infrared spectrometer was inadequate for resolving the rotational structure of all but the lightest molecules. To improve the resolution he devised a simple and elegant modification of the infrared prism monochromator by placing a pair of right-angle mirrors at the exit slit to reflect the radiation back through the prism (Walsh, 1951). To isolate the desired multiple-pass beam from the other beams, he placed a rotating “chopper” in front of the additional mirrors to modulate only the multiple-pass beam and fed the output of the detector to an amplifier tuned to the frequency of the chopper. Perkin-Elmer secured an exclusive license for the double-pass monochromator and in 1953 began manufacturing a kit of Walsh Mirrors to allow their standard infrared spectrometer to be converted to a double-pass system.
After arriving at CSIR Walsh also initiated a project to investigate the fundamental processes occurring in spectrographic atomic emission sources similar to the General Purpose Source Unit he developed at the BNF in London. Although such source units were by then well established in laboratories in England, the CSIR unit proved to be rather unreliable and Walsh became disillusioned with it.
Atomic Absorption Method. One Sunday morning in March 1952, while gardening at his home, Walsh had a flash of thought, something that stemmed from his previous experiences in atomic emission spectroscopy and infrared molecular absorption spectroscopy. He had been wondering why it was that molecular spectra were usually obtained in absorption while atomic spectra were obtained in emission. He could see that atomic absorption spectra offered many important advantages over atomic emission spectra as far as spectrochemical analysis was concerned. Early next morning he set up a simple experiment consisting of a standard sodium vapor lamp as a source of the sodium yellow D lines and an air-coal gas flame as the sampling medium. The sodium vapor lamp was operated from a 50 Hz mains electric supply to provide an alternating source of light, and the D lines were isolated, but not resolved from each other, by means of a simple low-resolution spectrometer. The combined intensity of the D lines transmitted by the flame was recorded by a photomultiplier at the exit slit of the monochromator, and the output signal fed to the AC input of a cathode ray oscillograph. When a solution containing a few milligrams of sodium chloride was sprayed into the air supply of the flame, the cathode spot on the oscillograph deflected to zero, thus establishing the principle of the atomic absorption method of spectrochemical analysis.
Apparently, while reading Samuel Tolansky’s book High Resolution Spectroscopy(1947), Walsh learned that a hollow-cathode discharge can provide a source of sharp spectral lines for a very wide range of elements. In early 1953 he and a colleague, John Shelton, set out to construct hollow-cathode lamps of the type described by Tolansky, in which the rare gas was pumped continuously through traps in a closed circulating system to remove molecular impurities liberated by the cathode and the walls of the tube. During a visit to the United States in mid-1953, Walsh became aware of the work of Gerhard Dieke and H. Milton Crosswhite (Letter to the editor, Journal of the Optical Society of America 42, 1952, p. 433) who were using compact sealed-off hollow-cathode lamps in which the gaseous impurities were removed by a “getter” of activated uranium. Walsh and Shelton then abandoned the complex gas circulating system and began the development of sealed-off hollow-cathode lamps with zirconium getters for all the elements that could be determined by atomic absorption. The first satisfactory sealed-off hollow-cathode lamps were constructed and tested towards the end of 1953.
Walsh had now arrived at a satisfactory method for making the atomic absorption measurements and a basic experimental arrangement that had all the essential components of a modern commercial atomic absorption spectrophotometer: a sealed-off hollow-cathode lamp as the source, a flame as the sampling absorber, and a “chopper” and synchronously tuned amplifier to separate the emission of the source from the luminous emission of the flame absorber. A provisional patent application was lodged on 17 November 1953. Soon after filing the final patent specification (Australian Patent Specification 163,586, Oct. 21, 1954), Walsh submitted his landmark paper “The Application of Atomic Absorption Spectra to Chemical Analysis” (Walsh 1955). At virtually the same time, a paper titled “A Double-Beam Method of Spectral Selection with Flames” was published by Kees Alkemade and Jan Milatz (Applied Science Research B4, 1955, pp. 289–299), who had arrived independently at the concept of atomic absorption spectroscopy. Alkemade and Milatz, however, did not pursue their work further.
The first working atomic absorption spectrophotometer was exhibited in March 1954 at an exhibition of scientific instruments held by the Victorian Division of the (British) Institute of Physics at the University of Melbourne (see Figure 1). The instrument demonstrated the analysis of copper samples, using a copper hollow-cathode source. However, there was also provision for a sodium vapor lamp, and viewers were invited to dip their (salty) finger into a beaker of water, and this would register a deflection on the strip chart recorder.
Commercialization of Atomic Absorption. During 1953 Walsh had toured England and the United States and discussed the possible commercial exploitation of atomic
absorption with a number of instrument manufacturers. The only person to show any enthusiasm in commercializing atomic absorption equipment was Alexander Menzies, a physicist and director of research for Hilger and Watts Ltd., with whom Walsh had previously had dealings through the manufacture of the BNF General Purpose Source Unit. CSIRO arrived at an exclusive license agreement with Hilger and Watts, based on the provisional patent application. During the period Hilger and Watts held an exclusive license (1953–1957), progress was slowed by technical difficulties, including the development of satisfactory hollow-cathode lamps. They had decided to manufacture the atomic absorption equipment as an attachment to an existing Hilger and Watts Uvispek spectrophotometer and there was no provision in the attachment for modulating the light from the source, and thus for discriminating the emission of the source from the emission of the luminous flame absorber. Although Hilger and Watts recognized the limitations of the Uvispek attachment, it was decided to continue with the manufacture of the simple attachment. The first atomic absorption instrument, the Model H 909, was sold in early 1958, and sales continued at about thirty to sixty instruments a year for several years.
By 1958 there was still no instrument company prepared to produce the type of atomic absorption instrument Walsh considered necessary. He then decided to produce a list of instructions on how to put together a do-it-yourself kit. Fred Box of CSIRO designed and built the prototype electronics, which included a broadband AC amplifier—the “Working Man’s Amplifier”—and a power supply to run the hollow-cathode lamps; George Jones and later John Sullivan of CSIRO developed and provided the expertise and hands-on skills for producing the hollow-cathode lamps; and a simple commercially available monochromator such as the Zeiss quartz-prism monochromator was recommended for isolating the relevant atomic absorption lines.
Walsh then went in search of businesses that were prepared to manufacture components that were not available commercially. The electronics part of the equipment was perfectly conventional, so he put out a tender for manufacturing six amplifiers and power packs. A small firm, Techtron Appliances, put in the lowest bid and got the business. He also toured the backyards of Melbourne and found a small machine shop, run by Stuart R. Skinner, to make various mechanical components. He then tried various glass-blowing people to make the lamps and found a small firm, Ransley Glass Instruments—later to become Atomic Spectral Lamps—that was willing to try. By mid-1962 more than thirty of these do-it-yourself kits had been supplied to Australian laboratories and about ten to other parts of the world, including New Zealand and South Africa.
In July 1962 Walsh and his CSIRO Chief, Lloyd Rees, arranged a symposium on atomic absorption spectroscopy, which was attended by about eighty potential users and CSIRO staff. At the end of the symposium the chairman of Techtron Appliances Pty. Ltd., Geoffrey Frew, declared his intention to manufacture a “complete” atomic absorption spectrophotometer. By early 1964 Techtron had produced the first all-Australian atomic absorption instrument, the Model AA-3, which incorporated a “Sirospec” grating monochromator designed by John McNeill at CSIRO, diffraction gratings ruled on a ruling engine designed and constructed at CSIRO, and an AC amplifier unit designed by Fred Box at CSIRO. The AA-3 was exhibited publicly for the first time at the Pittsburgh Conference on Analytical Chemistry in March 1964.
During his lecture tour to the United States in 1958, Walsh visited the Perkin-Elmer Corporation, with whom he had previously had dealings with regard to the double-pass infrared monochromator. A Perkin-Elmer representative indicated to him that the company would be interested in becoming a licensed manufacturer of atomic absorption equipment if it could be shown capable of determining calcium in blood serum. In March 1959 a colleague of Walsh's, John Willis, submitted a report of his atomic absorption work on calcium and magnesium in blood serum to Perkin-Elmer. In November 1959 Perkin-Elmer was granted a license from CSIRO to manufacture atomic absorption equipment and, in 1960, a group headed by Walter Slavin was established to develop an atomic absorption instrument. In March 1962 Perkin-Elmer began building a completely new atomic absorption instrument, the Model 303, which was released on the market in April 1963, at about the same time as the first Techtron atomic absorption instrument, the AA-2, which used an imported monochromator. By 1965 the Model 303 had already overtaken infrared spectroscopy as Perkin-Elmer’s largest product line and had captured the bulk of the atomic absorption market.
In August 1965 Techtron Appliances merged with Atomic Spectral Lamps to form Techtron Pty. Ltd., which manufactured the Techtron Model AA-4 with a synchronously tuned amplifier and a nitrous oxide-acelylene burner. This was followed by a period of rapid growth in the company. In October 1967 Techtron was approached with an offer of acquisition by Varian Associates, thus becoming Varian Techtron Pty. Ltd., and later Varian Australia Pty. Ltd. As of 2007 Varian Australia in Melbourne, with a staff of around 400, had the second-largest share of the atomic absorption market after the Perkin-Elmer Corporation, while GBC Scientific Equipment Pty. Ltd. in Melbourne, with a staff of around 180, was the third largest.
In 1966 Max Amos from Sulphide Corporation in Australia and John Willis from CSIRO published a paper on the use of the high-temperature nitrous oxide-acetylene flame, which extended the applicability of the atomic absorption method to more than sixty-five elements. From that stage onward there was a dramatic increase in interest in the atomic absorption method and it rapidly gained worldwide acceptance.
In 1968 A. W. Brown, a scientist with qualifications in business administration, was approached by CSIRO to conduct a cost-benefit analysis of the atomic absorption project. Brown’s study conservatively assessed the value of the net benefits to the Australian economy at around $22 million (in 1968 Australian dollars), compared with $1.3 million originally spent on the research (Brown, 1969). Later estimates gave the accumulated benefit to Australia by the year 1977 as in excess of $200 million, including overseas royalties, the setting up of new industry, and the productivity increases in a wide range of enterprises. Surprisingly, Brown found that the major benefits to the Australian economy were not through the manufacture of atomic absorption equipment but rather through benefits to the end user, that is, benefits associated with productivity gains, especially the ability to perform large numbers of assays very rapidly and with high accuracy. This component far outweighed the benefits of manufacture and royalties.
After development the atomic absorption method, Walsh’s research was directed toward developing novel instruments and techniques to simplify and improve atomic absorption equipment. In particular, he believed it should be possible to replace the monochromator, which was rather fragile, bulky, and expensive, with a simpler, more rugged device suitable for use in working environments where the samples were actually being taken. In 1965 he and John Sullivan developed the so-called resonance detector which consisted of a vapor cell of the appropriate element to selectively absorb the resonance lines from the source and a photomultiplier to detect the atomic fluorescence emitted by the vapor cell. The resonance detector was followed by the development of the ingenious technique of “selective modulation” for isolating atomic resonance lines (Walsh and Sullivan, 1966). With this technique, radiation from a sharp-line source such as a hollow-cathode lamp is passed through a pulsating vapor of absorbing atoms, and the resonance lines are detected using a synchronous amplifier tuned to the frequency of modulation of the atomic vapor.
For applications involving resonance detectors or the detection of the fluorescence radiation, light intensities higher than those available from standard hollow-cathode lamps were needed. In 1965 Walsh and John Sullivan developed the “high-intensity” hollow-cathode lamp (Walsh and Sullivan, 1965), which has two discharges—a hollow-cathode discharge to generate an atomic vapor by cathodic sputtering and a high electron-current discharge to excite the atoms. The Sullivan-Walsh high-intensity lamp allows the intensity of the resonance lines to be increased up to a hundredfold without significant increase in atom density, and hence line width, and it also allows most of the light output to be concentrated in the strongest resonance line. Such lamps are manufactured by Varian Australia Pty. Ltd., by the Perkin-Elmer Corporation, and by Photron Pty. Ltd. in Melbourne.
Walsh was particularly conscious of the limitations of the flame as an atomizer, such as incomplete atomization of most elements (giving rise to low sensitivity and possible “chemical interferences”); the necessity of having an oxidant in the flame rendering vacuum UV wavelengths inaccessible; the need for prior dissolution of the sample; the presence of various molecular species that can introduce unwanted background absorption signals; and the need for an explosive gas such as acetylene, which is undesirable in certain working environments such as hospitals. In 1959 Walsh and Barbara Russell reported that a hollow-cathode discharge can provide a simple and convenient means of generating an atomic vapor of essentially any solid element. With the sputtering method, energetic rare-gas ions formed in the hollow-cathode discharge bombard the surface of the cathode and eject atoms to produce an atomic vapor, thus providing a means BY which metals and alloys can be atomized directly without prior dissolution. Furthermore, the method should, in principle, not be subject to any of the above limitations of the flame. In 1973 Walsh, together with David Gough and Peter Hannaford, reported the first results, on the determination of a range of elements in solid samples of iron-base. An atomic absorption system based on the sputtering method of vaporization was later manufactured by the Analyte Corporation, United States, in 1988.
Later Career. In January 1977, just after his sixtieth birthday and after thirty years of service, Walsh retired from CSIRO. About a year later he became a formal consultant to Perkin-Elmer. He had earlier participated with Perkin-Elmer in some major commercial decisions, including decisions to construct their own hollow-cathode lamps, to manufacture a Zeeman attachment to correct for background absorption, and to manufacture the inductively coupled plasma (ICP) source. Between 1978 and 1982 he and his wife, Audrey, spent several European summers beside the Bodensee near Überlingen, Germany, where he made frequent visits to Perkin-Elmer’s Bodenseewerk. At that time the main research interest at Bodenseewerk was the hydride generation technique for atomic absorption. Walsh suggested that it might be interesting to combine the hydride work with a solar-blind photomultiplier to provide a simple non-dispersive atomic fluorescence spectrometer for the determination of arsenic and selenium. The engineers build a prototype that worked nicely. Some years later the Chinese built a highly successful hydride instrument.
During the early 1980s Walsh initiated a project to investigate a new type of spectrochemical analysis based on coherent forward scattering (Walsh 1984), which had been pioneered as a spectroscopic technique in the mid-1960s by George Series in Oxford. The technique relies on the fact that the light emitted by atoms in the forward direction is phase-coherent, and so the signal intensity is proportional to the square of the number of atoms rather than to the number of atoms, thus offering the prospect of much higher sensitivity than atomic absorption spectroscopy. The technique also has the advantage that the signal is insensitive to any background light scattered from particles in the atomic vapor. With Walsh’s help, Perkin-Elmer conducted AN extensive development program on coherent forward scattering and built a system derived from their Zeeman background correction instrument. The program was later abandoned when it was considered not to be commercially attractive. In 1982 Walsh was invited back to CSIRO as a senior research fellow, where he remained until shortly before his death in August 1998.
Honors and Awards. Walsh’s scientific contributions were recognized by a number of prestigious honors and awards. He was elected a fellow of the Australian Academy of Science in 1958, a fellow of the Royal Society of London in 1969, and a foreign member of the Royal Swedish Academy of Sciences in 1969. His list of awards includes the Britannica Australia Award for Science (1966), Talanta Gold Medal (1969), Maurice Hasler Award of the Society of Applied Spectroscopy USA (1975), Kronland Medal of the Czechoslovak Spectroscopy Society (1975), Royal Medal of the Royal Society of London (1976), Torbern Bergman Medal of the Swedish Chemical Society (1976), and Robert Boyle Medal of the Royal Society of Chemistry (1982). He was created a knight bachelor in 1977 for his services to science.
A complete bibliography of Alan Walsh’s works can be found in Historical Records of Australian Science 13 (2000): 179–206. His personal papers are kept in the Basser Library at the Australian Academy of Science in Canberra, Australia.
WORKS BY WALSH
“A General-Purpose Source Unit for the Spectrographic Analysis of Metals and Alloys.” Bulletin of the British Non-Ferrous Metals Research Association 201 (1946): 60–80.
“Design of Multiple Monochromators.” Nature 167 (1951): 810–811.
“The Application of Atomic Absorption Spectra to Chemical Analysis.” Spectrochimica Acta 7 (1955): 108–117; erratum, 252.
With Barbara J. Russell and John P. Shelton. “An Atomic Absorption Spectrophotometer and Its Application to the Analysis of Solutions.” Spectrochimica Acta 8 (1957): 317–328.
With Barbara J. Russell. “Resonance Radiation from a Hollow Cathode.” Spectrochimica Acta 15 (1959): 883–885.
With B. M. Gatehouse. “Analysis of Metal Samples by Atomic Absorption Spectroscopy.” Spectrochimica Acta 16 (1960): 602–604.
With W. Goerge Jones. “Hollow-Cathode Discharges: The Construction and Characteristics of Sealed-off Tubes for Use as Spectroscopic Light Sources.” Spectrochimica Acta 16 (1960): 249–254.
With G. Fred Box. “A Simple Atomic Absorption Spectrophotometer.” Spectrochimica Acta 16 (1960): 255–258.
With John V. Sullivan. “High Intensity Hollow-Cathode Lamps.” Spectrochimica Acta 21 (1965): 721–726.
With Judith A. Bowman and John V. Sullivan. “Isolation of Atomic Resonance Lines by Selective Modulation.” Spectrochimica Acta 22 (1966): 205–210.
With David S. Gough and Peter Hannaford. “The Application of Cathodic Sputtering to the Production of Atomic Vapours in Atomic Fluorescence Spectroscopy.” Spectrochimica Acta B, 28 (1973), 197–210.
“Atomic Absorption Spectroscopy—Stagnant or Pregnant?” Analytical Chemistry 46 (1974): 689A–708A.
“The Application of Atomic Absorption Spectrometry to Chemical Analysis.” Matthews Flinders Lecture of the Australian Academy of Science. Historical Records of Australian Science 5 (1980): 129–162.
“Atomic Absorption Spectroscopy—Some Personal Recollections and Speculations.” Spectrochimica Acta Part B 35 (1980): 639–642.
With J. M. Ottaway, Walter Slavin, and Sydney S. Greenfield. “Atomic Absorption Symposium.” Analytical Proceedings, 21 (1984): 54–55.
“The Development of Atomic Absorption Methods of Elemental Analysis 1952–1962.” Analytical Chemistry 63 (1991): 933A–941A.
Alan Walsh Memorial Issue. Spectrochimica Acta Part B 54 (1999): 1933–2194.
Amos, Max, and John B. Willis. “The Use of High-Temperature Pre-Mixed Flames in Atomic Absorption Spectroscopy.” Spectrochimica Acta 22 (1966): 1325–1343.
“Atomic Absorption Spectroscopy: Past, Present, and Future: To Commemorate the 25th Anniversary of Alan Walsh’s Landmark Paper in Spectrochimica Acta.” Spectrochimica Acta Part B 35 (1980): 637–993.
Brown, A. W. “The Economic Benefits to Australia from Atomic Absorption Spectroscopy.” Economic Record (June 1969): 158–180.
Carseldine, M. L. “The Development of Atomic Absorption Spectroscopy and Subsequent Instrument Manufacturing Industry that Has Arisen in Australia.” MSc thesis. Griffith University, Brisbane, 1984.
Hannaford, Peter. “Alan Walsh 1916–1998.” Historical Records of Australian Science 13 (2000): 179–206.
———. “Sir Alan Walsh.” Biographical Memoirs of Fellows of the Royal Society of London 46 (2000): 533–564.
Larkins, P. L. “Sir Alan Walsh: The Scientist and the Man.” Analyst 117 (1992): 231–233.
Willis, H. A. “Sir Alan Walsh, the Inventor of Atomic Absorption Spectrometry.” ESN Interviews, European Spectroscopy News 24 (1979): 18–23.
Willis, J. B. “Spectroscopic Research in the CSIRO Division of Chemical Physics 1944–1986.” Historical Records of Australian Science 8 (1989): 151–182.