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Sir Alan Walsh — a personal tribute
Spectrochimica Acta Part B 54 Ž1999. 1999]2003
Sir Alan Walsh } a personal tribute
It is seldom in one’s life that one can meet a person who can be said to inspire. Alan Walsh was such a person. My memories of him were of intense discussions conducted with a joke here and there, a twinkling eye Žperhaps a little drooped., a guffawing laugh, but real common sense science emerging from it all and advice offered unselfishly. As a young student I had tried to read his epic first paper w1x on atomic absorption spectroscopy and understood but little. The second paper w2x on the applied aspects of AAS was different, however. At Walsh’s suggestion, the now renowned experiment using a sodium street lamp, underrun, a Lundegardh burner and a simple ¨ monochromator to select the Na 589.0-nm line resulted in the astounding phenomenon of atomic absorption } a decrease of intensity when sodium was sprayed into the flame } being seen. We used a medium Hilger spectrograph originally and indeed, observed and measured atomic absorption. When Walsh first visited South Africa in 1960 he came to tell a number of disbelieving scientists about AAS but the enthusiasm he generated then, soon made these South African scientists begin to conduct experiments in AAS. Many of the first papers w3x to appear in local journals were a direct result of this visit. Over the years since those first days, many developments took place in South Africa, which could be seen as contributions to the field of AAS. More importantly, they played a vital role in advancing knowledge in spectroscopy and contributing to improved analyt-
ical methods applied in innumerable areas of science, industry, medicine, agriculture and mining in South Africa.
1. The early days In 1959, the first commercial AA spectrometer arrived in South Africa. It was a Hilger UVISPEK Ultraviolet spectrophotometer with an atomic absorption attachment. No instructions were received with this, one of the first built. Only after several severe explosions, broken hollow cathode lamps and singed arms and eyebrows was it discovered that the fuel gas was not acetylene, hydrogen or butane, but town gas, which unfortunately, was not available in Pretoria. The nebulizer gas also was not oxygen Žas suggested by the local Hilger agent. but compressed air. This lesson was the first in learning some of the complexities of flames, nebulization and atomisation, which led to many experiments with burners, mixed fuels and mixed oxidants. Initially airrpropane]butane gas were used. The explosions and destruction of the lamps, the very poor quality and short lifetimes of the Hilger hollow cathode lamps Žthe only ones available commercially then. led to the manufacture of in-house hollow cathode lamps w4x. Here Alan Walsh again proved to be of great help. His group had experienced some difficulties in making suitable hollow cathode lamps for all elements but eventually members of his team, notably George
0584-8547r99r$ - see front matter Q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 5 8 4 - 8 5 4 7 Ž 9 9 . 0 0 1 5 0 - 0
2000
Personal tribute r Spectrochimica Acta Part B: Atomic Spectroscopy 54 (1999) 1999]2003
Jones and Jack Sullivan, had developed techniques for making them and they were already becoming commercially available in Australia, but not in South Africa. Walsh unselfishly gave advice on the manufacture of hollow cathode lamps and it was not unusual to find, next to an atomic absorption spectrometer in an analytical laboratory, a vacuum system to evacuate and rejuvenate a hollow cathode lamp. These lamps were provided with suitable taps and connectors to enable a quick vacuum pump and argon refill to make then operable again ŽFig. 1.. Most of the early AAS instruments in South Africa were home-made. The most popular spectrophotometer was the Zeiss, the burners burning mostly propane]butanerair mixtures with glass dual concentric nebulizers. Alan Walsh, on another of his visits, indicated the value of the acetylene]air premixed flame and most workers changed to this type of flame. Later, when satisfactory commercial AA spectrometers became available, the technique was already well known among South African scientists. The major contribution of Willis and Amos w5,6x in developing the relatively safe nitrous oxide]acetylene flame Žand burners . made a significant breakthrough in the determination of
many elements forming refractory compounds in other flames.
2. Low pressure gas discharges and the atomic fluorimeter
Walsh gave a number of lectures during his several visits to South Africa. His visits to this country were not very popular among some of his fellow scientists abroad because of the political situation but Walsh’s attitude was that more good could emerge from scientific co-operation and development than isolation. He was right! His work with Jack Sullivan w7x and his team in the field of resonance radiation, low pressure gas discharges, cathodic sputtering and atomic fluorescence again opened up exciting new fields of analytical spectroscopy. This also influenced some South African scientists and some interesting experiments emerged. One of these, an extension of the Walsh sputtering chamber was an atomic fluorimeter which measured the emission intensity of specific elements radiated from a Grimm glow discharge source w8x, i.e. as a detector for emission analysis w9x.
Fig. 1. The demountable, rechargeable hollow cathode lamp developed in South Africa when commercial hollow cathode lamps were not available.
Personal tribute r Spectrochimica Acta Part B: Atomic Spectroscopy 54 (1999) 1999]2003
3. The atomic fluorimeter The arrangement consisted of a Grimm glow discharge as emission source connected to a sealed hollow cathode sputtering chamber but isolated by means of a quartz window. By using a pulsed current through the hollow cathode to create an atomic cloud and a time resolved measuring photomultiplier detector, the resonance fluorescence from the atomic cloud could be separated from the emission and background radiation. The Grimm glow discharge lamp, operating in the abnormal low pressure discharge mode with direct current radiates very narrow intense spectral lines, ideal for exciting resonance radiation and causing fluorescence. The fluorescence intensity is linear with the concen-
2001
tration of the analytical element in the sample on the Grimm lamp over a wide concentration range. The work was later extended w10x to provide multiple element measurements with the elements carbon, phosphorus and sulphur for steel and cast-iron analysis. ŽFig. 2. Unpublished work showed that the atomic fluorimeter could also be used with an inductively coupled plasma as source. The radiation from an ICP observed radially, originates from the outer sheath of the plasma passing through an ‘optically thin’ radiation region. Very little self-absorption occurs and although the spectral lines are much broader than from the Grimm glow discharge, they have high intensity at their centre. This is the wavelength at which absorption and consequent fluorescence takes place. By using an argon-flushed optical path, emission radiation in
Fig. 2. Schematic diagram of apparatus for the single or simultaneous dual-element measurement of fluorescent radiation excited by emission from a glow discharge lamp.
2002
Personal tribute r Spectrochimica Acta Part B: Atomic Spectroscopy 54 (1999) 1999]2003
the vacuum UV region could be used for fluorescence. Remarkably good sensitivity and freedom from spectral interferences was measured.
4. Isotopic measurements A small experiment shown diagrammatically in Fig. 3 was carried out which illustrates the value of atomic absorption to enable the determination of the lithium 6 and lithium 7 isotope ratios. The reason for this study in 1968 was to attempt to measure the enrichment of Li 6 as the lighter isotope at the point of contact between the Cape granites and shales of Sea Point, Capetown. Walsh had suggested the possibility of isotope measurements in his original paper on atomic absorption. Several workers followed these suggestions and carried out work on isotope measurements w11]14x.
Two lithium hollow cathode lamps were made, one from Li 6 and the other from Li 7 metal. The isotopic separation was achieved by the purity of the Li 6 and Li 7 metals and their radiation was resolved by means of interference filters. A rotary chopper synchronised with a lock-in amplifier enabled first the Li 6 absorption to be measured and then the Li 7 cyclically. The radiation from the Li 6 and Li 7 was measured alternately by photomultiplier A while the absorption was measured by B. The ratio could thus be plotted accurately. Synthetic solutions produced from the lithium isotopes were used for calibration. When Walsh, on one of his visits, saw the set-up, possibly because of his original predictions w1x, he exclaimed ‘I like this’. It was the finest compliment a young scientist could receive. Unfortunately, the sensitivity achieved in the rock samples was not sufficient to prove a migration of Li 6 in preference to the Li 7 in the contact zone and the work was never published.
Fig. 3. Diagram of Li w6x:Li w7x atomic absorption arrangement.
Personal tribute r Spectrochimica Acta Part B: Atomic Spectroscopy 54 (1999) 1999]2003
5. Conclusion There is little doubt that the name of Sir Alan Walsh must go down in the annals of scientific history as a person who did as much for analytical spectroscopy as anyone else before him. His contributions have had immeasurable effects in virtually every field where analysis for atomic species is done. He was as a warm-hearted person and a true inspirer such that most of those who met him, worked with him and listened to him, will remember him with great respect and affection. All who met Alan will remember him as a warm-hearted person never too proud to give advice and indeed inspire. Pat Butler, P.O. Box 17063, Groenkloof, Pretoria 0027, South Africa. References w1x A. Walsh, The application of atomic absorption spectra to chemical analysis, Spectrochim. Acta 7 Ž1995. 108]117. w2x B. Russel, J. Shelton, A. Walsh, An atomic absorption spectrophotometer and its application to the analysis of solutions, Spectrochim. Acta 8 Ž1957. 317]328. w3x A. Strasheim, F.W.E. Strelow, L.R.P. Butler, The determination of copper by means of atomic absorption spectroscopy, J. S. Afr. Chem. Inst. XIII Ž1960. 73]81.
2003
w4x L.R.P. Butler, Manufacture of hollow-cathode lamps for atomic absorption spectroscopy, J. S. Afr. Inst. Min. Metall. Part II Ž1962. 780]786. w5x M.D. Amos, J.B. Willis, Use of high temperature premixed flames in atomic absorption spectroscopy, Spectrochim. Acta 22 Ž1966. 1325]1343. w6x J.B. Willis, The nitrous oxide acetylene flame in atomic absorption spectroscopy, Nature 207 Ž1969. 715. w7x J.V. Sullivan, A. Walsh, Resonance radiation from atomic vapours, Spectrochim. Acta 21 Ž1965. 727]730. w8x W. Grimm, Eine neue Gilmmentladungslampe fur ¨ die optische emissionsspektrale Spectralanalyse, Spectrochim. Acta Part B 23 Ž1968. 443]454. w9x H.G.C. Human, N.P. Ferreira, R.A. Kruger, L.R.P. Butler, Analysis of metals using a glow discharge source with a fluorescent atomic vapour as spectral-line isolator, Analyst 103 Ž1978. 469]474. w10x H.G.C. Human, J.A. Strauss, L.R.P. Butler, The determination of C, P and S in steel and cast iron with glow-discharge emission source and an atomic fluorimeter as spectral line isolator, Spectrochim. Acta Part B 35 Ž1980. 207]214. w11x A.N. Zaidel, E.P. Korennoi, Spectral determination of the isotopic composition and concentration of lithium in solutions, Opt. Spectrosc. ŽUSSR. 10 Ž1961. 299]302. w12x D.C. Manning, W. Slavin, Lithium isotope analysis by atomic absorption spectrophotometry, Proc. Anal. Chem. Nucl. Reactor Technol. Galinburg, AEC TID-7665 Ž1962. 390]399. w13x J.A. Goleb, Y. Yokoyama, Discharge tube as an absorption source for the determination of lithium-6 and lithium-7 isotypes by atomic absorption spectrophotometry, Anal. Chem. Acta 30 Ž1964. 213]222. w14x J.F. Chapman, L.S. Dale, The determination of lithium isotype abundances with a dual-beam atomic absorption spectrometer, Anal. Chem. Acta 87 Ž1976. 91]95.
Sir Alan Walsh } a personal tribute
It is seldom in one’s life that one can meet a person who can be said to inspire. Alan Walsh was such a person. My memories of him were of intense discussions conducted with a joke here and there, a twinkling eye Žperhaps a little drooped., a guffawing laugh, but real common sense science emerging from it all and advice offered unselfishly. As a young student I had tried to read his epic first paper w1x on atomic absorption spectroscopy and understood but little. The second paper w2x on the applied aspects of AAS was different, however. At Walsh’s suggestion, the now renowned experiment using a sodium street lamp, underrun, a Lundegardh burner and a simple ¨ monochromator to select the Na 589.0-nm line resulted in the astounding phenomenon of atomic absorption } a decrease of intensity when sodium was sprayed into the flame } being seen. We used a medium Hilger spectrograph originally and indeed, observed and measured atomic absorption. When Walsh first visited South Africa in 1960 he came to tell a number of disbelieving scientists about AAS but the enthusiasm he generated then, soon made these South African scientists begin to conduct experiments in AAS. Many of the first papers w3x to appear in local journals were a direct result of this visit. Over the years since those first days, many developments took place in South Africa, which could be seen as contributions to the field of AAS. More importantly, they played a vital role in advancing knowledge in spectroscopy and contributing to improved analyt-
ical methods applied in innumerable areas of science, industry, medicine, agriculture and mining in South Africa.
1. The early days In 1959, the first commercial AA spectrometer arrived in South Africa. It was a Hilger UVISPEK Ultraviolet spectrophotometer with an atomic absorption attachment. No instructions were received with this, one of the first built. Only after several severe explosions, broken hollow cathode lamps and singed arms and eyebrows was it discovered that the fuel gas was not acetylene, hydrogen or butane, but town gas, which unfortunately, was not available in Pretoria. The nebulizer gas also was not oxygen Žas suggested by the local Hilger agent. but compressed air. This lesson was the first in learning some of the complexities of flames, nebulization and atomisation, which led to many experiments with burners, mixed fuels and mixed oxidants. Initially airrpropane]butane gas were used. The explosions and destruction of the lamps, the very poor quality and short lifetimes of the Hilger hollow cathode lamps Žthe only ones available commercially then. led to the manufacture of in-house hollow cathode lamps w4x. Here Alan Walsh again proved to be of great help. His group had experienced some difficulties in making suitable hollow cathode lamps for all elements but eventually members of his team, notably George
0584-8547r99r$ - see front matter Q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 5 8 4 - 8 5 4 7 Ž 9 9 . 0 0 1 5 0 - 0
2000
Personal tribute r Spectrochimica Acta Part B: Atomic Spectroscopy 54 (1999) 1999]2003
Jones and Jack Sullivan, had developed techniques for making them and they were already becoming commercially available in Australia, but not in South Africa. Walsh unselfishly gave advice on the manufacture of hollow cathode lamps and it was not unusual to find, next to an atomic absorption spectrometer in an analytical laboratory, a vacuum system to evacuate and rejuvenate a hollow cathode lamp. These lamps were provided with suitable taps and connectors to enable a quick vacuum pump and argon refill to make then operable again ŽFig. 1.. Most of the early AAS instruments in South Africa were home-made. The most popular spectrophotometer was the Zeiss, the burners burning mostly propane]butanerair mixtures with glass dual concentric nebulizers. Alan Walsh, on another of his visits, indicated the value of the acetylene]air premixed flame and most workers changed to this type of flame. Later, when satisfactory commercial AA spectrometers became available, the technique was already well known among South African scientists. The major contribution of Willis and Amos w5,6x in developing the relatively safe nitrous oxide]acetylene flame Žand burners . made a significant breakthrough in the determination of
many elements forming refractory compounds in other flames.
2. Low pressure gas discharges and the atomic fluorimeter
Walsh gave a number of lectures during his several visits to South Africa. His visits to this country were not very popular among some of his fellow scientists abroad because of the political situation but Walsh’s attitude was that more good could emerge from scientific co-operation and development than isolation. He was right! His work with Jack Sullivan w7x and his team in the field of resonance radiation, low pressure gas discharges, cathodic sputtering and atomic fluorescence again opened up exciting new fields of analytical spectroscopy. This also influenced some South African scientists and some interesting experiments emerged. One of these, an extension of the Walsh sputtering chamber was an atomic fluorimeter which measured the emission intensity of specific elements radiated from a Grimm glow discharge source w8x, i.e. as a detector for emission analysis w9x.
Fig. 1. The demountable, rechargeable hollow cathode lamp developed in South Africa when commercial hollow cathode lamps were not available.
Personal tribute r Spectrochimica Acta Part B: Atomic Spectroscopy 54 (1999) 1999]2003
3. The atomic fluorimeter The arrangement consisted of a Grimm glow discharge as emission source connected to a sealed hollow cathode sputtering chamber but isolated by means of a quartz window. By using a pulsed current through the hollow cathode to create an atomic cloud and a time resolved measuring photomultiplier detector, the resonance fluorescence from the atomic cloud could be separated from the emission and background radiation. The Grimm glow discharge lamp, operating in the abnormal low pressure discharge mode with direct current radiates very narrow intense spectral lines, ideal for exciting resonance radiation and causing fluorescence. The fluorescence intensity is linear with the concen-
2001
tration of the analytical element in the sample on the Grimm lamp over a wide concentration range. The work was later extended w10x to provide multiple element measurements with the elements carbon, phosphorus and sulphur for steel and cast-iron analysis. ŽFig. 2. Unpublished work showed that the atomic fluorimeter could also be used with an inductively coupled plasma as source. The radiation from an ICP observed radially, originates from the outer sheath of the plasma passing through an ‘optically thin’ radiation region. Very little self-absorption occurs and although the spectral lines are much broader than from the Grimm glow discharge, they have high intensity at their centre. This is the wavelength at which absorption and consequent fluorescence takes place. By using an argon-flushed optical path, emission radiation in
Fig. 2. Schematic diagram of apparatus for the single or simultaneous dual-element measurement of fluorescent radiation excited by emission from a glow discharge lamp.
2002
Personal tribute r Spectrochimica Acta Part B: Atomic Spectroscopy 54 (1999) 1999]2003
the vacuum UV region could be used for fluorescence. Remarkably good sensitivity and freedom from spectral interferences was measured.
4. Isotopic measurements A small experiment shown diagrammatically in Fig. 3 was carried out which illustrates the value of atomic absorption to enable the determination of the lithium 6 and lithium 7 isotope ratios. The reason for this study in 1968 was to attempt to measure the enrichment of Li 6 as the lighter isotope at the point of contact between the Cape granites and shales of Sea Point, Capetown. Walsh had suggested the possibility of isotope measurements in his original paper on atomic absorption. Several workers followed these suggestions and carried out work on isotope measurements w11]14x.
Two lithium hollow cathode lamps were made, one from Li 6 and the other from Li 7 metal. The isotopic separation was achieved by the purity of the Li 6 and Li 7 metals and their radiation was resolved by means of interference filters. A rotary chopper synchronised with a lock-in amplifier enabled first the Li 6 absorption to be measured and then the Li 7 cyclically. The radiation from the Li 6 and Li 7 was measured alternately by photomultiplier A while the absorption was measured by B. The ratio could thus be plotted accurately. Synthetic solutions produced from the lithium isotopes were used for calibration. When Walsh, on one of his visits, saw the set-up, possibly because of his original predictions w1x, he exclaimed ‘I like this’. It was the finest compliment a young scientist could receive. Unfortunately, the sensitivity achieved in the rock samples was not sufficient to prove a migration of Li 6 in preference to the Li 7 in the contact zone and the work was never published.
Fig. 3. Diagram of Li w6x:Li w7x atomic absorption arrangement.
Personal tribute r Spectrochimica Acta Part B: Atomic Spectroscopy 54 (1999) 1999]2003
5. Conclusion There is little doubt that the name of Sir Alan Walsh must go down in the annals of scientific history as a person who did as much for analytical spectroscopy as anyone else before him. His contributions have had immeasurable effects in virtually every field where analysis for atomic species is done. He was as a warm-hearted person and a true inspirer such that most of those who met him, worked with him and listened to him, will remember him with great respect and affection. All who met Alan will remember him as a warm-hearted person never too proud to give advice and indeed inspire. Pat Butler, P.O. Box 17063, Groenkloof, Pretoria 0027, South Africa. References w1x A. Walsh, The application of atomic absorption spectra to chemical analysis, Spectrochim. Acta 7 Ž1995. 108]117. w2x B. Russel, J. Shelton, A. Walsh, An atomic absorption spectrophotometer and its application to the analysis of solutions, Spectrochim. Acta 8 Ž1957. 317]328. w3x A. Strasheim, F.W.E. Strelow, L.R.P. Butler, The determination of copper by means of atomic absorption spectroscopy, J. S. Afr. Chem. Inst. XIII Ž1960. 73]81.
2003
w4x L.R.P. Butler, Manufacture of hollow-cathode lamps for atomic absorption spectroscopy, J. S. Afr. Inst. Min. Metall. Part II Ž1962. 780]786. w5x M.D. Amos, J.B. Willis, Use of high temperature premixed flames in atomic absorption spectroscopy, Spectrochim. Acta 22 Ž1966. 1325]1343. w6x J.B. Willis, The nitrous oxide acetylene flame in atomic absorption spectroscopy, Nature 207 Ž1969. 715. w7x J.V. Sullivan, A. Walsh, Resonance radiation from atomic vapours, Spectrochim. Acta 21 Ž1965. 727]730. w8x W. Grimm, Eine neue Gilmmentladungslampe fur ¨ die optische emissionsspektrale Spectralanalyse, Spectrochim. Acta Part B 23 Ž1968. 443]454. w9x H.G.C. Human, N.P. Ferreira, R.A. Kruger, L.R.P. Butler, Analysis of metals using a glow discharge source with a fluorescent atomic vapour as spectral-line isolator, Analyst 103 Ž1978. 469]474. w10x H.G.C. Human, J.A. Strauss, L.R.P. Butler, The determination of C, P and S in steel and cast iron with glow-discharge emission source and an atomic fluorimeter as spectral line isolator, Spectrochim. Acta Part B 35 Ž1980. 207]214. w11x A.N. Zaidel, E.P. Korennoi, Spectral determination of the isotopic composition and concentration of lithium in solutions, Opt. Spectrosc. ŽUSSR. 10 Ž1961. 299]302. w12x D.C. Manning, W. Slavin, Lithium isotope analysis by atomic absorption spectrophotometry, Proc. Anal. Chem. Nucl. Reactor Technol. Galinburg, AEC TID-7665 Ž1962. 390]399. w13x J.A. Goleb, Y. Yokoyama, Discharge tube as an absorption source for the determination of lithium-6 and lithium-7 isotypes by atomic absorption spectrophotometry, Anal. Chem. Acta 30 Ž1964. 213]222. w14x J.F. Chapman, L.S. Dale, The determination of lithium isotype abundances with a dual-beam atomic absorption spectrometer, Anal. Chem. Acta 87 Ž1976. 91]95.