Your safety warnings, XPS clarifications and memories of Theodora Greene
Not up to standards
We are concerned by the sensationalist tone of the article entitled ‘Are the last half century’s worth of results from widely-used spectroscopy tool wrong?’ (Chemistry World, March 2020, p10).
The article is associated with a picture of an XPS instrument and an operator, which is sourced from the Science Photo Library with appropriate permissions. Both the instrument and operator are easily identifiable and those with a moderate interest in XPS will recognise that the picture was taken at the National Physical Laboratory (NPL) in Teddington. The XPS instrument was manufactured by Kratos Analytical, which made the world’s first commercial XPS instrument in 1969. The association of the NPL and Kratos with the work of the authors is, we assume, accidental. However this accident invites a response.
NPL, along with other metrological institutes such as Nist in the US, have provided reference data and procedures to calibrate XPS instruments.These have been available in ISO standards for 20 years or so, and have been developed by experts in electron spectroscopies within ISO Technical Committee 201 on Surface Chemical Analysis, Sub-Committee 7 for XPS, to help analysts perform meaningful and consistent measurements. Instrument manufacturers and users generally pay careful attention to these standards and also contribute to their development. Experts will not rely on absolute peak energies to identify chemical states in insulators but on peak shapes, the presence of other elements, energy differences, stoichiometry and other information.
The title of the article poses a question that has a simple answer: no. The counter-argument is presented in the article itself, in the growth of academic papers using XPS as an analytical method and the fact that XPS instrument sales are at an all-time high to both industry and academia. No-one would invest in such expensive equipment unless it provided useful information and appropriate value, which it clearly does. To conflate the charge referencing issue with the validity of all XPS results is misleading.
The real issue is one of education, because charge referencing and assignment errors, among many other types of error, are usually made by multi-disciplinary non-experts who need simple, automated methods. Don Baer, who was featured in the article, is taking positive action in this regard and has commissioned a series of ‘How to perform XPS’ guides in the Journal of Vacuum Science and Technology.
Given the current concerns about the reproducibility of academic science it would be nice to see RSC journals take similar action for all forms of chemical analysis. As Don says: ‘the problems are not unique to XPS’
Alexander Gordon Shard CChem FRSC
National Physical Laboratory, Teddington, UK
Kratos Analytical, Manchester, UK
I am writing to tell you how much I enjoyed your delightful appreciation of Theodora Greene (Chemistry World, February 2020, p36). Chemistry World has published many fine histories of unheralded or little-known chemists who deserve to be recognised, and it was particularly rewarding to find one of a woman of my generation and whom I knew well.
I remember clearly when Theo’s future husband Fred met and fell in love with her; she was a student in Louis Fieser’s undergraduate organic lab in which Fred was a teaching assistant. She was bright and spirited, the daughter of Joshua Whatmough, who was the chairman of the department of linguistics at Harvard from its creation in 1928 until his retirement in 1963. He was a native of Lancashire, and Theo, as a result, had a charming British accent. Whatmough, from all accounts, was outspoken, often controversial, and a self-described eccentric.
Fred and Theo were both modest, decent, charming, delightful people, and Theo’s book was a treasure that has outlived most of the chemistry books published in that era. Thank you for bringing this story to light so beautifully.
Richard Hill MRSC
Athens, Georgia, US
Working to scale
An explosion that occurred recently in one of our laboratories at Newcastle University has highlighted the extreme care needed in the scaling up of certain oxidation reactions.
The incident involved the reaction between sodium perborate and acetic acid in the presence of acetic anhydride and the oxidation of 1-iodo-4-methoxybenzene to 4-methoxy-1-iodophenylbisacetate. The routine procedure involved the removal of solvent on a rotary evaporator housed in a local extraction ventilation (LEV) unit using a dry-ice cold trap. The vacuum, though not tested, was adequate for the procedure. This, in conjunction with the temperature of the water bath, was carefully controlled to prevent overheating of the solution.
A detonation occurred upon the release of the vacuum. This completely destroyed all of the glassware used for the procedure and shattered the reinforced safety glass on all sides of the LEV unit. The use of the specified unit minimised the extent of the injury to the PhD student who was conducting the experiment, though they still received some lacerations on their arms and hands. An independent investigation into the incident identified either peracetic acid or diacetyl peroxide as the explosive agent, which were in a concentrated form in the collecting flask.
The chemistry outlined above, or an adaptation of, is commonly used for oxidising iodoaryl and other compounds and so this caution is universal. Our experience has highlighted that both scaling-up and the use of excess perborate in the reaction adds significant risk and should be avoided.
A C Benniston CChem FRSC
Newcastle University, UK
Deb Morrison is at the University of Washington (Chemistry World, March 2020, p6).
In the same issue, we mistakenly printed an H instead of an I in the list of letters to be used in the wordoku puzzle (p64). Despite our best efforts to throw you off, many readers returned fully solved grids to the competition prize draw – we applaud your tenacity!