8. “Dear Reader“
Last edition we saw a correspondence about the use of the terms ‘Absorbance’and ‘Absorption’. It’s all a bit pedantic of course, but we can continue the debate! Don Clark of Pfizer Laboratories at Sandwich, Kent, UK. has sent the following:
Absorbance or Absorption? A personal view
“Following David Soderstrom’s comments on whether absorbance or absorption was the correct term to use, I’ve consulted the USP (because I work in the pharmaceutical industry) on the matter. In it are the following descriptions that apply to optical spectroscopy that I think are relevant to answering this question.
Absorbance [A]: The logarithm, to the base 10, of the reciprocal of the Transmittance [T].
Absorptivity [a]: The quotient of the absorbance (a) divided by the product of the concentration, expressed in g per litre, of the substance and the absorption path length in cm.
Absorption Spectrum: A graphical representation of absorbance, or any function of absorbance, plotted against wavelength or function of wavelength.
Transmittance [T]: The quotient of the radiant power transmitted by a specimen divided by the radiant power incident upon the specimen.
My interpretation of these definitions is that all UV; IR and fluorescence spectra are absorption spectra. However, for UV etc., where the Y-axis is generally in absorbance units, these data are usually absorbance spectra. Applying this to IR data, if the Y-axis is in %T, the spectrum is an absorption spectrum. If the Y-axis is in A, the spectrum is also an absorption spectrum, but is more commonly called an absorbance spectrum.
I conclude that all IR spectra should be described as absorption spectra.
Please send any further comment to IJVS” – Don Clark, Pfizer Central Research Division, Pfizer Limited
Good Lord – Don finishes with an invitation for you folks to continue the debate! I await responses with breath duly baited?
Ian Wesley of the Grain Quality Research Lab CSIRO in North Ryde NSW in Australia has written asking if people know of good sources of background material on the vibrational spectroscopy of starch and protein. I’m sure there is good literature in this field, but I can’t put my finger on it. If someone can help Ian his e-mail address is I.Wesley@pi.csiro.au , but please send me a copy. At the bottom of Ian’s e-mail was a highly topical comment –
Life is not meaningless – it just has a very low signal-to-noise ratio. Another e-mail from Ian Wesley
“On another topic, do you remember a paper published late 80’s/early 90’s in the vibrational spectroscopy of nylons? I seem to remember that it contained spectra of lots of different types of nylon and basically showed that, for example, nylon 6,6 had a different spectrum to other nylons. I remember reading it on many occasions, but can’t for the life of me think where it was published. I’m sure it was one of yours! It might help my understanding of the differences in wheat protein spectra. Is it to much to ask if you can remember this off the top of your head? It’s pretty difficult to do literature searches for polymers in a wheat research unit! ”
The references you need are: P.J. Hendra et al., Spec. Acta., Vol. 46A, No. 5, 747-756, (1990) and W.F. Maddams et al, Spec. Acta., Vol. 47A, No. 9/10, 1327-1333, (1991).
Bjarne Nielsen has e-mailed from the Technical University at Lyngby in Denmark “Yes I would like to download the whole journal in pdf-format. Although the print as it comes now is very fine I think pdf gives the best overall picture. If people can find IJVS they can certainly find and download adobe acrobat from a link on your page. Will it be possible to print out the whole journal with one order instead of printing the different sections separately ?”
Bjarne raises a really good point here. Since our editorial policy has always been that the first part of the journal should stand as a single document and that readers should then choose from the Contributed articles, the current situation is a bit illogical. Leave it with us!
A letter from Nae-Man Park from Korea
“I am interested in nanostructures-Si nanocrystal and quantum dots etc… In these structure quantum confinement is very important and I want to study Raman on nano-size structures.”
Dr. Park is suggesting we might help. I replied “I would like to run an issues on semiconductors and hope to do so soon. Any ideas of really good people who could contribute articles?”
Dmitri Bulushev e-mailed
“We have got recently an FT-Raman Perkin Elmer spectrometer for studies of heterogeneous catalytic reactions. At the moment, we don’t have any “in situ” Raman cell for this application. Our studies will be performed at flow conditions, gas pressure close to 1 bar, temperatures from the room to the maximum one which can be reached with the thermal background filter. At least, we need a possibility to treat catalysts at different atmospheres and temperatures higher than 400°C and then to take a spectrum at a lower temperature.
We would appreciate if you could provide us an information about the manufacturer who can produce such a cell and approximate price”.
The answer is Ventacon Ltd in the UK. Telephone on +44 1962 776314 or Fax on +44 1962 776390.
We have an e-mail from Vera Lucia Camorim from Brazil
“I’m really very glad and I’ve to confess that it was a great surprise to find such helpful publication in the web that is really helping us to solve problems or difficulties in spectroscopy particularly with Raman techniques. I’m facing lots of problems with solid samples specially with metal supported catalysts”.
Can anyone interested in this fascinating area please contact Vera – her e-mail is email@example.com. Copies to me please.