Volume 5 Edition 3

DEAR READERS

Alfonso Lopez wrote to us recently and I replied asking him what he uses IR for. Here is his reply and my subsequent response.

We use it mostly in ATR mode. We will use it in transmission in the future. Our FTIR is used mostly as a comparison QA database for the different materials we use in our business, which is engineering plastics. We also use it in deformulation to some degree. I would like to use it quantitatively to determine compound concentrations of different constituents, but have not enough experience within that area to utilize it efficiently.

I am most interested in learning some rule or basic physics and chemistry as to why cerain bonds will produce certain adsorptions. I am afraid that I do not have a strong chemistry background. If I come across a material I have not tested before, it takes me a while to determine what the adsorptions mean and interpret that into a probable material identity.

So – you examine polymers by ATR. The best established method of identifying polymers using FTIR is to purchase a software set and library database, run your spectra and let the software do the identifying for you. Several are available but probably the most well established ones are the Sadtler, Aldrich or Sigma series of spectra. For details see items 40, 41 & 42 of Spectroscopists Bookshelf. You may also find other items listed to be of value e.g. Item 7.

The libraries are composed of transmission spectra so I would recommend that for best results, you simply hot-press films of your polymers, record the spectra and library search. You may get good results from diamond ATR spectra, but the search algorithm may not be so reliable. The problem is that the relative band intensities in an ATR spectrum are not the same as those in the IR.

For QA purposes, the normal method is to develop your own library of spectra and use these in a data set within a chemometric routine. A flavour of what I mean (and it used ATR as the sampling method, can be found in a feature article some time ago in IJVS – S. Cooke, C. Deeley & M. Billingham, Int.J.Vib.Spect.,[www.irdg.org/ijvs] 2, 2, (1998). We plan to get an expert to generate a special edition in the future so keep reading.

The following request has come in from Yazeed Al-Dukhayyil in Saudi Arabia.

I’m searching for FTIR methods to analyze sulfite and chloride in cement, sand and aggregate. Can you be of any help.

I don’t have an answer, but I am sure some of you folks can help. Please reply directly to Yazeed at dukhayya@aramco.com.sa and copy the Editorial Office as usual.

An email from Claire Khalil…

Thank you for updating me on this wonderfully interesting website. I need some information on quantitative fourier transform infrared spectroscopy if possible and any suggested literature on this subject would be most helpful.

Claire, very nice to hear from you and to receive your enthusiastic comments. I’ve started writing a piece and it will appear in the next edition, not this one. If anyone can suggest a good source for Claire, please email her at claire_khalil@hotmail.com and copy us, so we can update your Spectroscopy Bookshelf.

This request from Lisa Edghill in Jamaica a while ago..

Sorry to trouble you, but I am trying to find an economical press to make KBr disks and I came across this journal. Do you have any suggestions? At the moment we use an enormous prehistoric instrument and we have to lug a vacuum pump back and forth. Any suggestions will be greatly appreciated.

I assume you have a KBr die and that it is OK, but your press is old. Of course, you don’t have to evacuate in most cases so your comment about the vacuum pump mat not be too significant! If you can afford it, Specac make a very nice neat press designed specifically to make KBr disks.

If money is tight you can certainly buy very cheaply a pump and hydraulic ram. If you have access to a workshop a simple frame can easily be made so you could have a new press very cheaply. A friend in Brazil adopted this approach, but we made a frame for her here in Southampton and sent the kit to her. The total cost was less than $500US. Would you like me to send you details of the Specac kit and hydraulic equipment available here in the UK? Specac’s Phone and fax details are as follows: Phone : +44 (0)1689 873134 
Fax: +44(0)1689 878527

An email from Dr G Nandini in India…

Sir, in future editions of IJVS, can you publish information regarding vibrational spectroscopy of peptides? This is the very hot field where few people are working on it. People like Prof. Samuel Krimm from Michigan University, USA have done good work in this field.

Thanks for the excellent idea. I will try to organise a special edition in this field. I agree it is very important. In the meantime if any readers know of good up-to-date reviews or surveys please contact Dr Nandini directly at nandini@ipc.ernet.in and copy the Editorial Office.

Now some questions from Oukseub Lee, a graduate student taking optical instrument spectroscopy to learn how to design an optical instrument for specific purposes…

Both NIR and FT Raman are actively used for pharmaceutical research especially for QA/QC. What are the criteria of applying each technique to the specific matters? If I work on a microscope for the research and I would like to use both techniques on the same microscope, do you think it is a possible or even efficient match? What would be the shortcomings? There are lots of spectroscopic companies, but it’s hard to find good match for this matter. I’ve been learning fundamental principles and basis applications of instrumental analysis. But it is not easy to apply my knowledge to the realistic problem, would you give me some suggestions and a few names of the products and companies dealing with this matter, if you know of them?

Thanks for your email. The questions you ask are very interesting and I certainly can come up with some answers. The idea that a microscope could be used for both Raman spectroscopy and near infrared transmission is not new, but there are problems. Rather than produce a quick answer (which would take me a considerable amount of time because it would have to be very detailed) could I ask for your patience? I will produce an article for the next edition of IJVS.

A newly registered reader Steve Hartung comments…

I’m surprised that I only recently found a link to IJVS while searching on keywords pertaining to KBr beamsplitter windows. Over the past year or so I have done extensive searching on keywords related to IR and FTIR spectroscopy but only recently and rather by accident managed to find IJVS.

Thanks Steve. Perhaps we should improve our link network! Thanks for the comments and thanks too for registering as a reader.

 

 

Please keep sending your comments and questions, sometimes it may take a while for us to answer, but we will. 
All your questions and our replies are published here in Dear Readers.