Dear Readers (Volume 5 Edition 6)

Before Christmas we had a few emails. The first is from Richard Duerst….

Your article (please correct me if I’m incorrect) on “How does FTIR work?” in the latest Internet Journal of Vibrational Spectroscopy was very enjoyable. It brought back memories of two old questions. Could you send me your perspectives on the following questions?

1. What are the trade-offs in gong from an 8- to a 16- to a 20-bit A/D convertors? and
2. What are the non-random noise contributions (and what equations are used to mix the random with the non-random noise sources) which limit the n (superscript: 0.5) improvement in the S:N?

Thanks in advance for the light you will shed on these two topics.

I think I know the answers to both your questions, but I need to check. I will come back to you in Article II.

We also heard from Marco van de Weert in Denmark…

I was pleasantly surprised to see your article on “How does FTIR work” in IJVS 5(5). Just minutes before I got the announcement for the latest edition of IJVS I had explained some of my co-workers about the FTIR technique, with a focus on the signal-generation process in a common FTIR instrument. You can imagine I urged my co-workers to also take a look at your article.

You also announced a to-be-written article with the possibility of changing various acquisition parameters to make the experiment suit your need. I am not sure how deep you wish to go into such things, so I would like to be so bold and make a formal request: Is it possible to include the effects of parameters like the zero-filling factor on the spectral appearance and to also include the implications for further data processing like derivatization and smoothing procedures? The reason I ask this, is my own experience with protein structural analysis using second derivative spectra in the Amide I region. Such analysis often includes (Savitzky-Golay) smoothing. I have found out the hard way that increasing the apparent resolution of the normal spectra by increasing the zero-filling factor works great, until you take a second derivative of that spectrum….nice wave pattern, though. I also found that one should increase the number of points for the SG smoothing, if one increases the point density in any way. All very obvious in hindsight, but you just don’t find any literature pointing the unwary experimentator to such ‘pitfalls’. I would say: there’s a task for IJVS here.

Thanks for your kind email. All the items you suggest are on the “must be included” list for Article II. rather than attempt a quick response, can I ask you to wait until the article is ready. promise Edition 1 of 2002!

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.