Frequently Asked Questions
Q: Can I search ATR/FTIR vs transmission FTIR spectra or vice versa?
A: Yes. Search over the fingerprint region. Since the greatest differences between ATR and transmission spectra are in the C-
Q: Can I add to the library?
A: No, but that’s OK. With most programs you can build user libraries and search them at the same time as an FDM library and the hit list will be merged so you get the same effect.
Q: What are the advantages of ATR over transmission sampling?
A: ATR sampling is faster, requires far less skill and is far more reproducible than transmission sampling. Most labs save time, effort and money with ATR.
Q: Why did FDM rerun several ATR libraries?
A: We reran everything to have superior libraries. The first generation of FDM ATR libraries were run on ATR crystals mounted with a metal foil seal. At that time, 2004-
Q: Which ATR libraries were rerun?
A: The FDM ATR Polymers, FDM ATR Retail Adhesives & Sealants, FDM ATR Organics, FDM ATR Inorganics, FDM ATR Dyes, and the FDM ATR Essential Oils. For this reason our libraries stand apart and above all others.
Q: Why does FDM provide ATR libraries with spectra measured on both diamond and Germanium crystals?
A: Diamond and ZnSe both have a refractive index of 2.4. Germanium’s refractive index is 4.0, which is considered much higher. Compounds with functional groups with strong absorbances will also have high refractive index values. Compounds with refractive index values near or above 2.4 will produce spectra that appear distorted from anomolous dispersion in the vicinity on the strong absorbance on a diamond or ZnSe ATR crystal at 43°, and more so at 45°, angles of incidence. Over the years people have tried to address this with ATR correction algorithms. We believe the best approach is to record a spectrum on a Germanium ATR crystal. Spectra recorded on a Germanium ATR crystal are more transmission-
Q: What is meant by saying spectra run on a Germanium ATR crystal are more transmission-
A: Because of Germanium’s high refractive index the effect of ATR peak broadening from anomolous dispersion on the high frequency (high wavenumber) side of a peak is greatly reduced compared to diamond or ZnSe. Thus, the peaks peaks are more transmission-