| Author | Message | ||
     Howard Mark (hlmark) Senior Member Username: hlmark Post Number: 128 Registered: 9-2001 |
Ian - As I've mentioned previously in various postings, this discussion group is for NIR spectroscopy, and while some of us know about other techniques, in general this may not be the best place to come to, in order to learn about those other methods. That said, here's a little bit about Raman, that I can help you with: it's also a technique of molecular spectroscopy, but is usually considered an adjunct, or perhaps a complementary, technique to mid-IR spectroscopy more than to NIR spectroscopy. It responds to fundamental molecular vibrations through an inelastic scattering process. Many vibrational modes that are inactive in mid-IR absorbance are active for Raman scattering, and vice versa; the bands are similarly narrow and distinctive as mid-IR absorbance bands are. For this reason it is extremely useful for elucidating molecular structure from first principals, and from library spectra, the same way mid-IR spectroscopy is. On the other hand, because of the fundamental nature of the physics involved, bands tend to be weak and, as you noted, subject to interference by fluorescence from the sample. It shares some properties with NIR, particularly the fact that by using a suitable NIR or visible laser to create the Raman spectra, you can measure samples in aqueous solutions. It should be eminently suitable for qualitative analysis, and ID applications, either by using the absorbance information in the "clasical" way, or similarly to the way NIR is used with chemometrics. On the other hand, it would not share the property of NIR spectroscopy to optically average over, and therefore be useful, with heterogeneous samples. Without having any experience on the matter, I would venture a guess that it would not be as easily used for quantitative analysis, again especially with heterogenous samples, because of the lower S/N properties of the measurement. Experts and proponents of Raman may argue this point. \o/ /_\ | ||
| Ian D goodyer (zinir) New member Username: zinir Post Number: 1 Registered: 5-2006 |
You may have discussed this already but I cannot find the correct thread. What would you NIR experts say were the main advantages and disadvantages of Near Infra-red spectroscopy over Raman. When would you use Raman rather than NIR and when would you definitely not use it? I know that, depending on the wavelength used Raman can suffer from fluorescence interference but any other specific points anyone wants to make? Many thanks Ian http://www.zinir.com |