What is Raman spectroscopy?
<p>In Raman spectroscopy, an unknown sample of material is illuminated with monochromatic (single wavelength or single frequency) laser light, which can be absorbed, transmitted, reflected, or scattered by the sample. Light scattered from the sample is due to either elastic collisions of the light with the sample's molecules (Rayleigh scatter) or inelastic collisions (Raman scatter). Whereas Rayleigh scattered light has the same frequency (wavelength) of the incident laser light, Raman scattered light returns from the sample at different frequencies corresponding to the vibrational frequencies of the bonds of the molecules in the sample.<br/><br/>
If you wish to learn more about Raman spectroscopy, visit our online Raman Spectroscopy Academy (https://www.thermofisher.com/us/en/home/industrial/spectroscopy-elemental-isotope-analysis/spectroscopy-elemental-isotope-analysis-learning-center/molecular-spectroscopy-information/raman-technology.html), where you will find basic Raman tutorials, advanced Raman webinars on sample applications, and a helpful instrument guide.</p>
Using the Beer-Lambert law in FTIR ATR for quantitative analysis of a time-sensitive, migrating substance (e.g., erucamide) in a polymer is difficult. How can this be overcome?
<p>The Beer-Lambert law is based on stable samples and reproducible conditions. In ATR, you have two concerns. First, the sample must make contact with the crystal in a consistent manner. If the material is rough or crystalline, you must ensure reproducibility. Grinding the material to a fine powder may be necessary. Second, ATR is a surface technique, examining the sample to a depth of around 1-4 microns. If the additive or target molecule is migrating further away, you will lose the signal. In this case, transmission, which illuminates the entire sample and entire thickness, may be a viable option (depending upon thickness). In some cases, the application of pressure can change the signal due to changes in the crystallinity or orientation of polymer strands in the sample. Any deeper insights would require an understanding of the specific sample involved.</p>
What types of sampling cells and detectors are used for protein analysis using Fourier Transform Infrared Spectroscopy (FTIR)?
<p>One key experimental step in protein analysis is the removal of the water bands (most proteins are in buffers). This requires highly controlled path-length transmission cells or ATR. Most historical work was done in 6-10 micron path length transmission cells using BaF2 or similar windows. The analytical region is roughly between 1400 and 1750cm-1 where these windows are transmissive. Recently, ATR devices using silicon, germanium, or diamond windows have become more prevalent. Reactions or binding of proteins to the crystal can occur with ZnSe devices (due to surface charges); sometimes this is desired but often it is not. Most of the literature is based on transmission cells. Protein analysis requires skill and consistency, so training is essential for most laboratories.</p>
