how to acquire high quality spectra in IR spectroscopy..?
what are good tips to obtaining a high-quality spectra?
- GeorgeSiO2Lv 78 years agoFavorite Answer
Solution spectra are much preferred over solid state (nujol mull, KBr disk) spectra. The less polar the solvent the better (stronger solvent interactions in polar solvents broadens bands: less resolution). So hexanes preferred over CH2Cl2. Opposing this you need a spectrum that gives ~90% transmittance for the strongest band. After you've done a few hundred spectra you can eyeball the amount (2-3 mg in 0.5 mL). We used1 mm spacers and NaCl windows (more robust than KBr) but cutoff is 650 cm^-1
For solid state grind like crazy (agate mortar and pestle for nujol mull): the more finally divided the particles the better the resolution. Once again 90% transmittance for the strongest peak. I have no experience with the new innovation of reflectance IR but presumably the finer the powder the better.