Potassium Bromide Disc Infrared Spectroscopy: A Useful Technique for Liquid Samples As is widely recognized, the ability to identify many functional groups by their characteristic vibration frequencies makes infrared spectroscopy one of the simplest, most rapid, and m a t reliable means for establishing the identityof a compound. Routine spectra are normally recorded utilizing solutions of the compound in question, or, when the compound is a solid, solid solutions in KBr. Use of the KBr-disc method need not be restricted to solids alone, however, and in many instances it is advantageous to use it on liquids as well. Examples are numerous, but only four of the more important ones will be mentioned: (1) The liquid is corrosive t o the NaC1-windows of the normally used solvent cell. (CaF2 cells are commercially available, but they are rather expensive and hence not standard equipment.) (2) The liquid can be diluted only with corrosive solvents. (3)Inter- and intra-molecular hydrogen bonds cannot be studied in protie solvents. (4) KBr does not usually give rise to any absorption bands in the infrared. The preparation of these solid solutions is surprisingly simple: To a dilute solution of the compound (approximately 2-5 mg in any suitable, low-boiling solvent) contained in a small round-bottomed flask an appropriate amount (200-500 mg) nf KBr is added. The solvent is completely evaporated on a rotary evaporator and the residue KBr is now uniformly impregnated with the liquid. The disc is then made in the usual manner from the impregnated KBr.
Ris$ National Laboratory DK-4000 Roskilde, Denmark
Jan R. 'adersen
Volume 56, Number 11. November 1979 / 761
