Canadian Forest Service Publications
Analysis of thiocyanates and isothiocyanates by ammonia chemical ionization gas chromatography–mass spectrometry and gas chromatography–Fourier transform infrared spectroscopy. 1993. Slater, G.P.; Manville, J.F. Journal of Chromatography 648: 433-443.
Available from: Pacific Forestry Centre
Catalog ID: 3313
Under NH3-chemical ionization (CI) conditions alkyl thiocyanates give mass spectra which show only the adduct ions (M + NH4)+ (base peak) and (M + NH4 · NH3)+. Allyl thiocyanate and aromatic thiocyanates show fragmentation similar to the corresponding isothiocyanates but still produce (M + NH4)+ as base peak and (M + NH4 · NH3)+ as a prominent ion. These properties allow the thiocyanates to be easily distinguished from isothiocyanates whose NH3-CI mass spectra indicate considerable fragmentation but little, or no, adduct ion formation. The isothiocyanates are further characterized by relatively abundant M+ and (M + H)+ ions in spectra of the C1-C5 alkyl isomers and the ion at m/z 115 as base peak for the longer-chain alkyl isothiocyanates.
Thiocyanates and isothiocyanates can also be differentiated on the basis of their gas-phase Fourier transform (FT) IR spectra. The spectra of isothiocyanates are dominated by a very intense absorption band at ca. 2060 cm-1 (-NCS) similar to that seen in liquid film spectra. Thiocyanates, in contrast, show only weak absorption at ca. 2165 cm-1. Due to their weak interaction with infrared, aromatic thiocyanates are difficult to detect by this technique. Allyl thiocyanate is a special case. Under normal GC-FT-IR conditions it quickly isomerizes to allyl isothiocyanate. Allyl thiocyanate was only detected in admixture with allyl isothiocyanate, with light-pipe temperatures below 100°C.