ANALYSIS OF THIOCYANATES AND ISOTHIOCYANATES BY AMMONIA CHEMICAL-IONIZATION GAS-CHROMATOGRAPHY MASS-SPECTROMETRY AND GAS-CHROMATOGRAPHY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY
Gp. Slater et Jf. Manville, ANALYSIS OF THIOCYANATES AND ISOTHIOCYANATES BY AMMONIA CHEMICAL-IONIZATION GAS-CHROMATOGRAPHY MASS-SPECTROMETRY AND GAS-CHROMATOGRAPHY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY, Journal of chromatography, 648(2), 1993, pp. 433-443
Under NH3-chemical ionization (CI) conditions alkyl thiocyanates give
mass spectra which show only the adduct ions (M + NH4)+ (base peak) an
d (M + NH, .NH3)+. Allyl thiocyanate and aromatic thiocyanates show fr
agmentation similar to the corresponding isothiocyanates but still pro
duce (M + NH4)+ as base peak and (M + NH4 . NH3)+ as a prominent ion.
These properties allow the thiocyanates to be easily distinguished fro
m isothiocyanates whose NH3-CI mass spectra indicate considerable frag
mentation 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 isot
hiocyanates 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) s
imilar to that seen in liquid film spectra. Thiocyanates, in contrast,
show only weak absorption at ca. 2165 cm-1. Due to their weak interac
tion with infrared, aromatic thiocyanates are difficult to detect by t
his technique. Allyl thiocyanate is a special case. Under normal GC-Fr
-IR conditions it quickly isomerizes to allyl isothiocyanate. Allyl th
iocyanate was only detected in admixture with allyl isothiocyanate, wi
th light-pipe temperatures below 100-degrees-C.