THE USE OF GAS-PHASE UV SPECTRA IN THE 168-330 NM WAVELENGTH REGION FOR ANALYTICAL PURPOSES - 1 - QUALITATIVE MEASUREMENTS

A novel instrument, which combines gas chromatographic separation with ultraviolet detection, has been employed in the qualitative study of molecular UV absorption spectra in the gas phase, The wavelength range available with the current instrument made studies in the region of 1 68-330 mn possible, The absorption spectra between 168 and 330 nm for similar to 1000 organic compounds and a number of inorganic gases were registered, For all the spectra recorded, 69% showed absorption maxim a shorter than 190 mn, and as much as 87% shorter than 200 nn, This in dicates the importance of the short UV wavelength region for analytica l purposes, The results showed that each compound studied gave rise to unique absorption spectra, The influence of temperature on the shape of the spectra was studied in the range of 15-205 degrees C. A slight broadening effect on spectral absorption bands (0.3 mm) and the vibrat ional structure (maximally 1.4 mn) with increased temperature was obse rved. However, this effect was shown to have no influence on the analy tical results, In the vast majority of cases, where structural isomers were investigated, there were clear differences between the recorded spectra, Compounds with the same functional group showed pronounced si milarities, The influence of conjugation and various substituents coul d be demonstrated, A commercial computer program was used for a comput er search of unknowns against the recorded reference spectra, This sho wed that the gasphase UV spectra are very well defined and that a sear ch always resulted in a very close agreement, even if concentrations a nd chromatographic conditions were different between the recording of reference and unknown, When a search was performed on a compound not p resent in the library, the result pointed out the correct class of com pounds.