The isomer-specific analysis of di-iso-propylnaphthalenes

Di-iso-propylnaphthalenes (DIPN), frequently observed low-level contaminants of the aquatic environment, were analysed as the sum of isomers by GC/MS in Rhine and Lippe river sediments. For future isomer-specific trace analysis, linear retention indices of the components of a technical DIPN formulation were determined on six different GC-columns. Gas-phase infrared spectra aquired by GC/FT–IR analysis on GC capillaries coated with apolar and polar stationary phases showed characteristic patterns of C–Har out of plane deformation vibrations which allowed all DIPN isomers to be distinguished. Theoretical IR spectra of all DIPN were calculated with the B3LYP functional using 6-311G(d,p) and 6-311G+(d,p) standard triple zeta basis sets. The resulting frequencies were scaled by a factor derived emprically. Theoretical and experimental IR spectra allowed the structures of seven major DIPN isomers and two minor components to be assigned to the corresponding GC-peaks. All DIPN isomers of a technical formulation were resolved on polar GC capillaries, and the composition of the technical DIPN mixture was determined.