QUANTIFICATION OF ISOLATED METHYL-GROUPS AQUATIC HUMIC SUBSTANCES BY MEANS OF H-1 AND C-13 NMR-SPECTROSCOPY

To determine the proportion of isolated methyl groups (i.e. methyl gro ups attached to hydrogen-free carbon) in a ground water humic substanc e (HS), four different techniques were applied: the standard proton sp in-echo technique, the H-1-INADEQUATE method, a short version of the l atter with a pi/4 pulse and the proton spin-echo DEFT technique. The s tandard spin-echo technique proved to be the most suitable. The propor tion of isolated paraffinic methyl groups is as high as 60%. Polycycli c isoprenoid structures are considered to be responsible for the occur rence of isolated methyl groups in HS.