ABSTRACT
The quantity of hydroxyl groups on adsorbent surface a0 H can be determined by
(3)
where K = ([H]/[O])adsorbentm = ([H]/[O])Aerosil = (Ooo initial-Ooo equilibrate)/ Doo equilibrate• mo2o and rna are mass of 0 20 taking part in the deuterium exchange reaction and mass of adsorbent, 0 00 = log (10 / /) is the optical density of 2760 cm-1 band free 00 groups on the Aerosil surface. If the specific surface area of adsorbent s is known, then the concentration of surface hydroxyl groups can be calculated:
(4)
This method was used for determination of concentration of silanol groups on surfaces of two adsorbents used in liquid chromatography, silica gel LiChrosorb SI 60 and silanized silica gel LiChrosorb RP 2. The average surface concentrations of silanol groups for LiChrosorb SI 60 and LiChrosorb RP 2 were 8.0 and 4.5 J,Lmoljm2 ± 5% respectively. Surface concentration of silanol groups of the first sample is the same as for all limiting hydroxylated silica [7,21], and for modified silica gel LiChrosorb RP 2 the concentration of hydroxyl groups is much smaller. This means that not all hydroxyl groups are removed from the surface, but only free hydroxyl groups; hydrogen-bonded surface silanol groups remain [7,8].
