Base-strengthening effect factors

In order to determine the applicability of retention indices, based on the alkyl arylketone scale, as the basis of a reproducible method of reporting retentions, the separation of 10 barbiturates and a set of column test compounds were examined on an octadecylsilyl bonded silica (ODS-Hypersil) column with methanol-buffer of pH 8.5 as eluent [100]. The effects on the capacity factors and retention indices, on changing the eluent composition, pH, ionic strengthened temperature, showed that the retention indices of the barbiturates were much less susceptible to minor changes in the eluent than the capacity factors. 

Theoretical chemistry-based calculations (88) have indicated that the Al—O—Si angle also affects the vibrational frequency. Decrease of the angle strengthens the OH bond which leads to an increase of the O—H stretching frequency. Concomitantly, the acidity of the hydroxyls decreases. One additional factor that can influence the v(OH) is the aluminum content. However, this effect is only noticeable with low-silica zeolites (Si/Al<6) (97). 

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