6533b86efe1ef96bd12cb23f

RESEARCH PRODUCT

Synthesis and properties of chemically modified dihydroxy-, hydroxyamino- and amino-functional silica packings in adsorption chromatography

subject

description

1,2-Dihydroxy-3-propoxypropyl (HPP), 1-amino-2-hydroxy-3-propoxypropyl (AHP) and 3-(2-aminoethylamino)propyl (AEAP) silica packings were synthesized by means of both a surface modification and a bulk modification procedure. In surface modification a complete monolayer of bonded groups could be achieved. The modifiers reacted with the silanol groups according to a bifunctional mechanism. Eluotropic series of solvents were established on these polar modified silicas referring to n-heptane having ɛ∘=0. The solvent parameter ratio of modified to bare silica was found to be constant over a wide range of solvent compositions as \(\varepsilon _{{\text{HPP - silica}}}^ \circ = 0.26\varepsilon _{{\text{silica}}}^ \circ ,{\text{ }}\varepsilon _{{\text{AHP - silica}}}^ \circ = 0.33\varepsilon _{{\text{ silica }}}^ \circ {\text{and }}\varepsilon _{{\text{ AEAP - silica}}}^ \circ = 0.37\varepsilon _{{\text{silica}}}^ \circ .\). The lower ɛ∘ values on modified silicas can be attributed to the homogenization of adsorbent surface by removal of the most active silanol groups during modification. This is also borne out by the fact that retention of solutes on polar modified silicas was scarcely affected by the water content of the eluent n-heptane. Depending on the polarity of the eluent, the retention of solutes reflects the hydrophobic and hydrophilic nature of the bonded moiety at the surface of modified silicas. Retention of acidic solutes increases in the sequence AEAP-silica>AHP-silica>HPP-silica due to specific acid-base interactions at constant eluent composition.