Comparison of the acidity of residual silanol groups in several liquid chromatography columns

• Published in: Journal of Chromatography A Vol. 986; no. 1; pp. 33 - 44
• Main Authors: Méndez, Alberto, Bosch, Elisabeth, Rosés, Martı́, Neue, Uwe D
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 31-01-2003; Elsevier
• Subjects: Acids; Analytical chemistry; Chemistry; Chromatographic methods and physical methods associated with chromatography; Chromatography, Liquid - instrumentation; Exact sciences and technology; Hydrogen-Ion Concentration; Other chromatographic methods; Silanes - chemistry; Silica columns; Silica, n-octadecyl bonded; Stationary phases, LC; Dissociation constants; Acidity; Silanol activity; Ion exchange; Charge exclusion; Lithium Nitrates; HPLC chromatography; Theoretical study; Retention factor; Dissociation constant; Experimental study; Mobile phase; Electrochemical detector; Conductometry; pH; Silica gel; Chemical properties; Mineral salt; Bonded stationary phase; Stationary phase
• ISSN: 0021-9673
• DOI: 10.1016/S0021-9673(02)01899-X

The silanol acidity of Waters Resolve C
18, Waters Resolve silica, Waters Symmetry C
18, Waters Symmetry silica, Waters XTerra MS C
18 and underivatized XTerra columns has been measured from the retention of LiNO
3 with a methanol/water (60:40) mobile phase buffered to different pH values. The Li
+ cation is retained by cationic exchange with the background cation of the mobile phase (Na
+) through the ionized silanols. The number of active silanols increases in the order: XTerra MS C
18≪Symmetry C
18<underivatized XTerra≪Resolve C
18<Resolve silica≈Symmetry silica. XTerra MS C
18 does not present any residual silanol acidity up to
s
s
pH
10.0 (pH in 60% methanol) as measured by LiNO
3. The underivatized XTerra packing and Symmetry C
18 present active silanols only at
s
spH values higher than 7.0. For the other three columns, two different types of silanols with different acidity (
s
sp
K
a values about 3.5–4.6 and 6.2–6.8, respectively) have been observed. Symmetry C
18 shows evidence of the presence of active basic sites that retain NO
3
− by anionic exchange.