Published:Journal of Chromatographic Science,
ISSN 0021-9665 Volume
46, Number 1, January 2008, pp. 45-52
Evaluating the Surface Charge of C18 Stationary
Phases
Eric Loeser
Chemical and Analytical Development, Novartis Pharmaceuticals,
East Hanover, NJ
The surface charge of four C18 stationary phases
was investigated by measuring the flow induced streaming potential,
a well known electrokinetic property of charged surfaces. Three
of the stationary phases (Symmetry, Gemini, and Xterra-MS) had
significantly positive streaming potentials at both pH 3 and
4.5. The fourth (Zorbax-SB) appeared to be essentially neutral
at pH 3 and became negative at pH 4.5. Apparent zeta potentials
ranged from approximately +16 to –4 mV. The retention behavior
was also investigated using chloride as model anion and glycinamide
(in its protonated form) as model cation. When the retention
factor (k) of glycinamide was subtracted from k of chloride anion,
the resulting delta k values showed very similar trends as apparent
zeta potential values, suggesting that the simple chromatographic
method could be used to estimate zeta potential values, or that
the zeta potential values could be useful for ranking columns
according to ion exchange or exclusion behavior. The anion exchange
capacity of the Symmetry and Gemini columns was also estimated,
using a published chromatographic procedure, and the results
suggest about 2 microEq. capacity per gram of packing.
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