The distribution of hydrophobic ionogenic organic compounds
(HIOC's) between aqueous and nonaqueous phases has been
investigated. The HIOC's are aniline and methyl substituted
anilines. The aqueous phases are methanol-water mixed solvents with
varying pH and ionic strength. The nonaqueous phases are silica and
alkyl derivatized silica with ethyl- (C-2), octyl- (C-8), and
octadecyl- (C-18) silanes.
A gas-liquid equilibration method has been developed to
determine the Henry's law constants and the activity coefficients of
methyl anilines in methanol-water mixed solvents. The logarithm of
the Henry's law constants vary quadratically with the volume fraction
of methanol.
The chromatographic study has been performed to investigate the
effect of three mobile phase factors, fraction of methanol, pH, and
ionic strength, on the retention of methyl anilines on different
stationary phases.
The logarithm of mass distribution ratios, log k's, of methyl
anilines vary linearly with the volume fraction of methanol. The
ratios of H / k' of methyl anilines increase with increase in
methanol in the mobile phase, indicating an increase in the activity
coefficients in the stationary phases. This observation is found to
be true for different methyl anilines in different stationary phases.
A partition model is presented to describe the effect of pH and
ionic strength on the retention of HIOC's in the mobile phase. The
variation in log k' among neutral and ionic methyl anilines can be
explained by linear free energy relationships. Equations are
established to predict retention of neutral or ionized methyl
anilines from their octanol-water partition coefficients at any
methanol content in the mobile phase. Acid dissociation constants of
methyl anilines determined from the dependence of log k' on pH are in
close agrement with those determined by potentiometric titrations.
The effect of ionic strength on the retention of both neutral and
ionic species of methyl anilines is negligible. That is, the
contribution from electrostatic energy and salting out effect are not
significant.
The chromatographic study is extended to study the retention of
methyl anilines on silica as a function of pH and methanol at a
constant ionic strength. The dependence of retention on pH is
qualitatively interpreted from an ion exchange reaction between the
dissociated silanol groups in the surface and the ionized methyl
anilines. The effect of methanol on the retention of methyl anilines
and of pyridine on silica is described by a quadratic relationship
between the log k' and volume fraction of methanol. / Graduation date: 1990
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/38251 |
| Date | 05 September 1989 |
| Creators | Jayasinghe, Dudley Shelton |
| Contributors | Westall, John C. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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