Published:Journal of Chromatographic Science,
ISSN 0021-9665 Volume
45, Number 8, September 2007, pp. 492-506
The Influence of Mobile Phase Demixion on Thin-Layer
Chromatographic Enantioseparation of Ibuprofen and Naproxen
Mieczyslaw Sajewicz[1], Krzysztof Kaczmarski[2],
Monika Gontarska[1], Sylwia Kiszka[1], and Teresa Kowalska[1],
[1]Institute of Chemistry, Silesian University, 9 Szkolna Street,
40-006 Katowice, Poland and
[2]Department of Chemical and Process
Engineering, Technical University of Rzeszów, Al. Powstanców
Warszawy 6, 35-959 Rzeszów, Poland
In our earlier article we presented the results
of tracing the enantioseparation of the two test analytes (ibuprofen
and naproxen) by means of video densitometry and scanning densitometry.
In that way we demonstrated an excellent performance of this
combined approach to the thin-layer chromatographic detection
in the area of enantioseparation. In this paper we study an impact
of the four different mobile phases on the enantioseparation
of the scalemic mixtures of ibuprofen and naproxen on the silica
gel layers impregnated with L-arginine as chiral selector. The
main component of all the investigated mobile phases is 2-propanol.
Mobile phase 1 consists of pure 2-propanol, while mobile phases
2–4 contain, respectively, ca. 0.66, 1.32, and 1.98 g/L
of glacial acetic acid in 2-propanol. Acetic acid is used to
protonate L-arginine, as the involved retention mechanism consists
of the ion pair formation between L-arginine in the cationic
form and the chiral 2-arylpropionic acids (2-APAs), ibuprofen
and naproxen, in the anionic form. It is shown that in the absence
of glacial acetic acid no enantioseparation can be obtained.
Then with adding of 0.66 g/L glacial acetic acid partial enantioseparation
of the naproxen and ibuprofen antimers is obtained, with a simultaneous
effect of the mobile phase demixion. With the amount of acetic
acid increasing, the effect of demixion becomes increasingly
perceptible. In that case the displacement effect is observed
(and mathematically modeled), which results in compressing of
the antimer pairs by the second front of mobile phase. The obtained
results allow a deeper insight into the mechanism of enantioseparation
with the two test 2-APAs. A combined impact of the crystalline
chirality of silica gel and the molecular chirality of l-arginine
on the vertical and the horizontal enantioseparation of ibuprofen
and naproxen is also discussed.
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