Journal
JOURNAL OF CHROMATOGRAPHY A
Volume 1446, Issue -, Pages 149-157Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.chroma.2016.03.084
Keywords
Acid dissociation constant; Capillary coating; Capillary electrophoresis; Coumarin derivatives; Electrophoretic mobility
Funding
- Ministry of Science and Higher Education of Poland [IP2014 033273]
- National Science Centre, Poland [2015/17/N/ST4/03792]
- Krakowskie Konsorcjum Materia-Energia-Przyszlosc within KNOW
- European Regional Development Fund within Polish Innovation Economy Operational Program [POIG.0 2.01.00-12-0 23/08]
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In this work capillary electrophoresis has been used to determine acid dissociation constant of 20 structurally diverse coumarin derivatives. For a majority of compounds pK(a) value has been determined for the first time. The obtained values vary between 4.16-9.10 pH unit, pointing to the interesting structure acidity relationships. The amine permanently coated capillary has been applied for that purpose, because it has turned out to be more effective in pKa determination than the bare silica and other coated capillaries, ensuring good precision and shorter migration times. A traditional methodology relying on measurements in a broad pH range and fitting of a sigmoidal function has been compared to an alternative simplified approach, reported for the first time, where only two electrophoretic mobility values suffice for pK(a) estimation. The first value corresponds to the partially ionized form and it is measured experimentally, while the second one to the totally ionized form it is measured experimentally (two values method) or estimated directly from molecular mass (one-value method). We show that despite a limited measurements number, the alternative approach may be consistent with the traditional methodology, yielding the relatively low pKa deviation. Its reliability has also been confirmed by the analytical predictions, comprising resolution, migration order, migration times and peaks overlapping. Therefore, combination of the amine capillary with the simplified calculation method is an attractive tool for fast and reliable pKa estimation. (C) 2016 Elsevier B.V. All rights reserved.
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