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Microcoil NMR Study of the Interactions between Doxepin, β‑Cyclodextrin, and Acetate during Capillary Isotachophoresis
journal contribution
posted on 2012-08-21, 00:00 authored by Christopher
J. Jones, Cynthia K. LariveThe capillary isotachophoresis (cITP) separation of the
isomers of the tricyclic antidepressant doxepin using β-cyclodextrin
(β-CD) as a buffer additive is investigated by online microcoil
NMR detection. Capillary electrophoresis (CE) is also used to determine
the binding constant between the doxepin E and Z geometric isomers
and β-CD. Although the doxepin isomers could be easily baseline
resolved by CE, their separation by cITP was more challenging due
in part to the high concentration of doxepin after cITP-focusing.
The use of online 1H NMR detection allows observation of
changes in doxepin dynamics due to formation of the β-CD inclusion
complex, changes in the fraction complexed and the intracapillary
pH. It also provides novel experimental evidence that a weak complex
between β-CD and acetate contributes to its active transport
from the leading electrolyte through the sample band to the trailing
electrolyte in this cationic cITP separation. The results of these
cITP-NMR experiments provide new mechanistic details about the interactions
of the buffer counterion acetate with various components of the separation
system and have important implications for other analyses based on
formation of cyclodextrin inclusion complexes.
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Keywords
electrolytedoxepin dynamicsseparation systemtricyclic antidepressant doxepinbuffer counterion acetatemicrocoil NMR detectionformationcationic cITP separationbuffer additive1 H NMR detectionCEsample bandCapillary electrophoresisintracapillary pHdoxepin Ecyclodextrin inclusion complexesMicrocoil NMR Studyfraction complexedCapillary IsotachophoresisThe capillary isotachophoresisdoxepin isomers
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