Determination of Caffeine in Various Coffee Types by Capillary Electrophoresis Through the Anionic Complex with 3,4-Dimethoxycinnamate - Caffeine: Chemistry, Analysis, Function and Effects - page 190

N

The limit of detection of the methods is compatible with the requirement of
the Brazilian norm about decaffeinated products.

Key Facts

d n 0 t 2 n g | 9

N Pi-complexes are formed because of the planar structure of two molecules
and the interaction between p-electrons as well as polar and hydrogen
bonds.
N Caffeine is stored inside the plant cells as a complex with chlorogenic acid.
When released, caffeine can permeate through the membrane.
N The p-complexes of caffeine and cinnamate analogues are bigger than
caffeine alone, which reduces the diffusion coefficient. However, as a
charged species, it can be now conducted by an electric field.

Definitions of Words and Terms
Electroosmotic flow (EOF): Flow of solution originated when the surface has a
zeta potential difference of zero and a significant electric field is applied. In the
electrophoresis context, it is originated by the interface between the solution
and the inner wall of the capillary.
Micellar Electrokinetic Chromatography (MEKC): Electrophoretic technique
in which ionic micelles are used to mobilize neutral analytes.
Background electrolyte (BGE): The electrolyte solution that is used to fill the
capillary and the reservoirs in an electrophoresis experiment. Frequently, this
solution is also a buffer.
Co-ion: The BGE ion with the same charge of the analyte.
Counterion: The BGE ion with the opposite charge of the analyte.
Joule heating: Heating caused when an electrical current flows through a body
with resistivity greater than zero. In capillary electrophoresis, although the
heating power is typically below one watt, the volume of solution is so small
that Joule heating can cause evaporation of the solution inside the capillary.
Mobility: The proportional constant that describes the velocity of a charged
particle in a viscous medium as a function of the electric field applied on it.
Ionic mobility: natural mobility,orintrinsic mobility, The mobility of an ion
completely free and fully dissociated in a medium.
Effective mobility: The average mobility of ionic species involved in a set of fast
equilibriums.
Apparent mobility: The result of the combination of effective mobility and the
EOF mobility.
EOF mobility: The proportionality constant that describes the velocity of the
EOF as a function of the electric field applied on the capillary.
Hydrodynamic radius: It is the apparent radius of a sphere that encompasses
the central molecule or ion and its solvation shell.