Frans_M_Everaerts_Isotachophoresis_378342.pdf

AMINO ACIDS
Fig.13.3. Schematic diagram illustrating that mixed zones are found in isotachophoretic analyses if
the differences in effective mobilities are too small. A black square indicates that a mixed zone is
obtained between that pair of amino acids if they are present in one sample. The experiments were
carried out in the operational system listed in Table 13.3.
are too small. If so, a method may be found for determining complexation constants in
isotachophoretic analyses by varying the field strength in various experiments.
13.1.5. Separation in aqueous propanal solutions
It is well known that amino acids easily form complexes (Schiff bases) with aldehydes.
If amino acids are dissolved in a solution that contains an aldehyde, differences in
mobility can be expected because the solvent property changes, the amino acid molecule
is larger after complex formation and its pZ value changes because the complex is formed
with the amino group(s). The first two effects result in a small difference and the last
effect in a large difference in mobility. The last effect occurs at very low concentrations
of the aldehyde, assuming that the aldehyde character is great enough.
Experiments with sugars did not show substantial differences in the effective mobilities
of the various amino acids, especially if they were added in relatively low concentrations.
Formaldehyde, which has a strong aldehyde character, and acetaldehyde were found
to be very unstable. Even during analysis, formic acid and acetic acid, respectively, are
formed. Research is continuing to find a suitable combination of a non-ionic stabilizer(s)
in order to work reproducibly with formaldehyde and acetaldehyde.
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