Frans_M_Everaerts_Isotachophoresis_378342.pdf

AMINO ACIDS
TABLE 13.1
OPERATIONAL SYSTEM AT pH 5.4 SUITABLE FOR CATIONIC SEPARATIONS
Solvent: H, 0.
Electric current @A): Ca. 50-100.
Electrolyte
-~
Leading Terminating
Cation K+ DL-Ala’
Concentration 0.01 N Ca. 0.01 N
Counter ion
PH
CH, COO-
5.4
OH- [added as Ba(OH),]
>I
Additive 0.05% Polyvinyl
alcohol (Mowiol)
None
nitrogen. Moreover, barium hydroxide of pro analysi quality must be added to the
terminating electrolyte in order to prevent any carbonate (hydrogen carbonate) from
penetrating into the narrow-bore tube via the reservoir filed with the terminating
electrolyte. The addition of barium hydroxide to the leading electrolyte did not improve
the separation, however. Because of the high mobility of Ba2+, less sharp boundaries
can be expected.
If suitable precautions are taken, some carbonate (hydrogen carbonate) may still be
detected if an anion with a lugher effective mobility is used as the leading ion. This
carbonate (hydrogen carbonate), however, did not obscure both the qualitative and
quantitative results. Only a leading ion with an effective mobility higher than or equal to
that of the carbonate (hydrogen carbonate) ion can be used, otherwise the carbonate
may no longer be visible but may still disturb or at least obscure the analytical result, if
it is supported continuously. The resolution will decrease and zone electrophoretic
phenomena can soon be expected e.g., ‘elution’ by the carbonate (hydrogen carbonate)
ions.
Several suitable buffers are commercially available that enable one to work at high pH.
Some of them, including bis(3-aminopropyl)amine, trime thylenediamine, L-arginine,
1-methylpiperidine, octylamine, ethanolamine and L-lysine, were tested for purity and
effective mobility*. Some of the compounds were found to be very impure and even
could not be purified satisfactorily by the usual methods such as distillation, recrystallization
or ion exchange. Some of the counter ions show unexpected phenomena, e.g.,
enforced isotachophoretic systems or undesirable complex formation. Of the compounds
mentioned above, only 1 -methyl piperidine, L-arginine, L-lysine, octylamine and
ethanolamine gave good results.
In Tables 13.2 and 13.3, two operational systems are given in which analyses were
performed and for which more data will be given later.
*If a counter ion (buffer) is too mobile, a considerable proportion of the electricity is carried by this
counter ion, which results in less sharp zone boundaries and a decrease in resolution.
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