Frans_M_Everaerts_Isotachophoresis_378342.pdf

i
3
T
364 SEPARATIONS IN NON-AQUEOUS SYSTEMS
- - c_
t t t
Fig.16.1. Isotachopherograms of the separation of dl-malic acid (A), oxalic acid (B) and a mixture of
oxalic and dl-malic acids C. A: 1 = Chloride; 2 = dl-malate; and 3 = cacodylate. B: 1 = Chloride; 2,
3 = components that belong to the oxalate [the oxalate (2) and possibly an ester (3)] ; 4 = cacodylate.
C: 1 = Chloride; 2 = oxalate; 3 = malate; 4 = the ester of oxalate and methanol (?); 5 = cacodylate.
isotachopherogram of pure dihydroxymaleic acid is given. The terminator was cacodylic
acid.
The substances listed in Table 16.2 are almost all organic acids; in general, inorganic
acids were sparingly soluble in methanol. Because of its lower dielectric constant,
complex formation occurs to a much greater extent in methanol than in water, and also
the greater effect of the activity coefficients and the decreasing effect on the mobility
make methanol unsuitable for isotachophoretic experiments with inorganic ionic species.
For the halides, however, which have almost identical effective mobilities in water and
cannot be separated, some experiments were carried out in methanol. As with alkali
metals (see section 16.3.1), the halides have greater differences in mobilities in methanol
and can easily be separated. In Table 16.3, the absolute ionic mobilities and measured
step heights in water and methanol are given. The leading electrolyte in water was
0.01 N hydrobromic acid and in methanol 0.01 N hydriodic acid. In Fig.16.3, the
separation of the halides is shown, with sodium dihydrogen orthophosphate as terminator.
In the sample used to obtain Fig.16.3, formate was added in order to have the possibility
of comparing the step heights with those in Table 16.2.
16.3. SEPARATION OF CATIONIC SPECIES IN METHANOL USING A THERMO-
METRIC DETECTOR
Some cationic species were measured in three different systems, viz., the unbuffered
system MHCl, listed in Table 16.4, and the buffered systems MKAC and MTMAAC listed
in the Tables 16.5 and 16.6 respectively.