Frans_M_Everaerts_Isotachophoresis_378342.pdf

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CHOICE OF ELECTROLYTE SYSTEMS
Fig.5.7. Isotachopherogram for the separation of a mixture of ADP, GDP, CDP and UDP in the
operational system at pH = 3.7 (Table 14.2). The detection was performed with a thermometric
detector. T = increasing temperature; t = time. The time in this experiment was short (15 min)
because there is a great difference in the effective mobilities. The electric current was stabilized
at 70pk 1 = Chloride; 2 = UDP; 3 = GDP; 4 = ADP; 5 = CDP; 6 = caproate.
electrolyte system for their separation. In Table 5.6, some pK values of fatty acids in
methanol are given; most of them are about 8, and we therefore have to choose a pH,
of 8-9 in order to separate them according to pK values. As a buffering counter ionic
species, Tris or Triethanolamine can then be used.
We chose as the counter ionic species Tris in combination with chloride as the leading
ion. The step heights of some fatty acids were measured for some concentration ratios
of hydrochloric acid and Tris, and the results are given in Table 5.12. With the chosen
electrolyte, the fatty acids could easily be separated and in Fig.5.8 the isotachopherogram
for the separation of some fatty acids is given for system A. The detection was performed
with a thermometric detector (copper-constantan thermocouple).
Example E If sample ionic species do not show any W absorbance, a UV detector
can still be applied by using a W-absorbing counter ionic species. The sample zones can