Frans_M_Everaerts_Isotachophoresis_378342.pdf

108 CHOICE OF ELECTROLYTE SYSTEMS
Fig.5.8. Isotachopherogram for the separation of some fatty acids in a methanolic system (for
operational system see Table 16.1). The detection was performed with a thermometric detector.
T= Increasing temperature; t = time. The electric current was stabilized at 70 PA. 1 = Chloride;
2 = formate (C, 1; 3 = acetate (C2); 4 = butyrate (C4); 5 = n-caproate (C6); 6 = ncaprylate (C,);
7 = n-caprate (&); 8 = n-laurate (C12); 9 = n-myristate (C14); 10 = n-palmitate (C16); 11 = n-stearate
(CIB); 12 = cacodylate.
Example G. Sometimes, different sample ionic species have identical effective mobilities
at a certain pH, so that they form stable mixed zones. By using different electrolyte
systems with different pH, values, they can generally be separated according to their
pK values. However, if we do not know the composition of the ionic species present in the
sample, difficulties can arise. The use of both a conductivity and a UV detector can
then be advantageous.
In Fig.5.10, the isotachopherograms are shown for phosphate, salicylate and a mixture
of them. The conductimetric signals are identical and the mixed zone cannot be recognized.
In this experiment, the leading electrolyte was a solution of 0.01 N hydrochloric acid
and 0-alanine at a pH of 4 and the terminator was 0.01 N glutamic acid. Because the pK
values of orthophosphoric acid are 2.12,7.21 and 12.67 and the pK value of salicylic acid
fT