Frans_M_Everaerts_Isotachophoresis_378342.pdf

318 AMINO ACIDS, PEPTIDES AND PROTEINS
9-
1
8- - 20 Sm2
7-
6-
5-
4-
3-
2-
Fig.13.2. Isotachopherogram of the separation of a mixture of amino acids obtained with the
operational system listed in Table 13.2. 1 = Chloride; 2 = Asp; 3 = I, -Tyr; 4 = Ser; 5 = Tyr; 6 = Phe;
7 = Ala; 8 = Leu; 9 = p-Ala. All are L-amino acids. A = Increasing UV absorption; R = increasing
resistance: t = time.
13.1.4. Separation by use of complex formation
It is well known that amino acids form complexes with metal ions, e.g., Cu*+.
In an
aqueous solution of copper(I1) sulphate, the addition of various amino acids cause a
colour change, which indicates that a complex is formed. Isotachophoretic experiments
have shown that only a few of these complexes are sufficiently stable to be detected as
real complexes. An isotachopherogram of a copper-histidine complex is shown in
Fig.13.4C. In the isotachopherogram in Fig.13.4A, 0.2 pl of 0.01 M L-histidine solution
was injected, in Fig.13.4B 0.2 pl of 0.005 M copper(l1) sulphate solution was injected and
in Fig.13.4C 0.4 pl of the solution obtained by mixing equal volumes of these two solu-
tions was injected, with the operational system specified in Table 13.1.
When other amino acids were examined, however, their complexes were found to be
too unstable. No further research was carried out on this aspect. It may be that the field
strength applied in isotachophoretic analyses is too great or the complexation constants