Frans_M_Everaerts_Isotachophoresis_378342.pdf

24 PRINCIPLES OF ELECTROPHORETIC TECHNIQUES
a
0
s
pH IffCREASlNO
4 5 6 7 8
L
c
pH INCRPASINO
Fig.2.10. Separation of the amphiprotic substances A, B and C with PI values of 4, 6 and 8,
respectively, by isoelectric focusing. The amphiprotic substances are eventually concentrated into
narrow zones where the pH of the buffer gradient is equal to the PI value of the amphiprotic substance
in each instance. (a), Sample introduction; (b), separation of A, B and C. s = position of introduction
of sample.
In Fig.2.10, ths situation is shown for the separation of three substances with pf
values of 4,6 and 8, respectively. The substances A, B and C are introduced at a pH of 6,
Le. the net charge of A is negative (pH is higher than its pZ value), the net charge of B
is zero (pH = pf) and the net charge of C is positive (pH is lower than its pf value).
Substance A will migrate towards the anode until it reaches a pH of 4, substance B stays
at the position where pH = 6 and substance C migrates towards the cathode until it
reaches a pH of 8. After a certain time, A, B and C are separated and concentrated into
narrow zones with pH values of 4,6 and 8, respectively.
Further information on equipment, performances, carrier ampholytes, etc. is given in
detad in the literature.
2.6. DISCUSSION
In the preceding sections, the four main types of electrophoresis have been described,
and in Fig.2.11 their characteristics are summarized. In each instance a sample is
introduced (at an injection point X) that consists of two anionic species B and C and one