Frans_M_Everaerts_Isotachophoresis_378342.pdf

AMINO ACIDS 317
TABLE 13.5
STEP HEIGHTS (mm) FOUND IN THE LINEAR TRACE OF THE CONDUCTIVITY DETECTOR
SIGNAL IN THE ISOTACHOPHEROGRAMS OBTAINED WITH THE OPERATIONAL SYSTEM
LISTED IN TABLE 13.3.
Amino PH
acid
L-Asp
L-cys
L-Glu
I, -L-Tyr
L-Ser
L-Thr
DL-Tyr
DL-Met
GlY
L-His
L-Phe
L-Ala
L-Val
L-Trp
3-L-Hyp
L-Ile
L-Leu
p-Ala
9.01 9.22 9.42
32
40.5
37.5
61
93
95.5
122
118.5
135
122
130
176
169
171
170
188
190
24 0
29
36
33.5
58
82
87.5
111.5
110.5
124.5
128.5
121
165
160
162
161.5
180
178
233
27.5
31
33.5
51
78
88
104
106
117
109
116
155
153
156
152.5
171
170
205
much because 0-alanine is a stronger acid than water under the conditions chosen. Conducti-
metric recordings of analyses in which double-distilled water, adjusted to a high pH, and
analyses in which water plus a suitable terminator are applied, showed that the zone
boundaries were less well defined and that the conductivity finally attained is smaller.
An isotachopherogram obtained in the operational system specified in Table 13.2 is
shown in Fig.13.2. Fig.13.1 and 13.2 also show the differences that can be found in
Tables 13.3 and 13.4.
Fig.13.3 illustrates the possible mixed zones that can be expected if a mixture of
amino acids is analyzed. Two amino acids with close effective mobilities were injected in
the system specified in Table 13.3, at a pH of the leading electrolyte of 9. A black square
indicates that a mixed zone can be expected in a time of analysis of about 12 min (70pA).
A decrease in the concentration of the leading electrolyte did not result in substantial
differences in the effective mobilities of the various amino acids. An increase must be
avoided because the amino acids are not sufficiently soluble. So far in our laboratory no
research has been carried out to find electrolyte systems in which the amino acids are
more soluble. Combinations of non-ionic substances with water seem to have good
prospects, as the amino acids are not sufficiently soluble in methanol.