Frans_M_Everaerts_Isotachophoresis_378342.pdf

DISTURBANCES CAUSED BY H+ AND OH 26 1
TABLE 9.1
STEP HEIGHTS (mm) OF SOME CATIONS WITH A LEADING ELECTROLYTE OF 0.01 N
POTASSIUM ACETATE AND ACETIC ACID AT DLFFERENT pH VALUES
Cations 4.0 4.3 4.5 4.91
Adenine
Adenosine
-
12
30
12+37
69 + 90
85 + 120
~
156
Guanine 11.5 13 85 -
Uridine 12 12 77 119
Cytidine 12 12 t 40 103 145
Guanosine 12 12 80 120
TABLE 9.2
CALCULATED pH VALUES OF THE SAMPLE ZONES FOR CATIONS WITH THE LEADING
ELECTROLYTE (A) POTASSIUM FORMATE (0.01 m-FORMIC ACID AND (B) SODIUM
FORMATE (0.01 N)-FORMIC ACID AT DIFFERENT pH VALUES
Leading Cations PHL
electrolyte Mobility 3.25 3.5 3.75 4.0 4.1 4.2 4.5 5.0
A 50
30
10
30
30
30
30
30
B 38.8
30
20
(10-5cm2/V - sec) pK
14
14
14
6
5
4
3
2
14
8
8
- 3.34 3.61 3.87 3.98 4.08 4.38 4.88
- - - 3.55 3.68 3.80 4.12 4.65
- - - 3.54 3.67 3.79 4.10 4.49
-
-
-
-
-
-
3.48
-
3.60
-
3.70
-
3.93
3.38
4.13
3.51
3.068 3.368 3.637 3.896
- - 3.458 3.749
been obtained. At low pH, the amino acids had the same step heights. Van Hout [ 11 also
found the same step heights for an electrolyte system at pH 5 (see also Chapter 13).
Calculated pH values in the zones for some cationic species are shown in Table 9.2; where
no pH is given, no real zero points were present.
From Table 9.2, it can be seen that monovalent substances with low pK values (2 or 3)
cannot be separated by isotachophoresis, whereas completely ionized cationic species can
be analyzed even at low pH. In order to see what happens when separating these cations,
experiments were carried out with Tris' as a terminator and Li' as a sample ion with
leading electrolytes consisting of 0.01 N potassium formate-formic acid and 0.01 N
sodium formate-formic acid at different pH values. In Table 9.2, Li' (mobility 38.8 - lo-'
cmZ/V - sec) always shows real zero points with the leading electrolyte sodium formate-
formic acid, whereas Tris' (mobility about 30 * lo-' cmZ/V * sec) does not show real zero
points at pH 3.25 and 3.5.