Chemistry Reference
In-Depth Information
1
6
10
20
Cod liver oil
29
21
Carbowax 20M
38
18
22
1
15
13
26
46
4
39
40
5
25
23
28
2
3
12
8
7
9
45
16
14
30
37
36
5
10
15 20
Time (min)
25
30
FIGURE 2.2
Gas chromatography (GC): Analysis of fatty acids (in the form of methyl
esters) on a fused silica column coated with Carbowax 20M.
resin is often made from polymeric material, coated or bound with a resin. There are
four main types of ion exchange resin differing in their functional group:
1. Strongly acidic (typically, sulfonic acid groups, e.g., sodium polystyrene
sulfonate)
2. Strongly basic (quaternary amino groups, e.g., trimethylammonium groups)
3. Weakly acidic (mostly carboxylic acid groups)
4. Weakly basic (primary, secondary, and ternary amino groups, e.g.,
polyethylamine)
Mechanistically, for cation exchange chromatography, the resin retains the posi-
tively charged cations because the stationary phase displays a negatively charged
functional group, shown in the following equation:
R - X
-
C
+
+ M
+
B
-
⇄ R - X
-
M
+
+ C
+
+ B
-
With respect to anion exchange chromatography, anion resins retain the anions
due to the presence of the positively charged functional groups:
R - X
+
A
-
+ M
+
B
-
⇄ R - X
+
B
-
+ M
+
+ A
-
In either case, the ionic strength of either C
+
or A
-
in the mobile phase can be
adjusted to shift the equilibrium position and thus the elution time.
2.5 CHARCOAL
Black, refined and of fine mesh or macroporous, charcoal is very abundant. There
are several advantages to using charcoal: very cheap, plentiful, and can be used with
either aqueous or organic solvents or a combination of both (e.g., aqueous methanol).
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