Agriculture Reference
In-Depth Information
alization of components on a thin-layer plate. Detection methods similar to
those used in HPLC are used in capillary electrophoresis. The type of separa-
tion, ion, organic ion, or ionic biomolecule will determine which detection
method is best.
9.5.5.
Electrophoresis Applied to Soil
Gel electrophoresis has been applied to soil DNA and RNA extracts using
procedures similar to those used in DNA testing used for forensic analysis.
Capillary electrophoresis has also been applied to the analysis of ionic species
extracted form soil. While these processes show promise for the elucidation
of valuable information about soil, neither is used for common, routine soil
analysis [11-13].
9.6.
IDENTIFICATION OF COMPOUNDS SEPARATED BY
CHROMATOGRAPHIC PROCEDURES
There are three ways of “identifying” compounds once they are separated. The
simplest is that for which chromatography is named. If a mixture of colored
compounds is separated, and then where and when they elute or are found on
a thin layer or gel is identified by searching for the color. After separating and
visualizing a colorless component, it must be identified. This can be done in
one of two ways. The first and simplest is by
R
f
or
R
t
, which are the distance,
relative to some fixed point, that compounds move during a chromatographic
procedure or between the time they enter and exit the chromatographic
column [see equation (9.1) and Table 9.4 for further details on the use of
R
f
and
R
t
]. The formulas for
R
f
and
R
t
are:
distance spot moved
distance elutant moved
R
=
f
(9.1)
R
=
Time from injection to top of peak
t
Table 9.4. The
R
f
Values of Spots on Thin-Layer Sheets
Shown in Figure 9.6
a
Spot
Calculation
R
f
A
1
3/15
0.20
A
2
9/15
0.60
B
1
2/15
0.13
B
2
9/15
0.60
B
3
12/15
0.80
a
The distance that the solvent front moved is 15 cm; therefore, this
is the denominator for all calculations.
