Introduction to Soil Chemistry
Introduction to Soil Chemistry
Introduction to Soil Chemistry
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alization of components on a thin-layer plate. Detection methods similar <strong>to</strong><br />
those used in HPLC are used in capillary electrophoresis. The type of separation,<br />
ion, organic ion, or ionic biomolecule will determine which detection<br />
method is best.<br />
9.5.5. Electrophoresis Applied <strong>to</strong> <strong>Soil</strong><br />
Gel electrophoresis has been applied <strong>to</strong> soil DNA and RNA extracts using<br />
procedures similar <strong>to</strong> those used in DNA testing used for forensic analysis.<br />
Capillary electrophoresis has also been applied <strong>to</strong> the analysis of ionic species<br />
extracted form soil. While these processes show promise for the elucidation<br />
of valuable information about soil, neither is used for common, routine soil<br />
analysis [11–13].<br />
9.6. IDENTIFICATION OF COMPOUNDS SEPARATED BY<br />
CHROMATOGRAPHIC PROCEDURES<br />
There are three ways of “identifying” compounds once they are separated.The<br />
simplest is that for which chroma<strong>to</strong>graphy is named. If a mixture of colored<br />
compounds is separated, and then where and when they elute or are found on<br />
a thin layer or gel is identified by searching for the color. After separating and<br />
visualizing a colorless component, it must be identified. This can be done in<br />
one of two ways. The first and simplest is by R f or R t, which are the distance,<br />
relative <strong>to</strong> some fixed point, that compounds move during a chroma<strong>to</strong>graphic<br />
procedure or between the time they enter and exit the chroma<strong>to</strong>graphic<br />
column [see equation (9.1) and Table 9.4 for further details on the use of R f<br />
and R t]. The formulas for R f and R t are:<br />
R<br />
R<br />
f<br />
t<br />
identification of compounds 189<br />
distance spot moved<br />
=<br />
distance elutant moved<br />
= Time from injection <strong>to</strong> <strong>to</strong>p of peak<br />
Table 9.4. The R f Values of Spots on Thin-Layer Sheets<br />
Shown in Figure 9.6 a<br />
Spot Calculation Rf A1 3/15 0.20<br />
A2 9/15 0.60<br />
B1 2/15 0.13<br />
B2 9/15 0.60<br />
B3 12/15 0.80<br />
a The distance that the solvent front moved is 15cm; therefore, this<br />
is the denomina<strong>to</strong>r for all calculations.<br />
(9.1)