An Overview of Basic Principles of Analytical Methods - Field Sampling: Principles and Practices in Environmental Analysis - page 261

(GC); in this case the method is called gas chromatography/mass spectrometry (GC/MS).
This methodology allows the simultaneous separation of a complex sample into its
component compounds and the characterization and identification of these isolated
individual components.
The second group of methods is based on separation or extraction principles. A sample
is prepared and used in the instrumental portion of the method. Many organic methods
are based on a chromatographic method for sample speciation and characterization.
Chromatography requires the use of a detection method (usually one of the preceding
spectrometric methods) for a complete analytical procedure. This means the sample
extract is prepared using an extraction method, loaded onto a gas chromatograph for
separation, characterization, and speciation of the complex sample components. Once
separated, these components are detected and quantitated using a detector.
All extraction methods are based on the physical/chemical separation between different
phases, such as partition between liquid/liquid or liquid/ solid phases. Separation
principles are based on the extraction of a group of compounds from the sample using the
principle of differing solubility (e.g., a group of organic compounds will have a greater
affinity for a strong nonpolar or less polar solvent that is immiscible with the sample
matrix being extracted). An example of this would be a water or soil sample that is
extracted using methylene chloride as the extraction solvent. Methylene chloride is not
soluble in water, and so organic compounds extracted into it are separated from their
original matrix. Table 10.3 summarizes the various types of extraction methods in
common use today.
Separation conditions can be varied by changing the pH of the sample being extracted
or by using a different solvent. Changing the pH of water changes the protonation [H + ] of
the solutes contained in it. For instance, acidification increases the chance that the solute
will be protonated, and this means that the solute will have a different net charge. This
change in the charge is the reason that the solute compounds have a greater affinity for a
solvent of different polarity. This is also an example of the importance of the pH of the
original sample during analysis.

TABLE 10.3 Extraction Methods

Name Abbreviation Phases Matrix

Aqueous samples
Classic

Liquid/liquid, solid/liquid Liquid or solid

Solid phase SPE Absorbent column Liquid only

Supercritical
fluid

SCF Liquefied gas used in the liquid state under

pressure

Solids

Nonaqueous samples
Solution

Aqueous or organic solvent Homogeneous

liquid

Phase separated Separate phases and extract using one of the

above

Two separate
phases