Chromatographic Methods for Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 250

Table 10.1 Common stationary phases for gas-liquid chromatography in gas
chromatography a

Maximum

Stationary phase Polarity temperature Environmental applications

350 C Polydimethyl siloxane Nonpolar General-purpose nonpolar

phase, hydrocarbons, PAHs,
PCBs, drugs, steroids

350 C Poly(phenylmethyldimethyl) Intermediate Halogenated compounds, fatty

siloxane (10% phenyl) acid methyl esters,

alkaloids, drugs

250 C Poly(phenylmethyl) Intermediate Pesticides, drugs, steroids,

siloxane (50% phenyl) glycols

200 C Poly(trifluoropropyldimethyl) Intermediate Chlorinated aromatics,

siloxane nitroaromatics, alkyl-

substituted benzenes

Polyethylene glycol Very polar 250 C Alcohols, aldehydes, ketones,

and separation of aromatic
isomers, e.g., xylenes

Poly(dicyanoallydimethyl) Very polar 240 C Polyunsaturated fatty acids,

siloxane free acids, alcohols

a Stationary phases are arranged in order of increasing polarity. Adapted from Principles of Instrumental
Analysis, 5th edition by Skoog et al. (1998). Reprinted with permission of Brooks/Cole, a division of
Thomson Learning: http://www.thomsonrights.com.

methyl groups is replaced by functional groups such as phenyl (C 6 H 5 ),
cyanopropyl (C 3 H 6 CN), and trifluoropropyl (C 3 H 6 CF 3 ). The increase in the
percentage of substitution of these relatively polar groups increases the polarity of
the liquids to various degrees.
In selecting a column from various stationary phases, one common rule is ''like
dissolves like.'' In other words, one chooses a nonpolar column for a nonpolar
mixture and a polar column for a polar mixture. Using a less polar column will
provide the best resolution for the most difficult separation, whereas a more polar
column will benefit when difficult isomer separations are required. An exception to
this generalization occurs when one attempts to separate similar solutes, such as
isomers (For instance, isomers of xylene that are more or less nonpolar and have
similar boiling points). A nonpolar stationary phase will not be satisfactory for their
separation because they do not vary much in either boiling point or in polarity.
Instead, a polar stationary phase, like DB-WAX, is required to separate compounds
with small differences in polarity (McNair and Miller, 1998).

HPLC Column Stationary Phase

Of the four types of liquid chromatography introduced, we will only describe the
stationary phases for adsorption-based LSC and the partition-based LLC.