Gas Chromatography (GC) (IUPAC Compendium of Chemical Terminology):
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Lecture 3. <strong>Gas</strong> chromathography.<br />
POLYSILOXANES:<br />
R<br />
* Si O<br />
R<br />
n<br />
*<br />
Polysiloxanes are the most common stationary phases. They are available in the<br />
greatest variety and are the most stable, robust and versatile.<br />
The most basic polysiloxane is the 100% methyl substituted. When other groups are<br />
present, the amount is indicated as the percent <strong>of</strong> the total number <strong>of</strong> groups.<br />
Cyanopropylphenyl percent values can be misleading. A 14% cyanopropylphenyldimethyl<br />
polysiloxane contains 7% cyanopropyl and 7% phenyl (along with 86%<br />
methyl). The cyanopropyl and phenyl groups are on the same silicon atom, thus<br />
their amounts are summed.<br />
POLYETHYLENE GLYCOLS:<br />
* CH 2<br />
CH 2<br />
O *<br />
n<br />
Polyethylene glycols (PEG) are widely used as stationary phases. Stationary phases<br />
with "wax" or "FFAP" in their name are some type <strong>of</strong> polyethylene glycol.<br />
Polyethylene glycols stationary phases are not substituted, thus the polymer is<br />
100% <strong>of</strong> the stated material. They are less stable, less robust and have lower<br />
temperature limits than most polysiloxanes.<br />
With typical use, they exhibit shorter lifetimes and are more susceptible to damage<br />
upon over heating or exposure to oxygen.<br />
The unique separation properties <strong>of</strong> polyethylene glycol makes these liabilities<br />
tolerable. Polyethylene glycol stationary phases must be liquids under <strong>GC</strong><br />
temperature conditions.<br />
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