Polyethylene Gycol GC Columns
Polyethylene glycols (PEG) are widely used as stationary phases (Figure 6). Stationary phases with "wax" or "FFAP" in their name are some type of polyethylene glycol. Polyethylene glycols stationary phases are not substituted, thus the polymer is 100% of the stated material. They are less stable, less robust and have lower temperature limits than most polysiloxanes. With typical use, they exhibit shorter lifetimes and are more susceptible to damage upon over heating or exposure to oxygen. The unique separation properties of polyethylene glycol makes these liabilities tolerable. Polyethylene glycol stationary phases must be liquids under GC temperature conditions.
Figure 6. Polyethylene Glycol
There are two types of polyethylene glycols in common use as GC stationary phases. One has a higher upper temperature limit (DB-WAXetr and HP-Innowax), but exhibits slightly higher activity (i.e., peak tailing for some compounds). The other has a lower upper temperature limit and a lower low temperature limit but exhibits better reproducibility and inertness (DB-WAX and HP-WAX). The separation characteristics of the two stationary phases are slightly different. Another variation of polyethylene glycol phases is pH modifi- cations. FFAP columns are terephthalic acid modified polyethylene glycols (DB-FFAP and HP-FFAP). These columns are used for the analysis of acidic compounds. Base modified polyethylene glycol stationary phases are also available for the analysis of basic compounds (CAM and HP-Basic WAX). Strong acids and bases often exhibit peak tailing for standard columns. pH modified stationary phases may decrease the amount of tailing for strong acids or bases.