Principles and Practice of Chromatography - Chromatography Applications > Gas Chromatography Applications > Hydrocarbon Analysis > Page 75

The sample vial was then removed and the trap purged dry with 40 ml/min. of dry helium for 5 min. The trap was then transferred to a small heating oven and the contents desorbed onto the column at 250˚C with a 4 min. bake at 260˚C. A chromatogram of the separation that was obtained is shown in figure 38.

The open tubular column used was 60 m long, 0.75 mm I.D. carried a 1 mm film of the stationary phase Supelcowax 10. This stationary phase is strongly polar and corresponds to a bonded polyethylene glycol. The strong fields from the hydroxyl groups polarize the aromatic nuclei of the aromatic hydrocarbons and thus retention was effected largely by polar interactions between the permanent and induced dipoles of the stationary phase and solute molecules respectively.

 

Courtesy of Supelco Inc.

 

Figure 38 The Separation of 10 ppb Quantities of Aromatic Hydrocarbons from Water

 

The flow rate was 10 ml/min. in conjunction with the FID detector. The column was held at 50˚C for 8 min. and then programmed to 100˚C at 4˚C per min. More than adequate separation is achieved and even the m and p xylenes are well resolved. This might indicate that a significantly shorter analysis was possible. The aromatic hydrocarbons were present in the original aqueous solution at 10 ppb and so the 5 ml of water contained about 50 pg. of each aromatic hydrocarbon.