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.

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.

Courtesy of Supelco Inc.

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

Essential Oils

Without the use of gas chromatography the analysis of essential oils would be extremely difficult. Prior to the technique being developed, only the major components of the oils could be separated, achieved by distillation with high efficiency columns. Even so, such columns rarely contained more than 100 theoretical plates (distillation plates), were very slow in operation, and took many days to complete an analysis. Due to the limited separation efficiency of the distillation column, even the major components were contaminated with traces of other materials, many of which had strong olfactory intensity and, thus, confused the olfactory character of the major component. The gas chromatograph had a startling impact on the essential oil industry. Not only was the complex nature of the raw materials disclosed for the first time, the character of each pure individual components could be accurately ascertained by olfactory assessment of the eluted peaks (using a non destructive detector such as the katherometer, and smelling them).