Highly Efficient Collection of Oxygenated Sesquiterpenes by Means of a Triple Deans Switch Tridimensional Preparative Capillary Gas Chromatographic System

The prep-MDGC system developed consisted of three chromatographs, equipped with three Deans switch transfer devices and a 0.53 I.D. column combination of SLB-5ms/Supelcowax 10/SLB-IL59 ionic liquid stationary phase (Supelco).This column set provides orthogonal selectivity for peak purification. The collection trap system was developed in our lab in order to obtain an easy and low cost tool for the collection of purified compounds using, depending on the necessity, a cold jet of pressurized CO2 to trap compounds with high volatility. Collection performance of components at milligram levels with both a different volatility and polarity is reported exploiting different packed materials and cooling effect inside the collection trap. As an example of a possible application to run with such a preparative system, namely the collection of a pure component to be used as standard, carrot seed essential oil was analyzed. The latter is rich in sesquiterpenic components, including carotol [(3R)-6,8a-dimethyl-3-propan-2-yl-1,2,3,4,5,8-hexahydroazulen-3a-ol)], not commercially available as standard, contained in the oil at 30% level. To compare the result the same collection was performed using a monodimensional conventional prep-GC system. The GC/MS chromatograms of the fractions collected using both the GC-prep systems showed a degree of purity higher than 99% for the multidimensional system while in monodimensional conditions carotol (LRI 1601) was coeluted with three peaks: caryophyllene oxide (LRI 1587) accounted for 20%, while other two peaks accounted for about 5% of carotol. It is clear thus as the collection of carotol required the injection of lower amount in monodimensional conditions in order to avoid the coelutions on the wide-bore column leading to an increased total collection time. This problem was overcome in multidimensional conditions where no coelutions appeared; furthermore, it is possible to increase the amount of sample injected per run (2-3 fold) highly decreasing the period required for the collection of milligram amount.