ENHANCED COLLECTION OF VOLATILE COMPONENTS BY USING A TRIPLEDEANS SWITCH TRIDIMENSIONAL PREPARATIVE CAPILLARY GAS CHROMATOGRAPHICSYSTEM

Being the collection of compounds from natural sources the goal of each preparative system, one of the needs is the injection of high amount of sample thus, in this concern, the column selection is of crucial importance. Sample capacity increases with column I.D. and the greatest capacity is provided from wide bore columns (0.53 mm I.D.), in fact, the latter can accommodate a larger mass of each analyte than narrow-bore capillary columns. Exceeding the sample capacity of a column will result in skewed peaks and decreased resolution. Therefore, if the samples to be analyzed contain compounds at high concentrations, or presents a wide range of concentrations, then a wide-bore column should be considered. Conventional GC analysis for preparative purpose presents different limitations when highly pure compounds have to be collected at milligrams level in a reasonable time. In fact, the collection of high amount of compounds from natural sources, often characterized by high complexity level, presents some issues: A) a limited amount of neat or diluted oil can be analyzed in each run due to the GC column sample capacity and efficiency, even if wide bore columns are used, and as a consequence, B) the total analysis time to collect a certain amount is greatly affected by the sample injection volume and finally, C) the purity degree of the collected fraction is often unsatisfactory due to the presence of coeluted compounds. As expected, the higher the injection volume, the lower is the total time required to collect a specific compound, thus the highest injection volume should be always used. It is clear thus as the collection of pure components requires the injection of lower amount in order to avoid coelutions on the wide-bore column, consequently to improve the purity of the peak collected but as above cited, this lead to an increased total collection time. With the intention to improve the productivity of the system a multidimensional prep-GC instrument is presented with the goal to reduce the total collection time and to improve the purity of the components collected. The prep-MDGC system consisted of three chromatographs, equipped with three Deans switch transfer devices. A SLB-5ms/ SupelcoWax 10/SLB-IL59 ionic liquid stationary phase 0.53 I.D. column combination (Supelco) was used in the three chromatographic dimensions in order to provide 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 at the end of the chromatographic separation. Depending on the necessity, a cold jet of pressurized CO2 was delivered at half height of the tube on the pack material to help the trap of compounds with high volatility. Collection performance of components at milligram levels with both a different volatility and polarity is reported exploiting different pack materials and cooling effect inside the collection trap.