Modern capillary GC injection generally uses the universal dual mode split/splitless injection port or inlet in which the pneumatic mode is selected at the outset. The inlet is maintained at a sufficiently high set temperature to allow instant vaporization of the sample after deposition in the inlet liner (usually 4mm i.d.) Of course this explosive vaporization is associated with the well documented undesirable phenomenon of needle discrimination. If analytes are in aqueous solution another effect is induced by the very high saturated vapor volume of water compared to other solvents. A 1 μL injection of water in hot splitless mode will give a vapor volume greater than the retaining capacity of the liner and can inhibit the subsequent vaporization of analytes.
There is another injection technique, which avoids many of the above problems and also offers the attractive possibility of actually removing solvents such as water before transfer of analytes to the column. This is temperature programmed sample introduction or PTV injection, proposed by Abel [1] and developed by Vogt et al [2]. The Programmable Temperature Vaporization (PTV) type inlet offers 3 modes of sample introduction: The previously described split and splitless modes and an additional “solvent vent” split mode. In all modes a major advantage is that the sample can be deposited in the liner at ambient temperature and only then are analytes transferred to the column by rapid heating of the inlet. For either a PTV or hot split/splitless inlet in initial split or splitless mode the pneumatic condition for transfer of analytes is predetermined by the choice of mode. However the PTV type inlet in solvent vent mode offers the additional possibility to inject at low temperature with the split valve open and then to revert to standard split or splitless mode for the heating step. It is intuitively clear that this approach can be used to initially remove solvents or even low boiling analytes. In the remainder of this Application Note, we will attempt to explain the interesting interplay between the properties of the analytes and the chosen solvent, as well as the PTV and pneumatic method parameters chosen, in order to fully exploit this technology for routine trace analysis.
