Fast Gas Chromatography using Vacuum Outlet Conditions

In this study the possibility of operating a wide-bore column with an inner diameter of 530 m at vacuum conditions was investigated as a route towards fast gas chromatography. High analysis speeds can be obtained as a result of the sub-ambient pressure conditions present in the column, and the consequently high diffusion coefficient of the solute in the mobile phase. The advantage of using a wide-bore column is the high sample capacity. To enable vacuum operation through coupling a wide-bore column to a mass spectrometer, three types of restricting the column flow were investigated. The first method uses a narrow bore pre-column (60 cm length×100 m i.d.), the second method relies on the use of a tapered on column supercritical fluid chromatography restrictor (SFC-restriction), whereas the third method makes use of a micro-injection valve. It was concluded that the best performance was obtained using the narrow-bore column restriction and the SFC-type restriction. Analysis examples in the seconds- and minutes-range are shown, with peak-widths ranging from 0.1 to 2 seconds at half height. It was concluded that with a film-thickness above 1.5 m, the advantage of the increase in analysis-speed due to low pressures is nullified due to retention time increase on a thick film column.