High speed analysis in capillary GC and GC-MS : a unified approach

For thin film columns operating under conditions of high inlet to outlet pressure ratio an equation will be given describing the dependance of analysis time on resolution. column selectivity, capacity factor, column radius, diffusivity and viscosity of the carrier gas. It will be shown that minimum analysis time for a given resolution is always obtained when the column is operated with a vacuum outlet, thus favouring the direct coupling without interfaces of capillary columns and mass spectrometers. Another important conclusion is the direct proportionality between column radius and analysis time, showing the advantage of the use of very narrow bore columns. Several applications of narrow bore columns, 50 wm and less, in combination with FlD and EC-detection, will be presented. Sample capacity and sample range of these columns will be discussed. Coupling of 50 wm columns to a mass spectrometer is shown to be beneficial in terms of speed and sensitivity. EI spectra can be identified from even 50 pg amounts. S.l.H. in the NICI mode enables detection limits in the femtogram level.