Direct trace gas chromatographic analysis using large sample on-column injection with bonded phase open tubular capillary columns
A new approach to direct trace gas chromatographic analysis is described which utilizes on-column injection of unusually large sample volumes (as much as 400 uL) onto bonded phase capillary columns. Trace substances of interest are adsorbed from the sample (organic or aqueous solution), at relatively low temperatures during the first pass through the column. Subsequently, the trace substances are thermally desorbed, trapped, and analyzed gas chromato- graphically utilizing the same column, or another column in series. With this technique, it is possible to achieve analysis readily at the part per billion level with a conventional flame ionization detector, or at the part per trillion level with an electron capture detector. This represents a several hundred-fold advance in sensitivity over conventional methods. Injection techniques for capillary GC are also presented with the focus on the solution of problems associated with the on-column injection technique, particularly chromatogram peak splitting and distortion effects. Finally, the effect of sample injection temperature on quantitation is examined in detail for on-column injection and split modes of sampling in capillary chromatography.