A detector for use with capillary tube columns in gas chromatography.

Abstract

A RECENT development in gas Chromatography is the use of columns made from metal capillary tubing, the inner surface of which is coated with a thin layer of stationary phase1. These columns promise greatly enhanced performance and resolution in the separation of volatile substances compared with the conventional packed-powder columns; for optimum performance, however, capillary tube columns require small-bore tubing, a thin layer of stationary phase and a slow rate of gas flow, approximately 1 ml./min. The small dimensions of these columns necessitate small loads in the region of 1 µgm. of the mixture to be separated, otherwise the stationary phase would bear excessive concentrations of the various components and the resolution of the column would suffer. The slow rate of gas flow combined with the outstanding resolving power of the columns causes the emergence of the more volatile components in a gas volume of only a few µl. These two properties of the capillary tube columns impose severe restrictions on the type of detector suitable for observing the emergence of vapour from the column. The smallness of the load demands high sensitivity, and the smallness of the retention volume demands a detector with a sensing volume at least as small. A detector was reported in which the concentration of vapour molecules emerging from the column was measured in terms of their ionization following collisions with metastable rare-gas atoms2. This detector is more than sufficiently sensitive for use with the capillary columns; it is, however, much too large (1–10 ml.) and cannot simply be scaled down in size to accommodate the requirements of the capillary columns. This communication describes a modified version of the detector with a sensing volume in the region of 1 µl.