Cryogenically Cooled Microloop System for Sampling and Injection in Fast GC

A new inlet system for fast gas chromatography has been built in which analyte compounds in the gas phase are cryogenically trapped onto a sample loop, isolated, revaporized, and injected. Sample loops are constructed of 20 cm lengths of 50 and 100 μm i.d. fused-silica tubing. Since the volume of these loops is small, analytes could be injected with initial bandwidths of less than 10 ms. Loops can be coated to increase the effectiveness with which compounds are trapped. Sample loops with thicker, less polar films trap hydrocarbons at relatively higher temperatures than those with more polar, thinner films. Use of 50 μm i.d. sample loops results in narrower injection bandwidths compared to 100 μm i.d. loops, but this does not necessarily translate into better chromatographic resolution. The wider bore tubes allow for more efficient sampling and shorter retention times for similar column head pressures. The injection system has been used to demonstrate sampling and fast GC analysis of a 10 ppbV mixture of volatile organic compounds.