Russian Doll Type Cryogenic Traps: Improved Design and Isotope Separation Effects

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Abstract
An improved cryogenic trap for removing micromole quantities of condensables from gas mixtures is described. It is based on the so-called Russian doll design, with which extraordinary trapping efficiencies at flow rates of up to 10 L/min are obtained. The active element consists of one or more nested glass fiber thimbles. Despite the large fiber area, quantitative retrieval of condensed CO(2) is obtained. The new design is demountable and incorporates a heat exchange section; trapping efficiency depends little on the level of coolant, as has been tested for CO(2). When fractionation is induced by incomplete trapping, a small isotopic enrichment in (13)C occurs. It also has been discovered that when He is used as carrier gas, a gas chromatographic effect for CO occurs in Russian doll traps, accompanied by a large isotope separation, in which the elution sequence corresponds to the vapor pressure ratios of the isotopomers.