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Last Update: 01/31/00

Selection of GC Guard Columns For Use With the GC Cryo-Trap

INTRODUCTION

The GC Cryo-Trap consists of a small heating/cooling chamber which surrounds the first 4 inches of the GC capillary or guard column. The GC Cryo-Trap is installed inside the GC oven just under the GC injection port to permit the trapping of volatiles and semi-volatiles at the front of the capillary column (Figure #I). Liquid C02 is normally used as the cooling gas to permit the trapping of volatiles at temperatures down to -70 deg. C. Liquid nitrogen can be used to permit trapping volatiles down to - 180 deg. C. A separate digital dual temperature range controller permits the accurate temperature setting and the regulation of both the cooling and the heating temperatures of the GC Cryo-Trap. After trapping the volatiles, the GC Cryo-Trap can be rapidly heated to a selected temperature up to 400 deg. C at a heating ramp rate in excess of 800 deg./min. Applications of the GC Cryo-Trap include thermal desorption and headspace GC techniques for the cryo-focusing and subsequent analysis of the volatile and semi-volatile organics.

Various guard columns can be utilized with the GC Cryo-Trap depending on the applications of the user. This paper studies the improvement in the retention range of volatiles that can be trapped as a function of the type of guard column used inside the GC Cryo-Trap. A variety of guard columns from deactivated fused silica with no liquid phase up through thick film megabore guard columns were studied using a mixture of hydrocarbons from ethane (C2) through nonane (C9). The purpose of this study was to determine the optimum guard column to use with the GC Cryo-Trap to permit the analysis of the widest range of volatile organics.

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