Aspects of double-column gas chromatography with glass capillaries involving intermediate trapping

Abstract

The versatility of semi- and fully automated double-column systems containing one or two glass capillaries is improved considerably by the incorporation of intermediate trapping devices for the analysis of complex mixtures, including very dilute and aqueous solutions. For the main separation, glass capillaries are used exclusively in order to achieve optimum resolution of all interesting species as well as narrow peak profiles for low detection limits of trace components. A length of 10–50 mm of the glass capillary acts as the trap; cooling and heating is executed by using a simple stainless-steel mantle tube with two separate entrances for either blowing cool nitrogen generated from liquid nitrogen or blowing hot nitrogen generated by electrical heating. There are four advantages in the use of trapping techniques in double column systems: 1. Broad or distorted peak profiles generated at the pre-separation or during the elution from the pre-column and the transfer to the main column are eliminated; ideal plug injection of the on-column type is attained by this procedure. 2. Repetitive pre-separation and comulative trapping allow enrichment of trace components. 3. The main separation can be performed with an isothermal mode of operation for retention index identification with high reproducibility. 4. Two sets of independent retention index data are obtained when stationary liquids of different polarity are used in the two columns of the system and the re-injection procedure is adopted.