Stationary Phases for Separation of Basic and Nonbasic Nitrogen Compounds or Hydrocarbons By Gas-Liquid Chromatography

Abstract

Retention data and bleed rates have been measured for some relatively stable liquid phases to obtain operational limits for gas-liquid chromatographic separation of polar shale-oil concentrates with boiling points above 200°C. Gas chromatographic separation of polar compounds with boiling points over 400°C in quantities adequate for spectral identification may be accomplished on packed columns with efficiencies near 5000 theoretical plates and with less than one percent column bleed contamination. Relative retention values were determined for some basic and nonbasic nitrogen compounds, and some hydrocarbons on polyethylene glycol (Carbowax 20M), polyethylene glycol terminated with terephthalic acid (Carbowax 20M-TPA), octyl-phenoxypolyethoxy ethanol (Triton X-305), and purified Apiezon L doped with Carbowax 20M-TPA. Retention data were obtained at 180° and 220°C on the polar liquid phases. Triton X-305 was found to show more alkyl character than Carbowax 20M. Column bleed rates were measured with five percent liquid phase at 220°C, the maximum temperature found appropriate for extended use of the polar columns. The Carbowax 20M bleed rate was 0.10 µg hydrocarbon-equivalent/min with very slightly less for the Carbowax 20M-TPA, while the Apiezon L rate was 0.01 µg min, all at 73 ml/min (25°C, 1 atm) flow rate. An Apiezon L column doped with five percent Carbowax 20M to reduce tailing exhibited a bleed rate characteristic of Carbowax 20M. Hydrogen flame response factors were determined for several heterocyclic nitrogen compounds. By the agreement of hydrogn flame response factors for samples put through polar and nonpolar columns it was concluded that the polar columns do not destroy the relatively unstable indole-type nitrogen compounds although they are strongly retained.