Direct sample introduction of high boiling compounds onto glass capillary columns. Comparison of manual and automatic sampling

Abstract

The performances of two systems for the direct introduction of high boiling compounds onto glass capillary columns are compared. Samples investigated consisted of hydrocarbons and steroids. The “Moving Needle” system (a manual version) developed in our laboratory is extensively described in the literature [1]. The standard deviation for quantitative measurements is approximately 2.5% rel. Recently a Pye Auto Solids Injector has been modified so as to meet the requirements set by capillary gas chromatography. The very large dead volume of this sampling system, due to the use of sample holders prevents the direct coupling of this system to a capillary column. After introduction of a sample holder the solid sample evaporates slowly and the sample compounds are spread throughout a large volume of carrier gas, this badly affects the resolution obtainable. To overcome this problem the oven of the chromatograph contains a capillary precolumn (of some 50 cm length), which during a short period after sample introduction is cooled by a flow of air. During this cooling period the sample compounds are effectively trapped in the pre-column. After one minute the cooling medium is turned off, the pre-column rapidly heats in the column oven and a sharp reinjection of the sample occurs. A complete description of the system is given. The repeatability of quantitative measurements {σrel} is better than 1.5%. There is no loss of resolution by using this sampling technique. Both systems described are compatible with isothermal and programmed operation. Also in both versions the solvent does not enter the capillary column to an appreciable extent.