Measurement and prediction of dead times and column diameter in capillary gas chromatography by using air, methane and some solvents

The experimental determination of the hold-up time of capillary columns when using flame ionisation detection is generally made by measuring the retention time of methane. In high-temperature analysis or when using specific detectors the front of the solvent peak is often taken empirically as the dead time marker. An evaluation of the accuracy of these procedures was carried out by taking into account the errors due to the selection of the peak front or apex. The behaviour of these values as a function of temperature was studied by using capillary columns coated with liquid phases of different polarity (polydimethylsiloxane and polyethylenglycol). The dead time values measured by injecting small amounts of inorganic gases, methane, methanol, dichloromethane and hexane, were compared with those calculated with Poiseuille's law using the column length and diameter and the carrier gas viscosity. The accuracy and precision of the dead time values differ when the retention times of various compounds and of the apex or front of their peaks is used. The effect of the uncertainty of the diameter of the column given by the manufacturer on the dead lime calculation was investigated and a method for the determination of the diameter by using experimental measurement of retention times is suggested. (C) 1998 Elsevier Science BN. All rights reserved.