THEORETICAL CALCULATION OF GAS HOLD-UP TIME IN CAPILLARY GAS-CHROMATOGRAPHY - INFLUENCE OF COLUMN, INSTRUMENT PARAMETERS AND ANALYSIS CONDITIONS AND COMPARISON OF DIFFERENT METHODS OF DEAD-TIME DETERMINATION

The gas hold-up time or dead time, t(m), of some capillary columns with different bonded liquid or carbon layer stationary phases was calculated by using equations derived by the classical theory of gas behaviour in narrow tubing, e.g., Poiseuille's law. The parameters of the equations (pressure, temperature, gas viscosity, diameter and length of the column) were measured experimentally and the effect of the approximation of the measure on the final value of t(m) was evaluated over a wide temperature range. The calculated t(m) values were compared with those obtained by using the retention time of methane, the extrapolation of homologous series, the elution of the front of the solvent peak, flow-rate measurement with a bubble flow meter and the automatic systems of commercially available instruments.