A chromatographic system, comprising: a carrier gas inlet for supplying carrier gas; a chromatographic column (40; 104) for receiving the carrier gas; a flow path through which the carrier gas is communicated from said carrier gas inlet to said chromatographic column (40; 104); a sorbent tube (20; 30; 100; 102) disposed in said flow path, said sorbent tube (20; 30; 100; 102) having an adsorbent (32; 110; 140) disposed therein for adsorbing and desorbing analytes to be measured; said sorbent tube including an inlet and an outlet for communicating the carrier gas through said sorbent tube; at least one flow controller (200, 204) disposed in said flow path for controlling the flow rate of the carrier gas at a known rate; characterized in that the system further comprises a first pressure transducer approximate the inlet of said sorbent tube; a second pressure transducer approximate the outlet of said sorbent tube; wherein said chromatographic system determines a permeability factor of the sorbent tube, k, by calculating k in accordance with the equation F a = k ⋅ p i - p o η ⋅ p o p a ⋅ T a T o where (p i -p o) is the differential pressure between the inlet and the outlet of the sorbent tube based on measurements by the first and second pressure transducers, F a is the equivalent flow rate at ambient pressure and temperature, p a is the ambient absolute pressure, T a is the ambient absolute temperature, p o is the absolute gas pressure at the sorbent tube outlet, T o is the absolute temperature at the vessel outlet, η is the viscosity of the gas flowing through the sorbent tube (20; 30; 100; 102) and k is the permeability factor of said sorbent tube (20; 30; 100; 102). a carrier gas inlet for supplying carrier gas; a chromatographic column (40; 104) for receiving the carrier gas; a flow path through which the carrier gas is communicated from said carrier gas inlet to said chromatographic column (40; 104); a sorbent tube (20; 30; 100; 102) disposed in said flow path, said sorbent tube (20; 30; 100; 102) having an adsorbent (32; 110; 140) disposed therein for adsorbing and desorbing analytes to be measured; said sorbent tube including an inlet and an outlet for communicating the carrier gas through said sorbent tube; at least one flow controller (200, 204) disposed in said flow path for controlling the flow rate of the carrier gas at a known rate; characterized in that the system further comprises a first pressure transducer approximate the inlet of said sorbent tube; a second pressure transducer approximate the outlet of said sorbent tube; wherein said chromatographic system determines a permeability factor of the sorbent tube, k, by calculating k in accordance with the equation F a = k ⋅ p i - p o η ⋅ p o p a ⋅ T a T o where (p i -p o) is the differential pressure between the inlet and the outlet of the sorbent tube based on measurements by the first and second pressure transducers, F a is the equivalent flow rate at ambient pressure and temperature, p a is the ambient absolute pressure, T a is the ambient absolute temperature, p o is the absolute gas pressure at the sorbent tube outlet, T o is the absolute temperature at the vessel outlet, η is the viscosity of the gas flowing through the sorbent tube (20; 30; 100; 102) and k is the permeability factor of said sorbent tube (20; 30; 100; 102).