to compare the results for different transit times peaks 14 and 15 respectively represent the responses upon arrival of c1 and c7 the comparable shape of the peaks and their regularity show an excellent transport in a thv tube the c1 peaks in zones 16 of fig5 a and 5 b result from washing of the thv line with pure c1 the absence of c7 peaks in these zones shows that no c7 is adsorbed in the thv line a 100 m long polyethylene tube that is 10 mm in inside diameter and 12 mm in outside diameter is tested with the same means as those used for testing the thv tube and from an identical injected sample fig6 a corresponds to a flow rate of 93 ml min fig6 b to a flow rate of 50 ml min peaks 17 and 18 respectively correspond to c1 and c7 zones 19 represent washing with pure c1 signal 18 relative to toluene is much wider and trailing in the polyethylene tube this degradation becomes more marked as the flow rate decreases i e when the transit time increases in comparison with the thv tube the polyethylene tube is markedly less efficient for heavy hydrocarbon transport even though the adsorption of toluene does not seem to be irreducible it is clear that the displacement of toluene in a polyethylene tube causes disturbances furthermore the transit time variation has an effect on the quality of the.