the desired traces from the conjoint extractives from the raw extract has taken place at the end of the purifying operations in the case of all 20 samples all electrically operated or controlled devices are stopped by a preadjustable time switch t n t n together with the parts t mv1 t mv2 t l1 t l2 v l and f are combined in one central control unit 4 set time switch for solvent circulation to the desired value these are the residence time and the time interval for connecting up the next sample coil 7 connect sample coils to the purifying tubes in the oven and flush with solvent after detaching the sample coils from the multiple way valve feed samples into coils and reconnect change the receiving tubes 8 calculate the total working time and set stop relay t n accordingly if the test conditions are not changed the functions 1 to 6 can be centrally switched on and off by t n 10 at the end of these operations reduce the purified samples in the condensers to a given volume and inject an aliquot part into a suitable gas chromatographic identifying and analysing apparatus the continuous current of solvent also permits the desired substances to be determined directly after the purification of the sample in an on line detection system as illustrated in fig2 the vapors emerging from the purifying tube are condensed in a ptfe coil in the cooling bath k the condensate.