Since liquid water changes into the vapor phase once it is introduced into an FID system, the flowrate of the HPLC eluent introduced into the FID system was limited. Actually, the FID system could not be ignited when about 10 ml min of water was introduced into it. Therefore, the capillary tube of 270 mm340 mm I.D. in size was used to control the flow-rate of the split HPLC eluent. Moreover, the restrictor of 50 mm30.1 mm I.D. in size had to be connected to the end of the HPLC system as a back-pressure regulator to maintain a stable flow of the split HPLC eluent introduced into the system, as shown in Fig. 1. Under these conditions, the back-pressure in the HPLC was 0.5 MPa and the flow-rate of the eluent introduced into the FID 1 system was almost 7 ml min