Direct temperature-controlled trapping system and its use for the gas chromatographic determination of organic vapor released from human skin

For controlling of trap temperature, the relationship between electric resistance of the trap tube and temperature is used. As the electric resistance of the trap tube (20 cm long stainless steel tubing) was very small, such as ca. 0.040 ohm for -70 degrees C and ca. 0.064 ohm for +90 degrees C, it was estimated by using the value of voltage output at both ends of the trap tube when a direct current (5 A) was applied for 6.5 ms at every 100 ms on the trap. By using this temperature measurement, a cycle of trapping is shortened, especially at the process of desorption, because it is possible to set a large increasing rate of temperature, such as 20 degrees C/s. The present trapping system has faster temperature response compared to that with a thermocouple. This system was applied for the study of the releasing of ethanol and water vapors from the human finger, which was treated as follows: dipping in 10% ethanol aqueous solution for 1 min, followed by washing with water and then drying in the air. In this case, a cycle of trapping took 53 s, and the period of total analysis was only 3 min. The present system is an efficient tool for the study of the exhalation of organic vapors from human skin.