PROBLEM TO BE SOLVED: To set an optimal inlet pressure in a gas chromatographic system. SOLUTION: A method and a system control the column head pressure in the gas chromatographic system by a pressure which is lower than the ambient pressure. The inlet of the GC system is provided with a valve for regulating the inlet pressure, and a pressure sensor for measuring the inlet pressure and outputting a signal indicating the measured inlet pressure. The GC system has an inlet pressure setting value for setting the inlet pressure to a negative pressure setting value, indicating a pressure lower than the ambient pressure; and the valve is driven by the negative pressure set value, and the inlet pressure changes until the measured inlet pressure becomes equal to the negative pressure set value. COPYRIGHT: (C)2005,JPO&NCIPI
