Patent ID: 8297107

Claim:
A system for regulating fluid flowing through a chromatographic column, comprising: a thermal desorption unit that supplies a carrier gas containing analytes to be measured, the thermal desorption unit including a removable sample vessel for obtaining a sample from an environment to be tested, a carrier gas inlet in fluid communication with the sample vessel via a solenoid valve, a sample station positioned in the flow path of a carrier gas for receiving the sample vessel, a heating device for heating the sample vessel in the sample station to thermally desorb the analytes therein a trap placed downstream of the sample vessel, and a second carrier gas inlet in fluid communication with the trap via a second valve; and a gas chromatograph in fluid communication with said thermal desorption unit, said gas chromatograph comprising a chromatographic column that receives the carrier gas containing the analytes supplied by said thermal desorption unit; and a temperature sensor connected to said thermal desorption unit that measures the temperature of said column and sends a signal to said thermal desorption unit indicating the measured temperature, said temperature sensor being a platinum resistor thermometer or a thermocouple; a transfer line assembly through which the carrier gas is communicated from the thermal desorption unit to said column; a signal cable by which said temperature sensor is connected to said thermal desorption unit, the signal cable being bound into the transfer line assembly; and a rotary valve, wherein the removable sample vessel, trap and transfer line assembly are selectively in communication with each other via the rotary valve, wherein said thermal desorption unit controls the pressure of the carrier gas supplied to said column based on the signal received from said sensor, wherein said thermal desorption unit adjusts the pressure of the carrier gas supplied to said column such that a substantially constant flow rate and a substantially constant velocity is maintained in said column, and wherein the pressure of the carrier gas supplied to the column is calculated in accordance with the equation P i = F a · T t · P a a · b · T a . ( a · T c T t + b ) + P o 2 where T t is the transfer line absolute temperature, T c is the column absolute temperature, T a is the standard ambient absolute temperature, P o is the gas pressure at the column outlet, P a is the standard ambient pressure, and a and b represent πd/256Lη for the transfer line and the column, respectively, where d is the diameter thereof, L is the length thereof, and η is the viscosity of the gas flowing therethrough.