Method and device for controlling flow rate of carrier gas in chromatographic apparatus

A method for controlling carrier gas flow rate through a gas chromatographic apparatus with capillary column subjected to temperature variations, by controlling carrier gas feed pressure following computerized processing of equation (1') of carrier gas standard flow variation as a function of carrier gas pressure, of chromatographic column temperature, and of gas parameters, said equation (1') being ##EQU15## wherein F.sub.st is carrier gas flow rate in standard conditions, T.sub.st is 298 degree K, p.sub.st is 1 atm., P.sub.i is the inlet carrier gas pressure, p.sub.o is the outlet carrier gas pressure, d is the inner diameter of the capillary column, L is the length of the capillary column, .eta. is the carrier gas viscosity, and T is the absolute temperature of an oven housing the capillary column, said method comprising:

• preliminarily passing a carrier gas through the apparatus, detecting pressure values, temperature and flow under stabilized conditions;
• preliminarily calculating a constant K.sub.1 representing the structural parameters based on values detected and on application of said equation (1'), said constant K.sub.1 is ##EQU16## applying said constant K.sub.1 in said equation (1') for controlling carrier gas flow rate through calculation;
• and
• adjusting said carrier gas feed pressure while said gas chromatographic apparatus is being utilized.

A device for controlling carrier gas flow rate in a gas chromatographic apparatus, said device comprising:

• an oven housing a gas chromatographic capillary column, a sample injector upstream of the column and a detector downstream of the column, a feeding line of carrier gas to the injector, said device comprises means for detecting the feeding pressure of the carrier gas, means for detecting capillary column temperature in the oven, means for introducing data relative to carrier gas to desired flow rate, at least one control valve for the carrier gas and means for storing and processing data so as to control said valve on the basis of data stored and detected, in order to obtain feeding pressure of the carrier gas so as to produce--moment by moment and with reference to a carrier gas flow rate variation equation as a function of inlet pressure, of column temperature and of system structural parameters, said equation is ##EQU20## wherein F.sub.o.sup.T is the volumetric flow rate, p.sub.i is inlet pressure, p.sub.o is outlet pressure, L is the length of the capillary column, .eta. is viscosity of the gas, and d is inner diameter of the capillary tube
• the desire flow rate of the same carrier gas through the gas chromatographic capillary column, characterized in that there are provided means for detecting the carrier gas flow rate in a stabilized condition of its passage through the gas chromatographic apparatus and means for sending the data detected of carrier gas flow rate and pressure, and of column temperature to the processing means, so as to calculate and store a constant factor K.sub.1 representing the structural data of the capillary column through which the carrier gas passes, wherein ##EQU21##

A method for controlling carrier gas flow range through a gas chromatographic apparatus with capillary column subjected to temperature variations, with the purpose of verifying the existence of pneumatic leakages in system, characterized by computerized processing of equation of carrier gas flow variation as a function of inlet pressure, of column temperature and system structural parameters through:

• preliminary determination at least of system structural parameters by detecting pressure, temperature and flow rate values in stabilized conditions of carrier passage through apparatus and by calculating a constant representing said parameters on the basis of values detected and in application of mentioned equation;
• storing the mentioned constant;
• repeating the preliminary determination of system parameters in a stabilized condition other than the previous one at least for the column temperature;
• recalculating the mentioned constant and confronting results of the two calculations.