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

• US 5,859,360 A
• Filed: 05/15/1996
• Issued: 01/12/1999
• Est. Priority Date: 09/16/1994
• Status: Expired due to Term

• Current Assignee: Fisons Instruments S.p.A. (Thermo Fisher Scientific Incorporated)
• Original Assignee: Fisons Instruments S.p.A. (Thermo Fisher Scientific Incorporated)
• Inventors: Colombo, Pieralbino, Munari, Fausto, Zilioli, Giacinto, Magni, Paolo, Trestianu, Sorin
• Primary Examiner(s): Houtteman, Scott W.
• Application Number:
  US08/646,308
• Time in Patent Office: 972 Days
• Field of Search: 73/19.05, 73/23.35, 73/23.36, 73/23.37, 73/23.38, 73/23.39, 73/23.4, 73/23.42
• US Class Current: 73/19.05
• CPC Class Codes: G01N 2030/025 Gas chromatography
• CPC Class Codes: G01N 2030/3084 ovens
• CPC Class Codes: G01N 2030/324 speed, flow rate
• CPC Class Codes: G01N 30/32 of pressure or speed G01N30/36 takes precedence
• CPC Class Codes: G01N 30/8658 Optimising operation parameters

Abstract

There is provided a method and apparatus for controlling the carrier gas flow through a gas chromatographic apparatus with capillary column subjected to variations in temperature, through control of feeding pressure achieved following computerized processing of the equation of the carrier flow rate as a function of inlet pressure, column temperature and system structural parameters, including preliminary determination of the system parameters through detection of pressure, temperature and flow rate values in stabilized conditions of carrier passage through apparatus and calculation of a constant representing said parameters on the basis of values detected and in application of the aforesaid equation; storage of aforesaid constant; utilization of constant in the mentioned equation for controlling carrier flow rate through calculation and control of its feeding pressure during utilization of the gas chromatographic apparatus.

Claims

1. A method for controlling carrier gas flow rate through a gas chromatographic apparatus with capillary column subjected to temperature variations, by controlling the carrier gas feed pressure following computerized processing of equation (1) of carrier gas flow variation as a function of carrier gas pressure, of chromatographic column temperature, of system structural parameters and of gas parameters, said equation (1) is ##EQU13## wherein F_o^T is carrier flow rate at, p_i is inlet carrier gas pressure, p_o is carrier gas outlet pressure, L is the length of the capillary column, η

is viscosity of the carrier gas, and d is inner diameter of the capillary tube, said method comprising;

preliminarily passing a carrier gas through the apparatus, detecting pressure values, temperature and flow under stabilized conditions;

preliminarily calculating a constant K₁ representing the system structural parameters based on the values detected and on said equation (1), said constant K₁ is ##EQU14## applying said constant K₁ in said equation (1) for controlling carrier gas flow rate through calculation; and

adjusting said carrier gas feed pressure thereby affecting the carrier gas flow rate while said gas chromatographic apparatus is being utilized.

2. The method according to claim 1, wherein a value of the term 1/η

of said equation (1) is preliminarily entered.

3. 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_st is carrier gas flow rate in standard conditions, T_st is 298 degree K, p_st is 1 atm., P_i is the inlet carrier gas pressure, p_o is the outlet carrier gas pressure, d is the inner diameter of the capillary column, L is the length of the capillary column, η

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 K₁ representing the structural parameters based on values detected and on application of said equation (1'"'"'), said constant K₁ is ##EQU16## applying said constant K₁ 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.

4. The method according to claim 3, wherein the carrier gas viscosity η

is obtained by empirical formula ##EQU17## wherein η

_st is the viscosity of the carrier gas in standard conditions, and T is the absolute temperature of said oven;

wherein said formula (1'"'"') becomes ##EQU18## wherein a constant term ##EQU19## is calculated based on values detected and on application of aforesaid equation (1"); and

wherein said constant K is applied 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.

5. 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_o^T is the volumetric flow rate, p_i is inlet pressure, p_o is outlet pressure, L is the length of the capillary column, η

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 K₁ representing the structural data of the capillary column through which the carrier gas passes, wherein ##EQU21##

6. 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.

7. A method for controlling the carrier gas flow rate 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 in that it comprises the calculation of carrier gas pressure for obtaining a prefixed flow rate value, and comparison between such prefixed carrier value and the value read by a flowmeter operating in the system.