CN102778523A - Method for measuring and controlling capillary column flow of gas chromatograph - Google Patents

Abstract

The invention discloses a method for measuring and controlling the capillary column flow of a gas chromatograph, characterized by using the column head pressure and outlet pressure of the capillary chromatographic column and the column dimension and column temperature of the capillary chromatographic column to measure the column flow of the capillary chromatographic column, and controlling the column flow of the capillary chromatographic column by controlling the column head pressure of the capillary chromatographic column. According to the method, the automatic control of the gas chromatograph capillary column flow and split ratio can be realized.

Description

A kind of measurement, control method of gas chromatograph capillary column flow

Technical field

The invention belongs to the analytical and testing instrument technical field, relate to the flow and the control technology of gas chromatograph capillary chromatographic column.

Background technology

Gas chromatographic column is one of core component of gas chromatograph, is divided into packing gas chromatography post and capillary gas chromatographic column.The capillary gas chromatographic column length range is 10～200 meters, and between 0.22 millimeter to 0.53 millimeter of the internal diameter magnitude range, the capillary column flow is looked the analytic target situation and selected in 0.5～lOml/min scope.The accurate measurement of gas chromatograph capillary column flow and control have material impact to the analysis of gas chromatograph.Because capillary column is in the chromatograph box of instrument, its inlet connects the instrument vaporizer, and outlet meets sensing chamber.And the temperature of vaporizer, detecting device, chromatograph box is the highest can be controlled in 450 (room temperature to 450 degree centigrade between adjustable), and these factors cause directly measuring the flow of capillary chromatographic column.Traditional measurement method is to inject by chromatographic column absorption dissolved gases at vaporizer, calculates the linear speed of gas through measuring this gas through the time of chromatographic column, and the internal diameter cross-sectional area that linear speed multiply by capillary column obtains the gas flow of capillary column.This method can not be measured in real time, more can not accomplish the automatic control of capillary column flow.The present invention provides a kind of flow measurement and control method of new gas chromatograph capillary chromatographic column, and is easy to and computing machine cooperates, and realizes the automatic measurement and the control of flow.

Summary of the invention

According to fluid mechanics principle, the rate of discharge of capillary chromatographic column is relevant with following factor: the resistance size of the inlet pressure of chromatographic column, the top hole pressure of chromatographic column, chromatographic column convection cell.And the resistance size depends on the kind (it is carrier gas that gas chromatograph is selected nitrogen) and the temperature of length, internal diameter and the gas of capillary chromatographic column.Derive concrete funtcional relationship easily according to the physics fluid mechanics principle:

$\mathrm{Fc}=K\·\frac{d^4}{L}\×\frac{{(p+p_0)}^2-{p_0}^2}{p_0}\×{10}^3$ ..............................................................①

Fc---column outlet flow (mi/min)

P---post is gone into article pressure (KPa)

p ₀---column outlet pressure (KPa)

L---column length (m)

D---column internal diameter (mm)

K---relevant coefficient with gas viscosity as far as nitrogen, depends on gas temperature.

Therefore, through measuring capillary column inlet pressure p, top hole pressure p ₀And capillary column oven temperature, degree (can confirm the K value), and import concrete capillary chromatography column dimension (inner diameter d and length L), can calculate Fc.

This method is through installing a pressure transducer in the capillary chromatographic column porch; One of (being generally atmospheric pressure) installation is used to measure atmospheric pressure transducer at the capillary outlet place; Capillary chromatographic column post oven temperature, of living in degree is recorded by temperature sensor, and all parameters are sent into computing machine and can real-time calculation display be gone out flow behind the post capillaceous.

This method is to definite method of K: because K is relevant with temperature, for certain gaseous species, temperature is the factor of unique K of decision.Room temperature to 450 degree scopes, whenever at a distance from 10 degree, is surveyed Fc (concrete grammar; The capillary chromatography column outlet pulled down from detecting device cause outside the chromatograph box, measure with digital flowmeter), 1. calculate K by formula; And the gained data are deposited in the computing machine, be used for actual use and calculate Fc.

1. can derive by formula:

$P=\sqrt{\frac{\mathrm{Fc}\&CenterDot;L\&CenterDot;p_0}{K\&CenterDot;{\mathrm{<figure-callout\; id="4"\; label="d"\; filenames="HSA00000499547600011.png,HSA00000499547600021.png"\; state="\{\{state\}\}">d</figure-callout>}}^4\&CenterDot;{10}^3}+{{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HSA00000499547600011.png,HSA00000499547600021.png"\; state="\{\{state\}\}">p</figure-callout>}}^2}_0}-p_0$ ..................................................................②

Therefore, through being that the flow of may command capillary column is to setting value Fc by 2. formula control P.

Description of drawings:

Below in conjunction with accompanying drawing and specific embodiment the present invention is further specified

Fig. 1 is a gas chromatograph capillary column carrier gas control flow chart

Fig. 2 is pressure and total flow metering circuit figure

Fig. 3 is pressure and flow control circuit figure

Among the figure, 1. total flow sensor; 2. total flow control valve; 3. chromatographic column inlet pressure transducer; 4. column cap pressure-controlled valve; 5. cold-trap;

6. detecting device; 7. vaporizer; 8. chromatograph box; 9. capillary chromatographic column; 10. barometric pressure sensor; 11. multi-way switch; 12.A/D converter; 13. computing machine; 14.D/A converter.

Embodiment:

Behind the cold-trap (5) of gas chromatograph vaporizer (7) shunting stream, through a stainless steel threeway chromatographic column inlet pressure transducer (3) is inserted, being connected on behind the cold-trap (5) is for preventing that sample gas from polluting inlet pressure transducer (3).Because about the general 0.4MPa of vaporizer (7) maximum pressure, can select the pressure transducer of 0.6Mpa range for use, this routine column inlet pressure force transducer (3) model is 4040PCIOOG5D.Barometric pressure sensor (10) can directly be welded on the instrument internal circuit board, and this routine model is MPX4100AP.Above pressure transducer analog passband signal is crossed multi-way switch (11), A/D converter (12) is sent in the computing machine (13).Have in the actual temperature chromatograph of gas chromatograph post case (8) and measure and deposit in the computing machine.In chromatographic operation interface, set up a column parameter button, be used to import the column internal diameter d and the column length L of capillary chromatographic column (9).1. (13) are by formula worked out a calculation procedure and can be measured the flow value that shows capillary column in real time in computing machine.

For the control of capillary column flow, 2. obtain capillary column inlet pressure P by formula, control P promptly controls the capillary column flow.Because gas chromatograph kapillary vaporizer (7) has part flow arrangement, in the shunting stream, install a column cap pressure-controlled valve (4) additional, control column head pressure P through the unlatching size of controlling column cap pressure-controlled valve (4) by the D/A converter (14) of computing machine.This opening of valves is big, and the capillary column inlet pressure just reduces, otherwise just increases.And the total flow that gets into vaporizer (7) is measured by total flow sensor (1), and by total flow control valve (2) control of serial connection with it.Also just controlled simultaneously bypass flow through control total flow and capillary column flow.Split ratio (bypass flow/capillary column flow) also just can be decided.Therefore,, can accomplish the split ratio that numeral is set capillary column flow and shunting fluidising chamber, accomplish the automatic control of capillary column flow and split ratio by this control mode.

Claims (2)

1. the flow measurement of a gas chromatograph capillary chromatographic column, control method is characterized in that: the gas flow of measuring and control capillary chromatographic column through column inlet pressure, column outlet pressure, temperature and the column parameter of capillary chromatographic column.

2. like claim 1 described gas chromatograph capillary chromatographic column flow measurement, control method, it is characterized in that obtaining gas viscosity, temperature correction curve, and then obtain the gas viscosity value through measuring temperature through the calibration of various temperature point.

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