JPH0219738Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field This invention relates to a gas chromatograph that automatically maintains the flow rate of carrier gas at a set flow rate value.

(b) Prior Art In analysis using a gas chromatograph, it is necessary to maintain the flow rate of the carrier gas at a predetermined value. The optimal carrier gas flow rate depends on the inner diameter of the column; generally, for a 1/4 inch inner diameter,
50~70ml/min, 25~30 for 1/8 inch
It is about ml/min.

However, these values are only a guideline;
In practice, the relationship between the separation of liquids with close boiling points, such as benzene and carbon tetrachloride, and the gas flow rate must be measured to determine the optimum flow rate for each column. In order to keep the carrier gas flow rate constant once set, it is generally only necessary to keep the gas pressure constant, so in most cases, the pressure reducing valve of the high-pressure cylinder of the gas used as the carrier gas or a pressure reducing valve designed for this purpose is used. Precise needle valve adjustment is sufficient.

However, in temperature programmed analysis, even if the gas pressure at the inlet is kept constant, the temperature of the column changes from moment to moment, and as the column temperature rises, the gas expands and its viscous resistance increases, making it difficult for the carrier gas to flow through the column. The outlet flow rate decreases. As a result, the sensitivity of the gas chromatograph detector changes, making quantitative analysis difficult. On the other hand, if a mass control valve is used, once the outlet flow rate is set to a predetermined flow rate, the inlet pressure is adjusted so that the outlet flow rate remains the same even if the column resistance changes. Since it has the characteristic of automatically changing, the inconveniences that occur when using a constant pressure valve are solved. As mentioned above, when maintaining the optimum carrier gas flow rate for each column,
Even when adopting the mass control method, which is a better control method for the flow rate of carrier gas when performing high-precision analysis in temperature-programmed analysis, in any case, the carrier gas must be used at a minute flow rate of about 100 ml/min at most. must be measured accurately and reproducibly with a flow meter.

Conventionally, rotameters and soap film flowmeters have been used as flowmeters to measure the carrier gas flow rate. The former has drawbacks such as not having very high accuracy, often causing problems such as the rotor hitting the pipe wall, and requiring different scales depending on the type of carrier gas. The latter creates a thin soap liquid film in a glass tube with graduated volume,
This glass tube is connected to the gas chromatograph with a rubber tube at the outlet, and the flow of carrier gas pushes up the soap solution film, causing the scale of the glass tube to rise. In this way, the flow rate (ml/min) is calculated by reading the time required for a certain volume of gas flow or the amount of movement of the soap liquid film in a certain period of time (15 to 20 seconds), and it is possible to calculate the flow rate (ml/min) relatively accurately. The flow rate of the carrier gas can be measured, but when a hydrogen flame ionization detector is used as a gas chromatograph detector, the carrier gas and hydrogen gas are sent through separate pipes and mixed at a certain ratio in the converging pipe. Therefore, it is difficult to perform measurements in the middle of the pipe, and it is also difficult to use soap liquid film flowmeters. Further, in both cases, it is difficult to extract the detection results as electrical signals, and it is impossible to construct a gas chromatograph that automatically maintains the flow rate of the carrier gas at a set flow rate value.

(c) Problems that the invention aims to solve This invention solves the problem that in conventional gas chromatographs, as mentioned above, when the column temperature rises, the gas expands and its viscous resistance increases, making it difficult for the carrier gas to flow. The sensitivity of the instrument changes,
Because it is not possible to accurately measure the carrier gas flow rate in the middle of the carrier gas supply pipeline, and because it is difficult to extract the detection results of the flowmeter as an electrical signal, the flow rate is automatically adjusted to match the optimal flow rate setting. The object of the present invention is to provide a gas chromatograph that eliminates the problem of uncontrollability, enables accurate and highly reproducible measurement even with a minute flow rate of carrier gas, and that allows quantitative analysis to be performed with high precision.

(d) Means for solving the problem The gas chromatograph according to this invention uses a heat pulse generator installed upstream of the carrier gas pipe to apply heat in a pulsed manner to the carrier gas via a filament heater inserted into the pipe. a generator, a temperature sensing element inserted further upstream of a carrier gas pipe into which the filament heater is inserted, and a temperature sensing element inserted downstream of the pipe at a constant interval with respect to the filament heater; a temperature detection device installed to detect temperature unevenness of the carrier gas given by the heat pulse generation device by a differential amplification signal with a temperature sensing element of the same type; the heat pulse generation device and the temperature detection device; The temperature unevenness mark attached to the carrier gas by the heat pulse from the heat pulse generating device moves through the pipe, and the travel time detected by the temperature detecting device is determined by the signals from both devices. A flow rate measuring device comprising a calculation device that measures the arrival time difference, calculates a moving average velocity of the carrier gas from this measured value, and further converts it into a flow rate of the carrier gas, and a flow rate measuring device that is coupled to the calculation device in a feedback manner. , and a flow rate regulator interposed in the carrier gas line.

(E) Function The gas chromatograph according to this invention controls the flow rate regulator so as to match the optimum flow rate value set by the flow rate measuring device consisting of the above-mentioned thermal pulse generator, temperature detecting device, and arithmetic unit. suppresses changes in the sensitivity of the tograph detector.

(F) Embodiment FIG. 1 is an explanatory diagram showing the basic configuration of a flow rate measuring device for a gas chromatograph according to this invention. In the figure, 1 is a carrier gas pipe, 2 is a filament heater made of platinum wire, for example, installed in the center of the upstream pipe, and 3 is a temperature sensing element, which is installed in the center of the downstream pipe, and can be used, for example, as a resistance thermometer element. This may be a platinum wire, or a thermocouple or thermistor element. In the figure, a few elements are shown in the flow direction of the conduit, but in reality, these elements are of extremely small heat capacity and are set at a constant interval L in the direction perpendicular to the flow. 2 by heat pulse generator
A heat pulse is applied to the filament heater, and the applied heat marks the carrier gas as temperature irregularities. A mark of temperature unevenness attached to this gas moves with the flow of the carrier gas, is caught by the temperature sensing element 3 installed downstream, and detected by the detection device. In this case, the temperature unevenness imparted to the carrier gas causes thermal diffusion to the carrier gas before and after it and to the pipe wall through which it passes, which reduces the signal transmitted to the detection device via the temperature sensing element. Therefore, in order to stabilize the baseline of the signal, a temperature sensing element 8 of the same type as the temperature sensing element 3 installed at the detection end was installed upstream of the carrier gas pipe 1 where the filament heater 2 for generating heat pulses was installed. This is used as a standard side and works differentially, and the detection device cancels noise and amplifies the signal.

The calculation device is connected to both the heat pulse generator and the detection device, and measures the time it takes for the temperature unevenness mark to move in the distance L between the filament heater 2 and the temperature sensing element 3, and at the same time calculates the moving average speed. is calculated and converted into a flow rate, and the flow rate is displayed on the display device in units of ml/min.

FIG. 2 schematically shows the change over time in the thermal pulse marked on the carrier gas by the filament heater 2, that is, the temperature unevenness mark marked on the carrier gas. A is a heat pulse at the instantaneous heat input point; B is a heat pulse in which the rectangular heat pulse becomes mountain-like as time passes as the carrier gas flows, due to heat conduction to the front and rear carrier gas and the pipe wall surface; C shows a heat pulse at the detection end where the peak becomes lower and the base becomes wider from side to side. Arrows indicate the direction of flow. In this case, if the mixing and diffusion of the carrier gas in the flow path 1 is small and the temperature unevenness created by the filament 2 is preserved before reaching the temperature sensing element 3, then there is a delay when the cross-correlation function reaches its maximum. The time (τmax) indicates the arrival time of the carrier gas. The distance between the heat input point and the detection point is L, and when this is fixed, τmax=f()
can be found from τmax.
Here is the average flow velocity, and τmax is the time when the temperature change at the detection end when heat is input in an impulse manner, that is, the impulse response reaches its maximum.

FIG. 3 is a graph showing the relationship between τmax and τmax. Since L is a short distance, the flow rate of pipe 1 consisting of a tube with a constant inner diameter is the average flow velocity ()
It is determined by the product of the flow area of the pipe and the flow area of the pipe. This means that the peak (curvature point) shown in Figure 2C is detected by an electronic circuit, the time (τmax) is determined, and the average flow velocity () is calculated from the time (τmax) and the set distance L. The flow rate is calculated from ( ) using a calculation device, and the flow rate is displayed in units of (ml/min) on a display device based on a signal from the calculation device.

FIG. 4 is a block diagram of the entire gas chromatograph apparatus which is an embodiment of this invention. In this figure, the heat pulse generating device, the detecting device, and the arithmetic device shown in FIG. 1 are collectively shown as a flow rate detecting section. 4 is a pressure regulating valve, 5 is a sample injection chamber, and 6 is a column. In this device, a flow rate measuring device is provided in front of the column inlet. If it is installed after the column outlet, the sample injected into the sample injection chamber 5 using a syringe will directly pass through the flow rate measuring device, contaminating elements such as the filament heater 2 and temperature sensing element 3, and measuring the flow rate. This is because the value becomes inaccurate. When a flow rate measuring device is provided in front of the column, it is necessary to control the pressure of the flow rate measuring device so that it is always constant, or to measure and correct the pressure. If the pressure and temperature of the flow measuring device are constant, the relationship between the travel time (τmax) of the heat pulse and the average flow velocity () shown in FIG. 3 is always constant regardless of the type of carrier gas. This is a feature of this device that is not found in other flowmeters other than soap film flowmeters.

In FIG. 4, the flow rate measuring device and the flow rate regulator are connected in a direct feedback manner, while the flow rate is displayed on a flow rate display device at any time. That is, if a set flow rate value is set in the flow rate measuring device, the flow rate regulator automatically controls the flow rate at all times, and the flow rate is maintained at the set flow rate value.

Figures 5-1 to 5-3 are block diagrams showing various examples of flow rate regulators for controlling the flow rate based on the output signal from the detection section in this device. 5th-
Figure 1 shows the case where the flow rate setting knob of the pressure regulator is driven by the signal from the flow rate measuring device, and Figure 5-2 shows the case where the variable resistor 7 that can increase or decrease the flow resistance of the pipe line is driven. is the case where the flow rate setting knob of the mass flow control valve (mass flow controller) is driven.

(g) Effects The gas chromatograph according to this invention is constructed and operates as described above, and therefore has the following effects.

Since the flow rate measuring device and the flow rate regulator are coupled in a feedback manner to each other, the flow rate of the carrier gas can be maintained at the set flow rate value. Even if the carrier gas becomes difficult to flow and the sensitivity of the detector changes in a conventional gas chromatograph, making quantitative analysis difficult, it is possible to improve the flow of the gas chromatograph by using, for example, a mass control valve in the operating section of the flow rate regulator. Quantitative analysis can be performed with high precision.

Further upstream of the carrier gas pipe where the filament heater for generating heat pulses is inserted, another temperature sensing element of the same type as the detection end of the temperature detection device is inserted, and this is used as the standard side to operate differentially to detect the temperature detection device. It is possible to amplify the signal by canceling the noise mixed in with the signal from the thermosensor transmitted to the thermosensor, and it is therefore possible to measure even minute carrier gas flow rates accurately and with excellent reproducibility. It becomes possible to maintain high analytical accuracy.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the basic configuration of a gas chromatograph flow measuring device which is an embodiment of this invention.
Figure 2 is a schematic explanatory diagram showing how the shape of the heat pulse marked on the carrier gas changes over time, and Figure 3 is the time it takes for the heat pulse to travel the distance between the carrier gas heat pulse input point and its detection point. FIG. 4 is a graph showing the relationship between the average flow velocity of the carrier gas and the average flow velocity of the carrier gas pipe, and FIG. 4 is a block diagram of the entire apparatus of the embodiment. Figures 5-1, 5-2 and 5-3 are block diagrams showing various examples of flow rate regulators for controlling the flow rate based on the output signal from the flow rate detection device in this device. 1...Pipe line, 2...Filament heater, 3,
8... Temperature sensing element, 4... Pressure regulating valve, 5... Sample injection chamber, 6... Column, 7... Variable flow path resistor.

Claims (1)

[Scope of utility model registration request] A heat pulse generator installed to apply heat to the carrier gas in a pulsed manner through a filament heater inserted into the carrier gas pipe upstream of the carrier gas pipe, and a heat pulse generator installed further upstream of the carrier gas pipe into which the filament heater is inserted. obtaining a differential amplification signal from the same type of temperature sensing element as the temperature sensing element inserted downstream of the conduit at a certain interval with respect to the filament heater;
As a result, a temperature detection device installed to detect temperature unevenness of the carrier gas given by the heat pulse generation device is connected to both the heat pulse generation device and the temperature detection device, and the heat pulse generation device Temperature unevenness marks placed on the carrier gas by heat pulses move through the pipe,
A calculation in which the travel time detected by the temperature detection device is measured based on the difference in arrival time of signals from both devices, a moving average velocity of the carrier gas is calculated from this measured value, and it is further converted into a flow rate of the carrier gas. 1. A gas chromatograph comprising: a flow rate measuring device comprising a flow rate measuring device; and a flow rate regulator connected in a feedback manner to the arithmetic unit and interposed in a carrier gas pipe.