JPH0619092Y2 - FID detector for gas chromatograph - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is based on a flame ionization detector (Flame Ionization D).
et ector; hereinafter simply referred to as FID detector), and a FID detector for a gas chromatograph capable of simplifying the structure and improving detection accuracy.

(Prior Art) This type of detector, which is often used in a gas chromatograph or the like, generally includes a nozzle communicating with a separation column and a collector located immediately above the nozzle, and applies a high voltage to one of them. A high electric field electron trap area is formed, while hydrogen is mixed with the carrier gas flowing out of the column, and air is supplied from below the nozzle to generate a hydrogen flame at the nozzle tip. The sample injected into the carrier gas is sent into it for ionization, the ion current is detected by the collector, and a signal proportional to the number of sample molecules flowing into the hydrogen flame within a unit time is obtained. .

In the above detector, as a means for forming a high electric field electron trapping region, a nozzle applying method of applying a high voltage to a nozzle and a collector applying method of applying a high voltage to a collector are conventionally used according to a high voltage applying method. Has been adopted.

(Problems to be solved by the invention) However, in the former case, as a result of requiring high insulation around the nozzle, the structure becomes complicated due to the need for a shield structure for adjacent members and a special flow passage design for hydrogen and air passages. In the latter case, since a high voltage is inserted between the collector and the electrometer amplifier, it is indispensable to increase the impedance between the detector housing and the amplifier as a means for preventing signal attenuation and noise mixing. In that case, many impedance elements are required, and there is a problem that the circuit becomes complicated.

An object of the present invention is to provide a FID detector for a gas chromatograph, which can solve such conventional problems and can simplify the structure and improve the detection accuracy.

(Means for Solving the Problems) Therefore, in the FID detector for gas chromatograph of the present invention, a high voltage is applied to the collector and the nozzle is grounded to the body to amplify the signal current. In a FID detector for a vehicle, a cable having a core wire connected to a collector and a shield is attached to a body, one end of the shield is insulated from the body, and a negative feedback type differential conducting to the core wire and the shield is provided. The input terminal of the dynamic amplifier is connected, a feedback resistor is connected between one of the input terminals that conducts to the core wire and the output terminal of the amplifier, and a collector is applied to the other input terminal that conducts to the shield. Connect a direct current power supply, ground one end of the power supply to the gas chromatograph housing, and do not need an impedance element between the amplifier and ground In addition to simplifying the structure and reducing wiring work, one end of the shield is insulated from the body, and the potential of the power supply is offset to the differential amplifier, preventing the mixing of noise from both the body and the ground side. However, it is characterized in that the detection accuracy is improved.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings.
In the figure, reference numeral 1 is a detector mounting base in electrical connection with a gas chromatograph housing 2 on which a FID detector 3 is erected.

The detector 3 comprises a tubular body 4 and a tubular collector case 5 connected to the upper end of the body 4, of which a concave combustion chamber 6 is opened at the upper end of the body 4. Nozzle 7 is accommodated at the bottom of 6 with the ejection port facing upward,
An air passage 8 is opened at the close position.

An air-fuel mixture chamber 9 communicating with the nozzle 7 is opened at the lower end of the body 4, a column 10 is connected to the lower portion of the chamber 9, and a hydrogen flow passage 11 is opened in the middle and high portion thereof.

The collector case 5 has a ventilation chamber 12 formed therein, which communicates with the combustion chamber 6, and a tubular collector 13 is vertically accommodated in the chamber 12. Above collector 13
Has its lower end spaced apart from the nozzle 7 and is insulated from the adjacent body 4 and collector case 5 by appropriate means.

Further, a tubular cable holder 14 communicating with the ventilation chamber 12 is projectingly provided on the upper part of the collector case 5, one end of the cable 15 is inserted into the holder 14, and the core wire 16 of the cable 15 is at the upper end of the collector 13. It is connected to the.

A lead wire 17 is connected to the other end of the core wire 16, and a shield 18 incorporated in the cable 15 has one end insulated from the cable holder 14 and the other end connected to a lead wire 19. These lead wires 17, 1
An electrometer amplifier 20 composed of a negative feedback type differential amplifier is connected to 9.

A power source 21 for forming a high electric field is connected in parallel to the lead wire 19, and one end thereof is grounded to the housing 2. An isolation amplifier 22, which is a differential amplifier, is connected to the output terminal of the amplifier 20 and can output a voltage proportional to the difference voltage between the power supply 21 and the output of the amplifier 20. In the figure, 23 is a feedback resistance voltage conversion resistor of the amplifier 20, and 24 is an exhaust hole opened at the upper end of the collector case 5.

FIG. 2 shows a second embodiment of the present invention, and the same reference numerals are used for the components corresponding to those of the above-mentioned embodiment.

That is, in this embodiment, both ends of the shield 18 are grounded to the housing 2 and the cable holder 14, and the collector 1
It is characterized in that the electrical connection between the cable 3 and the cable 3 can be made by a general-purpose connector.

(Operation) In the FID detector configured as described above, since the high voltage power source 21 is applied to the collector 13 and one end of the power source 21 is grounded to the gas chromatograph housing 2, the resistance of the power source 21 is a high impedance element. Functioning in the same manner as the above, and does not require many impedance elements as in the conventional collector application method.

In addition, since the nozzle 7 is grounded to the gas chromatograph housing 2 via the body 4, the insulating structure around the nozzle 6 is not required, and a special height around the nozzle 6 as in the conventional nozzle applying method is eliminated. No insulation structure is required.

Therefore, the structure around the nozzle 6 is correspondingly simplified,
Further, since no special flow path structure for hydrogen, air, carrier gas, etc. introduced to the body 4 is required, the structure around the nozzle 6 is also simple in this respect, and its manufacture and assembly are easy.

When actually performing the component analysis of the sample using such an FID detector 3, the sample is injected into a carrier gas whose pressure is adjusted to a predetermined pressure, and this is sent into the column 10 to form a stationary phase or a gas phase. It is distributed at a fixed ratio and moved from the outlet of the column 10 to the FID detector 3.

The carrier gas introduced to the detector 3 is mixed in the air-fuel mixture chamber 9
At the same time, it is mixed with hydrogen and ejected from the nozzle 7 together with the sample, while air is supplied from the bottom of the combustion chamber 6 and these are ignited at the tip of the nozzle 7 to generate a hydrogen flame.

When the sample is sent into the hydrogen flame generated in this way,
Hydrocarbons and the like in the sample generate ions by the chemical ionization reaction, which move between both electrodes of the nozzle 7 and the collector 13. A high electric field is formed between the nozzle 7 and the collector 13, and an ion current having a value proportional to the number of ions flows between these electrodes.

The ion current is detected via the collector 13, and this is input to the electrometer amplifier 20 via the core wire 16 of the cable 15 and amplified to a predetermined value by the amplifier 20. In this case, the lead wires 17 and 19 which are the input terminals of the amplifier 20 are kept at the same potential, and the core wire 16 and the shield 18 of the cable 15 which are electrically connected to them are also kept at the same potential. The leakage current, that is, the attenuation of the input signal and the mixing of noise are prevented. Moreover, since one end of the shield 18 on the cable holder 14 side is insulated or opened, the prevention of mixing of noise is enhanced.

Moreover, the power source 21 is connected between the electrometer amplifier 20 and the gas chromatograph housing 2, and the power source 21
The electric potential of becomes the offset voltage of the amplifier 20 and regulates the noise level that enters from the gas chromatograph housing 2 side, and prevents the mixing of noise from the housing 2 side.

Further, since the resistance component of the power source 21 acts in the same manner as a high impedance element, there is no need for high impedance as in the conventional collector application method, and the cable 15
Even if the length is long, there is no concern about the attenuation of the input signal or the mixing of noise and it does not affect the detection accuracy, so that the wiring between the FID detector 3 and the amplifier 20 can be provided with flexibility and can be used under various usage conditions. Thus, the signal amplified by the amplifier 20 is input to the isolation amplifier 22, and the amplifier 22 outputs only the signal of the difference between the two inputs, that is, the signal superimposed on the input, which is output by an electrometer (not shown). ) Is entered. Therefore, a highly accurate chromatogram based on the above signal is drawn on the recorder (not shown).

(Effect of the Invention) As described above, in the FID detector for gas chromatograph of the present invention, the cable having the core wire connected to the collector and the shield is attached to the body, and one end of the shield is insulated from the body. It is possible to prevent mixing of noise from the body.

Further, the present invention connects an input terminal of a negative feedback type differential amplifier which is electrically connected to a core wire and a shield, and a feedback resistor is provided between one input terminal which is conductive to the core wire and an output terminal of the amplifier. , And a DC power supply for applying a collector to the other input terminal that is electrically connected to the shield is connected, and one end of the power supply is grounded to the gas chromatograph housing, so that the resistance of the power supply functions as an impedance element. Unlike the collector application method, many impedance elements are not required, the structure is simplified, and the wiring work can be reduced.

Moreover, since the power supply voltage functions as the offset voltage of the differential amplifier and the noise level is regulated by the offset voltage, it is possible to prevent noise from entering from the ground side and improve the detection accuracy in combination with the above. You can

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention, and FIG. 2 is an explanatory view showing another embodiment of the present invention. 3 ... FID detector, 7 ... nozzle 13 ... collector 20 ... electrometer amplifier 21 ... power supply

Claims (1)

[Scope of utility model registration request] 1. A high voltage is applied to the collector, and
In a FID detector for gas chromatograph in which a nozzle is grounded to a body to amplify a signal current, a cable having a core wire connected to a collector and a shield is attached to the body, and one end of the shield is connected to the body. The input terminal of the negative feedback differential amplifier that is electrically insulated from the core wire and the shield is connected, and feedback is provided between one of the input terminals that is conductive to the core wire and the output terminal of the amplifier. A FID detector for a gas chromatograph, characterized in that a DC power supply for applying a collector is connected to the other input terminal which is connected to a resistor and is electrically connected to a shield, and one end of the power supply is grounded to a gas chromatograph casing.