JP4779807B2 - ICP emission spectrometer - Google Patents

Description

  The present invention relates to an ICP (Inductively Coupled Plasma) emission spectrometer.

  The plasma torch and its peripheral part in the ICP emission spectroscopic analyzer are configured as shown in FIG. FIG. 2 shows an example of a triple tube plasma torch. The plasma torch 20 has a concentric cylindrical triple tube structure, a sample gas tube 21 is disposed at the center thereof, a plasma gas tube 22 around it, and a coolant for flowing a cooling gas therearound. The gas pipe 23 surrounds the structure. A high frequency coil 31 is wound around the outside of the coolant gas pipe 23 for two to three turns.

  The sample gas pipe 21 is supplied with the atomized sample in a carrier gas (argon gas) flow. Specifically, in the nebulizer 42 into which the carrier gas is introduced, the sample liquid 41 is sucked up by the spraying principle, atomized, and blown into the spray chamber 43. The sample that has become an aerosol is carried into the sample gas pipe 21 by the carrier gas and ejected from the tip nozzle of the sample gas pipe 21.

  A relatively low-speed plasma gas (argon gas) ejected from the tip nozzle of the plasma gas tube 22 is ionized by the high-frequency electromagnetic field produced by the high-frequency coil 31, and a high-temperature plasma flame 32 is formed. Outside the plasma flame 32, coolant gas (argon gas) ejected from the tip nozzle of the coolant gas pipe 23 flows at a relatively high speed.

  The sample is put on a carrier gas and ejected from the tip nozzle of the sample gas tube 21, introduced into the central portion of the plasma flame 32, atomized and emitted. This emission spectrum is dispersed by a spectroscope (not shown), and qualitative and quantitative analysis of elements in the sample is performed.

  As described above, the ICP emission spectroscopic analyzer requires three systems of argon gas, carrier gas, plasma gas, and coolant gas, to control the flow rate in order to form plasma. The carrier gas carrying the analysis sample in the three systems needs to be controlled in flow rate with high accuracy, particularly with high stability. The above flow rate is not a volume flow rate but a mass flow rate. In the conventional ICP emission spectroscopic analyzer, the flow rate of the carrier gas is controlled by a mass flow controller or a mass flow meter + electromagnetic proportional valve that measures the flow rate using the heat conduction of the gas. In this case, precise control of the flow rate can be easily realized and the flow rate control can be performed without being affected by fluctuations in the room temperature, but it is difficult to be expensive.

On the other hand, in the gas chromatograph analyzer, there is an apparatus for controlling the flow rate as follows. A pressure sensor for measuring the primary pressure, a resistance tube, a differential pressure sensor for measuring the differential pressure at both ends of the resistance tube, and a control valve are sequentially connected to the carrier gas supply flow path. The carrier gas flow rate is controlled without using a pressure regulator by controlling the control valve by the signal from the differential pressure sensor to control the carrier gas flow rate. (For example, see Patent Document 1)
In this case, the flow rate of the gas controls the flow volume to be constant, and the mass flow rate of the carrier gas fluctuates due to variations in the gas temperature and the temperature characteristics of the pressure sensor and the differential pressure sensor. Since the volume of the flowing gas is constant, the mass flow rate of the gas is inversely proportional to the absolute temperature of the gas. When the gas temperature changes by 1 ° C., the mass flow rate changes by approximately 0.3%. Further, the temperature coefficient of sensitivity of the pressure sensor and the differential pressure sensor is about 0.1% / ° C.
Japanese Patent Laid-Open No. 10-300737

  In an ICP emission spectroscopic analyzer, the flow rates of carrier gas, plasma gas, and coolant gas for forming plasma are affected by low-temperature and room temperature without using an expensive mass flow controller or mass flow meter + electromagnetic proportional valve. Control with no method.

In order to solve the above-mentioned problems, the present invention includes a carrier gas supply unit, a gas supply channel for supplying a carrier gas to a plasma torch, and a gas pressure of the carrier gas supplied to the gas supply channel. A pressure sensor to be detected, a differential pressure sensor that measures a differential pressure across the resistance pipe connected to the gas supply channel, and the pressure sensor and the differential pressure sensor of the gas supply channel are to be measured ICP emission spectroscopy comprising a thermostatic chamber storing a flow path, a control valve for controlling the flow rate of the carrier gas, and a control device for controlling the control valve based on detection values of the pressure sensor and the differential pressure sensor In the analyzer, an ICP characterized in that a part of the gas supply flow path in the thermostatic chamber is a buffer pipe that stabilizes the temperature of a gas to be measured by the pressure sensor and the differential pressure sensor. An optical spectrometer.

  According to the present invention, in an ICP emission spectroscopic analyzer, the flow rates of carrier gas, plasma gas, and coolant gas for forming plasma are controlled with high accuracy and stability in an inexpensive manner that is not affected by room temperature. be able to. Therefore, it can be expected to provide an inexpensive apparatus, and even if the calibration frequency is reduced, high-accuracy quantitative analysis can be performed, so that the analysis efficiency can be expected to be improved.

  The gas temperature stabilizing buffer tube disposed in the optical thermostat is made of a resin having low thermal conductivity in the vicinity of the entrance to the optical thermostatic bath, and is made of metal having high thermal conductivity behind it. It is held by a small resin member.

  The pressure sensor disposed in the optical thermostat is held by a resin member having a small thermal conductivity.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing the flow rate control of argon gas in the ICP emission spectroscopic analyzer of the present invention. FIG. 2 is a diagram showing a plasma torch and its peripheral part in a general ICP emission spectroscopic analyzer.

  Reference numeral 1 denotes a buffer tube, which is disposed in an optical thermostat 13 whose temperature is controlled to 38 ° C., for example. Argon gas supplied from an argon gas cylinder or the like is introduced, and the outlet temperature is set to 38 ° C.−0.1. It has a function of stabilizing to about ° C. Specifically, the buffer tube 1 is composed of a polyolefin tube having an inner diameter of 4 mm, an outer diameter of 6 mm, and a length of 5 m. Is introduced, it has the ability to stabilize the temperature at its outlet to about 38 ° C-0.1 ° C.

  The pressure sensor 2 is disposed in the optical thermostat 13 and is constituted by a semiconductor pressure sensor or the like, and transmits the primary pressure and gas temperature information of the argon gas to the control device 12 as a resistance value.

  The differential pressure sensor 3 is disposed in the optical thermostatic chamber 13 and is composed of a semiconductor pressure sensor. The differential pressure sensor 3 measures the differential pressure at both ends of the resistance tube 6 connected to the carrier gas flow path and transmits it to the control device 12. . The resistance tube 6 is disposed in the optical thermostat 13. The differential pressure sensor 4 is disposed in the optical thermostatic chamber 13 and is composed of a semiconductor pressure sensor. The differential pressure sensor 4 measures the differential pressure at both ends of the resistance tube 7 connected to the plasma gas flow path and transmits it to the control device 12. . The resistance tube 7 is disposed in an optical thermostat 13. The differential pressure sensor 5 is disposed in the optical thermostat 13 and is constituted by a semiconductor pressure sensor. The differential pressure sensor 5 measures the differential pressure at both ends of the resistance tube 8 connected to the coolant gas flow path and transmits it to the control device 12. . The resistance tube 8 is disposed in the optical thermostat 13.

  The control valve 9 is connected to the flow path of the carrier gas, and controls the flow rate of the carrier gas by a control signal from the control device 12. The control valve 10 is connected to the flow path of the plasma gas, and controls the flow rate of the plasma gas by a control signal from the control device 12. The control valve 11 is connected to the coolant gas flow path, and controls the flow rate of the coolant gas by a control signal of the control device 12.

  The carrier gas shown in FIG. 1 is used as the carrier gas shown in FIG. 2 and is introduced into the nebulizer 42. The plasma gas shown in FIG. 1 is used as the plasma gas shown in FIG. 2 and is introduced into the plasma gas pipe 22. The coolant gas shown in FIG. 1 is used as the coolant gas shown in FIG. 2 and introduced into the coolant gas pipe 23.

Since the present invention has the above configuration, the temperature of the argon gas downstream from the pressure sensor 2 and the primary pressure and the differential pressure transmitted to the control device 12 are not affected by fluctuations in the ambient temperature (room temperature) and are accurate. A stable flow rate (mass flow rate) can be controlled.
Hereinafter, the flow rate control will be described using the carrier gas as an example. The following equation (1) exists among the flow rate of the carrier gas, the primary pressure measured by the pressure sensor 2, and the differential pressure measured by the differential pressure sensor 3. (For example, see Patent Document 1)

Q = K × P1 × ΔP (1)
Q: carrier gas flow rate, K: coefficient determined by resistance tube 6, P1: primary pressure measured by pressure sensor 2, ΔP: differential pressure measured by differential pressure sensor 3, flow rate desired by analyst ( = QSET) is input to the controller 12. The control device 12 stores the formula (1) therein, and always inputs the primary pressure P1 measured by the pressure sensor 2 into the formula (1). The control device 12 obtains the differential pressure (= ΔPSET) corresponding to the flow rate desired by the analyst (= QSET) from the equation (1), and then the differential pressure measured by the differential pressure sensor 3 becomes ΔPSET. A control signal is sent to the control valve 9.
The control device 12 receives the minute temperature change information of the argon gas transmitted from the pressure sensor 2 as a change in resistance value, corrects the flow rate, and performs flow rate control with higher accuracy.
The flow rates of plasma gas and coolant gas are similarly controlled.

  The carrier gas, plasma gas, and coolant gas whose flow rates are controlled are respectively introduced into the nebulizer 42 and the plasma torch 20 shown in FIG. The sample is put on a carrier gas and ejected from the tip nozzle of the sample gas tube 21, introduced into the central portion of the plasma flame 32, atomized and emitted. This emission spectrum is dispersed by a spectroscope (not shown), and qualitative and quantitative analysis of elements in the sample is performed.

In the embodiment shown in FIG. 1, resistance tubes 6, 7, and 8 and differential pressure sensors 3, 4, and 5 are disposed, but these are removed and the outlet of the buffer tube 1 and the control valves 9, 10, The present invention can be applied even if the 11 entrances are directly connected.
Further, in the embodiment shown in FIG. 1, the temperature information of the argon gas is transmitted from the pressure sensor 2 to the control device 12 as a resistance value, but the present invention can be applied even if this is deleted. It is not limited to the example shown.
In the illustrated example, the buffer tube 1 is made of a polyolefin tube. However, the buffer tube 1 is made of a resin having a small heat conductivity in the vicinity of the entrance to the optical thermostatic chamber 13, and is made of a metal having a large heat conductivity in the rear thereof. The present invention includes these modifications.

  The present invention relates to a flow control of argon gas in an ICP emission spectroscopic analyzer.

It is a figure which shows the flow control of the argon gas in the ICP emission-spectral-analysis apparatus of this invention. It is a figure which shows the plasma torch and its peripheral part in a general ICP emission-spectral-analysis apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Buffer pipe 2 Pressure sensor 3 Differential pressure sensor 4 Differential pressure sensor 5 Differential pressure sensor 6 Resistance pipe 7 Resistance pipe 8 Resistance pipe 9 Control valve 10 Control valve 11 Control valve 12 Control apparatus 13 Optical system thermostat 20 Plasma torch 21 Sample gas Tube 22 Plasma gas tube 23 Coolant gas tube 31 High-frequency coil 32 Plasma flame 41 Sample liquid 42 Nebulizer 43 Spray chamber

Claims (1)

A carrier gas supply unit; a gas supply channel for supplying the carrier gas to the plasma torch; a pressure sensor for detecting a gas pressure of the carrier gas supplied to the gas supply channel; and the gas supply channel. A differential pressure sensor for measuring a differential pressure across the resistance tube, a thermostatic chamber in which the pressure sensor and the differential pressure sensor among the gas supply channels are stored, and a flow rate of the carrier gas In the ICP emission spectroscopic analysis apparatus comprising: a control valve for controlling the control valve; and a control device for controlling the control valve based on detection values of the pressure sensor and the differential pressure sensor, the gas supply channel in the thermostat An ICP emission spectroscopic analysis apparatus characterized in that a part of the buffer is a buffer tube that stabilizes the temperature of a gas to be measured by the pressure sensor and the differential pressure sensor.

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