JPH08219986A - Atomic absorption spectrophotometer - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent abnormal heating of tubes in a nuclear reactor. When the plasma detection unit 24 detects Ar plasma generated when the tube 10 is abnormally heated, the heating control unit 20 gives a command to the power supply 22 to cut off the heating current I, 22 cuts off the current I. As a result, the heating of the tube 10 is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an atomic absorption spectrophotometer for atomizing a sample by a flameless atomization method, and more particularly to improvement of an atomization furnace in this atomic absorption spectrophotometer.

[0002]

2. Description of the Related Art In order to perform analysis with an atomic absorption spectrophotometer, it is necessary to atomize a sample in a molecular state. As one of the atomization methods, there is a flameless atomization method in which a sample is heated by a small electric furnace to be atomized. In the flameless atomization method, a graphite atomization furnace in which a sample is injected into a graphite tube and a large current is passed through the tube to heat the graphite tube is mainly used. At this time,
Since the heating temperature of the tube is one of the important setting conditions for atomization, it is necessary to detect the temperature as accurately as possible and control it. As a method therefor, generally, the temperature of the tube is measured by detecting the light emitted from the graphite tube, and heating is performed while controlling the current flowing through the tube.

FIG. 2A is a basic configuration diagram showing a conventional temperature control part in a graphite atomization furnace, and FIG.
(B) is a schematic diagram which shows the cross section of the holder of an atomization furnace.
The sample to be analyzed is a holder 12 that holds the tube 10.
And, it is atomized by being injected into the tube 10 through the sample injection hole 14 penetrating the upper part of the tube 10 and being heated therein. In order to prevent oxidation (burnout) of the tube 10, the inside of the tube 10 and the holder 12 and the tube 10
An inert gas such as Ar gas or N2 gas is flown in the space between and. A photometric hole 16 is provided on the side surface of the holder 12, and the intensity of light emitted from the tube 10 through the photometric hole 16 is measured by an optical sensor 18. The output signal of the optical sensor 18 is supplied to the heating controller 20 that controls the heating current I supplied from the power supply 22 to the tube 10. The heating control unit 20 estimates the temperature of the tube 10 from the intensity of light, and sets the current value of the heating current I to the power supply 22 so that the tube 10 reaches a desired temperature.
The power supply 22 supplies the set heating current I to the tube 10. As mentioned above, in this nuclear reactor,
The light emitted from the tube 10 is fed back as temperature information, and the heating current I of the tube 10 is controlled so that a desired tube temperature can be obtained.

[0004]

However, in the graphite atomization furnace, the soot generated when the tube 10 is heated adheres to the photometric hole 16 to reduce the amount of light passing therethrough.
Smoke generated as a result of the sample injected from the sample injection hole 14 adhering to the outside of the tube 10 reduces the amount of light reaching the optical sensor 18. In such a case, the heating control unit 20 determines that the temperature of the tube 10 is low and supplies an excessive current. As a result, the tube may be abnormally heated and burned out in the worst case. This is not only a safety problem, but also a problem that the burned tube has to be replaced and extra work is required.

The present invention has been made to solve the above problems, and an object thereof is to prevent abnormal heating of a tube in an atomization furnace of an atomic absorption spectrophotometer. It is to provide an atomic absorption spectrophotometer with high safety and capable of performing efficient analysis work.

[0006]

The atomic absorption spectrophotometer according to the present invention comprises an atomization furnace for heating a sample by flowing an electric current through the tube while flowing an inert gas in and out of the tube in which the sample is injected. In the atomic absorption spectrophotometer having, a detection means for detecting the plasma generated from the inert gas, and a heating control means for interrupting or reducing the current flowing through the tube when the plasma is detected by the detection means, Prepare

[0007]

In the nuclear reactor of the atomic absorption spectrophotometer according to the present invention, the abnormal heating state of the tube is detected by detecting the plasma generated from the inert gas flowing inside and outside the tube. For example, Ar gas, which is usually used as an inert gas, is turned into plasma at a temperature of about 3000 to 3200 ° C., and thus the heating temperature of the tube is appropriate 300.
No plasma is detected below 0 ° C. Therefore, it is possible to know that the graphite tube is abnormally heated by detecting the generation of plasma.

Therefore, the heating control means in the atomic absorption spectrophotometer according to the present invention, when the plasma is detected by the plasma detection means, judges that the temperature of the tube is abnormally high, and flows into the tube. The heating of the tube is stopped immediately by interrupting or reducing the current.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a basic configuration diagram showing a portion related to temperature control in a graphite atomization furnace of an atomic absorption spectrophotometer according to an embodiment of the present invention, and FIG. 1B is a schematic diagram showing a cross section of a holder. It is a figure. In the present embodiment, the plasma detection unit 24 is provided in the vicinity of the sample injection hole 14 above the holder 12.
Is provided and the detection signal is fed back to the heating control unit 20. Further, a notification unit 26 for giving a warning to the operator by a lamp or the like is provided, and a detection signal from the plasma detection unit 24 is supplied to this.

When the tube 10 is abnormally heated, the Ar gas in the tube 10 and the holder 12 becomes a plasma state and flows out of the holder 12 through the sample injection hole 14. When the plasma detector 24 detects this plasma, it supplies a detection signal to the heating controller 20. The heating control unit 20 receives the plasma detection signal and gives a command to the power supply 22 to cut off the heating current.
Shut off. As a result, the heating of the tube 10 is stopped.

When the tube 10 is thus abnormally heated, it is highly likely that the tube and the holder are contaminated with soot and the adhered sample, and it is necessary to clean them. Therefore, in this embodiment, the notification unit 26
Receives a plasma detection signal and turns on a lamp or emits a warning sound in order to call the operator's attention. By providing the notification unit 26, the operator can accurately know the opportunity of maintenance work such as cleaning, and therefore, the effect of improving the efficiency of analysis work can also be obtained.

In the present embodiment, the plasma detector 24
Is composed of two electrodes 242 and a dielectric constant monitor 244 which are arranged to face each other. A pair of electrodes 242
Are arranged at positions sandwiching the plasma flowing out from the sample injection hole 14, and the dielectric constant between the electrodes is measured. When plasma is present between the electrodes, the dielectric constant is higher than when it is absent. Therefore, the permittivity monitoring unit 244 always keeps the electrode 2
The dielectric constant between 42 is monitored, and when it exceeds a preset threshold value, it is determined that plasma is generated, and a detection signal is output.

As another configuration example of the plasma detector 24, a constant voltage may be applied between the two electrodes and the current flowing between the electrodes may be measured. That is, the conductivity between the electrodes is measured and monitored, and when the conductivity exceeds a preset threshold value, it is determined that plasma is generated and a detection signal is output.

Although other plasma detection methods may be used, the atomic absorption spectrophotometer according to the present invention may detect whether or not plasma is generated. Therefore, sufficient effects can be obtained by the detection with the relatively simple configuration as described above.

In the above embodiment, as the inert gas,
Although the case where Ar gas is used has been described, other inert gas such as N2 gas is also plasmatized at a temperature similar to that of Ar gas, and therefore the same effect can be obtained with the same configuration.

Although the generation of plasma is monitored from the sample injection hole, it is obvious that a dedicated hole for plasma detection may be provided in another portion of the holder.

[0017]

As described above, according to the present invention,
The abnormal heating of the tube can be detected by detecting the plasma generated from the inert gas, and the current flowing through the tube can be interrupted or reduced to quickly stop the heating of the tube. Therefore, abnormal heating of the tube can be prevented and safety can be ensured, and extra work such as replacement of the burned tube is eliminated.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a portion related to temperature control of an atomization furnace in an atomic absorption spectrophotometer according to an embodiment of the present invention (a).
And (b) a sectional view of the inside of the holder of the nuclear reactor.

FIG. 2 is a configuration diagram (a) of a portion related to temperature control of an atomization furnace in a conventional atomic absorption spectrophotometer (a) and a cross-sectional view (b) of an inside of a holder of the atomization furnace.

[Explanation of symbols]

 10 ... Tube 12 ... Holder 20 ... Heating control unit 22 ... Power supply 24 ... Plasma detection unit 26 ... Notification unit 242 ... Electrode 244 ... Dielectric constant monitoring unit

Claims (1)

[Claims] 1. An atomic absorption spectrophotometer having an atomization furnace for heating a sample by flowing an electric current through the tube while flowing an inert gas into and out of the tube into which the sample is injected, and generating from the inert gas. An atomic absorption spectrophotometer, comprising: a detection unit that detects plasma; and a heating control unit that shuts off or reduces the current flowing through the tube when the detection unit detects plasma.