JP2701770B2 - Atomic absorption spectrophotometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flameless atomic absorption spectrophotometer, and more particularly to a flameless atomic absorption spectrometer using a pyrocoated graphite tube.

[0002]

2. Description of the Related Art In a frameless atomic absorption spectrophotometer, a sample is dried, incinerated, and atomized by directly heating a sample, or placing a sample on a boat and placing the boat in a sample atomization furnace and heating the sample to a high temperature. Atomic absorption analysis is performed by generating atomic vapor by passing the light and transmitting light of an appropriate wavelength into the atomic vapor. In many cases, a graphite furnace is used as the atomization furnace. The graphite furnace heats the graphite tube itself by supplying electricity to the graphite tube from the electrodes at both ends of the graphite tube. There are usually two types of graphite tubes used, one is a graphite tube not covered with a pyrolytic graphite layer (hereinafter referred to as a normal tube), and the other is a coating with a pyrolytic graphite layer (pyro coating). This is a graphite tube (hereinafter, referred to as a pyroformed tube).

FIG. 2 is a schematic block diagram showing an example of a temperature control system of a flameless atomic absorption spectrophotometer. Reference numeral 20 denotes a graphite tube (usually a tube or a pyrolysis tube) of an atomization furnace, and the sample injected into the graphite tube is atomized by heating the graphite tube 20 with electric current. Reference numeral 22 denotes a graphite electrode, and reference numeral 24 denotes a heating power supply for energizing the graphite tube. In order to control the temperature of the graphite tube 20, a photosensor 26 as an optical temperature sensor is installed at a position where the light emission of the graphite tube 20 can be received. The detection signal from the photo sensor 26 is amplified by the amplifier 28 and input to the comparator 30. In the comparator 30, the reference signal Vr for the set temperature set by the temperature programmer 32 is used.
And the current I of the heating power supply 24 is controlled such that the detection signal of the photosensor 26 matches the reference signal Vr, and the graphite tube 20 is feedback-controlled to a constant temperature. The condition setting such as the temperature raising program and the parameters for the temperature programmer 32 is performed by a computer control unit 38 including a display unit 34 and an operation unit 36 by using data stored in a memory inside the control unit.
Alternatively, it is performed by a general method according to an input from an operator.

[0004]

Among the two types of tubes, the pyrolyzed tube is prepared by keeping a graphite tube at a high temperature in an inert gas such as Ar and introducing a small amount of methane or the like into the tube. A dense graphite layer is formed on the surface of the graphite tube, thereby extending the life of the graphite tube. For these two types of graphite tubes, use the one that is suitable for the measurement conditions such as what to measure. Therefore, the atomic absorption spectrophotometer can be used by replacing the tube in the atomization furnace.

However, since the two types of tubes have different emissivities on the tube surface, when they are heated to the same temperature, the setting of the temperature program must be changed according to each tube. If the temperature is controlled by the same temperature program without such a change, the pyrolyzed tube is controlled at a higher temperature than the normal tube. Also, even if you change the setting according to the type of tube, you may mistakenly set the pyrotube when using a normal tube, which may cause a measurement error. became.

[0006] Furthermore, when the heating is repeated, the surface state of the pyrolyzed tube is liable to change, so that a change in temperature due to a change in the emissivity of the surface may occur. An object of the present invention is to solve the above problems and to provide an atomic absorption spectrophotometer that can perform correct temperature control regardless of the type of graphite tube.

[0007]

An atomic absorption spectrophotometer according to the present invention, which has been made to solve the above-mentioned problem, heats a graphite tube of a sample reactor by energizing the graphite tube, and emits light from the graphite tube. In a flameless atomic absorption spectrophotometer that monitors and controls the energization by using a signal from an optical temperature sensor attached to the outer wall of the tube, a pyrocoated graphite tube is used, and a part of the outer wall of the graphite tube is used. A pyro coating removing section is provided, and light emission monitoring by the optical temperature sensor is performed by light emission from the pyro coating removing section. Hereinafter, how the atomic absorption spectrophotometer works will be described.

[0008]

In the atomic absorption spectrophotometer of the present invention, the luminescence when using a pyrolysis tube monitors the luminescence from the pyro-coating removal part, and is the same as the measurement of the luminescence in a normal tube without pyro-coating. Conditions are available. Therefore, it is not necessary to change the setting of the temperature programmer according to the type of the graphite tube, so that the temperature can be accurately measured. Further, since the temperature of the tube is substantially measured, the fluctuation of the surface emissivity is small and stable temperature control can be performed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a graphite tube part of an atomic absorption spectrophotometer showing one embodiment of the present invention. Since the atomization furnace and the temperature control system to which the graphite tube is attached are the same as those in the conventional example shown in FIG. 2, the description will be omitted by using the same reference numerals.

[0010] The pyrolysis tube 20a used in the atomic absorption spectrophotometer of the present invention is a tube made of graphite, and the surface thereof is pyrocoated. Then, the measurement light is passed through the pyrolysis tube 20a in the axial direction, and electrodes 22 are connected to the vicinity of both ends of the pyrolysis tube 20a, and electricity is supplied from a heating power supply. The sample injection port 23 is located at the upper center of the pyrolysis tube 20a.
Is opened, from which the sample is introduced. In addition, a side portion of the central portion of the pyrolysis tube 20a is a square pyrocoat removal portion 2 from which the pyrocoat is removed.
1 is provided. There is no particular problem as long as the pyrocoating removing section 21 is large enough to monitor light emission by the photosensor 26 as an optical temperature sensor attached to a position facing the pyrocoating removing section 21. For example, strips may be removed along the outer periphery of the tube at the center to improve productivity.

The pyrocoating removal section 21 may be removed by shaving the entire tube after pyrocoating, or may be formed by masking during pyrocoating.

Next, the operation of the present apparatus will be described. The boat on which the sample is placed is placed in the pyrolysis tube 20a, and the graphite tube 20 is heated by the heating power supply 24.
The sample is atomized by the current heating. The temperature of the pyrolyzed tube 20a is monitored by the photo sensor 26. The photo sensor 26 is a pyro coating removing unit 21
Since luminescence from is monitored, measurement under the same conditions as in a normal tube can be used. Therefore, the temperature programmer 32 uses the temperature-raising program or parameter data normally used for the tube as a common one independent of the type of the tube, without any change. The reference signal Vr for the set temperature obtained based on the data set in this way is compared with the detection signal from the photosensor 26, and the current I of the heating power supply 24 is fed back so as to match the reference signal. Controlled.

[0013]

As described above, according to the present invention,
A pyro-coating removal part was provided on a part of the outer surface of the pyro-coated graphite tube, and the heating of the graphite tube was performed by monitoring the light emission from the pyro-coating removal part. It is not necessary to separately set the temperature control of the ordinary graphite tube, and it is possible to reduce the occurrence of measurement errors and measurement errors. Also, even if the pyrolysis tube is used repeatedly, the fluctuation of the emissivity does not become so large, stable temperature control becomes possible, and the reproducibility of measurement can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a graphite tube portion of a frameless atomic absorption spectrophotometer according to one embodiment of the present invention.

FIG. 2 is a schematic block diagram of an example of a temperature control system of the frameless atomic absorption spectrophotometer.

[Explanation of symbols]

 20: Graphite tube 20a: Pyrolyzed tube 21: Coating removal part 22: Electrode 24: Heating power supply 26: Photo sensor

Continuation of front page (56) References JP-A-54-163093 (JP, A) JP-A-61-217743 (JP, A) JP-A-55-85243 (JP, A) JP-A-58-166243 (JP) JP-A-4-110640 (JP, A) JP-A-6-180283 (JP, A) JP-A-63-313037 (JP, A) JP-A-4-1423 (JP, U) JP-A-4-1423 (JP, U) 4-29845 (JP, U)

Claims (1)

(57) [Claims] 1. A frame for energizing and heating a graphite tube of a sample atomization furnace and monitoring the light emission of the graphite tube based on a signal from an optical temperature sensor attached to an outer wall surface of the graphite tube. In an atomic absorption spectrophotometer of the less system, while using a pyro-coated graphite tube,
An atomic absorption spectrophotometer, wherein a pyro-coating removal portion is provided on a part of an outer wall surface of a graphite tube, and light emission monitoring by the optical temperature sensor is performed by light emission from the pyro-coating removal portion.