JPH07117488B2 - 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 an atomic absorption spectrophotometer for quantitatively analyzing metallic elements contained in various substances, and more particularly to a flameless atomic absorption spectrophotometer.

[0002]

2. Description of the Related Art In a flameless atomic absorption spectrophotometer, a sample is dried directly, or placed on a boat, put in a heating furnace and heated to a high temperature to dry, incinerate, and ash the sample. Atomization is performed to generate atomic vapor, and light of an appropriate wavelength is transmitted through the atomic vapor to perform atomic absorption analysis. A graphite furnace is often used as the heating furnace. In a graphite furnace, heat is generated by energizing the graphite tube from electrodes on both ends of the graphite tube.

In order to control the temperature so that the sample is heated to a constant temperature, light emitted from the inner and outer walls of the graphite tube is received by a photosensor, and the detection signal of the photosensor is input to the control device of the heating power source of the heating furnace. Then, the heating furnace temperature is controlled. Graphite tubes deteriorate with use and eventually reach the end of their lives. Conventionally, in order to determine the life of a graphite tube, the number of times the graphite tube can be used is determined based on experience, and the number of times that the graphite tube can be used is entered in advance in the atomic absorption spectrophotometer as data, and the number of times is used for each measurement. Is counted down from the data, and when the counter reaches 0, the graphite tube is replaced. The reality is that the life of a graphite tube is not accurately determined.

[0004]

The state of wear of the graphite tube depends on the operating temperature and the heating time.
When performing continuous measurement by continuous operation or the like, it becomes a big problem where to set the replacement time of the graphite tube. If the graphite tube is damaged during the measurement, sparks due to electric discharge occur in the heating furnace, and the heating furnace needs to be maintained. In addition, if the graphite tube is damaged, there is a situation in which the data up to that point during continuous measurement must be discarded. It is an object of the present invention to automatically determine the life of a graphite tube in a heating furnace so that the graphite tube can be replaced before it is damaged.

[0005]

In the present invention SUMMARY OF] monitors the current flowing when the graphite tube heated, automatically determines the life of the graphite tube according current variation of it. The present invention will be described with reference to FIG.

In the method of judging the life of the graphite tube from the amount of change in the current flowing through the graphite tube, the current value measuring unit 12 for measuring the current flowing through the graphite tube during the heating operation under a constant condition, and the measured current value And the current value at the time of heating this time are compared with the current value at the time of heating once or several times before stored in the current memory 18 to obtain the amount of change, and the amount of change Is provided with a life judging section 14 for judging the life of the graphite tube by comparing it with a reference change amount ΔI ₀ corresponding to the life of the graphite tube, and an output section 16 for notifying that the life has come.

[0007]

As the graphite tube wears out, the resistance value R increases, so that the current value I decreases to obtain the same temperature. That is, if the electric power applied to the graphite tube is W, then W = I ² R, and when W is constant, the larger the resistance value R is, the smaller the current value I is. By monitoring the current value I, it is possible to automatically determine the time to replace the graphite tube.

FIG. 2 is a comparison for judging the life from the current value itself.
It represents an example operation. In this method, in order to determine the life of the graphite tube, a reference current value I ₀ at a certain set temperature is stored in advance as data, and when the measured current value In becomes equal to or less than the reference current value I _0. A warning is issued that the battery has reached the end of its life, and the signal is used to control the supply of electricity to the graphite tube.

FIG. 3 shows the present invention in which the life is judged from the amount of change in current.
It represents the action of Ming . Since the current value of the graphite tube decreases as it is used, as shown in Fig. 4, the current change amount between this time and the previous time (shown by the broken line in the figure) or at the time of the measurement several times before this time Compare the amount of change in the current with the amount of change in the reference to determine the life of the graphite tube.

According to FIG. 3, heating of the graphite tube is started at a certain set temperature, the value of the current flowing through the graphite tube at that time is measured, and stored as the current value In of this time. Then, the amount of change (Im-In) from the measured current value Im at the previous heating is calculated, and it is compared with the amount of change in current ΔI ₀ that serves as a criterion for life determination. If m is n-1, the life will be judged at each measurement,
If m is a number smaller than n by n-2 or n-3, the current change amount is compared with the reference change amount once every plural times to determine the life. The amount of change becomes large if the amount of change in current is calculated once every several times. When the measured change amount (Im-In) becomes equal to or larger than the reference change amount ΔI ₀ , a warning is issued that the life has expired, and control such as prohibiting energization to the graphite tube is performed.

[0011]

EXAMPLE FIG. 5 schematically shows an example. Reference numeral 20 denotes a graphite tube of a graphite furnace in a heating furnace, a boat on which the sample is placed is installed therein, and the sample is heated by the heat generation of the graphite tube 20 to be atomized. 22 is a graphite electrode,
Reference numeral 24 is a heating power source for energizing the graphite tube 20. In order to control the temperature of the graphite tube 20, a photo sensor 26 is arranged at a position where the graphite tube 20 receives the light emission. Photo sensor 26
The detection signal of is amplified by the amplifier 28 and input to the comparator 30. In the comparator 30, the temperature is compared with the reference signal Vr for the set temperature set by the temperature programmer 32, and the current I of the heating power source 24 is controlled so that the detection signal of the photo sensor 26 matches the reference signal Vr. 20 is controlled to a constant temperature.

In order to detect the value of the current flowing through the graphite tube 20 in the present invention, a current sensor 34 is provided in the current path from the heating power source 24 to the graphite tube 20, and the detection output of the current sensor 34 is amplified by the amplifier 36. Are taken into the control unit 38. The control unit 38 determines the life of the graphite tube 20 from the current value taken in and issues a warning via the display unit 42, and also controls the temperature programmer 32. An operation unit 40 for instructing an operation and a display unit 42 such as a CRT for displaying a warning are connected to the control unit 38.

Considering the correspondence between FIGS. 1 and 5, the current value measuring unit 12 in FIG. 1 corresponds to the current sensor 34 and the amplifier 36, and the current storage unit 18 and the life judging unit 14 are realized by the control unit 38. . The output unit 16 corresponds to the display unit 42. The control unit 38 is realized by a personal computer, a microcomputer or a CPU. The warning is not limited to the display but may be notified by a sound such as a buzzer.

[0014]

According to the present invention, the life of the graphite tube is automatically determined by monitoring the amount of change in the amount of electricity applied to the graphite tube, so that the graphite tube can be replaced before it is damaged. In particular, when using a pyrogenized graphite tube, it is possible to prevent the mistake of continuing the analysis without knowing whether the pyro coating on the surface of the graphite tube has peeled off, which is useful for proceeding the analysis operation correctly. is there.

[Brief description of drawings]

FIG. 1 is a block diagram showing a portion for determining a life according to the present invention.

FIG. 2 is a flowchart showing an example of an operation of a comparative example .

3 is a flowchart showing an example of operation of the present invention.

FIG. 4 is a diagram showing changes in current value of a graphite tube.

FIG. 5 is a block diagram showing a main part of one embodiment.

[Explanation of symbols]

 12 current value measuring unit 14 life judging unit 16 output unit 18 current storage unit 20 graphite tube 24 heating power supply 32 temperature programmer 34 current sensor 38 control unit 42 display unit

Claims (1)

[Claims] 1. A flameless atomic absorption spectrophotometer in which a sample or a boat on which a sample is placed is installed in a graphite tube of a heating furnace, and the graphite tube is energized to heat the sample to generate atomic vapor. A current value measuring unit that measures the current flowing through the graphite tube during heating operation under constant conditions, and the measured current values are sequentially stored
Current storage unit and the current value for the current heating
Compared with the current value stored in the part at the time of heating once or several times before
Then, the amount of change is obtained, and the amount of change is calculated as
An atomic absorption spectrophotometer comprising a life determining unit that determines the life of the graphite tube by comparing it with a reference change amount corresponding to the life of the tube, and an output unit that notifies that the life has expired.