JPS6344190B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a flameless atomizer for atomic absorption spectrometry, and particularly to monitoring deterioration of a heating element. In conventional flameless atomizers for atomic absorption spectrometry, the heating element, which affects analysis accuracy, was replaced by the analyst's visual inspection, or after a certain number of analyzes was completed, regardless of the lifespan of the heating element. Ta. As a result, not only was the heating element was wasted, but the timing for replacing the heating element was missed, and the conditions for a series of analysis results became inconsistent. Analysis time was wasted. Separately, during continuous operation of flameless atomizers involved in automatic analysis, deformation and breakage due to deterioration of the heating element may cause damage to peripheral equipment, such as damaging the tip of the automatic sample injector. Ta. The purpose of the present invention has been made to eliminate the above-mentioned drawbacks, and it provides convenience to the analyst by monitoring and displaying the deterioration of the heating element, and also detects the end of the life of the heating element and interrupts the analysis. An object of the present invention is to provide a flameless atomizer for atomic absorption spectrometry, which is equipped with a mechanism for emitting a signal for atomic absorption analysis. As shown in Fig. 1, the flameless atomizer is made by injecting a sample 4 into a heating element 2 having pores.
The sample 4 is processed in the order of drying, ashing, and atomization by generating heat through electric current from the power supply section 3. Excluding the effects of coexisting substances such as acids in the sample, the drying, ashing, and atomization procedures are determined by the magnitude of the current and the duration of the current, depending on which substance in the sample is to be effectively atomized. Executed according to the program. This program assumes that the state of the heating element 2 is constant for each analysis, and matches the current value applied to the heating element 2 with the temperature of the heating element 2. However, in reality, the inert atmosphere 1 Since the heating element 2 contains some impurities such as moisture and oxygen, the heating element 2 gradually deteriorates even though it generates heat by being energized therein. That is, the degree of deterioration differs depending on the type and concentration of acid contained in the sample and what is atomized. For example, in the analysis of cadmium at an atomization temperature of 2000°C and the analysis of chromium at an atomization temperature of 2800°C, the deterioration of the heating element for the latter is approximately five times greater. In addition, there are cases where the sample contains almost no acid, and cases where the sample contains only a few percent of sulfuric acid.
The latter deteriorates about three times as much as the case where it is included. Using a graphite cell as a heating element, an experiment was conducted to atomize chromium in the same sample according to Table 1.
Figure 2 shows the results of 200 repetitions.

[Table] In Figure 2, Ec is the graph when the current that would correspond to the atomization temperature of 2800°C when electricity was first applied to the graphite cell was applied with constant current control throughout 200 analyses. This is a graph in which the terminal voltage change of the eye cell is plotted every time. ΔW is a graph showing weight changes of Graphite cells measured every 50 times. S is a graph showing the rate of change in absorption sensitivity every 50 times with respect to the initial absorption sensitivity. σ/m is a graph showing the change in the coefficient of variation (σ/m) obtained by dividing the dispersion (dispersion σ) of the atomic absorption analysis values every 20 times by the average value m. These experiments revealed that there is a causal relationship between the manner in which the terminal voltage of the graphite cell increases as it deteriorates and the manner in which the coefficient of variation σ/m of the atomic absorption analysis value increases. The present invention has been made focusing on the above-mentioned points,
This invention attempts to monitor the deterioration of the heating element by monitoring its terminal voltage.The state of the heating element is displayed according to changes in the terminal voltage, the lifespan of the heating element is detected, and the flameless atomizer is operated. It is characterized by controlling the More specifically, as shown in Figure 2, we captured the phenomenon that the deterioration of Graphite cells rapidly progresses after a certain number of analyzes (for example, around 100 times), and analyzed the deterioration and lifespan of Graphite cells. This is what we are trying to detect. Next, an embodiment of the present invention is shown in FIG. The primary side of the transformer 309 is connected to the power supply 301 via the thyristor 303. The secondary side of the transformer includes a current detection element 311 and a voltage detection circuit 3.
21 and the graphite cell 2. The current control section 329 constitutes a control loop together with the current detection element 311, the current detection circuit 307, and the thyristor control section 305, and controls the output of the transformer 309 at a constant current by referring to the current value setting signal from the current value setting section 325. . The current value setting section 325 sends a current value setting signal according to a predetermined program to the current control section 329 and the display section 3.
27, to be given to the status monitoring unit 323. The state monitoring section 323 compares the signal obtained by detecting the voltage across the graphite cell by the voltage detection circuit 321 with the current value setting signal, and sends a display signal to the display section 327 in accordance with the difference signal. This makes it possible to display the deterioration state of the heating element based on the magnitude of the difference signal. When the difference signal exceeds a certain threshold value, a life detection signal is sent to the current value setting section 325 to cut off the output of the transformer 309 or issue an alarm. More specifically, in the status monitoring unit 323, the current value setting unit 325 compares the signal detected by the voltage detection circuit 321 with the current value setting signal when the output current of the transformer 309 is 100A, for example, and calculates the difference between the two. A display signal is sent out accordingly. This comparison is performed every analysis or after a certain number of analyses. The current value setting signal is preferably a current value corresponding to a temperature lower than the atomization temperature. This is because, for each analysis, the graphite cell is heated through a temperature corresponding to the current value, so that the graphite cell can be monitored for each analysis. The current value setting signal is determined separately in advance based on the relationship between the current flowing through the graphite cell and the terminal voltage at that time.
The voltage detection circuit 32 may be determined uniformly or during the first analysis after replacing with a new graphite cell.
In some cases, the signals detected from 1 are stored. In the former case, the structure of the state monitoring unit 323 is simple, and in the latter case, it is not affected by individual variations in graphite cells. The state monitoring section 323 may send a signal to the display section 327 when the comparison result exceeds a certain threshold value. The display unit 327 may display the results of the comparison by the status monitoring unit 323 in stages, such as when the difference from the current value setting signal is 5% or 10%. Further, this display may be performed using an audio level meter, LED, liquid crystal, or the like. The reason for this is that if you create a calibration curve and calibrate the concentration using a standard solution, the reproducibility (σ/
This is because although m) is deteriorated, the absorption sensitivity may be within a practically acceptable range depending on the analysis. The condition monitoring unit 323 may detect the end of life and send a signal to the current value setting unit 325, and then send a signal to interrupt the analysis. As described above, according to the present invention, it is possible to monitor the deterioration of the heating element, and to deal with the deterioration of the heating element at an early stage, without missing the time to replace it, and to prevent a decline in analysis accuracy. It is possible to provide a flameless atomizer for atomic absorption spectrometry that prevents waste of samples, heating elements, and analysis time.

[Brief explanation of drawings]

Figure 1 is a diagram of the principle of a flameless atomizer, Figure 2 is a diagram showing the results of repeated experiments to understand the deterioration state of the heating element, and Figure 3 is an implementation of the overall configuration of the flameless atomizer according to the present invention. It is a figure which shows an example. 321...Voltage detection circuit, 323...State monitoring section, 325...Current value setting section, 327...Display section, 329...Current control section.

Claims (1)

[Scope of Claims] 1. In a flameless atomizer for an atomic absorption spectrometer having a power supply section that supplies current to a heating element on which a sample is placed in accordance with a current value setting signal, the flameless atomizer is configured to detect the terminal voltage of the heating element. a voltage detection circuit, which compares the signal from the voltage detection circuit with the current value setting signal and sends a signal for displaying the state of the heating element according to the magnitude of the difference signal between the two; a status monitoring unit that issues a signal to interrupt the operation of the atomic absorption spectrometer when the magnitude of the signal exceeds a certain threshold; and a status monitoring unit that receives the signal from the status monitoring unit and displays the status of the heating element. 1. A flameless atomizer for an atomic absorption spectrometer, characterized in that the flameless atomizer comprises a display section that displays