JPH0473093B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a frameless atomic absorption spectrometer, and more particularly to a graphite tube consumption monitoring device for a sample nuclearization reactor.

B. Prior art A sample atomization reactor for flameless atomic absorption spectrometry is a graphite tube, in which light is passed in the tube axis direction, and the sample solution dropped into the tube is heated by passing electricity through the tube itself. Here, energization is performed according to the following schedule. In the first stage, a small current is applied to dry the sample, and in the second stage, a medium current is applied to incinerate the sample at a slightly high temperature.
In the final sample atomization stage, a large current is applied to raise the furnace temperature to its maximum temperature, and the sample is atomized in the process of increasing temperature.

The graphite tube nuclear reactor used for atomic absorption spectrometry gradually wears out during repeated use and its electrical resistance changes, which changes the furnace temperature and affects measurement sensitivity and reproducibility of measurement results. . This point has been considerably improved by adopting a constant temperature control method that utilizes the relationship between the amount of thermal radiation from the graphite tube and the tube temperature, but as the graphite tube wears out, the surface condition changes and the thermal radiation increases. Due to reasons such as the relationship between the amount and furnace temperature being different,
Deterioration in measurement sensitivity, measurement reproducibility, etc. is unavoidable. In addition, if automatic analysis is performed over and over again using the same graphite tube over a long period of time, the tube will wear out and may eventually break.
In addition to simply damaging the tube, this can lead to damage to the sample injector, loss of valuable samples, and failure to obtain the expected analytical results.

Therefore, it is necessary to constantly monitor the state of wear and tear on the graphite tube and manage the state of the graphite tube. Conventionally, methods for this purpose include: (1) Monitoring the state of wear and tear visually and intuitively.

(2) Dispose of the product after a certain number of uses, regardless of wear and tear or lifespan.

methods were used. However, method (1) relies on human intuition, so even if the tube wears out to the extent that the analysis conditions (current value, etc.) should be changed, it may be necessary to continue using it or to miss the time to replace the tube. There have been cases where the situation described above has arisen. Furthermore, method (2) leads to waste of graphite tubes and cannot be said to be a preferable method.

C. Purpose The present invention aims to solve the above-mentioned problems by automatically monitoring the state of wear of a graphite tube for sample atomization.

D. Configuration When the constant temperature control described above is performed, since the temperature is constant, there is a certain relationship between the heating current of the graphite tube and the degree of wear of the tube.
That is, as the tube wears out, the electrical resistance of the tube increases, so less heating current is required to maintain a constant temperature. Utilizing this fact, the warning means is activated when the output of the heating current detector falls below a certain level.

E. Embodiment FIG. 1 shows an embodiment of the present invention. GT is connected to the secondary side of the step-down transformer T by the graphite tube of the sample reactor. The amount of power supplied to the graphite tube GT is adjusted by controlling the firing phase angle of the triac TA. DT is a photodiode that receives thermal radiation from the graphite tube GT and outputs a signal. That signal is an amplifier
It is amplified by SA1, and the output Vs of SA1 is input to the control amplifier CA. The relationship between the output Vs of SA1 and the temperature of the graphite tube GT has been investigated in advance and input into the temperature programmer TP.
The temperature programmer TP outputs the temperature signal at each stage to the control amplifier CA as a reference level signal Vr according to a preset schedule. The control amplifier CA amplifies the signal of the difference between the above Vs and Vr and sends it to the pulse generator PG, which generates a pulse at a timing according to the above input signal and applies it to the control terminal of the triac TA. By controlling the ignition phase, the amount of power supplied to the graphite tube GT is controlled so that the graphite tube GT reaches the temperature specified by the temperature programmer TP. Figure 2 shows one cycle of the AC power supply and the phase relationship of the output pulse Vp of the pulse generator PG during that cycle, and the phase angle θ is controlled to control the area of the conduction period indicated by diagonal lines, that is, the amount of electricity supplied. .

The part surrounded by a chain line in FIG. 1 is a graphite tube wear degree detection circuit according to the present invention. A current detection coil CT is linked to the primary side of the transformer T, and the output of the coil is applied to comparators CP1 and CP2 via an amplifier SA2. Reference levels VT1 and VT2 are applied to CP1 and CP2 by potentiometers, respectively. Among these reference levels, VT1 is set in accordance with the output of amplifier SA2 corresponding to the first lower limit value of the heating current at an appropriate stage of the energization schedule of the graphite tube, for example, the first drying stage.
VT2 is similarly set to match the second lower limit value, and the relationship is VT2>VT1. The temperature programmer TP is designed to check the outputs of the comparators CP1 and CP2 in the first stage of the energization schedule. CP1 and CP2 output signals when the output of amplifier SA2 becomes lower than reference levels VT1 and VT2. As mentioned above, VT2>VT1
As the graphite tube wears out, the heating current decreases, so as the graphite tube wears out, the CP
2 issues a signal first, and when the temperature programmer TP detects this signal, it activates a warning means DP such as a buzzer to notify the operator that the tube GT should be converted. If the wear progresses further, the comparator
CP1 also begins to emit a signal, and when TP detects this signal, it stops the analysis operation. This two-stage system is in preparation for unattended automatic analysis, but even if an operator is present, the Graphite Tube GT may be immediately activated for some reason even if a warning is issued. It also provides preparation for continuing analysis for a while in the event that replacement is not possible.

F. Effect The present invention monitors the consumption state of the reactor by using the constant temperature control system of the sample reactor.
There is no subjectivity involved in choosing when to replace the nuclear reactor, there is no waste as would occur when replacing the reactor periodically, and unreliable measurements are performed using a deteriorated reactor. Failures such as equipment damage and sample loss are also prevented. In particular, in the present invention, as described above, the state of deterioration of the graphite tube is detected at two stages, a relatively early stage and a late stage, and a warning is issued based on the detection of relatively early stage deterioration, and the state of late stage deterioration is detected. Since the analysis operation is stopped during analysis, there is no need to worry about not knowing when the analysis operation will stop, and you can continue to use the same sample reactor with peace of mind until a warning is given, and then continue using the same sample reactor. The operator can now choose to replace the furnace at his own discretion or continue analysis for a while and then replace the furnace, and there is no need to worry about damaging the furnace by forcing him to continue using one furnace. It will also disappear.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a device according to an embodiment of the present invention;
The figure is a graph explaining conduction phase angle control. GT...graphite tube of sample reactor, DT...photodiode, TP...temperature programmer, DP...warning device, PG...pulse generator, CP1, CP2...comparators.

Claims (1)

[Claims] 1. A constant temperature control system that detects the temperature of the graphite tube of the sample reactor, adjusts the heating current of the graphite tube, and controls the temperature of the graphite tube in multiple stages; , detecting the heating current,
A means for comparing this with two preset upper and lower reference levels is provided, and a warning means is activated upon detecting that the heating current has fallen below the higher of the two reference levels; An atomic absorption spectrometer characterized in that it is equipped with a graphite tube consumption monitoring system that stops the analysis operation when it detects that the temperature has fallen below the lower of the two reference levels.