JPS60253851A - Atomic absorption analyzer - Google Patents

Abstract

PURPOSE:To make it possible to enhance the reproducibility of measurement, by controlling a graphite tube to constant temp. to detect a current value and generating a signal having preset functional relation to control the current of the graphite tube. CONSTITUTION:The output Vs of a photodiode transmitting upon the reception of thermal radiation from the graphite tube GT connected to a voltage drop transformer T is inputted to a control amplifier CA and a temp. signal at each stage is applied to the amplifier CA as a reference level signal Vr from the temp. programmer TP in which the fuctional relation with the temp. of the tube GT was stored and the amplifier CA applies the signal of the difference between the signals Vs and Vr to a triac TA through a pulse generator PG and controls supply power from the triac TA so as to adjust the tube GT to indicated temp. By this method, the temp. change rate of a temp. rising process becomes constant.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a temperature efficient device for a sample nuclear reactor for flameless atomic absorption spectrometry analysis.

Conventional technology The sample reactor for flameless atomic absorption spectrometry is a graphite tube in which light is passed in the direction of the tube axis, and the sample solution dropped into the tube is passed through the tube itself and heated. . The electricity is turned on according to the following schedule. In the first stage, a small current is applied to dry the sample.
In the second stage, a medium current is applied to slightly ignite the sample, and in the final stage, a large current is applied to raise the furnace temperature to the maximum temperature, atomizing the sample in the process of raising the temperature.

In the conventional one-time constant temperature control method that achieves the above-mentioned energization schedule, constant temperature control is performed in the second stage, the ashing stage where a medium current is passed, and the final stage, the highest temperature stage (atomization stage). However, the intermediate process in which the temperature rises from the ashing stage to the atomization stage is not a constant temperature limit state. The rate of temperature increase during this intermediate process is determined by the maximum voltage applied to the graphite tube and the electrical resistance of the graphite tube.The electrical resistance varies from tube to tube, and even if the same tube is used many times, the tube itself This will change because of the fact that it gradually wears out.

On the other hand, the atomization temperature in the final stage is set so that the peak of atomic absorption necessary for analysis occurs during this intermediate process, so the electrical resistance value of the graphite duplex affects the analysis results and Reproducibility decreases. For example, if the heating rate is slow, the time width of the atomic absorption peak that appears will widen, but since the sample vaporizes slowly, the concentration of atomic vapor will be low, and the peak height will be low. The amount of heat dissipated increases, and the peak area becomes smaller than when the heating rate is high.

C. Purpose The purpose of the present invention is to improve the reproducibility of measurements by keeping the temperature change during the heating process from the ashing stage to the atomization stage constant, regardless of variations in graphite tubes or deterioration due to use. .

2. Detect the electrical resistance value of the graphite tube by using the energization in the first stage or second stage (ashing stage) of the component energization, and control the current in the intermediate process of the first half to control this process. The temperature change rate at is kept constant each time.

E. Embodiment FIG. 1 shows an embodiment of the present invention. The GT is connected to the secondary side of the step-down transformer T by a graphite tube of the sample reactor. The amount of power supplied to the graphite chew/GT is adjusted by controlling the firing phase angle of the triac TA. DT is a photodiode which receives thermal radiation from the graphite tube GT and outputs a signal.

The functional relationship between the signal and the temperature of the graphite tube GT is investigated in advance and stored in the temperature programmer TP as temperature data for the first stage, second stage, etc.

The temperature programmer TP generates a pulse at a timing according to the input signal and applies it to the control terminal of the triac TA to control the firing phase of the TA, and the graphite tube GT controls the temperature programmer TP. The power supplied to the tube is controlled so that the temperature is maintained at the specified temperature.

The portion surrounded by a chain line in FIG. 1 is the maximum current setting circuit according to the present invention. A current detection coil C is installed on the primary side of the transformer T.
The outputs of the coils are input to the function generator FII via the amplifier SA2. The output of the amplifier SA2 is a signal corresponding to the current value 1 supplied to the graphite tube GT, and has the property of decreasing if the graphite tube has deteriorated at one stage of the energization schedule, for example, the second ashing stage. In other words, as a graphite tube is used repeatedly, it gradually wears out, its wall thickness becomes thinner, and its resistance increases, so less current is required to obtain the same temperature.Function generator FI Relationship between the output of amplifier SA2 at one stage of the energization schedule, for example, the second ashing stage, and the maximum current value to make the temperature change rate the same each time during the intermediate process of moving to the next stage, the sample atomization stage. This function generates a function, and the form of this function is determined in advance through experiments.S/H is a sample and hold circuit that holds the output of the function generator FI just before the end of the second stage using the signal from the temperature programmer TP. SW is a switch that is normally OFF and is turned ON in response to the above sample hold signal 1 from the temperature programmer TP.Therefore, when the energization schedule reaches the final stage, the above switch becomes QN, and the input signal of the pulse generator PG is turned ON. is pulled down to the output of the sample-and-hold circuit SO by a clamper CL consisting of a resistor and a diode, and the firing phase of the triac TA is advanced.
The maximum current is supplied to the graphite tube according to its degree of deterioration, and the temperature rises at a predetermined rate.
Atomization of the sample is performed.

In one example, two function generation means are used, but these are graphs showing the relationship between the configuration in which a computer that also serves as a temperature programmer TP calculates based on a given experimental formula. T1 is the temperature of the first drying stage of energization, T2 is the temperature of the multi-two stage ashing stage, and T3 is the temperature of the final atomization stage. Figure 2 shows an extended time axis of the atomization stage, and the chain line indicates the current. At the end of the ashing stage, at time t3, the current temporarily changes from the medium current to the maximum current value set by the above-mentioned point t. In response to this, the temperature of the graphite tube increases gradually from time 13 and reaches the maximum value t at time t3'. An atomic absorption peak appears within the time range from t3 to t3' during this temperature rising process. By changing the maximum current value Im, this temperature increase slope can be adjusted as shown by the solid dotted line. The above structure operates so that the slope of the temperature increase process is the same every time.

Effects The present invention has the above-mentioned configuration, and will be explained with reference to FIG. 2. Conventionally, T, 3 was simply controlled to be constant during the atomization stage, so the temperature increase process t3 to t3 '
The angle of inclination of the temperature increase between the graphite tubes differs depending on the resistance of the graphite tube, and even the same tube deteriorates each time it is used, so it changes each time, and there was a limit to the reproducibility of measurement. Accordingly, the temperature increase slope between t3 and t3' is the same every time, so the reproducibility of measurement is improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2a is a graph of temperature change, and FIG. GT, Graphite tube, DT, Photodiode for temperature detection, TP, Temperature programmer, PG...Pulse generator, CT...
・Current detection coil, F7...Function generator, S/H・
...Sample and hold circuit. Agent Patent Attorney Kosuke Agata

Claims (1)

[Claims] At the appropriate stage of the energization schedule for the sample reactor and other reactors,
The current value supplied to the graphite tube of the sample reactor, which is controlled at a constant temperature, is detected, a signal having a preset functional relationship with the current value is generated, and the signal is used to control the sample atomization stage. An atomic absorption spectrometer characterized by an I-type strainer to control the current supplied to the graphite tube.