JP2565068B2 - 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 atomizing a sample by a flameless atomization method. More specifically, the temperature of an atomization furnace in such an atomic absorption spectrophotometer. Regarding control.

[0002]

2. Description of the Related Art In order to perform analysis with an atomic absorption spectrophotometer, it is necessary to atomize a sample in a molecular state. As this atomization method, in addition to the flame atomization method in which a flame (flame) of a burner heats it to a high temperature for atomization, a flameless atomization method in which a sample is heated and atomized by a micro electric furnace There is. In the flameless atomization method, a graphite atomization furnace is mainly used in which a sample is injected into a graphite tube, and a large current is passed through the tube to heat it to atomize the sample. Conventional methods for controlling the temperature of this graphite atomization furnace include:
The method of performing feedback control (temperature control method) so that the detection value of the light emission amount of the graphite tube by the photo sensor becomes equal to the target value (output value of the photo sensor corresponding to the set temperature), and the current value flowing through the graphite tube The main method was a method (current control method) of performing feedback control so that the value becomes equal to the target value (current value corresponding to the set temperature). Among them, the current control method has a drawback that the reached temperature is different because the amount of heat generation changes when the resistance of the tube changes even if the tube is heated with the same current value. On the other hand, in the temperature control method, since the temperature of the tube is directly measured by the photo sensor, there is little error in the reached temperature due to the change in the resistance of the tube, and the temperature rising rate is fast and responsive control is possible Has features. Therefore, the temperature control method is generally often used as the temperature control method of the graphite atomization furnace.

[0003]

However, in the temperature control system, when tubes having different shapes (for example, tubes having different diameters) are used to change the injection amount of the sample into the tube, the photosensor and the outer wall surface of the tube are not used. Since the distance between and changes, an error occurs between the reached temperature and the set temperature. As a result, it is necessary to reset the relationship between the set temperature and the target value of the photo sensor each time the tube shape changes (replacement of the ROM that stores the target value of the photo sensor corresponding to each set temperature). Becomes This allows
The operation for analysis becomes complicated and the time required for analysis becomes long.

The present invention has been made to solve such a problem, and an object of the present invention is to set the temperature of the tube to a target temperature (set temperature) regardless of the shape of the tube of the graphite atomization furnace. The present invention is to provide an atomic absorption spectrophotometer capable of performing accurate analysis easily and quickly by controlling the temperature so that

[0005]

In order to achieve the above object, in the present invention, an atomic absorption spectrophotometer having an atomization furnace for heating a sample by injecting an electric current through the tube is injected from the tube. A photosensor for detecting the amount of emitted light, a storage unit for storing a target value of the photosensor corresponding to each set temperature of the atomization furnace, and a temperature is set to start heating by the atomization furnace. Heating control means for controlling the electric power supplied to the tube so that the detection value by the photosensor becomes equal to the target value stored in the storage means corresponding to the set temperature, the voltage across the tube, and the tube. Detecting means for detecting the current flowing through the sensor, and the value of the voltage and the current when the detected value of the photosensor is equal to the target value. Calibration means for calculating the power supplied to the storage device, and calibrating the target value corresponding to the set temperature stored in the storage means based on the amount of change when the supplied power changes from a predetermined reference value, It has a configuration with.

[0006]

According to this structure, when the temperature is set and the heating of the atomic reactor is started, the detected value of the photosensor becomes equal to the value stored in the storage means as the target value corresponding to the set temperature. Thus, the heating control means controls the power supplied to the tube. As a result, when the tube is in the standard state, the standard value of electric power is supplied to the tube in the steady state, and the temperature reached by the graphite atomization furnace becomes equal to the set temperature.

Now, if the standard shape tube used in the graphite atomization furnace is replaced with a different shape tube, the distance between the outer wall surface of the tube and the photosensor changes, so that the temperature and the phototube of the tube change. The relationship with the sensor output value changes. As a result, even if heating control is performed with the same set temperature (the target value of the photo sensor remains the same), the power supplied to the tube changes in the steady state due to tube replacement, and the reached temperature is However, there is an error with the set temperature. The power supplied to the tube is obtained from the voltage across the tube detected by the detection means and the current flowing through the tube,
Thus, the calibration means detects how much the supply power changes from the reference value (the value of the supply power when the reached temperature of the tube becomes equal to the set temperature in the steady state) due to the replacement of the tube. Based on the amount of change thus detected, the calibration means calibrates the target value corresponding to the set temperature stored in the storage means. At this time, if the calibrated supply power is made equal to the supply power before tube replacement based on the amount of change, it is possible to suppress the occurrence of an error between the ultimate temperature and the set temperature due to tube replacement.

Even if the tube is not replaced, the relationship between the temperature of the tube and the output value of the photosensor changes due to changes in the surface condition of the tube (changes in emissivity, etc.). There may be an error in. Also in this case, the power supplied to the tube in the steady state is calculated, and how much this supply power changes from the reference value (the value of the power supply when the reached temperature of the tube becomes equal to the set temperature in the steady state) Is detected and the target value of the photosensor is calibrated in the same manner as described above, it is possible to suppress the occurrence of an error between the reached temperature and the set temperature.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a portion related to temperature control in a graphite atomization furnace of an atomic absorption spectrophotometer which is an embodiment of the present invention. In the present atomic absorption spectrophotometer, a sample is injected into a graphite tube 10 and an electric current is passed through the tube 10 to heat the sample, thereby atomizing the sample. The temperature of the tube 10 is measured by detecting the amount of light emitted from the tube 10 with the photo sensor 12. The output of the photo sensor 12 is amplified by the sensor amplifier 18 and then input to the error amplifier 20 as a signal Vt. On the other hand, the temperature programmer 16 stores the target value of the photosensor corresponding to each set temperature, and the target value of the photosensor corresponding to the current set temperature is input to the error amplifier 20 as a signal Vr. The error amplifier 20 outputs the target value Vr of this photosensor and the current output value (value corresponding to the current temperature).
Vt is compared, and the output corresponding to the error is input to the power supply 14. The power supply 14 controls the current (supply power) flowing through the tube 10 based on the output of the error amplifier 20. That is, when Vt <Vr, the temperature of the tube 10 is lower than the set temperature, so that the power supplied to the tube 10 is increased, and when Vt> Vr, the temperature of the tube 10 is higher than the set temperature, so that the power is supplied to the tube. Reduce power.
As a result, in the steady state, Vt = Vr, and the tube 1
The temperature of 0 is maintained at the set temperature.

In this embodiment, in order to measure the electric power supplied to the tube 10, a current sensor 22 for detecting the current flowing through the tube 10 and a voltage sensor 26 for detecting the voltage across the tube 10 are provided. Then, the signals representing the current value and the voltage value detected by these are amplified by the sensor amplifier 24 or 27 and then input to the calibration unit 28. The calibration unit 28 calculates the power supplied to the tube 10 in the steady state from these signals, and calibrates the target value stored in the temperature programmer 16 based on the calculated power supplied. That is, when the relationship between the temperature of the tube and the output of the photosensor 12 changes due to replacement of the tube 10 or the like, the above-mentioned temperature control (heating control of the tube 10) is performed.
Even when the temperature reaches a steady state (Vt = Vr), the power supplied to the tube is a reference value corresponding to the current set temperature (when the reached temperature of the tube becomes equal to the set temperature in the steady state. However, an error occurs between the temperature reached by the tube 10 and the set temperature. Therefore, the calibration unit 28 detects how much the supplied power calculated as described above has changed from the reference value corresponding to the current set temperature, and is stored in the temperature programmer 16 according to the change amount. The target value of the photo sensor 12 is calibrated.

FIG. 3 is a flow chart showing an example (first calibration method) of the calibration method by the calibration unit 28.
In this calibration method, the calibration unit 28 calibrates before performing an analysis operation when the tube 10 is replaced. For example, when the standard tube A is replaced with another tube B having a different shape, calibration is performed as follows. However, when the tube A or B is used, the power supplied to the tube in the steady state and the output of the photosensor have a relationship as shown in FIG.

When heating is performed with the set temperature being T while the tube A is being used, the output of the photosensor 12 reaches the target value VSA corresponding to the set temperature T in the graphite atomization furnace having the above configuration. The temperatures are controlled so as to be equal, and the reached temperature is T in the steady state. At this time, from FIG. 2, the power supplied to the tube A is W
A is the reference value of the supplied power corresponding to the set temperature T. Therefore, in order to obtain the same ultimate temperature T even after exchanging the tube from A to B, the supply power is also set to W
Must be A. However, when heating is performed with the set temperature being T, that is, the target value of the photosensor 12 being VSA, as shown in FIG.
do not become. Therefore, after replacing the tube with B, the target value of the photosensor 12 stored in the temperature programmer 16 is calibrated as shown in FIG.

First, in step S10, heating is performed with the set temperature set to T, that is, the target value of the photosensor set to VSA. In step S20, this heating is in a steady state (the output value of the photosensor 12 is constant at VSA).
Current IB flowing to tube B and voltage VB across tube B when current sensor 22 and voltage sensor 2
6, and the power WB supplied to the tube B is calculated from them. Then, in step 30, the ratio WA / WB of the reference value WA of the supply power corresponding to the set temperature T and the supply power after tube replacement (the supply power actually detected and calculated) WB is used to perform the calibrated photo. Target value V of sensor
Ask for SB. That is, VSB = VSA × (WA / WB), and the calibration unit 28 sets the temperature programmer 16 so that the target value of the photosensor 12 corresponding to the set temperature T becomes VSB.
Calibrate the target value stored in. In the calculation of VSB, WA is a reference value (the value of power supply when the temperature reached by the tube is equal to the set temperature in the steady state).
The value stored in advance in the calibration unit 28 is used as.
As can be seen from FIG. 2, if the power supplied to the tube B is proportional to the output of the photosensor 12, the power supplied to the tube B in the steady state when the temperature is controlled with the target value VSB. Becomes WA, that is, the same as before the tube replacement, and the reached temperature becomes equal to the set temperature T. Therefore, by performing such a calibration,
It is possible to suppress the occurrence of an error between the ultimate temperature and the set temperature.

FIG. 4 is a flow chart showing another example (second calibration method) of the calibration method by the calibration unit 28. In this calibration method, the calibration unit 28 calibrates for each measurement during a normal analysis operation. For example, the calibration procedure when the nth measurement is performed in the atomic absorption spectrophotometer is as follows (see FIG. 4). First, in step P10, heating is performed with the set temperature set to T, that is, the target value of the photosensor 12 set to VSn. This heating is common with the heating in the usual analytical operation. In step P20, the current In flowing into the tube 10 and the voltage Vn across the tube 10 when the steady state (the output value of the photosensor 12 is constant at VSn) is detected during this heating, and the tube 10 is detected from these. Calculate the power supply Wn to the Then, in Step P30,
Using the ratio W0 / Wn of the reference value W0 of the supply power corresponding to the set temperature T and the supply power (supply power actually detected and calculated) Wn in the current measurement (nth measurement), the first value The target value VSn + 1 of the photosensor in the next measurement (n + 1th measurement) is obtained in the same way as the calibration method. That is, VSn + 1 = VSn × (W0 / Wn), and the calibration unit 28 sets the temperature programmer 1 so that the target value of the photosensor 12 corresponding to the set temperature T becomes VSn + 1.
Calibrate the target value stored in 6. In the calculation of VSn + 1, W0 uses a value stored in advance in the calibration unit 28 as a reference value (a value of power supply when the reached temperature of the tube becomes equal to the set temperature in the steady state). According to such a calibration method, since the calibration is performed for each measurement in the atomic absorption spectrometry, not only the temperature error (error between the set temperature and the reached temperature) caused by the change of the tube shape due to the exchange of the tube, but also the It is also possible to suppress the occurrence of a temperature error caused by a change in the surface condition of the tube (change in emissivity, etc.). In this calibration method, calibration is performed for each measurement of atomic absorption spectrometry.
The above calibration may be performed every predetermined number of measurements.

By the way, as a method for suppressing the error between the set temperature and the reached temperature due to the change in the state of the tube 10 (change in the relationship between the temperature of the tube 10 and the output of the photosensor 12), the current sensor 22 and Voltage sensor 26
A method of performing temperature control (heating control) so that the supplied electric power detected by is equal to a reference value corresponding to the set temperature can be considered. However, as in the above example,
The supplied power detected by the current sensor 22 and the voltage sensor 26 is used only for calibration of the target value, the temperature of the tube 10 is directly detected by the photosensor 12, and the temperature is controlled so that the detected value becomes equal to the target value. Is more advantageous in terms of responsiveness because the heating rate is faster.

[0016]

As described above, according to the present invention, when the relationship between the temperature of the tube and the output value of the photosensor changes due to the replacement of the tube of the graphite atomization furnace, the change of the surface condition of the tube, etc. The target value (output value of the photo sensor) corresponding to the set temperature is calibrated. Therefore, the sample can be heated and atomized at the target temperature (set temperature) regardless of the state of the tube. As a result, accurate atomic absorption analysis can be performed easily and quickly regardless of the shape and surface state of the tube.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a portion related to temperature control in a graphite atomization furnace of an atomic absorption spectrophotometer which is an embodiment of the present invention.

FIG. 2 is a diagram for explaining a method of calibrating a target value of a photo sensor in the above embodiment.

FIG. 3 is a flowchart showing a first method of calibrating a target value of a photo sensor in the above embodiment.

FIG. 4 is a flowchart showing a second method for calibrating the target value of the photosensor in the above embodiment.

[Explanation of symbols]

 10 ... Graphite tube 12 ... Photo sensor 14 ... Power source (heating control means) 16 ... Temperature programmer (storage means) 20 ... Error amplifier (heating control means) 22 ... Current sensor (detection means) 26 ... Voltage sensor (detection means) 28 ... Calibration unit (calibration means)

Claims (1)

(57) [Claims] 1. An atomic absorption spectrophotometer having an atomization furnace for heating a sample by applying an electric current to a tube in which a sample is injected, and a photosensor for detecting the amount of light emitted from the tube; Storage means for storing the target output value of the photosensor corresponding to each set temperature, and when the temperature is set and heating by the atomization furnace is started,
Heating control means for controlling electric power supplied to the tube so that a detection value by the photosensor becomes equal to a target output value stored in the storage means corresponding to the set temperature; a voltage across the tube; Detecting means for detecting a current flowing through the tube, calculating the power supplied to the tube from the voltage and current values in a state where the detection value of the photosensor is equal to the target output value, When a change from a predetermined reference value is made, a calibration unit that calibrates a target output value corresponding to the set temperature stored in the storage unit based on the amount of change, is provided. Photometer.