JPH04355347A - Atomic absorption spectrophotometer - Google Patents

Abstract

PURPOSE:To improve temperature accuracy and reproducibility of a heating furnace by automatizing the calibration of a current-temperature relationship. CONSTITUTION:Relationship between a value of current flowing through a graphite tube and temperature is held at a current-temperature holding section 2 and a relationship between the temperature and radiation intensity is held at a light-temperature relationship holding section 4. A current control section 6 controls the temperature of the graphite tube at a high temperature area by a light temperature control system based on the light-temperature relationship and at a low temperature area by a current control system based on the current- temperature relationship. A calibration section 8 calibrates the current- temperature relationship of the current-temperature holding section 2 from an electric energization value from the current-temperature relationship at a specified temperature in a temperature area of the light temperature control system and an actual electric energization value of the graphite tube.

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 metal elements contained in various substances, and more particularly to a flameless atomic absorption spectrophotometer.

0002

[Prior Art] In a flameless atomic absorption spectrophotometer, a sample is placed in a graphite tube in a heating furnace and heated to a high temperature to dry, ash, and atomize the sample to produce atomic vapor. Atomic absorption spectrometry is performed by transmitting light of an appropriate wavelength through the atomic vapor. In the heating furnace, electricity is applied to the graphite tube from electrodes at both ends of the tube to generate heat.

To control the temperature of the heating furnace, a light temperature control method is used in the high temperature region, and a current control method is used in the low temperature region. The relationship between the temperature of the graphite tube and the intensity of radiant light from the graphite tube at that time does not change depending on the individual graphite tube, and does not change even if the graphite tube is worn out through use. On the other hand, the relationship between the current value flowing through the graphite tube and the temperature changes depending on variations among individual graphite tubes and the state of wear due to use. Therefore, it is necessary to calibrate the current-temperature table used in the current control method in the low temperature region.

Conventionally, the current-temperature table is calibrated by adjusting the gain of a current sensor that detects the current flowing through the graphite tube using a variable resistor. That is, a calibration temperature program (current control method) is executed, and the variable resistor is adjusted so that the output of the optical temperature sensor, which detects the temperature from the radiant light intensity of the graphite tube, becomes a value at a predetermined temperature.

[0005]

According to the conventional calibration method, it is necessary for the operator to calibrate the current-temperature table every time a measurement is made, which is cumbersome and causes individual differences. Further, since the calibration is also a volume adjustment of a variable resistor, precise calibration is difficult. An object of the present invention is to automate the calibration of the current-temperature relationship, thereby eliminating operator error, enabling precise calibration, and improving the temperature accuracy and reproducibility of a heating furnace.

[0006]

[Means for Solving the Problems] The present invention will be explained with reference to FIG. The current-temperature relationship between the current value passed through a graphite tube that is energized to generate heat, dry, ash, and atomize the sample to be analyzed to produce atomic vapor and the temperature of the graphite tube at that time is the current-temperature relationship. The light-temperature relationship between the temperature of the graphite tube and the intensity of radiant light from the graphite tube is held in the light-temperature relationship holding part 4 . Reference numeral 6 denotes a current control unit that controls the amount of current flowing through the graphite tube.The control method is to detect the intensity of radiated light from the graphite tube in the high temperature region and to control the current flow based on the light-temperature relationship in the light-temperature relationship holding unit 4. A light temperature control method is used that applies feedback to the amount of current flowing through the graphite tube. In low temperature regions, the current flowing through the graphite tube is detected and the amount of current flowing through the graphite tube is controlled based on the current-temperature relationship between the current and the temperature holding section 2. A current control method is used that applies feedback to the current. A calibration unit 8 is provided to calibrate the current-temperature relationship of the current-temperature holding unit 2, and the calibration unit 8 calculates the amount of energization from the current-temperature relationship at a predetermined temperature in the temperature range of the light temperature control method. The current-temperature relationship of the current-temperature holding section 2 is calibrated from the actual amount of current flowing through the graphite tube. The output of the current control section 6 is sent to a D/A converter 10 to control energization to the graphite tube.

[0007] The calibration operation by the calibration section is performed by executing the calibration program when passing through the calibration temperature during the execution of the temperature program consisting of the steps of drying, ashing, and atomization, or during the process of lowering the temperature after measurement. implement. The calibration program may also be provided independently of the temperature program of measurement. Calibration section 8 determines the current - current of temperature holding section 2 -
Once the temperature relationship is calibrated, the amount of current flowing through the graphite tube is controlled in accordance with the calibrated current-temperature relationship in the low temperature region when the next temperature program is executed.

[0008]

[Operation] FIG. 2 shows the relationship between the reference voltage V generated to cause a current to flow through the graphite tube and the temperature of the graphite tube. The vertical axis also represents the current sensor output that detects the value of the current flowing through the graphite tube. The solid curve is expressed as V=f(T),
This is held in the current-temperature relationship holding section 2 as, for example, a current-temperature table. Suppose that when a current sensor measures the amount of current flowing into a graphite tube currently in use, the output of the current sensor is indicated by, for example, a broken line. The dashed curve is V=g(T)=αf
(T). α is a calibration factor. To properly control the temperature of the graphite tube, V=
A reference voltage according to g(T) must be output from the D/A converter 10.

Let Tc be the temperature at which calibration is performed. Tc is the temperature that can be accurately detected by radiation from the graphite tube. If the detection output of the current sensor is V' at the calibration temperature Tc, the calibration coefficient α is calculated as α=V'/Vo. Vo is the reference voltage corresponding to the temperature Tc of the graphite tube, and the current -
This is the value held in the temperature relationship holding unit 2. In the next measurement temperature program, the reference voltage is output according to V=αf(T).

FIG. 3 shows an example of a temperature measurement program, and this example is a STEP program that changes the temperature of the graphite tube stepwise up to the ashing temperature and atomization temperature.
Indicates the mode. Another temperature program mode is a RAMP mode in which the temperature is continuously changed. The calibration process of the present invention can be applied to either mode of temperature programming. If calibration is performed during the temperature increase process during execution of the measurement temperature program, please refer to Figure 4 (A).
The STEP mode shown in FIG. 1 or the RAMP mode shown in FIG. Calibration can also be performed when the temperature passes through the calibration temperature Tc during the temperature decreasing process during execution of the measurement temperature program, as shown in FIG. FIG. 5(A) shows the case of RAMP mode, and FIG. 5(B) shows the case of STEP mode. Calibration can also be performed independently of the measuring temperature program. In that case, raise the temperature of the graphite tube from room temperature to the calibration temperature Tc,
After maintaining the temperature for a predetermined period of time, the temperature is lowered to room temperature.

6 and 7, the operation when performing calibration during the temperature increase process of the measurement temperature program will be explained again. Create a measurement temperature program and decide when to perform calibration in the temperature program. For example, in the example of FIG. 4, the timing can be determined by the stage number for performing calibration or the time for performing calibration. In order to be able to perform calibration during the course of a temperature program, the temperature program must include a stage where the temperature is equal to or higher than the calibration temperature Tc. Temperature program is at calibration temperature T
When the temperature program includes a stage where the temperature is equal to or higher than c, execution of the temperature program is started, and when the stage for calibration is reached, calibration is executed. When the heating mode is STEP mode, the process moves from that stage (N-1) to a calibration program (FIG. 7) to be described later. After the calibration is completed, the next stage N is executed, and the remaining stages are executed to complete the temperature program. On the other hand, in RAMP mode, stage N
When the calibration temperature Tc is reached during the execution of the calibration program, the calibration program is executed. After completing the calibration, continue executing stage N,
Finish the temperature program by running the remaining stages. If a temperature equal to or higher than Tc is not set in the measurement temperature program, all stages of the temperature program are sequentially executed and the temperature program is ended. In this case, no calibration is performed during the measurement temperature program.

FIG. 7 shows a calibration program. When the calibration process begins, the temperature of the graphite tube is controlled to the calibration temperature Tc, and the temperature of the graphite tube is observed while monitoring the intensity of radiation from the graphite tube. When the temperature reaches Tc, read the value of the current sensor. Sampling is repeated, for example, five times. The sampled data is compared with the data in the current-temperature relationship holding section to determine a calibration coefficient.

FIG. 8 represents another example of a calibration program. In Figure 7, the value of the current sensor is sampled when the temperature of the graphite tube passes Tc in the middle of the measurement temperature program, but in Figure 8, the value of the current sensor is sampled when the temperature reaches Tc and is maintained for a predetermined time tc. to read the current sensor value. This improves the reproducibility of current sensor readings.

[0014]

Embodiment FIG. 9 shows a schematic diagram of an embodiment. 12
is an atomization device, and includes a graphite tube that is energized by a heating power source 14 to generate heat. A sample is placed inside the graphite tube, and the sample is heated and atomized by the graphite tube. Reference numeral 16 denotes a light source that irradiates measuring light onto the atomic vapor generated by the atomization device, and for example, a hollow cathode lamp is used. Reference numeral 18 denotes a spectrometer unit that spectrally spectra the measurement light that has passed through the atomization device, 20 a detection unit that detects the spectroscopic light, and 22 a signal processing unit that performs processes such as calculating absorbance from the detection signal of the detection unit 20. Department. Approaching the atomization device 12 and receiving radiation light from the graphite tube,
A photosensor (not shown) is provided to monitor the temperature of the graphite tube, and a current sensor (not shown) is also provided to detect the current flowing through the graphite tube. 24 is a control device, which includes a CPU and an interface (I/O), controls lighting of the light source 16,
Controls the spectroscopic operation of the spectrometer section 18, inputs measurement data from the signal processing section 22, inputs detection signals from the photosensor and current sensor, and controls the energization of the graphite tube of the atomization device 12 by the heating power source 14. Control. 26 is an operation unit, and 28 is a display device.

FIG. 10 shows a circuit for controlling the current flowing through the graphite tube in one embodiment. The current to the graphite tube 30 is supplied by converting an AC 200V power source using a transformer 32. The energization control is performed by the triac 34, and the triac 34
It is controlled by a firing pulse signal from the PU (including interface I/O) 40. graphite tube 3
For example, a photodiode is arranged as a temperature sensor 36 in order to detect radiation light from zero. A current sensor 38 is also arranged to detect the amount of current applied to the graphite tube 30. The detected values of the temperature sensor 36 and the current sensor 38 are taken into the CPU 40.

FIG. 11 shows a heating furnace in one embodiment. (A) is a longitudinal cross-sectional view, and (B) is a cross-sectional view taken along line A-A in (A). Both ends of the graphite tube 30 are held by graphite electrodes 44 and 46 to be energized, and a sample injection hole 48 is bored in the center of the graphite tube 30. The graphite tube 30 is closed by window plates 50a and 50b provided on the outside of both electrodes 44 and 46 on its axis, and an inert gas is flowed into the graphite tube 30 from an inner gas passage 52, and the graphite Inert gas is flowed from the outer gas passage 54 to the outside of the tube 30. A sample is dropped into the graphite tube 30 from the sample injection hole 48, and measurements are performed using the measurement light 56 passing through the graphite tube 30 at each step of drying, ashing, and atomization. A radiant light monitor hole 58 is formed on the side of the electrode 44 to detect the radiant light of the graphite tube 30, and a photodiode is arranged as a temperature sensor 36 outside of this hole 58.

FIG. 12 more specifically shows a circuit for temperature calibration and graphite tube temperature control in one embodiment. The current sensor 38 passes through an amplifier 60, and the photodiode 36 passes through a two-stage amplifier 6.
2 and 64 to each contact point of a relay (or analog switch) 66, and the CPU 40
It has also been incorporated into The relay 66 is connected to the photodiode 36 side when temperature control is performed using the light temperature control method, and is connected to the temperature sensor 38 when temperature control is performed using the current control method.
connected to the side. The output from the CPU 40 is input to one input terminal of the comparator 68 via the D/A converter 10, and the output of the photodiode 36 from the relay 66 or the output of the current sensor 38 is input to the other input terminal of the comparator 68. are compared. The output of the comparator 68 is sent to the firing pulse generation circuit 70 and the try-up 34
A signal is generated to control the Current in Figure 1 -
The temperature relationship holding section 2, the light-temperature relationship holding section 4, the current control section 6, and the calibration section 8 are realized by the CPU 40 in FIG.

[0018]

[Effects of the Invention] The atomic absorption spectrophotometer of the present invention is equipped with a calibration program that calibrates the relationship between the current flowing through the graphite tube and temperature. Upon initiation, the device will automatically calibrate. Therefore, there is no need for operators to manually adjust the gain of the current sensor as in the past, and there are no individual differences between operators, allowing for accurate calibration. Accuracy is improved and reproducibility is also improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating the present invention.

FIG. 2 is a diagram showing the relationship between the reference voltage V generated to cause a current to flow through the graphite tube and the temperature of the graphite tube.

FIG. 3 is a diagram showing an example of a measurement temperature program.

FIG. 4 is a diagram illustrating an example in which calibration is executed during a temperature increase process of a measurement temperature program.

FIG. 5 is a diagram illustrating an example in which calibration is executed during a temperature decreasing process of a measurement temperature program.

FIG. 6 is a flowchart showing a temperature measurement program including a calibration process.

FIG. 7 is a flowchart diagram illustrating an example of a calibration process.

FIG. 8 is a flowchart diagram illustrating another example of the calibration process.

FIG. 9 is a block diagram showing an atomic absorption spectrophotometer according to one embodiment.

FIG. 10 is a circuit diagram showing a circuit for controlling the current flowing through the graphite tube in one embodiment.

FIG. 11 is a diagram showing a heating furnace in one embodiment, (A)
is a longitudinal cross-sectional view, and (B) is a cross-sectional view taken along line A-A in (A).

FIG. 12 is a circuit diagram more specifically showing a circuit for temperature calibration and graphite tube temperature control in one embodiment.

[Explanation of symbols]

2 Current-temperature relationship holding part 4 Light-temperature relationship holding part 6 Current control section 8 Calibration section

Claims (1)

[Claims] Claim 1: In an atomic absorption spectrophotometer equipped with a heating furnace built into a graphite tube that is energized to generate heat and dry, ash, and atomize the sample to be analyzed to produce atomic vapor, a current-temperature relationship holding unit that represents the relationship between the current value and the temperature of the graphite tube at that time; a light-temperature relationship holding unit that represents the relationship between the temperature of the graphite tube and the intensity of radiant light from the graphite tube; In the low temperature region, a light temperature control method is adopted in which the intensity of the radiant light from the graphite tube is detected and feedback is applied to the amount of current flowing through the graphite tube based on the light-temperature relationship. a current control section that takes a current control method that detects the current and applies feedback to the amount of current to the graphite tube based on the current-temperature relationship, and a current-temperature relationship at a predetermined temperature in the temperature range of the optical temperature control method. From the amount of current flowing through the graphite tube and the actual amount of current passing through the graphite tube, the current −
An atomic absorption spectrophotometer comprising: a calibration section for calibrating temperature relationships.