JPH03181845A - Atomic absorption spectrometer - Google Patents

Abstract

PURPOSE:To omit the unnecessary measurement or measuring time of a zero point and to enhance the throughput of measurement by automatically judging whether the measurement of the zero point is necessary to determine a photometric time. CONSTITUTION:At first, trial sampling photometry for 500msec is performed. Next, the integration time of an integrator 20 is set as long as possible through an integration time controller 24. Subsequently, it is inspected whether either one of the photometric average values of both light sources is equal to the max. output of an analogue/digital converter 21. Next, the applied voltage of a photomultiplier tube 17 is set sufficiently low through a high voltage controller 23. Subsequently, the proper applied voltage of the photomultiplier tube 17 is calculated from a relational expression of the applied voltage and current multiplication rate of the photomultiplier tube 17 using the photometric average value. Subsequently, one-point measurement is performed to perform the fine adjustment of applied power and the optimum integration period is calculated to take balance. Next, the presence of the re-measurement of a zero point is judged to determine the measuring time of the zero point and the zero point is measured according to a condition and the average value and dispersion of a new zero point are calculated and recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an atomic absorption spectrometer.

(Mechanism of the invention) Using the photometric amount obtained in 1.2 trial measurements in the absence of light absorption by the sample, an appropriate applied voltage value is determined by the applied voltage of the photomultiplier tube and the current multiplication relational expression. Calculate and determine
Without changing the state of the light source, the photometry period is determined and balanced so that the photometric amounts of both light sources are approximately the same through calculation processing, and the need for re-measurement is determined by calculation when measuring the zero point. , an atomic absorption spectrophotometer characterized in that, if re-measurement is necessary, the zero point measurement time is automatically determined based on the applied voltage value of the photomultiplier tube.

[Conventional technology]

In atomic absorption spectrometry, an element to be measured in an aqueous solution sample is atomized in an atomization section, and light having a wavelength specific to the element to be measured is transmitted through the atomized gas to detect the amount of light absorbed by the element to be measured. The concentration of the element is finally identified from the detected absorbance using a 1 m detector. In measuring the amount of light absorption, the amount of light absorption includes bank ground absorption that is not caused by absorption of the measured element, so correction is required to remove this. For this reason, normally, light from a bright-line spectrum light source such as a hollow cathode lamp and a continuous spectrum light source such as a heavy water cold lamp are alternately applied to the lower part of the sample atoms, and the amount of light absorbed by each is detected. The amount of light absorption of a hollow cathode lamp includes both elemental light absorption and background light absorption.

The amount of light absorbed by a deuterium lamp is only that due to the background. Therefore, by removing the amount of light absorbed by the deuterium lamp from the amount of light absorbed by the hollow cathode lamp, only the amount of light absorbed due to the target element to be measured can be accurately measured.

However, the amount of light from a hollow cathode lamp varies depending on the element, and the amount of light that can be detected from a deuterium lamp varies depending on the measurement wavelength.If the photometric amounts of the two light sources are significantly different, there will be a large error when removing the bank ground absorption amount. . For this reason, it is necessary to balance the two photometric quantities so that they are approximately equal when no sample is introduced. In addition, in order to widen the measurement range of absorbance as much as possible, the sensitivity must be adjusted so that both photometric quantities when no sample is introduced are near the maximum output of the photometric circuit.

This is done by changing the voltage applied to the photomultiplier tube, which is a light receiving element for photometry. Furthermore, in order to calculate the absorbance from the amount of decrease in the photometric amount when the sample is introduced, the photometric amounts of both lights when no light is absorbed by the sample must be recorded as a zero point.

The sensitivity adjustment of the photomultiplier tube, the balancing of both photometric quantities, and the recording of the zero point were performed in the following steps. The photomultiplier tube is repeatedly used so that the photometric output of the light source with the smaller photometric amount, either the hollow cathode lamp light source or the deuterium light source, is around 80 to 90% of the maximum output. Measure the light while gradually raising or lowering the applied voltage by small amounts and adjust the voltage. Once the applied voltage is determined, the photometric amount of the light source with the larger photometric amount is set to 80 to 90% of the maximum output of the photometric circuit so that both photometric amounts are approximately equally powerful.
Reduce the output of the light source itself to approximately %.

For this purpose, if both light sources are lit in pulses, shorten the pulse lighting period or lower the current value of the light sources to balance the 0th order, and to obtain the zero point, the 1st
After measuring for about 0 seconds, the photometric values of both lights are recorded.

[Invention tries to solve it! The conventional method has the following problems.

fl, l When the voltage applied to the photomultiplier tube is changed, several l
A stabilization wait time of about 0 milliseconds is required, and a large number of photometry trials are required to determine the optimum applied voltage, so a processing time of about 10 seconds is required.

(2) If the photometric quantities of both light sources are balanced by changing the pulse lighting period or current value of the hollow cathode lamp, the thermal equilibrium state of the hollow cathode lamp will be disrupted, and the emission intensity will become unstable. In addition, we measure light by changing the lighting period and current value by a small amount, and compare it with the target light metering amount each time.
Processing time is required due to the large number of attempts to reconfigure the balance.

(3) Zero point measurements are generally performed frequently to ensure measurement accuracy. Moreover, the measurement time requires about 10 seconds, and the processing takes time.

Means for Solving Problem C] The present invention implements the following means in order to solve the above problems.

Using the photometric quantity obtained from the trial measurement at +111.2 degrees, an appropriate applied voltage value is calculated and determined from the applied voltage of the photomultiplier tube and the current multiplication relational expression.

(2) Adjust the amount of photometry by changing the photometry period without changing the state of the light source. Further, the photometry period is determined by arithmetic processing so that the photometry amounts of both light sources are approximately equal.

(3) In the measurement of the zero point, the photometric amount at the new zero point is sampled for a short period of time, and whether or not re-measurement is necessary is determined by calculation, and if unnecessary, the measurement is omitted. Further, the measurement time at the zero point is determined by the voltage value applied to the photomultiplier tube.

[Effect]

The above means has the following effects.

The optimum applied voltage value for the il+ photomultiplier tube can be determined in a very short period of time.

(2) The photometric amounts of both light sources can be made equal in a short period of time while the light source light amount remains stable.

(3) Unnecessary zero point measurement itself and measurement time can be omitted, and measurement throughput can be improved.

〔Example〕

Before starting the description of the embodiments of the present invention itself, the configuration of the photometry system will be described first for ease of explanation.

FIG. 2 is a block diagram showing the configuration of a photometric system implementing the present invention. 12 is a holocathode lamp, 13 is a deuterium lamp, I4 is a semi-transparent mirror, I5 is a sample atomization section, 16 is a spectrometer, 17 is a photomultiplier tube, 18 is a preamplifier, 19 is a light receiving corrector, 20 is an integrator, 21 is an analog-to-digital converter, 22 is a pulse lighting controller,
23 is a high pressure controller, 24 is an integral time controller, and 25 is a control computer. The hollow cathode lamp 12 and the deuterium lamp 13 are alternately turned on at regular intervals under the control of the pulse lighting controller 22. ■Measurement cycles include the hollow cathode lamp lighting period, the light source lighting period for bank ground correction, and the light receiving correction. It consists of three periods of time, and is repeated at 2 millisecond intervals. Both light guides pass through a semi-transparent mirror 14, are absorbed by a sample atomization unit 15, are separated into wavelengths specific to the target element to be measured by a spectrometer 16, are received by a photomultiplier tube 17, and are converted into electrical signals. be done. Thereafter, the electrical signal is amplified by the preamplifier 18, corrected for errors caused by light reception by the light receiving corrector I9, stored in the integrator 20, and converted into a digital signal by the analog-to-digital converter 21. , and are taken into the control computer 25. The control computer 25 reads the digitized photometric values for each cycle, controls the voltage applied to the photomultiplier tube 17 via the high voltage controller 23, and controls the voltage applied to the integrator 20 via the integration time controller 24. Controls the integration period and stores the zero point value. It also executes the processing of the present invention. The integral time controller 24 can independently set the integral periods of both the hollow cathode lamp 12 and the deuterium lamp 13, and operates in conjunction with the pulse lighting controller 22.

The present invention will be explained in detail below. FIG. 1 is a flowchart illustrating the processing procedure of the present invention. As mentioned above, the following processing is performed in the absence of light absorption by the sample, and the determination of the optimal voltage applied to the photomultiplier tube 17, the balancing of the photometric values of both light sources, and the measurement of the 0 and 0 points are all carried out at once. conduct.

In process 1, a trial sampling photometry is performed for 500 milliseconds, and measurement is performed in the sense of sampling photometric values in order to know the current state of the photometry system. The control computer 25 reads the photometric values every 2ξ seconds as described above, but since the photometric values as they are will have large variations, the photometric values are smoothed by adding them about 50 times, resulting in one measurement. It is marked as a point. To obtain one measurement point, it will take 1004 seconds. Therefore, in 500 milliseconds, 5
Data after point clearing is obtained. The data of these five points are further averaged, and the average value is used in subsequent judgment processing.

Next, in judgment 2, the photometric average values of both light sources are 80 to 90% of the maximum output of the analog-to-digital converter 21.
If the value falls within the range of Bypass.

Next, in process 3, the integrator 2
Set the zero integration period as long as possible.

In this execution example, it is normally set to about 660 microseconds. After that, one-point measurement is performed and used as the photometric average value in subsequent processing.

Next, in judgment 4, it is checked whether one of the photometric average values of both light sources is equal to the maximum output value of the analog-to-digital converter 21. If both are at the end of the maximum output value, processing 5 is performed. Since it is not necessary, branch it.

Next, in process 5, the voltage applied to the photomultiplier tube 17 is set to a sufficiently low level of about 200 volts via the high voltage controller 23. Thereafter, wait for about 50 milliseconds for the photomultiplier tube 17 to stabilize, perform one point measurement, and use the photometric average value in subsequent processing.

Next, in process 6, using the photometric average value, an appropriate applied voltage to the photomultiplier tube 17 is calculated based on a relational expression between the voltage applied to the photomultiplier tube and the voltage/current multiplication factor.

It is known that the following relationship exists between the voltage applied by a photomultiplier tube and the voltage/current multiplication factor.

G=K-V"'.

Here, G is the amplification factor of the entire photomultiplier tube, K is a constant, ■ is the voltage applied between the anode and the cathode of the photomultiplier tube, and α is 0.5 depending on the dynode shape and material. 7～
It is a coefficient between 0.8 and the number of dynode stages of an n photomultiplier tube. According to the above equation, under the same amount of received light, the following relational expression is established between the output electrical signal amount of the photomultiplier tube 17 and the applied voltage.

Here, electricity No. 13 IA applies the applied voltage A to the photomultiplier tube 1
The electrical signal amount B is the electrical signal amount when the applied voltage B is applied to the photomultiplier tube 17. In this example, n is 9, and α was determined to be 0.7 as a result of actual measurements, and was therefore adopted. Of the average photometric amounts of the light source, whichever is the smaller photometric amount is substituted into the electric signal IA, and the applied voltage of the photomultiplier tube 17 at this time is substituted into the applied voltage, and the analog-to-digital converter In step 21, a photometric value equivalent to 85% of the maximum output value is substituted into the electrical signal NB to calculate the applied voltage B. This voltage value is the optimum voltage value to be applied to the photomultiplier tube I7, and is applied to the photomultiplier tube 17 via the high voltage controller 23.
wait until it stabilizes.

Next, in process 7, one point measurement is performed and the photomultiplier tube 1 is again
It is confirmed that the applied voltage of step 7 is optimal, and this measured value is used as the average measured value in subsequent processing. In the unlikely event that the smaller of the average photometric amounts of both light sources is 80 to 90% of the maximum output of the analog-to-digital conversion 2g21.
If it is not within this range, make slight adjustments to the applied voltage. Once the applied voltage is determined, the average photometric amount used in subsequent processing is remeasured at one point.

Next, in process 8, an integration period is calculated such that the larger value of the average photometric amounts of both light sources falls within the range of 80 to 90% of the maximum output of the analog-to-digital converter 21. , sets the integration period of the integrator 20 via the integration time controller 24. In many cases, the larger value of the photometric value at the time of processing 8 is equal to the maximum output value of the analog/digital converter 21. If it is equal to the maximum output value, halve the current integration period and re-measure, then reduce the integration period to half again and perform one-point measurements until the larger photometric value reaches the end of the maximum output value. Once the photometric value at the end of the maximum output value is obtained, the optimum integration period is calculated using the following formula.

Integration period A = Integration period B x Photometry (aA + Photometry value B Here, integration period A is the optimal integration period to be found, and integration period B is the current integration period. Photometry value A is the value of the analog-to-digital converter 21. The photometric value is equivalent to 85% of the maximum output value, and the photometric value B is the photometric value measured under the conditions of the integration period B. The calculated integration period A is set in the integrator 20 via the integration time controller 24. Then, sampling similar to Process I is performed again.

Next, in decision 9, it is determined whether re-measurement of the zero point is necessary. In the zero point measurement in each figure, both the average and variance of the zero point photometric values are calculated and recorded.

Next, add the constant times the variance to the average value of the zero point to create the upper limit of the zero point, and subtract the constant times the variance from the average value of the zero point to create the lower limit of the zero point. Compare the photometric value obtained with the previous upper and lower limit values. If the photometric value obtained by sampling measurement is within the upper and lower limits, it is determined that re-measurement of the zero point is unnecessary, branching is performed, and the following processing is bypassed. Note that the constant multiplication value used for the above upper and lower limit values requires consideration from the safety factor, but in this embodiment, 2 is used.

Next, in the processing IO, the zero point measurement time is determined from the applied voltage value of the photomultiplier tube 17. The elements to be measured are classified into three groups: a group where the hollow cathode lamp 12 is bright, a normal group, and a dark group.

This classification scale uses the voltage value applied to the photomultiplier tube 17, dividing the voltage into 350 volts or less, 450 volts or less, and other voltages, and measuring time for each of 2 seconds, 5 seconds, and 10 seconds.
Next, in step 11, the zero point is measured according to this condition, and the new average 11 and variance of the zero point are calculated and recorded.

〔Effect of the invention〕

According to the present invention, the determination of the voltage applied to the photomultiplier tube and the balancing of the photometric values of both light guides can be completed in about 1 to 2 seconds. In addition, even if you set a schedule to perform zero point execution at fixed time intervals, if it is determined that the measurement is unnecessary, it will be automatically omitted, so the throughput of all measurements will not decrease and you can achieve highly reliable measurements. can now be executed.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing an embodiment of the processing procedure of the present invention, and FIG. 2 is a block diagram of a photometry system used in the embodiment of the present invention. ]... Sampling measurement (processing 1) 2... Judgment of balance (judgment 2) 3... Re-measurement (processing 3) 4... Judgment of maximum value (judgment 4) 5... Re-measurement ( Process 5) 6...Optimum applied voltage calculation (Process 6) 7 ・ ・ 8 ・ ・ 9 ・ ・ 10 ・ ・ 11 ・ 12 ・ 13 ・ 14 ・ 15 ・ 16 ・ 17 ・ 18 ・19・ 20・ ・ 21・ ・ 22・ ・ 23・ ・ 24・ ・ 25・ ・Re-measurement (Processing 7) ・Balancing (Processing 8) ・Zero point judgment (Judgment 9) ・Measurement time determination (Processing 10)・Zero point measurement (Process 11) ・Holo cathode lamp ・Deuterium lamp ・Semi-transparent mirror ・Sample atomization section ・Spectrometer ・Photomultiplier tube ・Preamplifier ・Flame light corrector ・Integrator analog-to-digital converter ・Pulse lighting controller, high voltage controller, integral time controller, control computer flow + 1 light system on the back of the page, Figure 7, Figure 2

Claims (1)

[Claims] It has a configuration in which the light from a light source that emits an emission line spectrum of the target element and the light from a light source that emits continuous spectrum light are transmitted alternately into the sample atomization section, and the light from both spectra after passing through the atomization section is photometered. The applied voltage is adjusted by calculating the applied voltage of the photomultiplier tube and the current multiplication relational expression so that the magnitude of the photometric value of the light from both light sources in the absence of light absorption by the sample in the section is near the maximum output of the photometric circuit. and a means for determining the integration period by calculation so that the photometric values of both light sources are approximately equal, and automatically determining whether or not zero point measurement is necessary. An atomic absorption spectrophotometer, characterized in that it has means for determining photometry time.