JPS6210375B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an atomic absorption spectrometer. In atomic absorption spectrometry, a sample is atomized and the absorbance is measured by passing light with a wavelength specific to the element to be detected in the atomized gas. The light that has passed through the oxidation part is attenuated, and it appears that the resonance absorption by the element to be detected has increased. Such light attenuation, or background absorption, due to non-specific causes for an element occurs to the same extent even with light at a wavelength near the wavelength specific to the element to be detected. The above-mentioned background absorption can be corrected by measuring the absorbance of light having a wavelength close to that of light. For this reason, normally an emission-line spectrum light source such as a hollow cathode lamp that emits light with a wavelength specific to the element to be detected and a continuous spectrum light source such as a deuterium lamp are used, and both lights are alternately applied to the sample atoms. The target element is detected by signal processing. I am trying to extract only the information absorbed by. In this case, the luminous intensity of the deuterium lamp differs from the luminous intensity of the hollow card lamp at each wavelength, and if the difference in luminous intensity between the two is too large, the background absorption may be estimated too low or the transmitted light intensity may be converted into absorbance (logarithmic conversion). Since linearity deteriorates, it is necessary to balance the intensity of light incident on the sample atomization section of both light sources.

For this reason, in the past, the light intensities of both light sources were balanced by a light attenuation method using a configuration as shown in FIG. In Figure 1, D2 is a deuterium lamp, HCL
is a hollow cathode lamp, HM is a semitransparent mirror, and A is a sample atomization unit. In this example, the deuterium lamp D2 and the hollow cathode lamp HCL are alternately flashed. Here, the light intensity of both light sources is balanced by appropriately setting the ratio between the transmittance and reflectance of the semi-transparent mirror HM. For example, if the light intensity of the D2 lamp is 4 times the light intensity of the HCL lamp, the reflectance of the semi-transparent mirror HM is
0.2, and the transmittance is 0.8. Consider the S/N ratio of the output of the photometric element in this case. Noise is mainly generated from the light receiving element, and the S/N ratio is generally proportional to the square root of the amount of incident light, so the S/N ratio when the light from each light source is incident on the light receiving element without being attenuated is Based on the standard,
The light from the D2 lamp is reduced to 1/5, so S/
The N ratio has decreased to 1/√5, and the S/N ratio has decreased to 1/√1.25 for the light from the HCL lamp. Even if a sector mirror is used instead of the semi-transparent mirror HM and a neutral filter NF is inserted into the optical path of the D2 lamp (if the D2 lamp is brighter than the HCL lamp) to balance the light intensity of both light sources, one light source cannot be used. (In this example, the light from the D2 lamp) is accompanied by a reduction in the S/N ratio.

The present invention was made for the purpose of solving the above-mentioned problem of the conventional method regarding the balance of the light intensity of two light sources in atomic absorption spectrometry, that is, the problem of a decrease in the S/N ratio. The light is input to the light receiving element through the sample atomization unit without attenuation, and after the output of the light receiving element is separated into signals corresponding to the light of two types of light sources, the amplification degree of both signals is adjusted, resulting in two types of signals. An object of the present invention is to provide an atomic absorption spectrometer in which the light intensity of a light source is balanced. The present invention will be explained below with reference to Examples.

FIG. 2 shows an embodiment of the present invention. D2 is a deuterium lamp, HCL is a hollow cathode lamp, SM is a sector mirror, and DSM is its driving device.
A is a sample atomization part like a flame or a furnace, and MC
is a spectrometer, and PM is a photomultiplier as a photodetector. PA is a preamplifier that amplifies the output of the photodetector PM, and DR is a sector mirror drive device.
This is a signal switching circuit that performs switching operations in synchronization with the rotation of the sector mirror SM using the DSM. L
1, L2 is a logarithmic converter, and L1 outputs the absorbance (including background absorption) of the sample when the output Eh of the preamplifier PA is applied while the light from the hollow cathode lamp HCL is incident on the photodetector PM. , L2 is applied with the output Ed of the preamplifier PA while the light from the deuterium lamp D2 is incident on the light receiving element, and outputs the batho background absorbance. SB is a subtraction circuit that subtracts the outputs of L1 and L2 above to obtain L1.
Eliminate the background absorption term from the output of
DP displays the absorbance of the sample obtained in this way due to the target element.

The above is the basic configuration of the atomic absorption spectrometer, and the parts described below are the parts according to the present invention. S.H.
1 and SH2 are both sample and hold circuits.
CA is an error amplifier, and the reference voltage Er is applied to the lower input terminal in the figure, and the output of the preamplifier PA is applied to the upper terminal. Sample and hold signals are alternately applied to the sample and hold circuits SH1 and SH2 to hold the output of the error amplifier CA. The sample and hold signal is generated from the sector mirror drive device DSM, and is applied to SH1 while the preamplifier PA is outputting the signal Eh in response to the light from the hollow cathode lamp HCL. Further, while PA is outputting a signal Ed corresponding to the light from the deuterium lamp D2, a sample hold signal is applied to SH2. With this configuration, SH1 holds the signal of the difference between the photometric output Eh of the hollow cathode lamp HCL and the reference voltage Er, and SH2 holds the photometric output Ed of the light of the deuterium lamp D2.
The signal of the difference between the voltage Er and the reference voltage Er is held. The signal held in this way is transferred to the voltage-to-voltage converter HT.
The voltage is converted into a high voltage and applied to the dynode of the photomultiplier PM of the photodetector to control the sensitivity of the PM. Sample hold circuit SH1,
There is a changeover switch Sw1 between SH2 and the voltage-voltage converter HT, and the sector mirror drive device
Switching is performed by DSM, and when the light from the hollow cathode lamp HCL is incident on the photodetector PM, the output of SH1 is applied to the converter HT, and when the light from the deuterium lamp D2 is incident on the PM. is SH2
The output of is applied to HT. There is an open/close switch Sw2 between the error amplifier CA and the sample and hold circuits SH1 and SH2, and Sw2 is open during analysis operation.

The operation of the above configuration will be described. Prior to analysis, the switch Sw2 is closed to operate the entire apparatus in a state where there is no background absorption or absorption by sample elements in the sample atomization section A (when a flame is used, there is no flame). While the sector mirror SM is rotating and the light from the hollow cathode lamp HCL is incident on the photodetector, the switch Sw1 is in contact with the contact a side, and the output of the sample and hold circuit SH1 is converted to a high voltage and applied to the dynode of the photodetector PM. applied. S.H.
1 is a hollow cathode lamp HCL as mentioned above.
Since the signal corresponds to the difference between the output Eh of the preamplifier PA and the reference voltage Er, which is proportional to the light intensity of the signal, this feedback circuit acts so that the output Eh of the PA settles down to Er. Similarly, while the sector mirror SM rotates and the light from the deuterium lamp D2 is incident on the light receiving element PM, the switch Sw1 is in contact with the contact b side and the light receiving element PM, preamplifier PA, and error amplifier
The output Ed of the preamplifier PA becomes Er due to the feedback circuit of CA, sample hold circuit SH2, voltage-voltage converter HT, and photodetector PM. In this way, when the switch Sw2 is opened after an appropriate period of time, a signal is sent to the sample hold circuit SH1 such that the output of the preamplifier PA becomes Er when the light from the hollow cathode lamp HCL enters the light receiving element PM without being absorbed. Similarly, SH2 holds a signal such that the output of the preamplifier PA becomes Er when the light from the deuterium lamp D2 is incident on the PM.
When the device is operated with switch Sw2 open, the preamplifier PA responds to the light intensity of the hollow cathode lamp HCL and deuterium lamp D2 in a state where there is no background absorption or absorption by the sample.
The outputs of are equal to each other and are Er. Now, when the sample atomization section is activated and the sample is introduced, the output of the PA becomes Er.
Information including the background absorption and absorption by the sample and information on only the background absorption can be obtained.

FIG. 3 shows another embodiment of the present invention, in which parts corresponding to those in FIG. 2 are given the same reference numerals.
In this embodiment, the light from the deuterium lamp D2 is transmitted to the light receiving element.
The preamplifier is always connected to the PM.
The output Ed of the PA is compared with the reference voltage Er by the error amplifier CA2, and the sensitivity of the light receiving element PM is controlled by the difference between the two. During this period, the gain of the preamplifier PA is set to a certain constant value. In addition, the switch was made with no background absorption or absorption by the sample.
When Sw2 is closed and the device is operated, the sample and hold circuit SH contains a preamplifier when the light from the hollow cathode lamp HCL is incident on the photodetector PM.
The difference between the PA output Eh and the reference voltage Er is the error amplifier.
The gain of the preamplifier PA is controlled so as to be inputted and held through CA1 and made equal to Eh and Er.
During this time, as mentioned above, the feedback circuits of CA2, HT, and PA are operating so that the output Ed of PA corresponding to the light from the deuterium lamp is equal to Er, so in this state, Eh = Ed = I'm becoming Er. Next, when the switch Sw2 is opened, the sample-and-hold circuit SH holds a signal for making Eh equal to Er when there is no background absorption or absorption by the sample. When sample atomization section A is activated (no sample is introduced), the sensitivity of PM increases by the amount of light incident on the photodetector PM that decreases due to background absorption, and Ed remains at a constant value Er. and Eh also increases due to increased PM sensitivity.
Maintained by Er. When a sample is introduced, Ed remains the same as Er, but Eh decreases by the amount of atomic absorption by the sample. Therefore, by logarithmically converting each value and subtracting them, the absorbance due to atomic absorption of the sample can be determined.

The atomic absorption spectrometer of the present invention has the above-described configuration and measures the light from both light sources without any particular attenuation, so the photometric S/N ratio is the highest possible. Since the photometric outputs when there is no background absorption of light from the two light sources or absorption by the sample are approximately balanced, the influence of curvature of the conversion characteristics on logarithmic conversion to determine absorbance is extremely small.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the main parts of a conventional example, and FIGS. 2 and 3 are block diagrams of different embodiments of the apparatus of the present invention. D2...Deuterium lamp, HCL...Hollow cathode lamp, SM...Sector mirror, A...Sample atomization section, MC...Spectrometer, PM...Photodetector, PA...Preamplifier, DR...Signal switching Circuit, L1, L2...Logarithmic converter, SB...Subtraction circuit, SH1, SH2...Sample hold circuit,
HT...Voltage-voltage converter, DSM...Sector mirror drive device.

Claims (1)

[Claims] 1. It has a configuration in which light from a light source that emits bright line spectrum light of the target element and light from a light source that emits continuous spectrum light are alternately transmitted through the sample atomization section, and the light that has passed through the sample atomization section is photometered. The gain of the photometric circuit is adjusted so that the photometric outputs of the light emitted from the two types of light sources and transmitted through the sample atomization section are the same when there is no background absorption or absorption by the sample in the sample atomization section. An atomic absorption spectrometer characterized by comprising means for setting and holding.