SU1453189A1 - Method of atomic-absorption measurements - Google Patents

Abstract

This invention relates to an analytical control technique. The goal is higher sensitivity. In the atomic absorption measurement method, the excitation of a radiation source is carried out by current pulses, varying in amplitude. The selection of the analytical signal is carried out by measuring the atomic absorption coefficients of the analyzed element at different widths of the resonance circuit. The radiation source is excited by a sequence of 4 current pulses. In this case, the first two radiation pulses are recorded at the wavelength of the resonance line of the element being animated, and the third and fourth pulses - at the wavelength of the additional line. According to the analytical signal, separated at the wavelength of the resonance line, and according to the level of attenuation of the intensity of the third radiation pulse, the normalization of the injectivity of the fourth radiation pulse is carried out. The concentration of the element to be analyzed is determined by the increase in the intensity of the radiation from the normalized pulse, observing the following condition 2ulf / & i 4I on / di, where dip, 1 DSP increment of intensities, respectively, of the resonant and additional radiation lines; ui is the increment of the amplitude of the excitation current pulse of the radiation source. 1 il. (L ate with

Description

00

;about

The invention relates to the technique of analytical control of substances and spectral analysis and can be used in the means of atomic absorption spectrometry for the ekspress; analysis of technological products in enterprises of various sectors of the national economy: nonferrous and ferrous metallurgy, chemistry, geology, medicine, etc.

The purpose of the invention is to enhance. sensitivity of atomic absorption measurements.

The drawing shows a block diagram of a device that implements the proposed method.

The device consists of a spectral lamp 1, an atomizer 2, a monochromator 3, which includes the device A wavelength modulation, a photodetector (PMT) 5, a unit 6 for measuring the analytical signal allocated to the resonant line. The input of block 6 is connected by a photomultiplier tube 5, and the output is connected to the first control- ing unit | of the setpoint generator 7 of the fourth impulse amplitude. The background absorption block 8 of the third pulse, the input of which is connected to the photomultiplier 5, is connected via the corrector 9 to the control input of the unit 10 of the amplitude of the third pulse and to the second control input of the unit 7. At the same time, the measuring unit The 11th fourth pulse of the PMT 5 is connected to the recorder 12. The output of the setpoint 13 of the amplitudes of the sequence of two jeHHMX pulses is connected to the outputs of the setters 10 and 7 and connected to the input of the stabilizer 14 of current pulses, the output of which is connected to the spectral lamp 1. yizatsii rows synchrotron devices 4, 6, 7, 8, 10, 11 and 13 are connected to the command device 15.

The method is carried out as follows.

On command from the device, 15 sets the signal in the form of double pulses. This signal is controlled by the stabilizer 14 of the pulsed toKa, on whose travel S this moment is two different amplitudes of the pulse of the excitation current of the Spectral lamp, the amplitudes of the current pulses being chosen so as to ensure that the background absorbance

tg

15

20 25 ao 40

five

due to the effect of broadening of the radiation line. The radiation pulses are allocated by a monochromator 3, the modulation device 4 of which, on command from device 15, is fixed at the value of the wavelength of the resonance line. This ensures the selection of the light signal of the first two points in the resonance line of the element being analyzed. The output light signal is converted by the PMT 5 into an electrical one, which is processed by block 6, at the output of which a control voltage is generated that is proportional to the atomic absorption with allowance for background attenuation on the resonant line. The output voltage from block 6 is fixed for the duration of the third and fourth pulses and arrives at the first control input of the setter 7. Upon completion of the double pulses, a third excitation pulse of the spectral lamp 1 is generated from the device 15 by the sensor 15 and the stabilizer 14, radiation from which it is extracted using modulator 4 at the wavelength of the additional line. From the spectrum of the source of the radiation. No additional line is selected, based on

2 - i,

i 1 i.

Having passed the conversion to the PMT 5, the signal is sent to block 8, which takes into account the background attenuation at the wavelength of the additional line. The signal generated at the output of block 8, through the equalizer 9, controls the amplitude adjusters of the third and fourth pulses (respectively 10 and 7). By controlling the amplitude of the third pulse, the correction is performed according to the compensation principle of the background absorption for the long wave of the additional line and, in addition, a correction signal is generated for the generator 7 of the amplitude of the fourth pulse. Upon termination of the third impulse, a quarter quarter-7 impulse is formed, the initial amplitude of which is equal to the initial anp nN thude of the third impulse. In the process of forming the fourth current pulse, its amplitude increases due to the action of signals received by 31/4

devices 6 and 9. In this case, the control signal from block 6 gives the current increment (and, as a result, light) corresponding to the atomic absorption on the resonance line with the background absorption, and the control signal from the equalizer 9 takes into account the background absorption on additional line wavelength. The light signal generated in such a way — the fourth pulse is released at the additional-line wavelength, is converted into a photomultiplier tube 5 and sent to measuring unit 11, where it is processed and then recorded to the recorder 12. The device is synchronized | Mando device 15.. : Thus, since when working

those devices (FIG. 1) are met

, 1p

 lg

 L1 DyP

 Ji

This increment of the signal extracted in block 11 is twice as large as the signal at the output of block 6, which increases the sensitivity of the measurements, and introducing a correction for the background absorption at the additional line wavelength improves the accuracy of the measurements.

The choice of the amplitudes of the pulses of the excitation currents is determined by the value of the rated operating current for a given type of spectral lamp. At the same time, the amplitudes of the first two pulses are sufficiently rigidly determined, which is due to the ratio of the widths of the resonant line contours necessary to take into account the background absorption (for the lamps of the hollow cathode of the drug type used, the ratio of the amplitudes of currents is about 25 mA and 500 mA). Initially equal. To each other, the amplitudes of the third and fourth impulses: are chosen at the level where the ratio 2R / p is realized.

- lAon / di (for a studied type of drug lamps - this is the amplitude range of currents from 25 to 50 mA). The third pulse serves to take into account the background absorption on the additional line and its amplitude: there is not directly associated with the change in output signals from the photomultiplier: from the first two pulses. The resulting measurement is carried out on four

89

°

five

0

0

The pulse volume allocated to the additional line therefore the control signal for the fourth pulse current is affected by the background absorption correction signal on the additional line and the atomic absorption signal from the first two pulses taking into account the background absorption on the resonance line.

The compensation principle of background absorption correction on an additional line by the third pulse is implemented by comparing the actual signal with the reference signal level corresponding to the initial pulse amplitude. In the presence of a frontal absorption, the recorded signal is attenuated, and a signal of a balance with a reference level is produced. This unbalance signal changes the amplitude of the excitation current of the third and fourth pulses until the unbalance signal generated by the third pulse becomes zero. In this way, the amplitudes of the third and fourth pulses are simultaneously corrected.

The coefficient 2 is determined by the results of experimental studies. As a matter of principle, the larger the coefficient, the higher the sensitivity of the measurements; however, in practice, when studying the spectral distributions of line-emitting sources, it is quite rare that additional lines meet the coefficient 2.

F

formula of invention

The method of atomic absorption measurements, including the excitation of a radiation source by current pulses, changes. amplitude, segregation of analytes. signal by measuring the atomic absorption coefficients of the analyzed element at different widths of the resonant emission line, which differs in that, in order to increase the sensitivity of the measurements, the radiation source is excited by a sequence of four current pulses, the first two radiation pulses being recorded at the wavelength of the resonance line of the element being analyzed, the third and fourth pulses are at the wavelength additionalU53189

by the analytical signal extracted at the wavelength of the resonance line, and by the level of the intensity of the third radiation pulse, they are normalized

jHHe intensity of the fourth radiation pulse, and the concentration of the element being analyzed is determined by

to increase the intensity of radiation of a normalized pulse, observe the following condition

6

41 HD

l

the increment of intensities, respectively, of the resonant and additional emission lines; increment of the amplitude of the excitation current of the radiation source.

Claims (1)

Claim A method of atomic absorption measurements, including excitation of a Radiation source by current pulses, varying in amplitude, extracting an analytical signal by measuring the atomic absorption coefficients of the analyzed element at different widths of the contour of the resonance radiation line, characterized in that, in order to increase the measurement sensitivity, the radiation source is excited by a sequence of four pulses per current, while the first two radiation pulses are recorded at the resonance wavelength the line of the analyzed element, the third and fourth pulses - at the wavelength of the additional line, according to the analytical signal extracted at the wavelength of the resonance line, and the level of attenuation of the intensity of the third radiation pulse, the intensity of the fourth radiation pulse is normalized, and the concentration of the analyzed element is determined by increasing radiation intensity of the normalized pulse, observing the following condition, £ 1p 2 ^d di di where 4140l ~ increment of intensities of the resonant and additional emission lines, respectively; di is the increment of the amplitude of the excitation current of the radiation source.