SU1518684A1 - Spectral method of determining concentration of substances and atomic-absorption analyzer - Google Patents

Abstract

The invention is intended for use in atomic absorption spectral instrumentation. The purpose of the invention is to improve the measurement accuracy by minimizing the noise of photodetectors. The method consists in the fact that simultaneously with the working signal an additional signal is also recorded, and in the process of measurements the difference between their intensities is adjusted so as to obtain a constant value of the total recorded by the photoreceiver signal. The signal of the spectral lamp 1 is fed to the input of the photodetector 5, which also receives the signal of the correction source 11. The signal level of the source 11 is set by the source 9 of the reference voltage through the amplifier 10 power. The feedback circuit, acting from the output of the buffer amplifier 6, stabilizes the total light signal at the input of the photodetector 5. The signal taken from the output of the differential device 7 is a recording operating signal. Due to the constant level of the light signal at the input of the photodetector 5 with any changes in the flux of the lamp 2, the final contribution of noise to the measurement result is minimized. 1 il.

Description

one

(21) 4378831 / 31-25; 4378847 / 31-25

(22) 02.16.88

(46) 10/30/89. Bul P 40

(71) Belarusian State University. V.I. Lenin

(72) K.P.Kureychik, G.V.Valeev and M.M.Mavlyutov

(53) 535.853 (088.8)

(56) USSR author's certificate

N 1068731, cl. G 01 J 3/42, 1983.

USSR author's certificate N 705266, cl. G 01 J 3/42, 1978.

USSR author's certificate N 71 1441, cl. G 01 J 3/42, 1979.

USSR author's certificate N 700787, cl. G 01 J 3/42, 1978..

(54) SPECTRAL METHOD FOR DETERMINING THE CONCENTRATION OF SUBSTANCES AND ATO SHO-ABSORB-PION ANALYZER

(57) The invention is intended for use in atomic absorption spectral instrumentation. The purpose of the invention is to improve the accuracy of measurements by minimizing the noise of photoaccelerators. The method consists in the fact that simultaneously with the working signal, the additional signal is also recorded, and during the measurement the difference between the intensities is adjusted so as to obtain a constant value of the signal accumulated in total by the photoreceiver. Spectral signal (L

lamp 1, is fed to the input iJ) oTo- receiver 5, which also receives the signal of the correction source 11. The signal level of the source 11 is set by the source 9 of the reference voltage through the amplifier 10 power. The feedback circuit, acting from the output of the buffer amplifier 6, stabilizes the total light signal

at the input of the photodetector 5. The signal taken from the output of the differential device 7 is a register

working signal. Due to the constant level of the light signal at the input of the photodetector 5 at any time and any change in the flux of the lamp 2, the final contribution of noise to the result of measurement 1

minimized, 1 Il.

The invention relates to technical physics and is intended for use in atomic absorption spectral instrumentation.

The purpose of the invention is to improve the accuracy of measurements of the condensation of insects by reducing the contribution of photo receiver noise.

Figure 1 shows the block diagram of the device; 2 shows timing diagrams for the operation of the device.

To implement the method for determining the concentration of substances, it is necessary to successively deliver two current pulses of smaller and larger amplitude to the radiation source. The light fluxes that have passed through the analytical cell are denoted by I, and 1. The light flux of the additional source is denoted by IQ. Suppose that 1 TO, and 1; 1o, 1 og light fluxes of the working radiation source falling on the analytical cell.

The atomic absorption coefficient is denoted by (K, and the concentration of the analyte is denoted by C. The fluctuations introduced by the photomultiplier are denoted by c, a, i, and the first and second cases.

In view of the above, the concentration of the substance for the prototype is determined. To do this, write the system of equations

I, H, -

-fu.c

 T

1 og

-fU-zc

  .

Consolation Log - AU +121

t W (i (v

(2)

no equations from another have

& D In-i - ln- | -22-; & | c, -fU2

S F1

S f f

It can be seen that the member In-l- / fu will

Sf2 v

tend to zero if ftp, / or t M is co. The latter is not feasible due to physical limitations. Therefore, it is necessary to obtain equality

VI means that with

The first and second measurements, the magnitudes of the fluxes incident on the photodetector, must be equal. This is achieved as follows. Before measurements, the intensity "by adjusting the reference voltage is set so that Ig 7 IQI; la I. Then you can write that with the total registration

M, 1, - I,; M I - 1 (3)

oo

Therefore, to ensure minimization of the effect of fluctuations in expression (2), it is necessary to maintain the difference M I a - I.

The device contains a power supply unit 1 for a spectral lamp, an optical system 3, an atomizer 4, a photodetector 5, a buffer amplifier 6, a differential stage, a recording system 8. The output of buffer amplifier 6 is connected to one of the inputs of power amplifier 10. As the latter, a differential amplifier (operational amplifier) can be used, supplemented by a powering output stage on a transistor. A source 9 of the reference voltage is connected to the second input of the power amplifier. The output of the power amplifier is connected to a source of corrective radiation 11, the luminous flux of which through system 3 enters the photodetector. System 8

515

The recorder contains a device 12 for separating 1 mp. (in Fig. no block 12 synchronization signals are given). The output of block 12 is connected to the inputs of the harmonizers 13 and 14. Their outputs are connected to a subtractor 15, which is loaded on a digital display 16 (for example, a digital voltmeter).

The device works as follows.

Block 17 performs the functions of a pulse generator and synchronizes all the blocks. Unit 17 may, in the forward case, be implemented on two generators of the type G5-54, connected via a synchronization input. Block 17 generates pulses shown in Fig. 2 (plot a), which control block 1. The latter produces pulses of the lead type in Fig. 2 (plot a). In the simplest case, the block can be performed on two transistors, in the collectors of which the lamp 2 is connected, and the bases are connected to the synchronization outputs of block 17. At the same time, the signal change on the bases of the transistors of block 1 is shown in FIG. 2 (egpore a).

Fig. 2 (plot b) shows an exemplary view of the luminous flux emitted by the lamp 2. It can be shown that the concentration of the element being detected at durations c, and t2 is significantly different, with t-,) L., Defined by the following formula

1 ya

g AD l2

 bfU

where & D is optical density;

4 (11 is the difference between the atomic absorption coefficients; bf |) bfg of photodetector fluctuations

 at illumination by light streams F, and F.

It can be seen that in order to reduce the measurement errors caused by the influence of cf fluctuations and (pj of the photodetector 5, the equality Φ must be fulfilled (rfi- This is achieved in a measurable way. In the absence of a sample in the atomizer, the intensity of the source 1 1 by means of reference source 9 and power amplifier 1 O is set so that, and (Fig. 2, plot b). For this purpose, the feedback from the output of block 6 to the input of block 10 is temporarily disconnected. After its restoration to the input of block 10, the post

4 6

 total signals; el JI; IMTI 2 and 11; If, for example, inteisis (Ilios. of lamp 2 increases, then, in the reverse of the connection, the intensity of the source 1 1 is lost and vice versa (Fig. 2). As a result the input of the photodetector is 5 ps / ii-rginae rc)) the variable resorption of flashes, which leads to equality, ---, -.

TaKia, when rutulirovanii

the intensity of the block I 1, the signal L I, or i 12 always adds to the total; light signal up to the value of i ,.

Simultaneously at the entrance of pa: nail C

cascade 7 comes from: the legal from the output of block 6 and the output of amplifier 10 power. Since iiocj e; i: Hii sngngs is proportional to D, 1UIH LTL on the differential Kagkala 7 1I |.-Ts isKOMV .m signature, or ,, iio iklo ;; un. - my photodetector and these signals are the same. After splitting the slice ;: shedloi block 12, they logarithm yy. The bars 13 and 14 are subtracted by block 15 and are indicated by block 16.

Thus, the way it is (- t in the m o r about the ycTpoiicTRa gi ed ip 1ttottstnom is more likely to be measured at the expense of the com; ;( M1 (: ,

contributed by a photomultiplier.

Formula and about b D e i about n and

one . The spectral oprelomol and the BeuiPCTH contrast are computed, and the INTONSIPNOS 1 is measured using the KIITO instrument. .lafMiiiUv

LNGs of falling and about pg. The slich loop analytite is a total and determined by calculation method. 1Y at, about tl and h and y y and i; with that then with

In order to improve the accuracy of i-Yureiin, the working signals measure the oddish pc with an additional light signal, the intensity of which before measurements is not set to N HbL; e and the intensity of the largest working signal, while the intensity of the additional signal is set equal to the current difference between initial intensity and intensity of the recorded operating signal.

2. An atomic absorption analyzer containing at least one spectral lamp with a PNT block, an optical system, an atomizer, a dwTo receiver, a buffer amplifier, and a recording sweep, characterized in that, for the purpose of noff. (-ibno contains a source of corrective radiation, a power amplifier, a reference voltage lag, and a differential stage, with the input of the differential stage connected to the input of the recording system, the outputs of the buffer amplifier and the source of reference voltage are connected rows power amplifier whose output is connected to a source of corrective radiation and odno1u input of the differential stage, the second input of which is coupled to the output of the buffer amplifier, the correction radiation source input coupled to the output of the atomizer.

Srig.G.

Claims (2)

Formula and sample <> N and I 1. The spectral method for determining the concentration of substances, according to which the intensity of the incident and spill signals is measured, most of the time the analytical cell is calculated and the desired result is calculated by calculating the result, in order to increase the measurement accuracy, working signals are measured simultaneously with an additional light signal, the intensity of which before measurements is set not less than the intensity of the largest working signal, while in the process of measuring the intensity of the additional signal is set equal to the current difference between its intensity and the intensity of the detected operation signal. 2. An atomic absorption analyzer containing at least one spectral lamp with a power supply, a ttic system, an atomizer receiver, a buffer amplifier, the topic of registration, which is important because, in order to measure the accuracy, , but it contains a source of corrective radiation, a power amplifier, a reference voltage source and a differential stage, the input of the differential stage being connected to the input of the registration system, the outputs of the buffer amplifier and the reference voltage source are connected to the corresponding inputs of the amplifier of Tell power and whose output is connected to the correction radiation source and to one of the inputs of the differential stage, the second input of which is connected to the output of the buffer amplifier, while the source of corrective radiation input coupled to the output of the atomizer.