SU1341556A1 - Method of measuring concentration of impurity - Google Patents

Abstract

This invention relates to analytical chemistry, in particular to emission spectral analysis methods. The goal is to improve measurement accuracy while reducing measurement time. Sample radiation, excited by a light source, is transmitted to two photodetectors, the output signals of which are measured. The concentration of the object is determined by the calibration curve based on the measured signal ratio of both photodetectors. The error is eliminated by measuring the parameters of the sample with time, since the comparison of the radiation intensity of the object and the internal standard is carried out at the same time. In order to eliminate the error due to changes in sensitivity, the ratio of signals from photo detectors is normalized to the ratio of signals from these same photodetectors. Concentration is measured by the formula: C C, / (W-and,), - and „./ (i and, d) where Uo, and and are the signals of the main detector when measuring the reference; And (, g and | - the signal of an additional detector when measuring the reference, U, Ui, Uo2, U are similar values for the measurement with the sample. 1 ill. I (L with 4 O SP 3t

Description

eleven

The invention relates to analytical chemistry and emissive ry spectral analysis with measurement of Raman radiation lines and can be used in chemical production to control the composition of the products obtained, in particular compounds of scheelite.

The aim of the invention is to improve the measurement accuracy while reducing the measurement time.

The drawing shows schematically a device for implementing the proposed method.

The method consists in the following. : Since the concentration of impurity C is determined by the ratio of maximum intensity I, the Raman line of the impurity to the maximum intensity of the Raman line of the main product, which is compared with the calibration. addiction, i.e.

(one)

C K i

2

In the proposed method, the scanning of the entire CR spectrum of the sample is replaced by measuring the CR intensity at a frequency corresponding to I, and at a frequency 2 corresponding to 1. In (1 K-coefficient.

In addition, in order to eliminate the error associated with changes in the sample and in the environment during the time between measurements I and I, measurements of both signals are carried out simultaneously using two photodetectors.

In order to increase the error associated with the differences in changes over time in the conditions of both channels, including changes in the optical transmission coefficient of the optics, the sensitivity and dark current of the photodetectors (AF), etc. Calibration based on the scattered radiation of the excitation source of the RS was introduced.

Let be

U, (t) -K, (t) l,; Ujt) Kjt) l ,, (2)

where K, (t) and K (t) are the time-dependent sensitivity coefficient, respectively, of the PT, measuring the intensity of the Raman line of the impurity, and of the AF, which measures the peak intensity of the Raman line of the main product, U, (t) and Ujjlt) the voltages at the inputs of the meters correspond to the channels. Denoting the time-dependent transmissions corresponding to the cx channels) and T (t), we obtain

u, (t) K, (t) T, (t) T; i,,.

DZJtT K JtjT JtTT; ;

where T and T are the transmissions of neutral attenuators placed in front of the corresponding OP to obtain a signal in the range in which the meter provides the minimum measurement error. The transmission of neutral spectral attenuators varies with time by no more than 10, and

five

0

of time.

If the radiation of the excitation source of the RC with intensity 3 at the maximum of the excitation line at frequency 5 is applied to both phase transitions by the Relele mechanism and the corresponding transmission values of neutral attenuators T and T are selected, then instead of (3) we get

 Wo., Y9.1, (

NO

Uo2 (to)

to ft TT ff TT

g iv o M g about /

TG "

2

vb.

I

(four)

Since the time between the measurements of N and NO is 1-3 s, the changes in K, T, T and T during this time are insignificant, i.e. you can accept tt (,. Note that if the proposed method does not match by 1-3 s the concentration measurement time and the correction time for the slow relative drift of the channel characteristics, then for one AF the measurement moments 1 and 1 do not match at the same time, which introduces a large error. Dividing (3) by (4), taking into account () we get

and, and.

S-K

and, and

(3)

t t

where b is a constant value. T, ij

By replacing a sample with a known concentration of impurity Cd instead of a sample and measuring the corresponding signals U,, and 2, UQ ,, U () ,,. We find the final expression for the measured concentration ™:

x

and,. and,

and, t

I) og

, s

and

,

and",

(6)

55

And p im. The radiation of a light source with a frequency excites a CR in sample 2. The radiation of a CR is divided into two detection channels, primary and secondary. In front of the photodetectors of both channels, a frequency selector 3 is placed, having two rigidly fixed positions relative to both photodetectors. In the first position, element 3 transmits to the main photodetector only radiation of a CR with a frequency of V, J to an additional photodetector — only radiation of a CU with a frequency of where –3, and -Oj is the frequency of the maximum intensity of the CI, respectively, of the impurity and main product. Element 3 consists of four consecutively interfering light filters, the first of which has a maximum transmission at the frequency, the second at O, the third and fourth at about -On the first position of the selector 3, the first filter is located in front of the photodetector 4, the second - in front of the photoreceiver 5, the third and fourth are located outside the optical path of the radiation KP. In the second position of element 3, the first and second filters are removed from the optical path of the measured radiation, the third filter is located in front of the photodetector 4, the fourth - in front of the photodetector 5. Since the intensities 1, 1 and I, j and the sensitivity of the photodetectors 4 and 5 can vary significantly from filters Equipped with selected attenuator so that the signals of both photodetectors in both positives of element 3 are close and have a value close to the upper boundary of the selected input range of meters 6 and 7. This ensures The minimum and approximately equal relative errors of measurements of the output signals of the photoreceivers 4 and 5 are found. The entire set of interfering and neutral filters is fixed on a moving frame, which is fixed. Since the signal of the impurity and the main product is measured at the same time and is carried out

correction of changes in channel sensitivity, eliminated the effect of drift and instability.

Claims (1)

Invention Formula A method for measuring impurity concentrations, including exposure of a sample of a source of radiation to a sample, registration of an impurity with a main detector of radiation intensity in the spectral interval d, registration of the main product with an additional detector in the spectral interval nd, calibration using a reference concentration a sample with a known content of impurity C, characterized in that, in order to increase the measurement accuracy while reducing the measurement time, after measurements with an object and after measurements with a standard, not both detectors emit radiation in the spectral interval d) coinciding with x or signals the detectors are measured separately, and the concentration of the impurity GX is found from the extrusion  . „E and., Uo, U, .Uo, S. - (C) c-7u--, Uf J02 de and 0 ( and and and 02 And and. and, and ,,, and, the signals of the main detector when measuring with a reference, respectively, in the spectral interval L- and l-5, I, the signals of an additional detector when measuring with a reference, respectively, in the spectral intervals, are the same values when measuring k with the sample. gp 97  V V2 yj