RU1830556C - Mass spectrometric method of gas mixture composition analysis - Google Patents

Abstract

Usage: the invention relates to analytical chemistry and can be used to control the gaseous medium of active elements of lasers, in microelectronics, and where sensitive and accurate control of the composition of a gas is necessary with its limited amount for analysis. The use of the invention allows to reduce the amount of test gas going for analysis, to increase the sensitivity and accuracy and Informativeness due to more complete use of the mixture being analyzed. The essence of the invention: in the initial period of the gas inlet into the ion source, its flow is intensified by increasing the number of holes in the inlet diaphragm, the mass spectra are scanned repeatedly, when the mass spectra are recorded, the time of occurrence of each peak is recorded, and the intensities of the ion currents of each component are extrapolated time of inlet, based on the dependence of the flow values of each component during inlet on time according to the exponential law and the value of the average ion currents of each component The ones corresponding to the moment of inlet are judged on the composition of the gas mixture. 3 ill. i $.

Description

The invention relates to analytical chemistry and, in particular, to mass spectrometric analysis of the composition of gases.

The invention can / can be used to control the gaseous environment of active elements of lasers, to control gases in microelectronics, and especially where sensitive and accurate control of the gas composition is required with a limited amount of gas being analyzed.

Thus, the aim of the invention is to reduce the amount of test gas and increase the sensitivity,

accuracy and information content due to more complete use of the test mixture.

The invention will be clear from the following example: the analyzed gas (helium-Z + neon-20 mixture) in an amount of 3.95 m3 Pa from an inlet tank with a volume of 1 m3 by molecular flow through the inlet diaphragm, in the form of a gold foil 3 m thick with 48- It was fed into the ion source of an MX 1321 mass spectrometer with openings with a diameter of 6-10 m.

Repeatedly (6 times), mass spectra were recorded with an exact fixation of the time of occurrence of each peak (each comp00

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nents) that has passed since the gas was launched into the ion source. The results are shown in table 1.

The F / V values required for extrapolation were found from the decay of the ion currents of the components without using a sweep. For gels -3, 8833, and for neon-20 F / V-1.5040-. As can be seen, the value (F / V for both -3 gel and neon-20 is 6.7261.

The results of extrapolation of the intensities of each of the peaks (ion currents, Table 1) and the results of statistical processing are given in Table. 2

Thus, the ratio of the ion current of the gel -3 to the ion current of neon-20, equal to 7.2716, was obtained. To find the partial pressure ratio of the components of the mixture, it is necessary to multiply this ratio by the coefficient of relative sensitivity (ORC) of the mass spectrometer for these components,

The results of this analysis are presented in the form of graphs for clarity: for gel -3 in Fig. 1 and for neon-20 in Fig. 2, which shows the change in the intensity of the peaks (ion currents) of the components during gas injection (with six scans of the mass spectrum ) and the extrapolation curves of the intensity of each of the peaks at the time the gas was introduced into the ion source. The time scales for both graphs are the same. In a real representation, the graphs should be combined, but because of the large difference in the intensities of the peaks of the -3 and neon-20 gels, they are presented separately, and the scales along the axis of the ion current intensity are taken different.

To control the reproducibility and accuracy of the method, analyzes of the same helium-3 + neon-20 mixture were performed over a week on a MX1321 mass spectrometer. In each experiment, the same amount of gas mixture equal to 3.95 10 m Pa was used. Obtaining the ratio of the ion current of gel -3 to the ion current of nerna-20 and the average value are given in Table 3.

A second example of the use of the invention was as follows. With the same volume of the inlet reservoir as in the first example, the conductivity of the inlets of the inlet diaphragm (their number) was increased so that for gel -3 F / V it was 6.798 and for neon-20, 634-. A gas (helium-Z + neon-20 mixture) in an amount of 6.59 m3 Pa (i.e., 6 times less than in the first example) was supplied from an inlet reservoir to an ion source. Analysis results and

extrapolations of the intensities of each of the peaks (ion currents) of the components and statistical processing are given in Table. 4.

As a result, the ratio of the ion current of the gel -3 to the ion current of neon-20, equal to 8.8070, was obtained. The gas was taken from a different container than in the first example.

The results of this analysis are also presented in the form of a graph in Fig. 3, which shows the change in the intensity of the peaks (ion currents) of the components during gas inlet (at six scans of the mass spectrum) and the extrapolation curves of the ion currents of gel -3 and neon-20 by the time gas start in

5 ion source.

As can be seen from the comparison of the results of the first and second examples of gas analysis with the same volume of the inlet tank, but with an increase in the conductivity of the holes of the diaphragm by 17.51 times, it allowed reducing the amount of gas for analysis by 6 times while maintaining the accuracy of the analysis.

The advantage of the proposed method can also be understood from the following.

5 comparisons. In the above experiments, with an accuracy of analysis of approximately 1% (including errors due to the mass spectrometer itself, ion current detection system, etc.) to obtain

0 information on the composition of the gas mixture is useful (informative) used 42% and 87.4% of gels -3 and 14.5% and 56% of neon-20, respectively, in the first and second examples, from which to analyze the amount of gas, while

5 time, as in the prototype, with an error of 1% only due to the pressure drop (without error of the measurements themselves) only 1% of gas is used, and the main part (99%) is emitted.

Claims (1)

0 Using the invention, it is possible to determine the composition of the gas mixture with high accuracy for small amounts of gas to be analyzed. The claims 5 A method for mass spectrometric determination of the composition of a gas mixture by which the test mixture is injected into the ion source in the molecular mode through a diaphragm with holes, 0 separation of ions in relation to mass to charge and registration of the mass spectrum, which consists in the fact that, in order to reduce the amount of the test gas and increase the sensitivity, accuracy and information content by making better use of the test mixture, the gas flow is intensified in the ion source in the initial period of the inlet by increasing the number of holes in the diaphragm, repeatedly scan the mass spectra at registration of mass spectra additionally record the time of occurrence of each peak, extrapolate the values of the intensities of the ion currents of each component at the time of inlet based on the time dependence of the flux of each component during inlet: lojHjtie vtj. where j is the index of the component of the mixture; G is the number of the mass spectrum; loj is the ion current j-ro component corresponding to the moment the gas is launched into the ion source. AND; Ijti is the ion current value of the J-ro component at time ti (moment of registration), A; e - the basis of natural logarithms; FJ is the conductivity of the aperture holes for the j-ro component, m3 / s: in this case Fi v ... Fj / const, where Mj is the mass number of the atom (molecule) of the corresponding j-ro component; ti is the time from the moment the gas was launched into the ion source until the moment of registration of the ion current j-ro component of the 1st mass spectrum, s; V is the volume of the inlet reservoir, m3, and the composition of the gas mixture is judged by the magnitude of the average ion currents of each component corresponding to the moment of inlet. Table 1 3 values discarded by stat. processing by the t-criterion at a 95%. table 2 Table 3 Value dropped by stat. processing by meriorium at. 395. UZU 775 Time from the moment M has started Figure 1 Table 4 935 ;  I " 3X7  Yes 1 J 290 280 O 45 225 405 605 785 945 Time since the start of the inlet, (s) Fig 2. b  fa / "C. r 1000 . -AND. And .J-L. . . {00200300 Time since the start of the inlet (s)  ... .Fig. Z. Compiled by G. Chöjemov, Editor S. Kulakova Tehred M. Morgenthal Corrector L. Fil Order 2524 Mintage VNIIIPI of the State Committee for Inventions and Discover at the USSR State Committee for Science and Technology 113035, Moscow, Zh-35, Rauska nab., 4/5