RU2426104C1 - Method of x-ray spectral determination of content of hydrogen, carbon and oxygen on organic compounds and device to this end - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: analysed specimen is X-ray irradiated. X-ray radiation comprises at least two discrete lines in various X-ray spectrum sections. X-ray spectral line intensity in secondary radiation is measured. Note here that measured are intensities of coherent and incoherent dissipated lines of exciting radiation located in short- and long-wave X-ray spectra to derive regression relationship for standard specimen to define content of carbon, hydrogen and oxygen in analysed specimens. ^ EFFECT: higher accuracy, validity and reliability. ^ 7 cl, 4 dwg

Description

The invention relates to the field of analytical chemistry and technical physics, as well as to various fields of science, engineering and technology, where information on the composition of the studied objects is required, and primarily in the study, development of technology and the production of organic compounds.

The invention can be used in analytical and research laboratories that analyze organic compounds, including the determination of hydrogen, carbon and oxygen, since these elements are the main and most important components of these compounds, determining many of their physical and operational properties.

An analogue of the proposed method (methods for determining the content of hydrogen, carbon and oxygen in organic compounds) is the classical Liebig method [1, 2], based on the burning of a sample of the substance in dry oxygen or air, previously freed from water and carbon dioxide vapors, in special tube furnaces . After combustion, gases are passed through pre-weighed calcined calcium chloride, which absorbs water vapor, and soda lime, which absorbs carbon dioxide. By increasing the weight of the absorbers, the mass fraction of C and H in the initial sample is judged (Oxygen is determined by the difference from 100%). The disadvantages of this method are the duration of the process and the low accuracy of the determination of oxygen, determined by the difference from 100%.

A known method of x-ray fluorescence analysis, which allows to determine elements from beryllium to uranium, including oxygen and carbon, which is the closest to the claimed invention and selected as a prototype [3, p.523]. The essence of the known method is to excite the fluorescence spectrum of the test sample with the primary spectrum of an x-ray tube, then decompose the fluorescence spectrum by wavelengths on a crystal analyzer or a multilayer artificial structure (MISE) and record the intensities of the x-ray characteristic lines of carbon and oxygen by an x-ray detector. By the value of the recorded intensities using various techniques receive information about the quantitative content of these elements.

Significant disadvantages of the prototype are low sensitivity, low penetrating ability of their characteristic radiation, leading to a decrease in the reliability of the analysis (when determining light elements (lithium - neon)) and the inability to directly determine hydrogen, the x-ray spectrum of which is completely absent. The reason for this is the low fluorescence yield of these elements, the insignificant depth of the layer in which X-ray fluorescence is formed, the significant absorption of fluorescence by air and elements of the measuring setup, and the absence of X-ray emission spectra for hydrogen and helium. The developed methods of X-ray fluorescence analysis are not applicable for the determination of these elements. Other disadvantages also include the high cost of the equipment, the high error in the determination of hydrogen (by difference) and the need to perform analysis in vacuum, which virtually eliminates the possibility of analyzing volatile compounds.

A known device adopted by the authors for the prototype, all-wave X-ray fluorescence spectrometer S4 EXPLORER company BRUKER AXS [4], which is the closest to the claimed device for implementing an x-ray spectral method for determining the content of carbon and oxygen in organic compounds. The well-known all-wave X-ray fluorescence spectrometer contains a high-power X-ray tube, a vacuum chamber of samples, where the test sample, a crystal analyzer and an X-ray detector are located; which are located in the vacuum chamber of the spectrometer.

A disadvantage of the known device is the low accuracy of determining carbon and oxygen, due to the fact that the probability of a radiation transition (fluorescence yield) for these elements is low (0.002 and 0.006, respectively), the radiation of these elements is strongly absorbed by the elements of the spectrometer, and the fluorescence intensity strongly depends on the quality of the measured surface sample. In addition, the known device has a high cost, since the implementation of X-ray fluorescence determination of carbon and oxygen is possible only on vacuum spectrometers using special crystal analyzers -MIS and flow proportional soft X-ray counters (44.792 and 23.71 Å); as a result, such spectrometers are the most expensive in the market of x-ray analytical equipment. The determination of hydrogen on these spectrometers is impossible, since hydrogen does not have x-rays.

The technical result of the claimed group of inventions is to increase the accuracy, reliability, reliability and cost of the device and the method for determining hydrogen, carbon and oxygen in organic compounds implemented on it.

The claimed group of inventions is aimed at achieving a single technical result and is free from these disadvantages.

The specified technical result is achieved by the fact that in the method of x-ray spectral analysis of determining the content of hydrogen, carbon and oxygen in organic compounds consisting of carbon, hydrogen and oxygen, based on the irradiation of the sample with x-ray radiation, in which there are at least two discrete lines in different parts of the x-ray spectrum, and measuring the intensity of the x-ray spectral lines of the secondary radiation emitted by the sample, in accordance with the claimed image HAND measured intensity of coherently and incoherently scattered excitation radiation lines arranged in the short and long wavelength ranges of the spectrum and the X-ray intensity and the ratio of intensities of these lines build regression dependence on standard samples, and it determines the carbon content, hydrogen and oxygen in the samples.

In addition, the indicated technical result is achieved by the fact that Ka1 or Kb1 lines of elements with atomic numbers Z from 37 (Rb) to 47 (Ag) located in the spectral energy range from 13 to 25 keV are used as short-wavelength lines of the primary spectrum, and in As the lines in the long-wavelength region of the spectrum, Ka1 or Kb1 lines of elements with atomic numbers Z from 22 (Ti) to 30 (Zn), located in the energy range from 4.5 to 10 keV, are used.

In addition, this technical result is achieved by the fact that, as the x-ray characteristic lines, a gamma line of Fe ⁵⁵ radioisotope sources located in the long-wavelength range of the X-ray spectrum and Cd ¹⁰⁹ located in the short-wavelength range of the X-ray spectrum are used.

In addition, the specified technical result is achieved by the fact that when determining the elemental composition of the sample, the coefficients calculated on the basis of the fundamental parameters of the interaction of radiation with the substance are used as regression coefficients.

The specified technical result is also achieved using a device for determining hydrogen, carbon and oxygen in organic compounds, containing an x-ray tube, the holder of the test sample, a crystal analyzer, an X-ray detector and a personal electronic computer, in which, in accordance with the claimed invention, between the window of the x-ray tube and the test sample placed in the holder, replaceable secondary emitters are installed, from elements with atomic numbers Z from 39 (Y) to 47 (Ag), whose characteristic lines are located in the short-wavelength region of the X-ray spectrum and from elements with atomic numbers Z from 22 (Ti) to 30 (Zn), whose characteristic lines are located in the long-wavelength region of the X-ray spectrum.

In addition, this technical result is achieved in that the device further comprises a semiconductor detector located between the holder of the test sample and a personal electronic computer

In addition, this technical result is achieved by the fact that in front of the window of the x-ray tube a secondary emitter is installed, consisting of two layers of chemical elements with a thickness of 1 to 15 μm, while one of the layers is made of a chemical element in the range of atomic numbers Z from 39 (Y) to 47 (Ag), and the other layer is from an element in the Z range from (Ti) to (Zn).

At the same time, to determine the light elements by X-ray spectroscopy methods, other physical processes are used than in the known methods that arise during the interaction of X-ray radiation with a substance, namely, coherent and incoherent scattered X-ray radiation by objects of analysis, the composition of which is mainly formed by light elements. Significantly different dependences of the intensities of coherent and incoherently scattered radiation on the atomic number, especially pronounced for light elements, allow the analysis of two- and three-component materials based on these elements, including the determination of hydrogen, on X-ray spectrometers without using vacuum. This is especially important when analyzing volatile organic compounds, especially liquids and gases.

The problem is solved by the proposed method for X-ray fluorescence analysis of organic compounds consisting of carbon, hydrogen and oxygen, including irradiating the test sample with X-ray radiation containing characteristic lines of chemical elements in the energy range from 4.5 (Ti Ka) to 22.2 keV (Ag Ka) and measuring the intensities X-ray spectral lines of secondary radiation emitted by the sample.

In contrast to the prototype, in the proposed method, in order to be able to additionally determine hydrogen, increase the representativeness of the analysis and conduct it in air using a conventional energy dispersive or wave dispersive X-ray spectrometer with a limited spectral range, the intensities of coherent and incoherently scattered characteristic lines of the exciting radiation located in short-wave (from 10 to 23 keV) and long-wave (from 4.5 to 10 keV) ranges of the X-ray spectrum, and using the linear regression coefficients of the regression equation, the factors of which are the intensities of the coherently and incoherently scattered lines and their relations, they judge the elemental composition of the sample.

To perform an analysis of samples of organic compounds in an X-ray spectrometer, a secondary X-ray emitter made of elements with atomic numbers from 39 (Y) to 47 (Ag) is installed between the X-ray tube and the sample to be measured for coherently and incoherently scattered radiation in the short-wavelength region of the spectrum then, between the window of the x-ray tube and the test sample, a secondary emitter 2 is installed, made of elements with atomic numbers from 22 (Ti) to 30 (Zn), for Reference measurements coherently and non-coherently scattered radiation in the wavelength region of the spectrum, and the measured intensities of determining the content of hydrogen, carbon and oxygen in the samples of organic compounds.

The goal is also achieved by the claimed method and device, in which:

- the anode of the x-ray tube is made of a chemical element in the range of atomic numbers Z from 39 (Y) to 47 (Ag), and a secondary emitter is installed in front of the window of the x-ray tube in the form of a foil from the element in the range Z from 22 (Ti) to 30 (Zn) the thickness of which is chosen so as to pass a significant portion of the characteristic radiation of the anode;

- the anode of the x-ray tube is made of a chemical element in the range of atomic numbers Z from 22 (Ti) to 29 (Cu), and a secondary emitter is installed in front of the window of the x-ray tube in the form of a foil from an element in the range Z 39 (Y) to 47 (Ag), the thickness of which is chosen so as to pass a significant fraction of the characteristic radiation of the anode;

- the anode of the x-ray tube is made of an alloy of two chemical elements, one of which is located in the range of atomic numbers Z from 39 (Y) to 47 (Ag), and the other in the range of Z from 22 (Ti) to 30 (Cu);

- in front of the window of the X-ray tube, a secondary emitter is installed, consisting of two layers of chemical elements, the first layer is made of a chemical element in the range of atomic numbers Z from 39 (Y) to 47 (Ag), and the second layer is made of an element in the range Z from 22 ( Ti) up to 30 (Zn), while the thickness of the second layer is chosen so as to pass a significant fraction of the characteristic radiation of the first emitter;

- a secondary emitter consisting of two layers of chemical elements is installed in front of the x-ray tube window, the first is made of a chemical element in the range of atomic numbers Z from 22 (Ti) to 30 (Zn), and the second layer is made of an element in the range of Z from 39 (Y ) to 47 (Ag), while the thickness of the second layer is chosen so as to pass a significant fraction of the characteristic radiation of the first emitter.

Such technical solutions are implemented on an airborne X-ray spectrometer using a simple LiF200 crystal analyzer and sealed gas-filled proportional counters for hard X-ray radiation.

To improve the quality of measurements of x-ray intensity in the short-wavelength region of the spectrum, it is proposed to use a semiconductor x-ray detector, since this will allow obtaining better resolution of coherently and incoherently scattered radiation.

The claimed group of inventions allows to eliminate the main disadvantages of the prototype due to the greater likelihood of a radiation transition for the K-levels of secondary emitter elements (from 0.22 for titanium to 0.83 for silver), as well as the possibility of using cheaper equipment compared to the capabilities of the prototype. However, in the claimed invention, hard x-ray radiation of the secondary emitter elements is less critical to the surface quality of the test sample.

Identified distinguishing features in the proposed solution, as well as their relationship, were not found in the solutions known in science and technology by the filing date of the application, therefore, the claimed technical solution meets the criterion of “significant differences”.

The intensity of the scattered radiation, determined by the elemental composition of the analyzed material, is proportional to the ratio of the mass differential scattering coefficient to the mass attenuation coefficient:

where dσ _cg , dσ _nc and μ are linear functions of mass fractions of elements c ₁ , c ₂ and c ₃ .

Given the condition c ₁ + c ₂ + c ₃ = 100%, we obtain three equations, the solution of which with known scattering and attenuation coefficients will allow us to find the concentrations of the controlled elements. In the general case, using calibration samples of known composition, the least squares method (least squares) allows one to construct a calibration equation for a three-component system without knowing the interaction coefficients.

As a theoretical justification for the implementation of the claimed method, the values of the differential scattering coefficients at a scattering angle of 90 °, usually used in X-ray spectrometers, calculated from the expressions given in [5, 6] and the attenuation coefficients for the CuKα lines 1.542 Å is the long-wavelength region of the spectrum) and PdKα (0.5869 Å is the short-wavelength region of the spectrum) for H, C, and O.

Table 1. Items CuKα Pdkα N FROM ABOUT N FROM ABOUT dσ _cg , cm ² / g 0.000194 0.00627 0.00987 2.735 ∗ 10 ^-7 0.0016278 0.002202 dσ _nc , cm ² / g 0.02281 0.00844 0.008155 0.02191 0.0102567 0.009894 µ _cg , cm ² / g 0.3915 4.5437 11.4512 0.3674 0.4038 0.7662 µ _nc , cm ² / g 0.392 4.7582 11.997 0.3686 0.4333 0.8438

To evaluate the proposed method, we considered arrays of sample models of two and three-component organic compounds for calibration (for example, 23 samples) and to evaluate the correct determination of the composition (for example 11 samples).

To verify the correct determination of the required elements, we used models of various organic compounds: hydroquinone, glucose, sugar, starch, phenol, alizarin, butyl alcohol, stearic, citric, oxalic acid, benzophenone.

For these samples (two and three-component organic systems), the intensities of the coherently and incoherently scattered lines of PdKα and CuKα were calculated using the data in Table 1 and using the formulas:

.

.

For calibration, an equation of the general form was used:

Ci = a ₀ + ∑a _j I _j + b ₁ I _Cunc / I _Cucg + b ₂ I _Pdnc / I _Pdcg

The ranges of element contents in calibration samples and the obtained standard deviations (S ₀ ,%) for calibration characteristics by analytes are shown in table 2.

Table 2. Analit C _Min ,% C _max ,% S ₀ ,% N 5 fifteen 0.04 ABOUT 0 55 0.23 FROM 40 95 0.25

, % и

, % - средниеThe ranges of element contents in models of organic compounds for determining the composition and the results of determining the composition (

% and

,% - average

absolute and relative deviations of the calculated contents from the original) are given in table 3.

Table 3. Carbon Hydrogen Oxygen C _min = 26% C _max = 86,% C _min = 2,% C _max = 14% C _min = 8,% C _max = 58,%

, %

%

%

%

%

%

%

%

%

% 57.22 0.14 0.24 6.59 0.013 0.20 36.19 0.091 0.25

From the table it follows that the average relative deviations do not exceed 0.25%.

The experimental calibration was carried out on a SPECTROSCAN MAX-GV portable X-ray scanning spectrometer. We used a BHV-17 X-ray tube (Pd anode), in the spectrum of which there is a pronounced copper line, a LiF crystal analyzer [200], a primary radiation incidence angle of φ = 55 °, a fluorescence emission angle of ψ = 40 °, respectively a scattering angle of яния = ψ + φ = 95 °. The intensities of the PdKA, Pdnc, CuKA, and Cunc lines were measured in the second reflection order at a voltage of 40 kV on the anode of the x-ray tube and a current strength of 4 mA at an exposure time of 100 s.

Figure 1 shows the x-ray spectra of the second order of reflection for coherently and incoherently scattered lines of copper (a) and palladium (b), measured on aspirin, plexiglass and polyethylene.

Table 4 shows the compositions of organic compounds by which the experimental verification of the method was carried out.

Table 4. Substance Formula % H % O % C one Paraffin C ₁₈ H ₃₈ 15.05 84.95 2 Polyethylene CH ₂ 14.37 85.63 3 Propyl alcohol C ₃ H ₇ OH 13.41 26.62 59.96 four Methyl alcohol CH ₃ OH 12.58 49.93 37.49 5 Plexiglass C ₅ O ₂ H ₈ 8.05 31.96 59.98 6 Sugar C ₁₂ H ₂₂ O ₁₁ 6.48 51.42 42.11 7 Naphthalene C ₁₀ H ₈ 6.29 93.71 8 Boric acid H ₃ BO ₃ 4.89 77.63 17.48 (B) 9 Aspirin C ₉ H ₈ O ₄ 4.48 35.52 60 10 Alizarin C ₁₄ H ₈ O ₄ 3.33 26.67 70 eleven Maleic acid C ₄ H ₄ O ₄ 3.47 55.14 41.39

The correlation of theoretical and experimental intensities for Cunc is shown in figure 2. The correlation coefficient g was 0.9996.

An example of a calibration dependence for the determination of hydrogen in organic compounds is shown in Fig.3.

The ranges of element contents in the studied samples of organic compounds and the obtained standard deviations (S ₀ ,%) for calibration characteristics by analytes are shown in table 5.

Table 5. Analit C _Min ,% C _max ,% S ₀ ,% H 3.5 15.5 0.20 O 0 78 1.00 C 0 86 1.41

From the table it follows that satisfactory standard deviations for the calibration characteristics are obtained.

Figure 4 shows a diagram of an x-ray spectrometer, allowing to implement the proposed method.

The spectrometer for determining light elements in organic compounds shown in Fig. 4 includes an X-ray tube (1), a secondary emitter (2), a sample holder (3), a LiF200 crystal analyzer (4), an X-ray detector - a sealed gas-filled counter (5), PC (6), semiconductor detector (7).

The claimed device operates as follows.

The primary x-ray radiation of the x-ray tube (1) is incident on the secondary emitter 1 (2), which converts the primary x-ray radiation into short-wavelength characteristic radiation with a wavelength corresponding to the material of this emitter. This monochromatized radiation is scattered on the surface of the test sample placed in the holder (3), and a semiconductor detector (7) is incident on which the scattered radiation is divided into coherent and incoherent components and the intensity of these components is recorded. The signal registered by the detector enters the PC (6). Then install the secondary emitter 2 (2), which converts the primary x-ray radiation in the long-wavelength characteristic radiation with a long wavelength corresponding to the material of this emitter. This monochromatized radiation is scattered on the surface of the test sample placed in the holder (3), and gets on the crystal analyzer (4), on which the scattered radiation is divided into coherent and incoherent components, the intensity of which is detected by the detector (5). The signal registered by the detector enters the PC (6). Using a linear regression coefficient equation with respect to the coefficients of a personal computer, the factors of which are the intensities of coherently and incoherently scattered lines in the short-wave and long-wave spectral regions and their ratios, the elemental composition of the sample is determined and the content of hydrogen, carbon, and oxygen in the studied samples is determined.

Information sources

1. Pryanishnikov ND Workshop on Organic Chemistry. State Scientific and Technical Publishing House of Chemical Literature, M., 1956

2. Elemental analysis of organic compounds. Federal Agency for Education. Ekaterinburg University, Department of Chemistry, Department of Organic Chemistry. Yekaterinburg, 2008

3. Mosichev V.I., Nikolaev G.I., Kalinin B.D. Metals and alloys. Analysis and research. Atomic spectroscopy methods. Atomic emission, atomic absorption and X-ray fluorescence analysis: Ref. St. Petersburg: NPO Professional, 2006, 716 p. (prototype for the method).

4. X-ray fluorescence spectrometer S4 EXPLORER company BRUKER AXS. Prospectus of the company http // www.bruker.ru (prototype for the device).

5. R. I. Plotnikov, G. A. Pshenichny, Fluorescence X-ray radiometric analysis. M., Atomizdat, 1973, p.16-18.

6. G.V. Pavlinsky. Fundamentals of X-ray physics. M., Fizmatlit, 2007, p. 95-113.

Claims (7)

1. The method of x-ray spectral analysis of determining the content of hydrogen, carbon and oxygen in organic compounds consisting of carbon, hydrogen and oxygen, based on the irradiation of the sample with x-ray radiation, in which there are at least two discrete lines in different parts of the x-ray spectrum, and measuring the intensity of the X-ray spectral lines of the secondary radiation emitted by the sample, characterized in that they measure the intensities of coherently and incoherently scattered lines ozbuzhdayuschego radiation disposed in the short and long wavelength ranges of the spectrum and the X-ray intensity and the ratio of intensities of these lines build regression dependence on standard samples, and it determines the carbon content, hydrogen and oxygen in the samples. 2. The method according to claim 1, characterized in that Ka1 or Kb1 lines of elements with atomic numbers Z from 37 (Rb) to 47 (Ag) located in the spectral energy range from 13 to 25 keV are used as short-wavelength lines of the primary spectrum, and as lines in the long-wavelength region of the spectrum, Ka1 or Kb1 lines of elements with atomic numbers Z from 22 (Ti) to 30 (Zn) are used, located in the energy range from 4.5 to 10 keV. 3. The method according to claims 1 and 2, characterized in that as the x-ray characteristic lines use a gamma line of radioisotope sources Fe ⁵⁵ located in the long wavelength range of the X-ray spectrum, and Cd ¹⁰⁹ located in the short wavelength range of the X-ray spectrum. 4. The method according to claim 1, characterized in that when determining the elemental composition of the sample, the coefficients calculated on the basis of the fundamental parameters of the interaction of radiation with the substance are used as regression coefficients. 5. A device for determining hydrogen, carbon and oxygen in organic compounds, containing an x-ray tube, the holder of the test sample, a crystal analyzer, an x-ray detector and a personal electronic computer, characterized in that between the window of the x-ray tube and the test sample, placed in holder, replaceable secondary emitters are installed, from elements with atomic numbers Z from 39 (Y) to 47 (Ag), whose characteristic lines are located in the short-wavelength region of the X-ray spectrum and from elements with atomic numbers Z from 22 (Ti) to 30 (Zn), whose characteristic lines are located in the long-wavelength region of the X-ray spectrum. 6. The device according to claim 5, characterized in that the device further comprises a semiconductor detector located between the holder of the test sample and a personal electronic computer. 7. The device according to claim 5, characterized in that in front of the window of the x-ray tube a secondary emitter is installed, consisting of two layers of chemical elements with a thickness of 1 to 15 μm, while one of the layers is made of a chemical element in the range of atomic numbers Z from 39 ( Y) to 47 (Ag), and the other layer is from an element in the Z range from (Ti) to (Zn).

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