RU2730954C1 - Method of measuring mass concentrations of niobium and tantalum in air of working zone by mass spectrometry with inductively coupled plasma - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to analytical chemistry. Method of measuring mass concentrations of niobium and tantalum in air of a working zone by mass spectrometry with inductively coupled plasma, according to which sampling air of the working area is performed by drawing the analysed air through an analytical aerosol filter, at rate of 2–20 l/min for 30 minutes, recording air temperature and atmospheric pressure at sampling moment, filter is placed in quartz barrel and installed in muffle furnace, held for 1.5–2 hours at temperature of 400–450 °C, 1.0 g of potassium pyrosulphate is added, held at the same temperature until transition into a liquid state, then held for 10 minutes at temperature 800–850 °C, the sample is allowed to cool, 10 ml of 10 % aqueous tartaric acid solution and heating to produce a sand bath until dissolved, the sample is transferred to a volumetric flask and adjusted to the sample volume of deionized water to 100 cm³; 4.95 cm³ of the prepared sample is introduced into a test tube of an automatic sampler of a mass spectrometer, 0.05 cm³ of an internal standard is added with mass concentration of a terbium comparison element of 1000 mcg/dm³ and then, by inductively coupled plasma mass spectrometry, concentration of niobium and tantalum is determined using a calibration curve and taking into account the amount of air withdrawn for analysis to normal conditions.

EFFECT: invention provides the possibility of determining both niobium and tantalum in the working area at a level of from 0_00002 mg/m³ or higher.

1 cl, 10 tbl, 2 dwg

Description

The invention relates to the field of analytical chemistry and can be used by laboratories of institutions of the state sanitary and epidemiological service, research institutes working in the field of environmental hygiene in the implementation of industrial control over the air quality of the working area and prevention of adverse health effects of hazardous chemicals and measurement in the air of the working zone of mass concentrations of niobium and tantalum.

The working area of air is understood as the breathing area of the worker.

The industrial applications of niobium and tantalum are constantly expanding, which is typical of modern technologies.

To improve occupational safety, maintain occupational health, and study the effects of ultra-low exposure to chemicals, it is necessary to obtain accurate data in the study of occupational risk. For these purposes, modern highly sensitive methods of elemental analysis are needed.

At present, according to its analytical capabilities, one of the leading methods for the determination of metals in various objects is inductively coupled plasma mass spectrometry (hereinafter - ICP-MS). The method allows the determination of several elements from one sample simultaneously in a wide range of concentrations. The high sensitivity of the method makes it possible to determine the content of metals in average and one-time air samples, to expand the range of determined concentrations, and to expand the methodological base of analysis.

To measure the content of niobium and tantalum in the air of the working area, the following methods and guidelines (MU) have been approved: photometric method (MU No. 5993-91, MU No. 1625-77); method of atomic emission spectroscopy with inductively coupled plasma (GOST R ISO 15202) for tantalum; the method of mass spectrometry with inductively coupled plasma (ISO 30011: 2010) regulates the analysis of solutions prepared from samples of aerosol particles in the air of the working area for niobium.

The list of known techniques is shown in Table 1.

The disadvantages of these known methods are:

- in methods 1 and 2, the impossibility of the simultaneous determination of several chemical elements, the laborious process of preparing standard samples from powders of niobium and tantalum oxides, additional preparation of some reagents from powders, the need to accurately observe the time from the moment of sample preparation to the moment of measurement on the device. In addition, Method 2 indicates that the presence of niobium is interfering.

- Method 3 indicates the possibility of determining only tantalum, the determination error (± 30%; ± 50%), which does not meet the requirements for methods for determining the concentration of pollutants in the air of the working area, which, according to GOST 12.1.016, should not exceed ± 25% ...

- Method 4 indicates the possibility of determining niobium, but does not indicate the method of sample preparation for the determination of niobium, a high determination error (± 30%; ± 50%), which does not meet the requirements for methods for determining the concentration of pollutants in the air of the working area, which should not exceed ± 25% (GOST 12.1.016).

In the closest to the proposed technical solution, method 4 (described in the international standard "ISO 30011: 2010 Air of the working area. Determination of the content of metals and metalloids in particles suspended in air using inductively coupled plasma mass spectrometry") indicates only the possibility determination of niobium, but the methods of sample preparation, ranges of determination, values of metrological characteristics are not indicated, therefore, it is impossible to establish coinciding or distinctive features.

In terms of sample preparation, method 2 is the closest to the proposed technical solution (described in MU No. 1625-77). However, in this known way, firstly, it is impossible to determine niobium and tantalum when they are present together, and secondly, it is not suitable for determination by means of inductively coupled plasma mass spectrometry.

The proposed method differs from the currently operating methods by the measurement method based on the use of inductively coupled plasma as a source of ions and a mass spectrometer for their separation and detection, the use of helium for suppressing interferences, sample preparation conditions, expanding the list of elements to be determined, and establishing metrological characteristics.

The technical problem solved by the proposed method is to ensure the possibility of determining niobium and tantalum in the air of the working area at a level of 0.00002 mg / m and above (the determination of trace amounts of metals at workplaces is necessary to study the effect of low concentrations on human health during chronic exposure , therefore, the result should be an exact value, and not just, for example, a qualitative indicator <0.5 MPC).

The technical result achieved by the proposed method consists in providing high sensitivity, accuracy, rapidity of the method, due to the simultaneous determination of the chemical elements of niobium and tantalum.

The specified technical result is achieved by the proposed method of measuring the mass concentrations of niobium and tantalum in the air of the working area by the method of mass spectrometry with inductively coupled plasma, according to which the air sample of the working area is taken by pulling the test air through an analytical aerosol filter at a rate of 2-20 l / min within 30 minutes, record the air temperature and atmospheric pressure at the time of sampling, the filter is placed in a quartz glass and installed in a muffle furnace, kept for 1.5-2 hours at a temperature of 400-450 ° C, 1.0 g of potassium pyrosulfuric acid is added, incubated at the same temperature until the transition to a liquid state, then incubated for 10 minutes at a temperature of 800-850 ° C, the sample is cooled, 10 ml of a 10% aqueous solution of tartaric acid is added, and heating is carried out in a sand bath until dissolution, the sample is transferred to volumetric flask and bring the volume of the sample with deionized water to 100 cm ³ ; 4.95 cm ^{3 of the} prepared sample is introduced into a test tube of an automatic sampler of a mass spectrometer, 0.05 cm ^{3 of an} internal standard with a mass concentration of the reference element terbium of 1000 μg / dm ^{3 is} added, and then the concentration of niobium and tantalum is determined by the method of mass spectrometry with inductively coupled plasma using a calibration graph and taking into account bringing the volume of air sampled for analysis to normal conditions.

The delivered technical result is achieved due to the following.

When studying the influence of metals when working in new areas of industry and introducing modern technologies, it is important to identify the exact concentrations. In international practice, methods are being developed that ensure the determination of ultra-trace metal concentrations in the air of workplaces (for example, a joint project of ASTM International and the International Organization for Standardization (ISO) on the development of a method for multi-element analysis of traces of chemical elements in air samples at the workplace using the ICP-MS method ).

When implementing the proposed method, when the filter is kept in a muffle furnace for 1.5-2 hours at a temperature of 400-450 ° C, it is ashed. When 1.0 g of potassium pyrosulfurate is added at a given temperature, potassium pyrosulfuric acid is melted and mixed with the ash obtained after ashing the filter. Exposure for 10 min at a temperature of 800-850 ° C ensures the fusion of the ash containing the analyte with potassium pyrosulfuric acid. Introduction of 10 ml of 10% aqueous solution of tartaric acid into the sample and subsequent heating in a sand bath until dissolution is necessary to transfer and maintain the analyzed elements in a dissolved state. As it turned out, only in such a time and temperature range is it possible to provide high-quality sample preparation. The use of an internal standard with a mass concentration of the reference element terbium of 1000 µg / dm ³ ensures measurement accuracy by leveling out spectral and non-spectral (matrix) interferences. Only with the selected ratio of reagents is it possible to accurately quantify niobium and tantalum in air from one sample.

The proposed method is based on the use of inductively coupled argon plasma as a source of ions and a mass spectrometer for their separation and detection.

Ensuring the possibility of determining niobium and tantalum from one sample of atmospheric air at the level of the reference and background concentration became possible due to the fact that the highly sensitive and selective ICP-MS method was used, and at the same time the conditions for analysis on the mass spectrometer, methods and conditions for sample preparation were established, the value blank experiment, due to sample preparation with the introduction of an internal standard, selection of conditions for the use of high-purity reagents and materials.

Thus, the claimed technical result is ensured by a set of certain operations, their sequence and modes in the claimed method, as well as by a set of reagents, their claimed ratio, used in sample preparation.

The proposed method was tested in laboratory conditions.

For its implementation, the following substances and equipment were used:

- Multi-element calibration standard for niobium and tantalum with a mass concentration of 10 mg / dm ^{3 of} niobium and tantalum in 5% nitric acid. The relative error of the certified values (at P = 0.95) is not more than ± 1.0% (Inorganic Ventures), USA);

- Extra pure nitric acid, GOST 11125;

- Wine acid, analytical grade, GOST 5817;

- Potassium pyrosulfuric acid, analytical grade, GOST 7172

- Deionized water, GOST R 52501;

- A solution for adjusting the sensitivity of the mass spectrometer containing lithium, magnesium, yttrium, cerium, thallium, cobalt 1 μg / dm ³ or 10 μg / dm ³ ;

- A solution with the content of the reference element terbium 10 mg / dm ³ ;

- Liquid argon of high purity (99.998%), TU-2114-005-00204760-99;

- Gaseous helium of high purity (99.995%), TU0271-135-31323949;

- An Agilent 7500 _cx Octopole Inductively Coupled Plasma Mass Spectrometer with the following characteristics:

mass scanning range, amu: 2-260;

detection limits: beryllium ≤1.5 ng / dm ³ , indium ≤0.5 ng / dm ³ , bismuth ≤0.5ng / dm ³ ;

sensitivity (imp./s per 1 mg / dm ³ ): lithium (7) ≥30⋅10 ⁶ ,

strontium (88) ≥80⋅10 ⁶ , thallium (205) ≥40⋅10 ⁶ ;

short-term stability, RMS: ≤3%;

long-term stability, RMS: ≤4%;

doubly charged ions, (cerium ²⁺ / cerium ⁺ ): ≤3%;

oxide ions (cerium II / cerium oxide): ≤1.5%;

background level at mass 9 (Be): <5 imp./s;

detector operating speed: ≥100 μs per ion;

microaerosol spray MicroMist;

peristaltic pump for sample delivery;

spray chamber with electronic Peltier cooling;

injector diameter 2.5 mm.

- Aspirator for air sampling (TU 4215-000-11696625);

- Muffle furnace providing temperature range (200-900) ° С;

When carrying out the processes of preparing solutions and preparing samples for analysis, the following conditions are observed:

- air temperature (20 ± 5) ° С;

- atmospheric pressure from 84.0 to 106.7 kPa (630-800 mm Hg);

- air humidity from 30% to 80%.

Below are examples of the preparation of basic solutions required for the implementation of the proposed method.

1. An example of the preparation of solutions of standard samples using as the main multi-element standard with mass concentrations of the analyzed elements Nb and Ta 10 mg / dm ³ .

2. Solution No. 1 with a mass concentration of ions of the analyzed elements of 100 μg / dm ³ is prepared from a solution of a standard sample with a mass concentration of the analyzed elements of 10 mg / dm ³ . Into a volumetric flask with a capacity of 50 cm ^3, add 0.5 cm ³ of a standard sample solution with a mass concentration of the analyzed elements of 10 mg / dm ³ with an automatic dispenser or pipette and bring the volume in the flask to the mark with 1% tartaric acid solution. Store for 3 to 5 days in polypropylene tubes.

3. Solution No. 2 with mass concentrations of the analyzed elements of 10 µg / dm ³ is prepared from solution No. 1 with mass concentrations of the analyzed elements of 100 µg / dm ³ .

In a volumetric flask with a capacity of 50 cm, add 5 cm ^{3 of} solution No. 1 with a dispenser or a pipette and bring the volume in the flask to the mark with a 1% solution of tartaric acid. Store for 3 to 5 days in polypropylene tubes.

When using more concentrated solutions for the preparation of basic solutions (for example, GSO 8854-2007 with a mass concentration of niobium 1.0 mg / g and GSO 8857-2007 with a mass concentration of tantalum 1.0 mg / g), a solution with a mass concentration of the analyzed elements 10 mg / dm ³ .

4. A solution of an internal standard with a mass concentration of the reference element terbium 1000 μg / dm ³ is prepared from a basic solution with a mass concentration of the reference element terbium 10 mg / dm ³ .

Into a volumetric flask with a capacity of 50 cm ^3, add with a dispenser or a pipette 5 cm ^{3 of a} basic solution with a mass concentration of the reference element terbium of 10 mg / dm ³ and bring the volume of the solution in the flask to the mark with a 1% solution of nitric acid. Store the solution in a polypropylene tube for 5 to 7 days at room temperature.

5. A solution of nitric acid 1%.

Measured with a dispenser or pipette, 4.7 cm ^{3 of} concentrated nitric acid is mixed with 495 cm ^{3 of} deionized water, measured by a cylinder. Store in plastic containers.

6. Solution of tartaric acid 10%. A weighed portion of 10 g of tartaric acid is mixed with 90 cm ^{3 of} deionized water, measured with a cylinder.

7. A solution of tartaric acid 1%. In a volumetric flask with a capacity of 100 cm ^3, add 10 cm ^{3 of a} 10% solution of tartaric acid with a dispenser or pipette and bring the volume in the flask to the mark with deionized water.

8. A solution for adjusting the sensitivity of a mass spectrometer with a mass concentration of thallium of 1 μg / dm ³ .

Adjustment solution with mass concentration of thallium 1 μg / dm ^{3 is} used without additional preparation procedures. 9. Preparation of calibration solutions:

Solution No. 1, solution No. 2, a solution of an internal standard of terbium 1000 μg / dm ³ and a solution of 1% tartaric acid in the volumes shown in Table 2 are introduced with a dispenser into test tubes for an automatic sampler with a capacity of 6 ml.

Construction of a calibration characteristic (calibration graph).

The calibration characteristic is the dependence of the detector signal intensity (the ratio of the intensities of the detector signals for the determined element and the internal standard) on the mass concentration of the determined element (the ratio of the mass concentrations of the determined element and the internal standard).

The calibration characteristic is set daily on the prepared calibration solutions. A series of calibration solutions, consisting of 5 solutions, are prepared immediately before use by diluting the solutions of the elements to be determined and a solution containing the reference element terbium (internal standard) (Table 2).

The construction of the calibration characteristic, processing and storage of the calibration results are performed by the software of the spectrometer.

Figures 1 and 2 show the calibration curves for niobium and tantalum, respectively. All graphs are presented as a straight line with a correlation coefficient r = 1.0000.

The proposed method is carried out as follows:

- carry out air sampling of the working area (breathing zone of the worker), aspirating air through AFA filters (analytical aerosol filters AFA-KhP, AFA-KhA, AFA-VP). Air sampling of the working area is carried out by pulling the test air through an analytical aerosol filter at a rate of 2-20 l / min for 30 minutes (in accordance with the requirements of GOST 12.1.005 with amendment No. 1 "SSBT General sanitary and hygienic requirements for working air zones "and Guidelines R 2.2.2006-05 (Appendix 9)" General methodological requirements for the organization and control of the content of harmful substances in the air of the working area ", section 2 -" Monitoring compliance with maximum MPC ", section 3" Monitoring compliance with the average MPC "). It is also indicated there that in order to determine the mass concentration of chemical elements, an air sample is taken by the aspiration method on AFA filters, for example, in a volume of 10-600 dm ³ for each sample in the breathing zone of a worker under typical production conditions. The air sampling time is 30 minutes, for the specified period one or several successive samples can be taken at regular intervals. During the shift and (or) at separate stages of the technological process, at least three samples must be sequentially taken at one point.

When determining the average shift concentrations, air samples are taken at all stages of the technological process, taking into account their duration and interruptions in work. The survey is carried out for at least 75% of the shift duration for at least 3 shifts.

- filters are placed in quartz glasses and installed in a muffle furnace,

- withstand 1.5-2 hours at a temperature of 400-450 ° C,

- add 1.0 g of potassium pyrosulfuric acid,

- kept at this temperature until the transition to a liquid state,

- then incubate for 10 minutes at a temperature of 800-850 ° C,

- the sample is cooled,

- add 10 ml of 10% aqueous solution of tartaric acid,

- heated, for example in a sand bath, until dissolved,

- the sample is transferred to a volumetric flask with a capacity of 100 cm ³ and brought to the mark (i.e., to a volume of 100 cm ³ ) with deionized water,

- close the flask,

- mix the sample,

- 4.95 cm ^{3 of the} prepared sample is introduced into the test tube of the automatic sampler of the mass spectrometer,

- add 0.05 cm ^{3 of an} internal standard with a mass concentration of the reference element terbium 1000 μg / dm ³ ,

- the test tubes are covered with laboratory sealing foil.

The prepared solutions are used to measure the mass concentrations of niobium and tantalum.

For each batch of samples (or at least for every 20 samples), blank and control samples are prepared simultaneously with the analyzed samples.

The unexposed filters serve as a blank sample.

The control sample is unexposed filters with the addition of a known amount of the element to be determined, while using filters of the same batch as the exposed filters. Use glassware from the same batch as used for analysis and add reagents as in the samples to be analyzed.

To account for spectral and transport interference, to improve the precision of the analysis, a comparison element (internal standard) is added to the samples. It is recommended to use a solution containing 1000 μg / dm ^{3 of the} reference element terbium as an internal standard.

The tests are carried out at a helium feed rate of 4.3 cm ³ / min and a sample feed rate of 0.4 cm ³ / min.

The concentration of the measured elements is determined using a calibration graph.

The results obtained by the proposed method are presented in tables 3 and 4.

Table 3 shows the results of measurements of standard solutions of niobium and tantalum applied to the AFA-KhP filters and passed the entire procedure of sample preparation and measurements on a mass spectrometer using the proposed method.

Table 4 shows the results of measurements of solutions obtained from fine powders of standard samples of niobium oxide and tantalum oxide deposited on AFA-KhP filters. Samples of oxides were taken taking into account the conversion factor for niobium and tantalum and prepared according to the proposed method.

From the results presented in tables 3 and 4, it can be seen that the found values of the mass concentrations of niobium and tantalum by the proposed method correspond to the applied amount. The extraction of the analyte from the sample by the proposed method is at least 92% (in accordance with the requirements of GOST R ISO 30011-2017, 90 ± 10% is permissible), and indicates the acceptability of this method for measuring niobium and tantalum.

Simultaneously with the preparation of the exposed filters, prepare a blank sample and a control (verification) sample. Unexposed filters serve as a blank sample; unexposed filters with the addition of a known amount of the element to be determined serve as a control sample. Blank and control samples are carried out through the entire course of the analysis.

мкг/дм³.The result of determining the element is presented as the average of parallel (at least two) measurements of the analyzed sample solution

μg / dm ³ .

Simultaneously with the preparation of the exposed filters, prepare a blank sample and a control (verification) sample. Unexposed filters serve as a blank sample; unexposed filters with the addition of a known amount of the element to be determined serve as a control sample. Blank and control samples are carried out through the entire course of the analysis.

мкг/дм³.The result of determining the element is presented as the average of parallel (at least two) measurements of the analyzed sample solution

μg / dm ³ .

The mass concentration of the analyzed chemical element in the air of the working area (mg / m ³ ) is calculated by the formula:

C - mass concentration of a chemical element in the air of the working area, mg / m ³ ;

- среднее значение массовой концентрации химического элемента в растворе пробы, мкг/дм³;

- the average value of the mass concentration of a chemical element in the sample solution, μg / dm ³ ;

- среднее значение массовой концентрации химического элемента в растворе холостой пробы, мкг/дм³;

- the average value of the mass concentration of a chemical element in a blank sample solution, μg / dm ³ ;

V ₁ - the initial volume of the mineralized sample, dm ³ , V ₁ = 0.01 dm ³ (after processing in a test tube heater);

K is the dilution factor (dilution prior to measurement on a mass spectrometer);

V ₂₀ is the volume of the air sample taken for the analyzed filters, reduced to standard conditions (pressure 760 mm Hg, temperature 20 ° C), dm ³ .

V _{20 is} calculated by the formula:

V is the volume of drawn air at a temperature t at the sampling point, dm ³ ;

Р - atmospheric pressure during sampling, mm. RT.art .;

t - air temperature at the moment of sampling, ° С.

The final result is the measurement result of a single sampled air sample.

Experimental data on measurements of niobium and tantalum by the proposed method are presented in Tables 5 and 6.

The data given in Tables 5 and 6 show that when measuring samples under repeatability conditions (each sample from 14-15 samples, measured twice under the same conditions), close measurement values were obtained. At the same time, close values were obtained between each of the samples presented (15 samples for niobium and 14 samples for tantalum), demonstrating in-laboratory precision. From these measurement results presented in Tables 5 and 6, the repeatability and reproducibility of the results are calculated). At the same time, according to the results of determinations (X _n ), given in these tables, one can judge the sensitivity of the method (analytical stage from 0.1 μg / dm ³ ).

To calculate the metrological characteristics of the method, the "introduced - found" method was used. Samples were analyzed with the addition of a certain amount of niobium and tantalum (the additive is 50-350% of the concentration in the working sample), to determine the correctness and accuracy of the analysis (relative error). The obtained results of measurements of niobium and tantalum in the prepared sample with additions of niobium and tantalum are shown in Tables 7 and 8. The amount of addition of niobium and tantalum at C = 0.1 μg / dm ³ .

The data given in Tables 7-8 show that the addition of the measured element introduced into the working sample after all stages of sample analysis preparation was found with a high degree of accuracy and correctness. In this example, 0.1 μg / dm ^{3 was} added to the sample of niobium and tantalum, 0.107 μg / dm ^{3 of} niobium was detected, and 0.105 μg / dm ^{3 of} tantalum was detected. Taking into account the values given in Tables 5-8, the accuracy indicators of 8.4% were calculated, while the accuracy indicators of the analytical stage of the analysis were calculated at 19%.

In the course of laboratory tests of the proposed method, the following metrological characteristics were established: the range of measurements of niobium and tantalum in the solution of an analytical sample, in the air of the working area, the values of indicators of accuracy, accuracy, repeatability, reproducibility.

Table 9 shows the ranges of measurements in the analytical solution of the sample, in the atmospheric air, the indicator of the accuracy of the method taking into account the stage of sampling, MPC for niobium and tantalum.

The data shown in Table 9 show that the proposed method makes it possible to determine with high accuracy niobium and tantalum in the air of the working zone: in the concentration range 0.00002-100 mg / m ³ for niobium and 0.00002-250 mg / m ³ for tantalum. The sensitivity of the method makes it possible to detect low concentrations to obtain reliable results of ultra-low effects of chemical elements used in industry, as well as high concentrations, which make it possible to detect the excess of standard indicators.

Table 10 shows the conditions for performing analysis on an Agilent 7500 _cx mass spectrometer in Reaction mode.

Thus, the claimed method provides a range of measurements in the air of the working zone of niobium and tantalum from one sample in the concentration range from 0.00002 to 100 mg / m ³ for niobium and from 0.00002 to 250 mg / m ³ tantalum with an accuracy rate of 20% ...

Claims (1)

A method for measuring mass concentrations of niobium and tantalum in the air of the working area by the method of mass spectrometry with inductively coupled plasma, characterized in that the air sampling of the working area is carried out by pulling the test air through an analytical aerosol filter at a rate of 2-20 l / min for 30 minutes, record the air temperature and atmospheric pressure at the time of sampling, the filter is placed in a quartz glass and installed in a muffle furnace, kept for 1.5-2 hours at a temperature of 400-450 ° C, 1.0 g of potassium pyrosulfuric acid is added, kept at this the same temperature until the transition to a liquid state, then incubate for 10 minutes at a temperature of 800-850 ° C, cool the sample, add 10 ml of a 10% aqueous solution of tartaric acid and heat it in a sand bath until dissolved, transfer the sample to a volumetric flask and bring sample volume with deionized water up to 100 cm ³ ; 4.95 cm ^{3 of the} prepared sample is introduced into a test tube of an automatic sampler of a mass spectrometer, 0.05 cm ^{3 of an} internal standard with a mass concentration of the reference element terbium of 1000 μg / dm ^{3 is} added, and then the concentration of niobium and tantalum is determined by the method of mass spectrometry with inductively coupled plasma using a calibration graph and taking into account bringing the volume of air sampled for analysis to normal conditions.

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