RU2390765C1 - Method of detecting benzene - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: method is based on detecting benzene using a sensor whose surface is modified with tert-butylthiacalix[4]arene which is tetra-substituted with ester groups on the bottom ring. This calixarene bonds benzene pairs in two steps contrary to pairs of other substances for which bonding takes place in a single step. The time difference for appearance of sensor response steps is related to content of benzene in the analysed mixture. ^ EFFECT: possibility of unambiguous detection of benzene in different media and determination of its quantitative content in mixtures with other substances, even with unknown qualitative composition of the mixture. ^ 2 dwg, 1 tbl, 10 ex

Description

The invention relates to the analytical chemistry of organic compounds and can be used for the qualitative and quantitative determination of benzene in various environments, for example, in air, in gas mixtures, in mixed organic solvents used for industrial purposes and in everyday life, as well as the presence of benzene in various solid materials , for example, in polymer samples.

A known method for the determination of benzene in the gas phase, based on the reaction of conversion of benzene to nitro compounds [1]. The disadvantage of this method is the inability to quantify benzene, the complexity or inability to determine benzene in the presence of other aromatic compounds, in particular its closest homologue, toluene.

For the qualitative and quantitative determination of benzene, incl. in mixtures with organic compounds, gas chromatography is widely used, which allows you to quickly and fairly sensitively determine the content of each component in the mixture. The disadvantage of the gas chromatographic method is the need to calibrate the device even for a qualitative determination of the compound, as well as the relatively high cost of equipment and consumables.

In addition to the methods listed above, chemical sensors are currently being used to detect hydrocarbon vapors of various nature in the gas phase and in solutions. The most promising of them are sensors based on piezoelectric quartz resonators. For the analysis of mixtures of organic compounds, a method is used based on the use of a set of sensors with coatings of various nature, each of which relatively selectively binds a specific component. Such sensors are commercially available under the name "electronic nose." In these sets of sensors, polymers are commonly used [2]. The disadvantage of methods that use such sensors is the ability to determine only individual compounds or simple binary mixtures, where the components differ significantly in properties and the qualitative composition is known.

In the known method [3], when analyzing naphthalene and anthracene in the presence of benzene in the gas phase,> 2 orders of magnitude greater sensitivity of the sensors to naphthalene and anthracene than to benzene was shown. It was not taken into account that the pressure of saturated naphthalene vapor is approximately 450 times lower than the pressure of saturated vapor of benzene, respectively, at the same concentration of naphthalene and benzene in the vapor phase, the activity of naphthalene will be higher, and the sensitivity of the sensor to it should be approximately the same number of times greater.

When determining organic compounds in water, the patent [4] showed the high sensitivity of piezoelectric sensors on crosslinked polymers with molecular imprinting (molecular imprinting — a method of obtaining molecular imprints on the surface of solids) to hexachlorobenzene compared to other analytes (cyclohexane, benzene, chlorobenzene, and anisole). It does not take into account that hexachlorobenzene has the highest activity coefficient in water, which is 100,000 times higher than the activity coefficient of the closest hydrophobicity of cyclohexane. Accordingly, with an equal concentration of these analytes in water, the sensitivity of the sensors will be greater to hexachlorobenzene, which has a high activity, which significantly limits the applicability of this sensor for determining benzene in the presence of the second component.

A known method for the determination of benzene in air in the presence of xylenes using a detector operating on the principle of volume-acoustic waves (OAV sensor), modified with polyethylene glycol-2000. The analytical signal represents the increment of the oscillation frequency of the OAV sensor as a result of sorption of hydrocarbons by the modifier. The method allows to determine benzene in the presence of xylenes at a given ratio of benzene: xylene in the analyzed air sample 3: 7. The range of determined concentrations of benzene: 0.1-0.3 g / m ³ , the error does not exceed 9% [5]. The disadvantage of this method is the ability to determine benzene only for a given ratio of components, when the thermodynamic activity of one of the components (xylene) in the mixture significantly exceeds the activity of the other (benzene). In fact, xylene is determined, and the benzene content is calculated based on the given ratio of benzene to xylene in the mixture (indirect method).

There is a method of determining benzene by detecting vapors on a sensor made in the form of a quartz resonator, the electrodes of which are coated with a film sensitive layer of a mixture of organosilicon polymers and oligohydride vinylorganosiloxane [6]. Also known is a method for determining the concentration of hydrocarbon vapors, including benzene, and gasoline in air on a sensor made in the form of a quartz resonator on volumetric acoustic waves with a sensitive film layer deposited on the electrodes. As a sensitive layer, polymers and copolymers of the polysilylacetylene group with a silicon content of 18–25% were used [7].

The disadvantage of these methods is the inability to determine individual compounds in mixtures. These sensors are used to determine the total content of a group of hydrocarbons, including aromatic hydrocarbons.

A significant drawback of the known piezoelectric sensors used to analyze vapor mixtures is that their selectivity to the mixture components is based on the difference in activity (relative vapor pressure) of the components given by the pressure of their saturated vapor at a fixed concentration [8], the one-stage shape of the sensor response curve is the same (non-specific) for all analytes identified.

Closest to the proposed method is a method for detecting binary mixtures of benzene and chloroform using piezoelectric sensors, the surface of which is coated with a layer of tert-butyl calix [6] arena [9]. The method is based on different rates of desorption of bound benzene and chloroform vapors. However, the method is applicable only to mixtures with a previously known qualitative composition, where the physical and chemical properties of the components differ significantly.

The objective of the invention is to develop a method that allows you to uniquely identify the presence of benzene in various environments and determine its quantitative content in mixtures with other substances, even with unknown qualitative composition of the mixture.

The problem is solved in that the determination of benzene is carried out by detection with a sensor whose surface is modified with calixarene, while tert-butylthiacalix [4] arenes tetrasubstituted with ester groups on the lower rim are used as calixarene.

The difference of the present invention from analogues is that tert-butylthiacalix [4] arenes used as a modifier are tetra-substituted by ester groups on the lower rim.

The possibility of determining benzene by the claimed method is due to the fact that tert-butylthiacalix [4] arenes, tetrasubstituted on the lower rim with ester groups, binds benzene vapors in two steps, unlike vapors of other substances for which binding occurs in one step. Thus, the presence in the analyzed mixture of other components does not prevent the detection of benzene, which is an indisputable advantage of the proposed method

The technical result consists in the fact that it is possible to conduct a qualitative and quantitative determination of benzene in mixtures with other organic compounds, including air samples, vapor-phase determination of benzene in samples of liquids and solids and materials. The vapor samples to be analyzed may be mixtures of benzene vapor and water vapor, toluene, hexane, pyridine, cyclohexane or other organic compounds.

As the calixarene phase is saturated with vaporous benzene, there are two phase (polymorphic) transitions in the calixarene phase with the successive formation of a stable intermediate and saturated clathrates. Other substances in the test mixture have a single-stage sensory response. The time difference between the appearance of sensory response steps is related to the benzene content in the analyzed mixture.

Tert-butylthiacalix [4] arenes can be substituted on the lower rim with ester groups such as (methoxycarbonyl) methoxy, (ethoxycarbonyl) methoxy, (propoxycarbonyl) methoxy, (isopropoxycarbonyl) methoxy.

As sensors, sensors with piezoelectric quartz resonators can be used, including resonators on surface acoustic waves and resonators on bulk acoustic waves or other sensors that allow the interaction of a modifier layer with an analyte to be recorded.

To perform the analysis of the proposed method, a sensor device such as quartz microbalances based on piezoelectric generators described in [10] can be used. As working sensors, 10 MHz piezoelectric quartz resonators are used. The sensor device contains four resonators placed in a cylindrical glass vessel with a volume of 47 ml. Three resonators are coated with a modifier layer, calixarene. The fourth resonator is used as a comparison resonator. The experiment is carried out in an atmosphere of air at 25 ° C. The liquid sample is dosed using a microsyringe through a special hole in the cover of the sensor cell. When binding with a modifier layer of organic compounds, a change in the frequency ΔF of the piezoelectric crystal resonator with time is recorded. The response of the ΔF sensor to the sample introduced into the measuring cell is recorded using a frequency converter under computer control. The accuracy of determining ΔF is 1 Hz.

One of the options for modifying the resonator with a sensitive calixarene layer and a method for regenerating the coating may be the method described in [10]. Modification of the resonator by coating the sensitive layer of calixarene is carried out, for example, as follows. A solution of calixarene in the solvent is applied to the surface of the resonator electrodes using a microsyringe. The solvent is removed, for example, by blowing with hot air, which leads to the formation on the surface of the resonator electrodes of a thin film of calixarene weighing approximately 1 μg. Before the experiment and after the experiment, the sensor coating is blown with a stream of hot air to constant mass. Touch device thermostat.

The regeneration of the sensory coating is carried out by removing bound sorbates from the sensory coating, for example, by saturating the coating with vaporous ethanol or benzene, followed by purging with hot air.

Qualitative determination of benzene is carried out by a two-stage form of the curve of the sensory response.

The quantitative determination of the benzene content in the mixture is carried out by evaluating the characteristic time Δt.

As the characteristic time Δt can be selected:

1. the time difference between the peaks of the differential curve of the sensory response, Figure 1.

2. the time difference between the appearance of the second stage on the curve of the sensory response and the output of the curve of the sensory response to saturation.

3. the time difference between the appearance of the first stage on the curve of the sensory response and the appearance of the second stage.

4. the time difference between the output of the sensor response curve to saturation after the first stage and the appearance of the second stage on the sensor response curve.

From the investigated prior art there is no information about the characteristics characterizing the claimed method, which is evidence of compliance of the claimed technical solution with the criterion of "novelty" presented to the invention, while the claimed method is not obvious to a person skilled in the analyzed field of technology, thus, the claimed technical solution meets the criterion of "inventive step" for inventions.

The claimed technical solution meets the criterion of "industrial applicability" to the invention, because Studies are conducted and the feasibility of the claimed method is proved.

The claimed technical solution is illustrated by the following materials, Fig. 1 is a graph illustrating the determination of the characteristic time, Fig. 2 is a graph illustrating a qualitative analysis of benzene (sensory responses to benzene samples of different concentrations are presented), the table shows the results of measurements of samples of benzene mixtures and toluene with different content of components, as well as mixtures of unknown composition.

The claimed method is as follows.

Qualitative determination of benzene

Example 1. The surface of the resonator is covered with a sensitive layer of modifier - tert-butylthiacalix [4] arenes, tetrasubstituted on the lower rim with ester groups: (5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis ( (isopropoxycarbonyl) methoxy) -2,8,14,20-tetrathiacalix [4] arene). After placing the sensor in the detection cell and establishing a stable zero signal, a liquid benzene sample is injected directly into the detection cell using a microsyringe.

The benzene concentration in the detection cell is 0.31 g / l. The presence of two steps on the sensory response curve indicates the presence of benzene. Figure 2.

Example 2. The preparation of the sensor is carried out analogously to example 1.

The benzene concentration in the detection cell is 0.33 g / ml. The presence of two steps on the sensory response curve indicates the presence of benzene. Figure 2.

Example 3. The preparation of the sensor is carried out analogously to example 1.

The benzene concentration in the detection cell is 0.49 g / l. The presence of two steps on the sensory response curve indicates the presence of benzene. Figure 2.

Quantification of benzene.

Analysis of mixtures of benzene with toluene.

The calibration schedule is performed on prepared samples with a known benzene content with a second component, where the concentration of the second component ranged from 0 to 20 volume percent. The calibration graph represents the dependence of the characteristic time Δt on the volume concentration of benzene in the liquid sample. The sensitivity of the method for the quantitative determination of benzene content in mixtures is 8.7 sec / vol.%.

Example 4. The modifier is tert-butylthiacalix [4] arenes tetrasubstituted on the lower rim with ester groups: (5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis ((isopropoxycarbonyl) methoxy) -2.8,14,20-tetrathiacalix [4] arenes). After placing the sensor in the detection cell and establishing a stable zero signal, a liquid benzene sample is injected directly into the detection cell with a syringe.

The dosing volume of benzene in the detection cell is 30 μl, which corresponds to its unit activity (the ratio of the partial pressure of the vapor of the substance in the system to the pressure of its saturated vapor) after equilibrium is established in the cell. The characteristic time and benzene content in the liquid sample are shown in Table 1.

Example 5. The modifier is tert-butylthiacalix [4] arenes tetrasubstituted on the lower rim with ester groups: (5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis ((isopropoxycarbonyl) methoxy) -2.8,14,20-tetrathiacalix [4] arenes). After placing the sensor in the detection cell and establishing a stable zero signal, a sample of a mixture of benzene and toluene is injected directly into the detection cell with a syringe.

The volume concentration of benzene in the sample sample is 90%, the concentration of toluene in the sample sample is 10%. The volume of dosing of the liquid mixture into the detection cell is 40 μl. The characteristic time and benzene content in the liquid sample are shown in Table 1.

Example 6. The preparation of the sensor was carried out by analogy with example 5. The volume concentration of benzene in the sample sample is 85%, the concentration of toluene in the sample sample is 15%. The volume of dosing of the liquid mixture into the detection cell is 40 μl. The results of the determination are given in table 1.

Example 7. The preparation of the sensor was carried out by analogy with example 5. The volume concentration of benzene in the sample sample is 80%, the concentration of toluene in the sample sample is 20%. The volume of dosing of the liquid mixture into the detection cell is 40 μl. The results of the determination are given in table 1.

Example 8. The preparation of the sensor was carried out by analogy with example 5. Sample sample mixture of benzene and toluene, the concentration of the components of the mixture is unknown. The dosing volume of a liquid mixture of unknown composition in the detection cell is 40 μl. The characteristic time Δt is determined. The volume concentration of the mixture is determined by the calibration graph. The results of the determination are given in table 1.

Example 9. The preparation of the sensor was carried out by analogy with example 5. A sample of a sample of unknown composition, the concentration of the components of the mixture is unknown. The dosing volume of a liquid mixture of unknown composition in the detection cell is 40 μl. The presence of two steps on the sensory response curve indicates the presence of benzene. The characteristic time Δt is determined. The volume concentration of the mixture is determined by the calibration graph. The results of the determination are given in table 1.

Example 10. The preparation of the sensor was carried out by analogy with example 5. Sample of a sample of unknown composition, the concentration of the components of the mixture is unknown. The dosing volume of a liquid mixture of unknown composition in the detection cell is 40 μl. The presence of two steps on the sensory response curve indicates the presence of benzene. The characteristic time Δt is determined. The volume concentration of the mixture is determined by the calibration graph. The results of the determination are given in table 1.

As can be seen from the above examples, the proposed method allows to qualitatively and quantitatively determine benzene in various environments in mixtures with organic compounds.

BIBLIOGRAPHY

1. B.H. Dolin Detection and Determination of toluene, xylene and other Substances - Ind. Eng. Chem., Anal. Ed. - 1943. - T.15 - p. 242-247.

2. Grate J.W. Acoustic Wave Microsensor Arrays for Vapor Sensing Chem. Rev. - 2000. - T.100 - p. 2627-2648.

3. RF patent 2173849 MPK7 G01N 27/12, op. 09/20/2001.

4. US patent 6890486, IPC7 G 01N 27/00, op. 03/13/2003.

5. S.A. Tunikova, Ya.I. Korenman, L.V. Rayakovich, M.B. Bastich. Determination of benzene in the presence of xylenes in air using highly sensitive frequency converters // Determination of organic substances in environmental objects. Training allowance. - M.: NIITEKHIM OJSC - 1997. - p. 1-2.

6. RF patent 2202780, IPC G01N 27/12, op. 04/20/2003.

7. RF patent 2159671, IPC G01N 27/12, op. 09/27/2000.

8. Grate J.W. Selective vapor sorption by Polymers and Cavitands on Acoustic Wave Sensors: Is This Molecular Recognition / Grate J.W., Patrash S.J., Abraham M.H., Du C.M. // Anal. Chem. - 1996. - T.68 - p. 913-917.

9. Wang C. Kinetic detection of benzene / chloroform and toluene / chloroform vapors using a single quartz piezoelectric crystal coated with calix [6] arene / C. Wang, F. Chen, X.-W. He // Analytica Chimica Acta. - 2002. - T.464. - p. 57-64.

10. L. S. Yakimova, M. A. Ziganshin, V. A. Sidorov, V. V. Kovalev, E. A. Shokova, V. A. Tafeenko, and V. V. Gorbatchuk, Molecular Recognition of Organic Vapors by Adamantylcalix [4] arene in QCM Sensor Using Partial Binding Reversibility // J. Phys. Chem. B. - 2008 .-- T.112. - p. 15569-15575.

Table 1 Example Number The volume concentration of benzene in the sample sample,% Characteristic time Δt, sec four one hundred 108 5 90 198 6 85 274 7 80 408 8 84 302 9 79 420 10 87 246

Claims (1)

A method for determining benzene by detecting with a sensor whose surface is modified with calixarene, characterized in that tert-butylthiacalix [4] arenes used as calixarene are tetra-substituted on the lower rim with ester groups.

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