RU2315988C1 - Composition of the diaphragm of the ion-selective electrode used for determination of the ions of lead - Google Patents

Abstract

FIELD: chemical industry; other industries; materials used in the composition of the diaphragms of the ion-selective electrodes.

SUBSTANCE: the invention is pertaining to the field of the ionometry, in particular, to the material intended for usage in the capacity of the sensitive component of the ion-selective electrodes for the quantitative determination of concentration the ions of lead in the water solutions. The invention provides, that the composition of the diaphragm of the ion-selective electrode for determination of the ions of lead in the capacity of the electrode-active component includes the diamides of the dipicolinic (2,6-piridindicarboxylic) acid, in the capacity of the plasticizer - dioctyl sebacate (DOS), and in the capacity of the lipophilic additive - cobalt chlorated dicarbolide (CChD). At that the composition has the following ratio of the components (in mass %): the electrode-active component - 1.0-3.0; the plasticizer (DOS) - 60.0-72.0; the lipophilic additive (CChD) - 0.1-6.0; the polyvinyl chloride - the rest. The invention allows to increase significantly the chemical sustainability(stability) of the diaphragm, in particular, in the presence of hydrogen and to conduct the measurement of the concentration of the ions of lead in the solutions with pH=0, and also to increase discrimination (selectivity) of the diaphragm to the ions of lead in the presence of some heavy metals. At that there are no chemical changes of the diaphragm and the significant change of the parameters of sensitivity. The range of the measured concentrations of the ions of lead makes from 10^-6 up to 10^-2.

EFFECT: the invention allows to increase significantly the diaphragm chemical stability in the presence of hydrogen, to conduct the measurements of the concentration of the ions of lead in the solutions with pH=0, to increase selectivity of the diaphragm to the ions of lead in the presence of some heavy metals practically without the chemical changes of the diaphragm or its sensitivity.

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Description

The invention (membrane composition) relates to ionometry, in particular to the search for materials intended for use as a sensitive element of ion-selective electrodes (chemical sensors) for the quantitative determination of the concentration of lead ions in aqueous solutions.

Known compositions of chalcogenide glass membranes for the determination of lead ions.

The known composition of the chalcogenide glass electrode membrane for determining lead ions [1], which, in order to expand the range of measured concentrations of lead ions in the region of concentrated solutions, includes, in wt.%: Lead sulfide - 35-56; silver iodide - 28-48, germanium disulfide - the rest. An increase in the length of the electrode function is achieved through the introduction of a new glass former - germanium disulfide, which provides the formation of a more rigid and conservative glass network, which significantly expands the range of measured concentrations of lead ions in the region of concentrated solutions. However, the known composition has insufficiently high selectivity coefficients for lead in the presence of other transition metal ions, for example, copper (10 ² , i.e., selectivity in favor of copper), and is unsuitable for measurements in solutions of complex composition, since the membrane is poisoned (irreversibly contaminated) ions of copper, silver, etc., and also not suitable for measurements in strongly acidic solutions, at pH below 2, due to the dissolution of the membrane material and the associated sharp deterioration in sensitivity and stability.

A known lead-selective electrode membrane [2], based on the use of diphenylmethyl-N-phenylhydroxamic acid as an ionophore. Ion-selective electrodes based on a theoretical yield of this compound (28.5 mV / decade) in response ions Pb ^2+. The disadvantage of this composition is the need to use solutions with a pH of 5-6, which drastically narrows the possibilities for the practical use of such electrodes.

Known ion-selective electrodes for determining lead ions, based on the use of various crown ethers [3-5]. Okolonernstsky slopes on PbA ⁺ (A-hydroxyl-ion, nitrate, acetate) were obtained for sensors with dicyclohexano-18-crown-6 and some other crowns as ionophores. The disadvantage of these electrodes is the insufficiently high selectivity to lead ions in the presence of other transition metals, in particular copper, as well as the low chemical stability of the materials, which does not allow measurements at pH below 4.

Various lead-selective electrodes are also known based on deposited film (coated-wire) sensor materials. Sensors based on 4-tert-butylcalix [6] arene are used to determine the lead content in various alloys and in industrial solutions of a plant manufacturing lead batteries [6]. The analysis of lead content in various mineral rocks was carried out using a lead-selective electrode based on N, N′-bis (5-methyl salicylidene) -p-diphenylene methane diamine [7]. Quantification of lead in some minerals can be carried out using polymer sensors based on various derivatives of 9,10-anthroquinone [8]. Significant disadvantages of sensors of this type, regardless of the composition of the sensitive membrane, are low mechanical strength, short service life (usually several days, at best, weeks) and insufficiently high selectivity, for example, in the presence of copper, as well as insufficiently high chemical stability of such membranes and the inability to work with these electrodes in solutions with a pH below 4.

A known membrane of a lead-selective electrode [9], intended for use as a sensitive element of a lead-selective electrode, which in composition is closest to the proposed invention. In the known composition of the membrane, in order to increase the selectivity of the membrane to lead ions in the presence of some heavy metals, the composition of the membrane includes an electroactive component, which is used 1,8-bis [2- (diphenylphosphinylmethyl) phenoxy] -3,6-dioxoctane, a plasticizer and polyvinyl chloride, the lipophilic additive is tetrakis- (4-fluorophenyl) potassium borate, in the following ratio of components, wt.%: electrode active component 1-2, plasticizer 63-72, lipophilic additive 0.1-2, polyvinyl chloride - the rest. Using the known composition of the membrane of the specified composition can increase the selectivity in the presence of silver ions from 10 ⁺¹ to 10 ^-1 in the presence of copper ions from 10 ^-1 to 10 ^-3 .

A disadvantage of the known membrane composition is the insufficiently high selectivity in the presence of copper ions, which are often found in real media, as well as the insufficient chemical stability of such electrodes and the inability to work with them at pH below 4.

The present invention is devoid of these disadvantages.

The technical result of the invention relates to:

- a significant increase in the chemical stability (stability) of the membrane, in particular in the presence of hydrogen ions (stability in acidic media) and the possibility of measuring the content of lead ions at pH 0;

- increasing the chemical stability of the obtained membranes, in particular, allows measuring the concentration of lead ions in solutions with pH 0. For example, membranes of compositions 3 and 6, see below, are sensitive to lead ions (angular coefficient of electrode function) of 28 mV / pPb at measurements in solutions against 1 M nitric acid (pH 0). In this case, there are no chemical changes in the membrane, for example, its dissolution, as well as a significant change in the sensitivity parameters, for example, the range of measured concentrations of lead ions is from 10 ^-6 to 10 ^-2 mol / l, even in solutions with pH 0, as can be seen in FIG. .one;

- increasing the selectivity (selectivity) of the membrane to lead ions in the presence of some heavy metals;

- the selectivity coefficient for the determined lead ions in the presence of alkali, alkaline earth and transition metal ions increases, in particular, in the presence of copper ions - from 10 ^-3 to 10 ^-5 . For example, membranes of compositions 3 and 6 show lead function in solutions against a background of 0.1 mol / L of copper ions, as can be seen in Figure 2. Selectivity coefficient IgK _{Pb, Cu} in this case is not less than 10 ^-5.

The specified technical result in the presence of some heavy metals is achieved by the fact that the composition of the membrane of the ion-selective electrode for determining lead ions, containing an electroactive component, a plasticizer, polyvinyl chloride and a lipophilic additive, in accordance with the invention contains: dipicolinic diamide as an electroactive component (2.6 -pyridinedicarboxylic acid, as a plasticizer - dioctyl sebacinate (DOS), as a lipophilic additive - chlorinated cobalt dicarbollide (HD) ), Wherein the composition has the following ratio of components, wt%: elektrodoaktivny component - 1.0-3.0;. plasticizer (DOS) - 60.0-75.0; lipophilic additive (CDK) - 0.1-0.5; polyvinyl chloride - the rest.

In addition, this result is achieved by the fact that various dipicolinic (2,6-pyridinedicarboxylic) acid diamides, for example, dipicolinic acid tetrabutyl diamide, can be used as the electroactive component.

In addition, this result is achieved in that the dipicolinic (2,6-pyridinedicarboxylic) acid diamides used as the electroactive component contain N, N′-diethyl-N, N′-ditolyl dipicolinic acid diamide.

However, this result is achieved in that the dipicolinic (2,6-pyridinedicarboxylic) acid diamides used as the electroactive component contain N, N′-diphenyl-N, N′-dimethyldiamide dipicolinic acid.

In addition, this result is achieved in that the dipicolinic (2,6-pyridinedicarboxylic) acid diamides used as the electroactive component contain N, N′-di (4-butylphenyl) dipicolinic acid diamide.

The specified technical result will also be achieved when other dipicolinic acid diamides having a similar chemical structure, but different functional groups that do not significantly affect the properties of the obtained ion-selective electrodes, are used as the electroactive component. The authors draw such a conclusion on the basis of the research results obtained, i.e. the practically minimal effect of the structure and the presence and type of functional groups in dipicolinic acid diamides on the properties of the obtained membranes of ion-selective electrodes, and based on known liquid extraction data: any of the known at least 30 dipicolinic acid diamides can be used as the electroactive component (from a number of homologous compounds), which is confirmed by the following examples.

The essence of the invention is based on the use of laws known for liquid chemical extraction, where synergistic mixtures of dipicolinic acid diamides and chlorinated cobalt dicarbolide are used to isolate various tri- and doubly charged metal ions from complex mixtures. The immobilization of components traditionally used in liquid extraction in the membrane of an ion-selective electrode leads to the possibility of developing ion-selective electrodes with widely varying compositions and properties.

The technical result achieved by the invention is illustrated by specific examples of laboratory tests conducted on the basis of St. Petersburg University.

Example 1

An ion-selective electrode membrane is prepared by dissolving selected weighed portions of all starting materials (polyvinyl chloride, plasticizer, electroactive component, lipophilic additive) in an organic solvent, for example cyclohexane, followed by thorough mixing. Then the solution (total weight of about 3 g) is poured onto a strictly horizontal surface and the membrane is dried for 2 days in the absence of dust. After complete evaporation, samples (actually membranes of ion-selective electrodes) of the required size (circles about 8 mm in diameter) were cut out from the obtained large membrane, which were then glued to the ends of the PVC tubes (electrode cases). After the glue had dried, the electrodes were filled with 0.01 mol / L sodium chloride solution and soaked one day before the first measurement in a solution of the same composition. Subsequently, between measurements, the electrodes were stored in air. Membranes with the following component ratios have optimal electrode properties. To prepare the membrane, take the following ratio of components, wt.%: The electroactive component (tetrabutyl dipicolinic acid diamide) - 1.0; plasticizer (DOS) - 60.0; lipophilic additive (CDK) - 0.1; polyvinyl chloride - the rest.

Example 2

The membrane of the ion-selective electrode is synthesized as described above (in example 1), and for its preparation, the following ratio of components is taken, wt.%: Electroactive component (tetrabutyl dipicolinic acid diamide) - 3.0; plasticizer (DOS) - 75.0; lipophilic additive (CDK) - 0.5; polyvinyl chloride - the rest.

Example 3

The membrane of the ion-selective electrode is synthesized as described above (in example 1), and for its preparation take the following ratio of components, wt.%: Electroactive component (tetrabutyl dipicolinic acid diamide) - 2.0; plasticizer (DOS) - 66.0; lipophilic additive (CDK) - 0.2; polyvinyl chloride - the rest.

Example 4

The membrane of the ion-selective electrode is synthesized as described above (in example 1), and for its preparation take the following ratio of components, wt.%: Electroactive component (N, N′-diethyl-N, N′-ditolyl dipicolinic acid diamide) - 1, 0; plasticizer (DOS) - 60.0; lipophilic additive (CDK) - 0.1; polyvinyl chloride - the rest.

Example 5

The membrane of the ion-selective electrode is synthesized as described above (in example 1), and for its preparation, the following ratio of components is taken, wt.%: Electroactive component (N, N′-diethyl-N, N′-ditolyl dipicolinic diamide) - 3, 0; plasticizer (DOS) - 75.0; lipophilic additive (CDK) - 0.5; polyvinyl chloride - the rest.

Example 6

The membrane of the ion-selective electrode is synthesized as described above (in example 1), and for its preparation take the following ratio of components, wt.%: Electroactive component (N, N′-diethyl-N, N′-ditolyl dipicolinic diamide) - 2, 0; plasticizer (DOS) - 66.0; lipophilic additive (CDK) - 0.2; polyvinyl chloride - the rest.

Measurement of the electrode characteristics of the membranes was carried out by measuring the emf of a galvanic cell:

Ag | AgCl, KCl _us | test solution | membrane | NaCl, 0.01 M, AgCl | Ag

A silver chloride electrode EVL 1M 3.1 filled with a saturated solution of potassium chloride served as a reference electrode. A salt bridge filled with 1 M potassium nitrate solution was used in all measurements.

To measure the pH of the solutions, an ESL 63-07 glass electrode was used, previously calibrated against standard buffer solutions.

The readings were taken on a multichannel digital voltmeter with a high input resistance connected to a personal computer for data collection.

All measurements were performed at room temperature (20 ± 2 ° C).

Figure 1 shows a typical electrode function (the dependence of the sensor potential on the logarithm of the concentration of lead ions) for the obtained electrodes with membranes described in examples 1-6. All investigated electrodes containing the above components in the claimed concentration range exhibit a similar function. When the pH of the solutions, carried out with the help of nitric acid, is reduced to a pH level of 0, the form of the electrode function practically does not change.

Figure 2 shows a typical electrode function of the membranes of these compositions in solutions against a background of 0.1 mol / l of copper nitrate. As can be seen from figure 2, the presence of a significant content of copper ions does not significantly affect the lead function and the coefficient of selectivity to lead in the presence of copper is not worse than 10 ^-5 .

Studies have confirmed the optimal limits of the declared ranges of the membrane composition of ion-selective electrodes (chemical sensors) for the quantitative determination of the concentration of lead ions in aqueous solutions. When changing the composition of the membranes beyond the proposed ranges of compositions, significant problems begin with the qualitative characteristics of the claimed invention, in particular with conductivity (it becomes extremely low, namely less than 10 ^-10 Ohm / cm, with a decrease in the amount of plasticizer and lipophilic additive), which does not allow measuring the potentiometric response of such sensors on any devices with sufficient accuracy: with mechanical strength - membranes with an increased number (above the limits specified in the application) the modifier simply spreads and begins to become soluble in water; an increase in the amount of lipophilic additives leads to a significant deterioration in selectivity; a decrease in the amount of diamide, compared with the declared, leads to a deterioration of all parameters, because there are too few electroactive substances, and an increase leads to a solubility limit, i.e. more diamide in solution during the preparation of the membrane does not dissolve or precipitate when the membrane dries. But all this happens when you go beyond the claimed range, and inside it - the parameters of the electrodes are the same. As an optimal example, the “average” compositions 3 and 6 are given. There is practically no difference between the two diamides (tetrabutyl dipicolinic acid diamide and N, N′-diethyl-N, N′-ditolyl dipicolinic diamide).

The table shows the slopes of the electrode functions (electrode sensitivity) in solutions of Zn ²⁺ , Cd ²⁺ , Cu ²⁺ , Pb ^{2+ ions} (zinc, cadmium, copper, lead) against a background of 0.05 M acetate buffer (1: 1 mixture of 0.1 mol / L sodium acetate and 0.1 mol / L acetic acid, pH 4.6). The angular coefficient (slope) of the electrode function is given in mV / pX, i.e. in millivolts per ten-fold change in the concentration (activity) of a given ion. Membrane compositions are indicated using the following abbreviations: TB - tetrabutyl dipicolinic acid diamide, ET - N, N'-diethyl-N, N'-diethyl dipicolinic acid diamide (dipicolinic acid diamides), DOS - dioctyl sebacinate (plasticizer), CDK - chlorinated cobalt dicarbolide (lipophilic supplement).

Table Angular coefficient, mV / pX Membrane (example number) Zn ²⁺ Cd ²⁺ Cu ²⁺ Pb ²⁺ TB HDK DOS (1) 1 ± 1 1 ± 1 0 ± 1 20 ± 1 TB HDK DOS (2) 0 ± 1 0 ± 1 1 ± 1 30 ± 2 ET HDK DOS (4) 0 ± 1 0 ± 1 1 ± 1 16 ± 2 ET HDK DOS (5) 0 ± 1 1 ± 1 2 ± 1 22 ± 2 TB HDK DOS (3) 0 ± 1 0 ± 1 1 ± 1 29 ± 2 ET HDK DOS (6) 0 ± 1 1 ± 1 2 ± 1 26 ± 2

As can be seen from the results of the studies shown in the table, it follows that in the acetate buffer, the claimed compounds have absolute selectivity to lead; those. The experiments did not reveal the sensitivity and selectivity of the membranes of these compounds to other ions.

The data from laboratory tests confirm the technical result achieved by using the membrane of the proposed composition for the determination of lead ions:

- the coefficient of selectivity to lead ions in the presence of heavy metal ions, in particular copper ions, increases significantly from 10 ^-3 to 10 ^-5 , which in practice gives great opportunities associated with the possibility of real determination of the concentration (quantitative content) of lead in many technological solutions and wastewater, where, as a rule, copper ions are present;

- significantly increases the chemical stability of the obtained membranes, in particular, the new composition allows the measurement of the concentration of lead ions in solutions with pH 0, which in practice gives great opportunities associated with the determination of lead ions on-line in industrially important environments, for example in solutions battery production, as well as in the processing of nuclear waste, such as spent nuclear fuel.

Thus, based on the above examples No. 1-6 and the table confirming the attainability of the indicated technical result, a predictive assessment can be made based on their general chemical and physical nature, in particular extraction properties, that the same result can be achieved when used as electroactive substances and many other known dipicolinic acid diamides in the same ratio as stated in the present invention - namely: N, N′-diphenyl-N, N′-dimethyldiamide dipicolinic acid; N, N′-diphenyl-N, N′-dibenzyl diamide dipicolinic acid; N, N′-di (4-butylphenyl) dipicolinic acid diamide.

List of references

1. RF patent No. 2034289 “Composition of a chalcogenide glass electrode membrane for determining lead ions”, priority 05/10/1989.

2. Didina S.E., Mitnik L. L., Koshmina N.V. Lead-selective electrodes based on liquid ion-exchangers // Sens. Actuators B, 1994, V.18, p. 396-407.

3. Shpigun L.K., Novikov E.A., Zolotev Yu.A. // J. Analit. Chemistry, 1986, Vol. 41, p. 482.

4. Novikov E.A., Shpigun L.K., Zolotov Yu.A. // J. Analit. Chemistry, 1987, T. 42, p. 1540.

5. Sheen S., Shih J. // Analyst, 1992, V.117, p. 1691-1702.

6. Vaishali S. Bhat, Vijeykumar S. Ijeri, Ashwini K. Srivastava, Coated wire lead (II) selective potentiometric sensor based on 4-tert-butylcalix [6] arene // Sens. And Actuators B, 2004, V. 99 (1), p. 98-105.

7. M. Mazlum Ardakany, Ali A. Ennsafi, H. Naeim, A. Dastanpour, A. Shamlli, Highly selective lead (II) coated-wire electrode based on a new Schiff base // Sens. and Actuators B, 2003, V.96, p. 441-445.

8. Hassan Karami, Mir Fazmollah Mousavi, M. Shamsipur, Flow-injection potentiometry by a new coated-graphite ion-selective electrode for determination of lead // Talanta 2003, V.60 (4), p. 775-786.

9. RF patent No. 205466 "Lead-selective electrode membrane", priority 23.09.1993 (prototype).

Claims (6)

1. The composition of the membrane of the ion-selective electrode for determining lead ions, including an electroactive component, a plasticizer, polyvinyl chloride and a lipophilic additive, characterized in that dipicolinic (2,6-pyridinedicarboxylic) acid diamides are used as the electroactive component, and dioctyl sebacinate is used as a plasticizer (DO ), as a lipophilic additive, chlorinated cobalt dicarbolide (CDK) is used, while the composition has the following ratio of components, wt.%: electroactive component 1 0-3.0; plasticizer (DOS) 60.0-72.0; lipophilic additive (CDK) 0.1-6.0; polyvinyl chloride - the rest. 2. The composition according to claim 1, characterized in that the dipicolinic (2,6-pyridinedicarboxylic) acid diamides used as the electroactive component contain tetrabutyl dipicolinic diamide. 3. The composition according to claim 1, characterized in that the dipicolinic (2,6-pyridinedicarboxylic) acid diamides used as the electroactive component contain N, N'-diethyl-N, N'-ditolyl dipicolinic acid diamide. 4. The composition according to claim 1, characterized in that the diamides of dipicolinic (2,6-pyridinedicarboxylic) acid used as the electroactive component contain N, N'-diphenyl-N, N'-dimethyldiamide dipicolinic acid. 5. The composition according to claim 1, characterized in that the diamicides of dipicolinic (2,6-pyridinedicarboxylic) acid used as the electroactive component contain N, N'-diphenyl-N, N'-dibenzyl diamide dipicolinic acid. 6. The composition according to claim 1, characterized in that dipicolinic (2,6-pyridinedicarboxylic) acid diamides used as the electroactive component contain N, N'-di (4-butylphenyl) dipicolinic acid diamide.

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