RU134655U1 - A POTENTIOMETRIC CROSS-SENSITIVE PD-SENSOR TO CATIONS AND ANAONS BASED ON PERFORATED SULFOCATION-EXCHANGE MEMBRANES - Google Patents

Abstract

Potentiometric cross-sensitive to cations and anions PD sensor based on perforated sulfocation-cation exchange membranes, consisting of two cases, one of which has an internal silver chloride reference electrode, the other has a perforated sulfation-cation exchange membrane in potassium form so that one end of the membrane is placed in the first casing, and the other extends beyond the second casing, characterized in that the perforated sulfocation exchange membrane is modified by nanoparticles E ZrOdo half the length, the concentration ZrOv modified half membrane is from 3.0 to 5.0 wt.%; the unmodified end of the membrane is located in the first body, and the modified end extends beyond the second body.

Description

The utility model relates to the field of potentiometric analysis methods using nanocomposite ion-exchange membranes with special properties. It can be used for the joint determination of components in anionic and cationic forms in aqueous and aqueous-organic food, medical and industrial environments.

A potentiometric sensor is known for the selective determination of lysine amino acids in aqueous solutions in the presence of neutral amino acids and NH ₄ ⁺ ions (RF patent No. 2376591, IPC G01N 27/28, 12/20/2009), consisting of a silver chloride comparison electrode, a membrane of a perforated sulfocationite polymer, two cases interconnected, in one of the cases a reference electrode is installed, in the other a membrane is installed so that one end is placed in the first case, and the other extends beyond the second case, and the membranes on may be formed as a strip or rod, or tube, and treated in ethylene glycol at 110 ° C. The distance between the boundaries of the sensor membrane with the comparison solution and the test solution corresponds to the length of the membrane (6-8 cm). The sensor response is measured relative to the silver chloride reference electrode using a high-resistance voltmeter.

The disadvantage of the described invention is that such a sensor cannot be used for the joint determination of anions and cations in aqueous and aqueous-organic media.

The prototype of this technical solution is a potentiometric multisensor measuring complex for the joint determination of organic electrolytes in aqueous solutions (RF patent 109862 IPC G01N 27/00, dated 10.27.2011), including a control unit, a high-resistance multichannel voltmeter, a silver chloride comparison electrode and at least two cross- selective PD sensors, each PD sensor consisting of two cases, one of which has an internal silver chloride reference electrode, and the other has a perfluorinated a sulfocationite polymer tube, or membrane, or rod in such a way that one end is placed in the first case, and the other extends beyond the second case; in each of the cross-selective PD sensors, the membranes are made of perforated sulfocationic polymers in different inorganic and organic ionic forms; and the cases in which the internal reference electrode of PD sensors is installed are filled with 1 M solutions of various inorganic and organic electrolytes corresponding to the ionic forms of perforated sulfocationic polymers.

The disadvantage of the proposed technical solution is the design complexity.

The objective of this technical solution is to create a single sensor, cross-sensitive to anions and cations, simultaneously present in aqueous and aqueous-organic media (food, medical and industrial) containing amino acids, vitamins, drugs, mercaptans and inorganic electrolytes in the region of pH> 7 .

The technical result of this utility model is to simplify the design.

The technical result is achieved by the fact that in a potentiometric cross-sensitive to cations and anions PD sensor (potentiometric sensor, the analytical signal of which is Donnan’s potential) based on perforated sulfocation-cation exchange membranes, consisting of two cases, one of which has an internal silver chloride comparison electrode, in the other is equipped with a perforated sulfocation exchange membrane in potassium form so that one end of the membrane is placed in the first housing and the other ystupaet beyond said second body, according to the proposed technical solution sulfokationoobmennaya perforated membrane modified ZrO ₂ nanoparticles to half the length, and ZrO ₂ concentration in the half of the modified membrane is from 3.0 to 5.0 wt.%; the unmodified end of the membrane is located in the first body, and the modified end extends beyond the second body.

On figa presents a design diagram of a cross-sensitive to the anions and cations of the PD sensor based on a perforated sulfocation exchange membrane.

On figb schematically presents a modified perforated sulfocation exchange membrane is presented.

On figv presents a micrograph of the modified end of the membrane.

Figure 2 shows the physico-chemical characteristics of the membranes MF-4SK and Nafion, modified with ZrO ₂ nanoparticles.

Figure 3 shows the calibration characteristic of the PD sensor, based on MF-4SK and Nation membranes, modified with ZrO ₂ nanoparticles, in alkaline cysteine solutions.

Figure 4 shows the calibration characteristic of the PD sensor based on MF-4SK membranes in alkaline glycine solutions.

Figure 5 shows the calibration characteristic of the PD sensor based on MF-4SK membranes in alkaline solutions of thioglycolic acid.

The design of the PD sensor is shown in FIG. 1a and includes two plastic (or glass) cases 1 and 2 with a volume of 5 and 0.5 cm ³ , respectively, filled with a 1 M KCl solution. Cases 1, 2 are connected through a rubber stopper 3 and hermetically sealed with rubber stoppers 4, 5. A silver chloride reference electrode 6 (silver wire coated with silver chloride) is fixed in the housing 1. In plugs 3 and 5, a perforated sulfocation exchange membrane 7 is fixed in potassium form in the form of a rod with a length of 6 to 8 cm, one half of which is volume-modified with ZrO ₂ nanoparticles, and the other half is the original unmodified membrane. The end of the membrane from the side of the unmodified part with a length of 0.5 cm is inside the body 1, the main part of the membrane with a length of 5 to 7 cm, respectively, is inside the body 2. The end of the membrane with a length of 0.5 cm from the side of the modified part protrudes beyond the body 2 and for a long storage is closed with a protective cap 8. Between measurements, the sensor should be stored in a 1 M KCl solution. The replacement of the comparison solution is carried out through plug 3.

The PD sensor is connected via a multi-channel voltmeter to the control unit.

The operation of the PD sensor is implemented as follows. A 1 M KCl solution is removed from the housing 2, after which the housing 2 is closed by a plug 5. The sensor with the free end of the membrane is immersed in the test solution. To calibrate the PD sensor, the potentials of the PD sensor and the glass pH-selective electrode are measured relative to the silver chloride comparison electrode 6 using an electronic multi-channel high-resistance analog-to-digital converter. Potential values are recorded after 2-5 minutes, processed using software, the concentration values of the determined components of the investigated solutions are displayed on the screen.

The procedure for producing perforated sulfocation exchange membranes 7 modified with ZrO ₂ nanoparticles is as follows. A sample of the membrane 6-8 cm long is kept for 24 hours in a saturated solution of zirconium zirconium ZrOCl ₂ with constant stirring at a temperature of 28 ° C so that only one end of the membrane is immersed, equal to half the total length (3-4 cm) ( figb). The membrane is then immersed in a 0.15 M ammonia solution to obtain hydrated ZrO ₂ in the membrane matrix. To obtain 4.0 ±, 01, 4.5 ± 0.1, 5.0 ± 0.1 wt.% ZrO ₂ at the modified end of the MF-4SK membrane, it is necessary to carry out 1, 2 or 3 treatment cycles, respectively. To obtain 3.0 ± 0.1, 3.5 ± 0.1, 4.0 ± 0.1 wt.% ZrO ₂ at the modified end of the Nation membrane, it is necessary to carry out 1, 2 or 3 treatment cycles, respectively.

The proportion of C ₂ O ₄ ^2- ion transfer upon diffusion of a 0.1 M solution of C ₂ O ₄ K ₂ at the modified end is 9%; diffusion permeability of a 0.1 M solution of C ₂ O ₄ K ₂ through the modified end of the membrane - (3.9-5.4) · 10 ^-8 cm ² / s with a membrane size of 6 × 0.1 × (0.010-0.016) cm .

The proposed membrane for the PD sensor should have the specified characteristics. According to transmission electron microscopy, the size of the ZrO ₂ particles embedded in the membrane matrix is 3-7 nm, the particles are evenly distributed over the volume of the modified part of the membrane (Fig. 1c). The modification leads to a decrease in the diffusion permeability coefficient determined by the rate of transfer of anions in the membrane and to an increase in the selectivity of cation transfer by the modified end of the membrane.

The proposed membrane operates as an electroactive material of the PD sensor as follows. Due to the nonuniform distribution of ZrO ₂ nanoparticles in the membrane, nonequivalence of ion transport from opposite ends is realized in it. The modified side of the membrane contains two types of hydrophilic sorption centers: fixed cation exchange sulfo groups and nanoparticles of the amphoteric dopant ZrO ₂ capable of sorbing cations and anions. The reactions that determine the potential of a PD sensor based on perforated sulfocation exchange membranes in potassium form in alkaline solutions modified with ZrO ₂ nanoparticles are ion exchange reactions proceeding according to the schemes:

Example 1

We compared the sensitivity of PD sensors to anions and cations using membrane samples modified with ZrO ₂ nanoparticles with a dopant concentration in the modified end of 2.8 to 4.5 wt.%. As the starting material for the preparation of membranes modified with ZrO ₂ nanoparticles, we used perforated sulfocation-cation-exchange membranes MF-4SK and Nation.

The objects of analysis were aqueous solutions of the cysteine amino acid containing an excess of potassium hydroxide. The pH values of the solutions ranged from 8.22 ± 0.05 to 10.50 ± 0.05. The ionic composition of such solutions is represented by anions CH ₃ СОСООО ^- , HS ^- , ОН ^- and cations K ⁺ , NH4 ⁺

The potentials of a PD sensor based on potassium membrane membranes modified with ZrO ₂ nanoparticles and a glass pH selective electrode were measured relative to a silver chloride reference electrode in an aliquot of a 5 ml solution using an electronic multichannel high-resistance analog-to-digital converter. The potential values were recorded after 2-5 minutes and were automatically displayed on a personal computer.

To assess the sensitivity of the PD sensor to cations and anions in the studied solutions, calibration equations were obtained that take into account the influence of three factors on the sensor response: pH; negative logarithm of the total concentration of K ⁺ , NH ₄ ⁺ cations in solution; negative logarithm of the total concentration of anions CH ₃ COOCOO ^- and HS ^- in solution:

where Δφ _D is the analytical signal of the PD sensor (mV); С ₊ - total concentration of K ⁺ and NH ₄ ⁺ (M) cations; С _- - total concentration of anions СН ₃ СОСООО ^- and HS (М); b ₀ is the free term of the calibration equation (mV); b ₁ , b ₂ , b ₃ - pre-logarithmic coefficients (mV / pС), which are estimates of the sensitivity of the response of the sensor to the corresponding ions.

An increase in the concentration of ZrO ₂ in the modified part of the membrane leads to an increase in the sensitivity coefficients of the PD sensor to anions (Fig. 3), because the number of centers (ZrO ₂ nanoparticles) sorbing anions increases, and the number of centers (fixed sulfo groups of the membrane) that impede the sorption of anions decreases due to their blocking by dopant particles. The cation sensitivity for cysteine solutions will change non-monotonously, because with increasing dopant concentration, redistribution of contributions to the sensor response of cations sorbed by sulfo groups and dopant particles occurs.

The greatest increase in the sensitivity of the PD sensor to anions compared with its sensitivity to cations was obtained for the highest dopant concentrations at the modified end of the membrane 4.5 wt.% For MF-4SK, 2.8 wt.% For Nation. The use of MF-4SK membranes in potassium form with a ZrO ₂ concentration in the modified end of 4.5 wt% provides a comparable high sensitivity of PD sensors to anions (55 mV / pC) and cations (46 mV / pC) in alkaline cysteine solutions ( figa). The use of Nation membranes in potassium form with a concentration of ZrO ₂ at the modified end of 2.8 wt.% Provides 7.5 times greater sensitivity to anions than to cations in alkaline cysteine solutions (Fig.3b).

This allows the use of PD sensors based on perforated sulfocation exchange membranes, gradiently modified with ZrO ₂ nanoparticles, as cross-sensitive for organizing multisensor systems for the joint determination of anions and cations present in aqueous and aqueous-organic media in the pH range> 7 containing organic and inorganic electrolytes.

Example 2

The sensitivity of PD sensors based on MF-4SK membranes modified with ZrO ₂ nanoparticles to anions and cations in alkaline glycine solutions was assessed. The dopant concentration at the modified end of the membrane was 4.5% by weight.

The objects of analysis were aqueous solutions containing the amino acid glycine (Gly) and potassium hydroxide. The pH values of the solutions ranged from 10.70 ± 0.05 to 14.00 ± 0.05. The ionic composition of such solutions is represented by Gly ^- , OH ^- , K ⁺ ions and Gly ^± zwitterions.

The potentials of a PD sensor based on potassium membrane membranes modified with ZrO ₂ nanoparticles and a glass pH selective electrode were measured relative to a silver chloride reference electrode in an aliquot of a 5 ml solution using an electronic multichannel high-resistance analog-to-digital converter. The potential values were recorded after 2-5 minutes and were automatically displayed on a personal computer.

To assess the sensitivity of the PD sensor to cations and anions in alkaline glycine solutions, calibration equations were obtained that take into account the influence of three factors on the sensor response: pH; negative logarithm of the concentration of K ⁺ in solution (pC ₊ ); negative logarithm of the total concentration of Gly ^- and Gly ^± in solution (pС):

. The use of MF membranes 4SK-potassium form in a concentration of 4.5 wt% dopant in a modified end provides an increase in sensitivity of the sensor to the PD-Gly ^-, Gly ^± 2 times and OH ^- by 1.7 times and reduced sensitivity to K ⁺ 9 times compared with the original unmodified membrane (figure 4). Thus, the use of MF-4SK membranes gradient modified with ZrO ₂ nanoparticles with a dopant concentration in the modified end of 4.5 wt% ensures the cross sensitivity of the PD sensor to Gly ^- , Gly ^± , OH ^- , K ⁺ in solutions at pH> 7, in contrast to the PD sensor based on the initial unmodified membrane, mainly sensitive to K ⁺ .

Example 3

The sensitivity of PD sensors based on MF-4SK membranes modified with ZrO ₂ nanoparticles to anions and cations in alkaline solutions of thioglycolic acid was assessed. The dopant concentration at the modified end of the membrane was 5.0 wt.% On the modified side.

The objects of analysis were aqueous solutions containing mercaptoacetic acid and potassium hydroxide. The pH values of the solutions ranged from 10.65 ± 0.05 to 13.83 ± 0.05. The ionic composition of such solutions is represented by HSCH ₂ COO ^- , SCH ₂ COO ^2- , OH ^- , K ⁺ ions.

The potentials of a PD sensor based on potassium membrane membranes modified with ZrO ₂ nanoparticles and a glass pH selective electrode were measured relative to a silver chloride reference electrode in an aliquot of a 5 ml solution using an electronic multichannel high-resistance analog-to-digital converter. The potential values were recorded after 2-5 minutes and were automatically displayed on a personal computer.

To assess the sensitivity of the PD sensor to cations and anions in alkaline solutions of mercaptoacetic acid, calibration equations were obtained that take into account the influence of three factors on the sensor response: pH; negative logarithm of the concentration of K ⁺ in solution (pC ₊ ); negative logarithm of the total concentration of HSCH ₂ COO ^- and SCH ₂ COO ^2- in solution (pС _- ):

. The use of MF membranes 4SK-potassium form in a concentration of dopant in the modified end 5.0 wt% provides an increase in PD sensor sensitivity HSCH ₂ COO ^- and SCH ₂ COO ^2- 7.4 times and OH ^- 3.6 times, as well as a decrease in sensitivity to K ⁺ in 2.4 times compared with the original unmodified membrane (figure 5). Thus, the use of MF-4SK membranes modified with ZrO ₂ nanoparticles with a dopant concentration at the modified end of 5.0 wt% ensures the cross sensitivity of the PD sensor to HSCH ₂ COO ^- , SCH ₂ COO ^2- , OH ^- , K ⁺ c solutions at pH> 7, in contrast to the PD sensor based on the initial unmodified membrane, mainly sensitive to K ⁺ .

Claims (1)

Potentiometric cross-sensitive to cations and anions PD sensor based on perforated sulfocation-cation exchange membranes, consisting of two cases, one of which has an internal silver chloride reference electrode, and the other has a perforated sulfation-cation exchange membrane in potassium form so that one end of the membrane is placed in the first housing, and the other extends beyond the second housing, characterized in that the perforated sulfocation exchange membrane is modified nanoparticles E ZrO ₂ up to half the length, and ZrO ₂ concentration in the half of the modified membrane is from 3.0 to 5.0 wt.%; the unmodified end of the membrane is located in the first body, and the modified end extends beyond the second body.

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