RU2546045C1 - Ion-selective membrane for determining ionic surfactants - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used for potentiometric determination of anionic and cationic surfactants, such as alkyl sodium sulphates, alkylpyridinium and tetraalkylammonium salts in multicomponent mixtures, detergent and cleaning compositions, process solutions, waste water and medicinal preparations. According to the invention, an ion-selective electrode membrane consists of polyvinyl chloride as a polymer matrix, dibutyl phthalate as a plasticiser and an electrode-active compound containing copper and sodium dodecyl sulphate, wherein the electrode-active compound further contains 1,10-phenanthroline, wherein the copper, 1, 10-phenanthroline and sodium dodecyl sulphate are taken in ratio of 1:2:2, respectively, and components of the membrane are in a certain weight ratio.

EFFECT: invention enables to obtain a polymer membrane which is sensitive to homologues of alkylpyridinium, tetraalkylammonium and alkyl sodium sulphates, and producing an ion-selective electrode based on said membrane, for rapid quantitative determination of ionic surfactants in water bodies.

4 ex, 5 tbl, 11 dwg

Description

The invention relates to analytical chemistry in the field of potentiometry, i.e. to ion-selective electrodes, which can be used for potentiometric determination of anionic and cationic surfactants (surfactants), for example, alkyl sulfates, salts of alkylpyridinium, tetraalkylammonium in multicomponent mixtures and for the analysis of detergents, cleaning compositions, technological solutions, wastewater.

The inventive ion-selective membrane can be used to determine ionic (cationic, anionic) surfactants in various objects, for example, drugs, shampoos, detergents, cosmetics, wastewater, etc.

A topical issue in analytical chemistry is the control of the content of surfactants in detergents, cosmetics, and medicines to control the quality of products, as well as in waste and natural waters at the maximum permissible concentrations (MPC) in order to protect the environment and human health. The effectiveness of quality control of products containing surfactants is ensured by the introduction of modern physical and chemical methods of analysis into the practice of chemical and technological industries, among which the potentiometric method with ion-selective electrodes occupies an important place.

The objects of this study are homologues of alkyl sulfates, alkyl pyridinium and tetraalkylammonium, which are the basis of various synthetic detergents (washing powders, tablets and liquids for dishwashers, fabric softeners, hair and skin care products, disinfecting medicines, etc.).

For separate determination of ionic surfactants in liquid media, spectroscopic, electrophoretic, chromatographic methods are used, for example, high performance liquid chromatography, electrochemical.

It was proposed to use spectrophotometry (detergents, shampoos, soaps, natural, flushing and waste waters), sorption and extraction-photometric methods (natural and drinking waters), chemiluminescence (model solutions, and drinking water, conditioner shampoos), capillary electrophoresis (household chemicals, toothpaste, cosmetics and pharmaceuticals, natural and waste water, sewage sludge), high effect conventional liquid chromatography (natural waters), ion-pair reversed-phase chromatography (wastewater of enterprises), liquid chromatography with mass spectrometric detector (river and wastewater, sewage sludge) [Kulapin AI, Arinushkina TV Methods for the separate determination of synthetic surfactants (review) // Factory Laboratory. Diagnostics of materials. - 2001 - T.67, No. 11, - p.3; Lange K.R. Surfactants: synthesis, properties, analysis, application. St. Petersburg: Profession, 2005; Kulapina E.G., Chernova R.K., Makarova N.M., Pogorelova E.S. Methods for the determination of synthetic surfactants (review) // Review Journal of Chemistry. - 2013 - T.3, No. 4, S.297-337].

However, the analysis of the compositions of synthetic detergents, cosmetics and medicines, waste and natural waters, etc. for the content of ionic surfactants using known methods is characterized by laboriousness, toxicity, and the complexity of the hardware design.

One of the promising methods for determining ionic surfactants in wastewater and synthetic detergents is potentiometry using various sensors, for example, ion-selective electrodes (ISE). The method is characterized by expressivity, selectivity, simplicity and accessibility of equipment.

There are solid-state sensors for determining ionic surfactants based on the ionic associates of n-hexadecyltrimethylammonium 1-pentanesulfonate and tetrabutylammonium dodecyl sulfate. ISE data can quantify alkyl benzene sulfonates, alkyl sulfates, alkyl sulfate esters, quaternary ammonium salts and fatty amine oxides [Campbell W.C., Dowle Ch.J. European Patent Application GB 8716809 G01N 27/30, G01N 21/00. 07/16/1987].

A membrane formed from a water-insoluble polyelectrolyte and a surfactant to which the electrode is sensitive is proposed in the patent [Petrak KL, Weller E.Ch. UK Patent application GB 2076545 A. 05.23.1980]. Polyelectrolytes were formed from monomers: olefins, acrylates, styrenes or vinyl esters. Comonomers that can be used in addition to those listed above include styrene, vinyl pyridine, vinyl acetate, vinyl chloride, alkyl acrylates and methacrylates. Cationic comonomer groups may contain a tertiary nitrogen atom, which transforms into a quaternary nitrogen during complexation: pyridine, imidazole, quinoline, isoquinoline, pyrimidine, phenanthroline, benzthiazole, purine, pyrazole, acridine or picoline; anionic ones contain carbocyclic or sulfo groups. Complexes of poly (ethyl acrylate) ₁₀ - co - (1-vinylimidazole) and poly (ethyl acrylate) ₁₀ - co - (3-benzyl-1-vinylimidazole chloride) complexes were presented as examples of electrode-active membrane components.

A known method of ionometric determination of ionic surfactants based on the use of ISE with membranes containing ionic associates of sodium alkyl sulfates with salts of alkyl pyridinium as an EIA [Kulapin AI, Mikhailova A.M., Materova EA Selective solid-contact electrodes for determining ionogenic surfactants // Electrochemistry. 1998.- T.34. - No. 4. - S. 421].

A method for the separate determination of cationic, anionic and nonionic surfactants by potentiometric titration with an ion-selective electrode containing a membrane based on the ionic associate of cetylpyridinium tetraphenylborate has been patented [Kulapin A.I., Arinushkina T.V. RF patent 2141110 C1, No. G01N 27/42 of 11/10/1999]. The invention relates to the field of analytical chemistry and can be used for separate determination of ionic and nonionic surfactants in various objects, for example shampoos, detergents, wastewater, etc.

However, the range of the determined contents of salts of alkyl sulfates and alkyl pyridinium in such ISEs is 10 ^-6 (10 ^-5 ) -10 ^-2 (10 ^-3 ) mol / l, which does not allow the determination of ionic surfactants at and below the MPC of fishery reservoirs . The response time of such electrodes in dilute solutions is 2-3 minutes, making the analysis long.

The known complex [Co (1,10-phenanthroline) ₂ (C _l4 H ₂₉ NH ₂ )] ²⁺ Cl ₂ · 3H ₂ O, which studied the antimicrobial properties against gram-positive and gram-negative bacteria and fungi [Kumar RS, Arunachalam S. Synthesis , micellar properties, DNA binding and antimicrobial studies of some surfactant-cobalt (III) complexes // Biophysical Chemistry. 2008 .-- V.136. - P.136; Kumar RS, Paul P., Riyasdeen A., Wagniéres G., van den Bergh H., Akbarsha MA, Arunachalam S. Human serum albumin binding and cytotoxicity studies of sur-factant-cobalt (III) complex containing 1,10-phenanthroline ligand // Colloids and Surfaces B: Biointerfaces. 2011. - V.86. - P.35-44].

Authors [Nomura T., Sato A. Adsorptive determination of copper (II) in solution as an ion-pair of bisneocuproinecopper (I) and dodecylsulfate ions on an electrode-separated piezoelectric quartz crystal // Analytica Chimica Acta. 1998. V.374. - P.291-296] adsorbed an ionic pair of a copper (I) complex with 2,9-dimethyl-1,10-phenanthroline (non-cuproin) and dodecyl sulfate ion on a quartz plate of a piezoelectric quartz sensor.

However, such complexes were not used in potentiometry.

Closest to the claimed patent is the work [Schipunov Yu.A., Shumilina EV Associations of dodecyl sulfate with copper complexes with alkyl derivatives of diamines. Optical properties and ion-selective electrodes // Zh. analyte. chemistry. 1996.- T.51. - No. 7. - S.758], in which a polymer membrane composition based on an associate of a complex of copper with 1 N, N′-dialkylethylenediamine and dodecyl sulfate was proposed for the manufacture of ion-selective electrodes. The electrodes allow ionometric determination of sodium dodecyl sulfate in water in the concentration range from 10 ^-6 to 8 · 10 ^-3 M. The life of the electrodes is 7-8 months; response time - 1 min in concentrated solutions (> 3 · 10 ^-4 M) and 3 min in diluted solutions (<1 · 10 ^-4 M).

However, the electrodes we obtained have a lower detection limit, longer electrode life, and shorter response time in dilute solutions.

The objective of the invention is the creation of an ISE membrane for the rapid determination of homologues of salts of alkylpyridinium, tetraalkylammonium and alkyl sulfates in wastewater, detergents, pharmaceuticals and the creation of an ion-selective electrode sensitive to ionic surfactants based on the obtained membrane for their quantitative determination in aqueous media.

The technical result is to lower the detection limit of ionic surfactants in aqueous media, to reduce the error in determining the result, to reduce the response time of the electrode in dilute solutions.

The problem is solved in that the membrane of the ion-selective electrode, consisting of polyvinyl chloride as a matrix, dibutyl phthalate as a plasticizer and an electrode-active compound containing copper and sodium dodecyl sulfate, according to the solution, the electrode-active compound additionally contains 1,10-phenanthroline, and copper, 1,10-phenanthroline and sodium dodecyl sulfate are taken in a ratio of 1: 2: 2, respectively, and the membrane components are in the following ratio, wt.%:

Polyvinyl chloride 24.9-24.6 Dibutyl phthalate 74.6-73.9 Electrode active compound 0.5-1.5

The invention is illustrated by drawings.

Figure 1 presents the design of the solid contact electrode, where the positions indicated:

1 - down conductor;

2 - polyvinyl chloride tube;

3 - graphite rod;

4 - ion-selective membrane.

Figure 2 shows the saturation curve (the dependence of the optical density on the volume of 1,10-phenatrolin) to determine the composition of the complex copper-1,10-phenanthroline.

Figure 3 shows the determination of the composition of the copper-1,10-phenanthroline complex by the isomolar series method.

Figure 4 presents the titration curve of 10 ml of 1 · 10 ^-2 M solution of sodium dodecyl sulfate 5 · 10 ^-2 M solution of a complex of copper (II) with 1,10-phenanthroline.

Figure 5 shows a graph of the dependence of the EMF (mV) on the time of the experiment (s) with an abrupt change in the concentration of the DDS solution.

Figure 6 shows a graph of EMF (mV) versus the negative logarithm of the concentration (pC) of anionic surfactants: tetradecyl sulfate (TTDS) (1), dodecyl sulfate (DDS) (2) and sodium hexadecyl sulfate (GDS) (3).

Figure 7 shows a graph of the dependence of the emf (mV) on the negative logarithm of the concentration (pC) of cationic surfactants: cetyltrimethylammonium bromide (CTMA) (1), octadecyliridinium (NDP) (2), cetylpyridinium (CP) (3) and benzyl dimethyl tetradecylammonium (BD) ( (4) chlorides.

On Fig presents a titration curve of anionic surfactants in the washing water of the washing machine. Synthetic Detergent (CMC) - Eared Nannies Powder.

Figure 9 shows the titration curve of anionic surfactants in the Eared Nanny CMC powder.

Figure 10 shows the titration curve of cationic surfactants in hair balm.

Figure 11 presents the titration curve of cationic surfactants in the drug "Chlorhexidine".

The inventive membrane can be used to determine ionic surfactants in wastewater, washing water washing machines, synthetic detergents, cosmetics and hygiene products, medicines.

As a rule, standard and indicator ion-selective electrodes (ISE) are used to measure EMF. The design of the indicator ISE contains an electrode housing, which is a polyvinyl chloride tube 2 with a graphite rod 3 and a collector 1.

The inventive membrane 4 is an elastic film containing a powder of polyvinyl chloride, previously dissolved in cyclohexanone, a plasticizer solvent - dibutyl phthalate and EAB - a complex compound of copper (II) with 1,10-phenanthroline and dodecyl sulfate.

The implementation of the membrane using a combination of copper with 1,10-phenanthroline and dodecyl sulfate as the electrode-active substance ensures the universality of the electrode, which can be used to determine homologs of both cationic and anionic surfactants. The choice of copper (II) cations as a complexing agent is due to the fact that copper salts are non-toxic and the complex of copper and pyridine is well known. As the ligand, 1,10-phenanthroline was chosen, since its structure contains two tertiary nitrogen atoms, which are tightly bound in aromatic cycles. During the complexation reaction, tertiary nitrogen atoms bind to a copper (II) ion and become quaternary. Thus, in the resulting electrode-active substance, which is part of the membrane of the potentiometric sensor, there are quaternary nitrogen atoms, as well as in the surfactants we define: tetraalkylammonium salts and alkylpyridinium salts, which allows us to obtain reproducible analytical signals to these compounds.

The authors developed a method for producing complex compounds. In a 100 ml beaker, 25 ml of sodium dodecyl sulfate solution C = 1 · 10 ^-2 M and 25 ml of copper (II) sulfate solution C = 1 · 10 ^-1 M are placed, 25 ml of a water-alcohol solution C = 1 · 10 is added ^-2 M of 1,10-phenanthroline. The obtained blue precipitate was filtered off on a Schott filter (pore diameter 40 nm) and washed with ethanol. The resulting precipitate is dried at a temperature of 50-60 ° C (in order to avoid decomposition of the electrode-active substance) for 5-6 hours to remove moisture.

The composition of the resulting complex of copper with 1,10-phenanthroline and dodecyl sulfate was studied. A spectrophotometric study of the complexation in the copper (II) - 1,10-phenanthroline system under the given experimental conditions was previously performed. The molar ratio of copper (II) and 1,10-phenanthroline in the complex was determined by saturation and isomolar series methods. The graph (figure 2) shows the saturation curve (the dependence of optical density on the volume of 1,10-phenanthroline) to determine the composition of the complex copper - 1,10-phenanthroline, C _Cu = C _Phen = 5 · 10 ^-2 M, V _{Cu ( II)} = 2 ml.

The graph shows that for each mole of Cu ²⁺ there are 2 mol of 1,10-phenanthroline.

Figure 3 shows the determination of the composition of the copper-1,10-phenanthroline complex by the isomolar series method: 0-9 parts of 1,10-phenanthroline (0-4.5 ml) C _Phen = 5 · 10 ^-2 M and 10 are poured into test tubes -1 part of copper (II) sulfate (5-0.5 ml) C _Cu = 5 · 10 ^-2 M.

The maxima of the isomolar series lie in the range of molar ratios of 6.6: 3.3, which corresponds to the composition of the complex Cu (II) - 1,10-phenanthroline 1: 2.

The composition of the electrode-active substance was determined by processing the curves of potentiometric titration of 1 · 10 ^-2 M sodium dodecyl sulfate with a solution of a complex of copper with 1,10-phenanthroline.

Figure 4 presents the titration curve of 10 ml of 1 · 10 ^-2 M solution of sodium dodecyl sulfate 5 · 10 ^-2 M solution of a complex of copper (II) with 1,10-phenanthroline.

Thus, it was found that the stoichiometric ratio of the reacting components of the ionic associate [Cu (Phen) ₂ ] ²⁺ and DDS ^- - anions is 1: 2.

We studied the electrode and dynamic properties of membranes based on the complex compound [Cu (Phen) ₂ ] DDS ₂ . The combination of copper with 1,10-phenanthroline in the inner sphere of the complex compound prevents the leaching of 1,10-phenanthroline and ensures the stability of the whole compound, its low solubility, high ion-exchange ability, which is confirmed by experimental studies and comparison of the properties of the ion exchanger with another electrode-active substance (see Tables 1, 2).

Table 1 Electrode properties of membranes based on organic ion exchangers (With _EAS = 1%, n = 4, p = 0.95) EAS Detectable Surfactant K _s Linearity, M Detection limit Angular coefficient, mV / rС mol / l mg / l [Cu (Phen) ₂ ] DCS ₂ Cetylpyridinium chloride (3.1 ± 0.4) · 10 ^-13 1 · 10 ^-4 -1 · 10 ^-6 6 · 10 ^-7 0.11 55-59 Sodium dodecyl sulfate 1 · 10 ^-3 -2 · 10 ^-7 1 · 10 ^-7 0.05 53-57 CPU-DDS Cetylpyridinium chloride (2.1 ± 0.4) -10 ^-12 1 · 10 ^-3 -1 · 10 ^-6 8 · 10 ^-7 0.27 54-56 Sodium dodecyl sulfate 1 · 10 ^-2 -1 · 10 ^-6 7 · 10 ^-7 0.24 57-58 [CuL ₂ ] DDS ₂ L = N, N′-dialkylethylenediamine Sodium dodecyl sulfate - 8 · 10 ^-3 -1 · 10 ^-6 - - 55-61 where K _s is the solubility product of ion exchangers

As a result of the experiments and studying the properties of the components of the EAS, it was concluded that the introduction of a complex of membranes of copper with 1,10-phenanthroline and dodecyl sulfate in the membranes reduces the detection limit of surfactants.

The dynamic characteristics of a membrane based on the Cu (Phen) ₂ DDS ₂ complex with an abrupt change in concentration are studied. The time to establish the stationary potential (response time) of the sensor in the entire studied range of concentrations did not exceed 15 seconds, which confirms the graph (Fig. 5) of the dependence of the emf (mV) on the experiment time (s) with an abrupt change in the concentration of the DDS solution.

table 2 The dynamic properties of the membrane based on the associates Cu (Phen) ₂ DDS ₂ and CP-DDS (comparative characteristic) (With _EAW = 1%, n = 4, p = 0.95) Eav concentration change Response time, t ₉₅ , s Potential drift, mV / day Service life, month Cu (Phen) ₂ DDS ₂ 10 ^-6 -10 ^-5 11.0 ± 0.5 0.5-1.0 12 10 ^-5 -10 ^-4 6.0 ± 0.2 10 ^-4 -10 ^-3 15.0 ± 0.6 CPU-DDS 10 ^-5 -10 ^-4 35.0 ± 2.0 1.0-2.0 12 10 ^-4 -10 ^-3 37.0 ± 2.0

The resulting sensor based on a complex of copper with 1,10-phenanthroline and dodecyl sulfate is characterized by a short response time, therefore, it has a high ion-exchange ability.

The response time of the sensor under study is much shorter than for the electrode based on the ionic associate of CP-DDS, and it is somewhat shorter in diluted surfactant solutions (see Table 2).

When using a complex of copper with 1,10-phenanthroline and dodecyl sulfate, the response time decreases, therefore, a rapid exchange of ions occurs both with the internal phase of the complex (1,10-phenanthroline) and with the external phase (dodecyl sulfatanion) compared to the previously studied ionic associate cetylpyridinium dodecyl sulfate.

The following are examples of the implementation of membranes with different concentrations of EAS:

EAS c = 0.5%.

1.6014 g or 74.6% of dibutyl phthalate, 2-3 ml of tetrahydrofuran were placed in a 10 ml bottle, and with constant stirring on a magnetic stirrer with slight heating at 50-60 ° C, 0.0107 g or 0.5% of copper complex compound was added. (II) with 1,10-phenanthroline and dodecyl sulfate and 0.5338 g or 24.9% polyvinyl chloride. Stirring was continued until the mixture was completely homogenized. The membrane composition was poured into a Petri dish with a diameter of 95 mm and left in air until tetrahydrofuran was completely removed.

Polyvinyl chloride 24.9% Dibutyl phthalate 74.6% Electrode active substance 0.5%

EAS with = 1.0%.

In a 10 ml bottle, 1.6014 g or 74.2% of dibutyl phthalate, 2-3 ml of tetrahydrofuran were placed, and with constant stirring on a magnetic stirrer with slight heating at 50-60 ° C, 0.0216 g or 1.0% of copper complex compound was added. (II) with 1,10-phenanthroline and dodecyl sulfate and 0.5338 g or 24.8% polyvinyl chloride. Stirring was continued until the mixture was completely homogenized. The membrane composition was poured into a Petri dish with a diameter of 95 mm and left in air until tetrahydrofuran was completely removed.

Polyvinyl chloride 24.8% Dibutyl phthalate 74.2% Electrode active substance 1,0%

EAS with = 1.5%.

1.6014 g or 73.9% of dibutyl phthalate, 2-3 ml of tetrahydrofuran were placed in a 10 ml bottle, and with constant stirring on a magnetic stirrer with slight heating at 50-60 ° C, 0.0325 g or 1.5% of copper complex compound was added. (II) with 1,10-phenanthroline and dodecyl sulfate and 0.5338 g or 24.6% polyvinyl chloride. Stirring was continued until the mixture was completely homogenized. The membrane composition was poured into a Petri dish with a diameter of 95 mm and left in air until tetrahydrofuran was completely removed.

Polyvinyl chloride 24.6% Dibutyl phthalate 73.9% Electrode active substance 1.5%

The obtained membrane composition was used for the manufacture of solid contact electrodes: a 7 mm diameter disk was cut out and glued to a cleaned and polished polyvinyl chloride case with glue containing 0.5 g of polyvinyl chloride, 0.25 g of dibutyl phthalate and 5 ml of cyclohexanone. The electrodes made in this way were conditioned for 1 day in a 1 · 10 ^-3 M solution of the corresponding ionic surfactant.

In the ionometric measurement of the concentration of ionic surfactants, an indicator electrode is used, which is placed in a solution of a surfactant, and then calibrated by measuring electrode potentials (EMF) of an electrochemical circuit composed of an indicator ISE and a standard silver chloride electrode using ionic surfactant solutions with a known concentration.

The EMF value was measured as a function of the concentration of solutions of homologues of alkyl pyridinium, tetraalkyl ammonium, and alkyl sulfates.

Figure 6 shows a graph of EMF (mV) versus the negative logarithm of the concentration (pC) of anionic surfactants: tetradecyl sulfate (TTDS) (1), dodecyl sulfate (DDS) (2) and sodium hexadecyl sulfate (GDS) (3). ESA: Cu (Phen) ₂ DDS ₂ .

Dependence of EMF (mV) on the negative logarithm of the concentration (pC) of cationic surfactants: cetyltrimethylammonium bromide (CTMA) (1), octadecyliridinium (NDP) (2), cetylpyridinium (CP) (3) and benzyl dimethyl tetradecylammonium (4DM) in Fig.7. ESA: Cu (Phen) ₂ DDS ₂ .

Anionic functions are performed in the concentration range 1 · 10 ^-3 -2 · 10 ^-7 (1 · 10 ^-7 ) M with angular coefficients 55 ± 5 mV / rС, cationic in the range 5 · 10 ^-4 (1 · 10 ^-4 ) -1 · 10 ^-6 (6 · 10 ^-7 ) M with angular coefficients of 60 ± 7 mV / rС. These characteristics indicate that the electrode is sensitive to ionic surfactants according to the Nernst equation that underlies the potentiometric analysis method.

The sensitivity (selectivity) of the electrode to non-ionic surfactants, homologues of ionic surfactants and inorganic ions that are part of wastewater and synthetic detergents is illustrated in Table 3, which presents potentiometric selectivity coefficients for various substances for a membrane based on Cu (Phen) ₂ DDS ₂ .

The data in Table 3 indicate the possibility of using an electrode based on the selected EAS for determining ionic surfactants in wastewater and synthetic detergents.

Table 3 Coefficients of potentiometric selectivity to various substances (With _EAS = 1%, n = 3, p = 0.95) Main ion Interfering ion To _sat Nonylphenol-12 (6.9 ± 0.4) · 10 ^-3 Cu ²⁺ (1.2 ± 0.1) · 10 ^-2 Ba ²⁺ (1.4 ± 0.1) · 10 ^-2 Cetylpyridinium Na ⁺ (2.2 ± 0.2) · 10 ^-2 NH ⁴⁺ (1.0 ± 0.4) · 10 ^-2 ODP (2.9 ± 0.4) · 10 ^-2 CTMA (1.0 ± 0.1) · 10 ^-1 BDMTDA (2.3 ± 0.1) · 10 ^-1 Nonylphenol-12 (6.1 ± 0.3) · 10 ^-3

(3.1 ± 0.1) · 10 ^-2 Cl ^- (1.6 ± 0.2) · 10 ^-2 Dodecyl sulfate

(1.4 ± 0.4) · 10 ^-2

(7.1 ± 0.4) · 10 ^-2 CH ₃ COO ^- (1.5 ± 0.1) · 10 ^-2 GDS (1.0 ± 0.2) · 10 ^-1 TTDS (2.3 ± 0.1) · 10 ^-1

An example of the use of an electrode with the claimed membrane for determining ionic surfactants in wastewater and washing water of washing machines.

In a titration beaker, 30-50 ml of wastewater or 20-50 ml of washing water from washing machines are pipetted and a solid contact selective electrode is placed. The silver chloride reference electrode is placed directly in the electrochemical cell or connected to the test solution by means of a salt bridge, which is a tube filled with a saturated solution of potassium chloride.

The sample is titrated with a 1 · 10 ^-3 M solution of cetylpyridinium chloride (for the determination of ACAS) or sodium dodecyl sulfate (for the determination of surfactants), adding 0.1-0.2 ml of titrant. A titration curve is constructed in coordinates E, mV - V, ml and an equivalence point is determined (for anionic surfactants in powder) (Fig. 8).

The total content of anionic surfactants is converted to sodium dodecyl sulfate, cationic surfactants to cetylpyridinium chloride.

The surfactant content is calculated by the formula:

where C _tit - the concentration of the titrant solution, mol / l;

V _TE - titrant volume at the equivalence point, ml;

V _al - the volume of an aliquot of the sample solution, ml;

M is the molar mass of sodium dodecyl sulfate (for determining anionic surfactants) or cetylpyridinium chloride (for determining cationic surfactants), g / mol.

Thus, the use of complex compound Cu (Phen) ₂ DDC ₂ as an EAS. allows determination of anionic and cationic surfactants in wastewater below the MPC level (MPC for DDS in the waters of fishery water bodies is 0.5 mg / dm ³ [Order of the Federal Agency for Fisheries of January 18, 2010 No. 20 “On approval of quality standards water of water bodies of fishery value, including standards of maximum permissible concentrations of harmful substances in the water of water bodies of fishery value ”]).

An example of the use of an electrode with the inventive membrane for determining anionic surfactants in synthetic detergents (CMC).

0.2-0.5 g of CMC (for example, eared nannies washing powder) is dissolved in distilled water in a 100 ml volumetric flask when heated in a water bath. An aliquot of 2-5 ml was selected and titrated with a solution of cetylpyridinium chloride to determine anionic surfactants (C _tit = 1 · 10 ^-2 M). A titration curve is constructed in the coordinates E, mV - V, ml and an equivalence point is determined (Fig. 9).

The total content of anionic surfactants is converted to sodium dodecyl sulfate.

The mass fraction of anionic surfactants in CMC is calculated by the formula:

where C _TIT is the concentration of titrant solution, mol / l;

V _TE - titrant volume at the equivalence point, ml;

V _to - the volume of the flask, ml;

M is the molar mass of the surfactant, g / mol;

V _al - the volume of an aliquot of the sample solution, ml;

m _hitch - weight of hitch CMC, g

The relative standard deviation according to these methods does not exceed 0.05.

An example of the use of an electrode with the claimed membrane for the determination of ionic surfactants in cosmetic preparations.

2-3 g of a cosmetic preparation (for example, Nivea shampoo) is dissolved in warm distilled water in a 100 ml volumetric flask. An aliquot of 2-5 ml was selected and titrated with a solution of cetylpyridinium chloride to determine anionic surfactants (With _tit = 1 · 10 ^-2 M) or sodium dodecyl sulfate to determine the surfactants (With _tit = 1 · 10 ^-3 M), adding 0.1 -0.2 ml of titrant. A titration curve is built in the coordinates E, mV - V, ml and an equivalence point is determined (for cationic surfactants in hair balm) (Fig. 10).

The total content of anionic surfactants is converted to sodium dodecyl sulfate, cationic - to cetylprimethylammonium bromide.

The mass fraction of ionic surfactants in cosmetics is calculated by the formula:

where C _TIT is the concentration of titrant solution, mol / l;

V _TE - titrant volume at the equivalence point, ml;

V _to - the volume of the flask, ml;

M is the molar mass of the surfactant, g / mol;

V _al - the volume of an aliquot of the sample solution, ml;

m _hitch - weight of hitch CMC, g

The relative standard deviation according to these methods does not exceed 0.05.

The developed technique can be used to determine ionic surfactants in other cosmetic preparations (balms and hair products).

An example of the use of an electrode with the claimed membrane for the determination of cationic PAEs in the drug “Chlorhexidine”.

In a titration beaker, 10 ml of the Chlorhexidine antiseptic drug are pipetted and a solid contact selective electrode is placed. A silver chloride reference electrode is connected to the test solution by means of a salt bridge, which is a tube filled with a saturated solution of potassium chloride.

The sample is titrated with a 5 · 10 ^-3 M dodecyl sulfate solution, adding 0.1-0.2 ml of titrant. A titration curve is built in the coordinates E, mV - V, ml and an equivalence point is determined (Fig. 11).

The total content of cationic surfactants is converted to chlorhexidine.

The content of cationic surfactants is calculated by the formula:

where C _tit - the concentration of the titrant solution, mol / l;

V _TE - titrant volume at the equivalence point, ml;

V _al - the volume of an aliquot of the sample solution, ml;

M is the molar mass of chlorhexidine, g / mol.

The relative standard deviation according to these methods does not exceed 0.05.

The developed technique can be used to determine cationic surfactants in other surfactant-containing drugs. Correctness was monitored by the input-found method.

Table 4 The results of determining the content of ionic surfactants in various objects (n = 3, P = 0.95) An object Surfactant

, масс. %Content

mass. % Sr Mg Found

mg Relative error,% Rinse water from the washing machine Anionic 9.28 ± 0.68 * 0,03 0.58 0.56 ± 0.04 3.4 Eared Nannies Powder Anionic 15.00 ± 0.52 0.01 0.86 0.88 ± 0.04 2,3 Shampoo "Nivea" Anionic 6.40 ± 0.48 0,03 4.32 4.43 ± 0.34 2,3 Dyed hair care product “LOREAL” Cationic 0.93 ± 0.05 0.02 0.73 0.75 ± 0.05 2.7 Chlorhexidine Cationic 0,057 ± 0,004 0,03 - - - * mg / l

Table 5 The results of the determination of cationic surfactants in drugs (n = 3, P = 0.95) An object Identified by KLAV The content of surfactants (declared)

Found

Sr Chlorhexidine chlorhexidine 0.05% (0.5 mg / ml) (0.057 ± 0.004)% 0,03

,

, Cl^-,

,

, СН₃СОО^-. Полученная мембрана ИСЭ на основе соединения Cu(Phen)₂DDC₂ обладает высокой чувствительностью к ионным ПАВ благодаря его устойчивости и низкой растворимости (произведение растворимости составляет (3,1±0,4)·10^-13. Чем ниже растворимость ЭАВ, тем выше чувствительность электрода.To summarize the above, the obtained values of the potentiometric selectivity coefficients made it possible to predict the possibility of using the developed potentiometric sensor based on a complex compound of copper (II) with 1,10-phenanthroline and dodecyl sulfate for determining ionic surfactants in wastewater and synthetic detergents at high concentrations of nonionic surfactants and inorganic ions: Cu ²⁺ , Ba ²⁺ , Na ⁺ ,

,

, Cl ^- ,

,

, CH ₃ COO ^- . The obtained ISE membrane based on the compound Cu (Phen) ₂ DDC ₂ is highly sensitive to ionic surfactants due to its stability and low solubility (the solubility product is (3.1 ± 0.4) · 10 ^-13 . The lower the solubility of the ESA, the higher electrode sensitivity.

The membrane composition provides a wide range of detectable surfactant contents: 1 · 10 ^-3 (1 · 10 ^-4 ) -1 · 10 ^-6 (2 · 10 ^-7 ) M. At the same time, the high properties of the surfactant used in the membrane provide a low detection limit for surfactants: 6 · 10 ^-7 (1 · 10 ^-7 ) M. This allows you to use the electrode for the analysis of ionic surfactants in wastewater below the MPC level in the waters of fishery water bodies.

The angular coefficient of the electrode functions of the ISE in solutions of ionic surfactants is 54-59 mV / rS.

The response time of the obtained electrode is 15 s, and in diluted solutions (10 ^-6 -10 ^-4 M) the potential is established faster than in more concentrated ones.

Thus, the obtained membrane composition for ISE expands the functionality of the express determination of ionic surfactants in various water bodies, synthetic detergents, and some drugs.

Claims (1)

An ion-selective electrode membrane consisting of polyvinyl chloride as a matrix, dibutyl phthalate as a plasticizer and an electrode-active compound containing copper and sodium dodecyl sulfate, characterized in that the electrode-active compound additionally contains 1,10-phenanthroline, and copper, 1,10- phenanthroline and sodium dodecyl sulfate are taken in a ratio of 1: 2: 2, respectively, and the membrane components are in the following ratio, wt.%:
Polyvinyl chloride 24.9-24.6 Dibutyl phthalate 74.6-73.9 Electrode active compound 0.5-1.5

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