EP3036536A1

EP3036536A1 - Coulometric titration cell

Info

Publication number: EP3036536A1
Application number: EP14747947.1A
Authority: EP
Inventors: Thomas Blank; Günter Pfuhl; Félix Bécheiraz
Original assignee: Mettler Toledo Schweiz GmbH
Current assignee: Mettler Toledo Schweiz GmbH
Priority date: 2013-08-19
Filing date: 2014-08-07
Publication date: 2016-06-29
Also published as: US20160161447A1; CN105474009B; CN105474009A; JP2016528507A; US10352896B2; JP6420343B2; EP2840390A1; WO2015024787A1

Abstract

Coulometric titration cell and a measurement arrangement comprising a coulometric titration cell, comprising a first electrochemical half-cell having a first electrode (205, 801, 7, 407, 507, 607, 907); a second housing (1, 401, 501, 601, 801, 901) comprising a second electrochemical half-cell having a second electrode (3, 403, 503, 603, 803, 903) and an electrolyte (2, 302, 402, 502, 602, 802, 902) into which the second electrode (3, 403, 503, 603, 803, 903) is immersed; a redox system having at least one first and second redox partner; at least one diaphragm (4, 604, 804) arranged between the first and second electrochemical half-cell; and a circuit (11, 411, 511) incorporating the first and second electrochemical half-cell; wherein, in operation, at least the diaphragm (4, 604, 804) and the first electrode (7, 407, 507, 607, 907) are in contact with the sample (14); characterized in that the second housing (1, 401, 501, 601, 801, 901) is closed, such that charge and mass transfer is possible only via the diaphragm (4, 604, 804); in that the electrolyte (2, 302, 402, 502, 602, 802, 902) is solid or consolidated and comprises a first redox partner, and in that the first and second redox partner of the redox system are chosen such that evolution of gas within the coulometric titration cell in operation is very substantially suppressed.

Description

Coulometric titration cell

The invention relates to a coulometric titration cell for carrying out

coulometric titrations and a measuring arrangement with such a coulometric titration cell.

The volumetric titration is in many industrial laboratories one of

Routine methods for the quantitative determination of the substance amount of a substance or an analyte in a fluid sample. Traditionally, for this purpose, a titrant is added from a burette of a sample, which is stirred, and follows the change, for example, in the pH or conductivity of the sample with corresponding sensors. Based on the titrant volume consumed up to the end point or equivalence point of the titration and the titer of the titrant, it is then possible to use the

Stoichiometry of the effluent reaction the unknown concentration or amount of analyte in the sample can be calculated. The "titer" is the quotient of the actual concentration of a titration or mass solution and the desired concentration of the same solution, and the titer is therefore a factor for labeling normal solutions.

Today, instead of manually operated burettes are common

Titration machines used, which are also referred to as titrators. Titrators comprise at least one automatic dosing element with which the titrant is added in predetermined increments or dynamically to a sample, at least one suitable sensor, a control unit and a display unit. The titrant is also usually liquid in a titrator, and it is necessary that the titre of the titrant is periodically checked and / or the titrant is newly prepared to detect a change due to aging and / or deterioration

To prevent contamination, as this leads to measurement errors.

In addition to the volumetric titration is also the coulometric titration or

Coulometry for the quantitative determination of the amount of substance or concentration of an oxidizable or reducible compound known. A coulometric

Titration cell comprises two electrochemical half-cells, wherein one electrochemical half cell acts as a working electrode and the other electrochemical half cell acts as a counter electrode arranged in an electrolyte. In coulometry that will

During the titration, titrant is generated electrochemically at the working electrode and the electric charge which is converted at the working electrode is determined. At the counter electrode, the reverse electrochemical process takes place, wherein the Electrolyte is consumed within the electrochemical half cell of the counter electrode during the titration due to the reduction or oxidation of the substances contained at the counter electrode. The two electrochemical half-cells of the coulometric titration cell can be separated from each other by a diaphragm which, depending on the type and polarity of the working electrode, allows charge and mass transfer between the two electrochemical half-cells, the transport through the diaphragm being unidirectional or bidirectional.

Depending on the configuration of the coulometric titration cells, for example acid or base titrations can be carried out and the coulometric

Titration cell be designed as a base or acid generator, wherein a

Base generator hydroxide ions {OH ^~ ) for acid titration and an acid generator hydroxonium ions {H ₃ 0 ⁺ ) produced for the base titration.

For example, WO 2009/076144 A1 discloses a coulometric titration cell with a platinum working electrode, a platinum counter-electrode and a multi-layered ion-exchange membrane as a diaphragm. When using a suitable

Electrolytes and a suitable ion-exchange membrane, the coulometric titration cell can be used either for acid titration or for base titration, depending on the polarization of the electrodes. For the acid titration, for example, an aqueous sodium hydroxide solution (NaOH) may be used together with a cation exchange membrane.

Furthermore, for coulometric titrations, other substances in situ

are generated, which then react with the analyte in the sample. If the sample contains iodide, it can be reduced to iodine at the working electrode and, for example, sulfur dioxide (SO ₂ ) in the sample can be determined.

However, the known coulometric titration cells have the disadvantage that, when carrying out the titration, gases are produced at the working and / or counterelectrode, which have to be removed from the coulometric titration cell; moreover, they are also due to the frequently used noble-metal electrodes expensive in production. In particular, the provision of small and compact coulometric titration cells is therefore not yet possible.

The object of this invention is to provide a coulometric

Titration cell, which is designed to be small and compact and during which essentially no gas evolution occurs during operation. This object is achieved by a coulometric titration cell for performing a coulometric titration on a sample with a first electrochemical half-cell having a first electrode, and with a second housing comprising a second electrochemical half cell with a second electrode and an electrolyte. The second electrode is immersed in the electrolyte. Furthermore, the coulometric titration cell comprises a redox system with a first and second

Redox partner, a diaphragm, which between the first and second

electrochemical half-cell is arranged, and a circuit in which the first and second electrochemical half-cell are integrated. In operation, at least the diaphragm and the first electrode are in contact with the sample. The second housing is closed, so that a charge and mass transport is only possible via the diaphragm. Furthermore, the electrolyte, which is solid or solidified, contains the first redox partner. In addition, the first and second redox partners of the redox system are selected so that gas evolution at the second electrode is substantially suppressed.

[001] The coulometric titration cell according to the invention is very advantageous since, owing to the choice of the first and second redox partners of the redox system, of which the first redox partner is arranged in the solid or solidified electrolyte, during operation gas evolution at the second electrode, which into the electrolyte dips, can essentially be prevented. This makes it possible to design the second housing, which surrounds the second electrochemical half cell, particularly small and compact.

In particular, the diaphragm separates the second electrochemical half cell from the first electrochemical half cell and, in use, from the sample or the

Measuring medium off. A charge and mass transfer between the two

electrochemical half cells or between the sample and the second

electrochemical half-cell can therefore only be done via the diaphragm.

In another embodiment, the second housing is interchangeably disposed in a first housing, so that the second electrochemical half cell can be easily replaced together with the second housing when the electrolyte contained therein is consumed. The first housing may also include the first electrochemical half cell.

Gas evolution within the coulometric titration cell can also be greatly reduced or even completely eliminated by choosing a suitable redox system be suppressed. The redox system can be one of the following

Substance combinations and / or compounds of these substances as first and second redox partners include: iodine / iodide, iron (II / III) cyanide compounds

(Fe (CN) _g ^{"/ 4_} ), zinc / zinc (II) compounds.

A zinc / zinc (II) redox system can in the inventive coulometric

Titration cell as the first redox partner include a zinc complex compound, such as Zn [(NH ₃ ) ₂ (H ₂ 0) ₂ ] ²⁺ as a chloride, nitrate or sulfate compound. As a second redox partner, for example, a zinc sacrificial electrode can be used as the second electrode. In a further embodiment, the second redox partner may be present in the form of zinc powder, which is added to the solid electrolyte. To increase the conductivity, the electrolyte may also contain as an additive an electrically conductive compound, such as graphite or conductive salts (eg K 2 SO 4,

Na20 ₃ SCH _3, Na ₂ 0 ₃ are SCF ₃₎ was added.

Preferably, the electrolyte or the second electrode comprises the second

Redox partner. Both redox partners can thus be present in the electrolyte. In a further embodiment, the first redox partner is present in the electrolyte and the second redox partner is contained in the second electrode, which can be realized, for example, by using a sacrificial electrode as a second electrode.

Preferably, the coulometric titration cell comprises a reversible redox system, so that depending on the circuit, the first electrode can be connected and used as the anode or cathode. A reversible redox system is designed such that the chemical equilibrium between the two redox partners is shifted in one direction or the other by the circuit of the first electrode as anode or cathode. With a reversible redox system, both acid and base titrations with the same coulometric titration cell are possible, at least to a certain extent, without having to exchange the electrolyte or the diaphragm.

The shift of chemical equilibrium between the two

Redox partners, allows at least partial regeneration of the coulometric titration cell and / or the flexible use of the same coulometric titration cell as an acid or base generator.

The first electrode and the second electrode are, in contrast to the known prior art, preferably free of noble metals. The first electrode may comprise a metal, a metal compound or mixtures thereof, preferably the metal is selected from the group comprising iron, chromium, molybdenum, nickel and / or titanium.

The second electrode may also be a metal, a metal compound or

Mixtures thereof, wherein the metal is preferably selected from the group comprising iron, chromium, molybdenum, titanium, nickel and / or zinc.

In particular, a zinc-containing second electrode can, for example, as

Victim electrode can be used.

In a further embodiment, the first and / or second electrode may consist wholly or partly of a glass carbon material or an electrically conductive polymer.

In a further embodiment, the first or second housing may contain an electrically conductive polymer or consist of an electrically conductive polymer, which can be integrated by virtue of its properties even in the circuit of the coulometric titration cell, so that the first or second housing as the first Electrode can act. In this way, it is possible to realize the coulometric titration cell in a particularly small, compact and cost-effective manner, since a separate first electrode can be dispensed with as the first electrode when using the first or second housing.

Suitable electrically conductive polymers for use in a coulometric

Titration cell are in particular polymers which contain one or more additives to increase the electrical conductivity. Suitable additives are

For example, graphite, metal particles, metal compounds and / or carbon nanotubes. The additive is preferably added to the polymer in an admixture of about 20 to about 35%.

A solid electrolyte may for example be an aqueous solution of the first

Redoxpartners or the first and second Redoxpartners include, for example, about 10% to about 40% silica gel was added to bind the water contained. In addition to silica gel and layer silicates, such as zeolites, or cellulose compounds, such as

Hydroxyethylene cellulose, used for water binding.

[0025] For example, used a Zn / Zn ²⁺ redox system, the result during the titration in the electrolyte Zn ^2+, which may be bound with a suitable chelating agents or ion exchangers. The complexing agent is also the Electrolytes added. As complexing agents or ion exchangers, for example, zeolites or similarly acting clay minerals or silicates can be used.

If, for example, an I ₂ / I ₃ ^_ or Fe (CN) _g ^{- 4- used} -Redoxsystem, it can be dispensed with the use of further complexing agents or ion exchangers, since in this case the first and second redox partners themselves are complexing agents , Again, these redox systems can work together with a solid or solidified

Electrolytes are used.

Solid electrolytes, such as hydrogels, which contain at least the first redox partner, can also be used instead of solid electrolytes. A hydrogel electrolyte for a coulometric titration cell can be generated, for example, by converting an aqueous n.sup. + Solution into a hydrogel, wherein X in particular comprises one of the following anions: CT, SOI ^~ , CH ₃ S0 ₃ , triflate: - CF ₃ S0 ₃ (triflate), p - Tol S0 ₃ (tosylate). For this purpose, linear polymer chains, such as poly-N-vinylformamide, or crosslinked polymer chains, such as a copolymer of glycerol methacrylate and N, N'-bis-acrylamide, are used. To ensure a sufficiently high ion transport in the hydrogel, it is important to adjust or adjust the viscosity of the hydrogels used. A suitable viscosity can be achieved by using about 10% to about 30% monomer by weight.

In addition, hydrogels have a technical production advantage, since they are introduced in liquid form into the second housing and there directly, so in situ, polymerized and so can be solidified.

The diaphragm which is between the first and second electrochemical

Semicellor is arranged, depending on the embodiment, a charge and mass transfer between the first and second electrochemical half-cell, which takes place bidirectionally or unidirectionally only from the second to the first electrochemical half-cell. Preferably, the diaphragm consists essentially of a porous ceramic, a porous glass and / or an ion-selective membrane.

The diaphragm can be configured as an anion-exchange membrane or cation-exchange membrane, wherein the type and design of the diaphragm depends on the use of the coulometric titration cell as the acid or base generator as well as the redox system used. Further, an inert salt may be added to the sample which does not chemically alter the sample and thus is chemically inert to the sample. Examples of such inert salts are, for example, potassium sulfate {K ₂ S0 ₄ ) or potassium nitrate (KN0 ₃ ). By adding an inert salt, the conductivity of the sample can be increased, which is usually present as a fluid, for example as a solution or suspension. Increasing the conductivity of the sample enables a coulometric titration to be carried out with a lower voltage applied between the first and second electrodes, since the increased ion mobility due to the addition of the inert salt increases the ion mobility

Charge balance between the sample and the coulometric titration cell improved.

Furthermore, the second electrochemical half-cell of the coulometric

Titration cell have a chemical or physical diffusion trap, which serves to prevent mass transfer from the second electrochemical half-cell into the sample or the measuring medium. The use of diffusion or ion traps to maintain the functionality of coulometric

Titration cells is known in principle.

A further aspect of the invention relates to the provision of a measuring arrangement for carrying out a coulometric titration on a sample with a coulometric titration cell having the features described above. The measuring arrangement also comprises a container which receives the sample during operation, a sensor for detecting the endpoint or equivalence point of the titration and a control and / or display unit. The coulometric titration cell is in operation at least via the diaphragm and the first electrode in contact with the sample. The second housing of the coulometric titration cell is closed, so that charge and mass transfer is only possible via the diaphragm. The electrolyte is solid or solidified and contains a first redox partner. In addition, the first and second redox partners of the redox system are chosen so that during operation gas evolution at the second electrode is largely suppressed.

As a sensor, for example, an ion-selective, potentiometric or conductivity sensor can be used in an inventive measuring arrangement, with which during the titration at least one parameter of the sample is detected until reaching the end or equivalence point.

Various embodiments of a coulometric titration cell according to the invention will be described in more detail with reference to the following figures, wherein the same Elements are provided with the same or similar reference numerals. The figures show:

Fig. 1 Schematic representation of a coulometric titration cell, in which a second housing is arranged interchangeably in a first housing;

Fig. 2 Schematic representation of another coulometric titration cell, wherein the first housing is formed as a first electrode;

3 Schematic representation of a measuring arrangement with a coulometric titration cell according to FIG. 2 and a sensor;

Fig. 4 Schematic representation of another measuring arrangement with a

Coulometric titration cell according to the invention and a sensor;

Fig. 5 Schematic representation of a flow measuring device with a

Coulometric titration cell according to the invention and a sensor;

6 shows a section through a further coulometric titration cell with an end face

arranged diaphragm;

Fig. 7 partial view of the coulometric titration cell of Figure 6 in section.

8 shows a section through a further coulometric titration cell with an end face

arranged diaphragm and formed as a first electrode second housing;

Fig. 9 partial representation of another coulometric titration cell with two laterally arranged diaphragms and a replaceable second housing.

Figure 1 shows a schematic representation of an inventive

coulometric titration cell with a second housing 1, which is filled with a solid or solidified electrolyte 2, in which a second electrode 3 dips. The second housing 1 is designed to be closed. A charge and mass transport is only possible by a diaphragm 4, which is arranged in the first housing so that it is in operation in contact with a sample to be titrated. An electrical connection 8 of the second electrode 3 is led out of the second housing 1.

Furthermore, the coulometric titration cell shown in FIG. 1 comprises a first

Housing 5, which has an opening 6 for contacting the sample. In the first housing 5, a first electrode 7 and the second housing 1 are arranged. The first housing 5 is closed with a cover 10 such that an exchange of the second housing 1 and the components contained therein is possible. Through the cover 10, in this embodiment also electrical contacts 8, 9 are guided over which the first and second electrodes 3, 7 are integrated in a regulated circuit 1 1, as it is indicated here greatly simplified.

FIG. 2 shows a further embodiment of an inventive device

coulometric titration cell which is substantially identical to the coulometric titration cell described in Figure 1. However, in this

Embodiment in the first housing 205 is not arranged a separate first electrode, but the first housing 205 itself represents the first electrode. Thus, the first housing 205 may act as a first electrode, it consists at least partially of an electrically conductive polymer and is connected via an electrical connection involved in the circuit 1 1, as indicated in Figure 2.

FIG. 3 shows a schematic representation of a measuring arrangement with a

coulometric titration cell 312 and a sensor 13. The illustrated

coulometric titration cell 312 corresponds to that shown in FIG

Embodiment, wherein a coulometric titration cell according to Figure 1 can be used. Both the sensor 13 and the coulometric

Titration cell 312 immerse in a sample 14 at which a titrimetric determination or a coulometric titration is to be carried out. The sample 14 or the measuring medium is arranged in a suitable container 15 during the titration. The sample 14 is usually a fluid, for example a solution or a

Suspension.

The sample 14 may be added to increase its conductivity an inert salt. As an inert salt here salt compounds are referred to, which behave chemically inert to the sample and these do not change chemically. , Examples of such inert salts include potassium sulfate (K ₂ S0 ₄ ) or potassium nitrate {KN0 ₃ ). Increasing the conductivity of sample 14 allows the coulometric titration to be carried out with a lower voltage applied between the first and second electrodes. since the increased ion mobility due to the addition of the inert salt compensates for the charge balance between the sample and the

coulometric titration cell improved. As sensor 13, for example, an ion-selective, potentiometric or conductivity sensor can be used. With the sensor 13, a corresponding parameter of the sample 14 is detected during the titration until reaching the end or equivalence point of the coulometric titration, as indicated here by a control and / or display unit 17. FIG. 4 schematically shows a further measuring arrangement with a sensor 13 and a coulometric titration cell in a further embodiment. These

Coulometric titration cell comprises a second housing 401, in which a second electrode 403 is arranged. The second electrode 403 is incorporated in a circuit 41 1 and the second housing 401 has an overpass 416, which contains a diaphragm or is formed as a diaphragm. The transfer 416 is in operation in contact with a sample 14, which is located in a container 15. Furthermore, during operation, a first electrode 407, which is likewise integrated in the circuit 41 1, and a sensor 13, which is connected to a suitable control and / or display unit 17, dip into the sample 14. During transfer, the transfer 416 establishes contact between the second electrochemical half-cell with the second electrode 403 and the first electrochemical half-cell with the first electrode 407, so that charge and mass transfer can take place between the two electrochemical half-cells.

FIG. 5 shows schematically a flow measuring arrangement with a sensor 13 and a coulometric titration cell. A sample 14 flows through a flow cell

515, in which the sensor 13 and a first electrode 507 are arranged. The sensor 13 is in turn connected to a control and / or display unit 17. The first electrode 507 and a second electrode 503 are integrated in a circuit 51 1. The second electrode 503 is disposed in a closed case 501 and immersed in an electrolyte 502 therein. The second electrochemical half cell with the second electrode 503 is via a transfer

516, which comprises a diaphragm, as already described in connection with FIG. 4, connected to the first electrochemical half-cell. The transfer 516 is designed in such a way that both charge and mass transport are possible during operation of the coulometric titration cell between the second and first electrochemical half cells.

The spatial separation of the first and second electrochemical half cell, as shown for example in Figures 4 and 5, the realization of a particularly small and compact coulometric titration cell is made possible.

Figures 6 to 8 show two further embodiments of an inventive coulometric titration cell in section, wherein Figure 7 is a partial view of Figure 6. The coulometric titration cell shown in Figures 6 and 7 comprises an elongate tubular second housing 601 filled with a solid or solidified electrolyte 602. A second electrode 603 is immersed in the electrolyte 602. The second electrode 603 in this embodiment is a thin plate or a thin plate made of a suitable electrode material, which is arranged on the inner wall of the housing 601.

In the operation of the sample or the measuring medium opposite end of the

Housing 601 is closed with a lid 624, which also the

Closing element of a handle member 618 is. The lid 624 may be removed, for example, to replenish or replace the electrolyte 602.

Preferably, the lid 602 is detachably connected to the handle member 618 and the second housing 601.

On the front side, on the immersed in operation in a measuring medium or a sample end, the second housing 601 is closed by a diaphragm 604, which is fixed by a holding member 621 on the second housing 601. In order that the sample can not penetrate into the second housing 601, is between the

Diaphragm 607 and the second housing 601 arranged a sealant 626, here an O-ring. On the sample side, in front of the diaphragm 604, a first electrode 607 is arranged, which in this embodiment is annular, so that the sample, in operation, can come into contact with the diaphragm 604 via the recess in the annular first electrode 607.

The front end of the second housing 601 is enclosed by a first housing 620 omitting an opening 625. In operation, the opening 625 ensures contact between the diaphragm 604 and the sample into which the coulometric titration cell is dipped end face. In the first housing 620, the first electrode 607 is also arranged.

Both the first and second electrodes 603, 607 are electrical

Connections 608, 609, which are guided by the lid 624, in a

Integrated circuit (see Figures 1 to 5).

The sensor 13 shown in Figures 3 to 5, for example, a

be ion-selective, potentiometric or conductivity sensor. With the sensor 13 at least one parameter of the sample 14 is detected during the titration until reaching the end or equivalent point, as indicated in the figures by the control and / or display unit 17. This control and / or display unit 17 It can also be used to regulate the voltage or the current between the first and second electrodes, to analyze the determined parameter values, to determine the result of the coulometric titration and to display it. The control and / or display unit 17 can be configured as separate components or as a combined component.

Furthermore, an adapter 619 is shown in FIG. 6, which serves to use the coulometric titration cell, for example, in a holder of a titrator.

FIG. 8 shows a further exemplary embodiment of a coulometric titration cell with an end-face diaphragm 804, which terminates an elongated tubular second housing 801. Between the diaphragm 804 and the second housing 801, as already shown in Figures 6 and 7, a sealing means is arranged. The diaphragm 804 is held or fixed to the second housing 801 with a holding member 821.

The second housing 801 is filled with a solid or solidified electrolyte 802 into which a rod-shaped second electrode 803 is inserted. The end of the second housing 801 facing away from the sample during operation is partially of one

Gripping element 818 enclosed and releasably closed with a lid 824, as already described in connection with Figures 6 and 7. Through the cover 724 electrical connections 808, 809 are led to the connection of the second electrode 803 and a first electrode. The first electrode is formed in this embodiment of the second housing 801, which comprises an electrically conductive polymer or an electrically conductive layer. The second housing 801 is connected to the electrical connection 809.

FIG. 9 shows a partial representation of a further coulometric titration cell with at least two laterally arranged diaphragms 922, 923 in section.

The coulometric titration cell again comprises an elongate and in the

Substantially tubular second housing 901, which is arranged exchangeably in a first housing 905. The second housing 901 is filled with a solid or solidified electrolyte 902 and is laterally separated by at least two

arranged diaphragms 922, 923 completed in operation against a sample. The diaphragms 922, 923 are sealed by two sealants 926 so that the sample in use contacts only the diaphragms 922, 923 with the second electrochemical half cell. Furthermore, a rod-shaped second electrode 903, as has already been described in connection with FIG. 8, is immersed in the electrolyte 902. On the end side of the measuring medium facing the end of the first housing 905, a first electrode 907 is mounted, which is embedded here as a flat disc in the first housing 905. Furthermore, the first housing 905 has at least two lateral openings 906 arranged so that in operation the diaphragms 922, 923 and the first electrode 907 may be in contact with the sample.

The first and second electrodes 903, 907 are in turn via suitable electrical

Connections incorporated in a circuit, which is not shown in this partial view.

Although the invention by the illustration of specific embodiments

has been described, it is obvious that many more

Embodiments with knowledge of the present invention can be provided, for example, by combining the features of the individual embodiments with each other and / or individual functional units of the embodiments are exchanged. In particular, the embodiments shown in FIGS. 6 to 9 can be configured with or without an exchangeable second housing, and furthermore the first electrode can be designed as a rod, sheet or plate. A coulometric titration cell according to the described exemplary embodiments can be used in one of the measuring arrangements shown for carrying out a

coulometric titration. Likewise, the coulometric titration cells according to FIGS. 6 to 8 can be designed with or without adapters. The adapter can be designed in various forms, which are suitable for use in a desired automatic titration or on a suitable stand.

List of reference numbers

[0059]

1, 401, 501, 601, 801, 901 Second housing

2, 302, 402, 502, 602, 802, 902 electrolyte

3, 403, 503, 603, 803, 903 Second electrode

4,604, 804 diaphragm

5, 205, 905 First housing

6, 906 opening

7, 407, 507, 607, 907 First electrode

8, 608, 808 Electrical connection

9, 609, 809 Electrical connection

10 lids

1 1, 41 1, 51 1 circuit

312 titration cell

13 sensor

14 sample

15, 515 container

416, 516 overpass

17 control and / or display unit

618, 718 handle element

619 adapter

620 First case

621, 721 retaining element

922 diaphragm

923 diaphragm

624, 724 lids

625 opening

626, 926 sealant

Claims

claims

1. Coulometric titration cell for carrying out a coulometric titration on a sample (14)

a first electrochemical half-cell having a first electrode (205, 801, 7, 407, 507, 607, 907);

a second housing (1, 401, 501, 601, 801, 901), which is a second

electrochemical half-cell having a second electrode (3, 403, 503, 603, 803, 903) and an electrolyte (2, 302, 402, 502, 602, 802, 902) into which the second electrode (3, 403, 503, 603, 803, 903) is immersed;

a redox system with at least a first and second redox partner;

at least one diaphragm (4, 604, 804) disposed between the first and second electrochemical half cells; and

a circuit (11, 41 1, 511) in which the first and second electrochemical half cells are incorporated;

wherein in operation at least the diaphragm (4, 604, 804) and the first electrode (7, 407, 507, 607, 907) are in contact with the sample (14);

characterized,

that the second housing (1, 401, 501, 601, 801, 901) is closed, so that a charge and mass transfer only via the diaphragm (4, 604, 804) is possible;

that the electrolyte (2, 302, 402, 502, 602, 802, 902) is solid or solidified and contains a first redox partner; and that the first and second redox partners of the redox system are selected so that during operation, a gas evolution at the second electrode is largely suppressed.

2. Coulometric titration cell according to claim 1, wherein this comprises a first housing (5, 205, 905), in which the second housing (1, 901) is arranged exchangeably.

3. Coulometric titration cell according to claim 1 or 2, wherein the redox system comprises one of the following substance combinations and / or compounds of these substances: iodine / iodide, iron (II / III) cyanide compounds, zinc / zinc (II) compounds.

4. Coulometric titration cell according to one of claims 1 to 3, wherein the second

Redox partner in the electrolyte (2, 302, 402, 502, 602, 802, 902) or in the second

Electrode (3, 403, 503, 603, 803, 903) is included.

5. The coulometric Titrationszelle according to any one of claims 1 to 4, wherein the redox system is a reversible redox system and the second electrode (3, 403, 503, 603, 803, 903) acts as an anode or cathode.

6. Coulometer-type titration cell according to one of claims 1 to 5, characterized in that the first electrode (7, 407, 507, 607, 907) of one of the following metals, a

Metal compound and / or a mixture thereof comprises: stainless steel, chromium,

Molybdenum, nickel and / or titanium.

7. A coulometric measuring cell according to any one of claims 1 to 6, characterized in that the second electrode (3, 403, 503, 603, 803, 903) comprises one of the following metals, a metal compound and / or a mixture thereof: stainless steel, Chrome,

Molybdenum, nickel, titanium and / or zinc.

8. Coulometer-type titration cell according to one of claims 1 to 7, characterized in that the first electrode (7, 407, 507, 607, 801, 907) and / or second electrode (3, 403, 503, 603, 803, 903) wholly or partly consists of a glass carbon material or an electrically conductive polymer.

9. The coulometric Titrationszelle according to any one of claims 2 to 8, wherein the first

Housing (205) or the second housing (801) comprises an electrically conductive polymer and acts as a first electrode.

10. Coulometer-type titration cell according to claim 9, characterized in that the

electrically conductive polymer comprises carbon nanotubes.

1 1. Coulombic titration cell according to one of claims 1 to 10, characterized

in that the diaphragm (4, 604, 804) comprises a porous ceramic, a porous glass and / or an ion-selective membrane.

12. Coulometnsche titration cell according to one of claims 1 to 1 1, characterized

in that the diaphragm (4, 604, 804) is an anion exchange membrane or a cation exchange membrane.

13. Measuring arrangement for performing a coulometric titration on a sample with

a coulometric titration cell according to any one of the preceding claims; a container (15, 515) which in use receives a sample (14);

a sensor for detecting the end point or equivalence point of the titration;

a control and / or display unit (17);

wherein the coulometric titration cell is in contact with the sample at least via the diaphragm and the first electrode;

characterized in that the second housing of the coulometric titration cell is closed, so that a charge and mass transfer is possible only via the diaphragm; and that the electrolyte is solid or solidified and contains a first redox partner, and that the first and second redox partners of the redox system are chosen so that during operation gas evolution at the second electrode is largely suppressed.

14. Measuring arrangement according to claim 13, characterized in that the sensor is an ion-selective, potentiometric or conductivity sensor with which during the titration at least one parameter of the sample is detected until reaching the end or equivalence point.