Measuring device and method for determining the total organic carbon of a dissolved sample

Abstract

The present application relates to a measuring device and a method for determining the total organic carbon of a dissolved sample. A measuring device for determining the total organic carbon of a sample in a liquid medium, the measuring device comprising a reactor block, the reactor block being formed from an electrically conductive and corrosion-resistant metallic material, the reactor block being in the form of a housing having a housing wall for accommodating a UV light source, and the reactor block having an inlet into the reactor block and an outlet from the reactor block, the housing wall delimiting a flow chamber in which the digestion of the sample for determining the organic carbon takes place, wherein the flow chamber is designed to accommodate the UV light source and the flow chamber is designed to pass a liquid medium irradiated by UV light, wherein the measuring device has at least one conductivity measuring device, the reactor block being designed as an electrode, in particular as an outer electrode of the conductivity measuring device; and a method for determining the total organic carbon of a dissolved sample using the measuring device.

Description

Technical Field

[0001] The invention relates to a measuring device for determining the total organic carbon of a dissolved sample and to a method for determining the total organic carbon of a sample in a liquid medium using the measuring device. Background Art

[0002] For process water monitoring in the pharmaceutical industry and other industries that produce pure and ultrapure water, it is necessary to measure the total organic carbon (TOC) in liquids in the trace range. In most measuring devices used for this purpose, the organic carbon is converted thermally or by means of UV radiation into CO2 and detected.

[0003] Typically, one of the following two methods is used for this purpose:

[0004] (i) A defined sample amount is digested and the amount of generated CO2 is converted into a gas stream. The CO2 concentration in the gas stream is detected in an NDIR (Non-Dispersive Infrared Sensor) measuring cell.

[0005] (ii) The liquid is digested by means of UV radiation and the concentration of CO2 dissolved in the liquid is measured by increasing the conductivity of the liquid.

[0006] In this method, organic carbon is degraded to CO2 by UV radiation (in the wavelength range <200 nm). A vacuum mercury lamp is usually used as the UV source. The CO2 produced dissolves in the liquid and causes an increase in conductivity. The increase in conductivity is related to the CO2 concentration in the liquid or to the original carbon concentration or to the proportion of organically bound carbon initially present in the liquid.

[0007] According to the prior art, there are several design variants for implementing the second method, i.e. digesting the liquid by means of UV radiation and measuring the concentration of CO2 dissolved in the liquid by increasing its conductivity. The two most common variants are discontinuous differential conductivity measurement and continuous differential conductivity measurement.

[0008] In a continuous differential conductivity measurement, instead of taking measured values ​​periodically as in a discontinuous differential conductivity measurement, measured values ​​are taken continuously. To this end, the conductivity is first measured in a first flow conductivity measurement cell. The sample is then digested in a UV flow reactor. The conductivity is then measured again in a second flow conductivity measurement cell. The carbon concentration can be calculated from the increase in conductivity.

[0009] Advantageously, a continuous measurement signal is generated, as a result of which concentration peaks can be reliably detected.

[0010] The disadvantage is that, although the residence time of the sample in the digestion reactor is constant due to the constant sample flow rate, different organic compounds have different digestion rates. Therefore, the sample may not be completely digested, or the degree of digestion may vary between various substances. As a result, measurement errors will occur.

[0011] Also disadvantageous are easily digestible compounds, such as organic acids or compounds (e.g. CHCl3), which in this case, in addition to CO2, produce other conductive and soluble compounds by digestion, which contribute to the basic conductivity of the sample and can likewise lead to measurement errors.

[0012] Drift in the conductivity measuring cell can also lead to measurement errors.

[0013] It should also be taken into account that an increase in the temperature of the liquid (e.g. due to heat from a lamp) influences the conductivity, which is why the two measuring cells have to be kept at a uniform temperature using e.g. a heat exchanger or a temperature compensation needs to be calculated.

[0014] Devices known from the prior art for the continuous measurement of organic carbon in liquids require a relatively large installation space due to components such as a first conductivity measuring cell, a heat exchanger in which a heating cartridge or a cooling unit can be applied, a digestion reactor, and also a second conductivity measuring cell. Summary of the invention

[0015] On the basis of this preliminary consideration, the object of the present invention is to improve a measuring device and a method, in particular for the continuous measurement of total organic carbon (TOC) in liquids, in order to alleviate at least some of the above-mentioned disadvantages.

[0016] The measuring device according to the invention for determining the total organic carbon in a sample, in particular a sample dissolved in a liquid medium, has a reactor block made of an electrically conductive and corrosion-resistant material. The material is preferably metallic. Particularly preferred are materials such as stainless steel, graphite, titanium and / or platinum.

[0017] Forming the reactor block from metal promotes thermal conductivity of the reactor block.

[0018] The reactor block takes the form of a housing having corresponding housing walls and having an inlet into the reactor block and an outlet out of the reactor block.

[0019] The reactor block can be in the form of a cube, a cuboid or a cylinder, for example, in which inlets and outlets are arranged at defined positions, through which the dissolved sample can be introduced into the measuring device and discharged.

[0020] Furthermore, the reactor block can have a housing wall with a wall thickness of at least 0.5 mm. The housing wall can also be designed to have a wall thickness of at least 15 mm, particularly preferably 21 mm to 200 mm thick, as a result of which advantages can be obtained, in particular in terms of design, such as holes with larger diameters in the wall for accommodating measuring components of corresponding diameter.

[0021] The UV lamp heats the reactor block. Optionally, the reactor block can be heated externally or internally or actively cooled. The large wall thickness of the reactor block allows the sample or liquid medium to be preheated up to the temperature of the flow chamber by the reactor block itself.

[0022] Optionally and advantageously, the reactor block has a first connecting channel in the housing wall, which is arranged parallel to the longitudinal axis of the reactor block. Depending on the wall thickness of the housing wall and the corresponding holes, the first connecting channel can have diameters of different sizes. The arrangement of the first connecting channel in the wall of the reactor block saves additional installation space.

[0023] Furthermore, the housing wall encloses a flow chamber in which digestion of the sample for determining the organic carbon takes place. The flow chamber may be a digestion chamber.

[0024] The housing wall separates the flow chamber from the surrounding environment.The term "environment" refers to the space outside the reactor block.

[0025] The flow chamber is designed to accommodate a light source, in particular a UV light source, and is designed to allow a sample irradiated by UV light or a liquid medium containing the sample to pass through. The UV light source can advantageously be part of the measuring device according to the invention. The UV light source can preferably be arranged replaceably in the flow chamber. The flow chamber can take the form of a self-contained cavity with an opening for the liquid medium to pass through. A plurality of openings can be provided. The UV light source can preferably be a vacuum mercury lamp. It has been shown that UV radiation, preferably in a wavelength range of <200 nm, is advantageous.

[0026] The measuring device has at least one conductivity measuring device. The conductivity measuring device can consist of one or more components. A plurality of components can be arranged to form a single component consisting of several components.

[0027] The reactor block is designed as an electrode, in particular an outer electrode, of a conductivity measuring device. As a result, the reactor block takes the form of a housing and at the same time takes the form of an outer electrode.

[0028] Such a compact arrangement of a measuring device which integrates several components into one assembly, resulting in increased measurement reliability in the detection of total organic carbon in liquids, has not been known before.

[0029] Furthermore, forming the reactor block from metal improves the thermal conductivity of the reactor block.

[0030] The reactor block is designed to absorb heat generated, for example, by the energy of the UV light source in the reactor chamber, and the reactor block is designed to dissipate said heat to the outside. As a result, the reactor block is also designed as a heat exchanger to compensate for temperature differences between the conductivity measuring cells integrated in the reactor block and to keep the temperature in the flow chamber of the reactor block constant at a defined heat level.

[0031] The arrangement of the first connecting channel in the housing wall of the reactor block is particularly advantageous, since, due to the thermal conductivity of the reactor block, the sample supplied into the first connecting channel is already preheated to a uniform reactor temperature.

[0032] Preheating advantageously shortens the response time of the analyzer, thereby enabling faster response times to be achieved via limit value monitoring.

[0033] In general, preheating the sample to the reactor temperature and maintaining a constant temperature in the chamber of the reactor block has a beneficial effect, since the reliability of the measurement is improved as a result.

[0034] Overall, this also makes it possible to dispense with heat exchangers, heating cartridges and / or cooling units as separate components.

[0035] As a result, the invention advantageously also reduces the installation space required for the measuring device and ensures increased measurement reliability.In addition, the integration of various components in a single assembly makes it possible to manufacture the measuring device in a space-saving manner.

[0036] Using fewer components also advantageously reduces the risk of failure and reduces leaks and leak locations. It is also advantageous to integrate multiple functions into one component, thereby reducing production costs.

[0037] The invention is particularly suitable for use in measurements for determining the concentration of organic compounds in liquids in the trace range.

[0038] In an advantageous embodiment of the invention, a first conductivity measuring cell of the conductivity measuring device may be arranged in the reactor block, the first conductivity measuring cell having at least two corresponding electrodes, wherein the two electrodes are an inner electrode and an outer electrode, and wherein the first inner electrode is arranged inside the first conductivity measuring cell and corresponds to the reactor block as the outer electrode. The first conductivity measuring cell may be arranged upstream of the flow cell where digestion of the sample takes place.

[0039] In the aforementioned embodiment, the second conductivity measurement cell of the conductivity measurement device is also arranged with at least two corresponding electrodes, wherein the two electrodes are an inner electrode and an outer electrode, and wherein the second inner electrode is arranged inside the second conductivity measurement cell and corresponds to the reactor block as the outer electrode. The second conductivity measurement cell may be arranged downstream of the flow cell where digestion of the sample occurs.

[0040] The inner electrode comprises an electrically conductive material.Since the two conductivity measuring cells are integrated in the reactor block, the temperature inside the two conductivity measuring cells is also uniform.

[0041] The first connecting channel can preferably be formed between the inlet and the first conductivity measuring cell. In addition, there must be a passage between the first conductivity measuring cell and the flow chamber, and there must be a passage between the flow chamber and the second conductivity measuring cell. Finally, a second connecting channel can be arranged between the second conductivity measuring cell and the outlet.

[0042] The second connecting channel may be less than 20% of the length of the first connecting channel.

[0043] Advantageously, a supply and discharge device is connected upstream of the inlet of the reactor block. In this case, the supply and discharge device comprises a supply line to the first valve and / or pump of the measuring device, wherein the third connecting channel extends between the first valve and the pump. A fourth connecting channel is arranged between the pump and the inlet of the reactor block, and a fifth connecting channel is arranged between the outlet of the reactor block and the second valve. Advantageously, the sixth connecting channel extends between the second valve and the first valve. The discharge line is arranged to start from the second valve. The third connecting channel, the fourth connecting channel and the fifth connecting channel can be formed, for example, by a pipe or hose extending outside the reactor block.

[0044] The supply and discharge device is preferably part of the measuring device.The upstream supply and discharge device expands the measuring device so that the sample can be conveyed through the measuring device in a loop or circuit.

[0045] Measuring errors caused by different digestion rates can be compensated by circulating flow.

[0046] The drift of the conductivity measuring cells can also be corrected by pumping the sample liquid in the loop until the conductivity in both measuring cells has reached a stable value. This makes it possible to ensure that the sample is completely oxidized.

[0047] Due to deposition and other influences, drift of the measuring device may occur. However, this can advantageously be corrected. For this purpose, the evaluation unit is advantageously designed such that an offset measurement, in particular an offset correction, can be performed during the determination of the measured value.

[0048] It is useful here that the first valve and the second valve can be switched between a plurality of operating modes. The first operating mode ensures a constant supply into the measuring device and a discharge from the measuring device, and the second operating mode ensures the return of the medium in the circuit. The valve control based on the respective operating mode can be performed by the control and evaluation unit.

[0049] It is also advantageous in this respect if the control and evaluation unit also controls the conductivity measurement by means of the conductivity measuring device, wherein the control and evaluation unit is designed to determine the content of organic carbon in the liquid medium taking into account the conductivity determined in the first conductivity measuring cell and the second conductivity measuring cell.

[0050] The flow chamber of the measuring device may be cylindrical. The flow chamber is arranged in the center of the reactor block and parallel to the longitudinal axis of the reactor block and symmetrically with respect to the UV light source and preferably encloses the UV light source.

[0051] The lateral distance between the outer inner wall of the side surface of the flow chamber facing away from the UV light source and the center of the longitudinal axis of the UV light source, which corresponds to the longitudinal axis of the reactor block, can be less than 8 mm. The lower distance between the outer inner wall of the lower circular segment surface of the flow chamber and the lower center of the longitudinal axis of the UV light source can also be less than 8 mm. The sample flow passing close to the UV light source makes it possible to increase the radiation intensity, so that carbon-containing compounds in the sample can also be completely oxidized.

[0052] The first conductivity measuring cell and the second conductivity measuring cell may be arranged at the same radial distance from the longitudinal axis of the reactor block.

[0053] This arrangement ensures predictable digestion over the entire vertical side surface of the preferably cylindrical flow chamber.

[0054] The reactor block may be formed in several parts, thereby facilitating the provision of holes and milled recesses during production. It is therefore also possible to more easily replace parts of the reactor block in the event of a malfunction.

[0055] The reactor block can preferably be made of stainless steel. However, the reactor block can also be made of other electrically conductive and corrosion-resistant metal materials or metal alloys, such as brass or the like. In many industries, for example in condensing boiler technology, it is known to use stainless steel as a heat exchanger. The application areas include, in particular, the use of heat, the heating of media and the cooling of media. In the solution of the object of the invention, these properties act synergistically in a stainless steel reactor block.

[0056] Advantageously, the first connecting channel and the second connecting channel, the inlet and the first passage, and the second passage and also the outlet have equal diameters. The diameter is preferably greater than 0.5 mm, particularly preferably between 1.5 mm and 4 mm.

[0057] Furthermore, it is advantageous if an annular gap is formed in each case between the wall of the first conductivity measuring cell and the wall of the second conductivity measuring cell and the inner electrode arranged in the respective conductivity measuring cell, and if the first annular gap and the second annular gap have exactly the same volume and geometric dimensions. The volume and geometric dimensions may be equal to the diameters of the first and the second connecting channel, the inlet, the first and the second passage and the outlet.

[0058] A sealing device, in particular a sleeve, can be arranged in the flow chamber, which sealing device is transparent at least for the UV radiation from the UV light source and into which the UV light source can be inserted. This allows the UV lamp to be replaced in the event of a malfunction even if the reactor block is filled with liquid. In this case, the liquid medium containing the sample is located between the sealing device and the inner wall of the flow chamber.

[0059] If a third annular gap is provided between the inner wall of the side surface of the flow chamber and the outer wall of the sealing device of the UV light source, the diameter of the gap is equal to the diameter of the first connecting channel and the second connecting channel and preferably measures between 0.5 mm and 4 mm. In this annular gap, the sample flows around the UV light source. The radiation emitted by the UV light source converts organic components in the sample into CO2. CO2 forms carbonic acid in the liquid medium, especially in water, which can be detected by means of a conductivity measuring cell due to the change in conductivity. At the same time, ozone formation due to excessive gap width of the annular gap should be avoided or minimized.

[0060] Ensuring sample flow in the system and distributing it widely over the surface of the UV light source has a favorable influence on measurement reliability and measurement accuracy.

[0061] The method according to the invention for determining the total organic carbon of a liquid sample, in particular a liquid sample dissolved in a liquid medium, using a measuring device, in particular using a measuring device according to the invention, comprises the following steps:

[0062] I. Provide measuring equipment;

[0063] II. introducing the liquid sample into the first connecting channel through the inlet of the reactor block, in which the sample is preheated to the reactor temperature;

[0064] III. The sample is transported to the first conductivity measuring unit, and the first conductivity measurement is performed by the control and evaluation unit;

[0065] IV. supplying the sample from the first conductivity measurement unit to a flow chamber in which the sample flows around a UV light source in a third annular gap, wherein radiation from the UV light source degrades the sample by forming CO2;

[0066] V. transferring the sample from the flow cell into a second conductivity measuring cell and performing a second measurement of the conductivity by means of the control and evaluation unit, and

[0067] VI. Discharging the sample from the second conductivity measuring cell through the outlet of the reactor block via the second connecting channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Other advantages, features and details of the present invention will become apparent from the following description, in which exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings. It will also be convenient for those skilled in the art to consider the features disclosed in combination in the drawings, the description and the claims separately and to combine the features into meaningful further combinations.

[0069] Shown below:

[0070] Figure 1 is a schematic diagram of the measurement device in constant current mode; and

[0071] Figure 2 is a schematic diagram of the supply and discharge arrangement as part of the measuring device in the circulation mode. DETAILED DESCRIPTION

[0072] Figure 1 A measuring device 100 for determining the total organic carbon of a sample dissolved in a liquid medium is shown. The measuring device has a reactor block 1 .

[0073] The reactor block 1 comprises a metallic material and is made of an electrically conductive and corrosion-resistant material, preferably stainless steel, having a wall thickness greater than 0.5 mm.

[0074] The reactor block 1 is designed as an outer electrode and is connected to an evaluation unit 18 via a first connection 20 by means of a supply cable 19. The reactor block 1 is designed to absorb heat and dissipate it to the outside, thereby acting as a heat exchanger.

[0075] The reactor block 1 has a liquid inlet 5, through which the sample is conveyed into the connecting channel 9. The connecting channel 9 is arranged in the wall of the reactor block 1. The heat generated by the UV light source 4 is absorbed by the housing wall 27 of the reactor block 1, whereby the sample introduced into the first connecting channel 9 is preheated to the reactor temperature.

[0076] The sample flows from the first connecting channel 9 into the first annular gap 29 of the first conductivity measuring cell 7 and flows around the first inner electrode 2. The first inner electrode 2, together with the reactor block 1 as an outer electrode, corresponds to the control and evaluation unit 18 via a first connection 20 of a supply cable 19, which has a second connection 21 to the supply cable 19 of the control and evaluation unit 18. The first inner electrode 2 is inserted into the wall of the reactor block 1, and due to the electrical isolation of the mounting point, for example in the form of a polymer seal or polymer casting, direct contact between the electrodes and thus short circuits between the electrodes are prevented. The evaluation unit performs a first measurement of the conductivity of the sample by means of the first inner electrode 2 and the outer electrode of the first conductivity measuring cell 7.

[0077] The sample is supplied from the first conductivity measuring unit 7 to the flow chamber 12 through the first passage 10, and the UV light source 4 is introduced into the flow chamber 12 in a medium-tight manner. The sample flows around the light emitting part of the UV light source 4 in the third annular gap 31, and the sample is digested by the radiation of the UV light source 4.

[0078] The UV light source used can have a connection head 4b with a seal 4a. The seal 4a can take the form of a quartz glass sleeve with a spherical cover of the UV light source 4. The seal can also be formed from other materials.

[0079] The sealing device 4 a prevents liquid contact with the UV light source 4 and advantageously simplifies replacement of the UV light source.

[0080] The sample is transferred from the flow cell 12 through the second passage 11 into the second annular gap 30 of the second conductivity measuring cell 8 and flows around the second inner electrode 3. The second inner electrode 3, together with the reactor block 1 as the outer electrode, corresponds to the control and evaluation unit 18 via the first connection 20 of the supply cable 19, the second inner electrode 3 having a third connection 22 to the supply cable 19 of the evaluation unit 18. The second inner electrode 3 is inserted into the wall of the reactor block 1, and due to the electrical isolation of the mounting point, for example in the form of a polymer seal or polymer casting, direct contact between the electrodes and thus short circuits between the electrodes are prevented. With the aid of the first inner electrode 2 and the reactor block 1 serving as the outer electrode of the second conductivity measuring cell 7, a second measurement of the conductivity of the sample is carried out by the evaluation unit 18. "Control and evaluation unit" and "evaluation unit" are used synonymously in this application.

[0081] The sample is discharged from the second conductivity measuring cell 8 via the second connecting channel 13 in the outlet 6 of the reactor block 1 .

[0082] Figure 2As part of the measuring device 100, a supply and discharge device 200 is shown for determining the total organic carbon of a sample dissolved in a liquid medium using the measuring device 100 in a circulation mode. The internal structure of the reactor block 1 is not shown in FIG. Figure 2 shown in, but with Figure 1 Constructed similarly.

[0083] In this variant, the sample is conveyed via the supply line 14 to the valve 15 a and via the third connecting channel 23 to the pump 16 and through the fourth connecting channel 24 into the inlet 5 of the reactor block 1 .

[0084] The sample is similar to Figure 1 After the sample leaves the outlet 6, it is returned to the inlet 5 of the reactor block 1 via the fifth channel 25, via the second valve 15b connected in a loop flow, via the downstream sixth connecting channel 26, via the first valve 15a connected in a loop flow, by means of the pump 16 and the fourth connecting channel.

[0085] As a result, the sample keeps flowing through the reactor chamber in the form of a loop or circuit until the conductivity in both conductivity measuring cells 7 and 8 has reached a stable value.

[0086] Reference Mark

[0087] 1 reactor block

[0088] 2First inner electrode

[0089] 3 Second inner electrode

[0090] 4UV light source

[0091] 5. Import

[0092] 6Export

[0093] 7. First conductivity measurement unit

[0094] 8 Second conductivity measuring unit

[0095] 9First Connection Channel

[0096] 10First Passage

[0097] 11 Second Passage

[0098] 12 Flow Chamber

[0099] 13 Second connection channel

[0100] 14 Supply Lines

[0101] 15a First valve

[0102] 15b Second valve

[0103] 16 Pumps

[0104] 17 discharge line

[0105] 18 control and evaluation units

[0106] 19 Supply cable

[0107] 20 First Connection

[0108] 21 Second Connection

[0109] 22 Third Connection

[0110] 23Third Connection Channel

[0111] 24 Fourth Connection Channel

[0112] 25 Fifth Connection Channel

[0113] 26 Sixth Connection Channel

[0114] 27 Shell wall

[0115] 28 longitudinal axis

[0116] 29 First annular gap

[0117] 30 Second annular gap

[0118] 31 Third annular gap

[0119] 4a Sealing device

[0120] 4b Connector

[0121] 100 measuring devices

[0122] 200 Supply and discharge devices

Claims

1. A measuring device (100) for determining the total organic carbon of a sample dissolved in a liquid medium, characterized in that The measuring device (100) has a reactor block (1), The reactor block (1) is made of an electrically conductive and corrosion-resistant material, wherein the reactor block (1) is designed as a housing having a housing wall (27), the housing having an inlet (5) into the reactor block (1) and an outlet (6) out of the reactor block (1), wherein the housing wall (27) separates a flow chamber (12) from the surroundings, the environment being the space outside the reactor block, wherein digestion of the sample for determining the organic carbon takes place in the flow chamber (12), wherein the flow chamber (12) is designed to accommodate a UV light source (4), and wherein the flow chamber (12) is designed to pass a sample to be irradiated by light from the UV light source (4), wherein the measuring device (100) has a conductivity measuring device arranged in the reactor block, and wherein the conductivity measuring device comprises: A first conductivity measuring unit (7); A second conductivity measuring unit (8); an outer electrode, wherein the reactor block (1) is designed as the outer electrode of the conductivity measuring device; a first inner electrode arranged inside a first conductivity measurement cell (7) within the reactor block, upstream of the flow chamber with respect to the flow of the sample; and A second inner electrode is arranged inside a second conductivity measuring cell (8) in the reactor block, downstream of the flow chamber.

2. The measuring device according to claim 1, characterized in that In the reactor block (1), a first connecting channel (9) is arranged in a housing wall (27) of the reactor block (1) parallel to a longitudinal axis (28) of the reactor block (1), the first connecting channel (9) being used to supply the sample to the conductivity measuring device.

3. The measuring device according to claim 1, characterized in that A first connecting channel (9) is arranged between the inlet (5) and the first conductivity measurement cell (7), a first passage (10) is arranged between the first conductivity measurement cell (7) and the flow chamber (12), a second passage (11) is arranged between the flow chamber (12) and the second conductivity measurement cell (8), and a second connecting channel (13) is arranged between the second conductivity measurement cell (8) and the outlet (6).

4. The measuring device according to claim 1, characterized in that A supply and discharge device (200) is arranged upstream of the inlet (5) of the reactor block (1) and is configured to define an electric circuit, wherein the supply and discharge device (200) has a supply line (14) from the measuring device (100) to a first valve (15a) and a pump (16), wherein a third connecting channel (23) extends between the first valve (15a) and the pump (16), wherein a fourth connecting channel (24) is arranged between the pump (16) and the inlet (5) of the reactor block (1), wherein a fifth connecting channel (25) is arranged between the outlet (6) of the reactor block (1) and the second valve (15b), wherein a sixth connecting channel (26) extends between the second valve (15b) and the first valve (15a), and a discharge line (17) is arranged starting from the second valve (15b).

5. The measuring device according to claim 4, characterized in that The conductivity measuring device comprises a control and evaluation unit (18) which is designed to determine the content of organic carbon in the liquid medium taking into account the conductivities determined in the first conductivity measuring unit (7) and the second conductivity measuring unit (8).

6. The measuring device according to any one of claims 1 to 5, characterized in that The flow chamber (12) is cylindrical, wherein the flow chamber (12) is arranged in the center of the reactor block (1) parallel to the longitudinal axis (28) of the reactor block (1) and symmetrically relative to the UV light source (4), and the flow chamber (12) encloses the UV light source (4).

7. The measuring device (100) according to claim 1, characterized in that The first conductivity measuring cell (7) and the second conductivity measuring cell (8) are arranged at the same radial distance from the longitudinal axis (28) of the reactor block (1).

8. The measuring device according to any one of claims 1 to 5, characterized in that The reactor block (1) consists of more than one part.

9. The measuring device according to claim 8, characterized in that The reactor block (1) is made of stainless steel.

10. The measuring device according to claim 3, characterized in that The first connecting channel (9) and the second connecting channel (13), the inlet (5) and the first passage (10), and the second passage (11) and the outlet (6) have the same diameter.

11. The measuring device according to claim 10, characterized in that The second passage (11) and the outlet (6) have a diameter greater than 0.5 mm.

12. The measuring device according to claim 10, characterized in that The second passage (11) and the outlet (6) have a diameter of 1.5 mm to 4 mm.

13. The measuring device according to claim 1, characterized in that A first annular gap (29) and a second annular gap (30) are formed between the walls of the first conductivity measuring cell (7) and the second conductivity measuring cell (8) and the walls of the first inner electrode (2) and the second inner electrode (3), respectively, wherein the corresponding first annular gap (29) and second annular gap (30) have the same volume and geometric dimensions.

14. The measuring device according to any one of claims 1 to 5, characterized in that A sealing device (4a) is arranged in the flow chamber (12), into which the UV light source (4) is inserted in a replaceable manner and arranged when the reactor block (1) is filled.

15. The measuring device according to claim 14, characterized in that A transparent sleeve is arranged in the flow chamber (12).

16. The measuring device according to claim 3 or 10, characterized in that A third annular gap (31) is arranged between the inner wall of the side surface of the flow chamber (12) and the outer wall of the UV light source (4) or the outer wall of the sealing device of the UV light source (4), and the gap has the same diameter as the first connecting channel and the second connecting channel.

17. The measuring device according to claim 16, characterized in that The same diameter of the gap as the first connecting channel and the second connecting channel is greater than 0.25 mm.

18. The measuring device according to claim 16, characterized in that The gap has the same diameter as the first connecting channel and the second connecting channel, ranging from 0.5 mm to 4 mm.

19. The measuring device according to claim 5, characterized in that The first valve (15a) and the second valve (15b) can be switched by the control and evaluation unit (18) into a plurality of operating modes of the measuring device (100), wherein a first operating mode of the measuring device (100) ensures a constant supply to and discharge from the measuring device (100), and wherein a second operating mode of the measuring device (100) ensures the return of the sample or of a medium in the circuit for dissolving the sample.

20. The measuring device according to claim 5 or 19, characterized in that The control and evaluation unit (18) is designed to carry out an offset measurement of the detected conductivity during the determination of the measured value.

21. The measuring device according to claim 20, characterized in that The control and evaluation unit (18) is designed to carry out an offset correction of the detected conductivity during the determination of the measured value.

22. A method for determining the total organic carbon of a sample dissolved in a liquid medium, the method comprising the steps of: I. Providing a measuring device (100), the measuring device (100) comprising: A reactor block (1) made of an electrically conductive and corrosion-resistant material, wherein the reactor block (1) is designed as a housing having a housing wall (27), the housing having an inlet (5) into the reactor block (1) and an outlet (6) out of the reactor block (1), wherein the housing wall (27) separates a flow chamber (12) in which digestion of the sample for determining the organic carbon takes place from the surroundings, which is the space outside the reactor block, wherein the flow chamber (12) is designed to accommodate a UV light source (4) and to allow the sample to pass through to be irradiated by light from the UV light source (4), and a conductivity measuring device, which is arranged in the reactor block and comprises: A first conductivity measuring unit (7); A second conductivity measuring unit (8); an outer electrode, wherein the reactor block is designed as the outer electrode of the conductivity measuring device; a first inner electrode arranged inside a first conductivity measurement cell defined within the reactor block upstream of the flow chamber with respect to the flow of the sample; and a second inner electrode disposed inside a second conductivity measurement cell defined downstream of the flow chamber; and a control and evaluation unit designed to determine the content of organic carbon in the liquid medium taking into account the conductivities determined in the first conductivity measuring cell and in the second conductivity measuring cell, wherein the housing wall further defines a first connecting channel for supplying the sample to the conductivity measuring device; II. introducing the sample into the first connecting channel (9) through the inlet (5) of the reactor block (1), in which the sample is preheated to the reactor temperature; III. conveying the sample to the first conductivity measuring unit (7), and performing a first measurement of the conductivity of the sample by the control and evaluation unit (18); IV. supplying the sample from the first conductivity measuring cell (7) into the flow chamber (12), wherein the sample flows around the UV light source (4) in an annular gap (31) between the inner wall of the side surface of the flow chamber (12) and the outer wall of the UV light source (4) or the outer wall of the sealing device of the UV light source (4), wherein the radiation of the UV light source (4) decomposes the sample by forming CO2; V. transferring the sample from the flow cell (12) into the second conductivity measuring cell (8) and performing a second measurement of the conductivity of the sample by means of the control and evaluation unit (18), VI. discharging the sample from the second conductivity measuring cell (8) through the outlet (6) of the reactor block (1), and VII. Determining the total organic carbon of the sample using the first measurement and the second measurement of conductivity.

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