Flow probe, device and method for instrumental process bath analysis

Abstract

The invention relates to a flow probe for the instrumental analysis of a measurement fluid (2) using infrared spectroscopy based on the principle of attenuated total internal reflection, as well as a device and a method for instrumental process bath analysis. The flow probe comprises an IR emitter (3), an internal reflecting element (5), an IR detector (4), and a flow cell enclosed by a flow cell wall (1), wherein the internal reflecting element (5) contacts the measurement fluid (2) with a first reflective surface (5.1). A reflection-enhancing support element (6) rests against an opposing second reflective surface (5.2) of the internal reflecting element (5). The solution according to the invention enables a compact, robust, and real-time analysis of process media, in particular for monitoring chemical parameters in industrial process baths.

Description

[0001] The invention relates to a flow probe, a device, and a method for instrumental process bath analysis, in particular for determining the material composition and the concentration of substances in liquid process media. The technology is suitable for analyzing process baths such as those used in the metalworking, electrochemical, or chemical industries.

[0002] The instrumental analysis of process media from process baths in the metalworking, electrochemical, or chemical industries has so far been carried out predominantly by sampling and subsequent laboratory analysis. In particular, the concentration of components such as acids or bases is determined using classical titration methods. This method requires sample preparation and transport of the sample from the point of use to a laboratory, which can lead to delays and potential distortion of the measurement results due to changes in the sample composition.

[0003] Infrared spectroscopy, and in particular Fourier-transform infrared spectroscopy (FTIR spectroscopy), has become established as an alternative to classical laboratory analysis. FTIR spectroscopy allows the chemical composition of liquids to be determined based on their infrared absorption spectra. In this process, infrared radiation is passed through a sample, and the resulting absorption at specific wavelengths provides information about the chemical composition of the process medium.

[0004] Attenuated Total Reflectance (ATR) techniques are frequently used for FTIR spectroscopy of liquid samples. In this technique, infrared radiation is coupled into an internal reflecting element (IRE) and undergoes total internal reflection at its reflective surface, which is in contact with the sample. An evanescent wave field is generated at this totally reflecting surface and interacts with the adjacent sample. The change in intensity of the evanescent wave allows for the analysis of chemical parameters of the sample.

[0005] US patent 2004 / 0126049 A1 discloses the use of ATR technology for testing process baths. It describes how a sample can be analyzed using ATR infrared spectroscopy, employing an internal reflecting element to establish the infrared spectroscopic interaction with the sample under investigation.

[0006] Furthermore, US Patent 2024 / 0142374 A1 discloses a flow cell for performing attenuated total reflection infrared spectroscopy (ATR-IR) on a sample fluid, in which a liquid sample fluid is introduced into the flow cell via an inlet portal and removed via an outlet portal. The flow cell is designed such that the liquid sample fluid can be spectroscopically analyzed using ATR-IR during transport within the cell. This configuration allows for continuous or intermittent analysis of the sample fluid under flow conditions.

[0007] However, there is still room for improvement regarding the application of ATR-FTIR spectroscopy for liquid analysis, particularly concerning the chemical resistance and long-term stability of the measuring instruments, as required in industrial environments for on-site analysis of process baths. Compact, robust systems suitable for continuous operation that enable real-time monitoring without complex sample manipulation are not yet sufficiently available.

[0008] The object of the invention is to provide a device and a method that enable reliable, timely, and, where possible, continuous analysis of process media. In particular, measurements should be possible without complex sample extraction and preparation. Furthermore, the solution should have a robust and compact design that ensures continuous operation even under the demanding conditions of aggressive and / or high-temperature process media. A uniform and reproducible interaction between the process medium being analyzed and the measuring surface should also be ensured to achieve high accuracy and long-term stability of the measurement results.

[0009] This problem is solved by a flow probe with the features of claim 1, a device for instrumental process bath analysis according to claim 8, and a method for instrumental process bath analysis according to claim 10. Advantageous embodiments of the invention are set out in claims 2 to 7 and 9.

[0010] According to the invention, the flow probe is designed for the instrumental analysis of a measuring fluid formed from a process medium by means of infrared spectroscopy based on the principle of attenuated total reflection.

[0011] The flow probe has an IR emitter (infrared emitter) for emitting infrared radiation with a defined spectral distribution. Preferably, the infrared radiation used lies in the mid-infrared region, i.e., in the wavelength range from 2.5 µm to 25 µm. Furthermore, the flow probe includes an internal reflection element (IRE) for guiding the infrared radiation coupled into the internal reflection element from the IR emitter via a radiation entry surface by total internal reflection between a first reflection surface (also called first interface) of the internal reflection element and a second reflection surface (also called second interface) of the internal reflection element opposite the first reflection surface.

[0012] Furthermore, an IR detector (infrared detector) is provided for detecting the infrared radiation guided through the internal reflection element and coupled out of the internal reflection element via a radiation exit surface of the internal reflection element.

[0013] The flow probe also includes a flow cell through which the measuring fluid flows in a predetermined flow direction, forming a measuring channel enclosed by a flow cell wall for the measuring fluid flowing through the flow cell. The internal reflection element is positioned within the flow cell such that the measuring fluid contacts the first reflective surface of the internal reflection element.

[0014] Finally, the flow probe has a reflection-enhancing, IR-inactive support element that lies completely flush against the second reflective surface of the internal reflective element.

[0015] The proposed flow probe offers a number of technical and application-specific advantages that enable reliable, precise, and process-related analysis of liquid process media. By using an IR emitter to emit infrared radiation with a defined spectral distribution, reproducible and selective excitation of molecular vibrations in the sample fluid is achieved. This forms the basis for accurate material identification and quantification using infrared spectroscopy.

[0016] The internal reflecting element guides the coupled infrared radiation via multiple total internal reflections between the first and second reflecting surfaces. An evanescent wave is generated at the first reflecting surface, which interacts with the flowing measurement fluid. This arrangement enables sensitive measurement without direct radiation transmission through the process medium, which is particularly advantageous for highly absorbing or turbid liquids. Simultaneously, the defined reflection geometry within the internal reflecting element allows for precise control of the interaction area and thus the detection conditions.

[0017] Positioning the IR detector at the radiation-emitting surface of the internal reflector allows for highly sensitive detection of the modulating effects of the measurement fluid on the infrared radiation. Since the entire optical path – from the IR emitter through the internal reflector to the IR detector – lies within the flow probe, a compact design with a short optical path length is achieved, making it particularly suitable for installation in confined process environments.

[0018] Another significant advantage lies in the design of the flow cell. The flow cell, through which the measuring fluid flows, is designed to form a clearly defined measuring channel in which the internal reflective element is in direct contact with the fluid. This enables continuous analysis in flow mode without the need for sampling or external preparation. This eliminates time delays and reduces the risk of inaccurate readings due to chemical changes or contamination of the sample.

[0019] The reflection-enhancing support element, which lies flush against the second reflective surface of the internal reflection element, ensures mechanically stable mounting and can also contribute to the optical optimization of total internal reflection, for example, by selectively adjusting the reflectance. This targeted integration not only increases the structural integrity of the optical assembly but also improves measurement accuracy and repeatability.

[0020] Overall, the flow probe allows for a robust, low-maintenance and process-integrable solution for real-time analysis of chemical parameters of process media.

[0021] The device according to the invention for instrumental process bath analysis comprises the described flow probe. This probe is part of a measuring circuit that can be connected to a process bath filled with the process medium to be analyzed. The process medium, in the form of the measuring fluid, can be diverted from the process bath into the measuring circuit and—after flowing through the measuring circuit—returned to the process bath. When the measuring circuit is connected to the process bath, the measuring fluid flows continuously through the circuit.

[0022] In addition to the described flow probe, the measuring circuit includes a fluid conveying unit and several measuring fluid lines connecting the flow probe and the fluid conveying unit.

[0023] The device for instrumental process bath analysis also includes a data processing unit connected to the flow probe for data transmission, for processing infrared spectra of infrared radiation detected by means of the IR detector of the flow probe, for data storage of the detected infrared spectra as well as reference infrared spectra and for spectral analytical evaluation of the infrared spectra detected by means of the IR detector of the flow probe.

[0024] The device for instrumental process bath analysis can be designed as a mobile measuring case. This allows for both single measurements, which represent the most common application scenario, and multiple measurements, which occur less frequently and require an additional setup. Alternatively, the device for instrumental process bath analysis can also be designed as a stationary measuring unit for single measurements, interval measurements, or continuous measurements. The device is therefore flexibly adaptable to different operating environments and application requirements.

[0025] The inventive method for instrumental process bath analysis for determining substances and their concentrations in the process medium located within a process bath is carried out using the proposed device for instrumental process bath analysis.

[0026] The procedure first involves connecting the measuring circuit, consisting of the flow probe, the fluid pumping unit, and the measuring fluid lines, to the process bath to divert and return the process medium containing the measuring fluid. Subsequently, the process medium, diverted from the process bath into the measuring circuit as measuring fluid, is continuously pumped through the measuring circuit by means of the fluid pumping unit, for example, a pump.

[0027] The infrared radiation with the defined spectral distribution is then directed into the internal reflection element of the flow probe by means of the IR emitter. As the measuring fluid flows through the flow probe, the infrared radiation is modulated by interaction during total internal reflection within the internal reflection element. The modulated infrared radiation is continuously detected by the flow probe's IR detector.

[0028] Subsequently, the substances and their concentrations are determined by comparing the recorded infrared spectrum with reference infrared spectra of process media with known composition and concentrations. The evaluation is performed by the data processing system. The methodology used for determining substances and concentrations is fundamentally known from the field of FTIR spectroscopy. The data processing system is configured and programmed accordingly to perform the corresponding spectral analysis of the recorded infrared spectra.

[0029] Using the device and method for instrumental process bath analysis, parameters or values, such as ion concentrations in the process medium, can be determined from recorded infrared spectra. Reference infrared spectra of process media with known bath parameters serve as the basis for parameter determination.

[0030] The apparatus and method for instrumental process bath analysis are applicable to the analysis of chemical processes, such as phosphating or blackening, electrochemical or galvanic processes, or etching processes (e.g., in semiconductor technology). Process baths whose process media can be monitored spectrally using the proposed technology include, for example, blackening baths, phosphating baths, electrochemical baths, electroplating baths, etching or pickling baths, or hot degreasing baths. The apparatus and method can also be used for the analysis of other process media, such as those from the agricultural sector. The apparatus and method are suitable for the entire pH range; the typical operating range is at temperatures up to 150 °C and pressures up to 10 bar.

[0031] According to one embodiment of the flow probe according to the invention, the flow cell wall has a penetration that is completely sealed by the internal reflective element. The first reflective surface of the internal reflective element faces the measuring channel and contacts the measuring fluid. The radiation entry surface and the radiation exit surface of the internal reflective element are located outside the measuring channel. Furthermore, one or more connecting elements form a sealing connection in the contact area surrounding the penetration between the reflective element and the flow cell wall. Because the first reflective surface of the internal reflective element faces the measuring channel and is in direct contact with the measuring fluid, infrared spectroscopy can be performed efficiently and without sample extraction in direct flow.The direct arrangement improves the sensitivity of the measurement, as there are no intermediate layers or disturbances between the measuring fluid and the reflective surface. Furthermore, the precisely defined optical coupling, in which the radiation entry and exit surfaces are located outside the measuring channel, ensures a contamination-free light path and protects the optical components from direct contact with the process medium.

[0032] The joining elements used to form a sealing connection, as described above, which can also serve as sealing connecting elements between other components of the flow probe, can be sealing elements and / or material-bonded connecting elements. The joining elements can, for example, be designed as elastomeric sealing elements, in particular as O-rings or flat gaskets. Sealing materials with high chemical resistance, such as perfluoroelastomers (FFKM), are particularly suitable, as they ensure a long-term stable seal even at elevated temperatures and in aggressive process media. Alternatively or additionally, the joining element can be designed as a material-bonded connection, for example in the form of an adhesive film, a solder, or a potting compound.Such material-bonded connections offer a durable, media-resistant, and mechanically robust bond between the reflective element and the flow cell wall. The choice of joining element depends on the mechanical, thermal, and chemical requirements of the respective application scenario, as well as on the desired maintenance concept, such as whether a detachable or permanently fixed connection is required.

[0033] Preferably, the internal reflecting element consists of a highly transparent, infrared-transparent, and mechanically stable material. Diamond is particularly suitable due to its high chemical resistance, high hardness, and excellent transmission in the mid-infrared spectral range. Alternatively, other materials can be used that exhibit sufficient optical transparency in the relevant infrared range as well as high mechanical and chemical stability. These include, in particular, zinc selenide (ZnSe), germanium (Ge), silicon (Si), or sapphire (Al₂O₃). The material selection depends on the wavelength range used, the process medium of the measuring fluid, and the thermal and chemical stresses in the intended process environment.

[0034] According to one embodiment of the flow probe according to the invention, the flow cell wall consists of a chemically resistant, mechanically robust, and process-suitable material. A design made of acid-resistant stainless steel is particularly advantageous, as it exhibits high corrosion resistance to numerous process media, including acidic and oxidizing solutions. Alternatively, polymer-based materials such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or polyetheretherketone (PEEK) can also be used, especially when a metal-free design is required or an extended chemical resistance profile is necessary. The choice of material depends on the chemical composition, temperature, and pressure of the respective process bath, as well as on the requirements for the mechanical stability and long-term durability of the flow cell wall.

[0035] Furthermore, the support element may be provided with a surface treatment in the contact area with the second reflective surface of the internal reflective element, which serves to improve the optical properties and reflection efficiency. The surface may be polished to create a particularly smooth reflective surface with defined reflection characteristics. Alternatively or additionally, the surface of the support element may be coated with an infrared-reflecting, IR-inactive (infrared-inactive) layer. A gold coating is particularly suitable for this purpose, as this material exhibits high reflectivity in the infrared spectral range and is also chemically inert. Other suitable coating materials include platinum, aluminum, or other precious metals or metal oxides with corresponding infrared optical properties.The choice of surface treatment depends on the requirements for reflection properties, thermal resistance and chemical resistance in the intended operating environment.

[0036] In a further embodiment, the flow probe features a flow-guiding and turbulence element positioned opposite the reflection element in the measuring channel. This flow-guiding and turbulence element is designed to direct the flowing measurement fluid precisely onto the first reflective surface of the internal reflection element while simultaneously creating turbulence within the fluid. This flow-guiding and turbulence element is also referred to as a turbulator. This ensures that the reflection surface is uniformly bathed at a defined flow velocity, enabling a reproducible interaction between the evanescent waves and the measurement fluid.

[0037] The flow-guiding and turbulence element can be designed in various geometric shapes, in particular as one or more baffles, deflectors, deflector ribs, cross ribs, baffle plates, strips, grooves, ribs, knobs, wings, or guide profiles. These geometries generate targeted flow deflections or turbulence, which both promote a uniform flow towards the reflection element and help to avoid dead zones and flow shadows in the measuring channel.

[0038] In particular, the flow-guiding and turbulence element can be axially displaceable, i.e., positioned or fixed along the flow direction of the measurement fluid, within the measurement channel. This allows for flexible adjustment of the flow path depending on the flow conditions or the measurement configuration used. This adjustability enables the position to be selected so that the flow towards the first reflective surface of the internal reflection element occurs under optimal conditions, thus improving signal quality and measurement stability.

[0039] Furthermore, the internal reflection element can be arranged in an internal bulge of the measurement channel formed by a bulge in the flow cell wall. This bulge locally expands the cross-section of the measurement channel and creates a fluid-dynamically defined space in which the measurement fluid is guided in direct contact with the first reflective surface of the internal reflection element. This geometric expansion of the flow space results in a longer residence time of the measurement fluid in the contact area with the reflection element, thus improving the sensitivity and reproducibility of the spectroscopic analysis. In conjunction with an opposing flow guide and vortex element, the flow can be directed into the bulge and further vortexed there to ensure dynamic and uniform fluid motion at the first reflective surface.

[0040] The invention is explained in more detail below with reference to exemplary embodiments and the drawings, wherein identical or similar features are provided with the same reference numerals; to this end, the drawings show: Fig. 1: A first version of the flow probe in longitudinal section view, and Fig. 2: A second version of the flow probe in longitudinal section view.

[0041] The flow probe according to Fig. 1 and Fig. 2 comprises a flow cell through which the measuring fluid 2, i.e., the process medium to be tested, branched off from a process bath, flows. The internal reflective element 5 is integrated into the wall 1 of the flow cell such that it is in direct contact with the measuring fluid 2. In the exemplary embodiment, the internal reflective element 5 is a diamond. The channel section in which the internal reflective element 5 contacts the measuring fluid 2 forms the measuring channel of the flow cell.

[0042] The internal reflection element 5 is an optical waveguide that directs the infrared radiation 9 generated by the IR emitter 3 and incident on the internal reflection element 5 to the IR detector 4 by total internal reflection. After exiting the internal reflection element 5, the multiply totally reflected infrared radiation 9 strikes the IR detector 4. During total internal reflection at the first reflective surface 5.1 of the internal reflection element 5, which faces the measurement fluid 2, evanescent waves are generated behind the totally reflective first reflective surface 5.1 of the internal reflection element 5. These evanescent waves interact with the measurement fluid 2 flowing past the first reflective surface 5.1 of the internal reflection element 5. This interaction, in turn, influences and modulates the infrared radiation 9 passing through the internal reflection element 5.By spectroscopic analysis of the infrared radiation 9 detected by the IR detector 4 and influenced (modulated) as it passes through the internal reflection element 5, the concentration of specific ions in the measuring fluid 2 can be determined, among other things.

[0043] The IR-inactive support element 6 is located at the second reflective surface 5.2 of the internal reflective element 5, opposite the first reflective surface 5.1 of the internal reflective element 5, where total internal reflection of the infrared radiation 9 also occurs. In the exemplary embodiment, the support element 6 exhibits the following Fig. 1. A reflection-enhancing, IR-inactive layer 6.1 is applied, which is in direct contact with the second reflective surface 5.2 of the internal reflection element 5 and supports the reflection of the infrared radiation 9 at the second reflective surface 5.2. This reflection-enhancing layer 6.1 can, for example, be a coating or layer of gold.

[0044] The internal reflective element 5 is attached to the flow cell wall 1 by means of the joining elements 8. The joining elements 8 can be sealing elements and / or material-bonded connections between the internal reflective element 5 and the flow cell wall 1.

[0045] Opposite the internal reflection element 5 in the measuring channel of the flow cell is the flow-guiding and turbulence element 7, which projects into the flowing measuring fluid 2 in the form of an impact rib, thus narrowing the measuring channel and directing the measuring fluid 2 specifically onto the first reflective surface 5.1 of the internal reflection element 5. Furthermore, the flow-guiding and turbulence element 7, also referred to as a turbulator, swirls the measuring fluid 2 to prevent segregation caused by flow effects.

[0046] In the exemplary embodiment according to Fig. 1 The flow cell or the flow cell wall 1 has a bulge in the area where the internal reflection element 5 is located, forming a protrusion of the measuring channel. The measuring fluid 2 is guided into this protrusion by means of the flow guide and turbulence element 7. In the exemplary embodiment according to Fig. 2 lacks the bulge; here the measuring channel is only slightly offset outwards from the flow cell wall 1 by the internal reflection element 5 placed on the flow cell wall 1.

[0047] The flow-guiding and turbulence element 7 is axially displaceable within the measuring channel, i.e., positionable and fixed along the flow direction of the measuring fluid 2 (the axial displaceability is illustrated by the double arrow on the flow-guiding and turbulence element 7). This allows the flow-guiding and turbulence element 7 to be axially adjusted so that the first reflective surface 5.1 of the internal reflective element 5 is optimally exposed to the flow.

[0048] Regarding further details and embodiments of the proposed technology for instrumental process bath analysis, reference is made to the German patent application with application number 10 2024 114 167.0, the contents of which are hereby incorporated into this patent application. Reference symbol list 1 Flow cell wall 2 Measuring fluid 3 IR emitters 4 IR detector 5 internal reflection element (IRE) 5.1 First reflective surface 5.2 second reflective surface 6 support element 6.1 IR-inactive layer 7 Flow guiding and turbulence element 8 joining element 9 Infrared radiation QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2004 / 0126049 A1

[0005] US 2024 / 0142374 A1

[0006]

Claims

[1] Flow probe for instrumental analysis of a measurement fluid formed from a process medium (2) by means of infrared spectroscopy according to the principle of attenuated total reflection, comprising - an IR emitter (3) for the emission of infrared radiation (9) with a defined spectral distribution, - an internal reflection element (5) for guiding the infrared radiation (9) coupled from the IR emitter (3) via a radiation entry surface of the internal reflection element (5) into the internal reflection element (5) by total internal reflection between a first reflection surface (5.1) of the internal reflection element (5) and a second reflection surface (5.2) of the internal reflection element (5) opposite the first reflection surface (5.1), - an IR detector (4) for detecting the infrared radiation (9) guided through the internal reflection element (5) and coupled out of the internal reflection element (5) in the direction of the IR detector (4) via a radiation exit surface of the internal reflection element (5), - a flow cell through which the measuring fluid (2) flows in a predetermined flow direction, forming a measuring channel enclosed by a flow cell wall (1) for the measuring fluid (2) flowing through the flow cell, wherein the internal reflection element (5) is arranged in the flow cell such that it contacts the measuring fluid (2) with the first reflection surface (5.1) of the internal reflection element (5), - a reflection-supporting, IR-inactive support element (6) that is covered by the second reflection surface (5.2) of the internal reflection element (5). [2] Flow probe according to claim 1, characterized by, that the flow cell wall (1) has a breakthrough which is completely closed by the internal reflection element (5), wherein the first reflection surface (5.1) of the internal reflection element (5) faces the measuring channel and contacts the measuring fluid (2), wherein the radiation entry surface and the radiation exit surface of the internal reflection element (5) are located outside the measuring channel, and wherein one or more joining elements (8) form a sealing connection in the contact area surrounding the breakthrough between the reflection element (5) and the flow cell wall (1). [3] Flow probe according to claim 1 or 2, characterized by , that the support element (6) in the contact area to the second reflective surface (5.2) has an infrared-reflecting, IR-inactive layer (6.1). [4] Flow probe according to one of claims 1 to 3, characterized by, that the flow probe has a flow guiding and turbulence element (7) which is arranged opposite the reflection element (5) in the measuring channel, wherein the flow guiding and turbulence element (7) directs the flowing measuring fluid (2) onto the first reflection surface (5.1) of the internal reflection element (5) and simultaneously turbulences it. [5] Flow probe according to claim 4, characterized by , that the flow-guiding and turbulence element (7) can be positioned axially displaceable in the measuring channel. [6] Flow probe according to any one of claims 1 to 5, characterized by , that the internal reflection element (5) is arranged in an inner bulge of the measuring channel formed by bulging of the flow cell wall (1). [7] Flow probe according to any one of claims 1 to 6, characterized by, that the flow cell wall (1) is made of acid-resistant stainless steel, the internal reflective element (5) is a diamond and the joining elements (8) are seals, the seals being made of perfluoroelastomers. [8] Device for instrumental process bath analysis, comprising a measuring circuit connectable to a process bath filled with a process medium for branching off a measuring fluid (2) formed from the process medium and for feeding the measuring fluid (2) back into the process bath after flowing through the measuring circuit, characterized by, that the measuring circuit comprises a flow probe according to one of claims 1 to 7, a fluid conveying unit and several measuring fluid lines connecting the flow probe and the fluid conveying unit, wherein the device further comprises a data processing unit connected to the flow probe for data transmission for processing infrared spectra of the infrared radiation (9) detected by means of the IR detector (4) of the flow probe, for data storage of the detected infrared spectra as well as of reference infrared spectra and for spectral analytical evaluation of the infrared spectra detected by means of the IR detector (4) of the flow probe. [9] Device according to claim 8, characterized by that the device is designed as a portable measuring case or as a stationary measuring unit. [10] Method for instrumental process bath analysis for determining substances and their molar concentrations in a process medium located within a process bath, characterized by that the method is carried out using a device according to one of claims 8 or 9, wherein the method comprises the following steps: - Connecting the measuring circuit consisting of flow probe, fluid pumping unit and measuring fluid lines to the process bath for branching off and feeding back the process medium forming the measuring fluid (2), - continuous pumping of the process medium, which is diverted from the process bath into the measuring circuit as measuring fluid (2), flowing through the measuring circuit, - Irradiation of infrared radiation (9) with a defined spectral distribution into the internal reflection element (5) of the flow probe by means of the IR emitter (3), - continuous acquisition of infrared spectra of the infrared radiation (9) modulated by interaction during total internal reflection in the internal reflection element (5) as the measuring fluid (2) flows through the flow probe, using the IR detector (4) of the flow probe, - Determining the substances and their concentration by comparing the recorded infrared spectrum with reference infrared spectra of process media with known composition and concentration using the data processing system.

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