Determination of sulfur dioxide in liquids

Abstract

A system (2) for determining an amount of SO2 in a liquid, the system comprising: a reaction vessel (10) for containing a sample (6) of the liquid and configured to have an internal volume sufficient to provide a headspace (12) above the contained sample (6) into which headspace gas can enter; a heater unit (14) thermally coupled to the reaction vessel (10); a gas flow system (16) for transferring the headspace gas from the headspace (12) to a measurement system (18); a cooler (20) for cooling the headspace gas in the gas flow system (16) before the headspace gas is delivered to the measurement system (18) to generate a condensate (40); and a liquid flow system (22) in fluid communication with the gas flow system (16) and the reaction vessel (10) and configured to transfer the condensate (40) from the gas flow system (16) to the reaction vessel (10).

Description

[0001] This invention relates to the determination of sulfur dioxide (SO2) in liquids. In particular, this invention relates to the determination of one or more of free SO2, bound SO2, and total SO2 in liquids (most particularly in drinkable liquid products (such as wine, beer, juice, or grape juice), other brewing products, or intermediates in the production of drinkable liquids).

[0002] Sulfur dioxide is important in winemaking and other drinking liquid production processes because it helps prevent microbial growth and liquid oxidation. These and other processes consume SO2 over time, resulting in insufficient SO2 protection in wine and other drinking liquids. Furthermore, SO2 and sulfites are known to be toxic and sensitizing to many individuals, necessitating monitoring and regulation of their levels in final drinking liquid products such as wine and beer.

[0003] Most countries have strict regulations on the maximum total sulfite content in drinkable liquids such as wine. From a winemaking perspective, high concentrations of sulfites can affect the sensory properties or characteristics of wine. Furthermore, excessive sulfur in grape juice can delay malolactic fermentation in wine, especially in wines with low pH levels. For these reasons, the concentration of sulfites in wine must be closely monitored and regulated.

[0004] It is well known that the presence and / or, in particular, the amount of free SO2 and other components of interest in drinkable liquid products or intermediate products in the production process of drinkable liquids can be determined by optical analysis of the gas in the headspace above the liquid sample. The presence and / or, in particular, the amount of a component can be readily determined by measuring the presence of a substance in the gas that indicates one or more components of interest in the liquid (which may be the same component).

[0005] As is known, for example, from EP 1 308 713, the composition of a liquid sample is determined by optical analysis of a headspace gas, which is allowed to build up in a sealed sample container with a volume greater than that of the liquid sample. This document specifically discloses a method for analyzing free SO2 in wine or other beverages using an infrared measuring instrument. According to this method, a liquid sample of a specific volume is introduced into a sealed container whose fluid-containing volume exceeds that specific volume. First, carbon dioxide (CO2) and other gases that may interfere with the measurement are removed from the headspace gas. Subsequently, a certain concentration of free SO2 is allowed to build up in the gaseous headspace. The gaseous sample is then removed from the headspace, and the concentration of free SO2 in the gaseous sample is measured using an infrared measuring instrument adapted to measure the attenuation of infrared radiation transmitted through the sample. Based on this measurement, the content of free SO2 in the beverage is determined.

[0006] EP 1 840 577 discloses an apparatus for detecting free SO2 from a liquid (typically wine) sample, and includes a measuring instrument adapted to detect free SO2 by one or more of a quantitative and qualitative measurement of the absorbance of optical radiation by a gas extracted from a headspace above the liquid sample. A gas flow system is configured to remove gas from the headspace and recirculate the extracted gas through the liquid sample back to the headspace to accelerate SO2 extraction. A metering device may also be provided for transferring a reagent (typically an acid) from a reservoir into the liquid to release a substance indicating the component of interest into the liquid for extraction into the headspace via the recirculated gas.

[0007] In the production of drinkable liquids (e.g., winemaking), it is generally important that both the free SO2 content and the total SO2 content are known. Standard reference methods (such as those described in the publication "Compendium of International Methods of Analysis-OIV," Volume 2, 2011, Ref. MA-AS323-04A, B, and C) disclose that the free SO2 content and the total SO2 content should be determined by two independent measurements. Free SO2 should be determined using acid hydrolysis at room temperature or lower (but typically at room temperature), while total SO2 should be determined again using acid hydrolysis at a significantly elevated temperature (typically around 100°C). Typically, for each of the free and bound SO2 determinations, approximately 15 mL of phosphoric acid is added to 50 mL of the sample liquid, and SO2 is extracted over 15 minutes.

[0008] EP 2 646 801 (the contents of which are incorporated herein by reference in their entirety) discloses a system for measuring one or more of free SO2, bound SO2, and total SO2 in a liquid sample by monitoring the evolution of SO2 over time during a single chemical hydrolysis reaction between the sample and a quantified hydrolytic reagent at elevated temperatures. Therefore, the analysis time is reduced compared to that associated with the aforementioned standard reference method. The disclosed system includes: a sample container with a volume sufficient to provide a headspace above the contained liquid sample, into which gas can enter; a gas flow system adapted to extract gas from the headspace, deliver the gas to a measurement system configured to monitor the evolution of SO2 in the delivered gas over time, and then recirculate the delivered gas back to the liquid sample in the container. A heater unit is provided for supplying thermal radiation to the sample container to raise the temperature of the sample therein to a level sufficient to promote the hydrolysis reaction. In such known systems, the headspace gas exits the heated sample container at an elevated temperature and cools as it flows through the gas flow system toward the measurement system (possibly enhanced using coolers positioned in series within the gas flow system). This can cause condensate to leave the gas phase and enter the gas flow system, which is problematic. The condensate (typically primarily water, and in the case of liquid samples containing alcohol) absorbs at least a portion of the SO2 present in the gas flow system, preventing that portion of SO2 from being measured by the measurement system. This condensation and absorption process is uncontrolled and negatively impacts the accuracy and precision of the measurement. If the SO2-containing condensate falls back into the liquid sample in the heated sample container, some of the absorbed SO2 is released almost instantaneously. This again negatively impacts data quality, and therefore accuracy and precision. Furthermore, the condensate can still be delivered from the headspace gas in the gas flow system to the detection system, where it can potentially cause contamination or damage.

[0009] The object of the present invention is to alleviate at least one of the problems associated with the above-described system.

[0010] This objective can be achieved using the system according to claim 1. By configuring the liquid flow system to separate the condensate from the headspace gas before measurement by the measuring system and return it to the reactor vessel, more stable measurements unaffected by the liquid in the gas can be obtained.

[0011] In the following description, various aspects of the invention will be described. Specific details are set forth for purposes of explanation in order to provide a thorough understanding of the invention. It will be apparent to those skilled in the art that other embodiments of the invention exist, which differ in detail but do not affect their essential characteristics. Therefore, the invention is not limited to what is shown in the drawings and described in the specification, but is determined only by the broadest interpretation of the appended claims, as indicated therein.

[0012] A better understanding of the features and advantages of the invention will be obtained by referring to the following detailed description (which illustrates illustrative embodiments utilizing the principles of embodiments of the invention) and the accompanying drawings, in which:

[0013] Figure 1 An embodiment of the system of the present invention is illustrated schematically; and

[0014] Figure 2 Schematic illustration of crossing Figure 1 The cross section AA of the gas-liquid separator.

[0015] Now consider Figure 1 The exemplary system 2, according to the present invention, schematically illustrates one or more of free SO2, bound SO2, and total SO2 in a drinkable liquid product. System 2 can be considered to generally include four subsystems: a reaction system 4; a gas flow system 16; a measurement system 18; and a liquid flow system 22.

[0016] The reaction system 4 of this embodiment includes a reactor dish 10 and a heater unit 14 configured to be in thermal contact with the reactor dish 10 to provide it with sufficient thermal radiation to promote the hydrolysis reaction. The required amount of thermal radiation depends on the liquids to be reacted, but typically a sufficient amount is needed to raise the temperature of these liquids above 60°C, preferably to near the boiling point of the contents of the reactor dish 10 (typically around 80°C, for example, between 75°C and 85°C). The reactor dish 10 is sized to define an internal volume larger than the expected volume of the sample 6 of the drinkable liquid product plus the hydrolysis reagent 8, which will be contained within the internal volume of the reactor dish 10 during use. This provides a headspace volume 12 above the liquids 8, 6 inside the reactor dish 10, into which gas (referred to as headspace gas) can enter during the hydrolysis reaction. In some embodiments, the reactor dish 10 may be provided with a closure 42 (possibly a removable closure) to seal the contents of the internal volume to prevent accidental leakage of fluids, particularly the headspace gas. In some embodiments, the reactor dish 10 may include a sealed end-user container (such as a corked or capped bottle, jar, or waxed paper container) and a suitable fluid connection may be established by puncturing the container. In some embodiments, the reactor dish 10 may include a disposable container pre-filled with a sample 6 of a drinkable liquid product, which may be introduced into the system 2. In another embodiment, the reactor dish 10 may include an injection pump, wherein the internal volume of the reactor dish 10 is constituted by the variable volume of the injection pump chamber.

[0017] Gas flow system 16 is configured to provide gas communication between headspace volume 12 and measurement system 18, allowing headspace gas to be transferred from headspace volume 12 to measurement system 18, where its SO2 content is measured. Preferably, gas flow system 16 according to this embodiment is configured to recirculate headspace gas after measurement by measurement system 18 to mix with fresh headspace gas from headspace volume 12. To achieve this, gas flow system 16 of system 2 includes an extraction conduit portion 16a; a delivery conduit portion 16b; and a return conduit portion 16c. These conduit portions 16a, 16b, 16c, together with any associated pump 46 and valve 48 (if present), form a headspace gas recirculation system (in... Figure 1 (Shown by B). Valve 48 may be a one-way valve operably connected to the extraction conduit portion 16a and the return conduit portion 16c to ensure a one-way recirculated gas flow direction within the gas flow system 16, thereby preventing the introduction of topspace gas from the measuring system 18 back into the topspace volume 12 of the reactor dish 10.

[0018] Cooler 20 is also configured as a component of system 2 and is configured to cool the headspace gas before it is delivered to measurement system 18 to generate condensate 40 in the headspace gas. In this embodiment, cooler 20 is located within system 2 and is in thermal contact with a section of extraction conduit portion 16a.

[0019] An extraction conduit portion 16a is configured to provide a fluid connection between the headspace volume 12 of the reactor vessel 10 and the liquid flow system 22. In this embodiment of system 2, the extraction conduit portion is configured to provide a fluid connection to the inlet 30 of a gas-liquid separator 24, which is in fluid communication with the liquid flow system 22. The gas-liquid separator 24 is adapted to separate condensate 40 from the cooled headspace gas before delivering the headspace gas to the measurement system 18, and to transfer the separated condensate 40 along with a portion of the headspace gas to the liquid flow system 22, such that the condensate 40 is removed into the liquid flow system 22 by the gas flow of that portion of the headspace gas entering the liquid flow system 22, after which the remaining portion of the cooled headspace gas is delivered to the measurement system 18. In some embodiments, a cooler 20 may be juxtaposed with the gas-liquid separator 24 to cool the headspace gas within the internal volume 28 and to generate condensate 40 primarily within the gas-liquid separator 24.

[0020] In some embodiments of System 2, and as Figure 1 As shown, the gas-liquid separator 24 includes a hollow cylinder 26 having an internal volume 28 defined by sidewalls 38 (cylindrical in this case). An inlet 30 passes through the sidewalls 38 and establishes fluid communication with the internal volume 28. Gas outlet 32 ​​and liquid outlet 34 each pass through the sidewalls 38 to provide fluid communication between the internal volume 28 and the delivery conduit portion 16b and the liquid flow system 22, respectively. The inlet 30, gas outlet 32, and liquid outlet 34 are relatively positioned to communicate with the internal volume 28 at multiple locations, such that the liquid outlet 34 is located below each of the inlet 30 and gas outlet 32 ​​at the location communicating with the internal volume 28 (in a direction parallel to the direction of gravity). Figure 1 (Indicated by arrow G). In this way, condensate 40 can be separated from the headspace gas within the internal volume 28 by gravity and transported through the liquid flow system 22 to the reactor vessel 4 by the flow of a portion of the headspace gas. In this embodiment, this portion of the headspace gas is continuously moved into the liquid flow system 22. In some embodiments, such as Figure 2As shown, inlet 30 can be positioned in sidewall 38 to introduce headspace gas into internal volume 28 at an angle of less than 90° to sidewall 38 (preferably close to an angle tangent to sidewall 38, such as between 1° and 15°, for example less than 5°). This introduces an angular velocity component into the headspace gas within internal volume 28, which enhances the separation of condensate from the headspace gas in gas-liquid separator 24, which can then operate in a manner similar to a known cyclone separator.

[0021] Back Figure 1 In some embodiments, and as Figure 1 As shown, the splash guard 36 or breathable membrane can be located within the internal volume 28 to prevent condensate from transferring to the measurement system 18 through the gas outlet 32. This helps prevent condensate from contaminating the gas flow system 16 and entering the measurement system 18.

[0022] Liquid outlet 34 is here connected via optional valve 60 to return conduit 22a of liquid flow system 22, which, together with any associated pump (i.e., pump 62) and other valves 60 (if present), forms a condensate recirculation system (in... Figure 1 (As shown in Figure C), the function of this condensate recirculation system is to transfer the condensate 40 recovered from the cooled headspace gas, along with the portion of the headspace gas in which the condensate 40 was transported in the liquid flow system 22, back to the reactor vessel 10. In some embodiments, the recovered condensate 40 and the portion of the headspace gas may be transferred to the headspace volume 12. In other embodiments, such as Figure 1 As shown, the recovered condensate 40 and the portion of headspace gas that carries the condensate 40 in the liquid flow system 22 can be transferred to the liquid (sample 6 plus a metered amount of hydrolysis reagent 8) in the reactor dish 10. The transfer to the liquid in the reactor dish 10 is preferred because the transferred condensate 40 can then generate bubbles along with the portion of headspace gas that has already carried the condensate 40 and pass through the liquid to help mix sample 6 and the metered amount of hydrolysis reagent 8, thereby promoting the release of SO2 from sample 6.

[0023] Gas outlet 32 ​​is in fluid communication with delivery conduit portion 16b of gas flow system 16 to supply substantially condensate-free headspace gas into delivery conduit portion 16b and forward toward measurement system 18.

[0024] The measurement system 18 is configured to receive gas from the gas flow system 16 and includes a measurement station 50 at which the SO2 content in the received headspace gas is monitored. SO2 monitoring can be achieved using known SO2 sensors (e.g., electronic or electrochemical cell type sensors), and in this embodiment, an optical SO2 sensor is employed. The measurement station 50 of the exemplary system 2 includes a flow cuvette 52 connected in series with the gas flow system 16 between the delivery conduit portion 16b and the return conduit portion 16c. Alternatively, the flow cuvette 52 can be replaced by a suitable optically transparent region of either the delivery conduit portion 16b or the return conduit portion 16c. The measurement station 50 further includes a complementary optical radiation supply source 54 and a detection element 56, which cooperate to monitor the absorption of optical radiation by SO2 present in the headspace gas delivered by the gas flow system 16 from the headspace volume 12 of the reactor vessel 10. As is well known, gaseous SO2 exhibits broad optical absorption in the ultraviolet (UV) spectral region, and its optical absorption around 277 nanometers (nm) is only slightly dependent on temperature changes. Therefore, the optical radiation supply source 54 of exemplary system 2 suitably includes a UV radiation supply source, preferably an LED supply source, such as one or more LEDs with a nominal wavelength of 275 nm. Such LEDs typically have loose specifications, typically an FWHM of 10 nm and a peak wavelength of 275 nm ± 5 nm. The complementary detection element 56 may include one or more photodiode-based detectors, such as those based on silicon carbide (SiC) photodiodes. Such SiC photodiode-based detectors have the advantage that their output is insensitive to ambient (indoor) light, thus requiring only minimal shielding protection against ambient (indoor) light. The detection element 56 is disposed within the measurement system 18 to detect UV radiation from the radiation supply source 54 after transmission through the topspace gas within the flowing cuvette 52, and to provide an output signal proportional to the intensity of the detected radiation. According to the well-known Beer-Lambert law, the amount of UV radiation absorbed by the gas in the headspace will be proportional to the concentration of SO2 present in the gas (because almost all the absorption in that spectral region will be due to SO2).

[0025] A signal processor 58 (shown herein as integrated with the measurement system 18) is connected to receive and analyze the output signal from the detection element 56 to establish a measurement of SO2 in the headspace gas in a manner known in the art. For example, the signal processor 58 may be configured with, or accessed via a telecommunications link, a calibration model (e.g., a multivariate calibration model) that correlates the output signal with the concentration of SO2 present in the headspace gas or a Lambert-Beer calibration model. It should be understood that, to achieve the desired functionality, the signal processor 58 may have one or more separate components cooperatively connected via a wired or telecommunications link.

[0026] The return conduit portion 16c of the gas flow system 16 provides a fluid connection between the measuring station 50 and the extraction conduit 16a to preferably return the headspace gas to a position in the extraction conduit 16a after the measurement in the flow cuvette 52, downstream of the headspace volume 12. Because the gas returned by the return conduit portion 16c does not flow through the headspace volume 12, the gas flow rate interacting with the vapor-containing gas from the heated sample 6 in the headspace volume 12 is relatively low, resulting in less condensation when the gas is cooled in the cooler 20. This produces more stable measurements at the measuring station 50.

[0027] Metering device 64 includes: a reservoir 66 for hydrolyzing reagent 8, fluidly connected via conduit 68 to the internal volume of reactor dish 10; a metering pump 70 for transferring hydrolyzing reagent 8 from reservoir 66 to reactor dish 10; and a controller 72 for controlling the operation of metering pump 70. Controller 72 is connected to signal processor 58 to receive control signals and trigger operation of metering pump 70 accordingly. It is contemplated that in other embodiments, the control signals may be generated by controller 72 and supplied to signal processor 58 during the transfer of hydrolyzing reagent 8, or may be generated and supplied to both independently of controller 72 or signal processor 58.

[0028] In this embodiment, the hydrolysis reagent 8 is an acid that, when added to sample 6 of the drinkable liquid product, adjusts the pH of sample 6 to induce the release of previously bound SO2 into sample 6 upon sufficient heating. This released SO2 then enters the headspace 12. In this way, SO2-rich gas can be rapidly generated in the headspace 14.

[0029] In an exemplary operation, liquid sample 6 (approximately 2 ml of wine or grape juice in this case) and an acid reagent (e.g., 1 ml of 25% phosphoric acid in this case) are sequentially pumped into reactor dish 10. A very small amount of defoamer (e.g., silicone oil or 1-octanol) can be added to the acid before pumping to prevent foaming, or a very small amount of defoamer can be added separately to reactor dish 10. This provides the advantage that, although the same chemical principles as the reference method are employed, the amount of reagent 8 used is much smaller than that used in the reference method. Reactor dish 10 is continuously heated, here to approximately 80°C (e.g., between 75°C and 85°C), to promote acid hydrolysis. The recirculated headspace gas is presented to the flow cuvette 52 of measuring station 50. Free SO2 is released almost instantaneously from liquid sample 6, reaching equilibrium with the gas phase. Bound SO2 is slowly hydrolyzed and also released, reaching equilibrium with the gas phase. This hydrolysis is allowed to proceed for approximately 30 seconds to approximately 4 minutes, depending on the desired accuracy of the determination. Sufficient accuracy can typically be achieved between 30 and 90 seconds. Even after 4 minutes, hydrolysis may not have fully reached a steady state, but accurate determination can still be made in a much shorter time than with reference methods. At multiple time points during the hydrolysis reaction and before reaching steady state, the measurement system 18 collects measurements of UV absorbed by the headspace gas. Based on the collected measurements, the evolution of SO2 concentration over time in the headspace gas within the flowing cuvette 52 can be derived directly from the measurements of UV radiation absorbed by the headspace gas within the signal processor 58. According to embodiments of the method of the invention, both the free and bound SO2 concentrations in the sample can then be derived by deconvolving the time curve of SO2 concentration in the flowing cuvette 52. Total SO2 can also be calculated, as the total is the sum of the free and bound states. The free SO2 content in the sample is correlated with the rapid release of SO2 concentration in the cuvette 52 (the height of the time-dependent SO2 evolution curve constructed from the collected measurements). After the free SO2 has been released, the bound SO2 is related to the release rate of SO2 (the slope of the constructed time-dependent SO2 evolution curve).

[0030] This derivation can be improved by using multivariate mathematical techniques (such as PLS) when deconvolving the time curves. A calibration model relating the time dependence of SO2 concentration evolution can be constructed by monitoring this evolution in samples with known concentrations, and then the calibration model can be applied to the deconvolution of the curves for samples with unknown concentrations using known chemometric techniques.

[0031] In some embodiments of System 2, the gas-liquid separator 24 may include a permeable membrane located in the gas flow system 16 to serve as a common boundary between the extraction conduit portion 16a and the delivery conduit portion 16b. The return conduit 22a of the liquid flow system 22 is thus configured to be in fluid communication with the extraction conduit portion 16a upstream of the permeable membrane (in the direction of gas flow in the headspace) and downstream of the cooler 20 (preferably near the permeable membrane). The permeable membrane is made of a material that allows gas to pass through but prevents the passage of condensate 40. As a non-limiting example, such a material may be a thin silicone or polydimethylsiloxane (PDMS) membrane product, a polyamide or cellulose acetate membrane product, or silica, zeolite, or a metal-organic framework. The condensate 40 is transported via the return conduit 22a of the liquid flow system 22 in a portion of the headspace gas to the liquid contained in the reactor dish 10 (primarily sample 6 and hydrolysate 8). Claims (as amended under Article 19 of the Treaty) 1. A system (2) for determining one or more of free SO2, bound SO2, and total SO2 in a drinkable liquid product, the system (2) comprising: a reaction system (4) having a reaction vessel (10) for containing a sample (6) of the drinkable liquid product and a hydrolysis reagent (8), the reaction vessel (10) being configured to have an internal volume sufficient to provide a headspace (12) above the sample (6) and the hydrolysis reagent (8), the headspace being capable of receiving gas as a headspace gas; a measurement system (18) for monitoring SO2; a heater unit (14) thermally coupled to the reaction vessel (10) to supply it with thermal radiation; and a gas flow system (16) configured to transfer the headspace gas from the headspace (12) to the measurement vessel. The system (18); and a cooler (20) adapted to cool the headspace gas in the gas flow system (16) to generate condensate (40); wherein the system (2) further includes a liquid flow system (22) in fluid communication with the gas flow system (16) and the reaction system (4), the liquid flow system (22) being adapted to transfer the condensate (40) from the gas flow system (16) to the reactor vessel (10); and a gas-liquid separator (24) in fluid communication with the gas flow system (16) and the liquid flow system (22) and configured to separate the condensate (40) from the headspace gas before delivering the headspace gas to the measurement system (18) and to transfer the separated condensate (40) to the liquid flow system (22). 2. The system (2) of claim 1, wherein the gas-liquid separator (24) comprises a column (26) having an internal volume (28) and being provided with: an inlet (30) in fluid communication with the gas flow system (16) and the internal volume (28); a first outlet (32) in fluid communication with the internal volume (28) and the gas flow system (16); and a second outlet (34) in fluid communication with the internal volume (28) and the liquid flow system (22), the second outlet (34) being positioned to communicate with the internal volume (28) at a location below the two locations where the inlet (30) and the first outlet (32) communicate with the internal volume (28) in a direction parallel to the direction of gravity. 3. The system (2) as claimed in claim 2, wherein the splash guard (36) is located within the internal volume (28) and before the first outlet (32) to inhibit liquid from moving from the internal volume (28) through the first outlet (32). 4. The system (2) as claimed in claim 2, wherein the inlet (30) is oriented at an angle of less than 90 degrees to the sidewall (38) of the column (26), the sidewall (38) defining the internal volume (28). 5. The system (2) as claimed in claim 1, wherein the cooler (20) is positioned in thermal contact with the gas-liquid separator (24). 6. The system (2) of claim 1, wherein the gas flow system (16) is further configured to recirculate the topspace gas from the measurement system (18) via the cooler (20) thereby avoiding the topspace (12). 7. The system (2) of claim 1, wherein the gas-liquid separator (24) is configured to transfer the separated condensate (40) to the liquid flow system (22) by conveying it in a portion of the headspace gas. 8. The system (2) of claim 1, wherein the measurement system (18) includes a complementary ultraviolet radiation supply source (54) and a detection element (56) arranged to monitor the amount of ultraviolet radiation supplied by the supply source (54) and absorbed by the top space gas transferred to the measurement system (18) as a monitoring indicator of SO2.

Claims

1. A system (2) for determining one or more of free SO2, bound SO2 and total SO2 in a drinkable liquid product, the system (2) comprising: The reaction system (4) includes a reaction vessel (10) for containing a sample (6) of the drinkable liquid product and a hydrolysis reagent (8), the reaction vessel (10) being configured to have an internal volume sufficient to provide a headspace (12) above the sample (6) and the hydrolysis reagent (8), into which gas can enter as a headspace gas; a measurement system (18) for monitoring SO2; a heater unit (14) thermally coupled to the reaction vessel (10) to supply it with thermal radiation; and a gas flow system (16). The gas flow system is configured to transfer the topspace gas from the topspace (12) to the measuring system (18); and a cooler (20) adapted to cool the topspace gas in the gas flow system (16) to generate condensate (40); wherein the system (2) further includes a liquid flow system (22) in fluid communication with the gas flow system (16) and the reaction system (4), the liquid flow system (22) being adapted to transfer the condensate (40) from the gas flow system (16) to the reactor vessel (10).

2. The system (2) as claimed in claim 1, further comprising: A gas-liquid separator (24) is in fluid communication with the gas flow system (16) and the liquid flow system (22) and is configured to separate the condensate (40) from the topspace gas before delivering the topspace gas to the measuring system (18) and to transfer the separated condensate (40) to the liquid flow system (22).

3. The system (2) as described in claim 2, wherein, The gas-liquid separator (24) includes a column (26) having an internal volume (28) and being provided with: an inlet (30) in fluid communication with the gas flow system (16) and the internal volume (28); a first outlet (32) in fluid communication with the internal volume (28) and the gas flow system (16); and a second outlet (34) in fluid communication with the internal volume (28) and the liquid flow system (22), the second outlet (34) being positioned to communicate with the internal volume (28) at a location below the two locations where the inlet (30) and the first outlet (32) communicate with the internal volume (28) in a direction parallel to the direction of gravity.

4. The system (2) as described in claim 3, wherein, A splash guard (36) is located within the internal volume (28) and before the first outlet (32) to prevent liquid from moving from the internal volume (28) through the first outlet (32).

5. The system (2) as described in claim 3, wherein, The entrance (30) is oriented at an angle of less than 90 degrees to the side wall (38) of the column (26), which defines the internal volume (28).

6. The system (2) as claimed in claim 2, wherein, The cooler (20) is positioned to be in thermal contact with the gas-liquid separator (24).

7. The system (2) as claimed in claim 1, wherein, The gas flow system (16) is further configured to recirculate the top space gas from the measurement system (18) via the cooler (20), thereby avoiding the top space (12).

8. The system (2) as claimed in claim 2, wherein, The gas-liquid separator (24) is configured to transfer the separated condensate (40) to the liquid flow system (22) by conveying it through a portion of the headspace gas.

9. The system (2) as claimed in claim 1, wherein, The measurement system (18) includes a complementary ultraviolet radiation supply source (54) and a detection element (56) arranged to monitor the amount of ultraviolet radiation supplied by the supply source (54) and absorbed by the top space gas transferred to the measurement system (18) as a monitoring indicator of SO2.

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