Determination of sulphur dioxide in a liquid

Abstract

A system (2) for determining an amount of SO2 in a liquid comprising a reaction vessel (10) for containing a sample (6) of the liquid and being configured with an internal volume sufficient to provide a headspace (12) above contained the sample (6) into which a headspace gas can pass; 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 its delivery 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 with the reaction vessel (10) and configured to transfer the condensate (40) from the gas flow system (16) to the reaction vessel (10).

Description

Determination of Sulphur Dioxide in a Liquid

[0001] The present invention relates to the determination of sulphur dioxide (SO2) in a liquid. Particularly the present invention relates to the determination of one or more of free, bound and total SO2in a liquid, most particularly in a potable liquid product such as wine, beer, juice or must, other vinification products or intermediates of the potable liquid production process.

[0002] Sulphur dioxide is important in the winemaking and in other potable liquid production processes as it aids in preventing microbial growth and the oxidation of the liquid. These processes and others consume the SO2over time, resulting in wines or other potable liquids with little SO2protection. Furthermore, SO2and sulphiting agents are known to be toxic and allergens to many individuals and their levels need to be monitored and regulated in final potable liquid products, such as wines and beers.

[0003] Most countries have strict guidelines as to the maximum levels of total sulphites permissible in a potable liquid, such as in wine for example. From a winemaking point of view, high concentrations of sulfites can affect the sensory attributes or characteristics of the wine. Additionally, too much sulphur in the must also delays the malolactic fermentation of wine, particularly in wines with low pH. 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 SO2and other components of interest in a potable liquid product or an intermediate product of the potable liquid production process may be determined by the optical analysis of headspace gases above a liquid sample. By measuring the presence in the gas of species indicative of the one or more components of interest in the liquid (perhaps being one and the same) then the presence and / or particularly the amount of that component can be readily determined.

[0005] It is known, from for example EP 1 308 713, to determine components of a liquid sample by optical analysis of a headspace gas that isallowed to become established in a sealed sample container having a volume greater than that of the liquid sample. This document discloses in particular a method for the analysis of free SO2in wine or other beverage by use of infrared measurement instrumentation. According to this method a liquid sample of a specific volumetric size is introduced into a sealed container having a fluid holding volume in excess of the specific volumetric size. Carbon dioxide (CO2) and other gases that may interfere with the measurement are first removed from the headspace gases. Thereafter a concentration of free SO2is allowed to establish in the gaseous headspace. A gas sample is then removed from the headspace and the concentration of free SO2in that gas sample is measured by means of the infrared measurement instrumentation adapted to measure the attenuation of infrared radiation transmitted through the sample. From this measurement the content of free SO2in the beverage is determined.

[0006] EP 1 840 577 discloses an apparatus for detecting free SO2from a liquid, typically wine, sample and comprises measurement instrumentation adapted to detect free SO2by one or both of a quantitative and a qualitative measurement of absorption of optical radiation by gas extracted from a headspace above the liquid sample. A gas flow system is configured to remove gas from and to recirculate extracted gas to the headspace through the liquid sample in order to speed up the extraction of SO2. A dosing device may also be provided for transfer of a reagent, typically an acid, from a reservoir into the liquid to effect release into the liquid of a species indicative of the component of interest for extraction into the headspace by the recirculated gas.

[0007] It is often important in potable liquid production, winemaking for example, that both free and total SO2content is known. Standard reference methods such as described in the publication “Compendium of International Methods of Analysis-OIV”, Edition 2011 Vol. 2, References MA-AS323-04A, B and C, disclose that free and total SO2content are to be determined in two separate measurements. Free SO2is to be determined at room temperature or lower but typically at roomtemperature using acid hydrolysis, whereas total S02is to be determined at significantly elevated temperatures, typically around 100°C, again using acid hydrolysis. Typically for each of the free and the bound determinations around 15mL (millilitres) of phosphoric acid is added to 50mL of sample liquid and SO2is extracted over a 15 minute period.

[0008] EP 2 646 801, the contents of which are included herein by reference in their entirety, discloses a system for the measurement of one or more of free, bound and total SO2in a liquid sample by monitoring a time evolution of SO2from a single chemical hydrolysis reaction between the sample and a dosed hydrolysis reagent at an elevated temperature. Thus, the analysis time is reduced as compared with that associated with the standard reference method described above. The disclosed system comprises a sample container having a volume sufficient to provide a headspace above a contained liquid sample into which a gas can pass; a gas flow system adapted to extract gas from the headspace, transport it to a measurement system which is configured to monitor a time dependent evolution of SO2in the transported gas and then recirculate it back into the liquid sample in the container. A heater unit is provided for supplying thermal radiation into the sample container to elevate the temperature of sample therein sufficient to facilitate the hydrolysis reaction. In this known system the headspace gas will leave the heated sample container at an elevated temperature and will cool, perhaps enhanced using a cooler located in-line in the gas flow system, as it flows in the gas flow system towards the measurement system. This can cause condensate to leave the gas phase and enter the gas flow system, which is problematic. The condensate, typically mainly water and, in the case of alcoholic liquid samples, also ethanol, absorbs at least a fraction of the SO2present in the gas in the gas flow system and prevents it from being measured in the measurement system. This condensation and absorption process is uncontrolled and influences accuracy and precision of the measurement negatively. If SO2loaded condensate falls back to the liquid sample in the heated sample container then part of the absorbedS02gets released almost instantly. This again has a negative impact on the data quality and therefore on accuracy and precision. Moreover, condensate can still be transported by the headspace gas in the gas flow system to the detection system, where it may cause contamination or damage.

[0009] It is an aim of the present invention to alleviate at least one of the problems associated with the above-mentioned system.

[0010] This aim may be achieved by a system according to Claim 1. By having a liquid flow system configured to separate condensate from the headspace gas before measurement by the measurement system and return it to the reaction vessel a more stable measurement, unaffected by liquid in the gas, may be obtained.

[0011] In the following description, various aspects of the invention will be described. For the purposes of explanation, specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent to one skilled in the art that there are other embodiments of the invention that differ in detail without affecting the essential nature thereof. Therefore, the invention is not limited by that which is illustrated in the figures and described in the specification, but only as indicated in the accompanying claims, with the proper scope determined only by the broadest interpretation of said claims.

[0012] A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth an illustrative embodiment, in which the principles of embodiments of the present invention are utilized, and the drawings of the accompanying figures, of which:Fig. 1 shows schematically an embodiment of a system of the present invention; andFig. 2 shows schematically a cross-section A-A through the gasliquid separator of Fig.l.

[0013] Considering now the exemplary system 2 for determining one or more of free, bound and total SO2in a potable liquid product according to the present invention which is illustrated schematically in Fig. 1. Thesystem 2 may be considered as generally comprising four sub-systems: a reaction system 4; a gas flow system 16; a measurement system 18; and a liquid flow system 22.

[0014] The reaction system 4 of the present embodiment comprises a reaction vessel 10 and a heater unit 14 which is disposed in thermal contact with the reaction vessel 10 to provide thermal radiation thereto in an amount sufficient to facilitate a hydrolysis reaction. The amount of thermal radiation needed depends on the liquids to be reacted but typically an amount sufficient to raise the temperature of these liquids to above 60°C is required and preferably to around the boiling point of the contents of the reaction vessel 10 which is typically around 80°C, such as between 75°C and 85°C. The reaction vessel 10 is dimensioned to define an internal volume which is greater than an expected volume of a sample 6 of the potable liquid product plus a hydrolysis reagent 8 that, in use, will be contained within the internal volume of the reaction vessel 10. This provides a headspace volume 12 internal of the reaction vessel 10 above the liquids 8,6 into which a gas, known as a headspace gas, can pass during the hydrolysis reaction. In some embodiments the reaction vessel 10 may be provided with a closure 42, perhaps a removable closure, to seal the contents of the internal volume against the unintentional egress of fluid, in particular the egress of the headspace gas. In some embodiments the reaction vessel 10 may comprise a sealed end user container such as a corked or capped bottle, a can or a waxed paper container and appropriate fluid connections may be established by piercing the container. In some embodiments the reaction vessel 10 may comprise a single use container which may be introduced into the system 2 pre-filled with the sample 6 of the potable liquid product. In still further embodiments the reaction vessel 10 may comprise a syringe pump, wherein the internal volume of the reaction vessel 10 is constituted by a variable volume of the syringe pump chamber.

[0015] The gas flow system 16 is configured to provide a gas communication between the headspace volume 12 and the measurement system 18 so that headspace gas may be transferred from the headspace volume 12to the measurement system 18 where a measurement of an S02content thereof is performed. As per the gas flow system 16 of the present embodiment, it is preferable that the gas flow system 16 is configured to also re-circulate headspace gas after measurement by the measurement system 18 to mix with new headspace gas from the headspace volume 12. To achieve this, the gas flow system 16 of the present system 2 comprises 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 pumps 46 and valves 48 if present, form a headspace gas re-circulatory system (illustrated by B in the Fig. 1). The valves 48 may be one-way valves operably connected to the extraction conduit portion 16a and the return conduit portion 16c to ensure a one-way recirculatory gas flow direction within the gas flow system 16, here avoiding introducing headspace gas from the measurement system 18 back into the headspace volume 12 of the reaction vessel 10.

[0016] A cooler 20 is also provided as a component of the system 2 and is configured to cool headspace gas before its delivery to the measurement system 18 to generate a condensate 40 in the headspace gas. In the present embodiment the cooler 20 is located within the system 2 in thermal contact with a section of the extraction conduit portion 16a.

[0017] The extraction conduit portion 16a is disposed to provide a fluid coupling between the headspace volume 12 of the reaction vessel 10 and the liquid flow system 22, in the present embodiment of the system 2 with an 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 the condensate 40 from the cooled headspace gas before delivery of the headspace gas to the measurement system 18 and to transfer the separated condensate 40 to the liquid flow system 22 together with a portion of the headspace gas so that condensate 40 is removed into the liquid flow system 22 by gas flow of the portion of the headspace gas into the liquid flow system 22 before delivery of the remainder of the cooled headspace gas to themeasurement system 18. In some embodiments the cooler 20 may be collocated with the gas-liquid separator 24 so as to cool the headspace gas within the internal volume 28 and generate condensate 40 primarily within the gas-liquid separator 24.

[0018] In some embodiments of the system 2, and as illustrated in Fig. 1, the gas-liquid separator 24 comprises a hollow column 26 having an internal volume 28 which is delimited by a side-wall 38, here a cylindrical side-wall. The inlet 30 passes through the side-wall 38 and establishes a fluid communication with the internal volume 28. A gas outlet 32 and a liquid outlet 34 each pass through the side-wall 38 to provide fluid communications between the internal volume 28 and the delivery conduit portion 16b and the liquid flow system 22 respectively. The inlet 30, the gas outlet 32 and the liquid outlet 34 are relatively positioned to communicate with the internal volume 28 at locations such that the liquid outlet 34 is located below (in a direction parallel to the direction of the action of gravity, illustrated by the arrow G in the Fig. 1) the locations at which each of the inlet 30 and the gas outlet 32 communicate with the internal volume 28. In this manner condensate 40 may be separated from the headspace gas within the internal volume 28 by the action of gravity and transported through the liquid flow system 22 to the reaction vessel 4 by a flow of the portion of headspace gas which is, in the present embodiment, constantly moved into the liquid flow system 22. In some embodiments, as illustrated in Fig. 2, the inlet 30 may be disposed in the side-wall 38 to introduce headspace gas into the internal volume 28 at an angle to the side-wall 38 less than 9O0,preferably close to tangential, such as between 1° and 15°, such as less than 5°, to the side-wall 38. This introduces an angular velocity component to headspace gas within the internal volume 28 which enhances the separation of condensate from the headspace gas in the gas-liquid separator 24, which may then operate in a manner of a known cyclone separator.

[0019] Returning to Fig. 1, in some embodiments, and as illustrated in Fig. 1, a splash plate 36 or gas permeable membrane may be located within the internal volume 28 in order to inhibit the transfer of condensate throughthe gas outlet 32 and to the measurement system 18. This helps prevent condensate from contaminating both the gas flow system 16 and into the measurement system 18.

[0020] The liquid outlet 34 is connected, here via an optional valve 60, to a return conduit 22a of the liquid flow system 22 which, together with any associated pumps, pump 62 say, and other valves 60 when present, form a condensate re-circulatory system (illustrated by C in the Fig. 1) which functions to transfer condensate 40 recovered from the cooled headspace gas back to the reaction vessel 10 together with the portion of headspace gas in which the condensate 40 is transported in the liquid flow system 22. In some embodiments the recovered condensate 40 and the portion of headspace gas may be transferred into the headspace volumel2. In other embodiments, as illustrated in Fig. 1, the recovered condensate 40 and the portion of headspace gas in which the condensate 40 is transported in the liquid flow system 22 may be transferred to the liquid (sample 6 plus dosed hydrolysis reagent 8) in the reaction vessel 10. Transfer to the liquid in the reaction vessel 10 is preferable as the transferred condensate 40 may then bubble through the liquid together with the portion of headspace gas in which the condensate 40 has been transported to help mix the sample 6 and the dosed hydrolysis reagent 8 and thereby facilitate the release of SO2from the sample 6.

[0021] The gas outlet 32 is in fluid communication with the delivery conduit portion 16b of the gas flow system 16 to supply essentially condensate free headspace gas into the delivery conduit portion 16b and onward towards the measurement system 18.

[0022] The measurement system 18 is disposed to receive gas from gas flow system 16 and is provided with a measurement station 50 at which the content of SO2in the received headspace gas is monitored. The monitoring of SO2may be achieved using known SO2sensors, for example electronic or electrochemical cell type sensors, and in the present embodiment an optical SO2sensor is employed. The measurement station 50 of the exemplary system 2 comprises a flow cuvette 52 which is connected in-line to the gas flow system 16between the delivery conduit portion 16b and the return conduit portion 16c. Alternatively the flow cuvette 52 may be substituted by a suitably optically transparent region of the delivery or the return conduit portions 16b, 16c. The measurement station 50 additionally comprises a complementary optical radiation supply 54 and detection element 56 co-operable to monitor absorption of optical radiation by SO2present in headspace gas delivered by the gas flow system 16 from the headspace volume 12 of the reaction vessel 10. It is well-known that gaseous SO2exhibits a broad optical absorption in the ultra-violet (UV) spectral region and that the optical absorption around 277 nanometers (nm) is weakly dependent on temperature variations. The optical radiation supply 54 of the exemplary system 2 therefore suitably comprises a UV radiation supply, preferably a LED supply, such as may comprise one or more nominally 275 nm LED(s). Such LEDs are often loosely specified, typically with a 10 nm FWHM and with a peak wavelength of 275 nm ± 5nm. The complimentary detection element 56 may comprise one or more photodiode based detector(s), such as silicon carbide (SiC) photodiode-based detector(s). Such a SiC photodiode-based detector has an advantage that it has an output that is insensitive to, and therefore needs minimal shielding from, ambient (room) light. The detection element 56 is disposed within the measurement system 18 to detect UV radiation from the radiation supply 54 after transmission through headspace gas within the flow 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 that is absorbed by the headspace gas will be directly proportional to the concentration of SO2present in that gas (since virtually all absorption in that spectral region will be due to SO2)

[0023] A signal processor 58, here shown as integral with measurement system 18, is connected to receive the output signal from the detection element 56 and to analyse the received output signal to establish a measure of SO2in the headspace gas in a manner known in the art. For example, the signal processor 58 may be provided with, or have access to via a telecommunications link, a calibration such as a multivariatecalibration, that links the output signal to the concentration of SO2present in the headspace gas or a Lambert-Beer calibration. It will be appreciated that to achieve the desired functionality the signal processor 58 may have one or more separate components cooperatively connected by a wired link or a telecommunications link.

[0024] The return conduit portion 16c of the gas flow system 16 provides a fluid connection between the measurement station 50 and the extraction conduit 16a to return headspace gas after measurement in the flow cuvette 52 preferably to a location in the extraction conduit 16a after the headspace volume 12. Since the gas returned by the return conduit portion 16c does not flow through the headspace volume 12 then there is a relatively lower gas flow to interact with the vapour laden gas from the heated sample 6 in the headspace volume 12 and thus less condensate produced when the gas is cooled in the cooler 20. This produces a more stable measurement at the measurement station 50.

[0025] A dosing apparatus 64 comprises a reservoir 66 for hydrolysis reagent 8 which is fluidly connectable to the inner volume of the reaction vessel 10 via a conduit 68; a dosing pump 70 for effecting the transfer of hydrolysis reagent 8 from the reservoir 66 to the reaction vessel 10; and a controller 72 for controlling the operation of the dosing pump 70. The controller 72 is connected to the signal processor 58 to receive a control signal and to trigger the operation of the dosing pump 70 in dependence thereof. It is envisaged that in other embodiments the control signal may be generated by the controller 72 transfer of the hydrolysis reagent 8 and supplied to the signal processor 58 or may be generated independently of either the controller 72 or the signal processor 58 and supplied to both.

[0026] In the present embodiment the hydrolysis reagent 8 is an acid which when added to the sample 6 of potable liquid product adjusts the pH of the sample 6 to cause, when heated sufficiently, the liberation into the sample 6 of the otherwise bound SO2. This liberated SO2is then available to pass into the headspace 12. In this manner a gas may be rapidly generated in the headspace 14 that is enriched with SO2.

[0027] In an exemplary operation the liquid sample 6, here approximately 2 ml of wine or must, and the acid reagent, here for example 1 ml of 25% Phosphoric acid, are sequentially pumped into the reaction vessel 10. A very small amount of antifoaming agent (e.g. silicone oil or 1-Octanol) may be added to the acid before pumping to avoid foaming or may be added separately into the reaction vessel 10. This provides the advantage that the amount of reagent 8 to be employed is much less than that employed with the reference methods although the same chemistry as the reference method is employed. The reaction vessel 10 is constantly heated, here to around 80°C such as between 75°C to 85°C, to facilitate the acid hydrolysis. The recirculated headspace gas is presented to the flow cuvette 52 of the measurement station 50. The free SO2is almost instantly liberated from the liquid sample 6 into equilibrium with the gas phase. Slowly the bound SO2is hydrolysed and is also released into equilibrium with the gas phase. This hydrolysis is allowed to proceed for between around 30 sec to around 4 minutes depending on the accuracy of determination that is wanted. Sufficient accuracy may typically be achieved between 30 sec to 90 sec. Even after 4 minutes the hydrolysis is not necessarily completed to a steadystate but still enables accurate determinations to be made in much less time than with the reference methods. At a plurality of times during the hydrolysis reaction and before steady-state a measure of UV absorbed by the headspace gas is collected by the measurement system 18. Based on the collected measurements, the evolution of the SO2concentration in the headspace gas within the flow cuvette 52 over time can be deducted within the signal processor 58 directly from the measurement of the amount of UV radiation absorbed by the headspace gas. According to an embodiment of the method of the present invention both the free and bound SO2concentrations in the sample can then be deducted from a deconvolution of the time curve of the SO2concentration in the flow cuvette 52. The total SO2can also be calculated since the total is a sum of free and bound. The free SO2content in the sample is correlated to the fast release (height of a temporal SO2evolution curve constructed from the collectedmeasurements) of S02concentration in the cuvette 52. The bound S02is correlated to the rate of release (slope of the constructed temporal SO2evolution curve) of the SO2after the free SO2has been liberated.

[0028] This deduction may be improved through the use of multivariate mathematical techniques, such as PLS, in the deconvolution of the time curve. Calibration models linking the time dependency of the evolution of the SO2concentration may be constructed by monitoring this evolution in samples having known concentrations and then applied to the deconvolution of the curves from samples with unknown concentrations using known chemometric techniques.

[0029] In some embodiments of the system 2 the gas-liquid separator 24 may comprise a gas permeable membrane located in the gas flow system 16 to act as a common boundary of the extraction conduit portion 16a and the delivery conduit portion 16b. The return conduit 22a of the liquid flow system 22 is then in configured in fluid communication with the extraction conduit portion 16a at a location upstream (in the direction of flow of headspace gas) of the gas permeable membrane and downstream of the cooler 20, preferably proximal the gas permeable membrane. The gas permeable membrane is constructed of a material which allows passage of gas but prevents passage of the condensate 40. Such a material may be, by way of non-limiting examples, thin silicone or polydimethylsiloxane (PDMS) membrane products, polyamide or cellulose acetate membrane products, or silica, zeolites or metal-organic frameworks. The condensate 40 is transported in a portion of the headspace gas, via the return conduit 22a of the liquid flow system 22, to the liquid (mainly sample 6 and hydrolysis agent 8) which is contained in the reaction vessel 10.

Claims

AMENDED CLAIMS received by the International Bureau on 06 June 2024 (06.06.2024)

1. A system (2) for determining one or more of free, bound and total SO2in a potable liquid product, the system (2) comprising a reaction system (4) having a reaction vessel (10) for containing a sample (6) of the potable liquid product and a hydrolysis reagent (8), the reaction vessel (10) being configured with an internal volume sufficient to provide a headspace (12) above the sample (6) and the hydrolysis reagent (8) into which a gas can pass as a headspace gas; a measurement system (18) for monitoring SO2;a heater unit (14) thermally coupled to the reaction vessel (10) to supply thermal radiation thereto; a gas flow system (16) configured to transfer the headspace gas from the headspace (12) to the measurement system (18); and a cooler (20) adapted to cool the headspace gas in the gas flow system (16) to generate a condensate (40); wherein the system (2) further comprises a liquid flow system (22) in fluid communication with the gas flow system (16) and with the reaction system (4), the liquid flow system (22) adapted to transfer the condensate (40) from the gas flow system (16) to the reaction vessel (10); and a gas-liquid separator (24) in fluid communication with the gas flow system (16) and with the liquid flow system (22) and configured to separate the condensate (40) from the headspace gas before delivery of 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) as claimed in Claim 1 wherein the gas-liquid separator(24) comprises a column (26) having an internal volume (28) and provided with an inlet (30) in fluid communication with the gas flow system (16) and the internal volume (28); with a first outlet (32) in fluid communication with the internal volume (28) and the gas flow system (16) and with a second outlet (34) in fluid communication with the internal volume (28) and the liquid flow system (22), the second outlet (34) positioned to communicate with the internal volume (28) at a location which, in a direction parallel to the direction of action of gravity, is below both locations at which the inlet (30) and the first outlet (32) communicate with the internal volume (28).

3. The system (2) as claimed in Claim 2 wherein a splash-plate (36) is located within the internal volume (28) at a location before the first outlet (32) to inhibit movement of liquid from the internal volume (28) through the first outlet (32).

4. The system (2) as claimed in Claim 2 wherein the inlet (30) is orientated at an angle less than 90 degrees to a side-wall (38) of theAMENDED SHEET (ARTICLE 19)column (26) which side-wall (38) delimits the internal volume (28).

5. The system (2) as claimed in Claim 1 wherein the cooler (20) is located in thermal contact with the gas-liquid separator (24).

6. The system (2) as claimed in Claim 1 wherein the gas flow system (16) is further configured to re-circulate headspace gas from the measurement system (18) via the cooler (20) avoiding the headspace (12).

7. The system (2) as claimed in Claim 1 wherein the gas-liquid separator(24) is configured to transfer the separated condensate (40) to the liquid flow system (22) by transport in a portion of the headspace gas.

8. The system (2) as claimed in Claim 1 wherein the measurement system(18) comprises a complementary ultraviolet radiation supply (54) and detection element (56) arranged to monitor an amount of ultraviolet radiation supplied by the supply (54) that is absorbed by the headspace gas transferred to the measurement system (18) as the monitor of SO2.AMENDED SHEET (ARTICLE 19)

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