Apparatus and method for measuring carbon dioxide

Abstract

This invention relates to a method for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid. The method includes a step of providing a fluid-tight container accommodating a liquid sample, the liquid sample having carbon dioxide dissolved therein. The method also involves agitating the liquid sample whilst allowing the volume of the container to change from a first volume towards a second volume associated with an equilibrium state. In the equilibrium state, a headspace pressure inside the container equals the pressure of the container surroundings, and the carbon dioxide dissolved in the liquid sample exists in chemical equilibrium with the carbon dioxide in a headspace volume. The method further includes a step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid based on the second volume. The present invention also relates to measuring apparatuses and methods for manufacturing measuring apparatuses.

Description

[0001] APPARATUS AND METHOD FOR MEASURING CARBON DIOXIDE

[0002] Field of the invention

[0003] The present invention relates to methods for measuring carbon dioxide, particularly carbon dioxide dissolved in a liquid, and apparatuses for measuring carbon dioxide.

[0004] Background to the invention

[0005] Measuring the level of carbon dioxide gas dissolved in a liquid is of particular relevance in the carbonated beverages industry. For example, as part of quality control checks it is important to be able to check the carbonation levels of beer (e.g., by operators in a brewery). In particular, it is important to be able to provide accurate measurements quickly and without the need for skilled operators.

[0006] It is known in the prior art to measure carbonation using the Heard method (Heard, B. T. "A rapid manometric / volumetric method for the determination of dissolved carbon dioxide content of beer in tanks." Journal of the Institute of Brewing 79.5 (1973): 371- 376) and the ASBC Beer 13C method (American Society of Brewing Chemists. Methods of Analysis, 14th ed. Beer-13 Dissolved Carbon Dioxide. The Society, St. Paul, MN, 2011). Generally, both of these methods involve drawing a volume of carbonated liquid into syringe, before closing the syringe (to provide a sealed measurement chamber) and partially withdrawing the syringe plunger so that the pressure inside the syringe is less than the pressure of the surroundings. The user holds the plunger at this expanded position whilst shaking the syringe. For both methods, the determination of the carbonation level is based on Henry’s Law which states that, for a given temperature, the partial pressure of a gas in equilibrium with a liquid is proportional to the amount of gas dissolved in that liquid. For the Heard method and the ASBC Beer 13C method, Henry’s Law applies after a chemical equilibrium is achieved by agitation of the fluid whilst the plunger is held at the expanded position.

[0007] It is in this context that the present inventions have been devised.

[0008] Summary of the invention

[0009] According to an aspect of the invention, there is provided a method for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid, the method comprising: providing a fluid-tight container accommodating a liquid sample, the liquid sample having carbon dioxide dissolved therein; agitating the liquid sample whilst allowing the volume of the container to change from a first volume towards a second volume associated with an equilibrium state; wherein, in the equilibrium state, a headspace pressure inside the container equals the pressure of the container surroundings, and the carbon dioxide dissolved in the liquid sample exists in chemical equilibrium with the carbon dioxide in a headspace volume; and determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid based on the second volume.

[0010] By determining an indication of the quantity or concentration of the carbon dioxide dissolved in a liquid using the second volume defined hereinbefore, it is possible to conveniently obtain accurate measurements. Other methods in the prior art rely on measuring multiple container volumes, including one where the container volume is held by the user so that the pressure inside the container is less than the surrounding pressure during agitation. The present inventor has realised that by allowing the container volume to vary towards an equilibrium state where the system is at mechanical equilibrium (i.e., the pressure inside equals the pressure outside) and chemical equilibrium (i.e., the rate of carbon dioxide dissolving into the liquid equals the rate of carbon dioxide being released from the liquid) that the volume associated with that equilibrium state can be used to provide accurate carbon dioxide measurements more conveniently compared to the other prior art methods. In particular, the inventor has realised that by applying gas laws (e.g., the Ideal Gas Law’s and Henry’s Laws) to this system, that a measured second volume as defined above can be used to determine the concentration / quantity of carbon-dioxide dissolved in a liquid. Compared to the prior art methods, fewer measurements of the container volume are required, thereby providing a reduction in measurement uncertainty. Further, it is not necessary to hold the container at a fixed volume during the agitation step, thereby the method is simpler (more convenient) to carry out.

[0011] The container is fluid-tight such that the container is capable of substantially preventing fluid (e.g., gas or liquid) leaving or entering the container. That is, the container is configured such that it can be substantially sealed. Whilst the container is in a fluid- tight state / sealed the volume of the container may change but the molar quantity of the gas (i.e., the gas dissolved in the liquid and the gas existing in the headspace) is substantially constant. Typically, the container will have at least one fluid inlet that can be opened and closed (e.g., via a valve). For the avoidance of doubt, it will be understood that the container will be considered fluid-tight where any very small rate of fluid leaving or entering the container is sufficiently small so as to have only a negligible effect on the accuracy of the measurements.

[0012] The indication of the quantity or concentration of the carbon dioxide dissolved in a liquid may be the indication of the quantity of the carbon dioxide dissolved in a liquid. The indication of the quantity or concentration of the carbon dioxide dissolved in a liquid may be the indication of the concentration of the carbon dioxide dissolved in a liquid.

[0013] The container may be defined at least in part by a first wall that is movable. For example, the wall may be moveable from a first position corresponding to the first container volume to a second position corresponding to the second container volume. In some embodiments, the wall may be defined by a piston surface. The container may be defined in part by a syringe barrel and a plunger (i.e., piston) within the barrel. Parts of the apparatus (e.g., the movable parts) may comprise a low friction material (such as a polyurethane coating) so that less differential pressure between the inside of the container and the external environment is required to vary the container volume. The liquid sample is agitated whilst the volume of the container is allowed to change. The agitating step may comprise mechanical agitation, such as shaking the container or stirring the liquid sample, and / or electrical agitation such as electrolysis of the liquid sample. In other words, it will be understood that agitating is substantially any process by which the carbon dioxide dissolved within the liquid sample is encouraged to reach the equilibrium state more quickly than if the container were not to be subject to the agitation.

[0014] The agitating step may cause and / or promote the release of the carbon dioxide from the liquid and the volume of the container to change towards the second volume. Typically, the agitation step will increase the rate of carbon dioxide being released from the liquid and the rate of the carbon dioxide being dissolved into the liquid from the headspace, so that the volume of the container changes towards the second volume associated with the equilibrium state more quickly.

[0015] It will be understood that the headspace pressure corresponds to the pressure of the gas within the container headspace.

[0016] In the equilibrium state, the headspace pressure inside the container equals the pressure of the container surroundings (i.e., any difference between the two is not sufficiently large to cause the volume to change further).

[0017] It will be understood that, at least after gas / vapor is released from the liquid, the container volume will comprise a liquid volume of the liquid sample and a headspace volume (i.e., the volume of vapor and / or gas above the liquid sample). In the equilibrium state, the headspace pressure (i.e., the pressure of the gas and / or vapour in the headspace volume) inside the container equals the pressure of the container surroundings.

[0018] It will be understood that the liquid sample may be a portion of the liquid of which the dissolved carbon dioxide is being measured. For example, the liquid sample may be a sample of liquid (e.g., beer) taken from a pressurised container.

[0019] Determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid based on the second volume may involve determining an indication of the concentration and / or quantity of carbon dioxide dissolved in the liquid sample.

[0020] The indication of the quantity of carbon dioxide dissolved in the liquid may be represented in terms of a molar quantity. Alternatively, the quantity of carbon dioxide dissolved in the liquid may be expressed in units of mass or volume. The indication of the concentration of carbon dioxide dissolved in the liquid may be expressed in units involving a ratio. For example, the concentration of carbon dioxide dissolved in the liquid may be indicated in terms of a ratio of volumes, a ratio of masses, or a mass to volume ratio. The indication of the concentration / quantity may be an indication that the concentration / quantity is within a specific range or above (or below) a predetermined value, rather than a precise value. The indication of the concentration / quantity may be an estimate.

[0021] In some embodiments, the step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid is also based on the volume of the liquid sample. In addition, it may be that the step of determining the quantity or concentration of the carbon dioxide dissolved in the liquid is based on the ratio of the difference between the second volume and the volume of the liquid sample to the volume of the liquid sample. It may be that an anti-foaming substance is added to the liquid sample before the volume of the liquid sample is determined to improve the accuracy of the liquid sample volume measurement.

[0022] Using the Ideal Gas Laws and Henry’s Gas Laws, the inventor has realised that the quantity or concentration of the carbon dioxide dissolved in the liquid may be determined based on the volume of the liquid sample and the second volume of the container. In particular, the inventor has realised that the concentration / quantity of carbon dioxide is determinable based on the ratio of the difference between the second volume and the volume of the liquid sample to the volume of the liquid sample.

[0023] The liquid volume may be the volume of the liquid at atmospheric pressure. In some embodiments, the liquid volume may be the volume of the liquid before the agitation step.

[0024] If the test is carried out at standard temperature and pressure, the concentration c of the dissolved carbon dioxide may be determined using the equation: where a is the Bunsen Coefficient for carbon dioxide in the liquid being tested, V2is the second volume, VLis the volume of the liquid sample, and c is expressed in units of the ratio of gas to solvent volume (i.e., gas volumes of solvent). The Bunsen Coefficient is defined as the volume of gas reduced to 273.15K and 1 atmosphere pressure which is absorbed by unit volume of solvent (at the temperature of measurement) under a partial pressure of 1 atmosphere. The Bunsen Coefficient varies with temperature and the product being tested. In some embodiments, the value used for the Bunsen Coefficient will be for a typical beer according to ASBC Beer-13.

[0025] In some embodiments, if the apparatus is to be used at a temperature other than standard pressure or temperature, the calculation for the concentration of the dissolved carbon dioxide may be modified to account for the effect of the difference in the temperature and pressure compared to standard temperature and pressure.

[0026] It may be that the step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid is based on no further volumes other than the volume of the sample liquid and the second volume.

[0027] By using the second volume the inventor has realised that it is possible to determine an indication of the concentration or quantity of carbon dioxide using only two volumetric measurements, thereby limiting the measurement uncertainty associated with volume measurements.

[0028] It may be that the step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid is further based on the partial gas pressure of a second gas present in the headspace of the container. The second gas may be water vapour.

[0029] By basing the carbon dioxide determination based on the partial gas pressure of a second gas present in the headspace, the accuracy of the determined indication is further improved. It may be that the step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid is further based on a pressure measurement and / or a temperature measurement. The temperature measurement may be the temperature of the liquid.

[0030] The inventor has realised that a particularly rapid determination of an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid can be achieved even based on an estimated temperature and / or an estimated pressure. The accuracy of the determination may be further improved by using measured values for the temperature and pressure.

[0031] It may be that the liquid sample has an initial concentration and / or an initial quantity of the carbon dioxide dissolved therein, wherein determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid comprises determining the initial concentration or initial quantity, respectively.

[0032] It may be that the step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid comprises obtaining a first value for the quantity or concentration of the carbon dioxide dissolved in the liquid, and obtaining an adjusted value for the quantity or concentration of the carbon dioxide dissolved in the liquid based on a measured temperature and / or a measured pressure.

[0033] By obtaining an adjusted value for the quantity or concentration of carbon dioxide based on measured a measured temperature and / or pressure the accuracy of the determination is improved.

[0034] It will be understood that any steps of any of the above-mentioned method may be automated. In other words, it may be that a step can be performed without any manual intervention. It may be that a next step can be started after a preceding step without any manual intervention.

[0035] According to another aspect of the invention, there is provided a method of manufacturing a measuring apparatus for carrying out the method according to any preceding claim, comprising: providing the container for accommodating the liquid sample; and providing a carbon dioxide indicator for indicating the concentration or quantity of the carbon dioxide dissolved in the liquid based on the second volume and / or providing a sensor for sensing a container volume and a processor configured to receive an output from the sensor as an input.

[0036] In some embodiments, the method may involve a first calibration procedure to relate the second volume to the concentration or quantity of dissolved carbon dioxide. In embodiments where the container is defined in part by a movable wall (e.g., a piston), it may be that the first calibration procedure involves relating the position of the movable wall to the concentration or quantity of dissolved carbon dioxide. The method may involve marking a point on a surface of the container based on the first calibration procedure. The first calibration procedure may take into account the effect of the weight of components of the measuring apparatus on the position of the moveable wall.

[0037] In some embodiments, the method may involve a second calibration procedure to relate the position of the fluid interface of the liquid sample to the liquid sample volume. In embodiments wherein the container comprises valves / inlets, the second calibration procedure may take into account liquid contained in the valves and / or inlets. The method may involve marking a point on a surface of the container based on the second calibration procedure.

[0038] According to another aspect of the invention, there is provided a measuring apparatus for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid comprising: a container for accommodating a liquid sample, the container having a variable volume; a first carbon dioxide indicator; wherein, in use, the container defines a closed system which can progress towards satisfying a first equilibrium condition and a second equilibrium condition; wherein the first equilibrium condition corresponds to a headspace pressure inside the container equalling the pressure of the container surroundings, and the second equilibrium condition corresponds to the carbon dioxide dissolved in the liquid sample existing in chemical equilibrium with the carbon dioxide in a headspace volume; wherein the volume of the container can change towards a second volume associated with at least the first equilibrium condition; and wherein the first carbon dioxide indicator is configured to provide an indication of the quantity or concentration of carbon dioxide dissolved in the liquid, following the progression of the closed system towards satisfying the first equilibrium condition and the second equilibrium condition, based on the second volume.

[0039] By providing a measuring apparatus having a first carbon dioxide indicator for providing an indication of the quantity or concentration of carbon dioxide dissolved in the liquid based on the second volume it is possible to achieve accurate carbon dioxide measurements in a convenient way.

[0040] The container defines a closed system such that the container has a closed configuration wherein fluid (e.g., gas or liquid) is prevented from leaving or entering the container, thereby allowing progression towards mechanical equilibrium and chemical equilibrium (i.e., the first and second equilibrium conditions being satisfied). That is, the container is configured such that it can define a substantially closed system (e.g., a substantially sealed configuration). Typically, the container will have at least one fluid inlet that can be opened and closed (e.g., via a valve).

[0041] It may be that, in use, the volume of the container can change towards the second volume whilst the liquid sample is agitated. It may be that the second volume is associated with the first equilibrium condition and the second equilibrium condition.

[0042] The carbon dioxide indicator may comprise a digital display. The carbon dioxide indication may comprise markings on a surface associated with the container (e.g., a surface of the container). The carbon dioxide indication may comprise a graduated scale - typically having numerical labels associated with at least a subset of the graduations to indicate corresponding dissolved carbon dioxide quantities and / or concentrations.

[0043] It may be that the first carbon dioxide indicator is configured to provide an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid based on the volume of the liquid sample. The first carbon dioxide indicator may be configured to provide an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid based on the ratio of the difference between the second volume and the volume of the sample liquid to the volume of the sample liquid. It may be that the first carbon dioxide indicator visually indicates the quantity or concentration of the carbon dioxide dissolved in the liquid, and the measuring apparatus further comprises a first volume indicator for visually indicating a liquid sample volume. In addition, it may be that the first volume indicator is associated with the first carbon dioxide indicator such that, in use, the concentration or quantity of carbon dioxide is determinable using the first carbon dioxide indicator if the liquid sample volume is determinable using the first volume indicator.

[0044] In some embodiments the first volume indicator may be a marking (e.g., a measurement line) associated with a surface of the container. The first volume indicator may provide an indication of the quantity of liquid that should be received into the container for the carbon dioxide determination to be made, thereby improving ease of operation of the apparatus since the user can quickly identify whether the volume of the sample liquid is appropriate.

[0045] It may be that the first volume indicator is one of a plurality of volume indicators and the first carbon dioxide indicator is one of a plurality of carbon dioxide indicators. In addition, it may be that each carbon dioxide indicator is associated with a respective volume indicator so that, in use, the concentration or quantity of carbon dioxide is determinable using one of the carbon dioxide indicators if the liquid volume is determinable using the associated volume indicator.

[0046] By providing a number of associated carbon dioxide indicators and volume indicators it is possible to provide an indication of the quantity / concentration of carbon dioxide over a wider range of sample volumes. Accordingly, the user has more flexibility over the volume of the sample liquid to use when carrying out measurements.

[0047] In some embodiments, the container comprises a surface in contact with the liquid sample associated with the or each of the carbon dioxide indicators and volume indicators, wherein, in use, the liquid sample volume is determinable based on the position of a liquid interface relative to at least one of the volume indicators.

[0048] The liquid interface is the interface between the liquid and a further substance. The further substance may have a different density than the fluid. The further substance may be a lower density substance such as gasses within the container headspace (e.g., carbon dioxide). In embodiments where the liquid interface is defined by a fluid meniscus, determining the liquid sample is based on the position of the peak or trough of the meniscus. In these embodiments, a line normal to the plane parallel to the liquid interface is a line normal to a plane tangential to the peak or trough of the meniscus.

[0049] In some embodiments where the container is defined in part by a movable wall (e.g., a piston) the liquid interface is the interface between the liquid and the moveable wall - for example in some embodiments where the container is defined by a syringe barrel and a piston within the barrel which moves to vary the volume of the container.

[0050] In some embodiments the surface is the inner surface of a wall of the container (e.g., the inner surface of a syringe body).

[0051] The carbon dioxide indicators and volume indicators may be provided on the surface of the container. A body may define the surface, the body having the carbon dioxide indicators and volume indicators, and the carbon dioxide indicators and volume indicators being visible through the surface. The carbon dioxide indicators and volume indicators may be etched or printed, for example the carbon dioxide indicators and volume indicators may be printed or etched on the surface. The carbon dioxide indicators and volume indicators may be provided on a different surface (such as a film) which is then provided with (such as attached to) the surface. Thus, the carbon dioxide indicators and volume indicators are associated with the surface whether they are provided directly on the surface, on a further surface of the body defining the surface in contact with the fluid, or on a different body attached or otherwise provided with the surface. Importantly, the carbon dioxide indicators and volume indicators are visible along with the intersection between the liquid interface and the surface in contact with the liquid.

[0052] It may be that the volume indicators are arranged along a reference line. In addition, it may be that each carbon dioxide indicator is arranged above or below the respective volume indicator along a first direction, wherein the first direction is normal to a plane parallel to the liquid interface, and wherein the reference line is defined by the intersection between the plane parallel to the liquid interface and the surface. The reference line may be defined by the intersection between the plane of the liquid interface (e.g., the plane intersecting with the peak or trough of the meniscus of the liquid interface and parallel to the liquid interface) and the surface. The reference line is typically perpendicular to a longitudinal axis of the container.

[0053] Typically, the first reference line is not marked on the surface (i.e. , it is a notional line), defined to aid with description of the inventive subject-matter included herein. Typically, the first direction is aligned with the direction of gravity (i.e. vertical) and the plane parallel to the interface is transverse to the first direction (i.e. horizontal).

[0054] It may be that the measuring apparatus further comprises a volume indicator for visually indicating a liquid sample volume, wherein the container comprises a surface associated with the volume indicator. In use, the liquid sample volume may be determinable based on the position of a liquid interface relative to the volume indicator.

[0055] In some embodiments, the or each volume indicator comprises a measurement line marking at least a first point and a second point; wherein, in use, the liquid sample volume is determinable based on the position of the liquid interface relative to the first point and the second point, wherein the measurement line between the first point and the second point has a gradient defined with respect to a first direction and a reference line; wherein the first direction is normal to a plane parallel to the liquid interface; wherein the reference line is defined by the intersection between the plane parallel to the liquid interface and the surface; wherein the first point and the second point are offset from one another along the first direction; wherein a first intersection point and a second intersection point are offset from one another along the reference line; wherein the first intersection point is the point closest to the first point where a first intersection plane intersects the reference line, and the second intersection point is the point closest to the second point where a second intersection plane intersects the reference line; and wherein the first intersection plane passes through the first point and is normal to a first tangent to the surface at the first point, the second intersection plane passes through the second point and is normal to a second tangent to the surface at the second point, wherein the first and second tangents are parallel to the plane parallel to the liquid interface.

[0056] By measuring the volume of the liquid sample using a measurement line defined hereinbefore, it is possible to obtain particularly precise measurements. Conventional volumetric measuring devices (e.g., conventional measuring cylinders) have graduation marks defined along a measurement line normal to a plane parallel to the liquid interface (i.e. typically vertically). The present inventor has realised that the same range of liquid volumes can be expanded over a measurement line having a longer length compared to the measurement line of a conventional measuring container (assuming that the containers being compared have the same shape and size) by orienting the measurement line at an angle away from the vertical. This allows for a greater number of measurement indicia to be provided on the line for a given vertical distance of the line, without having the indicia spaced so closely as to make it difficult or even impossible to read the measurement accurately, compared to a vertically- oriented measurement line. Thereby, it is possible to distinguish more reliably between similar fluid levels.

[0057] In use, the liquid volume can be determined based on the position of the liquid level relative to points along the measurement line, each point indicative of a pre-determined volume. The surface typically extends over the liquid interface. The liquid interface is typically between the first point and the second point in the first direction.

[0058] The measurement line may be provided on the surface of the container. A body may define the surface, the body having the measurement line and the measurement line being visible through the surface. The measurement line may be etched or printed, for example the measurement line may be printed or etched on the surface. The measurement line may be provided on a different surface (such as a film) which is then attached to the surface. Thus, the measurement line is associated with the surface whether it is provided directly on the surface, on a further surface of the body defining the surface in contact with the fluid, or on a different body attached or otherwise provided with the surface. Importantly, the measurement line is visible along with the intersection between the fluid interface and the surface in contact with the liquid. The measurement line may comprise a continuous line extending between at least the first and second point. In other words, the measurement line may extend continuously between the first point and the second point.

[0059] The first point and / or the second point may be a point along the measurement line. In other words, the first point and / or the second point may each be spaced from an end of the measurement line. In other embodiments, the first point and / or the second point may each be an end of the measurement line. For example, the first point may be one end of a line defining the measurement line and the second point may be the other end of the line defining the measurement line. In some embodiments, the first point and / or the second point may be associated with a marker (e.g., a marker to visually indicate a predetermined volume). Each marker may be a numerical label, for example.

[0060] The liquid interface may be positioned between the first point and the second point - i.e. , the liquid interface may appear to intersect the measurement line between the first point and the second point. Thus, the relative distance between the intersection of the liquid interface and the first point, and between the intersection of the fluid interface and the second point can be used to allow a liquid volume, between the volume associated with the first point and the volume associated with the second point, to be determined particularly precisely.

[0061] The first point and the second point are offset from one another as defined hereinbefore. The gradient of the measurement line is defined using the relative separation between the first point and the second point along the first reference line and the first direction. The first direction together with the reference line effectively provide a co-ordinate system which can be used to define the gradient of a measurement line associated with the surface in contact with the liquid, independent of the surface topography. Effectively, the co-ordinate system allows the measurement line to be mapped to a manifold which is associated with the surface.

[0062] It may be that the measuring apparatus further comprises an additional surface that is moveably attached to the surface, wherein the additional surface has the or each volume indicator provided thereon, and optionally the or each carbon dioxide indicator provided thereon. By providing the concentration indicators and / or volume indicators on an additional surface that is moveably attached to the surface in contact with the liquid it is easier for the user to view the measuring apparatus along an appropriate viewing direction (i.e., a line of sight along which the relevant indicator is visible and / or more accurate readings can be taken), thereby facilitating convenient and accurate measurements. For example, when the volumetric indicator comprises a measurement line, particularly accurate readings can be taken along a line of sight coincident with a viewing plane perpendicular to the liquid interface and coincident with the normal to the surface at the relevant point along the measurement line.

[0063] For example, a user that is positioned so that they cannot view the device along an appropriate line of sight the user can move the additional surface rather than change their own position or re-position the device as a whole. In some embodiments, the additional surface may be rotatably mounted relative to the surface in contact with the liquid. The additional surface may be part of a sleeve arranged to rotate around the container accommodating the liquid sample. For example, the container and the sleeve may both be cylindrical and arranged concentrically. In some embodiments, the additional surface may be slidable relative to the surface in contact with the fluid.

[0064] It may be that the measuring apparatus further comprises a first stopping mechanism for stopping the container volume from increasing relative to first predetermined volume. Alternatively, or additionally, it may be that the measuring apparatus further comprises a second stopping mechanism for stopping the container volume from decreasing relative to a second predetermined volume.

[0065] By providing a stopping mechanism for stopping the container volume from increasing relative to a first predetermined volume the container can receive a liquid sample having a predetermined volume more conveniently, thereby making the apparatus easier to operate.

[0066] In some embodiments, in addition to the first stopping mechanism, the apparatus further comprises an inlet for receiving the liquid sample into the container and an outlet for allowing liquid to leave the container as liquid is received into the container. Accordingly, it is possible to receive a sample of liquid into the container under pressure (to avoid dissolved carbon dioxide being released from the liquid as it is received into the container). By providing a stopping mechanism for stopping the container volume from decreasing relative to a second predetermined volume the inside of the container can be held at negative pressure, thereby allowing liquids with a relatively low level of dissolved carbon dioxide to be measured more easily.

[0067] It may be that the first stopping mechanism is configured to fix the container volume at the first predetermined volume. It may be that the second stopping mechanism is configured to fix the container volume at the second predetermined volume.

[0068] It will be understood that each or the stopping mechanism is a releasable stopping mechanism (i.e., any stopping mechanism can be temporarily disabled so that the volume of the container is allowed to increase and decrease).

[0069] The or each stopping mechanism may be a mechanical stop. For example, the or each stopping mechanism may comprise a button operated resiliently biased (e.g., using a spring) pin. The or each stopping mechanism may be an electro-mechanical stop - e.g., having a solenoid controlling the movement of a pin.

[0070] It may be that the measuring apparatus further comprises an agitator for agitating the liquid sample. The agitator may be a mechanical agitator (e.g., a stirrer). The agitator may be an electrical agitator (e.g., electrodes for electrolysis of the liquid sample). In other words, it will be understood that an agitator is substantially any means for encouraging the carbon dissolved within the liquid sample to reach the equilibrium state more quickly than if the container were not to be subject to the agitation.

[0071] By providing an agitator the liquid sample can be agitated more conveniently and with a greater degree of control.

[0072] It may be that the measuring apparatus further comprises: a processor configured to determine an indication of the quantity or concentration of carbon dioxide dissolved in the liquid, and / or optionally a sensor for sensing a container volume.

[0073] The processor may be configured to perform calculations and / or use look-up tables to determine an indication of the quantity or concentration of carbon dioxide dissolved in the liquid. The apparatus may further comprise computer-readable memory (e.g. non transitory computer-readable memory) storing instructions which, when executed by the processor, cause the processor to perform as described herein. The processor may be one or more processors.

[0074] It will be understood that the sensor for sensing a container volume may sense a parameter relating to the container volume rather than the directly sensing the volume. For example, in some embodiments where the container is defined by a piston and a syringe barrel, the volume sensor may be for sensing the position of the piston (e.g., the displacement of the piston relative to a first piston position corresponding to a container volume of 0 ml.) In some embodiments, the volume sensor is used to sense the volume of the container (or a parameter relating to the volume) when the liquid sample is being received into the container (e.g., through a container inlet) - so that the volume of the liquid sample can be automatically determined. Additionally, or alternatively, the volume sensor is used to sense the second volume (or a parameter related to the second volume).

[0075] The sensor for sensing the container volume may use capacitive sensing (e.g., the sensor may be a capacitive touch slider).

[0076] In some embodiments, the measuring apparatus comprises a user interface configured to receive an input, wherein the processor is configured to use the input received by the user interface and determine the concentration based on the input. In some embodiments, the input corresponds to the liquid volume. It may be that the input corresponds to the type of liquid (e.g., beer).

[0077] In some embodiments, the measuring apparatus comprises data storage for recording sensed measurements and / or determinations of the concentration / quantity of carbon dioxide (or any intermediate determinations). In some embodiments, the measuring apparatus comprises an output (e.g., a port or wireless transmitter) for outputting the stored data.

[0078] According to another aspect of the invention, there is provided a measuring apparatus for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid comprising: a processor; a container for accommodating a liquid sample, the container having a variable volume; a sensor for sensing a container volume; and wherein the processor is configured to determine an indication of the quantity or concentration of carbon dioxide dissolved in the liquid based on the container volume measured by the sensor.

[0079] It may be that the measuring apparatus further comprises: a temperature sensor configured to sense the temperature of the sample; and / or a pressure sensor configured to sense the atmospheric pressure, and / or wherein the measurement apparatus is configured to accept a pre-determined volume of liquid into the container.

[0080] By accepting a pre-determined volume of liquid into the container, one less volume measurement is required, thereby measurements can be performed more conveniently. Incorporating temperature and / or pressure sensor provides more information for providing more accurate determinations of the concentration or quantity of carbon dioxide. In some embodiments, the pressure and temperature measurements may provided as outputs from the measuring apparatus (e.g., visually displayed). In use, the pressure and temperature measurements may be used to improve the accuracy of the of the carbon dioxide determination.

[0081] In some embodiments involving a processor, the processor is configured to accept the sensed temperature and / or pressure as input(s) and use the sensed temperature and / or pressure measurements in the determination of the indication of the quantity or concentration of dissolved carbon dioxide in the liquid, thereby providing a more accurate measurement of the dissolved carbon dioxide.

[0082] According to another aspect of the invention there is provided a method for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid comprising: receiving input data indicative of a second volume of a fluid-tight container, accommodating a liquid sample, the liquid sample having carbon dioxide dissolved therein; and determining an indication of a quantity or concentration of carbon dioxide dissolved in the liquid based on the second volume; wherein the second volume is the volume associated with an equilibrium state, the volume of the container having been allowed to change towards the second volume during agitation of the liquid sample; and wherein, in the equilibrium state, a headspace pressure inside the container equals the pressure of the container surroundings, and the carbon dioxide dissolved in the liquid exists in chemical equilibrium with the carbon dioxide in a headspace volume.

[0083] According to another aspect of the invention, there is a processor configured to carry out the method mentioned immediately above.

[0084] According to another aspect of the invention, there is provided a computer program product comprising instructions which, when the program is executed on a computer processing means, causes the computer processing means to carry out any of the methods for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid discussed herein. The computer processing means may comprise the processor (or one or more processors) and the computer-readable memory each described hereinbefore.

[0085] According to other aspects of the invention, any of the above-mentioned methods or apparatuses may be for determining an indication of a quantity or concentration of a gas dissolved in a liquid. That is, the concentration / quantity of gases other than carbon dioxide may be determined.

[0086] For example, according to one aspect of the invention, there exists a method for determining an indication of a quantity or concentration of a gas dissolved in a liquid, the method comprising: providing a fluid-tight container accommodating a liquid sample, the liquid sample having the gas dissolved therein; agitating the liquid sample whilst allowing the volume of the container to change from a first volume towards a second volume associated with an equilibrium state; wherein, in the equilibrium state, a headspace pressure inside the container equals the pressure of the container surroundings, and the gas dissolved in the liquid sample exists in chemical equilibrium with the gas in a headspace volume; and determining an indication of the quantity or concentration of gas dissolved in the liquid based on the second volume.

[0087] Description of the Drawings

[0088] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0089] Figure 1-2 are schematic representations of apparatuses for determining a concentration or quantity of dissolved carbon dioxide in a liquid, according to embodiments of the invention;

[0090] Figure 3 is a schematic representation of a portion of an apparatus according to an embodiment of the invention;

[0091] Figures 4-7 are schematic representation of apparatuses according to embodiments of the invention; and

[0092] Figure 8 is a flow chart, illustrating a method of determining the carbonation of a liquid according to an embodiment of the invention.

[0093] Detailed Description of an Example Embodiment

[0094] Figure 1 and Figure 2 are schematic representations of measuring apparatuses 100 for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid. The measuring apparatuses each include a container 101 for accommodating a liquid sample. The container is defined by a syringe barrel 103 and a plunger 105. The plunger 105 is moveable relative to the syringe barrel 103, thereby allowing the container volume to vary. The measuring apparatus also includes a volume indicator 107 and a carbon dioxide indicator 109.

[0095] In use, fluid can be introduced into the container 101 through the inlet 113 via the valve 111 until the fluid interface reaches the level marked by the volume indicator 107. The valve 111 , can then be closed to seal the container 101. It will be understood that the valve is configured to be selectively opened and closed. The plunger can move relative to the syringe barrel 103 towards a second volume associated with an equilibrium state during agitation of the liquid (e.g., shaking of the syringe). The carbon dioxide indicator provides an indication of the quantity of the carbon dioxide dissolved in the liquid based on the second volume (i.e., based on the position of the plunger 104 relative to the syringe barrel 103) and liquid sample volume marked by the volume indicator 107.

[0096] In the embodiment shown in Figure 1 , the volume indicator comprises a line corresponding to a predetermined liquid sample level. In use, fora liquid sample having a volume corresponding to greater than or equal to the liquid level set by the volume indicator 107, a plunger position below the carbon dioxide indicator 109 indicates the carbonation of the liquid is below a predetermined level corresponding to the carbon dioxide indicator 109. Likewise, for a liquid sample having a volume corresponding to less than or equal to the liquid level set by the volume indicator 107, a plunger position above the carbon dioxide indicator 109 indicates the carbonation of the liquid is above a predetermined level corresponding to the carbon dioxide indicator 109.

[0097] The embodiment shown in Figure 2 is substantially similar in form and operation to the embodiment shown in Figure 1 apart from the hereinafter noted differences. The volume indicator 107 comprises a measurement line marking at least a first point 117 and a second point 119. In use, the container 101 accommodates a fluid 110. The fluid 110 within the container 101 defines a fluid interface 115. The liquid sample volume is determinable based on the position of the fluid interface 115 relative to the first point 117 and the second point 119. In this embodiment, the carbon dioxide indicator comprises a graduated scale - where the graduations mark a range of carbon dioxide quantities based on a liquid sample having a volume within the range covered by the volume indicator. In use, for a liquid sample having a volume within the range covered by the volume indicator (e.g., a liquid interface 15 which appears to intersect the measurement line between (or at) the first point 117 and the second point 119) the quantity of carbon dioxide dissolved in the liquid sample can be determined based on the position of the plunger 105 relative to the graduated scale of the carbon dioxide indicator 109.

[0098] Figure 3 shows the volume indicator 107 of Figure 2. Figure 3 shows a first direction 123 and a reference line 121 . The first direction 123 is normal to a plane parallel to the fluid interface 115. The reference line 121 is defined by the intersection between a plane parallel to the fluid interface 115 and the surface 102 of the syringe barrel 103. The measurement line between the first point 117 and the second point 119 has a gradient defined with respect to the first direction 123 and the reference line 121. Figure 4 is a schematic of a measuring apparatus 200 for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid. The measuring apparatus includes a container 201 defined by a syringe barrel 203 and a plunger 205, where the plunger 205 is moveable relative to the syringe barrel 203 to allow the container volume to vary.

[0099] The measuring apparatus includes a plurality of volume indicators 207a-207e and a plurality of carbon dioxide indicators 209a-209e. Each volume indicator 207a-207e is associated with a corresponding carbon dioxide indicator 209a-209e. That is, in use, if the liquid volume of the sample is within the range of volumes represented by volume indicator 207a then the corresponding carbon dioxide indicator 207a can be used to determine the quantity of carbon dioxide dissolved in the liquid. The carbon dioxide indicators 209a-209e are arranged around the syringe barrel 203 so that each one is marked above the corresponding volumetric indicator. In this embodiment, the plurality of volume indicators 207a-207e are portions of a continuous measurement line. It will be understood that in other embodiments, each volume indicator 207a-207e may be a separate line parallel to the fluid interface for indicating a predetermined liquid sample volume (for example).

[0100] Although not shown in Figure 4, at least a subset of the graduations of the carbon dioxide indicators 209a-209e are marked with a numerical indication of the quantity / concentration of dissolved carbon dioxide. These numerical indications are typically calculated for a predetermined temperature (e.g., 25°C) and atmospheric pressure. In practice, a correction may be applied after an initial indication of the dissolved carbon dioxide is determined (e.g., using a table of corrections) to account for any variation between the actual temperature and predetermined temperature and / or any variation between the actual pressure and atmospheric pressure.

[0101] Figure 5 is a schematic representation of a measuring apparatus 300 having a container 301 defined by a syringe barrel 303 and a plunger 305. The measuring apparatus 300 includes an inlet 313 to the container 301 and a valve to seal the container 301. The measuring apparatus 300 also includes a volume indicator 309 and a display 327 for providing an indication of the concentration / quantity of dissolved carbon dioxide (i.e., a carbon dioxide indicator). The display 327 is attached to the container 301 via housing 325. The housing 325 contains a processor 329 and supports a user interface 330. The measuring apparatus 300 also includes a position sensor 331 for sensing the position of the plunger 305. The apparatus further includes a temperature sensor for sensing the temperature of a liquid sample within the container 301 and a pressure sensor for sensing the pressure of the container surroundings.

[0102] In use, the user can open the valve 311 and draw a volume of liquid, through the input 313, into the container 301. The container 301 is sealed by closing the valve 311. The user can then measure the volume of the liquid sample using the volume indicator 309. The volume of the liquid sample can be received as an input to the processor 329 via the user interface 330. The sample liquid in the container 301 can be agitated whilst allowing the volume of the container 301 to change (e.g., allowing the plunger 305 to move relative to the syringe barrel 303). As the pressure inside the container 301 equilibrates with the pressure of the surroundings, the plunger 305 will come to rest. The processor 329 is configured to receive the sensed position of the plunger 305 at this stable point as an input. A measured temperature of the liquid sample and pressure of the surroundings measured by the respective sensors. The processor 329 is also configured to receive the sensed temperature and pressure data as inputs.

[0103] The processor 329 is configured to determine the quantity of carbon dioxide dissolved in the liquid sample based on the measured volume of the liquid sample, plunger position when equilibrium has been reached, sensed temperature of the liquid sample, and sensed pressure of the surroundings. The determined quantity is then shown by the display 327.

[0104] Figure 6 is a schematic representation of a measuring apparatus 400. The measuring apparatus 400 shown in Figure 6 is similar to the measuring apparatus 300 shown in Figure 5 apart from the hereinafter noted differences. The measuring apparatus 400 shown in Figure 6 also has a container 401 defined by a syringe barrel 403 and a plunger 405. The measuring apparatus 400 includes an inlet 413 to the container 401 and a valve 411 to seal the container 401. The measuring apparatus 400 includes a display 427 for providing an indication of the concentration / quantity of dissolved carbon dioxide (i.e. , a carbon dioxide indicator). The display 427 is attached to the container 401 via housing 425, wherein the housing 425 contains a processor 429. The measuring apparatus 400 also includes a position sensor 431 for sensing the position of the plunger 405, a temperature sensor for sensing the temperature of a liquid sample within the container 401 and a pressure sensor for sensing the pressure of the container surroundings.

[0105] The main differences between the measuring apparatus 400 shown in Figure 6 and the measuring apparatus 300 shown in Figure 5 are that the measuring apparatus 400 includes an outlet from the container 414 and a second valve 412 and does not have a user interface 330. Instead of a user interface the position sensor is further configured to measure the position of the plunger 405 as the liquid sample is received into the container 401. In use, the plunger position will be fixed as the liquid sample is received at pressure (so that no gas evolves from the liquid before agitation). Liquid is received in through the inlet 413 via the valve 411 and allowed to flow out of the container 401 through the outlet 414 and valve 412. Once a liquid sample has been received, the valves 411 , 412 can be closed to seal the container 401. The processor 429 is configured to receive the plunger position corresponding to the position of the plunger when the liquid sample is being received.

[0106] Figure 7 is a schematic representation of a measuring apparatus 500 having a container 501 for accommodating a sample of liquid. The container 501 has a variable volume and is attached to a base 543 via a support 539. The apparatus 500 can be held using the handle 541. The measuring apparatus 500 includes an inlet 513 to the container 501 , and outlet 514 from the container, and valves 511 , 512. The measuring apparatus 500 further includes a display 527, attached to the container 501 via housing 533, for providing an indication of the concentration / quantity of dissolved carbon dioxide. The measuring apparatus 500 has a volume sensor 531 for sensing the volume of the volume of the container 501. The volume sensor 531 is a capacitive touch slider. The housing 533 contains a processor. Sensed data / measurements are transmitted from the sensor via the cable 545.

[0107] The measuring apparatus further comprises a mechanical stopping mechanism 537 for fixing the volume of the container at a first volume for receiving a liquid sample through cooperation with the capacitive slider 531. In this embodiment, the stopping mechanism is positioned between the base 543 and the container 501. In other embodiments the stopping mechanism may be repositioned on the opposite side of the container 501 (and beside the volume sensor 531). Figure 8 is a flow chart, illustrating a method 600 of determining an indication of a quantity or concentration of carbon dioxide dissolved in liquid. The method 600 includes a step 610 of providing a fluid-tight container accommodating a carbonated liquid sample. The method 600 also includes an agitation step 620 of agitating the liquid sample whilst allowing the volume of the container to change. The volume of the container is allowed to change towards a second volume which corresponds to an equilibrium state - e.g., where the headspace pressure inside the container equals the pressure of the container surroundings, and the carbon dioxide dissolved in the liquid sample exists in chemical equilibrium with the carbon dioxide in a headspace volume. Typically the agitation is achieved by shaking the container - although other methods (e.g., stirring and electrolysis) are possible as described hereinbefore. In a determination step 630 an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid is determined (e.g., calculated) based on the second volume.

[0108] In summary, there is provided a method (600) for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid. The method includes a step of providing a fluid-tight container accommodating a liquid sample (610), the liquid sample having carbon dioxide dissolved therein. The method also involves agitating the liquid sample whilst allowing the volume of the container to change from a first volume towards a second volume associated with an equilibrium state (620). In the equilibrium state, a headspace pressure inside the container equals the pressure of the container surroundings, and the carbon dioxide dissolved in the liquid sample exists in chemical equilibrium with the carbon dioxide in a headspace volume. The method further includes a step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid based on the second volume (630). The present invention also relates to a method of manufacturing apparatuses for carrying out these methods, and the apparatuses themselves.

[0109] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to and do not exclude other components, integers, or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Features, integers, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

Claims1 . A method for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid, the method comprising: providing a fluid-tight container accommodating a liquid sample, the liquid sample having carbon dioxide dissolved therein; agitating the liquid sample whilst allowing the volume of the container to change from a first volume towards a second volume associated with an equilibrium state; wherein, in the equilibrium state, a headspace pressure inside the container equals the pressure of the container surroundings, and the carbon dioxide dissolved in the liquid sample exists in chemical equilibrium with the carbon dioxide in a headspace volume; and determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid based on the second volume.

2. The method according to claim 1 , wherein the step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid is also based on the volume of the liquid sample, and optionally wherein the step of determining the quantity or concentration of the carbon dioxide dissolved in the liquid is based on the ratio of the difference between the second volume and the volume of the liquid sample to the volume of the liquid sample, and / or optionally wherein the step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid is based on no further volumes other than the volume of the sample liquid and the second volume.

3. The method according to claim 1 or 2, wherein the step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid is further based on the partial gas pressure of a second gas present in the headspace of the container, and optionally wherein the second gas is water vapour.

4. The method according to any preceding claim, wherein the step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid is further based on a pressure measurement and / or a temperature measurement, and optionally wherein the temperature measurement is the temperature of the liquid.

5. The method according to any preceding claim, wherein the liquid sample has an initial concentration and / or an initial quantity of the carbon dioxide dissolved therein, wherein determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid comprises determining the initial concentration or initial quantity, respectively.

6. The method according to any preceding claim, wherein the step of determining an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid comprises: obtaining a first value for the quantity or concentration of the carbon dioxide dissolved in the liquid; and obtaining an adjusted value for the quantity or concentration of the carbon dioxide dissolved in the liquid based on a measured temperature and / or a measured pressure.

7. A method of manufacturing a measuring apparatus for carrying out the method according to any preceding claim, comprising: providing the container for accommodating the liquid sample; and providing a carbon dioxide indicator for indicating the concentration or quantity of the carbon dioxide dissolved in the liquid based on the second volume and / or providing a sensor for sensing a container volume and a processor configured to receive an output from the sensor as an input.

8. A measuring apparatus for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid comprising: a container for accommodating a liquid sample, the container having a variable volume; a first carbon dioxide indicator; wherein, in use, the container defines a closed system which can progress towards satisfying a first equilibrium condition and a second equilibrium condition; wherein the first equilibrium condition corresponds to a headspace pressure inside the container equalling the pressure of the container surroundings, and the second equilibrium condition corresponds to the carbon dioxide dissolved in the liquid sample existing in chemical equilibrium with the carbon dioxide in a headspace volume;wherein the volume of the container can change towards a second volume associated with at least the first equilibrium condition; and wherein the first carbon dioxide indicator is configured to provide an indication of the quantity or concentration of carbon dioxide dissolved in the liquid, following the progression of the closed system towards satisfying the first equilibrium condition and the second equilibrium condition, based on the second volume.

9. The measuring apparatus according to claim 8, wherein, in use, the volume of the container can change towards the second volume whilst the liquid sample is agitated, and wherein the second volume is associated with the first equilibrium condition and the second equilibrium condition.

10. The measuring apparatus according to claim 8 or 9, wherein the first carbon dioxide indicator is configured to provide an indication of the quantity or concentration of the carbon dioxide dissolved in the liquid based on the volume of the liquid sample, and optionally based on the ratio of the difference between the second volume and the volume of the sample liquid to the volume of the sample liquid.11 . The measuring apparatus according to any of claims 8 -10, wherein the first carbon dioxide indicator visually indicates the quantity or concentration of the carbon dioxide dissolved in the liquid, wherein the measuring apparatus further comprises a first volume indicator for visually indicating a liquid sample volume, and wherein the first volume indicator is associated with the first carbon dioxide indicator such that, in use, the concentration or quantity of carbon dioxide is determinable using the first carbon dioxide indicator if the liquid sample volume is determinable using the first volume indicator.

12. The measuring apparatus according to claim 11 , wherein the first volume indicator is one of a plurality of volume indicators and the first carbon dioxide indicator is one of a plurality of carbon dioxide indicators, and wherein each carbon dioxide indicator is associated with a respective volume indicator so that, in use, the concentration or quantity of carbon dioxide is determinable using one of the carbon dioxide indicators if the liquid volume is determinable using the associated volume indicator.

13. The measuring apparatus according to claim 11 or 12, wherein the container comprises a surface in contact with the liquid sample associated with the or each of the carbon dioxide indicators and volume indicators, wherein, in use, the liquid sample volume is determinable based on the position of a liquid interface relative to at least one of the volume indicators.

14. The measuring apparatus according to claim 13 when dependent on claim 12, wherein the volume indicators are arranged along a reference line, wherein each carbon dioxide indicator is arranged above or below the respective volume indicator along a first direction, wherein the first direction is normal to a plane parallel to the liquid interface, and wherein the reference line is defined by the intersection between the plane parallel to the liquid interface and the surface.

15. The measuring apparatus according to any of claims 8 -10, wherein the measuring apparatus further comprising a volume indicator for visually indicating a liquid sample volume, wherein the container comprises a surface associated with the volume indicator, wherein, in use, the liquid sample volume is determinable based on the position of a liquid interface relative to the volume indicator.

16. The measuring apparatus according to any of claims 11-15, wherein the or each volume indicator comprises a measurement line marking at least a first point and a second point; wherein, in use, the liquid sample volume is determinable based on the position of the liquid interface relative to the first point and the second point, wherein the measurement line between the first point and the second point has a gradient defined with respect to a first direction and a reference line; wherein the first direction is normal to a plane parallel to the liquid interface; wherein the reference line is defined by the intersection between the plane parallel to the liquid interface and the surface; wherein the first point and the second point are offset from one another along the first direction;wherein a first intersection point and a second intersection point are offset from one another along the reference line; wherein the first intersection point is the point closest to the first point where a first intersection plane intersects the reference line, and the second intersection point is the point closest to the second point where a second intersection plane intersects the reference line; and wherein the first intersection plane passes through the first point and is normal to a first tangent to the surface at the first point, the second intersection plane passes through the second point and is normal to a second tangent to the surface at the second point, wherein the first and second tangents are parallel to the plane parallel to the liquid interface.

17. The measuring apparatus according to any of claims 11-16, further comprising an additional surface that is moveably attached to the surface, wherein the additional surface has the or each volume indicator provided thereon, and optionally the or each carbon dioxide indicator provided thereon.

18. The measuring apparatus according to any of claims 8-17, further comprising a first stopping mechanism for stopping the container volume from increasing relative to a first predetermined volume and / or a second stopping mechanism for stopping the container volume from decreasing relative to a second predetermined volume.

19. The measuring apparatus according to any of claims 8-18, further comprising an agitator for agitating the liquid sample.

20. The measuring apparatus according to any of claims 8-19 further comprising: a processor configured to determine an indication of the quantity or concentration of carbon dioxide dissolved in the liquid, and / or optionally a sensor for sensing a container volume.

21. A measuring apparatus for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid comprising: a processor; a container for accommodating a liquid sample, the container having a variable volume; a sensor for sensing a container volume; andwherein the processor is configured to determine an indication of the quantity or concentration of carbon dioxide dissolved in the liquid based on the container volume measured by the sensor.

22. The measuring apparatus according to any of claims 8-21 further comprising: a temperature sensor configured to sense the temperature of the sample; and / or a pressure sensor configured to sense the atmospheric pressure, and / or wherein the measurement apparatus is configured to accept a pre-determined volume of liquid into the container.

23. A method for determining an indication of a quantity or concentration of carbon dioxide dissolved in a liquid comprising: receiving input data indicative of a second volume of a fluid-tight container, accommodating a liquid sample, the liquid sample having carbon dioxide dissolved therein; and determining an indication of a quantity or concentration of carbon dioxide dissolved in the liquid based on the second volume; wherein the second volume is the volume associated with an equilibrium state, the volume of the container having been allowed to change towards the second volume during agitation of the liquid sample; and wherein, in the equilibrium state, a headspace pressure inside the container equals the pressure of the container surroundings, and the carbon dioxide dissolved in the liquid exists in chemical equilibrium with the carbon dioxide in a headspace volume.

24. A processor configured to carry out the method of claim 23.

25. A computer program product comprising instructions which, when the program is executed on a computer processing means, causes the computer processing means to carry out the method of any of claims 1-6 or 23.

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