Systems and methods for preparing buffer solutions

Abstract

A system 10 for preparing a mixed buffer is disclosed, comprising a conduit 110 for transporting the mixed buffer, a supply configuration 120 for supplying a first buffer, a second buffer, and a salt substance to the conduit to form the mixed buffer, a control sensor configuration 130 configured to output a signal indicating the pH level of the mixed buffer, and a controller 140 configured to control the operation of the supply configuration based on the signal from the control sensor configuration 130. The control sensor configuration 130 comprises a first pH sensor 131 of a first sensor type, a second pH sensor 132 of a second sensor type, and a control sensor valve configuration 135 that can control the flow of the mixed buffer to selectively bypass at least one of the first pH sensor 131 and the second pH sensor 132.

Description

Technical Field

[0001] The present invention relates to the preparation of a mixed buffer solution, and more particularly to a system and method for supplying a mixed buffer solution into a conduit.

Background Art

[0002] A buffer solution, also known as a buffer, is generally known as an aqueous solution having a relatively stable pH level. Buffer solutions are evaluated for their ability to maintain a nearly constant pH value even when small amounts of acid or base are added. This is achieved by the presence of a weak acid and its corresponding conjugate base, or a weak base and its corresponding conjugate acid, in the solution. The buffer components act together to absorb or release hydrogen ions as needed, thereby keeping the pH stable.

[0003] Buffer solutions are used in a variety of applications, including chemical analysis, pharmaceutical manufacturing, and biological research. One exemplary application is liquid chromatography, where buffer solutions are used to control the pH and ionic strength of the mobile phase that passes a sample through a chromatography column, and the separation occurs based on differential interactions between the sample components and the stationary phase.

[0004] A buffer solution can be prepared by mixing controlled amounts of acid and base into water while measuring the resulting pH level. The pH level can be measured using various sensor configurations, such as a pH meter that measures the potential difference between an inner reference electrode and an outer reference electrode that is in electrical contact with the mixed buffer solution through a reference junction.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] The object of the present invention is to provide an improved technique for controlling the preparation of mixed buffer solutions. [Means for solving the problem]

[0007] According to a first aspect of the present invention, a system for preparing a mixed buffer is provided. The system comprises a conduit for transporting the mixed buffer and a supply configuration for supplying a first buffer, a second buffer, and a salt substance to the conduit, thereby forming the mixed buffer. The system further comprises a control sensor configuration configured to output a signal indicating the pH level of the mixed buffer and a controller configured to control the operation of the supply configuration based on the signal from the control sensor configuration. The control sensor configuration is positioned downstream of the supply configuration to be in contact with the mixed buffer and further includes a first pH sensor of a first sensor type, a second pH sensor of a second sensor type, and a control sensor valve configuration. The control sensor valve configuration is operable to control the flow of the mixed buffer to selectively bypass at least one of the first pH sensor and the second pH sensor.

[0008] A second aspect of the present invention provides a method for supplying a mixed buffer into a conduit. The method includes using a supply configuration to supply at least one of a first buffer, a second buffer, or a salt to the conduit to form a mixed buffer. The method further includes receiving a signal indicating the pH level of the mixed buffer downstream of the supply configuration, controlling the operation of the supply configuration based on the received signal, and controlling the flow of the mixed buffer to selectively bypass at least one of a first pH sensor and a second pH sensor of a control sensor configuration, wherein the first pH sensor is a first sensor type sensor and the second pH sensor is a second sensor type sensor.

[0009] This invention is based on the discovery of a previously unrecognized problem known as the "salt memory effect," which causes a pH sensor in contact with a salted buffer, such as NaCl, to report an incorrect value when switched to a salt-free buffer. Even though the error in the reported value has been observed to decrease over time, this error can cause an initial problem when switching to a salt-free buffer. The discovery of this problem led the inventors to propose a technique employing two sensors, which can be selectively bypassed depending on the actual salt concentration of the buffer. This allows one of these sensors to be used only with the salted buffer, and the other sensor to be used only with the salt-free buffer.

[0010] Various sensor types are associated with different operating ranges and conditions under which the sensor is expected to function correctly and produce reliable output. Sensor operation is influenced, for example, by the type of sensing element used, the sensor's sensitivity and resolution, and the method of signal processing and output. Using the sensor outside its specified operating range or under environmental conditions other than those specified may result in inaccurate or unreliable results.

[0011] This can be a problem for systems that are expected to be able to handle various types of mixed buffers, including liquids with low conductivity (e.g., no salt added or only very small amounts added) or high conductivity (e.g., with added salt), as well as cleaning solutions used in clean-in-place (CIP) processes where the cleaning solution circulates within the system to remove residue from previous batches. Ideally, the sensor should be able to operate under both low and high conductivity conditions and should also be CIP and autoclavable.

[0012] Advantageously, the present invention provides a dual-mode configuration in which one sensor type can be used for certain conditions, such as low-conductivity liquids, and another sensor type can be used for other conditions, such as high-conductivity liquids or CIP. Thus, the first and second sensor types may be of the same type, i.e., similar or identical, or different types, depending on the application and the type of mixed buffer used. When the salt memory effect is a major problem to be avoided, two identical sensor types may be arranged in a dual-mode configuration that allows the first sensor of these sensors to be dedicated to buffers with added salt, and the second sensor of these sensors to be dedicated to buffers with no or very little added salt. Alternatively, it is possible to utilize the advantages of each sensor type while avoiding the disadvantages of each by configuring the control sensor configuration using two different types of pH sensors. For example, the first sensor type may be more suitable for high-conductivity conditions (e.g., solutions with added salt) than the second type, which is more susceptible to the salt memory effect and therefore less suitable for situations where both low-conductivity and high-conductivity buffers occur. In a further example, the first sensor type may be configured to withstand NaOH, while the second type does not have CIP resistance.

[0013] A dual-mode configuration can be understood as a configuration configured such that a flow of mixed buffer selectively bypasses one of these sensors, thereby preventing it from being exposed to environmental conditions other than its specified operating conditions. Thus, the first sensor may be bypassed when preparing a mixed buffer without added salt, thereby the pH level being measured by the second sensor instead. Similarly, the second sensor may be bypassed when preparing a mixed buffer with added salt, thereby the pH level being measured by the first sensor instead. For this purpose, the first and second sensor types may be identical. In a similar manner, a dual-mode configuration may allow a flow of washing solution to be routed over one of these sensors, which is optimally suited to withstanding NaOH, while the other sensor is bypassed.

[0014] In one embodiment, the controller is configured to evaluate the pH level of the mixed buffer based on a signal from a control sensor configuration and to provide a relative mixing ratio of a first buffer and a second substance to obtain a predetermined pH level of the mixed buffer. The controller provides automatic control of the mixing process for preparing the mixed buffer, and the output from the control sensor configuration is used to provide corrective feedback to help obtain the desired pH level. Advantageously, the controller allows the desired pH level to be reached without requiring human input.

[0015] In one embodiment, the system further comprises a sample inlet, which is fluidically connected to a conduit and configured to supply a sample to the conduit. The sample can therefore be added to and mixed with a mixed buffer carried by the conduit. In one embodiment, the sample inlet may be located downstream of a control sensor configuration.

[0016] In one embodiment, the system may further comprise a monitoring sensor configuration located downstream of the control sensor configuration and, optionally, downstream of the sample inlet. The monitoring sensor configuration may therefore be configured to output a signal indicating the pH level of the mixed buffer when a sample is present. The monitoring sensor configuration may be employed to verify the pH level of the mixed buffer before it is transported to a downstream processing device, such as a chromatography column, or before it is discharged into a bag or container for later use. For this purpose, the system may be provided with a discharge valve configuration configured to control the discharge of the mixed buffer from the conduit to a processing device, bag, or container. The operation of the discharge valve may be controlled by a controller as described above. The controller may be configured to evaluate the pH level of the mixed buffer based on signals from the control sensor configuration or the monitoring sensor configuration and to control the operation of the discharge valve configuration based on the evaluated pH level. For example, the controller may be configured to discharge the mixed buffer from the conduit only when the evaluated pH level is within a predetermined range. If the evaluated pH level is outside the predetermined range, the discharge valve may be actuated to bypass the processing device or other downstream equipment, such as a bag or container.

[0017] In one embodiment, the monitoring sensor configuration includes a third pH sensor of a first sensor type, a fourth pH sensor of a second sensor type, and a monitoring sensor valve configuration that can be operated to guide a flow of mixed buffer solution to selectively bypass at least one of the third and fourth pH sensors. The monitoring sensor configuration is therefore configured in a manner similar to the control sensor configuration described above and can be operated in a dual mode in which the mixed buffer solution is selectively bypassed at that time. Thus, the third sensor may be bypassed when preparing a mixed buffer solution without added salt, thereby the pH level is measured instead by the fourth sensor while the third sensor is not exposed to the flow of mixed buffer solution. Thus, the fourth sensor may be bypassed when preparing a mixed buffer solution with added salt, thereby the pH level is measured instead by the third sensor. Furthermore, the monitoring sensor configuration may allow a flow of washing solution to be routed through one of these sensors, which is optimal for withstanding CIP, such as being exposed to NaOH, while the other sensor is bypassed.

[0018] In one embodiment, each of the first and second sensor types may be a potentiometric pH sensor that operates by measuring the potential difference between an inner reference electrode and an outer reference electrode that is electrically in contact with a mixed buffer solution. Thus, each of the first and second sensor types may include a reference junction arranged to form a selective barrier to the mixed buffer solution. This selective barrier may be referred to as a membrane or plug having a porous structure that allows ion transport. The average pore size of the reference junction of the first sensor type may be smaller than that of the reference junction of the second sensor type. Beneficially, it has been observed that a relatively large pore size makes the pH sensor faster and more stable compared to a sensor with a relatively small pore size. It has also been observed that sensors with a relatively large pore size are suitable for low-conductivity liquids, i.e., mixed buffer solutions with low ionic strength / no added salts. For these liquids, sensors with a relatively large pore size can, advantageously, produce a more accurate and reliable output compared to a sensor with a relatively small pore size.

[0019] While relatively small pore sizes can, on the other hand, favorably facilitate the use of pressurized reference electrolytes, it has been observed that this improves the pH sensor's ability to withstand prolonged exposure to washing solutions containing NaOH and even pure water. This type of sensor can therefore be referred to as CIP and autoclave-resistant sensors. They have also been observed to be less susceptible to the salt memory effect. The porosity of the reference junction allows the reference electrolyte to slowly leach into the buffer through the junction, and by reducing the average pore size, the reference electrolyte can last longer until replenishment is needed or the sensor must be replaced. Pressurizing the reference electrolyte can further reduce potential drift over time, enabling more stable measurements. Furthermore, the pressure difference across the barrier can help prevent the intrusion of contaminants and ions.

[0020] Some pH sensors in which the reference electrolyte is pressurized have been observed to exhibit somewhat reduced accuracy and stability at low conductivity (such as a mixed buffer with very little salt added or no salt added at all), especially when compared to the above-described sensor types having a relatively large pore size. However, the dual-mode operation of the present invention solves this problem because the pressurized pH sensor can be bypassed when a low-conductivity buffer is prepared. Instead, the pH level of the low-conductivity buffer can be measured by the large-pore size sensor.

[0021] In one embodiment, the first pH sensor can be bypassed in response to the mixed buffer having a relatively low conductivity, such as less than 5 mS / cm, 2 mS / cm or less. For the purposes of this specification, a mixed buffer having a relatively low conductivity can be understood to have a relatively low ionic strength or concentration and a mixed buffer in which no salt or only a very small amount of salt has been added during preparation.

[0022] Furthermore, the second pH sensor can be bypassed in response to the mixed buffer having a relatively high conductivity, such as 5 mS / cm or more. In the context of the present invention, a mixed buffer having a relatively high conductivity can be understood to be a liquid to which at least 50 mM of NaCl has been added during preparation. A significant salt memory effect has been observed for solutions having an added NaCl concentration of 50 mM or more, but the salt memory effect can be considered less significant or negligible for an NaCl concentration of less than 50 mM. Thus, by bypassing the second pH sensor for a mixed buffer having an added NaCl concentration of 50 mM or more, the risk that the second pH sensor will be affected by the salt memory effect can be reduced.

[0023] It will be understood that the mixed buffer can be prepared from a weak acid and a weak base, a weak acid and a strong base, or a weak base and a strong acid. Exemplary buffers that can be prepared using this system are Phosphate buffered saline (where the first buffering substance is disodium hydrogen phosphate and the second buffering substance is one of sodium chloride, potassium chloride, and potassium dihydrogen phosphate), Sodium acetate buffer solution (where the first buffering substance is acetic acid and the second buffering substance is sodium acetate), Citrate buffer solution (where the first buffering substance is citric acid and the second buffering substance is sodium citrate), Tris buffer solution (where the first buffering substance is Tris-HCl and the second buffering substance is Tris base), and Bis-Tris buffer solution (where the first buffering substance is Bis-Tris-HCl and the second buffering substance is Tris base) are included as some examples.

[0024] The above-mentioned buffering substances are sometimes referred to as "buffer salts", and these are examples of so-called weak electrolytes and do not necessarily dissociate completely into ionic components. Instead, they contribute to the buffer solution that is in equilibrium with water.

[0025] The term "salt substance", on the other hand, generally refers to a group of strong electrolytes that typically dissociate completely when dissolved in water. A salt substance may, for example, refer to NaCl and can be added to a mixed buffer solution to enhance its buffering capacity. Further examples include KCl, which, when added, can increase the ionic strength of the buffer solution, which can affect the conductivity coefficient of the acid and its conjugate base, or the chaotropic or water-displacing properties of the salt can be used. This can then change the equilibrium constant of the reaction governing the buffer system and enhance the effect on the resistance to pH changes. In addition, the presence of a salt substance also reduces the activity coefficient of the acid or base, which reduces the degree of ionization of the acid or base, and as a result, the change in pH after adding an acid or base can be smaller. It will be understood that the terms "salt" or "salt substance" as used in the present disclosure refer rather to substances of this type and not to the acid and base substances used to form the buffer system.

[0026] The term "sample," or "raw material," generally refers to a mixture of biological molecules containing the product of interest, which is fed into a column for further purification. The result of the entire purification process may be called the product. Examples of samples include serum or fractions thereof from human plasma, raw materials from cell cultures containing monoclonal antibodies, and their purified fractions.

[0027] Further features and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention, which are given by reference only to the accompanying drawings. [Brief explanation of the drawing]

[0028] [Figure 1] This is a schematic diagram of a system for preparing a mixed buffer solution according to one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view of a pH sensor according to one embodiment of the present invention. [Figure 3] This is a schematic outline diagram of a system according to one embodiment of the present invention. [Figure 4] This is a schematic block diagram illustrating various actions of the method according to one embodiment of the present invention. [Modes for carrying out the invention]

[0029] Figure 1 is a schematic diagram of a system 10 for preparing a mixed buffer according to one embodiment of the present invention. The system 10 comprises a conduit 110 for transporting the mixed buffer and a supply configuration 120 for supplying at least one of a first buffer, a second buffer, and a salt substance to the conduit to form the mixed buffer. A control sensor configuration 130 is provided to output a signal indicating the pH level of the mixed buffer to a controller 140 configured to control the operation of the supply configuration 120 based on the control sensor configuration 130. Thus, the signal from the control sensor configuration 130 can be used as a correction feedback to the controller 140, thereby helping to achieve a desired pH level. As illustrated in the figure, the control sensor configuration 130 comprises a first pH sensor 131 and a second pH sensor 132, which are arranged in parallel, and a control sensor valve configuration 135 allows selective bypass of at least one of the first and second pH sensors.

[0030] The characteristics of addition and optional selection are explained below.

[0031] The conduit 110 is configured to transport the mixed buffer to a downstream processing point 180, such as a chromatography column, a filtration device, or a container for storing or transporting the prepared buffer. The conduit 110 may be formed from stainless steel, silicone, or any other suitable material known in the art. The conduit 110 may further comprise connectors, joints, and couplings (not shown) that allow fluids and substances to be supplied to and discharged from the conduit 110.

[0032] The supply configuration 120 is configured to supply a first buffer, a second buffer, and optionally a salt to the conduit 110. The first buffer is supplied to the conduit via a first inlet 121, the second buffer via a second inlet 122, and the salt via a salt inlet 123. Further inlets may also be provided, such as an additive inlet 124 for supplying additives to the mixed buffer in the conduit 110, and a water inlet 125 for supplying a flow of water (typically water for injection - WFI) to mix with the buffer and optionally the salt and additive.

[0033] In Figure 1, inlets 121-125 are fluidically connected to the conduit 110 via their respective pumps 126, each of which may be operated individually to control the amount of buffer material, salt, additive, or water supplied to the conduit 110 to form a mixed buffer solution. Depending on the flow rate and velocity, the pumps 126 may be selected from peristaltic pumps, piston pumps, and diaphragm pumps. Typically, diaphragm pumps may be used.

[0034] The first inlet 121 and the second inlet 122 may be configured to supply an acidic buffer and a basic buffer to the conduit 110, respectively. A salt inlet may be configured to supply a salt solution (typically sodium chloride or ammonium sulfate). Examples of additives include urea, glycerol, and polysorbate solutions. The substances supplied to the conduit 110, namely the buffer, salt solution, and additives, may also be referred to as raw materials.

[0035] The order in which different raw materials are mixed can be changed, in particular, depending on the miscibility of each raw material, the solubility of the substances, and other factors.

[0036] The raw materials may be supplied in tanks connected to each of the inlets 121-125. Optionally, several different raw material tanks may be provided for each of the inlets 121-125. For example, several tanks containing solutions of different salts (or salt mixtures) or salt solutions of different concentrations may be provided for the salt inlet 123. Similarly, several tanks containing different acidic buffers or a single buffer at different concentrations may be provided for the first inlet 121, and the same may apply to the supply of a basic buffer to the second inlet 122.

[0037] As previously mentioned, mixed buffers can be prepared from a weak acid and a weak base, a weak acid and a strong base, or a weak base and a strong acid. Exemplary buffers that can be prepared using System 10 include phosphate buffer, acetate buffer, citrate buffer, Tris buffer, and Bistris buffer.

[0038] The control sensor configuration 130 is located downstream of the supply configuration 120, at least the first and second inlets 121, 122, and typically downstream of the salt inlet 123. The control sensor configuration 130 includes a control sensor valve configuration 135 configured to control the flow of liquid in the conduit to bypass only the first pH sensor 131, only the second pH sensor 132, or both pH sensors 131, 132, as an option. Which of the sensors 131, 132 to bypass may depend, among other things, on the type of sensor and its affinity to the type of liquid carried by the conduit 110. If the conduit 110 carries a washing solution containing, for example, NaOH, the flow may be directed to bypass whichever of the sensors 131 or 132 has the lowest tolerance to exposure to NaOH. For buffers, the carried flow may be directed to whichever of the sensors 131, 132 is expected to produce the most accurate and reliable output for that particular type of buffer.

[0039] As shown in the figure, the first and second pH sensors 131 and 132 are coupled in parallel along the conduit 110, which may allow them to operate in dual mode (i.e., a first mode in which the output is supplied by the first pH sensor 131 and a second mode in which the output is supplied by the second pH sensor 132). This parallel configuration can be achieved by two parallel conduit sections 111 and 112 connected to the main conduit 110 via first and second T-shaped junctions. The upstream T-shaped joint is formed by a control sensor valve configuration 135, which can be configured to take at least two different states: a first state in which the liquid flow is directed to the first conduit portion 111 and the first pH sensor 131, while contact with the second conduit portion 112 and the second pH sensor 132 is blocked; and a second state in which the liquid flow is directed to the second conduit portion 112 and the second pH sensor 132, while contact with the first conduit portion 111 and the first pH sensor 131 is blocked. A third state in which the liquid flow is directed into both conduit portions 111 and 112 is also intended, and a fourth state in which both conduit portions 111 and 112 are blocked may also be intended.

[0040] The first pH sensor 131 and the second pH sensor 132 may be potentiometric pH sensors that measure the potential difference between an inner reference electrode and an outer electrode that is in ion contact with a mixed buffer solution. The inner reference electrode may be separated from the buffer solution by a reference junction membrane or porous plug that forms a selective barrier allowing ions to pass through, as will be described in more detail in relation to Figure 2. In the embodiment illustrated in Figure 1, the first sensor 131 may have a reference junction membrane with a relatively small average pore size, or at least smaller than the average pore size of the reference junction membrane of the second pH sensor 132. For example, the average pore size of the reference junction membrane of the first pH sensor 131 may be 0.5 μm or less, such as 0.2 μm or less, while the average pore size of the membrane of the second pH sensor 132 may be 1 μm or more, such as 5 μm or more.

[0041] However, it should be understood that the above description is merely an example of two different types of pH sensors and their respective characteristics. Other types of sensors and their distinctive features may also be used, depending on the type of mixed buffer being produced, the relevant pH range, and the conductivity of the buffer. In some examples, the first and second sensor types may be similar, or even identical.

[0042] The control sensor configuration 130 may be used to monitor whether the desired characteristics of the liquid flow in the conduit 110 are correct and stable, and to provide feedback to the controller 140. The controller 140 uses this feedback to adjust the composition (i.e., mixing ratio) of the liquid flow so that the measured pH converges to a desired value.

[0043] The control sensor configuration 130 may also be used to monitor that the desired characteristics of the mixed buffer in the conduit 110 are correct and stable. For this purpose, the controller 140 may be configured to indicate any deviation and, in some cases, cause the discharge of the mixed buffer from the conduit 110 to stop.

[0044] In the embodiment shown in Figure 1, the properties of the mixed buffer transported by the conduit can be monitored by a sensor configuration 160 located downstream of the control sensor configuration 130 described earlier. The monitoring sensor configuration 160 may include a dual-mode sensor configuration configured similarly to the control sensor configuration, namely a third pH sensor 161 of a first sensor type, a fourth pH sensor 162 of a second type, and a monitoring sensor valve configuration 165 that can be operated to guide the flow of the mixed buffer and selectively bypass at least one of the third pH sensor 161 and the fourth pH sensor 162. Thus, the monitoring sensor valve configuration 165 may be configured to take at least two different states, namely a first state in which the flow is directed only to the third pH sensor 161 and a second state in which the liquid flow is directed only to the fourth pH sensor 162.

[0045] System 10 may further include a release valve configuration 170 configured to control the release of the mixed buffer from the conduit 110. The mixed buffer may be released, for example, into a container or disposable bag, or into a downstream processing device such as a chromatography column 180 or a filtration device. The operation of the release valve configuration 170 may be controlled by a controller 140, which may be configured to evaluate the pH level of the mixed buffer based on signals from a control sensor configuration 130 or a monitoring sensor configuration 160. The release valve configuration 170 may operate in a way that prevents the release of the mixed buffer if a deviation or error is detected in the evaluated pH level. In the example illustrated in this figure, the chromatography column 180 may be bypassed if the evaluated pH level is found to be outside a predetermined target range. The release valve configuration 170 may be configured, for example, to direct the flow of the mixed buffer through an outlet 171 instead of releasing the liquid into the column 180.

[0046] System 10 may further include a sample inlet 150 that is fluidically connected to the conduit 110 and configured to supply a sample to the conduit 110. The supply of the sample to the conduit 110 may be controlled by a pump 152, which may be configured similarly to the pump 126 described above in relation to the supply configuration 120. Thus, the pump 152 may be a peristaltic pump, a piston pump, or a diaphragm pump.

[0047] As shown in Figure 1, the sample inlet 150 may be connected to the conduit 110 at a location downstream of the supply configuration 120 and the control sensor configuration 130, and upstream of the monitoring sensor configuration 160. However, other configurations are also possible in which the sample inlet 150 is connected to the conduit 110 upstream of the control sensor configuration 130 or downstream of the monitoring sensor configuration 160.

[0048] Further sensors and other types of equipment may also be provided within the system 10. In one example, one or more conductivity sensors 190 may be configured to generate a signal indicating the conductivity of the mixed buffer solution. This signal is supplied to the controller 140, which may use the measured conductivity as corrective feedback when controlling the supply configuration 120. Additional equipment may include temperature sensors, air traps, and filters (not shown).

[0049] Figure 2 is a schematic cross-sectional view of a pH sensor 200 according to several embodiments of the present invention. The pH sensor 200 is configured similarly to the pH sensors 131, 132, 161, and 162 described with reference to Figure 1, and thus can form part of the control sensor configuration 130 or monitoring sensor configuration 160 shown in Figure 1.

[0050] The pH sensor 200 is a potentiometric pH sensor configured to measure the pH of a solution, such as a mixed buffer solution in a conduit, based on the potential difference between an inner reference electrode 225 and an outer reference electrode 235 when the pH sensor is immersed in a mixed buffer solution. The potential difference can be measured by a high-impedance voltmeter (not shown) connected to electrodes 225 and 235.

[0051] In this example, the inner reference electrode 225 and the outer reference electrode 235 are housed in a single glass body 245, or sensing probe, which has two separate compartments that allow the inner reference electrode 225 to be immersed in the inner buffer 230 and the outer reference electrode 235 to be immersed in the reference electrolyte 220, respectively. A glass membrane 240 is positioned at the distal end of the glass body, within which the end portions of the inner buffer 230 and the outer reference electrode 235 are placed. The outer reference electrode 235 may therefore also be referred to as the glass electrode.

[0052] Furthermore, the reference junction 210 is positioned to form a barrier between the reference electrolyte 220 and the solution being measured. The reference junction 210 is typically formed from small pores, or from a porous plug or membrane, allowing the reference electrolyte 220 to come into contact with the mixed buffer solution being measured. More specifically, the reference junction 210 may be configured to allow ions to move between the reference electrolyte and the solution being measured, while simultaneously preventing the movement of contaminants that could affect the accuracy of the pH measurement.

[0053] Several types of reference junctions 210 are used in the concept of the present invention, and these may represent different sensor types that may be employable in the dual-mode concept. In one example, the reference electrolyte 220 may be placed in a porous frit, i.e., a microporous glass that allows ion flow, and the reference junction 210 is formed by the interface between the porous frit and the mixed buffer. In another example, the reference electrolyte 220 is separated from the mixed buffer by a membrane, which may be formed of a porous ceramic such as a ceramic plug, or a polymer. In general, the reference junction 210 plays a crucial role in the accuracy and stability of pH measurement and can therefore be carefully selected with respect to the properties of the liquid being exposed.

[0054] In one embodiment, the first sensor type may have a porous reference junction having an average pore diameter smaller than that of the porous reference junction of the second sensor type. Relatively large pores can cause the pH sensor to be faster and more stable, especially with low-conductivity liquids, but at the same time may reduce the sensor's ability to withstand CIP.

[0055] On the other hand, relatively small pore sizes have been observed to improve the ability of pH sensors to withstand CIP (Clean-in-Place) with NaOH-containing washing solutions, and even prolonged exposure to pure water, compared to sensors with relatively large pore sizes. Furthermore, sensors with relatively small pore sizes have also been observed to have reduced resistance to washing solutions containing NaOH, for example. These can also cause the sensor to be more susceptible to the salt memory effect, as described above. The first sensor type may have an average pore size of 0.5 μm or less, such as 0.2 μm or less, while the second sensor type may have an average pore size of 1 μm or more, such as 5 μm or more.

[0056] In addition, or alternatively, the reference electrolyte 220 may be pressurized. In other words, a pressure gradient may be applied over the reference junction 210. Pressurizing the reference electrolyte 220 may improve stability, reduce contamination, and increase the accuracy of measurements.

[0057] In some cases, the first sensor type in a dual-mode configuration is a pressurized electrolyte type, while the second sensor type is not. Alternatively, both sensor types are pressurized.

[0058] It will be understood that various combinations of pressurized sensors, unpressurized sensors, large pore diameter reference junctions (in some examples, the average pore diameter is 1 μm or more), and small pore diameter reference junctions (in some examples, the average pore diameter is 1 μm or more) are possible within the scope of the present invention. Thus, the pH sensor 200 may be a pressurized small pore diameter sensor, a pressurized large pore diameter sensor, an unpressurized small pore diameter sensor, or an unpressurized large pore diameter sensor. Each of the first and second sensor types may be any of these four combinations. However, in a preferred example, the first sensor type may be a pressurized small pore diameter sensor, and the second sensor type may be an unpressurized large pore diameter sensor.

[0059] Figure 3 is a schematic outline of a system according to one embodiment, which can be configured similarly to system 10 described above with reference to Figure 1. Thus, system 10 comprises a supply configuration 120 for supplying raw materials to a conduit to form a mixed buffer, a control sensor configuration 130 configured to measure the pH level in the mixed buffer, and a controller 140 for controlling the operation of the supply configuration 120 based on the output from the control sensor configuration 130. Optionally, the system may further comprise a sample inlet 150, a monitoring sensor configuration 160, and a discharge valve configuration 170, as described above.

[0060] The output from the control sensor configuration 130, i.e., the signals generated by the first pH sensor and / or the second pH sensor, can be transmitted to the controller 140 via a wired or wireless connection. The signals can be used by the controller 140 to evaluate the pH level of the mixed buffer and provide corrective feedback to the supply configuration 120. However, the controller 140 can also be configured to calculate an initial mixing recipe for the preparation of the mixed buffer and then adjust the resulting pH using sensor feedback. Illustrative and non-exclusive examples of how such calculations may be performed are then described with reference to the Debye-Hückel equation.

[0061] For mixed buffers containing lower concentrations of buffers and / or salts, the iterative calculation procedure described, for example, in U.S. Patent No. 6,221,250, may be used to determine the relative mixing ratio of the raw materials. In this document, a modified version of the Debye-Hückel equation is used to determine the variable ratio of the components. Furthermore, an approximation of the ion size parameter in the Debye-Hückel equation is used. The ratios of the components are changed simultaneously in such a way that the pre-selected pH of the mixed buffer is obtained at each point in time, taking into account the interrelationship between the pH and ionic strength of the mixed buffer.

[0062] For higher concentrations of buffer and salt, the method described in International Application No. WO 2009 / 131524 A1 (PCT / SE2009 / 050399) can be used to determine the mixing ratio, where the relative component ratio is given by the Debye-Hückel formula.

[0063]

number

[0064] Determined using, Here, A is a constant, or rather a temperature-dependent parameter ~0.51 (where A = 0.4918 + 0.0007T + 0.000004T). 2 (which can be calculated precisely), T is the temperature in Celsius, Z is the charge of the ion, Z is the radius of the hydrated ion (in Å), and the quantity α is (in the original paper by Debye and Hückel) the "average approach distance of the positive or negative ion" and the ion size parameter in the Debye-Hückel equation. α The ionic strength of a liquid mixture is determined as the weighted average ionic size of all chemical species contributing to its ionic strength, with the ionic strength of each species used as a weighting parameter. More specifically, the ionic size parameter in the Debye-Hückel equation. α teeth

[0065]

number

[0066] It was decided as follows: Here, Ii is the ionic strength of chemical species i, α i is the ion size parameter of chemical species i, and I is the total ionic strength.

[0067] The ion size parameter in the Debye-Hückel equation is given as α = 0.5·(mass). 1 / 3It can also be approximated as +shell, where "shell" is typically fixed to a value in the range of 3.8 to 4.2, such as 4.0 for positively charged ions, and to a value in the range of 0 to 0.2, such as 0, for negatively charged ions.

[0068] An iterative procedure for determining the mixing ratio includes (i) determining the relative component ratios, wherein the predefined ionic strengths of the liquid mixture are assigned to the chemical species according to a predefined distribution among the chemical species; (ii) calculating the ionic strength of each chemical species in the mixture based on the relative component ratios determined in (i); (iii) determining a new set of relative component ratios taking into account the ionic strengths calculated in (ii); and (iv) repeating steps (ii) and (iii) until a predetermined convergence criterion is met.

[0069] Other methods for providing the mixing ratio may, of course, also be available.

[0070] The controller 140 may include circuitry configured to perform the functions of the controller. The circuitry may include a processor, such as a central processing unit (CPU), microcontroller, or microprocessor, configured to execute program code. The program code may, for example, be configured to perform an evaluation function for evaluating the pH level based on the signal output from any of the pH sensors 131, 132, 161, or 162 described above, and a mixing ratio function for calculating the relative mixing ratio of raw materials to prepare a mixed buffer having predetermined characteristics (such as pH and conductivity). The controller 140 may further include memory, which may be one or more of the following devices: buffers, flash memory, hard drives, removable media, volatile memory, non-volatile memory, random access memory (RAM), or other suitable devices. In a typical configuration, the memory includes non-volatile memory for long-term data storage and volatile memory that functions as system memory for the circuitry. The memory may exchange data with the circuitry over a data bus. Accompanying control lines and an address bus may exist between the memory and the circuitry.

[0071] The processing functions of the controller 140 may be embodied in the form of executable logic routines (e.g., lines of code, software programs, etc.) stored in the controller 140's non-temporary computer-readable medium (memory) and executed by the circuit. Furthermore, the processing functions of the controller 140 may be independent software applications or form part of a software application. The functions described may be considered as methods configured to be executed by a processing unit, such as the processor of the circuit. Also, while the functions described may be implemented in software, such functions may also be executed by dedicated hardware or firmware, or a combination of hardware, firmware, and / or software.

[0072] Figure 4 is a flowchart illustrating various steps of Method 300 for providing a mixed buffer according to several embodiments. Method 300 can be carried out using a system 10 similar to that described above in relation to Figures 1 and 3. For brevity, these figures are referenced for further details and features regarding the system and other configurations.

[0073] In an example of the present invention, method 300 includes using a supply configuration 120 to supply at least one of a first buffer, a second buffer, or a salt substance to a conduit 110 to form a mixed buffer 310. The flow of the mixed buffer may be controlled 320 to selectively bypass at least one of a first pH sensor 131 and a second pH sensor 132 of a control sensor configuration 130. Sensor outputs from the control sensor configuration 130 may be received 330 and used to control the operation of the supply configuration 120 340. The control 340 of the supply configuration 120 may include an error-based feedback loop in which the pH level of the mixed buffer is calculated 341 from the received signal, the difference between the calculated pH level and a predetermined pH level is determined 342, and the (adjusted) relative mixing ratio of the first buffer and the second buffer is provided to the supply configuration 120 based on the determined difference. This loop of measuring the pH level and adjusting the raw material mixing ratio can be repeated until the measured pH level converges toward a predetermined level.

[0074] The method further includes bypassing the first pH sensor 131 351 for mixed buffers having a conductivity of less than 5 mS / cm, such as 2 mS / cm or less, and bypassing the second pH sensor 132 352 for mixed buffers containing added salt substances.

[0075] In an example of the present invention, method 300 includes receiving a monitoring signal 361 from a monitoring sensor configuration 160, the monitoring signal indicating the pH level of the mixed buffer at a location within the conduit 110 where the monitoring sensor configuration 160 is located. This location may be located downstream of the sample inlet 150, and the monitoring signal may therefore indicate the pH level of the mixed buffer while the sample is being transported. The received monitoring signal may be used to determine 362 that the pH level is within a predetermined range before the mixed buffer is released 363 from the conduit 110. The mixed buffer may be released, for example, into a storage container for later use, or into a processing device such as a filter or chromatography column.

[0076] Various embodiments may provide means for bypassing sensors for the purpose of clean-in-place (CIP). Preferably, the sensor to be bypassed is of a type that does not have complete CIP resistance (for example, a second sensor type that does not have CIP resistance to cleaning with NaOH). Such NaOH may be supplied as a CIP solution having, for example, a 0.5 M or 1.0 M concentration of sodium hydroxide (or a sodium hydroxide solution such as about 0.5 M, about 1.0 M, or about 0.5 M to about 1.0 M). This makes it possible to provide several embodiments of the present invention in which daily manual intervention can be substantially eliminated or reduced. Various mechanisms that enable the bypassing of sensors are also contemplated (for example, a mechanism that can be operated to bypass a second pH sensor in order to enable the provision of a clean-in-place (CIP) function). Such mechanisms may be able to operate automatically as needed (for example, to provide a scheduled cleaning program).

[0077] The embodiments described above should be understood as illustrative examples of the present invention. Further embodiments of the present invention are contemplated. It should be understood that features described in reference to one embodiment may be used alone or in combination with other features described, in combination with one or more features of other embodiments of these embodiments, or in combination with other embodiments of these embodiments. Furthermore, equivalents and variations not described above may also be adopted without departing from the scope of the present invention, which are defined in the appended claims. [Explanation of symbols]

[0078] 10 Systems 110 Conduit 111, 112 Parallel conduit sections 120 supply configuration 121 First Entrance 122 Second Entrance 123 Salt Entrance 124 Additive Inlet 125 Water inlet 126 pumps 130 Control Sensor Configuration 131 First pH sensor 132 Second pH sensor 135 Control Sensor Valve Configuration 140 controllers 150 Sample Inlet 152 pumps 160 monitoring sensor configuration 161 Third pH sensor 162 The fourth pH sensor 165 Monitoring Sensor Valve Configuration 170 Discharge valve configuration 171 Exit 180 Downstream processing point 190 Conductivity Sensor 200 pH sensor 210 Reference joint 220 Reference Electrolyte 225 Inner reference electrode 230 Inner buffer 235 Outer reference electrode 240 glass film 245 Glass body 300 ways

Claims

1. A system (10) for preparing a mixed buffer solution, A conduit (110) for transporting the mixed buffer solution, A supply configuration (120) for supplying a first buffering substance, a second buffering substance, and a salt substance to the conduit, thereby forming the mixed buffer solution, A control sensor configuration (130) configured to output a signal indicating the pH level of the mixed buffer solution, A controller (140) configured to control the operation of the supply configuration based on the signals from the control sensor configuration, Equipped with, The control sensor configuration is configured to contact the mixed buffer downstream of the supply configuration, and the control sensor configuration is configured A first pH sensor (131) of the first sensor type, A second pH sensor (132) of the second sensor type, A control sensor valve configuration (135) that controls the flow of the mixed buffer and is operable to selectively bypass at least one of the first pH sensor and the second pH sensor, and System (10) further includes the following.

2. The aforementioned controller, Based on the signal from the control sensor configuration, the pH level of the mixed buffer solution is evaluated. To obtain a predefined pH level of the mixed buffer solution, the operation of the supply configuration is controlled to provide the relative mixing ratio of the first buffer and the second buffer. The system (10) according to claim 1, configured as follows.

3. The system (10) according to claim 1 or 2, further comprising a monitoring sensor configuration (160) located downstream of the control sensor configuration and configured to output a signal indicating the pH level of the mixed buffer solution.

4. The system (10) according to claim 3, wherein the monitoring sensor configuration includes a third pH sensor (161) of the first sensor type, a fourth pH sensor (162) of the second sensor type, and a monitoring sensor valve configuration (165) that is operable to guide a flow of mixed buffer solution to selectively bypass at least one of the third pH sensor and the fourth pH sensor.

5. The system (10) according to claim 3 or 4, further comprising a discharge valve configuration (170) configured to control the discharge of the mixed buffer solution from the conduit to the processing device (180).

6. The aforementioned controller, Based on the signal from the control sensor configuration or the monitoring sensor configuration, the pH level of the mixed buffer solution is evaluated. Based on the evaluated pH level, the operation of the discharge valve configuration is controlled. The system (10) according to claim 5, configured as described above.

7. The system (10) according to any one of claims 1 to 6, further comprising a sample inlet (150) that is fluidly connected to the conduit and configured to supply a sample to the conduit.

8. The system (10) according to claim 7, wherein the sample inlet is located downstream of the control sensor configuration.

9. The system (10) according to any one of claims 1 to 8, wherein the first sensor type is different from the second sensor type.

10. The system (10) according to claim 9, wherein each of the first and second sensor types comprises a reference junction membrane (210) arranged to form a selective barrier to the mixed buffer, the average pore size of the reference junction membrane of the first sensor type being smaller than the average pore size of the reference junction membrane of the second sensor type.

11. The system (10) according to claim 10, wherein the average pore diameter of the reference junction of the first sensor type is 0.5 μm or less, such as 0.2 μm or less, and the average pore diameter of the reference junction of the second sensor type is 1 μm or more, such as 5 μm or more.

12. The first sensor type is a system (10) according to any one of claims 1 to 11, comprising a pressurized reference electrolyte (220).

13. The system (10) according to any one of claims 1 to 12, comprising a mechanism operable to bypass the second pH sensor (132) in order to enable a clean-in-place (CIP) function to be provided.

14. A method (300) for providing a mixed buffer solution in a conduit, Using a supply configuration, supply at least one of the first buffering substance, the second buffering substance, or the salt substance to the conduit (310), thereby forming the mixed buffer solution; Step (320) of controlling the flow of the mixed buffer solution to selectively bypass at least one of the first pH sensor and the second pH sensor of the control sensor configuration, wherein the first pH sensor is a first sensor type sensor and the second pH sensor is a second sensor type sensor. The control sensor configuration includes the step (330) of receiving a signal indicating the pH level of the mixed buffer downstream of the supply configuration, Step (340) to control the operation of the supply configuration based on the received signal, Method (300), including the method (300).

15. The step of controlling the operation of the supply configuration is: The steps include: (341) calculating the pH level of the mixed buffer based on the received signal; The steps include determining the difference between the calculated pH level and a predetermined pH level (342), (343) A step of providing a relative mixing ratio of the first buffering material and the second buffering material based on the determined difference. The method according to claim 14 (300), including the method according to claim 14.

16. In response to the mixed buffer having a conductivity of less than 5 mS / cm, such as 2 mS / cm or less, the first pH sensor is bypassed (351), Step (352) of high-passing the second pH sensor in response to the supply of the salt substance to the mixed buffer solution The method according to claim 14 or 15 (300), including the method according to claim 14 or 15.

17. The monitoring sensor configuration includes the step (361) of receiving a monitoring signal indicating the pH level of the mixed buffer solution, The steps include determining that the pH level is within a predetermined range (362), The step (363) of releasing the mixed buffer from the conduit and The method according to any one of claims 14 to 16, further comprising (300).

18. The step of bypassing the second pH sensor (132), Steps to provide a clean-in-place (CIP) system and The method according to any one of claims 14 to 17, further comprising (300).

19. The method according to claim 18 (300), wherein the CIP step is provided by supplying a CIP solution containing a sodium hydroxide solution.

20. The method according to claim 19 (300), wherein the sodium hydroxide solution has a concentration of about 0.5 M, about 1.0 M, or from about 0.5 M to about 1.0 M.

21. The method according to any one of claims 14 to 20 (300), wherein the first buffering substance is an acid, the second buffering substance is a base, and the salt substance is NaCl.

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