High-pressure single-use electrochemical analytical sensor

Abstract

A single-use electrochemical analytical sensor (200) is provided. The sensor (200) includes a detection electrode (224) configured to contact a process fluid and a comparison chamber (260, 202) containing an electrolyte. A reference electrode (225) is disposed within the electrolyte. A reference junction (258) is configured to contact the process fluid and further configured to generate a flow of electrolyte within the process fluid. The comparison chamber (260, 202) is configured to be stored at reduced pressure and to be pressurized prior to operation. A method (400) of operating a single-use electrochemical sensor is also provided.

Description

[Technical Field]

[0001] background Over the past two decades, single-use or disposable bioprocessing systems have gained significant momentum to replace stainless steel systems in biopharmaceutical manufacturing. In contrast to traditional systems constructed with stainless steel equipment, single-use systems rely on highly engineered polymeric compounds and are pre-sterilized by gamma irradiation. For end users, they offer several significant advantages, including improved process turnaround time, reduced initial investment, and the elimination of complex processes such as pre-cleaning, sterilization, and validation. As a result, single-use bioprocessing systems are being adopted at an accelerating pace, from early research and development laboratories to large-scale commercial pharmaceutical manufacturing processes.

[0002] pH is a critical process parameter in many biopharmaceutical manufacturing processes. In bioreactor upstream applications, medium culture pH is continuously monitored and controlled within a narrow physiological range; deviations from this ideal pH range can adversely affect viable cell concentration, protein productivity, and quality. Conventional pH sensors used in biopharmaceutical manufacturing are based on electrochemical measurements using a highly pH-sensitive glass electrode and reference electrode. This is a proven and well-established technology in the biotechnology and pharmaceutical industries due to its high reliability, accuracy, and stability.

[0003] However, because conventional pH sensors are designed to fit into conventional stainless steel-style bioreactor systems, they have several significant limitations when used in single-use systems. First, conventional sensors must be sterilized by the end user using autoclave, steam-in-place, or clean-in-place procedures. They are generally not compatible with gamma irradiation sterilization processes, as gamma irradiation can damage sensor components and cause undesirable performance degradation. To ensure sufficient accuracy, conventional pH sensors typically require two-point calibration by the end user before use, which is cumbersome and increases process complexity. Furthermore, conventional pH sensors typically have a shelf life of only one year because the pH-sensing glass deteriorates over time, resulting in a decrease in sensor performance. Unfortunately, in single-use systems, the sensor is mounted in a plastic bioreactor bag as one single assembly, or in a tubing set for downstream applications, which is expected to have a much longer shelf life, so a longer shelf life for the sensor is highly desirable. Summary of the Invention

[0004] overview A single-use electrochemical analytical sensor is provided. The sensor includes a detection electrode configured to contact a process fluid and a comparison chamber containing an electrolyte. A reference electrode is disposed within the electrolyte. A reference junction is configured to contact the process fluid and to generate a flow of electrolyte within the process fluid. The comparison chamber is configured to be stored under reduced pressure and then pressurized prior to operation. A method of operating a single-use electrochemical sensor is also provided. [Brief explanation of the drawings]

[0005] [Figure 1A]FIG. 1 is a schematic showing the storage location of a pH sensor for low-pressure bioreactor applications. [Figure 1B] FIG. 1 is a schematic diagram showing the operating location of a pH sensor for low pressure bioreactor applications. [Figure 2] 1 is a graph showing the decay of pressure in the reference chamber of a pH sensor over time. [Figure 3A] FIG. 1 is a schematic diagram of a pH sensor for downstream applications, according to one embodiment. [Figure 3B] FIG. 1 is a schematic diagram of a pH sensor for downstream applications, according to one embodiment. [Figure 4] FIG. 1 is a flow diagram of a method of operating a single-use electrochemical analytical sensor, according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0006] Figures 1A and 1B are schematic diagrams showing the storage and operating locations, respectively, of a pH sensor for low-pressure (i.e., upstream) bioreactor applications. Single-use device suppliers typically assemble pH sensors into tubing sets and sterilize the assemblies with gamma irradiation. For such sensors, a shelf life of two years is desirable for this assembly, ensuring efficient supply chain management and providing a reasonable shelf life for users. When the reference chamber is pressurized during sensor manufacturing, any loss of fluid within this small, enclosed volume significantly reduces pressure.

[0007] 1A is a schematic diagram showing a storage location for a pH sensor. In the illustrated example, the pH sensor is generally shown in cross section with a distal end 102 configured to engage a process, such as a bioreactor bag, and a proximal end 104 having an electrical connector 106 configured to couple to a meter. One example of the connector 106 is known as a vario-pin connector.

[0008] Some electrochemical analytical sensors are considered amperometric because they produce a current indicative of a process variable, such as pH. Other types of sensors are considered potentiometric because they produce an electrical potential indicative of the process variable. As used herein, electrochemical analytical sensor is intended to include any analytical sensor that has an electrical property that changes with a process variable.

[0009] As shown in FIG. 1A, the sensor 100 is provided in a storage position configuration with the process plunger 108 spaced apart from the locking member 110. When in the storage configuration, the pH-sensing glass electrode 112 is held within a storage chamber 114 filled with a buffer solution. Referring to FIG. 1A, a reference electrode 116 is provided within an electrolyte 118, which is configured to be electrically coupled to the process via a reference junction 120. The sensor 100 is held in the storage position for both storage and for calibration immediately prior to operation. This is because the buffer solution within the storage chamber 114 has a known pH, and the sensor can be calibrated or otherwise characterized by measuring the pH with the electrode 112 and comparing the measurement to the known pH of the buffer solution.

[0010] FIG. 1B is a schematic diagram showing the operating position of pH sensor 100. Comparing FIG. 1B with FIG. 1A shows that process plunger 108 has been slid adjacent locking member 110. This sliding action extends end 122 from sidewall 124, thereby exposing pH glass electrode 112 to process 126. As shown in the figure, process 126 is also exposed to reference junction 120. Thus, sliding from the storage position to the operating position exposes wet storage chamber 114 to process 126. In the configuration shown in FIG. 1B, sensor 100 can be used to detect the pH of process fluids such as bioreaction fluids, cell culture fluids, and mash.

[0011] As shown in Figures 1A and 1B, the illustrated sensor provides wet storage for the pH glass and reference junction through a separate storage chamber and a slide-type sensor assembly that moves axially within the process connector and into the process during startup. The slide-type sensor assembly provides reliable measurements at low process pressures. Note that the sleeve of the process connector remains fixed relative to the process media, and the sensor moves as it is inserted into the process.

[0012] The single-use pH sensor is compatible with gamma irradiation sterilization and can be attached to a single-use bioreactor bag to form a complete assembly. The sensor incorporates its own built-in storage buffer, allowing for one-point standardization using this storage buffer, eliminating the need for two-point calibration by the end user. More importantly, the pH electrode and reference electrode remain moistened and fresh throughout the sensor's storage period, due to their contact with the storage buffer. This wet storage resulted in a long shelf life of two years while maintaining excellent sensor performance, including high accuracy, high sensitivity, and high stability. Rigorous real-time testing using unaged, one-year-aged, and two-year-aged prototypes demonstrated that the sensor maintained a high level of performance without degradation even after two years of storage.

[0013] After the cell culture process is completed in the bioreactor bag, the media is moved to a downstream portion of the process. Here, the media is forced through a filtration stage in small-diameter tubing at high pressures up to 90 pounds per square inch absolute (psi). This high process pressure can cause problems for traditional pH sensors. Traditional glass electrode pH sensors have a reference junction, which is a restricted path connecting the sensor's reference chamber and the electrolyte buffer therein to the process. An example of this junction is a porous ceramic cylinder placed between the reference chamber and the user's process. Another example is a polymer junction. For the sensor to function properly, there must be a flow of positive ions from the sensor's reference chamber to the process fluid.

[0014] Higher process pressures in downstream applications can disrupt this ion flow, resulting in fluctuations or drift in pH measurements. This disruption can be remedied by pressurizing the reference chamber. However, traditional methods of reference pressurization require special factory procedures. Because the reference junction is porous and the reference chamber is pressurized, the pressure decays over time, limiting the sensor's useful shelf life and service life.

[0015] Figure 2 is a graph showing the decay of the pH sensor's comparison pressure over time. More specifically, Figure 2 shows curve-fitted data for the comparison pressure decay of an improved, commercially available sensor (sealed junction, air-filled) using pressure decay data from 60 days to 14 days. The data in Figure 2 has been curve-fitted and extrapolated from -60 days to +180 days. The test data in Figure 2 indicates a maximum possible useful shelf life of six months, assuming the sensor's comparison chamber is initially pressurized to 90 psi and a minimum reference chamber pressure of 30 psi is required for the sensor to function properly. Furthermore, when the sensor is moved to the "working" position, the comparison junction (porous material) becomes an inherent leak point, causing pressure decay during use and limiting its operational lifespan. As discussed above, it is desirable to provide a downstream-compatible, single-use pH sensor with a viable useful shelf life comparable to that of the upstream sensor (2 years).

[0016] FIG. 3A is a schematic diagram of a pH sensor for downstream applications, according to one embodiment. In the illustrated example, the pH sensor 200 includes a comparison chamber 202 that can be pressurized upon installation. This maximizes the useful shelf life of the unit because there is no pressure differential to force the comparison fluid through the comparison junction or seal, and therefore no loss of pressure during storage. Instead, a user-operable mechanism 204 is used to generate the desired pressure within the comparison chamber 202. As an example, during process startup, a piston 206 is depressed or otherwise actuated within a cylinder 208 that is part of or fluidly coupled to the comparison chamber 202 to generate the desired pressure. Force on the piston 206 can be provided by compressing a spring 210, such as a wave spring, to provide a nearly constant pressure over time as the fluid in the secondary comparison chamber 202 is slowly forced through the porous comparison junction. Other types of springs can be used to provide constant pressure, including using the expansion of the reference chamber itself under pressure as the potential energy source, or compressing a gas within the chamber to act as a spring, which not only solves the shelf life problem but can also provide a longer operating life.

[0017] FIG. 3A illustrates a sensor 200 having an electrical connector 220 with multiple electrical contacts 222 therein. The contacts 222 are coupled to sensing elements within the sensor 200, such as a pH glass electrode 224 and a reference electrode 225. Furthermore, if the sensor 200 employs additional sensing elements, such as a temperature sensor and / or a pressure sensor, the contacts 222 facilitate electrical connection to such elements. The connector 220 may include any suitable features that facilitate cooperation with a mating connector, such as an externally threaded region 228. The connector 220 is preferably a sealed electrical connector such that the internal cavity 226 is fluidly isolated from any cable or connector coupled to the connector 220. In one embodiment, the connector 220 is a vario-pin connector. The connector 220 is secured to the sensor 200 by a sleeve 230 that contacts a sidewall 232 with an end 234 of a sidewall 236. Furthermore, the sidewall 236 preferably includes a groove 238 in which an O-ring 240 is disposed. When the sleeve 230 is threaded onto the side wall 232 , the inner surface of the sleeve 230 is sealed against the O-ring 240 .

[0018] Sidewall 236 is attached or otherwise secured to end 242, which includes flange 244 sized to extend beyond and around end 246 of sidewall 248. End 242 is constructed from the same polymeric compound as sidewall 236 and / or sidewall 248 and is attached thereto by any suitable method, including solvent welding, adhesive, ultrasonic welding, etc.

[0019] The sensor 200 also includes an insert 250 that contacts the inner diameter 252 of the sidewall 248 and includes a central bore 254 sized to accommodate the pH electrode 224 along the longitudinal axis of the sensor 200. The insert 250 also includes a sleeve 256 that extends along the length of the pH electrode 224 and through an opening in a reference junction disk 258. The disk 258 may be a porous ceramic disk configured to release a controlled amount of electrolyte over time into the process. However, embodiments may be implemented where the reference junction has other types of physical configurations, such as a small conduit or multiple such conduits.

[0020] The sidewall 248 defines a pair of comparison chambers 260, 202 and a conduit 262 fluidly connecting the primary comparison chamber 260 to the secondary comparison chamber 202. A flowable electrolyte is disposed at least partially within the comparison chambers 260, 202. The electrolyte may be a liquid or gel, but must be capable of flowing to some degree through the comparison junction 258. As shown, pressurizing the secondary comparison chamber 202 also pressurizes the primary comparison chamber 260. This pressurization helps maintain electrolyte flow from the comparison junction as process fluid pressure increases. In the configuration shown in FIG. 3A, the pressure-activated mechanism 204 includes an internal thread that couples to an external thread 264 on the sidewall 248. The pressure-activated mechanism is shown in its resting configuration, with the pistons 206, 266 adjacent the pressure-activated mechanism 204 and positioned substantially within the threads 264.

[0021] FIG. 3B is a schematic diagram of the post-activation configuration of sensor 200. Comparing FIG. 3B with FIG. 3A shows that activation of pressure-activated feature 204 moves pistons 266 and 206 toward electrode 224, thereby reducing the size of secondary comparison chamber 202 and pressurizing primary comparison chamber 260. Furthermore, in the illustrated configuration, both pistons 266 and 206 have moved the same distance. As electrolyte slowly flows out through comparison junction 258, a pressure compensation mechanism, such as spring 210, moves piston 206 away from its fixed, activated position. In this manner, pressure in primary comparison chamber 260 is maintained at a desired level until piston 206 bottoms out against sidewall 248. In one embodiment, sidewall 248, or a portion thereof, is formed from a transparent or translucent material to allow a user to visualize the position of piston 206 to determine the remaining life of pressure compensation provided by the pressure compensation mechanism.

[0022] 3A and 3B show the sensor 200 coupled to a process adapter 280, which is configured to position the sensor's sensing element within the process fluid. In the illustrated example, the process adapter 280 includes an internally threaded sensor port 282 configured to receive the external threads 284 of the sensor 200. The sensor 200 may also include one or more O-rings 286 configured to engage and seal with the process adapter 280. The process adapter 280 is shown as having a clean flange 290 for mating with a corresponding flange, although any suitable coupling mechanism may be used.

[0023] FIG. 4 is a flow diagram of a method for operating a single-use electrochemical analytical sensor, according to one embodiment. Method 400 begins at block 402, where a single-use electrochemical sensor is provided. The sensor can be a pH sensor 404, an ion sensor 406, or other sensor 408 that includes an electrolyte that must be flowed into the process fluid to generate a sensor signal. At block 410, a process coupler is obtained. If the sensor is to be coupled to a downstream single-use process, the process coupler can be process coupler 280 (shown in FIG. 3B). However, the process coupler is generally specific to the process installation and configured to place the sensor in or in suitable proximity to the process fluid to obtain a signal of the process variable. Next, at optional block 412, the sensor and process coupler can be sterilized. This can be done using gamma irradiation 414, X-ray irradiation, or other suitable method 416. The sterilized sensor and / or process coupler can be packaged or otherwise maintained in a sterile state until required for use. If such use is desired, block 418 is executed, in which the sensor is pressurized immediately prior to use. Such pressurization is preferably accomplished via manual operation of a knob or a user-operable pressure-activated mechanism, such as mechanism 204 (shown in FIG. 3B). Finally, in block 420, the pressurized sensor is used to detect the process fluid.

[0024] Thus, as shown in the figures, a sensor and method are provided that facilitates long-term storage because the sensor is not pressurized during storage. The sensor is then pressurized immediately prior to operation to enable accurate and precise operation in a pressurized process fluid environment, such as a downstream process. Furthermore, it is believed that the useful shelf life and product life of a pH sensor can be extended by increasing the viscosity of the reference electrolyte within the device. For example, a thicker reference gel can be used for this purpose. Using a more viscous reference gel can result in a longer service life. Furthermore, the introduction of the reference gel can reduce the internal pressure required for the sensor to operate well under high external process pressures.

[0025] Actuation of the piston can be accomplished in several ways. In one embodiment, a spring is compressed during assembly of the sensor, and the piston is locked in a predetermined position by a mechanism within the cylinder body that does not apply pressure to the system. When the piston cap is rotated 90 degrees, the piston moves out of the retention mechanism, providing the force that generates pressure in the system. Additionally, the actuating piston can be locked in the actuated position by a locking mechanism.

[0026] In another embodiment, the installer pushes or pulls the cap on the piston, while the user rotates the cap 90 degrees and a mechanism on the cylinder body holds the cap in place. Alternatively, the cap can be held in place by a snap-on mechanism without being rotated.

[0027] It should be noted that the pressurization method described herein is not limited to pH sensors, but is generally applicable to other potentiometric ion sensors, including, but not limited to, potassium sensors, sodium sensors, chloride sensors, and fluoride sensors, to name just a few. To the extent that the sensor's reference electrode relies on the diffusion of an internal reference electrolyte through a porous junction material, it can be pressurized using the method described above.

[0028] While the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present invention. For example, while the description provided above illustrates pressurizing the comparison chamber in a particular manner, such pressurization can take a variety of forms. The sensor can include a spring member that is pre-compressed at the factory and released in the field to pressurize the comparison chamber. As another example, an uncompressed spring member can be compressed in the field by pushing it in. As yet another example, an uncompressed spring member can be compressed in the field by pulling it out. As yet another example, an uncompressed spring member can be compressed in the field by a screw member. As another example, an uncompressed spring member can be compressed in the field by pushing it in and twisting it. As another example, an uncompressed spring member can be compressed in the field by pulling it out and twisting it.

Claims

1. 1. A single-use electrochemical analytical sensor, comprising: a sensing electrode configured to contact the process fluid; a comparison chamber containing an electrolyte; a reference electrode disposed within the electrolyte; a comparison junction configured to contact the process fluid, the comparison junction being further configured to generate an electrolyte flow within the process fluid; a pressure actuated mechanism fluidly coupled to the comparison chamber and configured, upon actuation, to generate pressure within the comparison chamber; Including, The pressure actuated mechanism a first movable piston arranged to generate pressure in the comparison chamber as the first movable piston moves; Including, The pressure actuated mechanism a second movable piston spaced apart from the first movable piston by a spring; The single-use electrochemical analytical sensor is configured such that the comparison chamber is pressurized by the pressure actuation mechanism prior to actuation.

2. 10. The single-use electrochemical analytical sensor of claim 1, further comprising an O-ring seal disposed around the first movable piston.

3. 10. The single-use electrochemical analytical sensor of claim 1, further comprising a mechanical latch mechanism that locks the second movable piston in a pressurized position.

4. 10. The single-use electrochemical analytical sensor of claim 1, wherein the spring is configured to operate to move a first movable piston away from a second movable piston as the electrolyte is flowed into the process fluid to maintain pressure within the electrolyte.

5. 5. The single-use electrochemical analytical sensor of claim 4, wherein a sidewall of the single-use electrochemical analytical sensor including the first movable piston is constructed from a material that allows the position of the first movable piston to be seen through the sidewall.

6. 10. The single-use electrochemical analytical sensor of claim 1, wherein the electrolyte is a gel.

7. 10. The single-use electrochemical analytical sensor of claim 1, wherein the comparison chamber is configured to be pressurized up to 90 psi.

8. 2. The single-use electrochemical analytical sensor of claim 1, wherein the detection electrode is a pH glass electrode.

9. 2. The single-use electrochemical analytical sensor of claim 1, wherein the reference liquid junction is a porous disk.

10. 10. The single-use electrochemical analytical sensor of claim 9, wherein the disk is constructed from a material selected from the group consisting of ceramics and polymers.

11. 10. The single-use electrochemical analytical sensor of claim 1, further comprising a downstream flow-through process coupler operably coupled to the single-use electrochemical analytical sensor.

12. 12. The single-use electrochemical analytical sensor of claim 11, wherein at least one of the single-use electrochemical analytical sensor and the process coupler is sterilized.

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