Production of In-Specification Buffer on Demand for Batch Processes – Allegro™ Connect Buffer Management System

Introduction
The Allegro Connect buffer management system (BMS) has the capacity to dilute in-line up to six different buffer concentrates, in-specification and on-demand for connected downstream process (DSP) operations. The system is used and connected in a one-to-one fashion with any DSP unit and works via process buffer level control to initiate or stop buffer production as needed. For automated control, the Allegro Connect BMS can operate either as a stand-alone unit or as a slave to a compatible DSP system (master unit). The in-line dilution of each concentrate is controlled via a proportional–integral–derivative (PID) controller utilizing buffer conductivity measurement to adjust the concentrate pump flow rate as necessary, enabling the dilution to remain within a given tolerance. Additionally, continuous in-line buffer pH measurement is taken to confirm the correct buffer is being produced.
In-line dilution conductivity and pH performance data generated from a typical application test with the Allegro Connect BMS is presented here to show the capability to successfully produce process buffers within the acceptable tolerances. This was completed using both constant speed and level control automated in-line dilution at dilution factors ranging from 5x to 20x.

Buffer Production for Batch Processes
The Allegro Connect BMS hardware and single-use system was installed and operated as per the instructions for use (Pall document reference number USD 3416). The system was set up for the in-line dilution of the maximum number of six concentrates (i.e. two stock and two process solution workstations), at dilution factors ranging from 5x to 20x. See Table 1 for the stock and process buffers studied and Table 2 for the control parameters used for in-line buffer dilution.


The in-line dilution of buffer concentrates can proceed in 2 modes, either in constant speed or level control:

• Constant speed: The buffer concentrate is diluted at the maximum speed based on the dilution factor. The processing phase is named ‘Cycle Fill’ and is used for DSP operations which have multiple, simultaneous buffer draws or low flow singular draws.
• Level control: The buffer concentrate is diluted at a controlled speed to match the draw rate, therefore maintaining a consistent buffer volume/ level within the process bag. This processing phase is named ‘Draw Fill’ and is used for DSP operations which have sequential long buffer draws.

Buffer Stabilization Prior to Filling
For in-line diluted process buffers to start filling the relevant process biocontainer, the buffer dilution must first be ‘stabilized’. A buffer dilution is considered stable when the conductivity and pH sensors read within specification for a default time of 10 seconds (editable in the recipe). On average, over all six process buffers studied, the Allegro Connect BMS took 40 seconds to stabilize and start filling a process biocontainer. Once within specification the PID control ensures the dilution remains within, or is quickly corrected to within, the conductivity tolerance. Deviations outside of conductivity or pH specifications will cause the diluted buffer to divert to drain if measurements remain outside of tolerance for a default of 10 seconds (editable in the recipe). After drain diversion, the system will re-stabilize the buffer dilution, then reinitiate biocontainer filling. This ensures only correctly produced buffers are accepted into process biocontainers for DSP use.
Figures 2 and 3 show the conductivity and pH buffer stabilizations of a Tris-based buffer over the first 2 minutes of triplicate constant speed runs at approximately 1360 and 1450 L/h for 20x and 10x dilutions, respectively.

Dilution flow rates are approximated as this varies based on the PID control of the concentrate pump via conductivity measurement. For the 20x and 10x Tris buffer concentrates presented here, it took 21 to 41 seconds to initially stabilize the buffer and 31 to 51 seconds to fill the biocontainer (range maxima shown on each figure). For both conductivity and pH measurements, once the in-line dilution was stable, measurements remained within specification with only slight deviations of ≤2 seconds for both triplicate data sets, showing good repeatability of buffer stabilization. These deviations were only noted for 20x dilutions due to the low concentrate flow rate, compared to 10x and 5x dilutions which remained fully within tolerance poststabilization. Constant speed stabilization times for all six buffers, over six replicate buffer stabilizations, can be seen in Table 3. All concentrates studied over the 5x to 20x dilution range were successfully diluted and stabilized within 60 seconds, therefore minimizing any process buffer wastage due to stabilization.

Buffer Stability During Constant Speed Filling
The first processing mode of buffer dilution is constant speed. This is controlled via a re-fill set-point, in which the Allegro Connect BMS will initiate buffer concentrate dilution up to the process biocontainer volumetric level set-point and then flush the flow path to avoid buffer contamination. This is run at the maximum achievable flow rate for the set dilution factor, ensuring quick, successive, buffer concentrate dilutions are completed to maintain volumes of process buffers at levels suitable for the connected DSP. The processing phase which utilizes this automated set-up is the cycle fill phase.
Figures 4 and 5 show the conductivity and pH measurement of a glycine-based buffer during triplicate cycle biocontainer fill runs at approximately 1450 and 1080 L/h for 10x and 5x dilutions, respectively. During each cycle, each process biocontainer was filled from 30 L ± 5 L up to 90 L ± 5 L based on the level sensor measurement. Both the conductivity and pH measurements remained within the acceptable tolerances of ± 5% and 0.15, respectively, for each full biocontainer fill for both 5x and 10x dilutions.

The average conductivity and pH deviations for all six process buffers studied can be seen in Table 4. All six process buffers studied remained within tolerance for both measurement parameters over the six repeated fills, within ± 1.4% and ± 0.12 for conductivity and pH, respectively. Hence, results confirm repeatable, accurate in-line dilutions of process buffers are achievable utilizing the Allegro Connect BMS at constant, maximum dilution speeds.

Buffer Stability During Level Control Filling
The second processing mode of buffer dilution is process buffer level control. This is controlled via a ‘deadband’ around the volumetric set-point. Once the process biocontainer level is below the low dead-band, the Allegro Connect BMS will initiate buffer dilution at the maximum allowable flow rate for the set dilution factor and fill the process biocontainer up to the set-point. Once the set-point is reached, the Allegro Connect BMS will adjust the flow rate until the draw rate is matched; this is the main stage of in-line dilution. When the DSP draw ends and the volume level in the process biocontainer starts to increase, the system reduces to the lowest achievable flow rate (~400 L/h), fills the process biocontainer up to the high dead-band level, stops buffer production and flushes the flow path. The processing phase is named ‘Draw Fill’ and is used for DSP where one process buffer is expected to be drawn at once (e.g. tangential flow filtration, diafiltration), therefore minimizing buffer wastage through re-stabilization post-biocontainer fill, as per cycle fill.
Figures 6 and 7 show the conductivity and pH measurement of a sodium phosphate-based buffer during a DSP draw (simulated via a pump downstream) at 1200 L/h for 1 hour and 1000 L/h for 30 minutes for 20x and 5x dilutions, respectively. For 5x dilution conductivity and pH measurements and 20x dilution pH measurements, all remained within specification for the full run. However, 20x dilution conductivity measurements showed deviations outside of the acceptable tolerance which caused the dilution to divert to drain 3 times, see asterisks on Figure 6 and 7.

Biocontainer fill reinitiated once the buffer re-stabilized (<60 s). Overall 3 buffer concentrates were assessed at 400, 1200 and 1000 L/h simulated draw rates and the average conductivity and pH measurements can be seen in Table 5. All measurements were within tolerance, where the conductivity and pH were within ± 0.37 % and ± 0.05 of the set-points, respectively. This shows the 20x dilution deviations seen did not affect the overall process buffer conductivity measurement, which is reaffirmed in Section 2.4 as all off-line samples taken from each process buffer were within specification.

Offline Sampling of Process Buffers
Samples were taken from each process bag to measure buffer pH and conductivity throughout the full set of application tests to confirm the Allegro Connect BMS in-line measurements were accurate. The number of samples taken for each buffer was dependent on the number of tests each buffer was incorporated into.
For each full process biocontainer produced when running in constant speed, a sample of ~1 L was taken for each process buffer studied and measured off-line using the same in-line BMS probe technology (Hamilton♦ RU Conducell♦ conductivity probe and Hamilton OneFerm♦ SU pH probe). For each level control run completed one sample of ~1 L was taken at the start, middle and the end of each simulated draw and measured offline as described above. The summary of data for each process buffer studied can be seen in Table 6. All six process buffers studied over ≥ 3 stock batches, measured offline conductivity and pH comparably to the in-line BMS measurements within the recipe specified tolerances of ± 5% and ± 0.15, respectively. Therefore, taking into account both the in-line and offline measurements, it can be confidently summarized that the Allegro Connect BMS is capable of quickly and effectively delivering in-specification, on-demand process buffers for batch purposes.

Conclusion
The Allegro Connect buffer management system is suitable for in-line buffer dilution for dilution factors from 5x to 20x and can produce in-specification and on-demand process buffer within the conductivity tolerance of ± 5% and pH set-point ± 0.15. In terms of batch processes, this system can stabilize buffer dilutions within 60 seconds prior to biocontainer fill and can support single buffer draws up to 1200 L/h for dilution factors from 10x to 20x and up to 1000 L/h for 5x dilution factors.

Frequently Asked Questions
What Upfront Work is Required to Successfully Utilize the Allegro Connect Buffer Management System?
You will need to optimize the buffer concentrate production to achieve the desired process buffer after dilution, thereby determining buffer set-points and tolerances for both conductivity and pH. Specifically, the concentrate pH must be optimized in a such a way that upon the selected dilution, the resulting pH value always falls within the specified tolerance band (Note: The Allegro Connect BMS measures pH and uses it as one of the criteria for in-specification buffer but it does not control via pH measurement).

Can I Run the System Outside of an Automated Recipe?
Yes, the Allegro Connect buffer management system can be run in a fully manual mode utilizing a process engineer or admin login through the main ‘Process’ tab on the HMI.
Can I Check the Conductivity and pH of the Buffer Concentrates Using the Allegro Connect Buffer Management System?
Yes, the concentrate conductivity and pH can be assessed during an automated concentrate sampling phase. This also acts as a check for flow path connection errors. There is a comparable connector-error check on the process buffer side during the first set of biocontainer fills in the ‘Max Fill’ phase.

Can I Check the Average Conductivity and pH for Each Buffer Diluted Using this System During Biocontainer Filling?
Yes, the batch report can be customized to provide any graphs or data desired by the customer. Additionally, all sensor data can be exported in an Excel♦ format from the Allegro Connect buffer management system via a USB or directly onto a connected network.

Can I Take an Offline Sample from the Process Buffer Biocontainers During Production?
Yes, samples from any of the 100 L 2D biocontainers can be completed by connecting a sampling bag to the luer connection on the top-face of the biocontainer.

Can I Produce Process Buffers Aseptically?
Yes, there is an optional filter cart (P/N: ACBMSFT or ACBMSFTWH) which can be used to filter process buffer dilutions prior to biocontainer fill using a Kleenpak™ Nova NP6 single-use capsules with Supor® EKV 0.2 μm media. This filter cart can accommodate up to six capsules to allow filtration of up to six process buffers. All biocontainers and extension tubing connected downstream of these filters are available with sterile connectors and disconnectors (Kleenpak® Presto sterile connectors and Kleenpak sterile disconnectors).

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The information provided in this literature was reviewed for accuracy at the time of publication. Product data may be subject to change without notice. For current information consult your local Pall distributor or contact Pall directly.

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