pH Control

• Introduction
• Modeling the Reaction
  • Constant Rate Kinetic Decay
  • Base Addition Rate Dependent
• Control
  • Smart Dose Addition (On/Off)
  • Base Addition Rate Dependent (PID)
• Hardware
• Try It Out
• Simulated Model Module

Introduction

Controlling pH is crucial in many laboratory workflows as numerous reactions are sensitive to pH changes. This pH Control & Monitoring Library provides a comprehensive solution for implementing pH control in reactions using peristaltic pumps and pH probes. The library was originally developed for the methacrylation of hyaluronic acid (HA), a specific reaction where the pH needs to be precisely regulated to drive the reaction forward. During the methacrylation of HA, methacrylic anhydride (MA) is added to an aqueous HA solution, causing a decrease in pH. To maintain the optimal pH level, a base, usually NaOH, needs to be continuously added as the reaction progresses.

For more information on the reaction and applications of hyaluronic acid, please refer to the following references:

• Schuurmans, Carl CL, et al. "Hyaluronic acid and chondroitin sulfate (meth) acrylate-based hydrogels for tissue engineering: Synthesis, characteristics and pre-clinical evaluation." Biomaterials 268 (2021): 120602.

• Tsanaktsidou, Evgenia, Olga Kammona, and Costas Kiparissides. "On the synthesis and characterization of biofunctional hyaluronic acid based injectable hydrogels for the repair of cartilage lesions." European Polymer Journal 114 (2019): 47-56.

• Burdick, Jason A., and Glenn D. Prestwich. "Hyaluronic acid hydrogels for biomedical applications." Advanced materials 23.12 (2011): H41-H56.

The kinetics of the reaction evolve with time, necessitating a higher rate of NaOH addition during the initial stages of the reaction.

Control

Smart Dose Addition (On/Off)

The Smart Dose Addition algorithm adds base to the reaction vessel in finite doses when the pH drops below the setpoint value. To calculate the dose volume, the algorithm takes into account the effect of the previous dose (change in pH per added volume) and adjusts the next dose volume to reach the desired setpoint. The algorithm includes a limit on the maximum change in dose volume for consecutive doses.

PID

The PID Control algorithm continuously adds base to the reaction vessel to achieve the target pH setpoint. The rate of base addition is calculated by the PID controller, which constantly evaluates the error (setpoint - current pH value), cumulative error (sum of errors), and rate of change of the error (d_error/dt). The PID controller adjusts the base addition rate based on these parameters to maintain the pH at the desired setpoint.

Hardware

The delivered system included 3 Boxer 9QQ peristaltic pumps and 3 pH electrode analog-to-digital converters. The pumps were mounted on a vertical scaffold to allow them to be positioned close to the reaction flasks inside a fume hood.

The pump chassis allows the 3 peristaltic pumps to be located inside a fume hood close to the reaction flask.

The electronics chassis located outside of the fume hood.

Try It Out

To run the pH control recipe locally in simulation mode:

1. Install the Aqueduct application.

2. Download the Aqueduct examples repository and extract the compressed archive.

3. Navigate to the Library page and upload the /apps/ph_control/ph_control directory from the extracted archive.

4. Navigate to the Dashboard page and upload the necessary .recipe, .setup, and .layout files found in the /apps/ph_control/models directory.

5. Activate the pH - PID control recipe from your Dashboard and navigate to the Sandbox to view the simulated process.