pH prediction and control in bioprocesses using mid-infrared spectroscopy

Area of Science:

• Biotechnology
• Analytical Chemistry
• Spectroscopy

Background:

• Traditional pH monitoring in bioprocesses often requires invasive probes or chemical indicators.
• Developing non-invasive methods is crucial for maintaining bioprocess integrity and efficiency.

Purpose of the Study:

• To present a novel on-line pH monitoring method using mid-infrared (MIR) spectroscopy for bioprocess applications.
• To demonstrate the non-invasive nature and accuracy of MIR spectroscopy for pH determination in cell cultures.

Main Methods:

• Utilized mid-infrared spectroscopy to analyze buffer species (e.g., phosphate buffer) in solutions across a wide pH range (2-12).
• Applied linear combination analysis of molar absorbance spectra of acid and deprotonated forms.
• Incorporated Debye-Hückel theory to account for non-ideal solution behavior and estimate activity coefficients for accurate pH prediction.
• Validated the method using batch cultures of Escherichia coli (E. coli).

Main Results:

• Spectra analysis accurately predicted pH with a standard error of less than 0.15 pH units.
• The MIR spectroscopic pH prediction showed a discrepancy of less than 0.12 pH units compared to conventional electrochemical probes.
• The method proved sufficiently fast for implementing feedback control for stable pH maintenance during cultivation.

Conclusions:

• Mid-infrared spectroscopy offers a viable, non-invasive alternative for on-line pH monitoring in bioprocesses.
• The developed spectroscopic method provides accurate and rapid pH measurements, suitable for process control.
• This technique eliminates the need for chemical indicators or invasive probes, simplifying bioprocess monitoring.