By Karolina Busson, Joanne Sheehy, Liz Anderson, Therese Westman, and Enrique Carredano
Volume 25, Open Access (January 2026)
In biopharmaceutical manufacturing, buffer preparation is traditionally performed manually by dissolving solid salts in water for injection (WFI) followed by offline mixing and specification testing. This method requires large buffer volumes, extensive infrastructure, and significant labor, often creating bottlenecks in production. To address these limitations and support process intensification, inline buffer preparation technologies have emerged.
Inline dilution (ILD) involves diluting concentrated buffers with WFI at the point of use. Inline conditioning (IC) advances this concept by blending single-component stock solutions of acid, base, and salt with WFI, enabling flexible, on-demand buffer formulation. IC also allows real-time adjustment of buffer properties such as pH, conductivity, and concentration through multiple feedback control mechanisms.
A critical requirement for IC is robust and accurate inline pH measurement, which remains challenging due to limitations in conventional pH sensor designs. Issues such as salt memory, a temporary bias caused by ion diffusion across the reference junction, and sensor drift, from exposure to sodium hydroxide or pure water, can compromise measurement reliability. The effects of sodium hydroxide are particularly pronounced during the chromatography runs where concentrated sodium hydroxide solutions are used to clean the chromatography column. Ideally, pH probes should remain in the system throughout these steps while the current recommendation is to take them out of the system.
To mitigate these effects, sensor manufacturers have introduced design enhancements including ion traps, pressurized potassium chloride reservoirs, and varied junction pore sizes. In this study, we evaluated several pH sensor types under conditions typical of chromatography applications. Sensors with pressurized potassium chloride demonstrated strong resistance to salt memory and sodium hydroxide exposure but showed reduced performance in low-conductivity buffers under dynamic flow and pressure.
Based on these findings, we propose a dual-sensor module: one sensor used for salt-free buffers, another for buffers containing sodium chloride and with the capability to be exposed to hydroxide during column cleaning-in-place (CIP). This configuration enables uninterrupted and inline pH monitoring, and continuous buffer release in line with a process analytical technology (PAT) approach, enhancing efficiency, sustainability, and cost-effectiveness in buffer preparation…
Citation: Busson, K.; Sheehy, J.; Anderson, L.; Westman, T.; Carredano, E. Maximizing performance of pH measurements for inline conditioning buffer preparation for chromatography. BioProcessing Journal 2026, 25. https://doi.org/10.12665/J24OA-Carredano
Posted online January 30, 2026