pHgradienter

A pHgradienter is a laboratory device or system designed to establish and maintain a spatial gradient of hydrogen ion concentration within a liquid sample. It is used to study processes and reactions that depend on changes in pH across a defined region.

Principle and implementations. In microfluidic versions, the gradient is produced by flowing two or more buffered solutions of different pH side-by-side in a channel, creating a laminar interface where diffusion generates a gradual pH change along the length of the channel. Gel-based or solid-state implementations form gradients by diffusion through a porous matrix or by sequential exposure to buffers with distinct pH values. The gradient can be static, defined by fixed reservoir conditions, or dynamically tunable by adjusting flow rates, buffer composition, or pump settings.

Operation and measurement. Gradient mapping typically relies on pH-sensitive indicators or embedded pH sensors that report the pH at various positions along the gradient. In static systems, measurements are taken after equilibration; in dynamic systems, continuous or time-lapse monitoring may be used to track changes in real time.

Applications. The pHgradienter is used for calibrating pH sensors, studying pH-dependent enzyme activity and stability, investigating transport phenomena under varying proton concentration, and performing cellular assays where cells experience a controlled pH gradient. It also supports materials research related to proton conductivity and buffer optimization for analytical workflows.

Design considerations and limitations. Key factors include chemical compatibility with acids and bases, control of diffusion-driven blur, temperature stability, ease of sampling and measurement, and sterility for biological work. Limitations include gradient instability due to diffusion, edge effects at channel boundaries, and potential shear stress in flow-based systems.