pHGradient

A pHgradient, or pH gradient, is a spatial variation in pH across a medium, resulting from differing hydrogen ion concentrations. Such gradients can be static or dynamic and occur in solutions, gels, microfluidic devices, and biological systems. They influence chemical equilibria, binding interactions, and the charge state of acids, bases, and proteins.

In laboratory settings, pH gradients are created by sequencing buffers with progressively different pH values, or by using ampholytes that form a continuous pH spectrum in an electric field. Immobilized pH gradients (IPG) are produced by embedding buffering groups with defined pKa values into a gel or membrane, yielding a fixed pH profile. Microfluidic and capillary systems can generate gradients by laminar flow of streams at different pH or by electrokinetic methods that continuously shift pH along the channel.

Measurement and characteristics: gradient shape can be linear or nonlinear and is described by its pH range (for example, pH 3–10). pH is typically measured with microelectrodes or pH-sensitive dyes; imaging methods and fluorescence probes enable spatial mapping of pH in small devices or gels.

Applications: isoelectric focusing uses a pH gradient to separate proteins by their isoelectric points. pH gradients also serve in chromatographic or electrophoretic separations, enzyme assays, and studies of proton transport. In biology, natural pH gradients exist across organelles and membranes, where proton pumping creates ΔpH that contributes to energy metabolism.