Hydrogen potential, or pH, is a measure of the chemical activity of hydrons (also known as protons or hydrogen ions) in solution. In particular, in aqueous solution, these ions are present in the form of the hydronium ion (the simplest of the oxonium ions).
More commonly, pH measures the acidity or basicity of a solution. Thus, in an aqueous medium at 25°C :
- a solution with pH = 7 is said to be neutral;
- a solution with pH < 7 is said to be acidic; the lower its pH, the more acidic it is;
- a solution with pH > 7 is said to be basic; the higher its pH, the more basic it is.
The pH plays a fundamental role in cell physiology, with each cell compartment having its own H+ potential. In general, the average pH is between 7 and 7.4, which is why the buffers used in electron microscopy are close to 7.4.
So adjust the pH of your buffers and fixative buffers to the cell compartments you’re studying, or if you’re interested in cell ultrastructure, adjust your pH to 7.2 or 7.4.