pH adjustment is the controlled addition of an acid or an alkali to bring a product to a target pH. It is one of the most common finishing steps in liquid chemical manufacturing, and one of the most common reasons a batch is held before release.
pH matters for more than specification compliance. It affects product stability, since many formulations degrade outside a particular range; it affects performance, as the activity of preservatives, surfactants and many actives is pH-dependent; and it affects safety and handling, because a product at an extreme pH may be classified as corrosive with consequences for labelling, packaging and transport.
In practice adjustment is done incrementally with mixing and measurement between additions, because pH does not respond linearly - near the target, a small addition can produce a large swing. Adding too much of a correcting agent then requires adding the opposite, which loads the product with salt and may push it out of specification in other respects.
The pH scale is logarithmic, so each unit represents a tenfold change in acidity - a point worth remembering when a specification tolerance looks generous. Buffered formulations resist pH change and are used where stability over shelf life matters. See acids and alkalis.
Set a pH range in the specification rather than a single target figure, and confirm at what temperature it is measured. A single-point specification is effectively unachievable in production and leads to batches being needlessly reworked.
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Last reviewed: August 2026. Regulation and guidance change — verify anything you rely on against the primary source. Tell us if something here is out of date.
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