impure

Impure is an adjective describing a substance or thing that is not pure—containing one or more substances different from its intended or primary composition. A pure substance has a definite chemical composition and uniform properties throughout; an impure substance contains impurities, which may be present as trace residues or as significant contaminants.

In science and engineering, purity is a central quality. Impurities can originate during synthesis, processing, storage, or environmental exposure. Purity is often quantified as a percentage or by listing the main component and detected impurities; analytical techniques such as chromatography, mass spectrometry, and spectroscopy are used to identify and measure them. Impurities influence physical properties like melting and boiling points, solubility, color, odor, and reactivity, and they can affect performance in applications.

Applications place strict limits on impurities. In pharmaceuticals, impurity profiles must meet regulatory standards because some impurities may be toxic or mutagenic; guidelines from regulatory bodies establish acceptable levels and testing methods. In electronics, metallic or dielectric impurities affect conductivity and device reliability. In metals and alloys, impurities alter hardness, ductility, corrosion resistance, and fatigue performance. In water and air, impurities influence safety, taste, odor, and environmental impact; water treatment targets removal of minerals, organic matter, and microorganisms. In semiconductors, controlled impurities—dopants—are introduced deliberately to modify electrical properties.

In moral or cultural contexts, the term is used metaphorically to describe tainting of character or ritual cleanliness, with “impure” referring to thoughts, motives, or actions considered unclean or improper.