A nonvolatile acid (also known as a fixed acid or metabolic acid) is an acid produced from sources other than carbon dioxide, and is not excreted by the lungs. They are produced from e.g. an
incomplete metabolism of carbohydrates, fats, and proteins. All acids produced in the body are nonvolatile except carbonic acid, which is the sole volatile acid. Common nonvolatile acids in humans are lactic acid, phosphoric acid, sulfuric acid, acetoacetic acid, and beta-hydroxybutyric acid.
nonvolatile metabolic acids