Chemical purity in the context of "Chemical"

In chemistry, substance is a unique form of matter with constant chemical composition and characteristic properties. Chemical substances may take the form of a single element or chemical compounds. If two or more chemical substances can be combined without reacting, they may form a chemical mixture. If a mixture is separated to isolate one chemical substance to a desired degree, the resulting substance is said to be chemically pure.

Chemical substances can exist in several different physical states or phases (e.g. solids, liquids, gases, or plasma) without changing their chemical composition. Substances transition between these phases of matter in response to changes in temperature or pressure. Some chemical substances can be combined or converted into new substances by means of chemical reactions. Chemicals that do not possess this ability are said to be inert.

In chemistry, work-up refers to the series of manipulations required to isolate and purify the product(s) of a chemical reaction. The term is used colloquially to refer to these manipulations, which may include:

• deactivating any unreacted reagents by quenching a reaction.
• cooling the reaction mixture or adding an antisolvent to induce precipitation, and collecting or removing the solids by filtration, decantation, or centrifugation.
• changing the protonation state of the products or impurities by adding an acid or base.
• separating the reaction mixture into organic and aqueous layers by liquid-liquid extraction.
• removal of solvents by evaporation.
• purification by chromatography, distillation or recrystallization.

The work-up steps required for a given chemical reaction may require one or more of these manipulations. Work-up steps are not always explicitly shown in reaction schemes. Written experimental procedures will describe work-up steps but will usually not formally refer to them as a work-up.

Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula PH₃, classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting fish, due to the presence of substituted phosphine and diphosphane (P₂H₄). With traces of P₂H₄ present, PH₃ is spontaneously flammable in air (pyrophoric), burning with a luminous flame. Phosphine is a highly toxic respiratory poison, and is immediately dangerous to life or health at 50 ppm. Phosphine has a trigonal pyramidal structure.

Reagent Chemicals is a publication of the American Chemical Society (ACS) Committee on Analytical Reagents, detailing standards of purity for over four hundred of the most widely used chemicals in laboratory analyses and chemical research. Chemicals that meet this standard may be sold as "ACS Reagent Grade" materials.

Reagent standards relieve chemists of concern over chemical purity. "ACS Reagent Grade", is regarded as a gold standard measure and is in some cases required for use in chemical manufacturing, usually where stringent quality specifications and a purity of equal to or greater than 95% are required. The American Chemical Society does not validate the purity of chemicals sold with this designation, but it relies on suppliers, acting in their self-interest, to meet these standards. In practice, the reliability of supplier stated purity is at times questionable.