Current GMP requirements (5) should be observed. The various stages in packaging chemical reference substances should be clearly defined and controlled, to avoid contamination of the sample, mislabelling of containers, or any other event which might result in mishandling or mismanagement.

Containers for chemical reference substances should protect their contents from moisture, light and oxygen and must be tested for moisture permeability. Additional measures may be necessary to ensure long-term integrity and stability. The best containers for chemical reference substances from the point of view of stability are sealed glass ampoules, but these have certain disadvantages. There is the risk of contaminating the substance with glass particles when the ampoules are opened, and reclosure is difficult. Sealable glass ampoules are therefore principally used for substances that must be kept in an oxygen-free atmosphere. Certain other substances may require even more elaborate protection. Most chemical reference substances, however, are conveniently supplied in reclosable containers which should be uniform in type and size to facilitate distribution. The lack of permeability to moisture is an important factor in determining the suitability of container closure systems.

Before undertaking any packaging operations, the health hazards of the item to be packaged should be assessed through information sources, e.g. the Material Safety Data Sheet. Appropriate precautions should be taken to protect the person handling the chemical reference substance.

The packaging of a batch of a chemical reference substance into containers is a small-scale operation for which suitable equipment is not always available to the manufacturer of the material. Therefore, the packaging of chemical reference substances is usually undertaken by the responsible issuing body. Screw-type feeders have been constructed, but generally the packaging of chemical reference substances is carried out manually. Substances which are expensive or only available in very small quantities may have to be divided between containers in solution and then lyophilized, or evaporated to dryness.

Some chemical reference substances must be packaged under an inert gas or in, conditions of controlled humidity. Therefore, the use of a glove-box or an air-tight cabinet is necessary.