text: ILAC describes the following five types of reference material:
  # Pure substances; essentially pure chemicals, characterised for chemical purity and/or trace impurities.
  # Standard solutions and gas mixtures, often prepared gravimetrically from pure substances.
  # Matrix reference materials, characterised for the composition of specified major, minor or trace chemical constituents. Such materials may be prepared from matrices containing the components of interest, or by preparing synthetic mixtures.
  # Physico-chemical reference materials, characterised for properties such as melting point, viscosity, or optical density.
  # Reference objects or artifacts, characterised for functional properties such as taste, odour, octane number, flash point and hardness. This type also includes microscopy specimens characterised for properties ranging from fibre type to microbiological specimens.