In analytical chemistry, an isotopic standard is a reference material used to calibrate instruments for isotopic analysis. It is a sample of known isotopic composition that can be used to compare the isotopic composition of an unknown sample. Isotopic standards are typically certified by a recognized standards organization, such as the International Atomic Energy Agency (IAEA) or the National Institute of Standards and Technology (NIST).

Isotopic standards are used in a variety of applications, including:

* Environmental science: to study the sources and transport of pollutants

* Archaeology: to date artifacts and determine their provenance

* Geology: to study the history of the Earth and its climate

* Astrophysics: to study the origin and evolution of stars and galaxies

* Nuclear science: to develop and test nuclear weapons

There are many different types of isotopic standards, each with its own unique composition and purpose. Some of the most common isotopic standards include:

* Carbon-13: used to study the cycling of carbon in the environment

* Nitrogen-15: used to study the cycling of nitrogen in the environment

* Oxygen-18: used to study the history of climate change

* Lead-206: used to date rocks and minerals

* Uranium-238: used to date the Earth and its solar system

Isotopic standards are an essential tool for scientists who study the properties and behavior of isotopes. They provide a reliable and accurate way to compare the isotopic composition of different samples and to gain insights into the natural world.