Sulfur-33 is an isotope of sulfur with an atomic mass of 34. It has an atomic spin of 3/2. This isotope is naturally occurring. There are 25 known isotopes of sulfur. They are used in nuclear isotopes, radioisotopes, and medical applications. The isotopic compositions of sulfur have been studied to identify pollution sources.
Sulfur is present in the atmosphere in the form of sulfate and other dissolved compounds. It is also present in gases and in solids. In addition, it is incorporated into the structures of proteins, steroid hormones, and polysaccharides. It is a vital element to all living organisms. As such, its isotopic composition is important for understanding how organisms metabolize it.
The biogeochemical cycle of sulfur requires accurate measurements. This is critical in distinguishing between mass-dependent and mass-independent fractionation processes. While sulfur is a very abundant element in the environment, its atomic mass is relatively low. Consequently, its natural abundance is only a few milligrams per kilogram of dry matter. For this reason, it is necessary to use a reference material that is enriched in 33S.
To achieve this, the Canyon Diablo meteorite sample was used as the original reference standard. Sulfur-33 is the primary isotope. Other sulfur reference materials are often used for comparability and consistency.
A working standard is necessary for the proper normalization of data. Several international sulfur reference materials are available for this purpose. Some of these include: IAEA-S-1, S-MIF-1, and S-MIF-2. Using S-MIF-1 or S-MIF-2, D33S values can be measured and used for reporting purposes.