About Isotopes

Isotopes are variants of chemical elements: while all isotopes of a given element contain the same number of protons, they vary in the number of neutrons they contain. Variation in neutron number produces chemically identical atoms with different masses, which can be exploited to allow tracing of specific individual atoms through a system.

Stable isotopes

Stable isotopes are generally defined as non-radioactive isotopic elements that do not decay over time. Radioactive isotopes may also be classified as stable isotopes when their half-lives are too long to be measured. These elements can often be found to occur in nature and include isotopes of carbon, nitrogen, hydrogen, oxygen, noble gases and metals. For example, three naturally occurring isotopes of hydrogen include protium (H) having one neutron, deuterium (2H) having two neutrons, and tritium having three neutrons.

Isotopically labeled compounds

Isotopically labelled compounds are compounds that incorporate isotopic elements within their molecular structure and are thus "labelled" by the isotope. These compounds are used to study chemical and biochemical reactions, metabolic pathways or cellular transport. Specifically, isotope-labelled compounds are routinely used for a variety of applications including magnetic resonance imaging (MRI), spectroscopy, nuclear magnetic resonance (NMR), and geochemical analyses. An example of using an isotopic label includes replacing the most common isotope of hydrogen, protium, with deuterium to observe hydrogen exchange reactions in water.

Isotope separation methods

Distillation and Diffusion Processes

Distillation or diffusion are processes which are for enrichment used when there are relatively large mass differences between different isotopes of an element.

Centrifuge enrichment

Centrifuge processes for enrichment includes gas centrifugation and improvements upon the gas centrifuge techniques. This process involves rotating cylinders in order to move the heavier gas molecules containing a given isotope to the outer radius of the cylinder while collecting the lighter gas molecules containing the given isotope in the center of the cylinder.

Electromagnetic enrichment

Electromagnetic isotope separation processes involves first vaporizing the isotope containing molecules followed by ionizing the vapor with positively charged ions. A mass spectrometer, known as the Calutron, is then used to redirect a stream of cations onto a target for collection.

Other methods: laser enrichment, photochemical enrichment and plasma separation

Laser enrichment processes provide for lower energy inputs and thus more economical enrichment. One method currently under investigation is known as the Separation of Isotopes by Laser Excitiation (SILEX). Another laser method that is used to enrich uranium containing the 235U atom is known as molecular laser isotope separation (MLIS) which involves using infrared laser at UF6 molecules and a second laser to free a fluorine atom resulting in precipitation of the remaining UF5 compound out of the gas.

Plasma separation involves the principle of ion cyclotron resonance and uses superconducting magnets to energize a given isotope in plasma consisting of an ionic mixture.



Metabolic studies

Biochemical markers and probes are used to research the uptake of compounds by the body. For example, nutritional studies are commonly performed using isotopic labeled compounds.

Brain and kidney function

Studies of brain and kidney function are performed by tracing isotopes throughout these organs for both diagnostics and treatment applications.


Precursors for therapeutic radioisotopes or radiation therapy are used for a variety of therapies. For example, neuroendocrine tumors are treated by radiotherapy using hormone bound lutetium-177 and yttrium-90.

Clinical pharmacology

Tracing drug metabolism requires the use of isotopes bound to drug in order to understand the processing of the given pharmaceutical by the body.



A wide range of biochemical processes can be studied using stable isotopes. For example, a technique known as stable isotope labeling by amino acids in cell culture (SILAC) is used in proteomics research to help identify disease biomarkers.


The use of isotope labeling allows chemists to study the mechanisms of chemical reactions, as individual atoms can be followed through a system.

Environmental science

Isotopes are valuable for studying release and spread of pollutants in the environment.


The tracing of isotope movement, either within a local system such as an estuary or on a global scale, can allow study of circulation patterns.


Various compounds labeled with nitrogen-15 are used in the study of processes such as plant metabolism and fertilizer uptake.

Recent Research & Development for Isotopes

Comparison of Lutetium-177 tin colloid and Rhenium-188 tin colloid radiosynovectomy in chronic knee arthritis., Shamim, Shamim Ahmed, Arora Geetanjali, Jha Pragati, Gupta Priyanka, Behera Abhishek, Mukherjee Anirban, Prabhu Meghna, Ansari Mohammad Tahir, Vyas Surabhi, and Bal Chandrasekhar , Nucl Med Commun, 2020 May 08, (2020)

Lithium and strontium isotope dynamics in a carbonate island aquifer, Rottnest Island, Western Australia., Martin, A N., Meredith K, Norman M D., Bryan E, and Baker A , Sci Total Environ, 2020 May 01, Volume 715, p.136906, (2020)

Barium Isotopes Track the Source of Dissolved Solids in Produced Water from the Unconventional Marcellus Shale Gas Play., Tieman, Zachary G., Stewart Brian W., Capo Rosemary C., Phan Thai, Lopano Christina, and J Hakala Alexandra , Environ Sci Technol, 2020 Mar 06, (2020)

New application of strontium isotopes reveals evidence of limited migratory behaviour in Late Cretaceous hadrosaurs., Terrill, David F., Henderson Charles M., and Anderson Jason S. , Biol Lett, 2020 Mar, Volume 16, Issue 3, p.20190930, (2020)

Biological diversity in an Islamic archaeological population: A radiogenic strontium isotope and craniometric analysis of affinity in Ottoman Romania., Allen, Kathryn Grow, Mills Ryan D., Knudson Kelly J., and von Cramon-Taubadel Noreen , Am J Phys Anthropol, 2020 Jan 06, (2020)

A solid support generator of the Auger electron emitter rhodium-103m from [Pd]palladium., Jensen, Andreas I., Zhuravlev Fedor, Severin Gregory, Magnus Charlotte Busk, Fonslet Jesper, Köster Ulli, and Jensen Mikael , Appl Radiat Isot, 2020 Feb, Volume 156, p.108985, (2020)

The role of Thallium-201 scintigraphy and Tc-99m pentavalent dimercaptosuccinic acid in diagnosis and grading of chondrosarcoma., Jo, Olivia, Schlicht Stephen, Slavin John, Di Bella Claudia, Pang Grant, Powell Gerard, Spelman Tim, and Choong Peter Fm , Eur J Radiol, 2020 Apr, Volume 125, p.108846, (2020)

Comparison of Iodide-125 and Ruthenium-106 Brachytherapy in the Treatment of Choroidal Melanomas., Ghassemi, Fariba, Sheibani Shahab, Arjmand Mojtaba, Poorbaygi Hosein, Kouhestani Emad, Sabour Siamak, Samiei Farhad, Beiki-Ardakani Akbar, Jabarvand Mahmood, and Tari Ali Sadeghi , Clin Ophthalmol, 2020, Volume 14, p.339-346, (2020)

Recent Advances in Iridium(I) Catalysis towards Directed Hydrogen Isotope Exchange., Kerr, William J., Knox Gary J., and Paterson Laura C. , J Labelled Comp Radiopharm, 2019 Nov 12, (2019)

Isolation and quantification of a Mo isotope solution from proton irradiated niobium., Roos, Per , Talanta, 2019 Nov 01, Volume 204, p.769-775, (2019)

Two-step extraction method for lead isotope fractionation to reveal anthropogenic lead pollution., Katahira, Kenshi, Moriwaki Hiroshi, Kamura Kazuo, and Yamazaki Hideo , Environ Technol, 2019 Nov, Volume 40, Issue 26, p.3473-3478, (2019)

PIDAZTA: Structurally Constrained Chelators for Efficient Formation of Stable Gallium-68 Complexes at Physiological pH., Giovenzana, Giovanni Battista, Farkas Edit, Vágner Adrienn, Negri Roberto, Lattuada Luciano, Tóth Imre, Colombo Valentina, Esteban-Gómez David, Platas-Iglesias Carlos, Notni Johannes, et al. , Chemistry, 2019 May 31, (2019)

The origin of rare alkali metals in geothermal fluids of southern Tibet, China: A silicon isotope perspective., Wang, Wei, Wei Hai-Zhen, Jiang Shao-Yong, Tan Hong-Bing, Eastoe Christopher J., Williams-Jones Anthony E., Hohl Simon V., and Wu He-Pin , Sci Rep, 2019 May 27, Volume 9, Issue 1, p.7918, (2019)

Laser Spectroscopy of Neutron-Rich Tin Isotopes: A Discontinuity in Charge Radii across the N=82 Shell Closure., Gorges, C, Rodríguez L V., Balabanski D L., Bissell M L., Blaum K, Cheal B, Ruiz R F. Garcia, Georgiev G, Gins W, Heylen H, et al. , Phys Rev Lett, 2019 May 17, Volume 122, Issue 19, p.192502, (2019)

Experimental and theoretical study of rhenium radioisotopes production for manufacturing of new compositional radiopharmaceuticals., Pourhabib, Z, Ranjbar H, A Samani Bahrami, and Shokri A A. , Appl Radiat Isot, 2019 Mar, Volume 145, p.176-179, (2019)