Oxygen isotope-Oxygen 18 is the use of oxygen. A stable isotope of element oxygen, the symbol is O, abbreviated as 18O. In 1929, W.F. Geok and H.L. Johnston used molecular spectroscopy to discover that natural oxygen is composed of three isotopes of oxygen 16, oxygen 17, and oxygen 18. According to modern measurements, the exact composition of oxygen isotopes in the air is oxygen 16: oxygen 17: oxygen 18 = 2667:1:5.5.

In 1937, H.C. Yuri and J.R. Hoffman first obtained water enriched with oxygen 18 (heavy oxygen water) by water rectification. The primary method of modern separation of oxygen 18 is still the water distillation method, which has obtained 99.8% H218O. Low-temperature rectification of carbon monoxide or nitric oxide can also separate oxygen18.

Because of the discovery of the heavy isotope of oxygen, the chemical scale (O=16.00000) of the atomic weight and the physical scale (16O=16.00000) are inconsistent. This is because the oxygen selected for the chemical scale is natural oxygen, and the presence of oxygen 17 and oxygen 18 makes the chemical scale larger than the physical scale, and the chemical scale is 1.000275 times the physical scale. Chemistry and physics are interrelated. Different scales will inevitably lead to confusion. After the two scales have been used together for a period of time, they have become more and more aware of the need for a consistent scale. It was not until 1961 that chemistry and physics jointly selected 12C=12 as the atomic weight standard, and the two scales were consistent.

Because oxygen does not have a long-lived radioactive isotope (see radioactivity), oxygen 18 is an important tracer atom and has been widely used in the study of chemical reaction mechanisms, catalytic mechanisms, and reaction processes related to life activities.

One is that in drug research, oxygen is an essential element in the structure of most drugs. In metabolism research, oxygen-18 is usually used instead of ordinary oxygen for isotope tracing, which can sensitively, accurately and quickly understand the law of drug activity and metabolic pathways in the body. This kind of tracer research is indispensable for the development of new drugs and is of great significance for guiding the application of drugs in the human body.

The second is the application in energy metabolism research: a molecule composed of oxygen-18 and hydrogen, the chemical formula is H218O, called oxygen-18 water. The quickest and most accurate method to measure the energy metabolism of free people is to use the double-labeled water technology (DLW): the double-isotope tracing method of hydrogen and oxygen. After humans or animals are fed a certain dose of H-2 (deuterium) and O-18 double-labeled water, the metabolic state can be measured by sampling and measuring the rate of isotope excreted from the body. The dual-label water technology has been widely used in sports medicine, child nutrition, food nutrition, weight loss, and astronaut diet, and has broad development prospects.

The third is that the PET (Positron Emission Tomography) technology developed in 1990 has provided unprecedented opportunities for the application of heavy oxygen water. Compared with imaging techniques such as CT and MRI that diagnose diseases from a morphological point of view, PET can provide information on the function, metabolism, or receptor binding of the disease at the molecular level, and is called "in vivo biochemical imaging." Because the biochemical changes of the disease are often earlier than the morphological changes, it can diagnose diseases more early, sensitively and accurately, especially tumors, coronary heart disease and brain diseases. More than 90% of the PET imaging agent is fluorine-18, and fluorine-18 is formed by proton bombardment in an accelerator with oxygen-18 as the target. Therefore, it has become the most important application of oxygen-18 as a positron emission target.