Only 0.2% of the oxygen-18O isotope exists in atmospheric oxygen. The Water-18O is manufactured by enriching the oxygen-18O over 98 atom% and is used to produce the [18F]FDG *1 PET diagnostic reagent for cancer. Water enriched in the oxygen-18 isotope (Water-18O) is widely used in medicine, agrochemistry and biochemistry. Oxygen-18 was first enriched to 99.5% in 1943 using thermal diffusion. To date, the use of electrolysis, chemical isotope exchange, gas diffusion, and rectification of oxygen, nitric oxide, and water has been described to enrich water with oxygen-18. Among them, the method of rectification of water, first demonstrated in 1944, is successfully used now in industry.
