oxygen18

Oxygen-18, often written as 18O or O-18, is a stable isotope of oxygen containing eight protons and ten neutrons. It has a mass number of 18 and a natural abundance of about 0.2% of atmospheric and terrestrial oxygen, with the most common isotope being 16O. As a non-radioactive isotope, 18O is widely used as a tracer in scientific research.

Because 18O is chemically almost identical to the more abundant 16O, its behavior in chemical reactions is largely the same, but the extra neutrons create small isotopic effects. These effects lead to slight fractionation during physical processes such as evaporation and condensation and during chemical reactions, enabling researchers to track the movement and transformation of oxygen in systems ranging from oceans to soils and biological organisms.

Applications and measurement:

The primary use of 18O is in studying the oxygen isotope ratio, typically expressed as δ18O relative to standard mean ocean water (SMOW). In geoscience and paleoclimatology, δ18O values in ice cores, carbonate minerals, and pore waters serve as proxies for past temperatures and hydrological conditions. In biochemistry and physiology, water labeled with 18O (for example, H2^18O) is used to trace metabolic pathways and to study enzymatic mechanisms, including oxygen incorporation into biochemical products.

Measurement techniques and standards:

Isotope ratio mass spectrometry (IRMS) and laser-based spectrometry are common methods for quantifying 18O/16O ratios. Results are calibrated against standards such as SMOW or Vienna SMOW to yield δ18O values with high precision.

Safety and availability:

18O is stable and non-radioactive, and laboratory samples are readily available for research and educational use, with standard laboratory safety practices.