In
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...
, a sample's oxygen–argon ratio (or oxygen/argon ratio) is a comparison between the concentrations of
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
(O
2) and the
noble gas argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice a ...
(Ar), either in air or dissolved in a liquid such as seawater. The two gases have very similar physical properties such as
solubility
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solubi ...
and
diffusivity
Diffusivity is a rate of diffusion, a measure of the rate at which particles or heat or fluids can spread.
It is measured differently for different mediums.
Diffusivity may refer to:
* Thermal diffusivity, diffusivity of heat
*Diffusivity of mas ...
, as well as a similar temperature dependence, making them easy to compare.
Applications
Biological activity in seawater
Measurements of
primary productivity in the ocean can be made using this ratio. The concentration of oxygen dissolved in seawater varies according to biological processes (
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
and
respiration) as well as physical processes (air-sea gas exchange, temperature and pressure changes, lateral mixing and vertical diffusion). Argon concentrations, by contrast, vary only by physical processes.
This technique was first used by Craig and Hayward (1987) when they separated oxygen supersaturations into a biological and a physical component. This O
2/Ar supersaturation can be defined as
∆(O
2/Ar)=((c(O
2 )/c(Ar)) / (c
sat(O
2)/(c
sat(Ar))) -1
where (∆O
2)/Ar is the difference between O
2 production via photosynthesis and removal via respiration, c is the concentration of dissolved gas and c
sat is the saturated concentration of the gas in water at a specific temperature, salinity and pressure.
Oxygen and argon concentrations can be compared using samples from water systems aboard ships using either a membrane inlet mass spectrometer (MIMS)
or an equilibrator inlet mass spectrometer (EIMS).
The measurements can then be used in conjunction with air-sea gas exchange values to calculate biologically induced air-sea O
2 fluxes and net community production.
Determining leakage rates in sealed packaging
Because oxygen and argon leak through packaging material at different rates, comparing the ratios inside a package can determine if and how quickly air from outside has leaked in.
Manufacturing
The characteristics of steel, in particular the carbon and chromium content, can be controlled by adjusting the oxygen/argon ratio during the manufacturing process.
The oxygen/argon ratio is also important in the creation of thin films used in the manufacture of lithium ion batteries.
References
{{DEFAULTSORT:Oxygen-argon ratio
Analytical chemistry