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Click on a term below to learn more about isotope ratio mass spectrometry.
A method of analysis where sample material is moved through a series of conversion and purification steps within a continuously flowing stream of carrier gas, typically helium. In most cases, this method allows for a single measurement of a sample.
Continuous flow interface
The carrier gas flow rate from a continuous flow system is typically an order of magnitude higher than an isotope ratio mass spectrometer (IRMS) can handle. A reduction in flow immediately upstream the IRMS is achieved with a plumbing interface.
A method of analysis where a sample gas and and reference gas are alternately put into the isotope ratio mass spectrometer (IRMS). This method typically allows for many measurements of a single sample and is generally considered the most precise way to use an IRMS.
An instrument used to combust solid or liquid material in a controlled excess oxygen reaction column. A carrier gas (typically helium) is used to move the combustion products through a series of oxidation or reduction as well as purification steps.
Light Stable Isotopes
Isotopes are elements with varying numbers of neutrons but identical numbers of protons and electrons. Some isotopes are unstable, or radioactive, with increasing numbers of neutrons. Elements with a relatively low mass are considered light. For example, carbon has a mass of 12 and is considered to be light. Lead, however, has a mass of 207 and would be considered heavy. In the environmental stable isotope community, light isotopes are generally considered to be hydrogen, carbon, nitrogen, oxygen, and sulfur.
Multiple isotopes of the same species following a physical fractionation that is dependent on mass. For example,
O is empirically different from
O by about half.
Symbols δ and Δ
These symbols are the lower case and capital greek letter delta. We use the lower case delta (δ) to indicate the ratio of heavy to light isotope relative to the same ratio of a standard. For example, the
C ratio of some sample material relative to the
C ratio of some internationally recognized standard. The capital delta (Δ) is used to express the difference of one δ with that of another (for example Δ
O of an oxygen containing species expresses the difference between δ
O and δ
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