On-line Determination of Oxygen-18 in Organic Matter by Isotope Ratio Mass Spectrometry (CAT#: STEM-ST-0061-LJX)

Introduction

Isotope ratio mass spectrometry can be used for the on-line determination of oxygen-18, at a naturally occurring level, in organic material. After pyrolysis of the samples to form carbon monoxide, which is performed at 1300°C in a vitreous carbon tube, the pyrolysis products are transported by a stream of helium gas. Using an open split, a small part of the effluent is transferred to the ion source of an isotope ratio mass spectrometer. The ratio is obtained from a measurement of the ion current intensities at m/z 30 and 28 (12C18O and 12C16O). The method was tested with the secondary water standard GISP (Greenland Ice Sheet Precipitation) and the carbonate standard NBS 19. The values obtained were -24.8‰ and 27.3‰ vs. VSMOW (Vienna Standard Mean Ocean Water) (IAEA reference values are -24.8‰ and 28.7‰ vs. VSMOW). The potential of the method was demonstrated by measuring the 18O content of samples of beet and cane sucrose and also samples of vanillin extracted from vanilla pods or of synthetic origin. © 1997 by John Wiley & Sons, Ltd.

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Principle Applications Procedure Materials Notes Related Products

Principle

Isotope ratio mass spectrometry (IRMS) leverages magnetic sector mass spectrometry to enable high-precision measurement of the stable isotope content of a sample. Typical measurements target hydrogen, carbon, nitrogen, and oxygen analyses—although elements with masses up to and including sulfur can be measured. Solid, liquid, or gas phase samples are converted to simple gases then introduced to the IRMS. During analysis, an electron impact source ionizes sample-derived gas which is then accelerated down a flight tube, separated by mass, and quantified using a series of Faraday cups. The high precision of IRMS enables enumeration of even very small isotopic fractionation associated with physical, chemical, and biological transformations or natural abundance measurements.

Applications

For explaining the detailed molecular mechanisms behind biological processes
For understanding and quantifying nutrient and material exchanges between ecosystems
For providing ultra-precise stable isotope analyses
For understanding the geological history of the Earth
For food authenticity, forensic science, medical research and anti-doping testing

Procedure

1. Fill the reaction tube and install it, connect the gas path
2. Check for helium leaks
3. Heat up the reactor, wait for the reaction tube to burn stable, adjust the state of the equipment
4. Wrap the sample in a tin cup and test the sample
5. Store and process data

Materials

• Sample Type:
Organic matter

Notes

1.The approach is also valuable for quantifying the reactivity and progression of an applied stable isotope tracer to help determine reaction rates and final disposition of applied substrates.
2.IRMS offers a way of measuring isotopic variations with extremely high levels of accuracy. It can be used to detect isotope values of lighter elements with no issues, making it instrumental in the analysis of organic and natural samples.

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