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Nitrogen isotope analysis of aqueous ammonium and nitrate by membrane inlet isotope ratio mass spectrometry (MIRMS) at natural abundance levels (CAT#: STEM-ST-0014-LJX)

Introduction

Existing methods for the measurement of the 15 N/14 N isotopic composition of ammonium and nitrate are either only suitable for labelled samples or require considerable sample preparation efforts (or both). Our goal was to modify an existing analytical approach to allow for natural abundance precision levels. Published reaction protocols were used to convert ammonium into N2 by NaOBr and nitrate into N2 O by TiCl3 . A membrane inlet system was developed and coupled to an isotope ratio mass spectrometer to allow precise determination of the analytes.




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:
Aqueous ammonium and nitrate

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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