Nitrogen isotope analysis of ammonium in aqueous solutions using a perfluorosulfonated ionomer membrane for...

Area of Science:

• Analytical Chemistry
• Environmental Science
• Isotope Geochemistry

Background:

• Accurate nitrogen isotope analysis of ammonium is crucial for environmental and geochemical studies.
• Traditional methods for ammonium analysis can be time-consuming and require larger sample volumes.

Purpose of the Study:

• To investigate the efficacy of custom-made solid-phase microextraction (SPME) fibers coated with Nafion for nitrogen isotopic analysis of ammonium.
• To optimize the SPME method for enhanced absorption and sensitivity in aqueous solutions.

Main Methods:

• Development of custom SPME fibers coated with Nafion (perfluorosulfonated ionomer).
• Conversion of aqueous ammonium to ammonia, followed by headspace absorption and gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) analysis.
• Comparison of Nafion-coated fibers with commercial polydimethylsiloxane (PDMS) fibers for ammonia absorption efficiency.

Main Results:

• Nafion-coated fibers demonstrated significantly higher ammonia absorption capacity (approximately 20 times) compared to PDMS fibers.
• Nitrogen isotopic fractionation between the Nafion fiber and ammonia gas was determined.
• The method enabled delta(15)N analysis with a standard deviation of 0.8 per thousand using as little as 0.4-0.5 micromol of ammonium from a small droplet sample.

Conclusions:

• Custom Nafion-coated SPME fibers provide a highly efficient and sensitive method for nitrogen isotopic analysis of ammonium in aqueous samples.
• The developed technique allows for precise delta(15)N measurements with minimal sample volume, suitable for various applications.
• The method's robustness and efficiency make it a valuable tool for environmental and geochemical research.