A simple new method for the determination of ammonium isotopes by gas chromatography-mass spectrometry
Wei Guo1,2, Ran Jiang1,2, Zhang Xinfeng1,2
1Pearl River Conservancy Commission, Pearl River Institute of Hydraulic Research, Guangzhou, 510610, China. 458750084@qq.com.
Abstract:
We report a new method for the determination of naturally abundant 15N (concentration of 15N) in ammonium (NH4+) in water samples, including drinking water, surface water, groundwater, and seawater, by gas chromatography-mass spectrometry (GC-MS) based on the isotopic analysis of hexamethylenetetramine. The resulting product was obtained by the reaction between ammonium ions and formaldehyde under the given conditions (pH = 6.0, 40 °C, 30 min). Then, the species was extracted (with chloroform) and concentrated at pH = 8.5 and measured by GC-MS. The results showed that the relative standard deviation (RSD) of the δ15N measurements was less than 10% and the recoveries were in the range of 71-118% (n = 5). The limit of detection was 20 μmol l-1. Compared to the previous method, the present method is simple and highly suitable to be used as a routine method for the 15N/14N analysis of NH4+.
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