Event Title

A Novel Method for Rapid Measurement of Ammonium Isotope Ratios with Time-of-Flight Mass Spectroscopy

Location

Davis 117

Start Date

30-4-2015 9:00 AM

End Date

30-4-2015 10:55 AM

Project Type

Presentation

Description

The use of 15-nitrogen (N) stable isotope tracers is a valuable tool for understanding N cycling in aquatic ecosystems, and experimental techniques using 15-N tracers range from mesocosms to stream reaches. Analytical measurement of 14-N:15-N ratios has traditionally involved incubations to concentrate N onto filters for analysis by isotope-ratio mass spectrometry. This process is time-consuming and often requires large sample volumes, a challenge for mesocosm experiments. Here, we present a technique for measuring 14-N:15-N in ammonium using ESI-TOF mass spectrometry. Small volumes of sample (<10 ml) are complexed with phenol using the Bertheiot reaction producing the traditional indophenol blue complex (mass 198 AMU). Excess reagents are removed and the indophenol concentrated using automated C18 solid phase extraction. The extracts are run through a spectrometer to measure total ammonia concentration and passed to the ESI-TOF to obtain the 14-N:15-N ratio. This technique measures ammonia concentrations and isotopic ratios at the ppb level to better characterize nitrogen cycling in lake and estuarine ecosystems.

Faculty Sponsor

Suzi Cole

CLAS Field of Study

Natural Sciences

Event Website

http://www.colby.edu/clas

ID

1394

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Apr 30th, 9:00 AM Apr 30th, 10:55 AM

A Novel Method for Rapid Measurement of Ammonium Isotope Ratios with Time-of-Flight Mass Spectroscopy

Davis 117

The use of 15-nitrogen (N) stable isotope tracers is a valuable tool for understanding N cycling in aquatic ecosystems, and experimental techniques using 15-N tracers range from mesocosms to stream reaches. Analytical measurement of 14-N:15-N ratios has traditionally involved incubations to concentrate N onto filters for analysis by isotope-ratio mass spectrometry. This process is time-consuming and often requires large sample volumes, a challenge for mesocosm experiments. Here, we present a technique for measuring 14-N:15-N in ammonium using ESI-TOF mass spectrometry. Small volumes of sample (<10 >ml) are complexed with phenol using the Bertheiot reaction producing the traditional indophenol blue complex (mass 198 AMU). Excess reagents are removed and the indophenol concentrated using automated C18 solid phase extraction. The extracts are run through a spectrometer to measure total ammonia concentration and passed to the ESI-TOF to obtain the 14-N:15-N ratio. This technique measures ammonia concentrations and isotopic ratios at the ppb level to better characterize nitrogen cycling in lake and estuarine ecosystems.

http://digitalcommons.colby.edu/clas/2015/program/83