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