NH4-N2O Conversion

Conversion of NH4+ to N2O through oxidation of NH4+ to NO2- by hypobromite (BrO-) and subsequent reduction of NO2- to N2O by hydroxylamine (NH2OH).

Written by Kunmanee Bubphamanee (~2022).

Protocol, volumes, and safety

• NH4+ solution is brought to 2.5 mL with H2O
• 0.250 mL of BrO- is added (1:10 with sample volume)
• Samples are shaken vigorously at RT
• NH4+ has now been converted to NO2-
• This first conversion is somewhat inefficient, as expected from the method paper.
• 0.05 mL of 390 mM NaAsO2 is added to reduce excess BrO-
• NO2- is quantified colorimetrically using Griess reagent
• Volume at this step is ~2.8 mL
• 400 uL of 6 M HCl is added to reduce pH to ~0-0.5
• Vials are crimp sealed
• NH2OH from a 240 uM stock is added at a ~1:2 molar ratio NO2-:NH2OH
• 350-600 uL of NH2OH depending on the NO2- measured.
• Vials shake for 16 h at 37 C
• 500 uL of 5 M NaOH is added to terminate the reaction
• NO2- has now been converted to N2O
• ~100% conversion is expected
• Any remaining NO2- is quantified colorimetrically using Griess reagent
• Total final solution volume = ~4.05 – 4.3 mL, Total headspace volume = ~5 - 5.25

References

• Liu D, Fang Y, Tu Y, Pan Y. (2014). Chemical Method for Nitrogen Isotopic Analysis of Ammonium at Natural Abundance. Analytical Chemistry 86: 3787-3792. doi: 10.1021/ac403756u

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