Ammonia is a reactive gas in our atmosphere that is key in air quality issues. Assessing its emissions and how it reacts is a hot topic that can be addressed from the past. Stable isotopes (the mass of the molecule) measured in ice cores (glacial archives) can teach us a lot. However, the concentrations in ice cores are very small. We propose a protocol to limit the contamination and apply it to one ice core drilled in Mont Blanc, describing the opportunities our method brings.