[Frenchmicrob]

Hello everyone,

I am a PhD student in microbiology from France and have encountered a problem with nitrite's (NO₂^-) colorimetric quantification. After storing at -20°C, my samples with allylthiourea in them (PubChem Substance ID 24846829http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=24846829&viewopt=PubChem) were found with 80% loss of nitrite (when compared to samples without nitrite stored in the same conditions).
Finding bibliographic evidence is hard since most of articles on allylthiourea and nitrite are only related to allylthiourea's role as nitrification inhibitor.

I do not know how to explain this phenomenon, and I wonder if someone could help me.

I thank you in advance.

[opsomath]

Have you tried a matrix control where you add allylthiourea and nitrite to a blank and attempt to quantify it after storage? Allylthiourea should be a strong reducing agent and nitrite is an oxidizing agent, there is probably a reaction occurring.

[opsomath]

After doodling some mechanisms, I definitely think that nitrite will oxidize any urea into N2, CO2, and either water or the appropriate alcohol if there is a substituent (allyl) on the urea.

It turns out that I am correct: https://www.crops.org/publications/sssaj/abstracts/28/4/SS0280040478?access=0&view=pdf

It appears that an alkaline pH inhibits this reaction, so you might want to try adding base to your samples.

[Frenchmicrob]

Thank you very much opsomath for the time you took. Your answer hepled me a lot!