The image below is from another forum where a user (not me) did MS/MS on DMT that had yellowed in air. He found it to contain DMT N-oxide. It is safe to assume he had not intentionally treated it with hydrogen peroxide or another oxidizer. I do not know how conclusive that is.Loveall said:I mostly agree, but in my personal experience it is usually DMT aggregation causing the off white color. I don't think N-oxide has been detected in a normal extraction.
There was also a paper on tryptophan degradation. It reported a number of oxygen-containing decomposition products formed in reactions of tryptophan with oxygen radicals in air. I do not think they reported N-oxide specifically, but tryptophan is -NH2 so the DMT decomposition may be different.
One way to confirm (or rule out) oxygen could be to add some sodium dithionite after basification. It could scavenge oxygen dissolved in the water and reduce N-oxide if it indeed forms.