It is important that diethylamine used in during the DEET (mosquito synthesis) reaction was dry (free from water). Why is this necessary? What result would happen if wet diethylamine was used?
The usual synthesis is DEET is to react diethylamine with the acid chloride formed from the reaction of 3-methylbenzoic acid. If the diethylamine is wet this will hydrolyse the acid chloride to the carboxylic acid and reduce the yield of the amide. The carboxylic acid can recovered, recycled and reused.
The next question is how to dry diethylamine?