What are the impurities in ENA?

Could you please elaborate on the impurities found in ENA? I'm particularly interested in understanding their chemical composition, as well as the potential impact they might have on the overall quality and performance of ENA. Are there any specific impurities that are more common or concerning than others? Also, how do manufacturers typically address these impurities to ensure the purity and safety of ENA? It would be great if you could provide some insights into this matter.