I am working with Shimadzu IT-TOF with ESI . I this triterpene which does not give me parent ion but gives two peak M-18 and M-18-18 ) (loses two water molecule )in positive mode at 7:3 ration in intensity. Is there any parameters i can play to reducing M-18-18 ionisation and have more of M-18 so i can go low in my detection limit?