Inverse/Negative Peaks LC/MS

Question

Hello. I am operating on EXPEC Triple Quadropole MS. I was trying to perform MS1 scan of Dimetridazole(in ESI positive mode ), which is solved in methanol, but I am getting those inverse peaks. Besides, no apparent peaks appear during an MRM transition of 142-->96, I have also tried 141.9 and other precursor ion weights, varying spray voltages, but nothing increases signal intensity. I am using MeOH and water as my mobile phases. What possible can lay behind all of this, what should I try? Can this be solution related problem? I would really appreciate all your responses, thanks!

m4esti · Answer

Hi Nino, 
 You are operating an EXPEC Triple Quad MS, and if you were to encounter this on a similar Agilent system, this is what the approach would be: 
 If the signal from your analyte is less than the signal from the background, and your analyte suppresses the background, then the MS1 response will show negative peaks. 
 You should consider the transition that your using: is it correct? Are the background ions at the transition? Has it worked in the past? Are you also using a LC detector? 
 Also, you can perform MS2 scans to evaluate if the M+H is there or if there is an adduct M+Na, etc.