I am using a Thermo LCQ with APcI and am having a problem w/ a possible cocaine contamination. Using acetonitrile solvent in conjunction with an ammonium formate buffer for analyisis. Covered most of the basics changed solvents, column, column guard, etc. Also flushed system with acetonitrile (at 550C over night) then tried this same "bake-out method with methanol the next night, and isoprpopanol the next night - did not effect the peaks at all. Had technical support advise that contaminant was probably in the APcI head so I replaced that with a new head. Low and behold contaminant vanished. Technician then re-extracted samples for a cocaine run and now the peak is back (might have come from sample taken from syringe from scene and not diluted properly). Characteristics of my contaminant are as follows: M/Z at 304 and 183, big mass is seen from 16.5 minutes to 22 minutes with a signal of 2.55 X 10^6. Any help with this matter would be greatly appreciated.