Blank human EDTA plasma samples from ten different healthy individuals were
extracted and injected into the LC-MS/MS system. A representative experiment is
shown Acetaminophen (10 μg/ml dissolved in 01 formic acid/acetonitrile,
3:7, v/v) was infused post-column via T-piece at a rate of 10 μl/min
using a syringe pump (Harvard Apparatus, Holliston, MA). The extent of ion
suppression was established by monitoring the signal intensity of the ion
currents in MRM-mode (m/z= 152
[M+H]+ → 110) at the
retention times of the analyte (marked by arrow) after injection of blank
extracted plasma samples into the LC-MS/MS system. Ion suppression would have
caused a “dip” in the acetaminophen signal produced by constant
infusion. The arrow marks the retention time of acetaminophen. Red: continuous
infusion of acetaminophen, blue: overlaid analysis of extracted sample with
acetaminophen peak.