Objective:       To show the high sensitivity of the 6490A Triple Quadrupole LC/MS System with iFunnel technology for quantitation of peptide samples in plasma. Background The Agilent 6490A Triple Quadrupole mass spectrometer incorporates iFunnel technology to achieve new levels of sensitivity and dynamic range for detection of target peptides in complex matrices such as human plasma. The innovative design of the ion funnel reduces contamination and neutral molecules thus improving overall signal and reducing system noise. Sensitivity is the key requirement for assays that are both specifi c and quantitative for target proteins. These assays are critical for clinical research of putative biomarkers, which may have low concentrations in commonly used biofl u ids such as serum and plasma. Often hundreds of target peptides need to be monitored in thousands of biological samples. This note describes the results achieved for the analysis of stable isotope-labeled standard peptides spiked into digested non-depleted plasma using the 6490 Triple Quadrupole LC/MS System with iFunnel technology.