Chromatographic behavior of co-eluted plasma compounds and effect on screening of drugs by APCI-LC–MS(/MS): Applications to selected cardiovascular drugs

Chromatographic behavior of co-eluted compounds from un-extracted drug-free plasma samples was studied by LC–MS and LC–MS/MS with positive APCI. Under soft gradient, total ion chromatogram (TIC) consisted of two major peaks separated by a constant lower intensity region. Early peak (0.15–0.4 min) belongs to polar plasma compounds and consisted of smaller mass ions (m/z<250); late peak (3.6–4.6 min) belongs to thermally unstable phospholipids and consisted of fragments with m/z<300. Late peak is more sensitive to variations in chromatographic and MS parameters. Screening of most targeted cardiovascular drugs at levels lower than 50 ng/mL has been possible by LC–MS for drugs with retention factors larger than three. Matrix effects and recovery, at 20 and 200 ng/mL, were evaluated for spiked plasma samples with 15 cardiovascular drugs, by MRM–LC–MS/MS. Average recoveries were above 90% and matrix effects expressed as percent matrix factor (% MF) were above 100%, indicating enhancement character for APCI. Large uncertainties were significant for drugs with smaller masses (m/z<250) and retention factors lower than two.