Quantitative bioanalysis using matrix‐assisted laser desorption/ionization mass spectrometry

The application of matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) for quantitative analysis was investigated with the use of internal standards. Three peptides/proteins in the mass range 1000–12000 were tested and the effect of various internal standards was evaluated. Horse cytochrome c was used as an internal standard for bovine cytochrome c, melittin for renin and an undecapeptide B analogue was employed as an internal standard for the decapeptide A. A linear response was found between the measured peak height ratio and the applied amount of analyte when an appropriate internal stanard was used. The quantitative abilities of MALDI‐MS were finally applied to the determination of the drug amperozide in plasma. The biological samples were prepared for analysis using liquid–liquid extraction prior to MALDI‐MS. A linear calibration graph was obtained using the 13C4 stable isotopically labelled amperozide as an internal standard.