Spectra of standard calibration of 12 known polymers, compared with spectra of solids derived from placenta sample following KOH-digestion and ultracentrifugation Representative mass spectra are show for both samples are then shown for (A) polypropylene (retention time = 4.5 min), (B) polyethylene (retention time = 13.2 min), and (C) polystyrene (retention time = 14.5 min). Lower left image (D) demonstrates the overlapping peaks from the pyrolysis system of the polymer standards and the pellet derived from placental samples.